Design of BiOCl/WO 3 @Polyaniline Organic–Inorganic Nanocomposite Photocatalyst for the Efﬁcient Decontamination of 2-Chlorophenol from Wastewater

: Advanced photocatalysts that can utilize solar energy for water puriﬁcation applications are always needed. The present article reports a facile fabrication of tungsten oxide (WO 3 )/bismuth oxychloride (BiOCl) immobilized on polyaniline (PAn) (BiOCl/WO 3 @PAn) heterojunction nanocomposite photocatalyst. The designed nanocatalyst was tested for 2-chlorophenol (2-CP) decontamination from the aquatic system. Synthesized WO 3 , BiOCl, and BiOCl/WO 3 @PAn nanocomposites were distinguished via UV-DSR, photoluminescence, SEM, TEM, XRD, and XPS analysis. The combination of PAn with WO 3 and BiOCl showed a synergistic impact on the photocatalytic efﬁciency of the BiOCl/WO 3 @PAn nanocomposite. The synthesized BiOCl/WO 3 @PAn nanocomposite showed higher visible light absorption behavior and bandgap energy reduction than the WO 3 and BiOCl. The obtained data shows that 2-CP photocatalysis by the BiOCl/WO 3 @PAn is controlled by degradation time, pH, and pollutant amount in the solution. The highest photocatalytic degradation of 2-CP (99.7%) was recorded at pH 5 and 25 mg/L concentration within 240 min. The photocatalysis mechanism and active radical scavenging study discovered that • O 2 − and • OH, were responsible for the 2-CP mineralization onto the BiOCl/WO 3 @PAn nanocomposite. The BiOCl/WO 3 @PAn nanocomposite showed enhanced decontamination properties over pristine catalysts. The reusability of the synthesized BiOCl/WO 3 @PAn nanocomposite was evaluated. It found that the photocatalyst could be recycled for up to four cycles for 2-CP degradation without signiﬁcantly losing the photocatalytic properties. The fabricated BiOCl/WO 3 @PAn nanocomposite catalyst presented exceptional catalytic and recycling properties, indicating an effective method for scavenging hazardous organic contaminants under solar irradiation and green technology for wastewater puriﬁcation.


Introduction
Globally, natural water resources are facing contamination problems due to the mixing of unwanted substances [1,2].Urbanization, industrialization, and anthropogenic activities such as releasing solvents, drugs, radioactive materials, and industrial wastes are directly or indirectly responsible for increasing water pollutants [3,4].The wastewater from manufacturing, petroleum refineries, and textile industries is primarily accountable for hazardous organic pollutants, including dyes, phenol, and their derivatives [5][6][7].The 2-chlorophenol is generated from oil refinery industries, and it is hazardous from 1 mg/L, thus having harmful effects on the living organism in the aquatic environment [8].Therefore, reducing the concentration of 2-CP is needed to remove wastewater by applying appropriate methods.
Different treatment methods, including catalytic oxidation, adsorption, liquid-liquid extraction, thermal oxidation, distillation, membrane separation, photocatalysis, etc., have been used to scavenge 2-chlorophenol from wastewater [9][10][11][12].An appropriate treatment method selection depends on potential techniques' operating cost and removal efficiency.Photocatalytic oxidations have gained the great attention of scientists due to their removal efficiency of organic pollutants and the capacity of water, mineral ions, and carbon dioxide production as the product [13,14].Therefore, researchers are using this method for water treatment and hydrogen production.Among other processes, photocatalysis using semiconductor materials is considered an efficient and advanced photochemical oxidation method for scavenging organic pollutants due to chemical stability, low cost, and capacity for complete mineralization.[15][16][17].
Semiconductor photocatalysis is one of the advanced photooxidation processes in which hydroxyl radicals are produced without using chemical reagents [18].The hydroxyl radical with 2.8 V as a high oxidation potential can sharply trigger contaminates in wastewater for complete removal.In addition, semiconductors are promising photocatalysts because of their narrow bandgap energy (Ebg) among conduction and valence bands (CB and VB).To enhance the utilization capacity of visible light, the energy bandgap of potential catalysts and visible light should be within the range of 3.0 eV [19].Researchers are using numerous semiconductor photocatalysts, including titanium oxide (TiO 2 ), copper (II) oxide (CuO), bismuth oxychloride (BiOCl), tungsten oxide (WO 3 ), etc. [20][21][22].
Among other semiconductor photocatalysts, WO 3 has a narrow bandgap (Eb 1.5-2.8eV) and is a potential candidate for photocatalysis due to its exciting properties, including chemical, electrochemical, and optical features [23].Compared to the other catalysts, tungsten oxide showed excellent chemical stability in triggering solar irradiation, promising photocorrosion resistance, and absorbing a wide range of visible spectrums [24].On the other hand, a layered photocatalyst, bismuth oxychloride (BiOCl), has been explored as an eco-friendly candidate for environmental remediation because of its open crystal structure, nontoxicity, indirect-transition band, and excellent chemical stability and corrosion resistance [25].Some researchers reported that semiconductor photocatalysts had shown some disadvantages, including swift recombination of electron-hole pairs, thus losing their photocatalytic performance, even though these are considered superior photocatalysts for the degradation of organic pollutants [26].Therefore, to overcome such weaknesses of conventional semiconductor photocatalysts, scientists are trying to introduce novel composite photocatalysts using different catalysts, including polymer-like polyaniline (PAn).In polymeric semiconductors, the polyaniline showed excellent optoelectronic and photophysical properties, including stability in excited states, tunable bandgap, extended surface area, thermal stability, chemical inertness, and high absorption area, etc.The presence of σ and π bond electronic cloud system in PAn shows a lower bandgap energy of 1.5 to 2.8 eV, and under light irradiation, it can act as an effective photosensitizer [14,27].A literature review demonstrated that few articles had been published on synthesizing the binary composite of polyaniline/WO 3 and polyaniline/BiOCl in sensing, catalysis, and electrochromic applications [28,29].Based on previous studies, a ternary composite of WO 3 , BiOCl, and polyaniline could be an excellent semiconductor photocatalyst for decomposing toxic chemicals in wastewater under natural solar light.
This study aimed to prepare a bismuth oxychloride/tungsten oxide@polyaniline (BiOCl/WO 3 @PAn) nanocomposite for the degradation of 2-CP from wastewater under solar light irradiation.The synthesized photocatalysts WO 3 , BiOCl, and BiOCl/WO 3 @Pan nanocomposite were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence spectroscopy (PL).Different operational factors, including the effect of solution pH, initial concentration, and reaction time, were evaluated for 2-CP photocatalytic degradation.The novelty of the BiOCl/WO 3 @PAn nanocomposite is that integration of the semiconducting properties of the BiOCl, WO 3 , and polyaniline and reduction of bandgap energy to enhance the photocatalytic properties in solar light.

Characterization of Photocatalysts
The surface morphology of synthesized photocatalysts, WO 3 , BiOCl, and BiOCl/ WO 3 @PAn nanocomposite are depicted in Figure 1.The agglomerated irregular shape particle cluster of WO 3 can be seen in Figure 1a.Similar morphology of WO 3 is reported in earlier studies [30].The SEM image of the BiOCl (Figure 1b) demonstrates the sheet-like morphology with different shapes and sizes.The morphology of the BiOCl/WO 3 @PAn nanocomposite is depicted in Figure 1c, which shows the well-distributed BiOCl covered with WO 3 @Pan, indicating successful fabrication of BiOCl/WO 3 @PAn nanocomposite.The elemental fractions of fabricated photocatalysts are also shown in Figure 1d-f.Compositions of chemical elements in the WO 3 , BiOCl, and BiOCl/WO 3 @PAn nanocomposite were analyzed using energy-dispersive X-ray spectroscopy (EDX).The EDX analysis of WO 3 (Figure 2d) confirmed the existence of O and W with respective fractions of 77.94% and 22.06% (atomic %).The chemical elements in BiOCl are O (25.15%), Cl (22.35%), and Bi (52.50%) (Figure 2e).The elementals observed in BiOCl/WO 3 @PAn nanocomposite Figure 2f showed the existence of C, N, O, Cl, W and Bi with fractions of 43.9%, 1.8%, 38.2%, 3.61%, 8.85%, and 3.31%, respectively, which assured the successful fabrication of BiOCl/WO 3 @PAn nanocomposite.The interaction and interfaces between the BiOCl, WO 3 , and PAn in BiOCl/WO 3 @PAn nanocomposite were further observed using the TEM.The TEM images of the BiOCl/WO 3 @PAn nanocomposite are shown in Figure 2. The distribution of the BiOCl, WO 3 , and PAn in BiOCl/WO 3 @PAn nanocomposite can be seen in Figure 2a, showing some sheet-like structure surrounded by the WO 3 and PAn particles.Figure 2b shows the better morphology of the BiOCl/WO 3 @PAn nanocomposite, demonstrating the good interactions between large BiOCl nanosheets and elongated WO 3 particles and PAn particles well matching with the SEM results.The HR-TEM images in Figure 2c show the lattice fringes of (020) planes belonging to WO 3 surrounded by a noncrystalline PAn matrix.The SEAD pattern of the BiOCl/WO 3 @PAn nanocomposite shows the polycrystalline nature of the synthesized catalyst.
The phase structure of the fabricated photocatalysts WO 3 , BiOCl, and BiOCl/WO 3 @PAn nanocomposite were analyzed using X-ray powder diffraction (XRD).The obtained spectrum is illustrated in Figure 3    The XPS analysis of BiOCl/WO 3 @PAn nanocomposite, presented in Figure 4, exhibited the existence of C1s, O1s, W4f, N1s, Bi4f, Cl2p, etc., with the corresponding peaks and the percentage of chemical elements-carbon (49.7%), oxygen (32.3%), tungsten (7.8%), nitrogen (5.8%), bismuth (3.3%), and chlorine (1.1%)-as depicted in the wide survey scan in Figure 4a.The C1s spectra can be deconvoluted into 284.59,285.84, and 288.95 eV peaks, as illustrated in Figure 4b.The O1s spectra contain two corresponding peaks at 530.91 and 532.21 eV, as depicted in Figure 4c.On the other hand, two peaks at 34.05 and 36.14 eV were recorded for W4f, as presented in Figure 4d.In addition, the other two peaks were deconvoluted into 401.88 and 403.91 eV for N1s spectra, as illustrated in Figure 4e.The Bi 4f spectrum is exhibited in Figure 4f with corresponding four spectra at 158.90, 159.89, 164.22, and 165.09 eV [32].The Cl2p spectra were shown in Figure 4g of three peaks at 198.54, 200.01, and 201.61 eV.The chemical elements of C, O, N, W, Bi, and Cl, with their corresponding peaks and spectrum, confirm the successful fabrication of BiOCl/WO 3 @PAn nanocomposite [33].
36.14 eV were recorded for W4f, as presented in Figure 4d.In addition, the other two peaks were deconvoluted into 401.88 and 403.91 eV for N1s spectra, as illustrated in Figure 4e.The Bi 4f spectrum is exhibited in Figure 4f with corresponding four spectra at 158.90, 159.89, 164.22, and 165.09 eV [32].The Cl2p spectra were shown in Figure 4g of three peaks at 198.54, 200.01, and 201.61 eV.The chemical elements of C, O, N, W, Bi, and Cl, with their corresponding peaks and spectrum, confirm the successful fabrication of Bi-OCl/WO₃@PAn nanocomposite [33].The light absorption properties of the BiOCl, WO₃, and BiOCl/WO₃@PAn nanocomposite were observed using UV-visible absorbance and photoluminescence spectroscopy.The UV-visible absorption spectra of the BiOCl, WO₃, and BiOCl/WO₃@PAn nanocomposite are depicted in Figure 5a.The observed spectra reveal that BiOCl/WO₃@PAn nanocomposite showed the highest absorption of light in the visible region, while BiOCl and WO₃ showed absorption edges around 380 nm and 410 nm.The absorption peak edge for BiOCl/WO₃@PAn nanocomposite is around 580 nm, indicating that coupling of the BiOCl, WO₃, and PAn enhances the light absorption properties of the catalyst, which may favor the decomposition of the organic pollutants.A continuous increase in light absorption is mainly due to the polyaniline, which helps in the absorption of more photons from the solar spectrum, separates the produced electrons and holes, and generates more active radical species for the decomposition of the pollutant molecules [34].The reduction in the bandgap energy of the BiOCl/WO₃@PAn nanocomposite compared to BiOCl and WO₃ indicates that the nanocomposite could be a more effective photocatalyst (Figure 5b,c).To confirm the reduction in the charge recombination, PL analysis of the BiOCl, WO₃, and BiOCl/WO₃@PAn nanocomposite was performed, and the results are demonstrated in The light absorption properties of the BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite were observed using UV-visible absorbance and photoluminescence spectroscopy.The UV-visible absorption spectra of the BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite are depicted in Figure 5a.The observed spectra reveal that BiOCl/WO 3 @PAn nanocomposite showed the highest absorption of light in the visible region, while BiOCl and WO 3 showed absorption edges around 380 nm and 410 nm.The absorption peak edge for BiOCl/WO 3 @PAn nanocomposite is around 580 nm, indicating that coupling of the BiOCl, WO 3 , and PAn enhances the light absorption properties of the catalyst, which may favor the decomposition of the organic pollutants.A continuous increase in light absorption is mainly due to the polyaniline, which helps in the absorption of more photons from the solar spectrum, separates the produced electrons and holes, and generates more active radical species for the decomposition of the pollutant molecules [34].The reduction in the bandgap energy of the BiOCl/WO 3 @PAn nanocomposite compared to BiOCl and WO 3 indicates that the nanocomposite could be a more effective photocatalyst (Figure 5b,c).To confirm the reduction in the charge recombination, PL analysis of the BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite was performed, and the results are demonstrated in Figure 5d.The PL spectrum indicated the highest intensity for BiOCl and lowest intensity for BiOCl/WO 3 @PAn nanocomposite, suggesting a reduction in the recombination rate of the photogenerated species [35].

Photocatalytic Studies
Photocatalytic degradation of 2-CP was evaluated under sunlight illumination using 0.05 g of catalyst in 100 mL of 25 mg/L 2-CP concentration at pH-5 for 4 h reaction time.The adsorption was conducted for the initial 30 min to establish the equilibrium under the dark condition.Parallel photolysis of 2-CP (without catalysts) was also investigated under sunlight irradiation.The experimental results are displayed in Figure 6a, the 2-CP degradation using BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite was significantly higher than the photolysis.About 99.58% 2-CP removal efficiency was attained by fabricated BiOCl/WO 3 @PAn nanocomposite, which is much higher than the BiOCl, and WO 3 .The BiOCl/WO 3 @PAn photocatalyst shows high removal capacity due to enhanced visible light absorption properties and narrow bandgap energy than BiOCl, and WO 3 [33].The bandgap energy of the BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite were observed from plot 5b as 3.42 eV, 2.9 eV, and 2.33 eV.The lower bandgap energy of the BiOCl/WO 3 @PAn nanocomposite suppresses the recombination of the electron-hole pair and produces a large number of active radicals for the decomposition of the 2-CP molecules [36].The interfacial contact between BiOCl, WO 3 , and PAn considerably enhances the surface charge separation and plays a synergistic effect to enhance the photocatalytic property of the BiOCl/WO 3 @PAn nanocomposite.Under solar light irradiation, photogenerated electrons moved from the valance band (VB) to the conduction band (CB) of the semiconductor photocatalyst and moved quickly to the CB of BiOCl and WO 3 , thus successfully suppressing the recombination of the charged electrons and holes [33,36].

Photocatalytic Studies
Photocatalytic degradation of 2-CP was evaluated under sunlight illumination using 0.05 g of catalyst in 100 mL of 25 mg/L 2-CP concentration at pH-5 for 4 h reaction time.The adsorption was conducted for the initial 30 min to establish the equilibrium under the dark condition.Parallel photolysis of 2-CP (without catalysts) was also investigated under sunlight irradiation.The experimental results are displayed in Figure 6a, the 2-CP degradation using BiOCl, WO₃, and BiOCl/WO₃@PAn nanocomposite was significantly higher than the photolysis.About 99.58% 2-CP removal efficiency was attained by fabricated Bi-OCl/WO₃@PAn nanocomposite, which is much higher than the BiOCl, and WO₃.The Bi-OCl/WO₃@PAn photocatalyst shows high removal capacity due to enhanced visible light  The photocatalytic degradation kinetics of 2-CP onto BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite was investigated by fitting the kinetics data to the pseudo-first-order kinetic model: where C 0 and C are the 2-CP concentration (mg/L) at initial and after time t.k ap is the apparent rate constant.Figure 6b shows the kinetic plot of the 2-CP degradation.
The rate constant k ap values are 0.0061, 0.0076, and 0.021 min −1 for BiOCl, WO 3 , and BiOCl/WO 3 @PAn nanocomposite.The most effective rate constant k ap value was obtained for BiOCl/WO 3 @PAn nanocomposite, indicating that synthesized nanocomposite is the most suitable catalyst for the degradation of 2-CP.
The solution pH is one of the vital parameters of photocatalysis.The pH influences the degradation of targeted pollutants due to photocatalyst interaction and surface charges [36].The surface interactions between the BiOCl/WO 3 @PAn nanocomposite and 2-CP molecules affect the degradation process under solar light illumination.To evaluate the effect the solution pH on 2-CP degradation onto BiOCl/WO 3 @PAn nanocomposite, the photocatalytic activity was investigated at the pH value (3,5,7,9) at an initial 2-CP concentration of 25 mg/L and 0.05 g of photocatalyst for a 100 mL sample.The experimental results in Figure 5c showing the maximum 2-CP degradation were recorded at pH 3-7.Thereafter, the degradation decreases with increases of pH value up to 9. The mechanism behind the higher decomposition at acidic and neutral pH can be interpreted based on the pKa of 2-CP, which is ≈8.5.The 2-CP molecules exist as neutral species at the pH below pKa values and do not show any repulsion with BiOCl/WO 3 @PAn nanocomposite [37].With the rise in the solution pH above 8.5, a negative charge is generated on 2-CP due to deprotonation, which showed the electrostatic repulsion with the BiOCl/WO 3 @PAn nanocomposite [38].Therefore, less decomposition was recorded due to the lack of interaction between 2-CP and BiOCl/WO 3 @PAn nanocomposite.
The photocatalytic activity of BiOCl/WO 3 @PAn nanocomposite was examined at different concentrations of 2-CP (25 to 100 mg/L).The experiment was conducted at pH 5 with 0.05 g BiOCl/WO 3 @PAn mass in 100 mL of solution.The 2-CP degradation decreased with increases in concentration, as displayed in Figure 6d.The lower concentration (25 mg/L) of 2-CP was favorable for maximum degradation (99.7%), and degradation gradually decreased with increases in pollutant concentration.BiOCl/WO 3 @PAn nanocomposite activity declined as higher pollutant concentration increased the viscosity and decreased optical density, which reduced the penetration of the photons into the solution, subsequently decreasing the photoexcitation of electrons [39].
To evaluate the effect of active radical scavengers on 2-CP degradation with the BiOCl/WO 3 @PAn nanocomposite, an experiment was conducted in the presence of ethanol and potassium persulfate (K 2 S 2 O 8 ) at pH 5 and 25 mg/L of concentration and 0.05 g catalyst in a 100 mL sample [40].The results illustrated in Figure 6e indicated that the 2-CP degradation dramatically decreased in the presence of K 2 S 2 O 8 , as only 26% removal occurred while 99.7% degradation was attained without any scavengers.On the other hand, 90% of 2-CP degradation was recorded in the presence of ethanol, which was closer to the actual degradation of 2-CP using BiOCl/WO 3 @PAn nanocomposite.K 2 S 2 O 8 is an • O 2 − scavenger (superoxide radical), and ethanol is an • OH scavenger (hydroxyl radical).The results demonstrated that photocatalytically produced superoxide radicals absorbed by the K 2 S 2 O 8 resulted in a noticeable reduction in the degradation process, while the presence of ethanol slightly decreased the photocatalysis of 2-CP.These results suggested that • O 2 − radicals are the main active species involved in decomposition process.

Reusability of BiOCl/WO 3 @PAn Nanocomposite
The reusability of photocatalysts is one of the vital characteristics of commercial use.The reusability of BiOCl/WO 3 @PAn nanocomposite was evaluated for 2-CP degradation under optimum conditions.The used BiOCl/WO 3 @PAn nanocomposite was washed with deionized water and dried at 80 • C before reuse.Experimental results are shown in Figure 7, indicating that BiOCl/WO 3 @PAn nanocomposite is effective after fourfold reuse.The efficacy of the BiOCl/WO 3 @PAn nanocomposite in 2-CP degradation negligibly decreased with the number of cycles.These results suggest that BiOCl/WO 3 @PAn nanocomposite is stable and can be used several times.

Reusability of BiOCl/WO₃@PAn Nanocomposite
The reusability of photocatalysts is one of the vital characteristics of commercial use.The reusability of BiOCl/WO₃@PAn nanocomposite was evaluated for 2-CP degradation under optimum conditions.The used BiOCl/WO₃@PAn nanocomposite was washed with deionized water and dried at 80 °C before reuse.Experimental results are shown in Figure 7, indicating that BiOCl/WO₃@PAn nanocomposite is effective after fourfold reuse.The efficacy of the BiOCl/WO₃@PAn nanocomposite in 2-CP degradation negligibly decreased with the number of cycles.These results suggest that BiOCl/WO₃@PAn nanocomposite is stable and can be used several times.

Photocatalysis Mechanism
The photocatalytic decomposition mechanism of the 2-CP onto BiOCl/WO 3 @PAn nanocomposite is shown in Figure 8.The optical analysis results demonstrated that BiOCl/WO 3 @PAn nanocomposite has the lowest bandgap energy (2.33 eV) compared to BiOCl (3.42 eV) and WO 3 (2.9 eV).Under solar light illumination, the photogenerated electrons and holes move according to the scheme presented in Figure 8.The photogenerated electrons from HOMO of PAn migrated to its LUMO [41].These electrons further shifted to the conduction band of BiOCl.The electrons from CB of BiOCl transferred to the CB of WO 3 .At the same time, h + from VB of WO 3 went to VB of BiOCl and to HOMO of the PAn.The separation and transfer of the charge species are very fast and give the active radical species.The • O 2 − are produced by the interaction of excited e − with O 2 on BiOCl/WO 3 @PAn nanocomposite surface.Similarly, • OH radicals are produced by the h + after the reaction with H 2 O molecules [42,43].A detailed reaction mechanism for the active radical generation is shown in the following equations.

Comparison of photocatalytic properties
The comparison of the photocatalytic properties of various photocatalysts with the BiOCl/WO₃@PAn nanocomposite for 2-CP decomposition is summarized in Table 1.Photocatalysis is highly dependent on experimental conditions.Therefore, a comparison of the photocatalytic properties of various photocatalysts and experimental conditions is

Comparison of Photocatalytic Properties
The comparison of the photocatalytic properties of various photocatalysts with the BiOCl/WO 3 @PAn nanocomposite for 2-CP decomposition is summarized in Table 1.Photocatalysis is highly dependent on experimental conditions.Therefore, a comparison of the photocatalytic properties of various photocatalysts and experimental conditions is included in Table 1.The results demonstrated that BiOCl/WO 3 @PAn nanocomposite is highly efficient compared to previously reported photocatalysts.

Chemicals and Instrumentation
The polyaniline was prepared using the pure grade of aniline (Sigma-Aldrich Co., USA) and ammonium persulfate (NH 4 ) 2 S 2 O 8 (BHD Chemical, Poole, England).The other chemicals, such as sodium bismuthate (NaBiO 3 ) and sodium tungstate (Na 2 WO 4 •2H 2 O), were purchased as analytical grade (Sisco Research Laboratories Pvt. Ltd.India).The initial pH of 2-CP was adjusted by 1.0 M NaOH and/or HCl using a sensoin + PH3 m (Spain).Photocatalytic studies were performed under continuous stirring with a Scilogex LED magnetic digital stirrer under visible solar illumination.Surface morphology and texture of WO 3 , BiOCl, and BiOCl/WO 3 @PAn nanocomposite were characterized by scanning electron microscopy using JSM-7500 F, JEOL, Japan.The crystal structure of photocatalysts was analyzed by X-ray powder diffraction (XRD) using a Rigaku Ultima IV, Tokyo, Japan.The chemical characterization and elemental analysis of materials were recorded using energy-dispersive X-ray spectroscopy (EDX).Photoluminescence spectra (PLS) of WO 3 , BiOCl, and BiOCl/WO 3 @PAn nanocomposite were measured with an RF-5301PC Shimadzu, Kyoto, Japan, spectrofluorophotometer.

Synthesis of BiOCl/WO 3 @PAn Nanocomposite
The polyaniline was prepared by adding 1.1 mL pure aniline in 40 mL of HCl (0.25 M) in an ice bath.An equimolar of ammonium persulfate prepared in 0.25 M HCl was mixed dropwise under continuous stirring for four hours.After some time, a blue-green precipitate of polyaniline was formed.A solution of sodium tungstate (0.9 g) and sodium bismuthate (0.4 g) prepared in 20 mL of 0.25 M HCl in a separated beaker was subsequently mixed with polyaniline solution under stirring for 40 min.Afterward, the material was heated at 120 • C for 30 min.Finally, the resultant photocatalyst was washed several times with deionized water and acetone, dried at 80 • C, and stored for photocatalytic studies.The dried mass of the BiOCl/WO 3 @PAn nanocomposite was about 1.3 g, containing about 23.09% BiOCl, 34.61% WO 3 , and 42.30% PAn.

Photocatalytic Studies
Photodegradation studies were conducted with 0.05 g of photocatalysts in a 100 mL solution of 25 mg/L 2-CP concentration under natural sunlight illumination, continuous aeration, and shaking conditions.The dark adsorption experiments were also performed to find the equilibrium time by mixing 0.05 g of catalyst in 100 mL 2-CP solution of 25 mg/L concentration.The photolysis and photocatalysis of 2-CP degradation were investigated under continuous stirring and aeration conditions in solar light.The temperatures (31 ± 2 • C), humidity (42 ± 7%), and solar radiation intensity (822 × 10 2 ± 92 lux) were recorded during experiments.The consequences of solution pH on 2-CP photocatalytic degradation were evaluated in the pH range of 3-9 using 0.05 g catalyst in 100 mL of 2-CP solution (25 mg/L) under continuous aeration and shaking conditions for 240 min.The effect of contact times was considered to optimize the reaction time of photocatalytic degradation of 2-CP up to 240 min at pH 4.9 and 25 mg/L of 2-CP concentration.The effect of 2-CP concentration on its degradation onto BiOCl/WO 3 @PAn nanocomposite was tested by varying the concentration between 25 to 100 mg/L at pH 4.9 for 240 min of solar light irradiation time.The decomposition of 2-CP in the presence of active radical scavengers was conducted by mixing the 0.05 mmol of ethanol and K 2 S 2 O 8 while 2-CP concentration was 25 mg/L, pH 4.9 and irradiation time was 240 min.The experimental samples were collected periodically and filtered using a 0.22 µm PTFE syringe membrane to avoid the remaining catalysts.The analysis of 2-CP was performed on a UV-visible DR 6000 spectrophotometer.

Conclusions
Herein, a BiOCl/WO 3 @PAn nanocomposite photocatalyst was successfully fabricated.The synthesized photocatalyst was applied for degradation of 2-CP from wastewater under sunlight irradiation.The photocatalytic degradation of 2-CP onto BiOCl/WO 3 @PAn nanocomposite showed 99.7% at solution pH 5 and 25 mg/L concentration, which was significantly higher than the photolysis as well as pure WO 3 and BiOCl.Optical property analysis demonstrated incorporation of BiOCl and WO 3 with PAn enhanced the visible light absorption and suppressed the charged species' recombination rate.Active radical scavenging studies revealed that • O 2 − is the most active species in 2-CP decomposition.The composite photocatalyst was found to be a reusable catalyst for up to four successive regenerations for 2-CP photocatalysis under sunlight illumination.Therefore, BiOCl/WO 3 @PAn nanocomposite is considered a promising photocatalyst for degrading organic pollutants from wastewater.

Catalysts 2023, 13 , 175 7 of 16 Figure 5d .
Figure5d.The PL spectrum indicated the highest intensity for BiOCl and lowest intensity for BiOCl/WO₃@PAn nanocomposite, suggesting a reduction in the recombination rate of the photogenerated species[35].

Figure 6 .Figure 6 .
Figure 6.(a) Photocatalytic properties of BiOCl, WO₃ and BiOCl/WO₃@PAn for the decomposition of 2-CP under solar light irradiation.(b) Pseudo-first-order kinetic plot of 2-CP degradation.(c) Degradation of the 2-CP onto BiOCl/WO₃@PAn over a wide range of solution pH.(d) Effect of 2-CP Figure 6.(a) Photocatalytic properties of BiOCl, WO 3 and BiOCl/WO 3 @PAn for the decomposition of 2-CP under solar light irradiation.(b) Pseudo-first-order kinetic plot of 2-CP degradation.(c) Degradation of the 2-CP onto BiOCl/WO 3 @PAn over a wide range of solution pH.(d) Effect of 2-CP concentration on the BiOCl/WO 3 @PAn efficiency.(e) Photocatalytic degradation of 2-CP onto BiOCl/WO 3 @PAn in the presence of active radical scavengers.

Figure 8 .
Figure 8.A proposed mechanism for the charge separation and generation of the active radical species on the surface of BiOCl/WO₃@PAn nanocomposite for 2-CP degradation.

Figure 8 .
Figure 8.A proposed mechanism for the charge separation and generation of the active radical species on the surface of BiOCl/WO 3 @PAn nanocomposite for 2-CP degradation.

Table 1 .
Comparison of the various catalysts' photocatalytic properties for 2-CP decomposition.