Preparation of Magnetic Composite Polyaniline/Fe 3 O 4 −Hydrotalcite and Performance in Removal of Methyl Orange

Abstract

Magnetic composite fabricated from polyaniline and Fe₃O₄-hydrotalcite (Pan/MHT) was successfully applicated for removal of methyl orange (MO) from wastewater. The structure and properties of Pan/MHT were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer-Emmett-Teller adsorption isotherm. Adsorption kinetic results indicated that the adsorption process followed pseudosecond-order kinetic model ( $R^{2} = 0.999$ ), MO adsorption onto Pan/MHT was well described by Freundlich isotherm ( $R^{2} = 0.994$ ), and the MO adsorption capacity of 2 Pan/MHT obtained the highest with $Q_{e} = 156.25 mg / g$ . Batch adsorption experiments were carried out using magnetic composite with the effects of initial MO concentration, solution pH, and adsorbent dosage. The results revealed that the magnetic Pan/MHT exhibited efficient adsorption of MO in the aqueous solution as a result of the affinity for organic dyes, microporous structure, and suitable surface area for adsorption (15,460 m²/g). The superparamagnetic behavior of Pan/MHT (with $H_{c} = 18.56 Oe$ , $M_{s} = 23.38 \times 10^{- 3} emu / g$ , and $M_{r} = 0.91 \times 10^{- 3} emu / g$ ) helps that it could be separated from the solution and performs as an economical and alternative adsorbent to removal and degrade azo dye from wastewater. Pan/MHT was also investigated to reuse after desorption of MO in 0.1 M HCl, and the results show that 2 Pan/MHT can be reused for 4 cycles with $Q_{e} = 79.66 mg / g .$

1. Introduction

Dyes are widely used in many fields, such as textile, cosmetic, pigment, paper industry, dyeing, or tanning industry. In particular, textile industry wastewater contains a lot of dyes with large molecule structure including the azo group which is sustainable and difficult to decompose [1]. The presence of organic dyes is a main cause of environmental pollution problems because they are nonbiodegradable; so, an effective method is necessary to remove them from wastewater sources. It is estimated that 10-15% lost in the effluent during the dyeing process [2]. If they are not promptly treated strictly before releasing to the environment, they can destroy the ecosystem of aquatic organisms and threaten the self-cleaning capacity of the receiving source and the human life.

In recent years, there are many applications for treatment such as membrane filtration, redox, electrochemical, adsorption, and biological methods. Among them, adsorption is the popular method because of its efficiency and economy. The adsorbents which were widely used to remove azo dyes are either inorganic such as activated carbon [3–6], hydrotalcite [7–10], diatomite [11–15] and bentonite [16–19], or organic such as chitosan, alginate, polysaccharide, and polymer materials [20–31] and also hybrid and composite material [32–39]. However, the most challenge for the above adsorbents is the low adsorption capacity and efficiency. Therefore, it is necessary to research and develop new material with good adsorption capacity to treat water contaminated with organic dyes to meet economic efficiency and save costs.

Hydrotalcite (HT) with the general formula is ${[M_{1 - x}^{2 +} M_{x}^{3 +} {(O H)}_{2}]}^{x +} {[{(A^{n -})}_{x / y} . m H_{2} O]}^{x -}$ (M²⁺: Mg, Zn, Ca, Fe, Ni…; M³⁺: Al, Cr, Fe…, and Aⁿ⁻: SO₄ ²⁻, CO₃ ²⁻, F⁻, Cl⁻, organic anions, or high molecular weight polymers). HTs are interested in using to remove many dyes including MO, amaranth (Am), diamine green B (DGB) and brilliant green (BG), and acid orange (AO) by surface adsorption, interlayer anion exchange, restructuration of calcined HT, and anion exchange [40–42].

Although both polyaniline (Pan) and HT have high adsorption capacity and have been widely used in water treatment. The most important problem is the ability to recover and reuse them. Filtration is an easy method and is widely used but it’s not so effective and fast as using the magnetic field. When combined with a magnetic particle Fe₃O₄, the composite or hybrid from HT will have a magnetic property. As a result, the composite produces a constant suspension in an aqueous solution and is immediately separated from the external environment. On the other hand, modification of hydrotalcite including investigation of magnetic Fe₃O₄/HT nanocomposites (MHT) may have great potential for photocatalysis and environmental remediation [43].

As a conductive polymer, polyaniline (Pan) meets the requirements for environmental treatment applications as both an adsorbent and a photo catalyst according to the following characteristics: high adsorption area, flexible bandgap, and steady−state of activation [44]. Pan nanofiber is an effective adsorbent in studying the removal of methyl orange (MO) and black [45, 46]. Pan is also fabricated as a nanotube and nanoparticle, and they all have high efficiency for removal of MO and crystal violet as well as methylene blue [38, 47–51]. Pan nanoparticles give the highest adsorption capacity due to their high surface area of 1083 m²/g. Besides, it was used as an efficient adsorbent to remove for crystal violet, and methyl orange with the maximum adsorption capacity reaching 245 and 220 mg/g, respectively. In addition, Pan acts as a photo catalyst thanks to its electrical conductivity to increase protonation. Oxidation reactions occur on the catalyst surface, decomposition of the pigment produces intermediate compounds, and the final products are CO₂, SO₄ ²⁻, NO₃ ⁻, and NH₄ ⁺. Therefore, the fast charge generation and slow charge recombination lead to enhanced photo catalytic activity.

In summary, both Pan and MHT have high efficiency in the removal of azo dye. However, studies on the adsorption applications of Pan are limited because Pan has a low surface area resulting in low adsorption efficiency. Therefore, many researches are carried out to composing Pan particles with other materials to enhance the adsorption capacity by various synthesis methods. Another way, many reports have shown that MHT material has been suitable for an adsorbent. So, the combination of Pan and MHT to create a Pan/MHT hybrid or composite material has great potential, and it is still not widely exploited for adsorption, especially in wastewater treatment to adsorp dyes (MO, Congo red, ...).

The structure of the hydroxide porous layer and the ability to exchange ions in MHT combined with Pan will give good capacitive properties and high environmental sustainability, because of the special structure that induces ion exchange, restructuration, and the large surface area, so that Pan/MHT can “trap” the MO dye molecules into its structure, recover MO molecules, and remove them from wastewater. In addition, by the restructuring ability, the Pan/MHT material can be desorped for reuse, easily recovered by magnets, saving costs.

For the above advantages of Pan/MHT composite, in this paper, we synthesized Pan/MHT composite with various mass ratios of $m_{Pan} / m_{MHT} = 0.5, 1, and 2$ . Then, we investigate the adsorption kinetic and isotherm. We also studied the effect of contact time, pH, and adsorbent dose onto the adsorption capacity of MO in water.

2. Experimental Section

2.1. Materials

All the used reagents (Zn(NO₃)₂.4H₂O, Al(NO₃)₃.9H₂O, FeCl₃, FeCl₂, NaOH, HCl, aniline, ammonium persulphate) were analytical grade reagents. Methyl orange (MO) is an azo dye, with the chemical formula C₁₄H₁₅N₃O₃S, and molecular weight is 305.35 g/mol and is often used as an indicator. In this work, MO was used to simulate industrial wastewater in order to evaluate the adsorption capacity of Pan/MHT.

2.2. Preparation of Magnetic Hydrotalcite (MHT)

MHT was preparated by coprecipitation method in the presence of Fe₃O₄ (Figure 1). An accurate amount of 0.1 g Fe₃O₄ was dispersed in distilled water (10 mL). A mixture of Zn(NO₃)₂.4H₂O and Al(NO₃)₃.9H₂O with Zn²⁺/Al³⁺ molar ratio of 2.0 was dissolved in 100 mL distilled water and then coprecipitated into the Fe₃O₄ dispersion. The pH of the reaction solution was kept at around $9.5 \pm 0.1$ . Then, the coprecipitated mixture was heated for aging at 80°C for 24 hours. The MHT was neutralized with distilled water and dried at 60°C for 6 hours obtain brown MHT powder.

Figure 1

Schematic illustration of synthesis steps for MHT.

2.3. Preparation of Polyaniline/MHT (Pan/MHT)

Pan/MHTs were fabricated using in situ oxidative polymerization (Figure 2). An accurate amount of 0.2 g MHT was dispersed in a distilled water (40 mL) and alcohol (10 mL) mixture. 0.5 mL of Tween 80 5% was added to the mixture and then sonicated in 30 minutes to acquire a well−dispersed colloidal suspension. The desired amount of aniline dissolved in 25 mL of HCl 0.1 M. The mixture was stirred for 1 hour for complete mixing at 4°C. An accurate amount of APS ( $n_{APS} / n_{aniline} = 1 / 5$ ) was dissolved in the rest of 25 mL HCl and precooled at 4°C for 15 min. APS solution was dropped into the reaction mixture and when completed, the reaction was kept at 4°C with mechanical stirring at 500 rpm. The polymerization was finished after 8 hours, then washed the suspension with a mixture of distilled water:ethanol (70 : 30) for 5 times, and dried in a vacuum dryer at 50°C for 5 hours to obtain a dark green composite Pan/MHT.

Figure 2

Schematic illustration of synthesis steps for Pan/MHT.

2.4. Characterization of the Composite Pan/MHT

The Fourier transform infrared (FT−IR) spectra of Pan, HT, Fe₃O₄, MHT, 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT composites were obtained using the KBr method on a Bruker Tensor 27 spectrometer, operated in 400−4000 cm⁻¹ region, at 2 cm⁻¹ resolution, and for 32 scans.

Powder X−ray diffraction patterns of Pan, MHT, 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT composites were obtained using a Bruker D8 Advance diffractometer with CuKα radiation (1,5406 Å) at room temperature in the atmospheric pressure. Data were collected in the range of 2 theta from 5 to 70° with a step of 0.02° and a scanning rate of 1°/min.

The structure and morphology of MHT, Pan, and Pan/MHT composites were observed by scanning electron microscopy (SEM). SEM observations were carried out using a Thermo Scientific E−SEM instrument.

The magnetic property of MHT and series of Pan/MHT were analyzed with a vibration sample magneparameter (VSM) method using a Lake Shore Crytotronics device.

The specific surface area and average pore size of Pan/MHT and MHT were determined by nitrogen adsorption t 76 K. The Brunauer−Emmett−Teller (BET) method was employed for the corresponding calculation.

2.5. Batch Studies

The adsorption experiments were performed using the batch equilibrium technique in aqueous solutions at room temperature. Duplicate 20 mg Pan/MHT samples were equilibrated by shaking with 25 mL of MO solution with initial concentrations ( $C_{0}$ ) ranging between 5 mg/L and 20 mg/L and the effect of pH of MO solution ranging between 3 and 10, and the effect of the adsorbent dose was also studied. The effect of contact time was studied at 15−720 minutes, and the equilibrium was reached at 120 minutes. The MO concentration in the supernatant was measured by a UV − VIS spectrophotometer at a wavelength corresponding to the maximum absorbance for MO (460 nm) and determined using a linear regression equation obtained by plotting a calibration curve for MO over a range of concentrations. All of the adsorptions of MO in batch studies were carried out using a Jasco V630 UV − VIS spectrophotometer.

The adsorption of MO on Pan/MHT could be calculated from the difference between the initial concentration ( $C_{0}$ ) and the equilibrium one ( $C_{e}$ ). The adsorption was expressed in terms of adsorption percentage (%) which was calculated from the following equations: $\begin{matrix} (1) & Adsorption % = \frac{C_{0} - C_{e}}{C_{0}} x 100 %, \\ C_{s} = \frac{C_{0} - C_{e}}{m} x V . \end{matrix}$

where $V (L)$ and $m (g)$ represent the mass of Pan/MHTs and the volume of the suspension, respectively. Here, $C_{s}$ is the capacity of MO sorption on Pan/MHT after adsorption equilibrium (mg/g).

2.6. Desorption and Reusability of Pan/MHT

For the reusability study, 0.1 g of Pan/MHT was used repeatedly for the adsorption of MO. An adsorption process was performed by adding 0.1 g Pan/MHT in 150 mL of MO at 20 mg/L and shaking for 24 hours to equilibrium adsorption. After that, the Pan/MHT was separated from the MO solution by using a magnetic bar, and the MO solution was analyzed by UV-VIS spectrophotometry to determine the MO adsorption capacity.

The desorption process was performed by dispersing Pan/MHT previously used in the adsorption process in 100 mL of HCl 1.0 M which promotes MO desorption. The desorption was performed in about 1 hour and then separating Pan/MHT by using a magnetic bar. The MO concentration in HCl was also analyzed by UV-VIS spectrophotometry. The cycles of reuse of the same Pan/MHT sample were carried out for a total of 4 cycles. The adsorption capacity of MO and desorption MO concentration was calculated for each cycle of reuse.

3. Results and Discussion

3.1. Characterization of Composite Particles Polyaniline/Mag−HT (MHT)

3.1.1. Fourier Transform IR (FT−IR)

The FT–IR characteristic of MHT as spectrum in Figure 3 shows that a strong absorption band at 1381 cm^–1 is assigned for elongation vibration –NO₃ which is also present for the interlayers of MHT. The weak adsorption at about 1640 cm^–1 is the vibration of –OH in the H₂O structure attached on the interlayer. The wide band at about 3463 cm^–1 is characteristic for elongated vibration of –OH groups from M–OH (Al–OH, Mg–OH, and Fe–OH), lattice, and alternating layer of water: 617, 447, and 409 cm^–1 due to elongated vibration of M–O (Al–O, Zn–O and Fe–O). Thus, Fe₃O₄ has successfully combined with HT material to fabricate MHT hybrid, and the FT −IR spectrum is consistent with that of Sulistyaningsih et al. [52].

Figure 3

FT−IR spectrum of Fe₃O₄ (a), MHT (b), and HT (c).

The FT–IR infrared spectrum shown in Figure 4 clarifies the nature of the interaction between Pan and MHT in Pan/MHT materials. In the infrared (MIR) region, the peaks between 4000 and 1800 cm^–1 are the prolonged vibration region of the O–H bonds in the hydroxyl group and N–H in the amine group. For MHT, the peak at 3447 cm^–1 is the tensile vibration of –OH that binds the hydroxyl group surface in the structure. The adsorption peaks below 800 cm^–1 at about 786 cm^–1 and 618 cm^–1 are characteristic for M–O bond (Al–O, Zn–O), and the peak at about 429 cm^–1 is assigned for Fe–O.

Figure 4

FT-IR spectrum of polyaniline (a), 2 Pan/MHT (b), 1 Pan/MHT (c), 0.5 Pan/MHT (d), and MHT (e).

Pan characterized with the strong absorptions at 3439, 2941, 1569, 1495, 1301, 1130, and 875 cm⁻¹, which was the evidence of the emeraldine form of polyaniline [53–55]. The vibration at about 3220 cm⁻¹ is assigned for protonated radical cation N − H⁺·, and the vibration at about 3443 cm⁻¹ is assigned for the N−H stretching. The characteristic band at 1515 cm⁻¹ was assigned to both C=N and C−N stretching of quinoid ring structure, and the band at 1481 cm⁻¹ was attributed to both C=C and C−N of benzenoid ring structure. All of these absorption peaks were characterized for the inplane bending vibration. The band at around 1301 cm⁻¹ indicated the vibration of the C − N stretching of benzenoid ring, and the one at around 875 cm⁻¹ was the C − H out of plane bending vibration parade-substituted benzene indicating polyaniline polymer formation. In addition, the strong band at 1130 cm⁻¹ was assigned for the C − N=C group attached on the quinoid ring.

3.1.2. X-Ray Diffraction

The XRD of the MHT, Pan, 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT are measured in the range of 2θ from 5° to 70°, and the spectrums are shown in Figure 5. The XRD spectrum of MHT from Figure 3(e) has characteristic peaks of HT and some characteristic peaks of Fe₃O₄ at $2 θ = {30.1}^{°} and {35.5}^{°}$ . The characteristic peaks of MHT and HT indicate that both have layered structures with the NO₃ ⁻ anion in the interlayer. In addition, in MHT material, the 34.6° peak that appeared in HT is divided into two subpeaks. The first peak at a smaller diffraction angle shows the peak of the hydrotalcite, and the second one at a slightly larger diffraction angle shows the magnetite core deposited on the surface of the hydrotalcite corresponding to the magnetite particle combined on the surface of HT. XRD diffraction spectra of MHT material are consistent with that of Sulistyaningsih et al. [52].

Figure 5

X-ray diffraction spectrum of polyaniline (a), 2 Pan/MHT (b), 1 Pan/MHT (c), 0.5 Pan/MHT (d), and MHT (e).

The results from the figure show the characteristic diffraction peak of Pan at $2 θ = 13^{°}$ , $2 θ = 21^{°}$ , and $2 θ = 25^{°}$ . Typical diffraction peaks of MHT at $2 θ = {11.7}^{°}$ , $2 θ = {11.8}^{°}$ , and $2 θ = {11.6}^{°}$ . With different from ratios of $m_{Pan} / m_{MHT}$ , there is also different typical diffraction peak of MHT at $2 θ = {11.6}^{°}$ and $2 θ = 12^{°}$ . It is because of the bond between Pan and MHT in the material, and the interaction between Pan and MHT can be influenced by hydroxides groups on the MHT surface, affecting the structure and material properties.

3.1.3. SEM Images

The morphology of the material was observed by SEM images in Figure 6. Pan/MHT morphology was observed, in which the distribution of Pan and MHT differed markedly in the proportions. The structural morphology of MHT is a porous material consisting of multilayers, and Pan has the structure of a long carbon chain. The distribution of MHT for Pan is different when changing the mass ratio of Pan. This result is completely consistent with the results of structural analysis by significantly reduced X−ray diffraction.

Figure 6

SEM images of MHT (a), polyaniline (b), 0.5 Pan/MHT (c), 1 Pan/MHT (d), and 2 Pan/MHT (e).

(b)

(c)

(d)

(e)

3.1.4. Vibrating Sample Magnetometer (VSM) Analysis

The magnetic properties of MHT and series of Pan/MHT were investigated using a vibrating sample magnetometer at room temperature, and the magnetization curves of MHT and series of Pan/MHT were shown in Figure 7. The roughly coincident hysteresis curves show that the grain size of the MHT metal phase is very small, nanometers in size and is a superparamagnetic material. Because MHT is the hybrid material from HT with only 1 wt% Fe₃O₄ particle, the superparamagnetic characteristic of MHT is the low value of Ms and Mr that are $2.73 \times 10^{- 3} emu / g$ and $0.10 \times 10^{- 3} emu / g$ , and $H_{c}$ is 20.06 Oe. Pan is a conductive polymer, and it tends to help increasing the ferromagnetic behavior for MHT. However, Pan is diamagnetic, so that when the mass ratio of $m_{Pan} / m_{MHT}$ increased, the values of $M_{s}$ and $M_{r}$ decreased as the results in Table 1. And this result is consistent with the announcement of Umare et al. and Jokar et al. [56, 57]. These magnetic properties are high enough that Pan/MHT materials can be separated from the solution by an external magnet.

Figure 7

Magnetization vs. applied magnetic field for MHT (a), 2 Pan/MHT (b), 1 Pan/MHT (c), and 0.5 Pan/MHT (d).

Table 1

Magnetic parameters of MHT and Pan/MHT composites.

Sample	$H_{c}$ (Oe)	$M_{s}$ (emu/g)	$M_{r}$ (emu/g)
MHT	20.06	$2.73 \times 10^{- 3}$	$0.10 \times 10^{- 3}$
0.5 Pan/MHT	17.19	$42.46 \times 10^{- 3}$	$1.59 \times 10^{- 3}$
1 Pan/MHT	18.09	$32.64 \times 10^{- 3}$	$1.29 \times 10^{- 3}$
2 Pan/MHT	18.56	$23.38 \times 10^{- 3}$	$0.91 \times 10^{- 3}$

The low $M_{r}$ value indicates that the Pan/MHT can be easily separated from the solution by an external magnetic field and redistributed into the solution after the magnetic field is disconnected. This will be an advantage for the separation, recovery, and reuse of the adsorbent as well as the catalyst. MHT has the lowest $M_{s}$ and $M_{r}$ which are $2.73 \times 10^{- 3} emu / g$ and $0.10 \times 10^{- 3} emu / g$ . When combined with Pan, the $M_{r}$ value of composites was decreased, but increasing the mass ratio of $m_{Pan} / m_{MHT}$ helped to decrease the $M_{s}$ and $M_{r}$ values. In particularly, the $M_{r}$ values of 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT are $1.59 \times 10^{- 3}$ , $1.29 \times 10^{- 3}$ , and $0.91 \times 10^{- 3} emu / g$ , respectively. Then, the $M_{s}$ values of 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT are $42.46 \times 10^{- 3}$ , $32.64 \times 10^{- 3}$ , and $23.38 \times 10^{- 3} emu / g$ , respectively.

3.1.5. Bruanauer–Emmett–Teller (BET)

The surface area is well known to be important for adsorption performance. While the pore size of MHT and 2 Pan/MHT is the same which are 26.2 Å and 24.6 Å, the BET surface areas of MHT and 2 Pan/MHT were calculated to be 2.796 m²/g and 15.460 m²/g. The higher surface of 2 Pan/MHT provides more active sites for MO adsorption. This result is consistent with the morphology of MHT and Pan/MHT from the SEM images in Figure 8.

Figure 8

Nitrogen adsorption–desorption isotherms (a) and pore disstribution (b) of MHT and 2 Pan/MHT.

(b)

3.2. Effect of Contact Time and Kinetic Adsorption

3.2.1. Effect of Contact Time

Figure 9 shows the effect of contact time of 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT with 100 mL of 20 mg/L MO solution. The adsorption amounts of MO increased rapidly in the initial 30 minutes for all samples. Then, the adsorption amounts increased slighter in the next 30 minutes. It becomes slow to attained equilibrium time which is 120 minutes for 0.5 Pan/MHT, 1 Pan/MHT, and 240 minutes for 2 Pan/MHT in the same conditions. The difference of equilibrium time for MO adsorption obtained by various adsorbents can be explained by the MO anion adsorption on the adsorbents by surface and anion exchange mechanism. The adsorbent with the higher mass ratio of Pan/MHT, the more MO can be adsorbed. This result is due to the complex adsorption mechanism of Pan such as surface adsorption, anion−exchange, …, which is consistent with the research of Monika et al. and Wang et al. [58, 59].

Figure 9

Effect of contact time on MO adsorption onto 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT.

Kinetic modeling of the adsorption process provides a prediction of adsorption rates and allows the determination of suitable rate expressions characteristic of the possible reaction mechanisms. In this study, the most frequently used models, the pseudofirst−order, the pseudosecond−order, and the intraparticle diffusion model were tested.

Pseudofirst−order kinetics: the linearized from of the pseudofirst−order linearized equation is given as $\begin{matrix} (2) & \log (Q_{e} - Q_{t}) = \log Q_{e} - \frac{k_{1}}{2.303} t, \end{matrix}$ where $t$ and $Q_{e}$ (mg/g) are the MO removal at time $t$ and at equilibrium. $k_{1}$ (min⁻¹) is the equilibrium rate constant of the pseudofirst-order equation. The plots of $\log (Q_{e} - Q_{t})$ vs. $t$ are shown in Figure 10(a), and $k_{1}$ is predicted $Q_{e}$ can be determined from the slope and intercept of the plot, respectively.

Figure 10

MO adsorption kinetics by 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT adsorbents. Pseudofirst−order model (a), pseudosecond−order model (b), and intraparticle diffusion model (c).

(b)

(c)

Pseudo−secondorder kinetics: the linearized form of the pseudosecond-order equation is given as $\begin{matrix} (3) & \frac{t}{Q_{t}} = \frac{t}{Q_{e}} + \frac{1}{k_{2} Q_{e}^{2}}, \end{matrix}$ where $k_{2}$ [g/(mg min)] is the equilibrium rate constant of the pseudosecond−order equation. The plot of $t / Q_{t}$ vs. $t$ is shown in Figure 10(b), and $k_{2}$ and $Q_{e}$ can be determined from the slope and intercept of the plot, respectively.

Intraparticle diffusion model: the intraparticle diffusion model assumes that film diffusion is negligible, and the only rate-controlling step is intraparticle diffusion in the adsorption process [60]. Hence, the adsorbed amount at time $t$ should be directly proportional to $t^{0.5}$ rather than $t$ . The model is given as $\begin{matrix} (4) & Q_{t} = k_{id} t^{0.5} + C, \end{matrix}$ where $k_{id}$ is the intraparticle diffusion rate constant (mg/g min^0.5), which can be calculated from the slope of the linear plot of $Q_{t}$ vs. $t^{0.5}$ and can be determined from the slope of the plot shown in Figure 10(c).

The kinetic parameters obtained from the application of different models are shown in Table 2. The pseudosecond−order model is the most suitable in describing the adsorption kinetics of MO in all three Pan/MHT composites, based on the correlation coefficient ( $R^{2} = 0.994$ , 0.998, and 0.999 corresponding to 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT), and the experimental and calculated values of $Q_{e}$ are not much different.

Table 2

Kinetic parameters of MO adsorption on Pan/MHT composite.

Adsorbents	$Q_{e, \exp}$ (mg/g)	Pseudofirst−order			Pseudosecond−order			Intraparticle diffusion
Adsorbents	$Q_{e, \exp}$ (mg/g)	$Q_{e, cal}$ (mg/g)	$k_{1}$ (min⁻¹)	$R^{2}$	$Q_{e, cal}$ (mg/g)	$k_{2}$ g/(mg min)	R²	$k_{id}$ Mg/g min^0.5	$C$	$R^{2}$
0.5 Pan/MHT	16.52	10.63	0.008	0.837	19,92	0.004	0.994	0.195	2.036	0.748
1 Pan/MHT	21.42	11.32	0.009	0.821	25,77	0.002	0.998	0.208	3.787	0.709
2 Pan/MHT	38.61	12.91	0.009	0.855	34,72	0.009	0.999	0.174	11.38	0.742

3.2.2. Effect of pH on the MO Adsorption

The result from Figure 11 shows that the adsorption efficiency of all three materials decreases gradually according to the pH value of the solution, the efficiency reaches the highest and most stable value at pH from 3 − 4, to pH 5, and the efficiency productivity started to decrease gradually. This is related to the surface area of the material, the presence of hydroxyl groups (OH−) on the surface of the material, and the exchange of protons (H+). This group is both capable of giving and receiving protons according to the pH of the solution when in solid−phase contact. The process of receiving protons on the surface takes place in an acid environment, while proton transfer occurs in an alkaline environment.

Figure 11

Effect of pH on MO adsorption onto 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT.

3.3. Adsorption Isotherms

3.3.1. Effect of Initial Concentration of MO on Sorption of MO

The effect of initial concentration on MO adsorption onto 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT is shown in Figure 12. The experiment was performed with a constant adsorbent dose of 20 mg/25 mL MO. The adsorption capacity of MO increased when increasing the initial MO concentration. The $Q_{e}$ values of 2 Pan/MHT are always higher than ones of 0.5 Pan/MHT and 1 Pan/MHT. This can be due to the structure of 2 Pan/MHT with high surface area as the result analyzed from BET and SEM methods above. For a solid-liquid system, the equilibrium of adsorption is one of the important physic-chemical aspects in the description of adsorption behavior. In this work, the models of Langmuir [61] and Freundlich [62] isotherm are evaluated. The results obtained from the different models provide the behavior of the adsorption mechanisms and the surface properties and affinities of the adsorbent.

Figure 12

Effect of initial MO concentration on MO adsorption onto 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT.

The Langmuir isotherm is used to describe the equilibrium between the surface of the solid and the solution and is valid for monolayer adsorption onto a surface with a finite number of identical sites. The Langmuir model equation is given as $\begin{matrix} (5) & \frac{C_{e}}{Q_{e}} = \frac{1}{Q_{m} b} + \frac{C_{e}}{Q_{m}}, \end{matrix}$ where $Q_{m}$ (mg/g) is the maximum monolayer adsorption capacity, and $b$ (L/mg) is the Langmuir constant related to the binding energy. The plots of $C_{e}$ vs. $C_{e} / Q_{e}$ are shown in Figure 13(a), and the values of $Q_{m}$ and $b$ are calculated from the slope and intercept of the plots, respectively.

Figure 13

Adsorption isotherms of MO on Pan/MHT composites with Langmuir isotherm model (a), Freundlich isotherm model (b), and Dubinin-Radushkevich isotherm model (c).

(b)

(c)

The Freundlich isotherm is an empirical equation that assumes that the adsorprion face becomes heterogeneous during the course of the adsorption process. The linearized form of the Freundlich model is given as $\begin{matrix} (6) & \log Q_{e} = \log k_{f} + \frac{1}{n} \log C_{e}, \end{matrix}$ where $k_{f}$ (mg/g) and $n$ are the Freundlich constants related to adsorption capacity and adsorption intensity, respectively. The plots of log $C_{e}$ vs. log $Q_{e}$ were shown on Figure 13(b), and the values of $1 / n$ and $k_{f}$ are calculated from the slope and intercept of the plots, respectively.

All the correlation coefficients, $R^{2}$ values, and the constants calculated from Langmuir and Freundlich models are listed in Table 3. The $R^{2}$ of both Langmuir and Freundlich models of all three adsorbents is higher than 0.91; so, the adsorption of MO onto Pan/MHT composite appropriate with either monolayer of dyeing molecules covers the Pan/MHT surface or interaction between adsorbents and MO molecules. All three $R^{2}$ values of the Freundlich model of Pan/MHT composites are higher than $R^{2}$ of the Langmuir model. In particularly, $R^{2} = 0.9506, 0.9472, and 0.9912$ corresponding to 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT. In addition, the $n$ values of three composites are higher than 2 ( $n = 2.0973, 2.119, and 2.1872$ for 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT, respectively) which indicates that the MO adsorption on Pan/MHT composite is not only monolayer surface adsorption. The mechanism of MO adsorption onto Pan/MHT composite is either of the surface adsorption or other types of interactions, such as electrostatic interaction, ion exchange, hydrogen bonding, and van der Waals forces. In all three composites, 2 Pan/MHT is the most suitable for the Freundlich model and the Langmuir model too. The MO adsorption capacity of 2 Pan/MHT is also the highest with $Q_{e} = 156.25 mg / g$ .

Table 3

Fitting parameters of adsorption isotherms for MO on Pan/MHT composites.

Adsorbents	Langmuir isotherm			Freundlich isotherm			Dubinin-Radushkevich
Adsorbents	$Q_{m}$ (mg/g)	b (L/mg)	$R^{2}$	$n$	$k_{f}$ (mg/g)	$R^{2}$	$Q_{m}$ (mg/g)	β (mol²/kJ²)	$R^{2}$	$E$ (kJ/Mol)
0.5Pan/MHT	92.59	0.017	0.924	2.097	5.562	0.951	38.93	6.699	0.528	0.273
1 Pan/MHT	123.5	0.016	0.913	2.119	7.437	0.947	50.77	6.538	0.513	0.277
2 Pan/MHT	156.3	0.019	0.941	2.187	10.81	0.991	71.49	6.893	0.635	0.269

Dubinin-Radushkevich (D-R) isotherm is generally used to describe the sorption isotherms of a single solute system (Figure 13(c)). The D-R isotherm can also help to confirm that the adsorption process was chemisorption or physical adsorption [63]. D-R equation is represented as follows: $\begin{matrix} (7) & \ln Q_{e} = \ln Q_{m} - β ε^{2} \end{matrix}$ where $Q_{e}$ is equilibrium adsorbent-phase concentration of adsorbate (mg/g), and $Q_{m}$ is theoretical saturation capacity (mg/g). The plots of ε ² vs. ln $Q_{e}$ were shown in Figure 10(c), and the values of β and $\ln Q_{m}$ are calculated from the slope and intercept of the plots, respectively. β is the activity coefficient related to the mean free energy of adsorption (mol²/kJ²), and ε is the polanyipotential (kJ/mol). $\begin{matrix} (8) & ε = RTln (1 + 1 / C_{e}), \end{matrix}$ where $R$ is the universal gas constant (8.314 J/mol.K), $T$ is the Kelvin temperature (K), and $C_{e}$ is the equilibrium aqueous phase concentration of adsorbate (mg/L).

The D-R model is mainly used to estimate the average free energy of adsorption (kJ/mol) $\begin{matrix} (9) & E = \frac{1}{\sqrt{2 β}}, \end{matrix}$ when $E < 8 kJ / mol$ , the adsorption is physical adsorption and when $E > 8 kJ / mol$ , the adsorption is chemisorption [64]. The adsorption energy values ( $E$ ) of 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT are under 8 kJ/mol. In particularly, $E = 0.273, 0.277, and 0.269 kJ / mol$ corresponding to 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT. This result indicates that the adsorption process of MO on three kinds of Pan/MHT composites is physical adsorption.

3.3.2. Effect of 2 Pan/MHT Dosage on the Sorption of MO

The result from Figure 14 shows the adsorption efficiency (H %) when using a different dose of 2 Pan/MHT (0.01, 0.02, and 0.03 g) and shows the adsorption efficiency increases when increasing 2 Pan/MHT dose.

Figure 14

Effect of adsorbent dose in MO adsorption onto 2Pan/MHT composite.

For all 3 doses of 2 Pan/MHT, MO was immediately adsorbed on 2 Pan/MHT and after 30 minutes, the adsorption efficiency obtained 55.39%, 63.88%, and 65.97% according to use of 0.01, 0.02, and 0.03 g of 2 Pan/MHT, respectively. Then, the adsorption efficiency increase slightly and reached to equilibrium after 240 minutes with the adsorption efficiency obtained 64.43%, 68.59%, and 77.37% according to the use of 0.01, 0.02, and 0.03 g of 2 Pan/MHT, respectively. This result is expected because the increase of adsorbent dose leads to a greater surface area.

The FT–IR spectra of MO, 2 Pan/MHT, and 2 Pan/MHT after adsorption of MO are shown in Figure 15(a). MO is characterized by the peak at 2896 cm^-1 for asymmetric CH₃ stretching vibration; the peaks at 1520 cm^-1 and 1421 cm^-1 are assigned for C=C–H in plane CH bend; peak at 817 cm^-1 is characteristic of the benzene ring. The peak at 1608.32 cm^-1 is assigned for –N=N–, and the peaks at 1201 cm^-1 and 1121 cm^-1 are assigned for –C–N. The peaks at 697 cm^-1, 623 cm^-1, and 574 cm^-1 are assigned for the stretching vibration -C-S-, and the peak at 1367 cm^-1 is assigned for the stretching vibration S=O. These characteristics also exist on Pan/MHT materials after adsorption, demonstrating the presence of MO dye on the material, and this result is consistent with the announcement of Harikumar et al. [65].

Figure 15

FT-IR spectra of MO (red line), 2 Pan/MHT (blue line), and 2 Pan/MHT after adsorption of MO (—) (a), SEM images of 2 Pan/MHT (b), and 2 Pan/MHT after adsorption of MO (c).

(b)

(c)

SEM images of 2 Pan/MHT and 2 Pan/MHT after adsorption of MO (Figures 15(b) and 15(c)) clearly show the material surface before and after MO adsorption. The surface and pores of 2 Pan/MHT after adsorption of MO are covered with the MO (adsorbed components), and the result is the surface of the material more homogeneous than the original. It is mean that the material samples after adsorption have almost filled gaps.

3.4. Desorption of MO and Reusability of Pan/MHT

Another parameter that defines the functionality of adsorbent material is its capacity to be regenerated and reused in several adsorption and desorption cycles. For this reason, MO adsorption and desorption experiments were performed with Pan/MHT by using a 0.1 M HCl solution as an eluent. This eluent was chosen because in acid conditions, Pan is in emeraldine salt and is doped with H+ ions, and MO is in its cationic form [66, 67]. Therefore, due to electrostatic repulsions, the MO molecules would be desorbed from the composite structure.

Figure 16 shows the adsorption and desorption efficiency of MO after 4 cycles. The result show that the MO adsorption decreases to 12.86%, 14.28%, and 9.16% according to using 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT. The MO desorption from 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT also decreases to 21.51%, 19.7%, and 13.57%, respectively. This can be due to the increase of Pan in a composite structure, which enhances both adsorption and desorption of MO on the adsorbent. Thus, Pan/MHT surface can be regenerated without a problem. Although MO is completely desorbed, the adsorption percentage decreases, and this behavior is because of the loss of Pan due to stirring and material management. Therefore, this material can be reused in multiple cycles if it wants to be coupled to a recirculation system.

Figure 16

MO adsorption and desorption cycles with 0.5 Pan/MHT (a), 1 Pan/MHT (b), 2 Pan/MHT (c), and the effect of solution pH on the reusability of 2 Pan/MHT for MO adsorption (d).

(b)

(c)

(d)

The results show that at a low pH 3 − 4, the MO adsorption capacity (H %) obtained over 80% after 3 cycles of reuse. When the solution $pH > 5 - 7$ , the MO adsorption decreased and obtained 60− 73% efficiency of MO removal after 3 cycles of reuse. This shows that the MO adsorption and desorption are suitable for performance in acidic environments at pH 3 − 4.

3.5. Mechanism of Adsorption

With all the results above, the process of adsorption, recovery, and desorption of MO on Pan/MHT was described as Figure 17(a). The adsorption and desorption mechanism of MO on Pan/MHT are the combination of chemisorption and physical adsorption, which can be illustrated in Figures 17(b)–17(d) and explained as below: (i)

In solution, MO molecule is dissociated into M-SO3^- with M is an organic part of dyeing molecule. Pan is a conducting polymer with NH⁺ group on full backbone that will interact with M-SO3^-. The electrostatic interactions are preferably involved in MO adsorption onto Pan particles. Besides, the adsorption experiment studied on Pan/MHT was found to have followed the pseudosecond-order model which indicates the chemisorption mechanism of Pan/MHT

(ii)

The presence of MHT gives the good adsorption of MO because of the anion exchangeable. For this mechanism, the anion associated with the interlayer Pan/MHT is exchanged with MO anionic molecules in solution. It also means that the MO anion will be trapped into the interlayer structure, and it indicates the physical adsorption mechanical of Pan/MHT

Figure 17

Schematic illustration of the adsorption and desorption mechanism of MO on Pan/MHT.

(b)

(c)

(d)

4. Conclusion

The MHT material has been synthesized with 0.1 g Fe₃O₄ added during the coprecipitation process with the Zn²⁺/Al³⁺ salt mixture to create a magnetic MHT material. Then, a series of Pan/MHT composites were successfully synthesized with different mass ratios of $m_{Pan} / m_{MHT} = 0.5, 1, and 2$ . All Pan/MHT composites were characterized by analyzing methods of SEM, FT−IR, XRD, BET, and VSM and then studying for MO adsorption. The key findings of this research are (i)

2 Pan/MHT was the best material with high surface area (15.46 m²/g), high Hc (18.56 Oe), and low Ms ( $23.38 \times 10^{- 3}$ ) and Mr ( $0.91 \times 10^{- 3}$ )

(ii)

According to the MO adsorption kinetic studies, all of 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT composites are suitable with pseudosecond−order model, based on the correlation coefficient ( $R^{2} = 0.994, 0.998, and 0.999$ corresponding to 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT), and the experimental and calculated values of $Q_{e}$ are not much different. 2 Pan/MHT had the highest adsorption capacity in studying the effect of time contact and pH of MO solution

(iii)

The $R^{2}$ of both Langmuir and Freundlich models of all three adsorbents is higher than 0.91; so, the adsorption of MO onto Pan/MHT composite appropriate with either monolayer of dyeing molecules covers the Pan/MHT surface or interaction between adsorbents and MO molecules

(iv)

The adsorption energy of all 0.5 Pan/MHT, 1 Pan/MHT, and 2 Pan/MHT is 0.273, 0.277, and 0.269 kJ/mol, and all of them are below 8 kJ/mol. This result indicates that the adsorption process of MO on three kinds of Pan/MHT composites is physical adsorption

(v)

Pan/MHT was also investigated to reuse after desorption of MO in 0.1 M HCl, and the result shows that 2 Pan/MHT can be reused for 4 cycles with $Q_{e} = 79.66 mg / g$

(vi)

The mechanism of MO adsorption onto Pan/MHT composite is either of the surface adsorption or other types of interactions, such as electrostatic interaction, ion exchange, hydrogen bonding, and van der Waals forces

Footnotes

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

This work was supported by Kurita Water and Environment Foundation (KWEF) for the award of KURITA Overseas Research Grant 2020 under Grant [20Pvn032-K43]. The authors thank to Institute of Chemical Technology for their warmly analysis equipment support.

References

el maguana

Elhadiri

Bouchdoug

Benchanaa

Boussetta

Optimization of preparation conditions of novel adsorbent from sugar scum using response surface methodology for removal of methylene blue

Journal of Chemistry 2018 2018

4150073

2093654

10.1155/2018/2093654

2-s2.0-85046830662

Kant

Adsorption of dye eosin from an aqueous solution on two different samples of activated carbon by static batch method

Journal of Water Resource and Protection 2012 4

4150073

2 93 98

10.4236/jwarp.2012.42011

Maheshwari

Deshpande

Zare

Vardhe

Removal of Dye from Aqueous Solution by Using Activated Carbon

Research Journal of Engineering Science 2017 6

4150073

Malik

P. K.

Dye removal from wastewater using activated carbon developed from sawdust: adsorption equilibrium and kinetics

Journal of Hazardous Materials 2004 113

4150073

1–3 81 88

10.1016/j.jhazmat.2004.05.022

2-s2.0-16644364790

15363517

Soonmi

H. O.

Removal of dye by adsorption onto activated carbons: review

Eurasian Journal of Analytical Chemistry 2018 13

4150073

4 332 338

Attia

A. A.

Rashwan

W. E.

Khedr

S. A.

Capacity of activated carbon in the removal of acid dyes subsequent to its thermal treatment

Dyes and Pigments 2006 69

4150073

3 128 136

10.1016/j.dyepig.2004.07.009

2-s2.0-24644481447

Heraldy

Santosa

Triyono

Wijaya

Anionic and Cationic Dyes Removal from Aqueous Solutions by Adsorption onto Synthetic Mg/Al Hydrotalcite-Like Compound

Indonesian Journal of Chemistry 2015 15

4150073

3 234 241

10.22146/ijc.21190

2-s2.0-84947572775

Lazaridis

Karapantsios

T. D.

Georgantas

Kinetic analysis for the removal of a reactive dye from aqueous solution onto hydrotalcite by adsorption

Water Research 2003 37

4150073

12 3023 3033

10.1016/S0043-1354(03)00121-0

2-s2.0-0037616281

12767306

El Khanchaoui

Sajieddine

Mansori

Essoumhi

Anionic dye adsorption on ZnAl hydrotalcite-type and regeneration studies based on “memory effect”

International Journal of Environmental Analytical Chemistry 2020 1 19

10.1080/03067319.2020.1772769

10.

Lam

V. T.

Dao

T.-U. T.

Nguyen

H.-T. T.

Nguyen

D. T. C.

H. T. N.

Nguyen

H. T. T.

S. T.

Loc

H. H.

Nguyen

T. D.

Process optimization studies of Congo red dye adsorption onto magnesium aluminium layered double hydroxide using response surface methodology

Polish Journal of Environmental Studies 2021 30

4150073

1 679 687

10.15244/pjoes/121048

11.

Erdem

Cölgeçen

Donat

The removal of textile dyes by diatomite earth

Journal of Colloid and Interface Science 2005 282

4150073

2 314 319

10.1016/j.jcis.2004.08.166

2-s2.0-10044293207

15589535

12.

Xia

Liu

Chen

Fang

Zhang

Efficient and sustainable treatment of anionic dye wastewaters using porous cationic diatomite

Journal of the Taiwan Institute of Chemical Engineers 2020 113

4150073

8 15

10.1016/j.jtice.2020.07.020

13.

Dang Son

B. H.

Quang Mai

Xuan du

Hai Phong

Quang Khieu

A study on astrazon black AFDL dye adsorption onto Vietnamese diatomite

Journal of Chemistry 2016 2016

4150073

8685437

10.1155/2016/8685437

2-s2.0-84978640765

14.

Zheng

Gao

Guan

Ren

Tian

Characteristics of cationic red X-GRL adsorption by diatomite tailings

Journal of Wuhan University of Technology-Mater. Sci. Ed. 2017 32

4150073

5 1038 1047

10.1007/s11595-017-1708-5

2-s2.0-85031311585

15.

Zhao

Y.-H.

Geng

J.-T.

Cai

J.-C.

Cai

Y.-F.

Cao

C.-Y.

Adsorption performance of basic fuchsin on alkali-activated diatomite

Adsorption Science & Technology 2020 38

4150073

5–6 151 167

10.1177/0263617420922084

16.

Guezzen

Adjdir

Medjahed

Didi

M. A.

Weidler

P. G.

Kinetic study and box–Behnken design approach to optimize the sorption process of toxic azo dye onto organo-modified bentonite

Canadian Journal of Chemistry 2020 98

4150073

5 215 221

10.1139/cjc-2019-0393

17.

Berez

Ayari

Abidi

Schäfer

Trabelsi-Ayadi

Adsorption-desorption processes of azo dye on natural bentonite: batch experiments and modelling

Clay Minerals 2014 49

4150073

5 747 763

10.1180/claymin.2014.049.5.10

2-s2.0-84929246873

18.

Zhang

Zhou

Muhammad

Tang

Liu

Zhu

Tong

Citric acid modified bentonite for Congo red adsorption

Frontiers in Materials 2019 6

4150073

10.3389/fmats.2019.00005

2-s2.0-85062473408

19.

Aldbouni

S. A. S.

Alhyali

E. A. S.

Alkazraji

A. A. H.

Equilibrium and thermodynamic studys of adsorption of azo dyes on the local bentonite clay

Journal of Education and Science 2019 28

4150073

2 50 70

10.33899/edusj.2019.161177

20.

Semeraro

Gabaldón

J. A.

Removal of an azo textile dye from wastewater by cyclodextrin-epichlorohydrin polymers

Cyclodextrin - A Versatile Ingredient, Ch. 13 2018

Rijeka

IntechOpen

10.5772/intechopen.72502

21.

Bayramoglu

Arica

M. Y.

Grafting of regenerated cellulose films with fibrous polymer and modified into phosphate and sulfate groups: application for removal of a model azo-dye

Colloids and Surfaces A: Physicochemical and Engineering Aspects 2021 614, article 126173

4150073

10.1016/j.colsurfa.2021.126173

22.

Zeng

Tan

Huang

Zhou

Facile synthesis of amphiphilic peach gum polysaccharide as a robust host for efficient encapsulation of methylene blue and methyl orange dyes from water

International Journal of Biological Macromolecules 2020 154

4150073

974 980

10.1016/j.ijbiomac.2020.03.151

32198040

23.

Song

Tan

Wang

Zhou

Superior amine-rich gel adsorbent from peach gum polysaccharide for highly efficient removal of anionic dyes

Carbohydrate Polymers 2018 199

4150073

178 185

10.1016/j.carbpol.2018.07.010

2-s2.0-85049730202

30143118

24.

Gao

Zhao

Cheng

Wang

Zheng

Removal of anionic azo dyes from aqueous solution using magnetic polymer multi-wall carbon nanotube nanocomposite as adsorbent

Chemical Engineering Journal 2013 223

4150073

84 90

10.1016/j.cej.2013.03.004

2-s2.0-84875655304

25.

Meng

Scheidemantle

Wang

Zhao

Toro-González

Singh

Wyman

C. E.

Ozcan

Cai

C. M.

Ragauskas

A. J.

Synthesis, characterization, and utilization of a lignin-based adsorbent for effective removal of azo dye from aqueous solution

ACS Omega 2020 5

4150073

6 2865 2877

10.1021/acsomega.9b03717

32095708

26.

da Silva

R. C.

de Aguiar

S. B.

da Cunha

P. L. R.

de Paula

R. C. M.

Feitosa

J. P. A.

Effect of microwave on the synthesis of polyacrylamide-g-chitosan gel for azo dye removal

Reactive and Functional Polymers 2020 148, article 104491

4150073

10.1016/j.reactfunctpolym.2020.104491

27.

Yildirim

Yilmaz

Sanlier

New copolymer of acrylamide with allyl methacrylate and its capacity for the removal of azo dyes

Polímeros 2015 25

4150073

2 137 145

10.1590/0104-1428.1615

2-s2.0-84933038317

28.

Ait Himi

El Ghachtouli

Amarray

Zaroual

Bonnaillie

Azzi

Removal of azo dye calcon using polyaniline films electrodeposited on SnO2 substrate

Physical Chemistry Research 2020 8

4150073

1 111 124

10.22036/pcr.2019.203023.1680

29.

Aliabadi

R. S.

Mahmoodi

N. O.

Synthesis and characterization of polypyrrole, polyaniline nanoparticles and their nanocomposite for removal of azo dyes; sunset yellow and Congo red

Journal of Cleaner Production 2018 179

4150073

235 245

10.1016/j.jclepro.2018.01.035

2-s2.0-85041461110

30.

Ghosh

Bar

Biswas

A. B.

Das

S. K.

Removal of methylene blue (Aq) using untreated and acid-treated eucalyptus leaves and GA-ANN modelling

The Canadian Journal of Chemical Engineering 2019 97

4150073

11 2883 2898

10.1002/cjce.23503

2-s2.0-85071122287

31.

Ghosh

Kar

Chatterjee

Bar

Das

Removal of methylene blue from aqueous solution using _Lathyrus sativus_ husk: adsorption study, MPR and ANN modelling

Process Safety and Environmental Protection 2021 149

4150073

345 361

10.1016/j.psep.2020.11.003

32.

Posati

Listwan

Sotgiu

Torreggiani

Zamboni

Aluigi

Keratin/hydrotalcites hybrid sponges as promising adsorbents for cationic and anionic dyes

Frontiers in Bioengineering and Biotechnology 2020 8

4150073

10.3389/fbioe.2020.00068

33.

Zheng

Wang

Shu

Yan

Utilization of diatomite/chitosan-Fe (III) composite for the removal of anionic azo dyes from wastewater: equilibrium, kinetics and thermodynamics

Colloids and Surfaces A: Physicochemical and Engineering Aspects 2015 468

4150073

129 139

10.1016/j.colsurfa.2014.12.015

2-s2.0-84920446631

34.

Zhang

Y. Z.

W. J.

Adsorption of sunset yellow FCF from aqueous solution by chitosan-modified diatomite

Water Science and Technology 2015 72

4150073

10 1861 1868

10.2166/wst.2015.412

2-s2.0-84954494257

26540549

35.

X.-J.

Wang

J.-D.

Cao

L.-Q.

Characterization and Adsorption Performance of Chitosan/Diatomite Membranes for Orange G Removal

e-Polymers 2016 16

4150073

2 99 109

10.1515/epoly-2015-0218

2-s2.0-84960484453

36.

Khodabandelou

A. A.

Darvishi Cheshmeh Soltani

Gudini

Tarrahi

M. J.

Fazelinia

Removal of azo dye from synthetic wastewater using immobilized nano-diatomite within calcium alginate TT - حذف رنگ آزو از فاضلاب مصنوعی با استفاده ازنانو-دیاتومیت تثبیت شده در آلژینات کلسیم

SSUJ 2016 14

4150073

6 17 35

37.

Liu

Yang

Zhang

Huang

Adsorption of an anionic azo dye by cross-linked chitosan/bentonite composite

International Journal of Biological Macromolecules 2015 72

4150073

1129 1135

10.1016/j.ijbiomac.2014.10.008

2-s2.0-84909957713

25453286

38.

Tie

Fang

Wang

Zhang

Deng

Tang

Adsorptive removal of a reactive azo dye using polyaniline-intercalated bentonite

Polish Journal of Environmental Studies 2017 26

4150073

3 1259 1268

10.15244/pjoes/67554

2-s2.0-85020791122

39.

Sienkiewicz

Kierys

Goworek

Polymer-hybrid silica composite for the azo dye removal from aqueous solution

Journal of Dispersion Science and Technology 2019 40

4150073

10 1396 1404

10.1080/01932691.2018.1515024

2-s2.0-85054575490

40.

Abdellaoui

Pavlovic

Barriga

Nanohybrid layered double hydroxides used to remove several dyes from water

ChemEngineering 2019 3

4150073

2 41

10.3390/chemengineering3020041

41.

Zaghouane-Boudiaf

Boutahala

Arab

Removal of methyl orange from aqueous solution by uncalcined and calcined MgNiAl layered double hydroxides (LDHs)

Chemical Engineering Journal 2012 187

4150073

142 149

10.1016/j.cej.2012.01.112

2-s2.0-84857801594

42.

Extremera

Pavlovic

Pérez

M. R.

Barriga

Removal of acid orange 10 by calcined mg/Al layered double hydroxides from water and recovery of the adsorbed dye

Chemical Engineering Journal 2012 213

4150073

392 400

10.1016/j.cej.2012.10.042

2-s2.0-84870292214

43.

Prasad

Tang

Liu

Magnetic Fe3O4 based layered double hydroxides (LDHs) nanocomposites (Fe3O4/LDHs): recent review of progress in synthesis, properties and applications

Journal of Nanostructure in Chemistry 2018 8

4150073

4 393 412

10.1007/s40097-018-0289-y

44.

Duhan

Kaur

Adsorptive removal of methyl Orange with polyaniline nanofibers: an unconventional adsorbent for water treatment

Environmental Technology 2020 41

4150073

23 2977 2990

10.1080/09593330.2019.1593511

2-s2.0-85063628856

30874498

45.

Tanzifi

Tavakkoli Yaraki

Karami

Karimi

Dehghani Kiadehi

Karimipour

Wang

Modelling of dye adsorption from aqueous solution on polyaniline/carboxymethyl cellulose/TiO₂ nanocomposites

Journal of Colloid and Interface Science 2018 519

4150073

154 173

10.1016/j.jcis.2018.02.059

2-s2.0-85042494470

29494878

46.

Bhaumik

McCrindle

R. I.

Maity

Agarwal

Gupta

Polyaniline nanofibers as highly effective re-usable adsorbent for removal of reactive black 5 from aqueous solutions

Journal of Colloid and Interface Science 2016 466

4150073

442 451

10.1016/j.jcis.2015.12.056

2-s2.0-84952926569

26771507

47.

Saad

Tahir

Khan

Hameed

Saud

Synthesis of polyaniline nanoparticles and their application for the removal of crystal violet dye by ultrasonicated adsorption process based on response surface methodology

Ultrasonics Sonochemistry 2017 34

4150073

600 608

10.1016/j.ultsonch.2016.06.022

2-s2.0-84976889264

27773286

48.

Muhammad

Shah

A.-H.

Bilal

Comparative study of the adsorption of acid blue 40 on polyaniline, magnetic oxide and their composites: synthesis, characterization and application

Materials 2019 12

4150073

18 2854

10.3390/ma12182854

2-s2.0-85072558989

31487925

49.

Ayad

el-Nasr

A. A.

Adsorption of cationic dye (methylene blue) from water using polyaniline nanotubes base

The Journal of Physical Chemistry C 2010 114

4150073

34 14377 14383

10.1021/jp103780w

2-s2.0-77956136413

50.

Ayad

el-Nasr

A. A.

Anionic dye (acid green 25) adsorption from water by using polyaniline nanotubes salt/silica composite

Journal of Nanostructure in Chemistry 2012 3

4150073

10.1186/2193-8865-3-3

51.

Sharma

Rekha

Mohanty

Nanoporous hypercrosslinked polyaniline: an efficient adsorbent for the adsorptive removal of cationic and anionic dyes

Journal of Molecular Liquid 2016 222

4150073

1091 1100

10.1016/j.molliq.2016.07.130

2-s2.0-84982980458

52.

Sulistyaningsih

Santosa

S. J.

Siswanta

Rusdiarso

Preparation of magnetite-mg/Al hydrotalcite through hydrothermal process and subsequent calcination

Advanced Materials Research 2015 1101

4150073

336 339

10.4028/www.scientific.net/AMR.1101.336

53.

Zhu

Gao

Tan

Chen

Polyaniline modified mg/Al layered double hydroxide composites and their application in efficient removal of Cr (VI)

ACS Sustainable Chemistry & Engineering 2016 4

4150073

8 4361 4369

10.1021/acssuschemeng.6b00922

2-s2.0-84979987392

54.

Tan

Yang

Wen

Guo

Wang

Coexistence of adsorption and coagulation processes of both arsenate and NOM from contaminated groundwater by nanocrystallined mg/Al layered double hydroxides

Water Research 2013 47

4150073

12 4159 4168

10.1016/j.watres.2012.11.056

2-s2.0-84879015152

23582669

55.

Wen

Fan

Tan

Chen

Wang

A Core-shell structure of polyaniline coated protonic titanate nanobelt composites for both Cr(VI) and humic acid removal

Polymer Chemistry 2016 7

4150073

4 785 794

10.1039/C5PY01721A

2-s2.0-84961292160

56.

Umare

S. S.

Shambharkar

B. H.

Ningthoujam

R. S.

Synthesis and characterization of polyaniline- Fe₃O₄ nanocomposite: electrical conductivity, magnetic, electrochemical studies

Synthetic Metals 2010 160

4150073

17-18 1815 1821

10.1016/j.synthmet.2010.06.015

2-s2.0-77956344772

57.

Jokar

Foroutani

Safaralizadeh

Farhadi

Synthesis and characterization of polyaniline/Fe₃O₄ magnetic nanocomposite as practical approach for fluoride removal process

Annual Research & Review in Biology 2014 4

4150073

21 3262 3273

10.9734/arrb/2014/9108

58.

Duhan

Kaur

Nano-structured polyaniline as a potential adsorbent for methylene blue dye removal from effluent

Journal of Composites Science 2021 5

4150073

1 7

10.3390/jcs5010007

59.

Wang

Chen

Wang

Feng

Yan

Removal of methylene blue by polyaniline/TiO₂ hydrate: adsorption kinetic, isotherm and mechanism studies

Powder Technology 2019 347

4150073

93 102

10.1016/j.powtec.2019.02.049

2-s2.0-85062450271

60.

Okoye

A. I.

Ejikeme

P. M.

Onukwuli

O. D.

Lead removal from wastewater using fluted pumpkin seed Shell activated carbon: adsorption modeling and kinetics

International Journal of Environmental Science & Technology 2010 7

4150073

4 793 800

10.1007/BF03326188

2-s2.0-78049244023

61.

Langmuir

The constitution and fundamental properties of solids and liquids. PART I. SOLIDS

Journal of the American Chemical Society 1916 38

4150073

11 2221 2295

10.1021/ja02268a002

2-s2.0-4043158815

62.

Freundlich

Über Die Adsorption in Lösungen

Zeitschrift für Physikalische Chemie 1907 57U

4150073

1 385 470

10.1515/zpch-1907-5723

63.

Dubinin

The equation of the characteristic curve of activated charcoal

Proceedings of the USSR Academy of Sciences 1947 55

4150073

327 329

64.

Günay

Arslankaya

Tosun

Lead removal from aqueous solution by natural and pretreated clinoptilolite: adsorption equilibrium and kinetics

Journal of Hazardous Materials 2007 146

4150073

1–2 362 371

10.1016/j.jhazmat.2006.12.034

2-s2.0-34250377943

17261347

65.

Joseph

Photocatalytic degradation of textile dyes by hydrogel supported titanium dioxide nanoparticles

Journal of Environmental Engineering and Ecological Science 2013 2

4150073

1 2

10.7243/2050-1323-2-2

66.

Haitham

Razak

Nawi

M. A.

Kinetics and isotherm studies of methyl orange adsorption by a highly recyclable immobilized polyaniline on a glass plate

Arabian Journal of Chemistry 2019 12

4150073

7 1595 1606

10.1016/j.arabjc.2014.10.010

2-s2.0-85065920880

67.

Mendieta-Rodríguez

L. S.

González-Rodríguez

L. M.

Alcaraz-Espinoza

J. J.

Chávez-Guajardo

A. E.

Medina-Llamas

J. C.

Synthesis and characterization of a polyurethane-polyaniline macroporous foam material for methyl orange removal in aqueous media

Materials Today Communications 2021 26, article 102155

4150073

10.1016/j.mtcomm.2021.102155