Preparation and Characterization of Sb 2 S 3 –TiO 2 Nanocomposite for the Enhanced Photocatalytic Degradation and Mineralization of Azo Dye

Abstract

Sb₂S₃–TiO₂ semiconductors heterojunction promote separation of electron–hole charges generated upon light irradiation. This enhancement in charge separation depends on the quality of interfacial contact between Sb₂S₃ and TiO₂, their composition, and their morphological and surface properties. In this study, the Sb₂S₃–TiO₂ nanocomposites were synthesized by two different methods (hydrothermal and mechanical mixing methods) with different percent compositions (5–20% of Sb₂S₃) and different calcination temperatures (200–600°C) to study their effects on improving the interfacial contact between both semiconductors. Among all synthesized samples, hydrothermally synthesized 10% Sb₂S₃–TiO₂ nanocomposite calcined at 300°C showed the highest photocatalytic degradation of methyl orange (MO) dye solution. X-ray powder diffraction pattern showed that the anatase phase of TiO₂ and the orthorhombic phase of Sb₂S₃ are retained in the nanocomposite. Scanning electron microscopy and energy-dispersive X-ray revealed formation of nanocomposite with purity. Transmission electron microscopy revealed that TiO₂ is deposited better on Sb₂S₃ in hydrothermally synthesized nanocomposite than in mechanically mixed composite. However, 300°C calcinations of the composite helped improve the interaction between TiO₂ and Sb₂S₃. Brunauer-Emmett-Teller (BET) surface area analysis showed the highest specific surface area for the hydrothermally synthesized 10% Sb₂S₃–TiO₂ nanocomposite calcined at 300°C. Considering all results, a reasonable mechanism of photocatalysis of Sb₂S₃–TiO₂ nanocomposite has been proposed. Furthermore, the chemical oxygen demand data showed substantial mineralization of MO dye by the 10% Sb₂S₃–TiO₂ nanocomposite calcined at 300°C.

Introduction

In recent years, environmental cleanup applications have been one of the most active areas in heterogeneous photocatalysis, and TiO₂ is the most researched photocatalytic material because of its efficient photocatalytic activity, chemical stability, reusability, low toxicity, and low cost (Nakataa and Fujishima, 2012). However, this material has some drawbacks, such as it is only sensitive to UV light due to its large band gap (3.1 or 3.2 eV), relatively high electron–hole recombination rate, and low surface area for adsorption of pollutants (Song et al., 2008). Composite synthesis of TiO₂ with other narrow band gap semiconductor nanoparticles is one of the ways to improve photocatalytic efficiency of TiO₂ (Chen and Mao, 2007). Recent studies show that many narrow band gap semiconductors have been used to enhance photocatalytic degradation efficiency of TiO₂, including CdS (Shi et al., 2012), Bi₂S₃ (Huang et al., 2011), PbS (Ratanatawanate et al., 2009), and SnO₂ (Vinodgopal et al., 1996). Along with these, antimony sulfide (Sb₂S₃) is also an attractive semiconductor for this approach because of its small band gap. It has band gap varying between 1.5 and 2.3 eV, which covers the range of solar spectrum; hence, it is one of the promising materials for photocatalytic degradation using solar energy. Thus evidently, coupling of narrow band gap semiconductor with TiO₂ increases the photocatalytic efficiency of pure TiO₂ (Boix et al., 2012). Recently, the composites of TiO₂ with Sb₂S₃ are being used extensively in semiconductor-sensitized solar cells and photocatalytic treatment of wastewater using solar energy (Sun et al., 2008) due to the extraordinary properties of Sb₂S₃ either as charge separator or as sensitizer.

Itzhaik et al. (2009) deposited Sb₂S₃ over TiO₂ in the Extremely Thin Absorber cells as semiconductor sensitizers instead of using dyes, which show 3.3% efficiency. Tsujimoto et al. synthesized Sb₂S₃-based Extremely Thin Absorber solar cells and observed an increase in its efficiency up to 4.1% (Tsujimoto et al., 2012). Boix et al. presented the model of TiO₂/Sb₂S₃/CuSCN semiconductor-sensitized photovoltaic cell with improved cell performance by focusing on their fundamental process of charge transport and recombination using CuSCN as hole transporter (Boix et al., 2012). Salunkhe et al. (2012) deposited Sb₂S₃ nanoparticles on mesoporous TiO₂ and used as photoanode in the FTO/TiO₂/Sb₂S₃/electrolyte/Pt device structure.

Li et al. synthesized pristine Sb₂S₃ by solid-state reaction and investigated its photocatalytic activity in visible light for degradation of methyl orange (MO). Its degradation rate was found to be much higher than those of P-25, CdS, and Bi₂S₃ under visible light irradiation (Li et al., 2008). Sun et al. (2008) synthesized Sb₂S₃ nanorods by a simple wet chemical method under refluxing condition and found good photocatalytic efficiency under visible light for degradation of MO and p-hydroxyazobenzene. They synthesized Sb₂S₃–TiO₂ heterojunction catalyst using the same Sb₂S₃ nanorods and optimized the composition of Sb₂S₃ over TiO₂ at 60% for efficient degradation of MO in visible light (Sun et al., 2012). Huang et al. (2011) synthesized Sb₂S₃ and Bi₂S₃ doped TiO₂ by gel hydrothermal method and investigated its photocatalytic activity for degradation of 4-nitrophenol. This enhancement in charge separation depends on the quality of interfacial contact between Sb₂S₃ and TiO₂, which may ultimately depend on the synthesis method, % composition, calcination temperature, and their morphological and surface properties, such as Brunauer-Emmett-Teller (BET) surface area.

In this view, in present investigation, an attempt has been made to reveal the key factors in synthesis of Sb₂S₃–TiO₂ nanocomposite with enhanced photocatalytic efficiency. It has been observed that the effect of composition of each component in the composite, calcination of composite, and method of synthesis all together affect the photocatalytic degradation efficiency of MO dye solution in the presence of white light when the Sb₂S₃–TiO₂ nanocomposite is used in a multilamp photoreactor.

Experiment

Materials

Titanium tetraisopropoxide (TTIP) was purchased from Alfa Aesar. Absolute ethanol, tartaric acid, and antimony trichloride were purchased from S D Fine-Chem Limited. Potassium thiocyanate was purchased from Fisher Scientific. The azo dye, methyl orange (MO dye) of Merck, was used as the model pollutant to study the photocatalytic efficiency of synthesized composite. Double-distilled water was used for preparation of solutions. All chemicals were AR grade and used without any further purification.

Synthesis of photocatalyst

Synthesis and characterization of TiO₂ were described previously (Shitole et al., 2013). Sb₂S₃ particles were synthesized by a simple wet chemical method under refluxing conditions (Ota et al., 2007).

In hydrothermal synthesis of Sb₂S₃–TiO₂ nanocomposite, the synthesized Sb₂S₃ particles were added to provide a weight ratio of Sb₂S₃ over TiO₂ as 5%, 10%, and 20%. In a typical experiment, synthesized Sb₂S₃ particles were dispersed into double-distilled water and sonicated for 15 min. A predetermined amount of TTIP was mixed with ethanol in 1:5 ratio. After complete dispersion of Sb₂S₃ in water, TTIP:ethanol solution was added dropwise under sonication and kept overnight with vigorous stirring. On the next day, whole solution was transferred to the Teflon-lined stainless steel autoclave and placed in muffle furnace for hydrothermal treatment at 140°C for 24 h for effective interaction of Sb₂S₃ with TiO₂ at high temperature and elevated pressure. After cooling the furnace to room temperature, autoclave was removed from the furnace, and the obtained composite was dried on a hot plate.

To study the effect of calcination on photocatalytic activity of the nanocomposite, the composite was calcined at various temperatures ranging from 200°C to 600°C for 2 h in muffle furnace. Furthermore, to study the effect of method of synthesis on the properties and photocatalytic activity of composite, Sb₂S₃–TiO₂ nanocomposite was also synthesized by the mechanical mixing method. In hydrothermally synthesized composite, 10% Sb₂S₃–TiO₂ calcined at 300°C for 2 h showed the best results for photocatalytic degradation of MO dye solution. Therefore, in mechanical mixing method, 90 mg of hydrothermally synthesized TiO₂ and 10 mg of Sb₂S₃ synthesized by wet chemical method were mixed and grinded in a mortar and pestle until they became homogeneous. Then, the ground sample was calcined in muffle furnace at 300°C for 2 h.

Material characterization

Sb₂S₃ and Sb₂S₃–TiO₂ nanocomposites were characterized by a range of analytical techniques. The X-ray powder diffraction (XRD) (Philips X'Pert PRO) patterns were recorded with Cu Kα radiation (α = 0.15406 nm) in the range of 10–80° 2θ at a scanning speed of 0.02°/s to determine the crystal structure. The morphology and structure of Sb₂S₃ and Sb₂S₃–TiO₂ nanocomposites were examined by transmission electron microscopy (TEM) (TECNAI G² 20 TWIN; FEI) and scanning electron microscopy (SEM) (JEOL JSM-6360 A) along with energy-dispersive X-ray (EDX). The sample was subjected to thermal gravimetric analysis (TGA) (DTG-60H, simultaneous DTA–TG apparatus) to get information regarding thermal stability of the product. The surface areas of synthesized samples were measured by Thermo Scientific Surfer BET Surface Area Analyzer.

Photocatalytic degradation experiments

We developed the successful design for laboratory-made multilamp photoreactor to study the photocatalytic activity. The laboratory-made photoreactor (Fig. 1) consisted of quartz reaction vessel in the center surrounded by four white light lamps (T5-8W 6400K; Hybec). The reaction solution was constantly aerated using aerator pump, and reaction temperature was controlled at 30°C ± 1°C by an air- cooling system. The photocatalytic test was performed with 40 mg catalyst dose and 100 mL solution of 2.5 × 10⁻⁵ M MO dye solution. The aliquots of suspension were taken out after every 15 min and filtered using 0.2 μm pore size, 13-mm-diameter Millipore disc, and the undecomposed MO dye was determined using Shimadzu UV–visible spectrophotometer (UV-1800 PC). Chemical oxygen demand (COD) values were measured by standard dichromate method using Spectralab 2015M COD Digestor and CT-15 COD Auto-Titrator. Total organic carbon (TOC) analysis was performed using commercially available test kits (NANOCOLOR TOC 60) from Macherey-Nagel, Germany, using thermodigester (Spectroquant TR 320) and spectrophotometer (NANOCOLOR VIS; Macherey-Nagel) (Kale and Thakur, 2015).

FIG. 1.

Laboratory-made multilamp photoreactor.

Results and Discussion

Characterization

XRD patterns of the Sb₂S₃ in Fig. 2a show the peaks for 020 peak at 2θ = 15.65°, 120 peak at 2θ = 17.51°, 310 peak at (25.04), 121 (29.21), 221 (32.36), 240 (35.50), and 501 (46.79) crystal planes, and their relative intensities were matching with the standard spectrum (JCPDS No. 42–1393) of the orthorhombic phase of crystalline Sb₂S₃. Absence of unwanted peaks confirms the purity of the product. Figure 2b–f shows the XRD of Sb₂S₃–TiO₂ nanocomposite from synthesized composite temperature to 600°C calcination temperature. The hydrothermally synthesized nanocomposite of Sb₂S₃–TiO₂ shows the peaks for both the anatase phase of TiO₂ and orthorhombic phase of Sb₂S₃ (Fig. 2b). The XRD also confirms the formation of crystalline and pure nanocomposite. The peak intensity increases as the nanocomposite calcination temperature increases from 200°C to 300°C. However, when the calcination temperature of nanocomposite increases to 400°C, the peaks for Sb₂S₃ are not observed, which is in accordance with the TGA data of Sb₂S₃ at 400°C, where the Sb₂S₃ oxidizes to Sb₂O₃. In the XRD pattern, the main peaks 25.42 (111) and 37.94 (141) for Sb₂O₃ (JCPDS No. 11–0689) might be shielded by the peaks of TiO₂ and hence cannot be seen distinguishably. When composite was calcined at 600°C, Sb₂O₃ vaporizes, and some Sb₂O₃ gets converted to Sb₂O₄ and so very less Sb₂O₄ is present in the nanocomposite. Hence, the XRD of nanocomposite at 600°C shows the peaks only for TiO₂ nanoparticles. Further characterization of the Sb₂S₃–TiO₂ nanocomposite, such as SEM, TEM, and BET, was carried out only for sample calcined at 300°C.

FIG. 2.

XRD patterns of Sb₂S₃ and 10% Sb₂S₃–TiO₂ nanocomposites calcined at 200°C, 300°C, 400°C, and 600°C and for TiO₂. XRD, X-ray powder diffraction.

Figure 3a and b shows the SEM images and EDX of the synthesized Sb₂S₃. These images reveal the flower-like morphology along with the formation of rods, which may be advantageous for the photocatalysis applications. Ota et al. (2007) reported that as the duration of reaction increases, Sb₂S₃ induces the rod-like morphology. The EDX spectrum of synthesized Sb₂S₃ shows the peaks for Sb and S, which confirms the purity of the Sb₂S₃. Figure 3c depicts the SEM image of Sb₂S₃–TiO₂ nanocomposite. Because of the more quantity of TiO₂ over Sb₂S₃ (10% Sb₂S₃ content), most of the Sb₂S₃ are covered and hidden under TiO₂ nanoparticles.

FIG. 3.

(a) SEM image of Sb₂S₃, (b) EDX of Sb₂S₃, (c) SEM image of the 10% Sb₂S₃–TiO₂ nanocomposite, and (d) EDX of 10% Sb₂S₃–TiO₂ nanocomposite. SEM, scanning electron microscopy; EDX, energy-dispersive X-ray.

TEM images (Fig. 4) illustrate the morphologies of Sb₂S₃ and Sb₂S₃–TiO₂ nanocomposites synthesized by hydrothermal and mechanical mixing methods. Figure 4a shows that Sb₂S₃ has a rod-like morphology. Figure 4b and c shows the TEM images of Sb₂S₃–TiO₂ hydrothermally synthesized nanocomposites without calcination and at 300°C calcination temperature. It is evident from Fig. 4b that before calcination, TiO₂ nanoparticles were dispersed around Sb₂S₃ rod, but after calcination at 300°C for 2 h, those dispersed TiO₂ nanoparticles were embedded on the surface of Sb₂S₃ rod as in Fig. 4c, indicating improved bonding between TiO₂ and Sb₂S₃ particles at higher calcinations. However, when the same composite was synthesized by mechanical mixing method, it shows the separate clusters of TiO₂ and Sb₂S₃ particles (Fig. 4d). These results indicate that the hydrothermal mixing method disperses the TiO₂ nanoparticles on the surface of Sb₂S₃ better than mechanical mixing method, and calcination supports for a strong bonding between them.

FIG. 4.

TEM images of (a) Sb₂S₃ rods and (b) 10% Sb₂S₃–TiO₂ hydrothermally synthesized nanocomposite (c) after calcination at 300°C and (d) 10% Sb₂S₃–TiO₂ mechanically mixed nanocomposite after calcination at 300°C. TEM, transmission electron microscopy.

Table 1 shows the specific surface area of Sb₂S₃, TiO₂, and 10 wt.% Sb₂S₃–TiO₂ calcined at 300°C nanocomposite determined by BET analysis. Because Sb₂S₃ prevents the agglomeration of TiO₂ nanoparticles, the surface area of nanocomposite increases in comparison with bare TiO₂ and Sb₂S₃ nanoparticles.

Table 1.

BET Surface Area Analysis

Photocatalyst	BET surface area (m²/g)
Sb₂S₃	31
TiO₂	97
Hydrothermally prepared 10% Sb₂S₃–TiO₂ nanocomposite	186

BET, Brunauer-Emmett-Teller.

Figure 5a shows the TGA and DTA curves of synthesized Sb₂S₃. The TGA shows the first weight loss around 290–380°C and second weight loss around 415–440°C. DTA shows the peaks for the same weight losses. This indicates the oxidation of Sb₂S₃ to Sb₂O₃. There is a presence of both Sb₂S₃ and Sb₂O₃ after the first weight loss, and in the second weight loss, all Sb₂S₃ oxidize to Sb₂O₃. The third weight loss occurs around 473–563°C, which occurs owing to vaporization of Sb₂O₃ and continued oxidation of Sb₂O₃ to Sb₂O₄. Actually, the oxidation of Sb₂O₃ to Sb₂O₄ results in weight gain, but this weight gain was counteracted by the vaporization of Sb₂O₃ (Town et al., 1975; Kelley et al., 1987).

FIG. 5.

TG/DTA of (a) synthesized Sb₂S₃ and (b) 10% Sb₂S₃–TiO₂ hydrothermally synthesized nanocomposite in air atmosphere.

Figure 5b shows the TG/DTA of hydrothermally synthesized Sb₂S₃–TiO₂ nanocomposite. TGA clearly reveals four weight losses. The first weight loss around 100°C was because of water evaporation, and the second weight loss around 200–350°C might be due to decomposition of organic matter. The third and fourth weight losses around 325–400°C and 450–550°C were because of oxidation and vaporization of Sb₂S₃ within the nanocomposite, respectively.

Photocatalytic activity study

Effect of composition

The effect of loading of Sb₂S₃ in the composite over TiO₂ was studied to achieve the higher photocatalytic activity for degradation of targeted pollutant. It is a crucial step to control the composition ratio of Sb₂S₃:TiO₂ to obtain the optimal synergistic effect between TiO₂ and Sb₂S₃.

Figure 6a displays the concentration changes of the initial 100 mL 2.5 × 10⁻⁵ M MO dye solution at 463 nm as a function of UV light irradiation time in the presence of TiO₂ and TiO₂–Sb₂S₃ nanocomposite catalyst with different mass ratios (5, 10, and 20 wt.% Sb₂S₃–TiO₂) in the presence of air. The bare TiO₂ nanoparticles synthesized by hydrothermal method show 64.15% degradation of MO dye solution, while for Sb₂S₃–TiO₂ composite, the degradation rate increases, and for 5 and 10 wt.% of Sb₂S₃ addition, the degradation becomes 81.10% and 86.29%, respectively. It clearly indicates the role of Sb₂S₃ in separation of electron–hole pair and transportation of electron resulting in increased degradation efficiency of nanocomposite. However, for 20 wt.% Sb₂S₃ loading, again the degradation rate decreases significantly up to 61.38%. It might be due to large amount of Sb₂S₃, hindering the absorption of UV light by TiO₂ nanoparticles.

FIG. 6.

(a) C/C₀ versus irradiation time for degradation of MO dye using TiO₂ and 5%, 10%, and 20% Sb₂S₃–TiO₂ nanocomposite to study effect of loading of Sb₂S₃, (b) C/C₀ versus irradiation time for degradation of MO dye using 10% Sb₂S₃–TiO₂ nanocomposite at various calcination temperatures to study effect of calcination, (c) C/C₀ versus irradiation time for degradation of MO dye using 10% Sb₂S₃–TiO₂ composite synthesized by hydrothermal (S1T Hydro) and mechanical mixing (S1T Mech) methods to study effect of synthesis method. (d) Dark experiment in presence of 10% Sb₂S₃–TiO₂ hydrothermally prepared nanocomposite. MO, methyl orange.

Effect of calcination temperature

Efficient catalyst in weight ratio (10% Sb₂S₃–TiO₂) was calcined between temperatures ranging from 200°C to 600°C for 2 h in muffle furnace and examined for its photocatalytic response for degradation of 2.5 × 10⁻⁵ M MO dye solution under UV light irradiation (Fig. 6b). Bare TiO₂ degrades 64.15% MO dye from solution, while the 10% Sb₂S₃–TiO₂ as prepared, calcined at 200°C, 300°C, 400°C, 500°C, and 600°C, degrades 73.09%, 86.31%, 95.31%, 70.53%, and 25.67% MO dye, respectively. 10% Sb₂S₃–TiO₂ nanocomposite shows the best activity at 400°C calcination temperature, but as evident from XRD and TGA data, after 300°C, Sb₂S₃ from nanocomposite starts getting oxidized. Up to 300°C, the nanocomposite contains only TiO₂ and Sb₂S₃, but above 300°C, along with TiO₂ and Sb₂S₃, oxidized Sb₂S₃ was also observed because the Sb₂S₃ in nanocomposite is thermally unstable above that temperature. Hence, 300°C calcination temperature was finalized to prepare nanocomposite of TiO₂ and Sb₂S₃ by mechanical mixing to compare its activity with hydrothermally synthesized 10% TiO₂–Sb₂S₃ nanocomposite. It is also observed that at 300°C, a mixture of Sb₂S₃ and Sb₂O₃ along with TiO₂ is more beneficial for photocatalytic degradation of MO dye solution, and interestingly above 400°C, Sb₂O₃–TiO₂ has been found to be more efficient than Sb₂S₃–TiO₂ nanocomposite (Liu et al., 2012).

Effect of method of synthesis

Nowadays, various types of composite synthesis methods have been developed. The method of synthesis largely affects the structure, morphology, and properties of composite. Hence, to study the effect of method of synthesis on the photocatalytic properties of nanocomposite becomes essential. Photocatalytic efficiencies of 10% Sb₂S₃–TiO₂ nanocomposite synthesized by mechanical mixing (S1T Mech) and hydrothermal (S1T Hydro) methods were tested by degrading MO dye solution. The result shows that the S1T Hydro composite exhibits enhanced photocatalytic performance by degrading 86.31% MO dye solution than S1T Mech composite degrading only 53.61% MO dye solution under UV light irradiation (Fig. 6c).

It concludes that the synthesis method greatly affects the photocatalytic degradation efficiency.

Chemical oxygen demand

The mineralization of model pollutant by S1T Hydro calcined at 300°C (S1T Hydro 300) and bare TiO₂ synthesized by the same method was studied by COD measurements. As shown in Table 2, after 2 h of photocatalysis reaction, there is a substantial decrease in the COD values of MO dye by S1T Hydro 300 nanocomposite than TiO₂ alone.

Table 2.

COD Values of MO Dye (in ppm) for Photocatalytic Degradation Using 10% Sb₂S₃–TiO₂ Nanocomposite and TiO₂ Nanoparticles

S. No.	Photocatalyst	COD (in ppm)
1	Initial	229.8
2	TiO₂	116.8
3	10% Sb₂S₃–TiO₂ calcined at 300°C	84

COD, chemical oxygen demand; MO, methyl orange.

Total organic carbon

Mineralization of model pollutant by 10% Sb₂S₃–TiO₂ hydrothermally prepared and calcined at 300°C and bare TiO₂ synthesized by the same method was studied by TOC measurements. Figure 7 shows that 64% mineralization was achieved for Sb₂S₃–TiO₂ nanocomposite compared to bare TiO₂ (49%). Obtained results are a direct indication of enhanced degradation and mineralization efficiency of 10% Sb₂S₃–TiO₂ hydrothermally prepared and calcined at 300°C nanocomposite compared with bare TiO₂.

FIG. 7.

Percent reduction in TOC for 10% Sb₂S₃–TiO₂ hydrothermally prepared and calcined at 300°C nanocomposite and bare TiO₂ for degradation of MO dye. TOC, total organic carbon.

Proposed mechanism

A coupling of Sb₂S₃ with TiO₂ increases the photocatalytic efficiency of pure TiO₂. The conduction band of TiO₂ is more anodic than Sb₂S₃ conduction band, which strengthens the driving forces of electron injection, as shown in Fig. 8. Hence, the TiO₂ and Sb₂S₃ semiconductor heterojunction generates a beneficial role in improving charge separation and extends TiO₂ response to a range of light irradiation.

FIG. 8.

(a) Band positions of TiO₂ and Sb₂S₃ semiconductors. (b) Mechanism of the photocatalysis of Sb₂S₃–TiO₂ nanocomposite—photocatalytic degradation of organic pollutant over Sb₂S₃–TiO₂ nanocomposite.

Based on reported works (Huang et al., 2011), a mechanism was proposed for the photocatalytic degradation of organic pollutants using Sb₂S₃–TiO₂ semiconductor heterojunction as a photocatalyst. Proposed mechanism is shown in Fig. 8b, with step-by-step equations. Upon irradiation, TiO₂ and Sb₂S_3, get excited, and electrons are injected from the conduction band of Sb₂S₃ to that of TiO₂, as shown in Eqs. (1) and (2). This electron reduces the molecular oxygen to superoxide radical anion and hydrogen peroxide [Eqs. (3) and (4)]. Holes from valence band of TiO₂ oxidize H₂O to hydroxyl radicals [Eq. (6)]. These hydroxyl radicals are powerful oxidizing agents and play an important role in the degradation of organic pollutants [Eq. (7)] (Huang et al., 2011; Sun et al., 2012). \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{ \rm{S}}{{ \rm{b}}_{ \rm{2}}}{{ \rm{S}}_{ \rm{3}}} \, \hbox {-} \, { \rm{Ti}}{{ \rm{O}}_{ \rm{2}}} \mathop{\longrightarrow}^{ \rm{h} \nu }{ \rm{S}}{{ \rm{b}}_{ \rm{2}}}{{ \rm{S}}_{ \rm{3}}} ( {{ \rm{e}}_{{ \rm{CB}}}} ^ - + { \rm{ }}{{ \rm{h}}_{{ \rm{VB}}}} ^ + ) \, \hbox {-} \, { \rm{Ti}}{{ \rm{O}}_{ \rm{2}}} \tag{1}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{ \rm{S}}{{ \rm{b}}_{ \rm{2}}}{{ \rm{S}}_{ \rm{3}}} ( {{ \rm{e}} ^ - } + { \rm{ }}{{ \rm{h}}^ + } ) \, \hbox {-} \, { \rm{Ti}}{{ \rm{O}}_{ \rm{2}}}\ \longrightarrow\ { \rm{S}}{{ \rm{b}}_{ \rm{2}}}{{ \rm{S}}_{ \rm{3}}} \left( {{{ \rm{h}}^ + }} \right) \, \hbox {-} \, { \rm{Ti}}{{ \rm{O}}_{ \rm{2}}} ( {{ \rm{e}} ^ - } ) \tag{2}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{{ \rm{e}} ^ - } + { \rm{ }}{{ \rm{O}}_{ \rm{2}}}\ \longrightarrow \ {{ \rm{O}}_{ \rm{2}}}^{ \bullet - } \tag{3}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{ \rm{2}}{{ \rm{e}} ^ - } + { \rm{ }}{{ \rm{O}}_{ \rm{2}}} + { \rm{ 2}}{{ \rm{H}}^ + }\ \longrightarrow \ {{ \rm{H}}_{ \rm{2}}}{{ \rm{O}}_{ \rm{2}}} \tag{4}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{{ \rm{h}}_{{ \rm{VB}}}} ^ + + { \rm{ }}{{ \rm{H}}_{ \rm{2}}}{ \rm{O }}\ \longrightarrow \ {{ \rm{H}}^ + } + { \rm{ O}}{{ \rm{H}}^ \bullet} \tag{5}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}\rm Organic \ pollutant + OH^\bullet + { \rm{O}}_{ \rm{2}}^{ \bullet -} \longrightarrow \ \hbox{degradation products}. \tag{6}\end{align*} \end{document}

Photocatalytic degradation of organic pollutant over Sb₂S₃–TiO₂ nanocomposite.

Conclusion

In summary, Sb₂S₃–TiO₂ nanocomposites were successfully synthesized by hydrothermal method. Furthermore, the effects of percent composition, calcination temperature, and synthesis method of Sb₂S₃–TiO₂ nanocomposite on the photocatalytic activities were investigated in detail. Obtained results show enhanced degradation (86.31%) of MO dye, with efficient 10% Sb₂S₃–TiO₂ nanocomposite synthesized by hydrothermal method calcined at 300°C compared to bare TiO₂ (64.15%), which is even more than mechanically mixed nanocomposite (53.61%). The obtained results of enhanced degradation in case of hydrothermally synthesized composite clearly explain the effect of method of nanocomposite synthesis. Hydrothermally synthesized sample facilitates in establishing good interfacial contact between TiO₂ and Sb₂S₃, thereby resulting in the effective separation of the photogenerated electron–hole pairs, leading to the faster rates of photocatalytic oxidation compared to bare TiO₂ and mechanically mixed sample. Furthermore, the encouraging COD and TOC data throw light on the substantial mineralization of the pollutant tested, which is essential from the environmental point of view. Thus, the nanocomposites synthesized under present investigation by hydrothermal method with efficient percent composition and calcination temperature possess potential applications in environmental remediation as well as solar cell application.

Footnotes

Acknowledgment

The authors are thankful to the ISRO-UoP Cell, Savitribai Phule Pune University, for research funding.

Author Disclosure Statement

No competing financial interests exist.

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