The Adsorption of Copper,Lead Metal Ions,and Methylene Blue Dye from Aqueous Solution by Pure and Treated Fennel Seeds

Abstract

This research work reports on pure and acid-treated fennel seed biomaterials for the removal of metal ions of copper Cu(II), lead Pb(II), and methylene blue (MB) dye from aqueous solution by batch adsorption. Pure fennel seeds were labelled as PFS; nitric and sulphuric acid-treated seeds were designated as NAFS and SAFS, respectively. The adsorbents were characterised by SEM, EDX, FTIR, XRD, and BET. The SEM images revealed that the surface of the adsorbents was porous. However, physicochemical characterization further revealed that BET surface area, pore size, and pore width increased for NAFS and SAFS compared to PFS. FTIR results revealed that the peaks for cellulose −COC and −OH decreased considerably for NAFS and SAFS; this indicated that cellulose was hydrolyzed during acid treatment. Adsorption data showed that all biomaterials had a higher affinity for MB dye more than Pb(II) and Cu(II) metal ions. The maximum adsorption capacities onto PFS were 6.834, 4.179, and 2.902 mg/g and onto NAFS are 15.28, 14.44, and 4.475 mg/g, while those onto SAFS are 19.81, 18.79 and 6.707 mg/g respective for MB dye, Pb(II), and Cu(II) ions. Postadsorption analysis revealed that adsorption of Pb(II) and Cu(II) was controlled mainly by the electrostatic attraction, while that of MB was synergistic of electrostatic attraction, π-π interaction, and hydrogen bond. It was found that the uptake processes of MB dye onto all adsorbents fitted Freundlich while both cations were described by Langmuir model. The thermodynamic parameters $Δ H$ ^o and $Δ G$ ^o indicated the endothermic nature and spontaneity of the processes, respectively.

1. Introduction

Pollution of water by harmful substances such as metals ions and dyes is a serious challenge faced by this generation. Over 100 million people worldwide do not have access to safe drinking water, and it is projected that this number will double in the near future [1, 2]. Excessive discharge of toxic metal ions and dyes into the environment and aquatic bodies primarily originates from numerous anthropogenic activities [3, 4]. Growing industrialization and urbanization have resulted in large amounts of pollutants such as toxic metals ions [copper Cu(II) and lead Pb(II)] and organic dye [methylene blue (MB)] that have been frequently encountered in water [5–7].

Copper, lead, and methylene blue are of importance in numerous factories and firms such as paints, textile, batteries, and mining. Copper is particularly identified as an essential mineral in biochemical processes at trace amounts. However, these substances are harmful to living organisms at high concentrations. Drinking water containing these toxic substances results in adverse health. Therefore, their presence in water is of critical concern.

Pb(II) ions are toxic and nonbeneficial to the human body. The maximum acceptable level of Pb(II) ions in drinking water has been set to 0.01 mg/L by the WHO [8]. Concentrations beyond the acceptable level are detrimental and cause dysfunction of the liver, kidney, brain, and reproduction system; mental retardation, and damages to the central nervous system [9]. On the other hand, Cu(II) ions are beneficial to the living organisms at low concentrations. The maximum acceptable concentration of Cu(II) ions in drinking water is 1.5 mg/L [10]. However, at high concentrations, Cu(II) causes stomach cramps, nausea, diarrhea metabolism disorder, damage to the neurological system, liver, kidney damage, and lungs [11]. MB dye has a poisonous effect on living organisms and the environment [12–16]. Its toxic effect includes mental disorder, vomiting, nausea, abdominal pain, eye burns, tissue necrosis, and cyanosis [17–19].

The degree of health problems caused by these substances is alarming. For this reason, several conventional technologies such as chemical, physical, and biological methods were developed for wastewater treatment. These includes filtration, advanced oxidation, flocculation and coagulation, catalysis, photo and chemical degradation, and adsorption [20]. However, due to low cost and easy operation, adsorption is the most appropriate and reasonable choice for the removal of organic pollutants and inorganic heavy metal ions from wastewater [21]. Adsorption is the process that involves deposition of pollutants onto the surface of the adsorbent, by interaction with functional groups on the surface [22, 23]. Biosorption is a green technology that typically employs agricultural materials as adsorbents for the removal of various pollutants from aqueous solution [24]. Agricultural and biogenic materials have attracted the attention of many researchers worldwide [7, 25, 26] due to the versatility shown by the materials in removing various pollutants from water.

In recent years, a number of agricultural materials and waste have been discovered for the removal of various pollutants in water. These biosorbents are materials such as paw-paw seeds [27], black cumin seeds [28], argan nut shell [29], rice husk [30], Corncob [31], and banana peel [32].

Fennel (Foeniculum vulgaris) is a perennial flowering plant species [33]. It belongs to a family of the Apiaceae [34]. It is cultivated in many parts worldwide. It is because the entire fennel plant is versatile; the leaves, seeds, stalks, and bulb are edible [35]. However, its flowers are used in the production of yellow and brown dyes [36]. For this reason, fennel plant and seeds are readily available and accessible. One of the commercial and traditional use of fennel seeds is to make fennel tea/drink [37, 38]. Thereafter, tons of used fennel seeds are disposed in the environment, and this in the near future will cause unbearable pollution. So the purpose of this study was to simulate the used fennel seeds and further chemically treat the seeds and apply them for the removal of Cu(II), Pb(II) ions, and MB dye from water.

The fennel seeds have been extensively used in medicine and culinary purposes [39–41]. This is because of the chemical content of the seeds such as vitamins, essential oil compounds, fiber protein, antioxidants, minerals, aroma, and flavour [34, 42]. The major structural constituents of fennel seeds are carbohydrates (51.5%), fats (33.5%), and proteins (15.6%). The carbohydrates found in fennel seeds are mostly lignocellulosic materials (hemicellulose, cellulose, and lignin) and small amounts of other natural occurring sugars [43]. Lignocellulosic materials are natural polymers, containing variety of monomers, especially different sugar units [35]. The structure of lignocellulosic materials consist abundant functional groups such as (−OH), (−CO), (−COOH), and (−C=C) which could be a good candidate for adsorption processes. However, very little attention has been given to fennel seeds as a potential adsorbent in the adsorption of pollutants.

The surface of agriculture materials has various functional groups. However, efforts have been made to enhance the adsorption performance of the materials. One process that addresses this issue is chemical modification by agents such as nitric acid [44] and sulphuric acid [45]. This promotes the content of oxygen containing functional groups and also increases the surface area as well as pore distribution on the surface of the material [46]. This results in the enhancement of the adsorption capacity.

Prior to this study, no similar work on fennel seeds was documented that reported on porous acid-treated fennel seeds. Also, to date, most studies on fennel seeds have explored the efficiency of removing pollutants primarily the adsorption focused on single pollutant removal ([47, 48] [49–51]). However, in reality, water pollutants coexist as mixtures in wastewater. No study has ever reported on the feasibility of fennel seeds when multiple pollutants coexist in solution. The targeted pollutants were selected due to their persistence in natural resources such as water and soil. The objective of this research work was to develop new porous fennel seed adsorbents for the removal of Cu(II), Pb(II), and MB from aqueous solution. The results from this study will add new knowledge to the database of fennel seed application in water treatment. The work also established the kinetics, thermodynamics, isotherms, and equilibrium studies of Cu(II), Pb(II), and MB towards fennel adsorbents. The reusability test of the adsorbents was evaluated.

2. Methodology

2.1. Chemicals and Materials

Unprocessed fennel seeds (brand: natural products) were purchased from Dischem Pharmacy in Vaal Mall, Vanderbijlpark. The following chemicals were used in this work: concentrated sulphuric acid (H₂SO₄)—99.99%, concentrated nitric acid (HNO₃)—70.00%, lead nitrate (Pb(NO₃)₂)—99.95%, copper(II) nitrate hydrate (Cu(NO₃)₂)·2H₂O—99.95%, and methylene blue (C₁₆H₁₈ClN₃S)—95.00%. All chemicals were AR grade and obtained from Sigma-Aldrich, Johannesburg, South Africa.

2.2. Preparation of Biosorbents

2.2.1. Pure Fennel Seeds (PFS)

Several packs of fennel seeds were milled to a fine powder using a household blender. The obtained powder was put in boiling water for 30 min then dried in the oven overnight then passed through a sieve mesh of 0.8-1 mm. Then, the sieved material was labelled pure fennel seeds (PFS).

2.2.2. Sulphuric Acid-Treated Fennel Seeds (SAFS)

Exactly, 100 g of PFS was weighed and transferred to a beaker containing 1000 mL and diluted H₂SO₄ solution (5 M). The solution and material were stirred for 120 min at room temperature. Thereafter, the material was isolated and soaked in distilled water several times to get rid of excess acid. Afterward, the material was dried in an oven overnight. The resultant material was labelled sulphuric acid-treated fennel seeds (SAFS).

2.2.3. Nitric Acid-Treated Fennel Seeds (NAFS)

Exactly, 100 g of PFS was weighed and transferred to a beaker containing 1000 mL and diluted HNO₃ solution (5 M). The solution and material were stirred for 120 min at room temperature. Thereafter, the material was isolated and soaked in distilled water several times to get rid of excess acid. Afterward, the material was dried in an oven overnight. The resultant material was labelled nitric acid-treated fennel seeds (NAFS).

2.3. Biosorption Procedure

A stock solution of 1000 mg/L containing Cu(II), Pb(II) ions, and MB dye was prepared using respective salts. A stock solution was prepared by dissolving 1 g each of the following salts: Cu(NO₃)₂, (Pb(NO₃)₂, and (C₁₆H₁₈ClN₃S), in 1 L volumetric flask. The ratio of Cu(II) : Pb(II) : MB in the stock solution was 1 : 1 : 1. Then, the working standard solutions (20, 40, 60, 80, and 100 mg/L) were prepared from the stock solution (1000 mg/L) by a series of dilutions. Adsorption study of Cu(II), Pb(II), and MB onto PFS, SAFS, and NAFS was done by varying parameters such as the initial concentration of the solution, contact time, pH, and temperature of the system. The initial concentration of the solution was studied at 298 K for 120 min on working standard solutions (20, 40, 60, 80, and 100 mg/L). Contact time was evaluated at 298 K at time intervals 5-120 min on working standard solution 100 mg/L. pH was tested at 298 K for 120 min at various pH 1-8 on working standard solution 100 mg/L. The temperature of the system was evaluated at 288, 298, and 308 K for 120 min on a working standard solution of 100 mg/L. For each parameter, 10 mg of the adsorbent was transferred into 20 mL of the specified working standard in capped vials. To confirm repeatability of the results, the samples were prepared in duplicates, then agitated and rocked on an orbital shaker at 200 rpm. After the time has elapsed, the solid was separated from the solution by centrifugation at 2500 rpm for 5 min. The remaining supernatant solution was run on AAS and UV-vis.

2.4. Adsorption Data Management

Adsorption capacity ( $q_{e}$ ) and adsorption percentage (%A) of PFS, SAFS, and NAFS towards Cu(II), Pb(II), and MB were determined by equations $q_{e} = (C_{o} - C_{e}) V / W$ and $% A = ((C_{o} - C_{e}) / C_{o}) \times 100$ , respectively. The symbols used in the equations for adsorption capacity and adsorption percentage are initial and final concentrations (in mg/L) represented by $C_{o}$ and $C_{e}$ . Symbols $v$ and $W$ are, respectively, designated for the volume of the solution (in mL) and the mass of the adsorbent (in mg), and further experimental data were determined by using adsorption kinetics, isotherms, and thermodynamics (explained in details in supplementary materials: SM1).

3. Characterization

The adsorbents were characterized by SEM, EDX, FTIR, XRD, and BET to determine the surface morphology, chemical composition, functional groups on the surface of the biomaterials, phase, and nitrogen adsorption-desorption, respectively. SEM images and EDX spectra were taken on a Nova Nano SEM 200 from FEI operated between 5 and 15.0 kV. Clean sample holder and forceps were used to glue the sample on adhesive double-sided carbon conductive tape. Fennel seed adsorbents are nonconductive; therefore, a coating machine was used. Thereafter, the samples were transferred into the SEM for analysis. Perkin Elmer FTIR/FTNIR spectrum 400 (Massachusetts, USA) was operated between 4000 and 500 cm^-1 to affirm the functional groups attached to the surface of the adsorbents. XRD spectra were obtained from MAXima_X 7000 operated between 2theta (10-60^o). Micromeritics ASAP 2020 plus (Micromeritics Instrument, Georgia, Corporation, USA) was used to determine the BET surface area of the biomaterial under nitrogen adsorption-desorption; the sample was degassed for 12 hrs at 40°C. The concentration of MB dye before and after adsorption was measured. A Thermo Scientific Evolution 220 UV-Visible spectrophotometer was used to measure the concentration of MB before and after adsorption. Inductive couple plasma spectroscopy (ICP) and Thermo Scientific iCAP 7000 Plus Series ICP-OES spectrometer (Thermo Fisher Scientific, Massachusetts, USA) using ASX-520 autosampler were used to measure the solutions containing Pb(II) and Cu(II) ions before and after adsorption.

4. Results and Discussion

4.1. Characterization

4.1.1. SEM Analysis

The surface morphology of the adsorbents was analyzed by SEM images shown in Figures 1(a)–1(f). The images of PFS (Figures 1(a) and 1(b)) revealed that the surface of pure biomaterial had pores and bulges of different shapes and sizes. Similar results were observed by [49, 51] reporting on fennel seeds. It was also observed that the structure of the pure biomaterial was heterogeneous. However, upon nitric and sulphuric acid treatment in Figures 1(c) and 1(d) (NAFS) and Figures 1(e) and 1(f) (SAFS), respectively, refinements were observed. The images of NAFS in Figures 1(c) and 1(d) revealed that acid treatment entered the plant cell tissues and caused significant structural changes. The surface has been transformed into somewhat flaky arrangements that are horizontal and relatively porous. Also, the images of SAFS in Figures 1(e) and 1(f) showed that acid treatment had caused damage to the cell tissues. Thus, the inner surface was exposed and revealed amorphous structure that had pores. However, the refinements in SAFS were less compared to NAFS. Porous surfaces are important in adsorption processes of metal ions and dyes [52]. The main reason for the changes and refinements in morphologies could be due to the hydrolysis of cellulose, lignins, and hemicellulose in the biomaterial during nitric and sulphuric acid treatment [53, 54].

Figure 1

SEM analysis of pure ((a, b) PFS) and treated ((c, d) NAFS and (e, f) SAFS) fennel seed adsorbents.

4.1.2. EDX Analysis

EDX analysis in Figures 2(a)–2(c) was carried to evaluate the elements present on the biomaterials. The plots indicate that carbon and oxygen (C and O) are the dominant constituents. This is in full agreement with the chemical composition of lignocellulose materials which are the main ingredients of biomaterials generally. These elements are typically recorded in agriculture materials [55, 56]. The results for PFS (Figure 2(a)) also recorded the presence of phosphorus (P) and chloride (Cl). Telkapalliwar and Shivankar, [57] reported similar results, and such elements are naturally occurring in plant-based materials. The plots of NAFS (Figure 2(b)) and SAFS (Figure 2(c)), moreover registered nitrogen (N) and sulphur (S), respectively. The presence of these elements may be attributed to the pretreatment of the biomaterial with nitric and sulphuric acids. This resulted in nitrogen (N) and sulphur (S) groups been functionalized to the treated biomaterials. The registered elements are compared in Table 1.

Figure 2

EDX plots of pure ((a) PFS) and treated ((b) NAFS and (c) SAFS) fennel seed adsorbents.

(b)

(c)

Table 1

EDX chemical composition comparison study of fennel seed adsorbents.

PFS		NAFS		SAFS
Element	Percentage (%)	Element	Percentage (%)	Element	Percentage (%)
C	49.20	C	54.55	C	72.23
O	44.45	O	40.99	O	26.02
P	2.68	N	4.06	S	1.75
Cl	3.67	Cl	0.40	—	—

4.1.3. FTIR Analysis

The FTIR spectra of the biomaterials are shown in Figure 3. It was observed that PFS had a peak for the hydroxyl (-OH) group at 3291 cm^-1. The peak for (−OH) was linked to cellulose (−COC) content in the biomaterial around 1016 cm^-1 [49]. However, both peaks significantly decreased in intensity and slightly shifted to high wavenumber in NAFS and SAFS. The changes in the spectra of NAFS and SAFS indicated that some of the components especially lignocellulose materials were hydrolyzed from the seeds during acid treatment [58]. The peak for (−CH=CH) at 2993 cm^-1 was observed in PFS and SAFS but not in NAFS. The strong peaks for (−CH) stretch at 2927 and 2858 cm^-1 were exhibited by all adsorbents; this was associated with (−CH) vibration of the carboxylic group [50]. PFS observed a peak for the carboxylic group (−COOH) at 1587 cm^-1. However, in both NAFS and SAFS, the peak for (−COOH) shifted to 1623 cm^-1. Carbonyl group (−C=O) for amide was observed at 1738 cm^-1 in all materials. A peak at 1306 cm^-1 was observed in NAFS alone; this might be due to the formation of nitrate (−NO) group on the surface of the material [59]. A new peak was formed in NAFS and SAFS at 1451 assigned to stretch of (−CO) group for primary alcohol [48]. A newly developed peak at 1141 cm^-1 in SAFS was attributed to the sulphonate (−SO) group introduced into the material during pretreatment ([60]), while for NAFS the peak around 1141 cm^-1 was assigned to (−CO) group for primary alcohol.

Figure 3

FTIR spectra of pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

4.1.4. XRD Analysis

The XRD results of PFS, NAFS, and SAFS are shown in Figure 4. The diffraction peaks in PFS at 19.89, 23.02, and 23.95^o are characteristic to amorphous cellulose in the biomaterial [58]. However, in NAFS and SAFS, a sharp peak at 19.89^o considerably decreased in intensity while a doublet positioned at 23.02 and 23.95^o disappeared. This was due to hydrolysis of cellulose from the biomaterial during nitric and sulphuric acid [61].

Figure 4

XRD spectra of pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

4.2. Physicochemical Characterization

The data in Table 2 show the results for physicochemical characterization of the fennel adsorbents. pH_(PZC) plays a vital role in adsorption processes; it influences the ionization state of the adsorbents. The data show that the values of pH_(PZC) for PFS, NAFS, and SAFS were found to be 7.53, 6.05, and 6.18, respectively. The results for PFS were close to neutrality, while those of NAFS and SAFS were slightly acidic. Moreover, the data revealed that BET surface area, pore size, and pore width increased for NAFS and SAFS compared to PFS. The obtained results suggested that NAFS and SAFS may be efficient adsorbents in the uptake processes.

Table 2

Physicochemical characterization of pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

Adsorbent	BET			pH_(PZC)
Adsorbent	Surface area (m²/g)	Pore size (cm²/g)	Pore width (nm)	pH_(PZC)
PFS	0.947	0.002759	1.55	7.53
NAFS	3.668	0.004920	2.80	6.05
SAFS	1.674	0.003519	2.69	6.18

4.3. Adsorption Studies

4.3.1. Concentration Effect and Isotherm Studies

The influence of initial concentration on the adsorption of Pb(II), Cu(II), and MB was evaluated on solutions 20-100 mg/L at 298 K in Figures 5(a)–5(c). The plots (Figures 5(a)–5(c)) showed that the uptake of the pollutants increased when the initial concentration of the solution was increased [62]. Therefore, the adsorption of Pb(II), Cu(II), and MB onto PFS, SAFS, and NAFS was concentration dependent. At the initial concentration of 20 mg/L, it was observed that the mass transfer was low, due to hindering forces such as high mass transfer resistance [63]. However, at the initial concentration of 100 mg/L, the chances of collision between Pb(II), Cu(II), and MB with the adsorbent surface were greater resulting in higher mass transfer [64]. It was observed that all biomaterials had a higher affinity for MB dye than for Pb(II) and Cu(II) metal ions. The maximum adsorption capacities on 100 mg/L solutions onto PFS were 6.834, 4.179, and 2.902 mg/g for MB, Pb(II), and Cu(II), respectively. Adsorption of pollutants from bulk solution was controlled mainly by three steps: (i) film and particle diffusions which involves movement of pollutants from the solution to the exterior surface of the adsorbents and then to the interior surface ([65]), (ii) pore diffusion whereby pollutants were trapped in the pores on the surface of the adsorbent ([66]), and (iii) electrostatic attraction and pi (π) interaction between MB and the adsorbents. Furthermore, the maximum adsorption capacities onto NAFS for MB, Pb(II), and Cu(II) were enhanced to 15.28, 14.44, and 4.475 mg/g. However, for SAFS, the maximum adsorption capacities further improved for all pollutants to 19.81, 18.79, and 6.707 mg/g, respectively.

Figure 5

Effect of the initial concentration of Pb(II), Cu(II), and MB onto pure (a) PFS and treated (b) SAFS and (c) NAFS fennel seed adsorbents (system parameters: $temperature = 298 K, pH = 7, contact time = 120 \min, and adsorbent mass = 10 mg$ ).

(b)

(c)

To evaluate whether the uptake processes followed the Langmuir or Freundlich isotherm model, the value of $r^{2}$ was used as the determining factor. The $r^{2}$ values of Langmuir and Freundlich were compared, and the model that gave the highest $r^{2}$ and closer to unity (1) was the one considered. It was observed from Table 3 that the uptake processes of MB onto all adsorbents had high $r^{2}$ values for Freundlich than Langmuir. The Freundlich model is linked to the formation of multilayer of MB on adsorbent heterogeneous surfaces ([67, 68]), while the uptake processes of Pb(II) and Cu(II) had high $r^{2}$ values for Langmuir than Freundlich. The Langmuir model is based on the premise that monolayer adsorption was formed onto sites having an equal affinity for both cations [69, 70].

Table 3

Isotherm models for the adsorption of Pb(II), Cu(II), and MB onto pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

Isotherms		PFS			NAFS			SAFS
Isotherms		MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)
Langmuir	$Q_{o}$ (mg/g)	11.59	10.47	2.754	15.85	18.98	9.201	21.78	25.84	8.002
	$B$	0.01531	0.06215	0.04680	0.1089	0.03282	0.08953	0.06925	0.01698	0.03618
	$r^{2}$	0.9696	0.9904	0.9951	0.9242	0.9980	0.9764	0.9689	0.9951	0.9974
Freundlich	$1 / n$	0.5017	0.1229	0.1527	6.314	0.2942	0.2178	6.141	0.3018	1.142
	$k_{f}$	1.800	1.287	0.5593	5.372	1.176	0.1532	3.978	1.122	2.659
	$r^{2}$	0.9966	0.9498	0.9594	0.9990	0.9959	0.9879	0.9942	0.9939	0.9712
Experimental ( $q_{e}$ )		6.834	4.179	2.902	15.28	14.44	4.475	19.81	18.79	6.707

4.3.2. Time Effect and Kinetic Studies

The efficiency of PFS, SAFS, and NAFS was estimated at different time intervals, to evaluate the uptake rate of each adsorbent towards Pb(II), Cu(II), and MB within 5-120 min (Figures 6(a)–6(c)). It was observed that processes in Figures 6(a)–6(c) followed a similar trend. Adsorption capacities of the adsorbents increased when contact time was increased [71]. Also, the removal rate of MB dye onto all adsorbents was rapid more than that of Pb(II) and Cu(II) cations. In Figure 6(a), it was observed that MB attained equilibrium faster and stabilized within 40 min, while the cations had a slow rate, both reaching equilibrium in 60 min. In Figure 6(b), the rate was higher and MB attained equilibrium in the initial 30 min while Pb(II) and Cu(II) ions reached equilibrium in 40 and 60 min, respectively. Thereafter, no significant increase was recorded. In Figure 6(c), it was observed that both MB and Pb(II) stabilized within the initial 40 min while Cu(II) in 30 min. It was observed that at the beginning of all the adsorption processes removal rate was rapid and this could be explained by the fact that abundant active sites, pores, and surface were available [72, 73]. However, as the time elapsed, the active sites were used and this resulted in little to no adsorption recorded [74].

Figure 6

Time effect studies on the adsorption of Pb(II), Cu(II), and MB onto pure (a) PFS and treated (b) SAFS and (c) NAFS fennel seed adsorbents (system parameters: $temperature = 298 K, pH = 7, working solution = 100 mg / L, and adsorbent mass = 10 mg$ ).

(b)

(c)

The data obtained from the effect of time was used to estimate the kinetic mechanisms involved in the adsorption of Pb(II), Cu(II), and MB on the biomaterials. In this work, three adsorption kinetics models were determined: PFO, PSO, and IPD in Table 4. To quantify the better fitted model either PFO or PSO the value of $r^{2}$ was used as the determining factor. Thereafter, $r^{2}$ values of both models were compared and the one that had the highest $r^{2}$ , closer to unity (1), was considered. Data in Table 4 indicated that all adsorption processes in this work had the highest $r^{2}$ values for PFO than PSO. Therefore, PFO was the better fitted model in the adsorption of Pb(II), Cu(II), and MB onto PFS, NAFS, and SAFS. This indicated the processes were more towards physisorption [75].

Table 4

Kinetic models for the adsorption of Pb(II), Cu(II), and MB onto pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

Models		PFS			NAFS			SAFS
Models		MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)
PFO	$q_{e}$ (mg/g)	6.800	5.277	3.143	15.01	14.09	4.893	19.04	19.51	6.483
	$K_{1}$ (min^-1)	0.634	0.061	0.064	0.206	0.055	0.136	0.148	0.048	0.029
	$r^{2}$	0.971	0.983	0.971	0.976	0.995	0.976	0.982	0.991	0.986
PSO	$q_{e}$ (mg/g)	9.204	5.947	3.619	28.92	23.57	14.31	28.56	27.84	9.891
	$K_{2}$ (g/mg min)	0.198	0.262	0.430	0.071	0.101	0.231	0.058	0.077	0.283
	$r^{2}$	0.943	0.944	0.968	0.963	0.967	0.944	0.978	0.951	0.934
Experimental ( $q_{e}$ )		6.971	5.543	3.193	15.98	13.73	5.102	19.83	18.67	6.19

4.3.3. Diffusion Processes

The adsorption mechanism(s) of Pb(II), Cu(II), and MB onto PFS, NAFS, and SAFS was further investigated by different diffusion processes such as intraparticle, film, and pore in (Table 5). It was observed that the values for intraparticle particle diffusion rate (K_i) were higher for PFS than for the treated adsorbents (NAFS and SAFS), while the surface adsorption parameter ( $C$ ) gave higher values for NAFS and SAFS than PFS. This trend suggests that surface adsorption was dominant on NAFS and SAFS than PFS. This further indicates that there was reduced rate of diffusion on the adsorbents surface, i.e., movement of the pollutants from the exterior to the interior surface [76]. The calculated intraparticle diffusion coefficient ( $D_{i}$ ) for the adsorbents was in the range of 10^-5 to 10^-13; this suggests that the uptake processes of Pb(II), Cu(II), and MB involved chemisorption systems [77]. The data in the table revealed that $D_{1}$ was higher for NAFS and SAFS than PFS, and this signified that film diffusion was also involved in the uptake processes [78]. However, the obtained values for (D₂) were low in PFS; this showed that there was restriction of pollutants in the internal surface of the adsorbent. For NAFS and SAFS, the values for $D_{2}$ were higher suggesting that pore diffusion was involved in the uptake processes [79].

Table 5

Diffusion parameter for the removal of Pb(II), Cu(II), and MB onto PFS, NAFS and SAFS.

Diffusion model		PFS			NAFS			SAFS
Diffusion model		MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)
Intraparticle diffusion	$C$ (mg/g)	2.397	2.027	1.078	13.61	11.91	2.301	16.92	16.26	2.744
	$K_{i}$ (g/mg min^0.5)	0.835	0.641	0.386	0.216	0.166	0.676	0.266	0.220	0.629
	$D_{i}$ (cm²/s)	$4.8 \times 10^{- 6}$	$4.1 \times 10^{- 6}$	$2.2 \times 10^{- 6}$	$2.7 \times 10^{- 5}$	$2.4 \times 10^{- 5}$	$4.7 \times 10^{- 6}$	$3.4 \times 10^{- 5}$	$3.3 \times 10^{- 5}$	$5.6 \times 10^{- 6}$
	$r^{2}$	0.971	0.976	0.972	0.989	0.987	0.970	0.986	0.985	0.989
Film diffusion	$D_{1}$ (cm²/s)	$3.1 \times 10^{- 8}$	$2.6 \times 10^{- 8}$	$1.3 \times 10^{- 8}$	$4.0 \times 10^{- 8}$	$3.2 \times 10^{- 8}$	$2.5 \times 10^{- 8}$	$5.0 \times 10^{- 8}$	$4.3 \times 10^{- 8}$	$3.1 \times 10^{- 8}$
Film diffusion	$r^{2}$	0.9774	0.9856	0.9723	0.9734	0.9788	0.9675	0.9754	0.9790	0.9682
Pore diffusion	$D_{2}$ (cm²/s)	$1.6 \times 10^{- 8}$	$1.5 \times 10^{- 8}$	$1.1 \times 10^{- 8}$	$2.3 \times 10^{- 7}$	$2.0 \times 10^{- 7}$	$2.1 \times 10^{- 8}$	$2.8 \times 10^{- 7}$	$2.8 \times 10^{- 7}$	$2.5 \times 10^{- 8}$
Pore diffusion	$r^{2}$	0.9432	0.9695	0.9698	0.9561	0.9556	0.9506	0.9521	0.9675	0.9570

4.3.4. Temperature Effect and Thermodynamic Studies

The effect of temperature on the sorption of Pb(II), Cu(II) ions, and MB dye was evaluated at 288, 298, and 308 K as shown in Figures 7(a)–7(c). It was observed that all processes (Figures 7(a)–7(c)) followed the same trends. The uptake of all pollutants increased when the temperature of the system was increased. The plots recorded a sharp increase in adsorption when the temperature of the system was increased from 288 to 308 K. This revealed that the uptake processes were endothermic in nature [20, 80]. The results indicated that temperature increase had a positive effect on the uptake reactions. Increasing the temperature of the system supplied the pollutants with enough kinetic energy to overcome the hindering forces such as mass transfer resistance [81]. Therefore, this enhanced the adsorption processes.

Figure 7

Temperature effect studies on the adsorption of Pb(II), Cu(II), and MB onto pure (a) PFS and treated (b) SAFS and (c) NAFS fennel seed adsorbents (system parameters: $working solution = 100 mg / L temperature = 298 K, pH = 7, contact time = 120 \min, and adsorbent mass = 10 mg$ ).

(b)

(c)

Thermodynamic parameters Gibbs energy ( $Δ G^{o}$ ), standard enthalpy ( $Δ H^{o}$ ), and standard entropy ( $Δ S^{o}$ ) in Table 6 were estimated from the data of temperature effect. The obtained data for $Δ H^{o}$ had positive values; this suggested that the adsorption of MB dye, Pb(II), and Cu(II) ions onto used biosorbents was endothermic processes [82]. This was in agreement with temperature effect results which revealed that the reactions favored high temperatures. It was also observed that the reactions had $Δ S^{o}$ values that were negative this indicated reduced degree of freedom at the solid-liquid at equilibrium [83]. The parameter $Δ G^{o}$ gave negative values; this suggested that the reactions were spontaneous and feasible [21].

Table 6

Thermodynamics for the adsorption of Pb(II), Cu(II), and MB onto pure (PFS) and treated (NAFS and SAFS) fennel seed adsorbents.

Parameter	PFS			NAFS			SAFS
Parameter	MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)	MB	Pb(II)	Cu(II)
$Δ H^{o}$ (KJ mol^-1)	3.665	2.723	2.397	9.275	8.028	3.818	18.75	16.05	5.916
$Δ S^{o}$ (J mol^-1 K^-1)	-9.820	-6.392	-4.682	-30.51	-25.96	-9.845	-64.76	-53.78	-17.26
$Δ G^{o}$ (KJ mol^-1) 288 K	-7.230	-7.480	-8.796	-4.444	-4.959	-8.358	-5.464	-0.652	-7.635
298 K	-5.564	-6.508	-8.165	-0.718	-1.623	-6.949	-1.430	-4.222	-6.893
308 K	-5.636	-6.437	-8.029	0.574	-0.696	-6.748	-3.367	-10.14	-4.734

4.3.5. pH Effect

The pH of the solution is among the most essential parameters in adsorption studies. It influences the oxidation state of the pollutants in the solution and the surface properties of the biomaterials [84]. Depending on the solution pH, Cu(II) ions exist as different species such as Cu(II), Cu(OH)⁺, Cu(OH)₂, Cu(OH)₃ ⁻, and Cu(OH)₄ ²⁻ ([22]), while Pb(II) ions can exist as Pb(II), Pb(OH)⁺, Pb₄(OH)₂ ⁴⁺, Pb₃(OH)₄ ²⁺, and Pb(OH)₂ [7]. Typically, MB solution is constituted of positively charged unprotonated cations [85]. Therefore, in this work, pH effect was evaluated at pH 1, 3, 5, 7, and 8 for the adsorption of Pb(II), Cu(II) cations, and MB dye on working standard 100 mg/L at 298 K as shown in Figures 8(a)–8(c). The adsorption trend of PFS is shown in Figure 8(a). It was observed from the plot that at strong acidic conditions around pH 1–3 the uptake of the pollutants was low. This was because at pH 1–3 effective competition was high for active sites between protons (H⁺) and pollutants [86]. The adsorption of (H⁺) protonated the surface of the biomaterial and resulted in enhancing the repulsion forces between pollutants and adsorbent surface resulting in low adsorption. However, when the pH of the solution was increased to pH 5, the uptake slightly increased. This could be explained by the fact that at pH 5 effective competition was less and as such improved the uptake [62]. Further increase in uptake was observed when the pH of the solution was increased to pH 7 and 8. This was because the surface of adsorbents was deprotonated, and this resulted in increased electrostatic interaction between the pollutants and functional groups such as −OH⁻, −CO⁻, and -COC groups [87]. The adsorption processes of SAFS and NAFS are shown in Figures 8(b) and 8(c), respectively. It was observed that the plots for SAFS and NAFS followed the same pattern. At acidic conditions pH 1, 3, and 5, the uptake of the pollutants was reduced. However, the uptake significantly improved when the pH of the solution was increased to 7 and 8. The adsorption of Pb(II), Cu(II) ions, and MB dye onto PFS, SAFS, and NAFS was pH dependent.

Figure 8

pH effect on the removal of Pb(II), Cu(II), and MB onto pure (a) PFS and treated (b) SAFS and (c) NAFS fennel seed adsorbents (system parameters: $temperature = 298 K, working solution = 100 mg / L, contact time = 120 \min, and adsorbent mass = 10 mg$ ).

(b)

(c)

4.3.6. Adsorption Mechanism

Establishing the adsorption mechanism(s) is of great importance. This is dependent on several factors such as the morphology and functional groups present on the surface of the adsorbent, as well as size and charge of the pollutant. The major structural constituents of fennel seeds are mostly lignocellulosic materials (hemicellulose, cellulose, and lignin). The lignocellulosic materials are natural polymers, containing repeating units of monomers. The structure of lignocellulosic materials consists abundantly of oxygen-rich functional groups such as (−OH), (−CO), and (−COOH) which could be a good candidate for adsorption processes [35, 43]. Therefore, it was anticipated that these functional groups were involved in the uptake processes. It was observed in Scheme 1 that the uptake of MB and the cations (Cu(II) and Pb(II)) was controlled by different adsorption mechanism(s). The removal of MB involved several processes such as (i) π-π interaction between the aromatic rings [39, 41, 88, 89], (ii) electrostatic attraction occurred positively charged (N⁺) from MB and (OH) from lignocellulosic materials [90], and (iii) hydrogen bonds formed by (N) molecules from MB and interacting with (O) molecules from lignocellulosic materials ([91]), while the uptake of both Cu(II) and Pb(II) was controlled mainly by electrostatic attraction.

Scheme 1

Proposed adsorption mechanism of Pb(II), Cu(II), and MB onto fennel seeds.

4.3.7. Effect of Competing Ions/Molecules on the Adsorption of Pb(II), Cu(II), and MB

The effect of competing ions/molecules was studied in order to investigate the influence it had on the adsorption processes. Figure 9(a) shows the adsorption of Pb(II) in the presence of competing ions/molecules (Cu(II) and MB) at different concentrations. It was observed that the adsorption potential of the adsorbent decreased when the concertation of competing ions/molecules was increased from 50 to 200 mg/L in the solution. Moreover, considerably decline in $q_{e}$ was recorded when the competing ions/molecules were 200 mg/L. In the presence of Cu(II) ions, $q_{e}$ declined from 4.02 to 3.54 mg/g. When MB was dissolved in the solution, it declined to 2.94 mg/g. This might be explained by the fact the adsorbent had high affinity for Cu(II) ions and MB dye. Also, when the adsorbate is held on the surface of PFS; it had the shielding effect on the functional groups [92]. This inhibited the electrostatic interaction between Cu(II) and the adsorbent, thus decreasing the adsorption capacity ( $q_{e}$ ) of the adsorbent [93]. Similar observation was recorded in (Figures 9(b) and 9(c)) for the adsorption of Cu(II) and MB, respectively. In Figure 9(b), the presence of Pb(II) ions decreased the adsorption of Cu(II) from 2.96 to 2.41 mg/g, while the introduction of MB decreased the adsorption to 2.04 mg/g. According to Figure 9(c), the $q_{e}$ of MB (6.92 mg/g) declined when Cu(II) and Pb(II) ions were added to the MB solutions to 6.60 and 6.44 mg/g, respectively.

Figure 9

Effect of competing ions/molecules on the adsorption of (a) Pb(II), (b) Cu(II), and (c) MB onto pure fennel seeds (PFS) (system parameters: $temperature = 298 K, working solution = 100 mg / L, contact time = 120 \min, and adsorbent mass = 10 mg$ ).

(b)

(c)

4.4. Postadsorption Studies

4.4.1. FTIR Analysis

FTIR spectra of PFS, NAFS, and SAFS were compared before and after adsorption. This was performed in order to identify the functional groups accountable for adsorption of the pollutants [94]. It was observed in Figure 10(a) that PFS exhibited the peak for (–OH) at 3291 cm^-1; however, after adsorption, the peak decreased in intensity. The peak assigned to (–COOH) at 1587 cm^-1 slightly shifted after adsorption to 1609 cm^-1. A new peak was developed after adsorption at 1455 cm^-1. The peak for (–COC) at 1016 cm^-1 considerably decreased in intensity after adsorption. The changes suggest that the functional groups were involved in uptake processes, while other groups such as (–CH=CH), (–CH), and (–C=O) remained unchanged before and after adsorption implying that the groups did not take part in the uptake. For NAFS in Figure 10(b), the peak at 1141 shifted after adsorption to 1150 cm^-1. The peak for (–COC) at 1016 cm^-1 also shifted to 1011 cm^-1. Other functional groups remained unchanged. For SAFS (Figure 10(b)), the peak for (–OH) was at 3295 cm^-1. However, after adsorption, this peak significantly decreased in intensity. The peaks for (–CO) and (–COC) respective at 1243 and 1016 cm^-1 also decreased in intensity after adsorption. Other functional groups remained unchanged.

Figure 10

FTIR spectra (a) PFS, (b) NAFS, and (c) SAFS before and after adsorption.

(b)

(c)

4.4.2. SEM Analysis

The SEM images of the adsorbents after adsorption were used to evaluate the stability of the adsorbents as shown in Figures 11(a)–11(f). It was observed that the effect of pollutants binding to the surface somehow caused changes to the morphology of the adsorbents. Particularly for PFS (Figures 11(a) and 11(b)) and SAFS (Figures 11(e) and 11(f)), the pores on the surface were larger after adsorption compared to before (i.e., PFS (Figures 1(a) and 1(b)) and SAFS (Figures 1(e) and 1(f)). Similar observations were made in a number of studies prior [95–97].

Figure 11

SEM images of pure ((a, b) PFS) and treated ((c, d) NAFS and (e, f) SAFS) fennel seed adsorbents after adsorption.

(b)

(c)

(d)

(e)

(f)

4.5. Reusability Test

The biosorbent reusability test was evaluated over three reuse cycles. The reusability results are shown in Figures 12(a)–12(c). After each cycle, the biosorbents were regenerated before reuse. It was observed in Figures 12(a)–12(c) that the biosorbents lost some of the adsorptive strength in consecutive cycles. This may be attributed to the inability of the biosorbents to desorb some of the pollutants from the pores and surface during the regeneration process; therefore, this resulted in low uptake in the following cycles.

Figure 12

Reusability test of pure (a) PFS and treated (b) NAFS and (c) SAFS fennel seed adsorbents towards the adsorption of Pb(II), Cu(II) ions, and MB dye.

(b)

(c)

4.6. Comparison Studies

The removal uptake of fennel seeds was compared with similar biosorbents listed in Table 7. The data shows that modified fennel seeds had good uptake than other biosorbents towards Pb(II), Cu(II) ions, and MB dye. The adsorbents used in this study are promising and have a good uptake.

Table 7

Comparison studies of fennel seeds for the adsorption of MB, Cu(II), and Pb(II) with other agriculture biomaterials.

Adsorbent	Pollutant	$q_{e}$ (mg/g)	pH	Contact time (min)	Concentration (mg/L)	Ref
Treated fennel seeds (SAFS)	MB	19.81	8	120	100	This study
Spent coffee grounds	MB	18.70	5	12 hours	500	[98]
Black cumin seeds	MB	16.85	4.8	120	100	[7]
Carbon from coir pith	MB	5.87	6.9	120	50	[99]
Brewery waste	MB	4.920	7	135	2.5	[100]
Treated fennel seeds (SAFS)	Pb(II)	18.79	8	120	100	This study
Moringa stenopetala seeds	Pb(II)	16.13	5	360	60	[101]
Black sapote seeds	Pb(II)	5.50	9	48 hours	—	[102]
Bagasse fly ash	Pb(II)	2.50	5	140	60	[103]
Banana peel	Pb(II)	2.18	5	20	80 μg mL^-1	Anwar et al., 2010
Treated fennel seeds (SAFS)	Cu(II)	6.707	8	120	100	This study
Watermelon rind	Cu(II)	5.730	—	10 hours	10	[104]
Barley straw	Cu(II)	4.640	7	240	10	[105]
Almond shell	Cu(II)	3.620	6	120	50	[106]
Potato peels	Cu(II)	0.3877	6	120	400	[107]

5. Conclusions

This work reports on biosorbent material of fennel seed treatment with HNO₃ and H₂SO₄ solutions for the removal of MB dye, Pb(II), and Cu(II). SEM images established that the surface morphology of the adsorbents was porous. EDX analysis revealed that elements C and O were the dominant constituents while trace amounts of P and Cl were recorded. FTIR spectra confirmed the presence of (−OH), (−COC), (−C=O), and (−COOH) groups on the surface of the adsorbents. The results for the concentration effect revealed that the uptake of the pollutants increased when the initial concentration of the solution was increased. At the initial concentration of 20 mg/L, it was found that the mass transfer was low, due to high hindering forces. However, at an initial concentration of 100 mg/L, the chances of collision between Pb(II), Cu(II), and MB with the adsorbent surface were greater therefore; this resulted in higher mass transfer. The maximum adsorption capacities on 100 mg/L solutions onto PFS were 6.834, 4.179, and 2.902 mg/g for MB, Pb(II), and Cu(II), respectively. However, onto NAFS, the maximum adsorption capacities for MB, Pb(II), and Cu(II) were enhanced to 15.28, 14.44, and 4.475 mg/g, while for SAFS the maximum adsorption capacities further improved for all pollutants to 19.81, 18.79, and 6.707 mg/g, respectively. Thus, the uptake of pollutants onto PFS, SAFS, and NAFS was concentration dependent. Isotherm data established that the uptake processes of MB dye onto all adsorbents fitted Freundlich while both cations were described by the Langmuir model. It was found that adsorption increased when the temperature of the system was increased. The thermodynamic parameter $Δ H^{o}$ had positive values which indicated the endothermic nature of the processes. The obtained values for $Δ G^{o}$ suggested that the uptake was spontaneous and feasible.

Footnotes

Data Availability

The data supporting the findings of this study may be made available from the corresponding author on request.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgments

The authors also acknowledge support of the Department of Chemistry, Vaal University of Technology, Vanderbijlpark, South Africa, for granting facilities. Support for this research was provided by the National Research Fund (NRF) of South Africa (Grant: TTK190403426819) and the Vaal University of Technology, Vanderbijlpark, South Africa.

Supplementary Materials

References

DeNicola

Aburizaiza

O. S.

Siddique

Khwaja

Carpenter

D. O.

Climate change and water scarcity: the case of Saudi Arabia

Annals of Global Health 2015 81

5787690

3 342 353

10.1016/j.aogh.2015.08.005

2-s2.0-84950298887

Shooto

N. D.

Thabede

P. M.

Naidoo

E. B.

Simultaneous adsorptive study of toxic metal ions in quaternary system from aqueous solution using low cost black cumin seeds (Nigella sativa) adsorbents

South African Journal of Chemical Engineering 2019 30

5787690

15 27

10.1016/j.sajce.2019.07.002

Jaishankar

Tseten

Anbalagan

Mathew

B. B.

Beeregowda

K. N.

Toxicity, mechanism and health effects of some heavy metals

Interdisciplinary Toxicology 2014 7

5787690

2 60 72

10.2478/intox-2014-0009

2-s2.0-84910613290

26109881

Chen

Tang

Yang

Tsang

Y. F.

Wang

Zhou

Polyamide 6 microplastics facilitate methane production during anaerobic digestion of waste activated sludge

Chemical Engineering Journal 2021 408, article 127251

5787690

10.1016/j.cej.2020.127251

Sprynskyy

Solid–liquid–solid extraction of heavy metals (Cr, Cu, Cd, Ni and Pb) in aqueous systems of zeolite–sewage sludge

Journal of Hazardous Materials 2009 161

5787690

2-3 1377 1383

10.1016/j.jhazmat.2008.04.101

2-s2.0-56249108033

18538472

Dar

O. A.

Malik

M. A.

Talukdar

M. I. A.

Hashmi

A. A.

Bionanocomposites in water treatment

Bionanocomposites Green Synthesis and Applications Micro and Nano Technologies 2020

Elsevier

505 518

Thabede

P. M.

Shooto

N. D.

Naidoo

E. B.

Removal of methylene blue dye and lead ions from aqueous solution using activated carbon from black cumin seeds

South African Journal of Chemical Engineering 2020 33

5787690

39 50

10.1016/j.sajce.2020.04.002

Jan

A. T.

Azam

Siddiqui

Ali

Choi

Haq

Q. M. R.

Heavy metals and human health: mechanistic insight into toxicity and counter defense system of antioxidants

International Journal of Molecular Sciences 2015 16

5787690

12 29592 29630

10.3390/ijms161226183

2-s2.0-84949870977

26690422

Malik

G. S.

Jain

C. K.

Yadav

A. K.

Removal of heavy metals from emerging cellulosic low-cost adsorbents: a review

Applied Water Science 2017 7

5787690

5 2113 2136

10.1007/s13201-016-0401-8

10.

Mahmud

H. N. M. E.

Haq

A. K. O.

Yahya

R. B.

Removal of heavy metal ions from wastewater aqueous solution by polypyrrole-based adsorbent

Royal Society of Chemistry 2015 6

5787690

1 13

11.

Dermiral

Gungor

Adsorption of copper(II) from aqueous solutions on activated carbon prepared from grape bagasse

Journal of Cleaner Production 2016 124

5787690

103 113

10.1016/j.jclepro.2016.02.084

2-s2.0-84977963096

12.

Sandoval

Hernandez-Ventura

Klimova

T. A.

Titanate nanotubes for removal of methylene blue dye by combined adsorption and photocatalysis

Fuel 2017 198

5787690

22 30

10.1016/j.fuel.2016.11.007

2-s2.0-85027924434

13.

Zhang

Chen

Wang

Zou

Chen

Zhang

Facile one-pot fabrication of nano-Fe₃O₄/carboxyl-functionalized baker’s yeast composites and their application in methylene blue dye adsorption

Applied Surface Science 2017 392

5787690

312 320

10.1016/j.apsusc.2016.09.050

2-s2.0-84991063342

14.

Dai

Sun

Long

Chen

Responses of habitat suitability for migratory birds to increased water level during middle of dry season in the two largest freshwater lake wetlands of China

Ecological Indicators 2021 121

5787690

10.1016/j.ecolind.2020.107065

15.

Xie

Xue

Chen

Shang

Luo

Phanerochaete chrysosporium-driven quinone redox cycling promotes degradation of imidacloprid

International Biodeterioration & Biodegradation 2020 151

5787690

10.1016/j.ibiod.2020.104965

16.

Chen

Peng

Leng

Jiang

Zhou

Leng

Effect of biomass type and pyrolysis temperature on nitrogen in biochar, and the comparison with hydrochar

Fuel 2021 291

5787690

10.1016/j.fuel.2021.120128

17.

Shooto

N. D.

Thabethe

P. M.

Bhila

Moloto

Naidoo

E. B.

Lead ions and methylene blue dye removal from aqueous solution by mucuna beans (velvet beans) adsorbents

Journal of Environmental Chemical Engineering 2019 8

5787690

1 11

18.

Duman

Tunc

Polat

T. G.

Bozoglan

B. C.

Synthesis of magnetic oxidized multiwalled carbon nanotube-κ-carrageenan-Fe 3 O 4 nanocomposite adsorbent and its application in cationic methylene blue dye adsorption

Carbohydrates Polymer 2016 147

5787690

79 88

10.1016/j.carbpol.2016.03.099

2-s2.0-84963811780

19.

Yang

Zhou

Yang

Wan

Luo

Tang

Tsang

D. C. W.

Simultaneous degradation of _p_ -arsanilic acid and inorganic arsenic removal using M-rGO/PS Fenton-like system under neutral conditions

Journal of Hazardous Materials 2020 399

5787690

10.1016/j.jhazmat.2020.123032

32937710

20.

Zhang

Zhong

Wang

Removal of ammonium from aqueous solutions using zeolite synthesized from electrolytic manganese residue

International Journal of Chemical Engineering 2020 2020

5787690

8818455

10.1155/2020/8818455

21.

Batool

Akbar

Iqbal

Noreen

Bukhari

S. N. A.

Study of isothermal, kinetic, and thermodynamic parameters for adsorption of cadmium: an overview of linear and nonlinear approach and error analysis

Bioinorganic Chemistry and Applications 2018 2018

5787690

3463724

10.1155/2018/3463724

2-s2.0-85050394159

22.

Yang

Wei

Zhong

Cui

Wei

Modifying hydroxyapatite nanoparticles with humic acid for highlyefficient removal of Cu(II) from aqueous solution

Colloids and Surfaces A: Physicochemical and Engineering Aspects 2016 490

5787690

9 21

10.1016/j.colsurfa.2015.11.039

2-s2.0-84947976566

23.

Kumar

Dwivedi

S. K.

A review on accessible techniques for removal of hexavalent Chromium and divalent Nickel from industrial wastewater: Recent research and future outlook

Journal of Cleaner Production 2021 295

5787690

10.1016/j.jclepro.2021.126229

24.

Rambabu

Thanigaivelan

Bharath

Sivarajasekar

Banat

Show

P. L.

Biosorption potential of Phoenix dactylifera coir wastes for toxic hexavalent chromium sequestration

Chemosphere 2021 268

5787690

10.1016/j.chemosphere.2020.128809

25.

Nkutha

C. S.

Shooto

N. D.

Naidoo

E. B.

Adsorption studies of methylene blue and lead ions from aqueous solution by using mesoporous coral limestones

Chemical Engineering 2020 34

5787690

151 157

10.1016/j.sajce.2020.08.003

26.

Nkutha

C. S.

Shooto

N. D.

Naidoo

E. B.

Adsorption of Cr(VI), Pb(II) ions and methylene blue dye from aqueous solution using pristine and modified coral limestone

Asian Journal of Chemistry 2020 32

5787690

10 2624 2632

10.14233/ajchem.2020.22815

27.

Shooto

N. D.

Naidoo

E. B.

Detoxification of wastewater by paw–paw (carica papaya L.) seeds adsorbents

Asian Journal of Chemistry 2019 31

5787690

10 2249 2256

10.14233/ajchem.2019.22051

2-s2.0-85071452262

28.

Thabede

P. M.

Shooto

N. D.

Xaba

Naidoo

E. B.

Magnetite Functionalized Nigella Sativa Seeds for the Uptake of Chromium(VI) and Lead(II) Ions from Synthetic Wastewater

Adsorption Science and Technology 2021 2021, article 6655227

5787690

10.1155/2021/6655227

29.

Mpatani

F. M.

Han

Aryee

A. A.

Kani

A. N.

Adsorption performance of modified agricultural waste materials for removal of emerging micro-contaminant bisphenol A: a comprehensive review

Science of the Total Environment 2021 780

5787690

10.1016/j.scitotenv.2021.146629

34030339

30.

Sudhakar

Mall

I. D.

Srivastava

V. C.

Adsorptive removal of bisphenol-A by rice husk ash and granular activated carbon–a comparative study

Desalination and Water Treatment 2016 57

5787690

26 12375 12384

10.1080/19443994.2015.1050700

2-s2.0-84930074290

31.

Liang

Jin

Zhou

Pan

The role of ash content on bisphenol A sorption to biochars derived from different agricultural wastes

Chemosphere 2017 171

5787690

66 73

10.1016/j.chemosphere.2016.12.041

2-s2.0-85006983169

28002768

32.

Zazouli

M. A.

Veisi

Modeling of bisphenol A (BPA) removal from aqueous solutions by adsorption using response surfacemethodology (RSM), world academy of science, engineering and technology

International Journal of Chemical and Molecular Engineering 2016 10

5787690

215 220

10.5281/zenodo.1111881

33.

Ahmad

B. S.

Talou

Saad

Hijazi

Cerny

Kanaan

Chokr

Merah

Fennel oil and by-products seed characterization and their potential applications

Industrial Crops and Products 2018 111

5787690

92 98

10.1016/j.indcrop.2017.10.008

2-s2.0-85030838807

34.

Abdellaoui

Bouhlali

E. T.

Derouich

El-Rhaffari

Essential oil and chemical composition of wild and cultivated fennel (Foeniculum vulgare Mill.): a comparative study

South African Journal of Botany 2020 135

5787690

93 100

10.1016/j.sajb.2020.09.004

35.

Barros

Carvalho

A. M.

Ferreira

I. C. F. R.

The nutritional composition of fennel (Foeniculum vulgare): Shoots, leaves, stems and inflorescences

LWT- Food Science and Technology 2010 43

5787690

5 814 818

10.1016/j.lwt.2010.01.010

2-s2.0-76749086924

36.

Haddar

Elksibi

Meksi

Mhenni

M. F.

Valorization of the leaves of fennel (Foeniculum vulgare) as natural dyes fixed on modified cotton: A dyeing process optimization based on a response surface methodology

Industrial Crops and Products 2014 52

5787690

588 596

10.1016/j.indcrop.2013.11.019

2-s2.0-84890193751

37.

Tardio

de Santayana

Morales

Ethnobotanical review of wild edible plants in Spain

Botanical Journal of the Linnean Society 2006 152

5787690

1 27 71

10.1111/j.1095-8339.2006.00549.x

2-s2.0-33748297686

38.

Tardío

Pascual

Morales

Wild food plants traditionally used in the province of Madrid, Central Spain

Economic Botany 2005 59

5787690

2 122 136

10.1663/0013-0001(2005)059[0122:WFPTUI]2.0.CO;2

2-s2.0-21444450222

39.

Ahmed

A. F.

Shi

Liu

Kang

Comparative analysis of antioxidant activities of essential oils and extracts of fennel (Foeniculum vulgare Mill.) seeds from Egypt and China

Food Science and Human Wellness 2019 8

5787690

1 67 72

10.1016/j.fshw.2019.03.004

40.

Masoudzadeh

S. H.

Mohammadabadi

Khezri

Stavetska

R. V.

Oleshko

V. P.

Babenko

O. I.

Yemets

Kalashnik

O. M.

Effects of diets with different levels of fennel (Foeniculum vulgare) seed powder on DLK1 gene expression in brain, adipose tissue, femur muscle and rumen of Kermani lambs

Small Ruminant Research 2020 193

5787690

106276

10.1016/j.smallrumres.2020.106276

41.

Ahmed

I. M.

Helal

A. A.

El Aziz

N. A.

Gamal

Shaker

N. O.

Helal

A. A.

Influence of some organic ligands on the adsorption of lead by agricultural soil

Arabian Journal of Chemistry 2019 12

5787690

8 2540 2547

10.1016/j.arabjc.2015.03.012

2-s2.0-85029814094

42.

Hayat

Abbas

Hussain

Shahzad

S. A.

Tahir

M. U.

Effect of microwave and conventional oven heating on phenolic constituents, fatty acids, minerals and antioxidant potential of fennel seed

Industrial Crops and Products 2019 140

5787690

111610

10.1016/j.indcrop.2019.111610

2-s2.0-85070186429

43.

Cataldi

T. R. I.

Margiotta

Zambonin

C. G.

Determination of sugars and alditols in food samples by HPAEC with integrated pulsed amperometric detection using alkaline eluents containing barium or strontium ions

Food Chemistry 1998 62

5787690

1 109 115

10.1016/S0308-8146(97)00154-4

2-s2.0-0032077926

44.

Jin

Peng

Liu

Zhang

Yang

Han

Sun

Wang

HNO₃ modified biochars for uranium (VI) removal from aqueous solution

Bioresource Technology 2018 256

5787690

247 253

10.1016/j.biortech.2018.02.022

2-s2.0-85042180112

29453051

45.

Nguyen

D. H.

Tran

H. N.

Chao

H. P.

Lin

C. C.

Effect of nitric acid oxidation on the surface of hydrochars to sorb methylene blue: an adsorption mechanism comparison

Adsorption Science and Technology 2019 37

5787690

7-8 607 622

10.1177/0263617419867519

2-s2.0-85073231014

46.

Güzel

Sayğılı

G. A.

Koyuncu

Yılmaz

Optimal oxidation with nitric acid of biochar derived from pyrolysis of weeds and its application in removal of hazardous dye methylene blue from aqueous solution

Journal of Cleaner Production 2017 144

5787690

260 265

10.1016/j.jclepro.2017.01.029

2-s2.0-85010894781

47.

Laskar

M. A.

Ali

S. K.

Siddiqui

Characterization of the kinetics and thermodynamics for the adsorption of zinc(II) on fennel seeds

Analytical Letters 2016 49

5787690

10 1537 1547

10.1080/00032719.2015.1113421

2-s2.0-84975270868

48.

Rao

R. A. K.

Khan

M. A.

Rehman

Utilization of Fennel biomass (Foeniculum vulgari) a medicinal herb for the biosorption of Cd(II) from aqueous phase

Chemical Engineering Journal 2010 156

5787690

1 106 113

10.1016/j.cej.2009.10.005

2-s2.0-72049099070

49.

Sulthana

Taqui

S. N.

Zameer

Syed

U. T.

Syed

A. A.

Adsorption of ethidium bromide from aqueous solution onto nutraceutical industrial fennel seed spent: kinetics and thermodynamics modeling studies

International Journal of Phytoremediation 2018 20

5787690

11 1075 1086

10.1080/15226514.2017.1365331

2-s2.0-85052884761

30156921

50.

Hussein

T. K.

Jasim

N. A.

Removal of crystal violet and methylene blue from synthetic industrial wastewater using fennel seed as an adsorbent

Journal of Engineering Science and Technology 2019 14

5787690

5 2947 2963

51.

Taqui

S. N.

Yahya

Hassan

Nayak

Syed

A. A.

Development of sustainable dye adsorption system using nutraceutical industrial fennel seed spent studies using Congo red dye

International Journal of Phytoremediation 2017 19

5787690

7 686 694

52.

Lebron

Moreira

V. R.

Santos

L. V. S.

Studies on dye biosorption enhancement by chemically modified Fucus vesiculosus, Spirulina maxima and Chlorella pyrenoidosa algae

Journal of Cleaner Prodiction 2019 240

5787690

118197

10.1016/j.jclepro.2019.118197

2-s2.0-85071632806

53.

Yoon

S.-Y.

Han

S.-H.

Shin

S.-J.

The effect of hemicelluloses and lignin on acid hydrolysis of cellulose

Energy 2014 77

5787690

19 24

10.1016/j.energy.2014.01.104

2-s2.0-84909999424

54.

Guo

Fang

C. C.

Smith

R. L.

Jr.

Solid acid mediated hydrolysis of biomass for producing biofuels

Progress in Energy and Combustion Science 2012 38

5787690

5 672 690

10.1016/j.pecs.2012.04.001

2-s2.0-84864948897

55.

Malik

D. S.

Jain

C. K.

Yadav

A. K.

Preparation and characterization of plant based low cost adsorbents

Journal of Global Biosciences 2015 4

5787690

1 1824 1829

56.

Hanumantharao

Kishore

Ravindhranath

Characterization and adsorption studies of Lagenaria siceraria shell carbon for the removal of fluoride. International Journal of ChemTech

Research 2012 4

5787690

4 1686 1700

57.

Telkapalliwar

N. G.

Shivankar

V. M.

Data of characterization and adsorption of fluoride from aqueous solution by using modified Azadirachta indica bark

Data in Brief 2019 26, article 104509

5787690

58.

Shooto

N. D.

Removal of lead(II) and chromium(VI) ions from synthetic wastewater by the roots of harpagophytum procumbens plant

Journal of Environmental Chemical Engineering 2020 8

5787690

6 104541

10.1016/j.jece.2020.104541

59.

Nandiyanto

A. B. D.

Oktiani

Ragadhita

How to read and interpret FTIR spectroscope of organic Material

Indian Journal of Science and Technology 2019 4

5787690

1 97 118

10.17509/ijost.v4i1.15806

2-s2.0-85062990710

60.

Elangovan

Philip

Chandraraj

Biosorption of chromium species by aquatic weeds: kinetics and mechanism studies

Journal of Hazardous Materials 2008 152

5787690

1 100 112

10.1016/j.jhazmat.2007.06.067

2-s2.0-39749189496

17689012

61.

Dussán

K. J.

Silva

D. D.

Moraes

E. J.

Arruda

P. V.

Felipe

M. G.

Dilute-acid hydrolysis of cellulose to glucose from sugarcane bagasse

Chemical Engineering Transactions 2014 38

5787690

433 438

10.3303/CET1438073

2-s2.0-84901417092

62.

Kuang

Zhang

Zhou

Adsorption of methylene blue in water onto activated carbon by surfactant modification

Water 2020 12

5787690

2 587

10.3390/w12020587

63.

Ocampo-Perez

Leyva-Ramos

Mendoza-Barron

Guerrero-Coronado

R. M.

Adsorption rate of phenol from aqueous solution onto organobentonite: surface diffusion and kinetic models

Journal of Colloid and Interface Science 2011 364

5787690

1 195 204

10.1016/j.jcis.2011.08.032

2-s2.0-80053183921

21911219

64.

Shooto

N. D.

Removal of toxic hexavalent chromium (Cr(VI)) and divalent lead (Pb(II)) ions from aqueous solution by modified rhizomes of Acorus calamus

Surfaces and Interfaces 2020 20

5787690

10.1016/j.surfin.2020.100624

65.

Eder

Müller

Azzari

Arcifa

Peydayesh

Nyström

Mass Transfer Mechanism and Equilibrium Modelling of Hydroxytyrosol Adsorption on Olive Pit-Derived Activated Carbon

Chemical Engineering Journal 2021 404

5787690

10.1016/j.cej.2020.126519

66.

Njoku

V. O.

Hameed

B. H.

Preparation and characterization of activated carbon from corncob by chemical activation with H₃PO₄ for 2,4-dichlorophenoxyacetic acid adsorption

Chemical Engineering Journal 2011 173

5787690

2 391 399

10.1016/j.cej.2011.07.075

2-s2.0-80052582030

67.

Al-Ghouti

M. A.

Daana

D. A.

Guidelines for the use and interpretation of adsorption isotherm models: A review

Journal of Hazardous Materials 2020 393

5787690

122383

10.1016/j.jhazmat.2020.122383

32369889

68.

Zhao

Liu

Tang

Niu

Cai

Meng

Giesy

J. P.

Synthesis of magnetic metal-organic framework (MOF) for efficient removal of organic dyes from water

Scientific Reports 2015 5

5787690

1 11849

10.1038/srep11849

2-s2.0-84936152803

26149818

69.

Lyu

Zhang

Xia

Chen

Wang

Luo

Wang

C. W.

Efficient adsorption of methylene blue by mesoporous silica prepared using sol-gel method employing hydroxyethyl cellulose as a template

Colloids and Surfaces A: Physicochemical and Engineering Aspects 2020 606, article 125425

5787690

10.1016/j.colsurfa.2020.125425

70.

Song

Zhang

Yan

Jiang

Chang

The Langmuir monolayer adsorption model of organic matter into effective pores in activated carbon

Journal of Colloid and Interface Science 2013 389

5787690

1 213 219

10.1016/j.jcis.2012.08.060

2-s2.0-84867916135

23041025

71.

Adebayo

G. B.

Adegoke

H. I.

Fauzeeyat

Adsorption of Cr(VI) ions onto goethite, activated carbon and their composite: kinetic and thermodynamic studies

Applied Water Science 2020 10

5787690

9 213

10.1007/s13201-020-01295-z

72.

Raghubanshi

Ngobeni

S. M.

Osikoya

A. O.

Shooto

N. D.

Dikio

C. W.

Naidoo

E. B.

Dikio

E. D.

Pandey

R. K.

Prakash

Synthesis of graphene oxide and its application for the adsorption of Pb⁺² from aqueous solution

Journal of Industrial and Engineering Chemistry 2017 47

5787690

169 178

10.1016/j.jiec.2016.11.028

2-s2.0-85007425357

73.

Mekonnen

Yitbarek

Soreta

T. R.

Kinetic and thermodynamic studies of the adsorption of Cr(VI) onto some selected local adsorbents

Journal of Chemistry 2015 68

5787690

10.17159/0379-4350/2015/v68a7

2-s2.0-84923315044

74.

Shooto

N. D.

Naidoo

E. B.

Maubane

Sorption studies of toxic cations on ginger root adsorbent

Journal of Industrial and Engineering Chemistry 2019 76

5787690

133 140

10.1016/j.jiec.2019.02.027

2-s2.0-85064887306

75.

Ahmad

A. A.

Din

A. T. M.

Yahaya

N. K. E. M.

Khasri

Ahmad

M. A.

Adsorption of basic green 4 onto gasified Glyricidia sepium woodchip based activated carbon: optimization, characterization, batch and column study

Arabian Journal of Chemistry 2020 13

5787690

8 6887 6903

10.1016/j.arabjc.2020.07.002

76.

Ofomaja

A. E.

Intraparticle diffusion process for lead(II) biosorption onto mansonia wood sawdust

Bioresource Technology 2010 101

5787690

15 5868 5876

10.1016/j.biortech.2010.03.033

2-s2.0-77951092007

20385492

77.

Pholosi

Naidoo

E. B.

Ofomaja

A. E.

Intraparticle diffusion of Cr(VI) through biomass and magnetite coated biomass: A comparative kinetic and diffusion study

Chemical Engineering 2020 32

5787690

39 55

10.1016/j.sajce.2020.01.005

78.

Mao

Yang

Zhao

Adsorption performance and mechanism of Cr(VI) using magnetic PS-EDTA resin from micro-polluted waters

Chemical Egineering Journal 2012 200-202

5787690

480 490

10.1016/j.cej.2012.06.082

2-s2.0-84865569462

79.

Onal

Akmil-Basar

Sarici-Ozdemir

Investigation kinetics mechanisms of adsorption malachite green onto activated carbon

Journal of Hazardous Materials 2007 146

5787690

1-2 194 203

10.1016/j.jhazmat.2006.12.006

2-s2.0-34250370111

80.

Gupta

Vidyarthi

S. R.

Sankararamakrishnan

Concurrent removal of As(III) and As(V) using green low cost functionalized biosorbent – Saccharum officinarum bagasse

Journal of Environmental Chemical Engineering 2015 3

5787690

1 113 121

10.1016/j.jece.2014.11.023

2-s2.0-84920467935

81.

Mohamed

H. S.

Soliman

N. K.

Abdelrheem

D. A.

Ramadan

A. A.

Elghandour

A. H.

Ahmed

S. A.

Adsorption of Cd²⁺ and Cr³⁺ ions from aqueous solutions by using residue of Padina gymnospora waste as promising low-cost adsorbent

Helyion 2019 5

5787690

10.1016/j.heliyon.2019.e01287

2-s2.0-85062221181

82.

Bhattacharjee

Dutta

Saxena

V. K.

A review on biosorptive removal of dyes and heavy metals from wastewater using watermelon rind as biosorbent

Environmental Advances 2020 2

5787690

100007

10.1016/j.envadv.2020.100007

83.

Burakov

A. E.

Galunin

E. V.

Burakova

I. V.

Kucherova

A. E.

Agarwal

Tkachev

A. G.

Gupta

V. K.

Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review

Ecotoxicology and Environmental Safety 2018 148

5787690

702 712

10.1016/j.ecoenv.2017.11.034

2-s2.0-85034950027

29174989

84.

Al-Degs

Y. S.

El-Barghouthi

M. I.

El-Sheikh

A. H.

Walker

G. M.

Effect of solution pH, ionic strength, and temperature on adsorption behavior of reactive dyes on activated carbon

Dyes and Pigments 2008 77

5787690

1 16 23

10.1016/j.dyepig.2007.03.001

2-s2.0-35148834878

85.

Malash

G. F.

El-Khaiary

M. I.

Methylene blue adsorption by the waste of Abu-Tartour phosphate rock

Journal of Colloid and Interface Science 2010 348

5787690

2 537 545

10.1016/j.jcis.2010.05.005

2-s2.0-77953915874

86.

Akpomie

K. G.

Dawodu

F. A.

Efficient abstraction of nickel(II) and manganese(II) ions from solution onto an alkaline-modified montmorillonite

Science 2014 8

5787690

4 343 356

10.1016/j.jtusci.2014.05.001

87.

Bedia

Peñas-Garzón

Gómez-Avilés

Rodriguez

J. J.

Belver

A review on the synthesis and characterization of biomass-derived carbons for adsorption of emerging contaminants from water

Carbon 2018 4

5787690

10.3390/c4040063

88.

Rahman

M. L.

Sarkar

S. M.

Yusoff

M. M.

Abdullah

M. H.

Efficient removal of transition metal ions using poly(amidoxime) ligand from polymer grafted kenaf cellulose

RSC Advances 2016 6

5787690

1 745 757

10.1039/C5RA18502E

2-s2.0-84952311645

89.

Zhu

Herbert

B. E.

Schlautman

M. A.

Carraway

E. R.

Hur

Cation–π Bonding

Journal of Environmental Quality 2004 33

5787690

4 1322 1330

10.2134/jeq2004.1322

90.

De Castro

M. L. F. A.

Abad

M. L. B.

Sumalinog

D. A. G.

Abarca

R. R. M.

Paoprasert

de Luna

M. D. G.

Adsorption of methylene blue dye and Cu(II) ions on EDTA-modified bentonite: isotherm, kinetic and thermodynamic studies

Research 2018 28

5787690

5 197 205

10.1016/j.serj.2018.04.001

2-s2.0-85046735370

91.

Zhang

Wang

Han

Wei

Reed biochar supported hydroxyapatite nanocomposite: characterization and reactivity for methylene blue removal from aqueous media

Journal of Molecular Liquids 2018 263

5787690

53 63

10.1016/j.molliq.2018.04.132

2-s2.0-85046638405

92.

Y. M.

Miao

Wei

Z. G.

Cui

S. Y.

Han

R. M.

Wei

Iron-tannic acid nanocomplexes: facile synthesis and application for removal of methylene blue from aqueous solution

Digest Journal of Nanomaterials & Biostructures (DJNB) 2016 11

5787690

1045 1061

93.

Maurya

N. S.

Mittal

A. K.

Cornel

Rother

Biosorption of dyes using dead macro fungi: effect of dye structure, ionic strength and pH

BioresourceTechnology 2006 97

5787690

3 512 521

10.1016/j.biortech.2005.02.045

2-s2.0-26444455624

16216733

94.

Mabungela

Shooto

N. D.

Mtunzi

Naidoo

E. B.

Binary adsorption studies of Toxic Metal Ions of lead and copper from Aqueous solution by modified Foeniculum vulgaris seeds (Fennel seeds)

Asian Journal of Chemistry 2021 33

5787690

7 1611 1619

10.14233/ajchem.2021.23223

95.

Chen

J. P.

Hong

L. A.

S. N.

Wang

Elucidation of interactions between metal ions and Ca alginate-based ionexchange resin by spectroscopic analysis and modeling simulation

Langmuir 2002 18

5787690

24 9413 9421

10.1021/la026060v

2-s2.0-0037180682

96.

Demirbas

Kobya

Sentirk

Ozkan

Adsorption kinetics for the removal of chromium(VI) from aqueous solutions on the activated carbons prepared from agricultural wastes

Water SA 2004 30

5787690

4 533 539

10.4314/wsa.v30i4.5106

2-s2.0-8444222030

97.

Mitic-Stojanovic

D.-L.

Zarubica

Purenovic

Bojic

Andjelkovic

Bojic

À. L.

Biosorptive removal of Pb²⁺, Cd²⁺ and Zn²⁺ ions from water by agenaria vulgaris shell

Water SA 2011 37

5787690

3 303 312

10.4314/wsa.v37i3.68481

98.

Franca

A. S.

Oliveira

L. S.

Ferreira

M. E.

Kinetics and equilibrium studies of methylene blue adsorption by spent coffee grounds

Desalination 2009 249

5787690

1 267 272

10.1016/j.desal.2008.11.017

2-s2.0-71249116033

99.

Kavitha

Namasivayam

Experimental and kinetic studies on methylene blue adsorption by coir pith carbon

Bioresource Technology 2007 98

5787690

1 14 21

10.1016/j.biortech.2005.12.008

2-s2.0-33748068105

16427273

100.

Tsai

W. T.

Hsu

H. C.

T. Y.

Lin

K. Y.

Lin

C. M.

Removal of basic dye (methylene blue) from wastewaters utilizing beer brewery waste

Journal of Hazardous Materials 2008 154

5787690

1-3 73 78

10.1016/j.jhazmat.2007.09.107

2-s2.0-43049165573

18006225

101.

Kebede

T. G.

Mengistie

A. A.

Dube

Nkambule

T. T. I.

Nindi

M. M.

Study on adsorption of some common metal ions present in industrial effluents by Moringa stenopetala seed powder

Journal of Environmental Chemical Engineering 2018 6

5787690

1 1378 1389

10.1016/j.jece.2018.01.012

2-s2.0-85042421245

102.

Cid

A. A. P.

Hernandez

V. R.

Gonzalez

A. M. H.

Hernandez

A. B.

Alonso

O. C.

Synthesis of activated carbon from black sapote seeds characterized and application in the elimination of heavy metals and textile dyes

Chinese Journal of Chemical Engineering 2020 26

5787690

10.1016/j.cjche.2019.04.021

2-s2.0-85070880165

103.

Gupta

V. K.

Ali

Removal of lead and chromium from wastewater using bagasse fly ash a sugar industry waste

Journal of Colloid and Interface Science 2004 271

5787690

2 321 328

10.1016/j.jcis.2003.11.007

2-s2.0-1242338025

14972608

104.

Liu

Ngo

H. H.

Guo

Tung

K. L.

Optimal conditions for preparation of banana peels, sugarcane bagasse and watermelon rind in removing copper from water

Bioresource Technology 2012 119

5787690

349 354

10.1016/j.biortech.2012.06.004

2-s2.0-84863003837

22750502

105.

Pehlivan

Altun

Parlayici

Modified barley straw as a potential biosorbent for removal of copper ions from aqueous solution

Food Chemistry 2012 135

5787690

4 2229 2234

10.1016/j.foodchem.2012.07.017

2-s2.0-84865320004

22980795

106.

Altun

Pehlivan

Removal of copper(II) ions from aqueous solutions by walnut-, hazelnut- and almond-shells

Clean: Soil, Air, Water 2007 35

5787690

6 601 606

10.1002/clen.200700046

2-s2.0-38049014994

107.

Aman

Kazi

A. A.

Sabri

M. U.

Bano

Potato peels as solid waste for the removal of heavy metal copper (II) from waste water/industrial effluent

Colloids and Surfaces, B: Biointerfaces 2008 63

5787690

1 116 121

10.1016/j.colsurfb.2007.11.013

2-s2.0-40849106450

18215510