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. 2023 Nov 1;8(45):42647–42658. doi: 10.1021/acsomega.3c05386

Ag2S Nanoparticles Supported on 3D Flower-Shaped Bi2WO6 Enhanced Visible Light Catalytic Degradation of Tetracycline

Hengcan Dai †,*, Xiaoliang Yang ‡, Fei Tang †
PMCID: PMC10652829  PMID: 38024701

Abstract

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A three-dimensional flower-shaped Bi2WO6 has been prepared by a hydrothermal procedure without the addition of an auxiliary agent and under neutral conditions with ultrapure water serving as solvent, and the Ag2S–Bi2WO6 composite with weight ratios of 5, 10, and 15% was prepared by a hydrothermal method. The crystallinity, morphology, mode of binding, and optical properties of the Ag2S–Bi2WO6 composite were characterized, the results of which showed that the composite had excellent dispersion, crystallinity, and purity. The composite with a weight ratio of 10% had the best photocatalytic performance, and the degradation rate of tetracycline reached 95.51% within 120 min, an increase of 27.35% over Bi2WO6. In experiments, some focus was given to the effect of the initial solution pH and the concentrations of humic acid and inorganic anions on the degradation efficiency. Based on free radical capture experiments and the semiconductor theory, the main active substances and mechanisms in the optical catalytic reaction process were studied, and speculation was given concerning the degradation pathway for the target pollutants. This study has conceived novel methods for the development of dual semiconductor systems consisting of a Ag NP composite and in doing so has provided new approaches for the development and photocatalysis for water pollution control.

1. Introduction

Because of persistence, accumulation, and ecological toxicity, antibiotics not only affect the ecological balance in the environment but also pose a serious threat to human health.1−4 Numerous studies have focused on the degradation method of antibiotics, such as adsorption,5 microbial degradation,6 Fenton,7 photocatalysis,8 and electrochemistry.9 Photocatalysis, as an advanced oxidation technology for energy saving and environmental protection, is widely used not only in hydrogen evolution and carbon dioxide reduction10 but also in water treatment because it can degrade pollutants into easily biodegradable intermediates in a short time or can directly mineralize H2O and CO2.11,12

Bi2WO6 is the simplest Aurivillius-type oxide, which is alternately composed of a [WO4]2– octahedral perovskite layer and a [Bi2O2]2+ ion layer. Its unique crystal structure enables it to have catalytic, piezoelectric, and oxygen ionization physical and chemical properties. Because of its small band gap and open layered void structure, which can provide more active sites for photocatalytic reaction, it has become one of the concerned photocatalytic materials. However, Bi2WO6 still has limitations such as the photogenic electron–hole high compound rate and slow charge transfer rate, which seriously limit its use in industry.13−15 As recorded in the literature, through semiconductor recombination, there is a matching band structure between semiconductors, and the spectral response range of Bi2WO6 can be broadened by using the band overlap effect; the transfer of the photogenerated electron–hole pairs was promoted, such as AgBr/Bi2WO6,16 Bi2WO6/ZnWO4,17 Al2(WO4)3/Bi2WO6,18 and AgI/Bi2WO6.19 Metal sulfides are important narrow-band-gap semiconductor materials that typically have excellent visible light absorption ability.20 As one of them, silver sulfide (Ag2S) is a good candidate for Bi2WO6 photosensitization due to its fast charge exchange properties, narrow band gap, and high stability as a nontoxic semiconductor.21,22

In this study, it is proposed for the first time that Ag2S and three-dimensional flower-shaped Bi2WO6 can form a novel dual semiconductor system by changing the preparation conditions of the precipitation method, and it has a different morphology, visible light responsiveness, and degradation mechanism compared with previous studies. The photocatalytic performance of the composite was studied by photocatalytic degradation of tetracycline (TCH), and the effects of the initial solution pH, the humic acid (HA) concentration, and different inorganic anions on the degradation efficiency are discussed to clarify the stability of the catalyst to water condition change.

2. Method

2.1. Preparation of Bi2WO6

All chemicals were of analytical purity and used without further purification. First, 9.70 g (20 mmol) Bi(NO3)3·5H2O and 3.30 g (10 mmol) Na2WO4·2H2O were, respectively, dispersed in 40 mL of ultrapure water and stirred for 40 min. Then, Na2WO4·2H2O solution was added to Bi(NO3)3·5H2O solution slowly, and magnetic stirring was performed for 50 min. The resulting solution was reacted hydrothermally at 200 °C for 12 h. Subsequently, the precipitate was rinsed three times alternately with ultrapure water and ethanol, filtered, and then dried at 70 °C for 10 h, yielding the Bi2WO6 sample.

2.2. Preparation of Ag2S–Bi2WO6

Bi2WO6 (1.00 g) was dispersed in 40 mL of ultrapure water and stirred for 30 min; then, 0.005 g of sodium dodecyl benzenesulfonate (SDBS) was added to the solution and stirred for 5 h. A small amount of AgNO3 was dissolved in 30 mL of ultrapure water and then added to the Bi2WO6 solution and stirred for 2 h. A corresponding weight of Na2S·9H2O was dissolved in 20 mL of ultrapure water, which was then added to the above solution, and the mixture was stirred continuously for 2 h. The samples were washed three times with ethanol and ultrapure water, respectively; filtered; and then dried at 70 °C for 12 h. Ag2S–Bi2WO6 composites with weight ratios of 5% (wt 5% BWO), 10% (wt 10% BWO), and 15% (wt 15% BWO) were prepared.

2.3. Characterization and Instrumental Parameters

The crystallinity of the samples was characterized by a D/max-2200X X-ray diffractometer (XRD) with a Cu target, the tube voltage was set at 40 kV, and the diffraction angle ranged from 10 to 80°. A Quanta 200 cold field emission scanning electron microscope (SEM) was used to characterize the structural morphology of the samples, with the SEM being equipped with a GENESIS4000 energy dispersive X-ray spectrometer; the working voltage was 3–5 kV. The chemical bonding of the samples was studied using an ESCALAB 250 X-ray photoelectron spectroscopy analyzer (XPS). The binding energy in the spectrum was calibrated by C 1s (284.62 eV); the energy was 1486.6 eV. Compositional analysis of the samples was carried out with an EHAX6293-H X-ray energy dispersion spectrometer (EDS). The current was set at 10 μA, and the voltage was 15 kV. The light absorption properties of the materials were studied by using a UV-3600 ultraviolet visible spectrophotometer (UV–vis). Photocatalytic degradation of solutions was studied by using an Agilent 1290II-6460 high-performance liquid chromatograph (HPLC–MS). The specific surface area and pore diameter of the material were determined by a TRISTAR-3000 analyzer. The zeta potential was measured by a Malvern Nano ZS particle size analyzer.

2.4. Photocatalytic Experiments

A 500 W tungsten halogen lamp (λ > 420 nm) was used as the visible light source, and 100 mL (concentration 10 mg/L) of the TCH solution was added into the double-wall quartz reactor. The temperature of the reaction solutions was kept constant by the actions of the magnetic blender and the cooling system. The Ag2S–Bi2WO6 composites (0.05 g) dispersed in the solution. The light source was turned off for the first 30 min so that the Ag2S–Bi2WO6 composites and TCH could achieve adsorption equilibrium. The absorbance was measured at 357 nm by the DR6000 UV spectrophotometer.

3. Results and Discussion

3.1. Material Characterization

3.1.1. XRD Analysis

The crystal phase and structure of the prepared photocatalyst were identified by X-ray diffraction, and the results are shown in Figure 1. The diffraction peaks of Bi2WO6 are strong and sharp, indicating that the catalyst has excellent crystallinity. The diffraction peaks at 28.2, 32.7, 47.0, and 55.7° can be assigned to the (131), (200), (202), and (331) lattice planes of Bi2WO6 (JCPDS No. 39-0256).23,24 The characteristic peaks at 31.82, 33.66, 34.74, and 36.81° correspond to the (120), (121), (112), and (022) lattice planes of Ag2S (JCPDS No. 14-0072), which indicate the prepared monoclinic structure of Ag2S.25 Furthermore, the diffraction peak of the Ag2S–Bi2WO6 composite does not shift significantly after loading Ag2S, indicating that loading of Ag2S particles does not change the lattice structure of Bi2WO6 but is located on its surface.26 As the content of Ag2S continues to decrease, the diffraction peaks of Ag2S are not obvious, the reason for the doping amount of Ag2S was low and the particles were small and highly dispersed.27,28

Figure 1.

Figure 1

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XRD of Ag2S–Bi2WO6 composites.

3.1.2. SEM and EDS Analysis

From the inspection of the SEM analysis for the morphology and composition of wt 10% BWO (Figure 2a,b), it can be seen that Bi2WO6 has a three-dimensional flower-shaped structure with a diameter of about 3 μm, with a more mesoporous structure and a large specific surface area and with Ag2S being attached to its surface. Using EDS, the elemental composition of the sample was determined, and it can be seen that the wt 10% BWO contained W, Bi, O, Ag, and S.

Figure 2.

Figure 2

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(a, b) SEM and (c–i) EDS of wt 10% BWO.

3.1.3. XPS Analysis

The chemical bonding form of Bi2WO6 and wt 10% BWO was analyzed by XPS, with the binding energy for the spectrum being calibrated using C 1s (284.62 eV). Figure 3a shows the full spectrum of Bi2WO6, in which the binding energies of W, B, and O are clearly visible; there are no other elements. In Figure 3b,c, it can be seen that the binding energies at 159.4 and 164.8 eV correspond to Bi 4f7/2 and Bi 4f5/2, respectively, which indicate that Bi exists as Bi3+ in Bi2WO6.29,30 The binding energies at 35.2 and 37.3 eV can be attributed to W 4f7/2 and W 4f5/2, and W exists as W6+.31,32 The binding energies of O 1s at 530.0 eV correspond to lattice oxygen (O–Bi and O–W); there is no other form of oxygen.33 In summary, the prepared Bi2WO6 was a pure phase compound.

Figure 3.

Figure 3

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XPS of Bi2WO6. (a) Full spectrum, (b) Bi 4f, (c) W 4f, and (d)O 1s.

In comparison with the XPS of Bi2WO6, there are newly emerged S 2p and Ag 3d binding energies of wt 10% BWO, and the location of binding energies of Bi 4f and W 4f has shifted slightly (Figure 4b,c). Because Ag2S surface modifies Bi2WO6, the electron cloud density for Bi and W changes, thus leading to a change in the electronic structure.34 The position and strength of lattice oxygen (Figure 5d) did not change, indicating that Ag2S bonded with Bi2WO6 through surface modification without change in the internal crystal structure. But the newly emerging binding energies of O 1s at 532.5 eV correspond to water species adsorbed on the surface of as-prepared sample, which is more conducive to the formation of hydroxyl radical and superoxide free radical.35 As shown in Figure 4e, the binding energies at 161.4 and 162.5 eV can be identified as S 2p3/2 and S 2p1/2, which correspond to S2–; the binding energies at 367.8 and 373.9 eV (Figure 4f) correspond to Ag 3d5/2 and Ag 3d3/2, respectively.25,36,37 According to previous researches,38,39 it can be clarified that the valence state of Ag in the composite is Ag1+. In conclusion, the Ag2S–Bi2WO6 composite was successfully combined by chemical energy.

Figure 4.

Figure 4

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XPS of wt 10% BWO. (a) Full spectrum, (b) Bi 4f, (c) W 4f, (d) O 1s, (e) S 2p, and (f) Ag 3d.

Figure 5.

Figure 5

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(a) UV–vis and (b) band gap energies of Bi2WO6 and the Ag2S–Bi2WO6 composite. (c) N2 adsorption–desorption isotherms of the synthetic samples.

3.1.4. UV–Vis and BET analysis

The wavelength range and intensity of absorption of visible light by a semiconductor play fundamental roles in photocatalytic oxidation reactions. Figure 5a shows the photosensitivity of Bi2WO6 and Ag2S–Bi2WO6 composites to visible light. Bi2WO6 absorbs radiation from the ultraviolet light to the visible; the absorption edge is located at about 460 nm, and there is no absorption after 550 nm, which is almost consistent with the results of recent literature.40,41 The Ag2S–Bi2WO6 composite absorption boundary has clearly red-shifted to about 550 nm, and there is still strong light absorption, but this extends to about 800 nm. The wt 10% BWO has the best visible light response and absorption range, conducive to the enhancement of photocatalytic activity.42,43Figure 6b shows the forbidden bandwidths corresponding to Bi2WO6 that occur at about 2.96 eV, whereas those for the wt 5%, wt 10%, and wt 15% BWO are about 2.78, 2.68 and 2.82 eV, respectively.44

Figure 6.

Figure 6

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(a) Photocatalytic degradation of different weight ratios. (b) UV–vis spectrum. The effect of pH (c) and zeta potential of wt 10% BWO as a function of pH value (d). The effect of (e) humic acid and (f) inorganic anions.

N2 adsorption–desorption measurements are performed to investigate the BET surface areas and pore sizes of Bi2WO6 and wt 10% BWO. As shown in Figure 5c, both of the hysteresis loops of measured isotherms for Bi2WO6 and wt 10% BWO can be identified as typical type IV curves with an H3 hysteresis loop, which denoted the presence of a slit-like mesoporous structure.45 The BET surface areas of Bi2WO6 and Ag2S–Bi2WO6 are 56.39 and 62.47 m2/g, respectively. After Ag2S is added, the surface of Bi2WO6 is enlarged, indicating that more active sites are provided for the removal of contaminated matter. However, the pore size of wt 10% BWO (8.82 nm) is smaller than that of Bi2WO6 (10.25 nm), which may be the reason that Ag2S fills the Bi2WO6 hole. The suitable surface area and pore structure contribute to higher photocatalytic activity.

3.2. Photocatalytic Degradation Experiments

3.2.1. Degradation of Tetracycline

As shown in Figure 6a, the degradation rate of Bi2WO6 was 68.16% within 150 min and was mainly attributed to the multilevel void structure that had a strong adsorption capacity. The photocatalytic property of Ag2S–Bi2WO6 increased significantly and not only had a higher surface area but also provided more active sites.46−50 The results showed that wt 10% BWO had the best photocatalytic efficiency, and the degradation rate of TCH was 95.51% within 150 min. The reason was that the composite inhibited the photogenerated electron–hole recombination.51 The photocatalytic efficiency of wt 15% BWO decreased, and the effect was mainly reflected in the photocatalytic stage rather than adsorption. The reason for this is that the adhesion of excessive black Ag2S on the surface of Bi2WO6 led to the shielding of the active site on the surface of the photocatalyst, which weakened the transmission performance of the incident light and affected the absorption of visible light by the composite.52−54

The UV–vis spectrum (Figure 6b) shows that as the reaction proceeded, the intensity of the characteristic peak at 357 nm gradually decreased. This result indicated that TCH was degraded, and the stable four-ring structure of TCH was destroyed by oxidation, gradually decomposing into small molecules.

3.2.2. The Effect of pH

pH is an extremely important parameter in wastewater treatment, which can be affected by changing the surface adsorption capacity of the catalyst or the hydrolytic form of the pollutants.55,56 As the pH was increased from 3 to 11, degradation at first increased and then decreased (Figure 6c). The degradation rate was less than 40% at pH 3, whereas the value was more than 90% at pH 7.

The photocatalytic oxidation reaction process occurs mainly on the surface of the photocatalyst, so a composite that can effectively adsorb the TCH is a prerequisite for the photocatalytic reaction.57,58 The pH directly affects the hydrolyzed form of the target pollutant. TCH exists mainly in the form of cations (TCH3+),59 zwitterions (TCH2±), anions (TCH–), and bianions (TC2–) for pH conditions that are lower than 3.3, between 3.3 and 7.7, between 7.7 and 9.7, and beyond 9.7, respectively.60,61 The variation of the zeta potential of wt 10% BWO with pH value is shown in Figure 6d. When pH is less than 6.5, wt 10%BWO is positively charged, and when pH is greater than 6.5, it is negatively charged. Therefore, when pH is less than 3.3 or greater than 7.7, wt 10% BWO and TCH both carry the same charge on the surface and should repel each other, thus reducing the adsorption amount. However, with change of pH, the adsorption capacity of wt 10% BWO does not change significantly, indicating that surface electrostatic forces play no major role. It has been found that TCHs in the anionic state (TCH–, TC2–) have a higher electron density than those in the cationic state (TCH3+) and hence are more likely to be attacked by active substances; it indicates that TCH is more easily degraded under neutral conditions.62 In summary, pH seriously affects the photocatalytic property but has no effect on the adsorption of the composite.

3.2.3. The Effect of Humic Acid

Humic acid (HA) occurs extensively in soil, natural water bodies, and all sewage and has a great impact on the forms and migration performance of TCH.63,64 The experimental results (Figure 6e) revealed that when the HA concentration increased from 0 to 20 mg/L, the degradation rate was severely inhibited in the photocatalytic stage. HA can act as a photosensitizer to promote the production of •OH and •O2–, thus improving the degradation rate of TCH. However, it will also be a competitive reaction with TCH for active substances or become a quenching agent reducing the content of active substances, thus inhibiting the photocatalytic efficiency.65,66 In this experiment, the inhibitory effect was stronger than the promoting effect of HA, but HA at an appropriate concentration can accelerate the adsorption of composite catalyst.67

3.2.4. The Effect of Inorganic anions

Inorganic anions exist widely in wastewater and have variable effects on TCH.68,69 The results are shown in Figure 6f. CO32– and HCO3– improved the degradation rate of TCH within 150 min because CO32– and HCO3 will be hydrolyzed to CO3– (E0 = 1.78 V, pH = 7) (eqs 1, 2) so that the CO3– can attack electron-rich groups such as phenols and nitrogen-containing compounds by means of electron transfer or hydrogen extraction, whereas the electron-rich groups such as phenol groups and dimethylammonium groups in the TCH structure become a priority as objects of destruction, thus accelerating the decomposition of TCH.70,71 NO3– will consume h+ to generate sparsely NO2–• and •O2–, which then further react with water to generate •OH, but with the addition of NO3–, the degradation rate was minimally affected, which suggests that the main active substances were the •O2– or •OH rather than h+72 (eqs 3 – 5). Cl– can seriously affect the degradation rate of TCH because the Cl– consumes •OH to form low reactive ClOH–• and Cl2–• (eqs 6 and 7), which further inferred that •OH was one of the main active substances.

3.2.4. 1
3.2.4. 2
3.2.4. 3
3.2.4. 4
3.2.4. 5
3.2.4. 6
3.2.4. 7

3.3. Stability of the Composite

The reuse rate of the composite is an important parameter and typically can serve as a measure of the stability of the catalyst.73,74 After four cycles of experiments, the degradation rates of TCH decreased to 78.60% (Figure 7a). The samples collected after four cycles were tested by XRD, and the characterization results are shown in Figure 7b. The new diffraction peak at 38.25° corresponds to Ag0.75 Ag2S is corroded by light, and part of Ag+ is restored to Ag0, which covers part of the active site; this is the main reason for the continuous decline of photocatalytic activity with repeated experiments.76,77

Figure 7.

Figure 7

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(a) Repeatability experiment, (b) XRD of the composite after repeated experiments, and (c) free radical trapping experiment.

3.4. Free Radical Trapping Experiment

To study the mechanism of the photocatalytic process, the main active species in the photocatalytic degradation of TCH were identified by conducting a free radical capture experiment. Isopropyl alcohol (IPA), p-benzoquinone (BQ), and ammonium oxalate (AO) were used as quenching agents for the hydroxyl radical (•OH), the superoxide radical (•O2–), and the photogenic hole (h+), respectively.78,79 Except for the dosage of BQ that was 1 mmol/L, the other quenchers were all 10 mmol/L. As shown in Figure 7c, the addition of AO had little effect on the photocatalytic degradation rate, indicating that h+ was not the main active pollutant in this experiment; this finding is consistent with the analysis results for the inorganic anions. In contrast, the degradation rates of TCH decreased sharply after the addition of IPA, indicating that •OH was the main active substance in the reaction system, which is the reason why the photocatalytic degradation rate dropped sharply after the addition of Cl–. BQ also had a great effect on the degradation rate, indicating that O2– was also one of the active substances.

3.5. Analysis of Photocatalytic Mechanism

The conduction band (CB) and valence band (VB) edges of Bi2WO6 and Ag2S can be calculated by the Mulliken empirical formula (eqs 8and 9)

3.5. 8
3.5. 9

where EVB and ECB are the potentials at the top of the valence band and the bottom of the conduction band relative to the standard (H2) electrode potential, respectively; X is the electronegativity of the semiconductor; Ee is the energy of the free electron (about 4.5 eV); and Eg is the band gap width of the semiconductor.

The electronegativity of Ag2S is 4.97 eV, and the band gap is about 1.05.80 The EVB values for Ag2S and Bi2WO6 are 1.00 and 3.38 eV, and the ECB values are −0.05 and 0.44 eV, respectively. In Ag2S–Bi2WO6 composites, the separation of photoproduced electron–hole pairs follows the common separation mechanism that is usually observed in composite photocatalysts (Figure 8a). The conduction band of Bi2WO6 (0.44 eV vs NHE) is higher than the redox potential of O2 (−0.046 eV vs NHE). Photocatalyzed electrons do not react with O2 to form •O2–.81 Similarly, the hole in the valence band of Ag2S (1.00 eV vs NHE) will not react with H2O (2.30 eV vs NHE) to form •OH. However, these findings contradict the results of the free radical trapping experiments.

Figure 8.

Figure 8

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Dual semiconductor systems' mechanism of the Ag2S–Bi2WO6 composite.

Therefore, the “dual semiconductor systems consisting of Ag NPs” are proposed (Figure 8b).82,83 Under visible light, part of Ag2S is reduced into Ag NPs that become attached to the surface of the Ag2S–Bi2WO6 composite, forming Ag@Ag2S–Bi2WO6. Ag NPs have two roles in dual semiconductor systems, that is, as electronic mediators and photosensitizers, which depend on the optical response of the two semiconductors.84,85 In this study, because Ag2S and Bi2WO6 can be excited by visible light, the Ag NPs function merely as an electron transfer medium. Meanwhile, photonic absorption results in the excitation of Bi2WO6 and Ag2S from their ground state to an excited state, electrons and holes are separated, and electrons in the conductive band of Bi2WO6 and the hole in valence band of Ag2S rapidly combine through the Ag NPs. Results show that the photocatalytic electrons concentrated in the Ag2S conduction band and the holes concentrated in the valence band of Bi2WO6, and this greatly accelerates the photogenerated electron–hole transfer and separation. The electrons in the conduction band of Ag2S (−0.046 eV vs NHE) readily react with O2 (2.30 eV vs NHE) to produce •O2–, and the holes in the valence band of Bi2WO6 (0.49 eV vs NHE) can result in the oxidization of hydroxyl group surfaces or surface-bonded water molecules so that highly reactive and nonselective •OH (−0.046 eV vs NHE) can be obtained (eqs 10–17). TCH pollutant is attacked and decomposed into nontoxic substances by •OH and •O2–. Therefore, the good photocatalytic performance of the “dual semiconductor systems consisting of Ag NPs” explains the reason why •OH and•O2– are the main active substances in this study.

3.5. 10
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3.5. 12
3.5. 13
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3.5. 15
3.5. 16
3.5. 17

3.6. Possible Degradation Pathways of TCH

According to the photocatalytic reaction mechanism, the nature of degradation of TCH is the result of the strong oxidation of photocatalytically active substances. Figure 9a shows the mass spectrum of 0 min and m/z 445.1 that can be attributed to TCH because the HCl is readily removed by TCH in the water solubilization process and becomes TC.86Figure 9b shows the mass spectrum of 120 min, from which it can be seen that the characteristic peak of TCH has decreased significantly, indicating that TCH in the reaction system has been degraded to other products. The degradation products mainly have characteristic peaks at 285, 343, 359, 400, 402, 416, and 431. It is speculated that there are two degradation pathways (Figure 10): First, TC loses the −CONH2 to from A (m/z 402), then A loses the −N(CH3)2 to form B (m/z 359), and C (m/z 343) was formed by losing −C=O of B. Finally, C loses −CH2CH(OH)CH3 to form D (m/z 285).87,88 Second, TC breaks the low-energy N–C bond as a result of attack by active substances, thus losing the N–CH3 and gaining intermediate E (m/z 431); then, E loses the −NH to form F (m/z 416); when F loses the C–OH, intermediate G (m/z 400) is gained.89

Figure 9.

Figure 9

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Mass spectra of tetracycline hydrochloride at (a) 0 and (b) 120 min.

Figure 10.

Figure 10

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Proposed photocatalytic degradation pathway of TCH.

These intermediates result in the production of a wide variety of small molecule organics of various structures through ring-opening reactions, central carbon cracking, or addition reactions. As the reaction continues, the intermediates will eventually be degraded into small molecules such as CO2,H2O and NH4+.

4. Conclusions

Three-dimensional flower-shaped Bi2WO6 and Ag2S–Bi2WO6 composites were prepared by a hydrothermal procedure and precipitation methods. According to the characterization and photocatalytic degradation experiments, the photocatalytic performance was demonstrated to be optimal when the weight ratios of the composites were 10%, and the degradation rate of TCH reached 95.51%, which was 27.35% higher than that for the pure Bi2WO6. The reason for this was that the dual semiconductor systems formed by Ag2S and Bi2WO6 reduce the photogenic electron–hole binding rate, thus producing a large number of highly oxidizing •OH and •O2– species. However, at neutral pH, the degradation efficiency was found to be the best, and the HA concentration correlated inversely with the degradation rate. Different inorganic anions were found to promote or inhibit the degradation efficiency of TCH, and the degradation rate was affected mainly by changing the content of main active substances. Because different factors will affect the degradation performance of the Ag2S–Bi2WO6 composite, it is suitable for the advanced treatment of industrial wastewater. According to mass spectrometry analysis, the degradation pathway of TCH proceeds via the open-loop decomposition of the benzene ring structure, which would eventually cause substrate degradation into small inorganic molecules such as CO2, H2O, and NH4+. It is hoped that this work can provide a benchmark for the design and preparation of a new dual semiconductor system photocatalyst to realize a more efficient, economical, and green application of photocatalysis in the field of water treatment.

Acknowledgments

The authors acknowledge the support of Xiaolaing Yang, Yukai Wang, and Fei Tang and their friends in the College of Civil Engineering, Guizhou University, Guiyang, China.

The authors declare no competing financial interest.

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