Preparation of CdS–Ag2S nanocomposites by ultrasound-assisted UV photolysis treatment and its visible light photocatalysis activity

Chao Han; Chu Cheng; Fengling Liu; Xinli Li; Guangxin Wang; Jiwen Li

doi:10.1515/ntrev-2022-0503

Article Open Access

Preparation of CdS–Ag₂S nanocomposites by ultrasound-assisted UV photolysis treatment and its visible light photocatalysis activity

Chao Han , Chu Cheng , Fengling Liu , Xinli Li , Guangxin Wang and Jiwen Li

Published/Copyright: January 25, 2023

Published by

Become an author with De Gruyter Brill

Submit Manuscript Author Information

From the journal Nanotechnology Reviews Volume 12 Issue 1

Abstract

Thiosulfate is a green leaching agent used in the hydrometallurgical process because it is both environmentally benign and can form the required soluble ion complexes. In this article, a novel method for the synthesis of CdS–Ag₂S nanocomposites from a solution of relevant ion complexes via ultrasound-assisted ultraviolet (UV) photolysis was proposed. An analysis of the mechanism revealed that the complexes undergo a series of photochemical reactions. The CdS–Ag₂S nanocomposites were synthesized by photochemical co-precipitation under UV-C irradiation. The microstructure, chemical composition, optical and electrochemical properties of the prepared nanocomposites were analyzed to verify the synthesis and investigate the product. The photodegradation of methyl orange (MO) under a xenon lamp was performed to determine the photocatalytic activity. Under visible light irradiation, the CdS–Ag₂S nanocomposites undergo the electrons transition (from valence band to conduction band) to form photogenerated electron–hole pairs realizing the effective separation of carriers and finally promote the degradation of MO to water and carbon dioxide. The subsequent degradation efficiency of the CdS–Ag₂S nanocomposites was found to be 87% after 90 min, and it was larger than 78% for pure CdS prepared via UV photolysis, indicating that the as-developed novel method can effectively fabricate CdS–Ag₂S photocatalyst with superior performance.

Keywords: CdS–Ag2S nanocomposites; UV photolysis; photocatalytic activity

1 Introduction

Environmental pollution and depleting energy resources have emerged as widespread concerns because of rapid industrialization [1,2]. To effectively solve these key problems, researchers have proposed the use of new solar-driven photocatalytic materials. For example, Mukhopadhyay [3] successfully synthesized CaFe₂O₄ nanoparticles by a chemical precipitation technique and applied them in the degradation of brilliant green (BG) dye. Bose [4] fabricated the magnetic MgFe₂O₄ nanoparticles via a facile co-precipitation technique. Tripathy [5] used carbon-doped zinc oxide nanoparticles as a catalyst for the degradation of BG dye. Liexiao [6] adopted a one-step hydrothermal route to synthesize an interesting type of Bi₂O₂CO₃ hierarchical nanotubes. In particular, cadmium sulfide has been widely studied by scientists for this purpose owing to its low price, simple preparation method, and suitable band gap (2.4 eV) [7,8]. However, high photo-generated carrier recombination, poor conductivity, and significant photo-corrosion problems restrict its use in large-scale practical applications [9]. Well-known CdS-containing nanocomposites, such as CdS/MoS₂, CdS/Bi₄V₂O₁₁, CdS/Cu₂xSe, and CdS/Bi₄Ti₃O₁₂, have been constructed to address these issues [10,11,12,13]. Furthermore, silver compounds, such as AgPO₄, AgCl, AgBr, AgI, and AgVO₄, with very high photocatalytic activity have been used to create excellent photocatalytic systems utilizing these CdS nanocomposites [14,15]. Ag₂S, which possesses a bandgap range of 0.9–1.0 eV, is a semiconductor (n-type) with a distinctive structure and good physical properties. Additionally, owing to its excellent photoelectric properties, doping with Ag₂S is an effective strategy for enhancing the photocatalytic activity of CdS-supported catalysis because it lowers the photo-generated carrier recombination rate and reduces photo-corrosion. According to numerous reports, combining Ag₂S with CdS semiconductors can increase the overall photocatalytic activity. As a result, the synthesis of Ag₂S and CdS has recently received significant research attention [16,17,18,19].

The most widely used method for preparing a CdS–Ag₂S nanocomposite photocatalyst preparation is to load Ag₂S onto CdS carriers via deposition precipitation. However, during the preparation process, Ag₂S will self-nucleate, preventing close contact between Ag₂S and CdS, thereby hindering the transmission of photogenerated carriers to a certain extent. Several methods have been applied in Ag₂S and CdS preparation, such as ion implantation, thermal evaporation technique, and sol–gel methods [20,21]. Among them, the chemical co-precipitation method is an effective and time-efficient method to obtain Ag₂S and CdS nanoparticles. As a result, most researchers employ the chemical co-precipitation method with various chemical reagents and conditions to synthesize these nanoparticles. Based on previous studies, this study proposes a novel photochemical co-precipitation method to obtain these nanocomposites. In this proposed method, thiosulfate has been used as a green chemical reagent for the metallurgical leaching of cadmium and silver. The thiosulfate leaching solution containing cadmium and silver thiosulfate complexes can potentially be used as a source of cadmium and silver [22,23]. This thiosulfate complex solution exhibits intense absorption in the ultraviolet (UV)-C region (200–280 nm). The photolysis of the cadmium and silver thiosulfate complexes has been previously studied [24,25]. However, the ultrasound-assisted photolysis of the cadmium and silver thiosulfate complex and the photocatalytic activity of the resulting CdS–Ag₂S have not been thoroughly investigated.

In this study, a novel UV photolysis co-precipitation method was applied to fabricate a CdS–Ag₂S photocatalyst from cadmium and silver poly-metallic thiosulfate complex solutions. Benefitting from the ion photochemical properties, the poly-metallic thiosulfate complex solution was obtained, which was then subsequently used to generate the CdS–Ag₂S nanocomposites. In dyeing wastewater, there are three representative pollutants, such as azo dyes, triphenylmethane dyes, and anthraquinone dyes. Among them, azo dyes account for 70–80%. Methyl orange (MO) is a typical azo dye with toxicity, stable chemical properties, and difficult biodegradation. The performance of CdS–Ag₂S was evaluated using the typical MO dye as a model compound, and the activity of the nanocomposites was investigated through the visible photocatalytic degradation of MO.

2 Methods

2.1 Reagents

Sodium thiosulfate (Na₂S₂O₃), cadmium chloride (CdCl₂), and silver nitrate (AgNO₃) used in the preparation of the simulated leaching solution were purchased from Sinopharm Chemical Reagent Co., Ltd. All the chemicals were of reagent grade. De-ionized (RO or UP) water prepared using a water purification machine was used both as a washing agent and as a solvent.

2.2 Procedure

The solution of the simulated Cd–Ag thiosulfate complexes solution was obtained by stoichiometrically mixing cadmium chloride (CdCl₂), silver nitrate (AgNO₃), and sodium thiosulfate (Na₂S₂O₃) in a stoichiometric manner, as explained below. The four steps in the CdS–Ag₂S composite preparation and testing are elaborated as follows: In Step 1, the simulated Cd–Ag thiosulfate complex solution (250 mL, Cd: 100 mg/L, and Ag: 10 mg/L) was produced in an Erlenmeyer flask through complexation reactions between the Cd²⁺, Ag⁺, and S 2 O 3 2 − ions. In Step 2, the co-precipitation of CdS and Ag₂S was conducted using UV-C photolysis. Given a sufficient reaction time, cadmium and silver can co-precipitate completely in a 10:1 ratio. Thereafter, an ultrasound was used to enhance the dispersion of the suspension containing the CdS and Ag₂S precipitates. In Step 3, a centrifuge was used to separate the fabricated CdS–Ag₂S nanocomposites. In Step 4, the photocatalytic activity of the synthesized CdS–Ag₂S nanocomposites (25 mg) was examined via the degradation of MO (5 mg/L, 100 mL). Figure 1 shows a schematic diagram of the CdS–Ag₂S synthesis procedure.

Figure 1

Schematic diagram of the CdS–Ag₂S synthesis method.

2.3 Analytical methods

To further clarify the reaction mechanism, the UV decomposition rate of the cadmium/silver-thiosulfate complex was investigated in detail. Accordingly, the UV-induced photolysis rate constant of the Cd–Ag thiosulfate complex was estimated. A Bruker D8 X-ray diffraction (XRD) was used to confirm the phase composition of the precipitate. The Highscore software was used to analyze XRD data with a standard card. The surface morphology of the CdS–Ag₂S nanocomposites was characterized using a JSM-5610LV SEM system. A Fourier transform infrared (FTIR) spectrophotometer (Perkin Elmer Spectrum 65) was also used to analyze the prepared sample. An Escalab 250xi XPS system was applied to study the composition and valence state of the elements on the precipitate surface. The analysis was conducted without sputtering or charge neutralization using monochromatic Al Kα X-radiation at a take-off angle of 90°. The C 1s line at 284.6 eV was used to calibrate the binding energies. The XPS Peak software was used to fit the XPS data, and the NIST XPS database was used to cross-check component information. A UV-2550 UV-Vis spectrometer was applied to obtain the UV-Vis DRS of the samples. The electrochemical properties of the samples were characterized by an electrochemical workstation. In the transient photocurrent study, light and dark experiments were performed every 20 s.

3 Results and discussions

3.1 Investigation of the UV photolysis precipitation

The thiosulfate leaching solution contains cadmium/silver-thiosulfate complex ions ([CdAg₂(S₂O₃)_2n]^4(n–1)−, n = 1 or 2), which are sources of metal and sulfur. A previous study demonstrated the ability of metal-thiosulfate to absorb UV energy and then decompose into metal sulfide. In this work, the UV photolysis mechanism that results in the formation of the cadmium/silver-thiosulfate complex was studied. The step-by-step details of the reaction mechanism are as follows: after absorbing energy from the UV-C (200–280 nm) radiation, the cadmium/silver-thiosulfate complex ions activate and enter an unstable excited state. The primary reaction of the photochemical process is described in equation (1). Subsequently, as shown in equation (2), the water molecule in the solution coordinates this activated Cd–Ag thiosulfate complex into the activated Cd–Ag hydroxide complex and thiosulfate ion. Finally, the activated Cd–Ag thiosulfate complex ions react with the activated state Cd–Ag hydroxide complex in the activated state to dissociate the S–S bond in the latter, resulting in the oxidation product of sulfate ions ( S 2 O 3 2 − → SO 4 2 − ) and reduction product of sulfur ions ( S 2 O 3 2 − → S²⁻). A decrease in the solution pH was also observed owing to the formation of hydrogen ions – equations (2) and (3). Equations (2) and (3) represent the secondary reactions of the photochemical process, and equation (4) represents the overall reaction, which yields cadmium sulfide, silver sulfide, thiosulfate ions, sulfuric ions, and hydrogen ions.

(1) [CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − → h v {[CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − } ⁎ { n = 1 or 2},

(2) {[CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − } ⁎ + 2 n H 2 O → h v {[CdAg 2 (OH) 2 n ] 2( n − 2) − } ⁎ + 2 n S 2 O 3 2 − + 2 n H + { n = 1 or 2},

(3) [CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − + {[CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − } ⁎ + {[CdAg 2 (OH) 2 n ] 2( n − 2) − } ⁎ → hv 3CdS + 3 Ag 2 S + 6SO 4 2 − + (4 n − 6)S 2 O 3 2 − + (12 − 2 n )H + + (2 n − 6)H 2 O { n = 1 or 2},

(4) [CdAg 2 (S 2 O 3 ) 2 n ] 4( n − 1) − + 2 H 2 O → hv CdS + Ag 2 S + 2 SO 4 2 − + (2 n − 2)S 2 O 3 2 − + 4H + { n = 1 or 2} .

To clarify the UV reaction mechanism, the photolysis rate constant of the Cd–Ag thiosulfate complex was investigated in this reaction together with the UV decomposition rate of the silver cadmium thiosulfate complex. Figure 2 shows the rate constant of the UV-C photolysis of various metal thiosulfate complexes. The photolysis rate constant of a pure Cd–thiosulfate complex (Cd: 80 mg/L) and an Ag–thiosulfate complex (Ag: 80 mg/L) was calculated as 0.00124 and 0.00622 min⁻¹, respectively. Additionally, the ratio of Cd to Ag in the synthesized nanocomposites depends on the decomposition rate of cadmium and silver. Furthermore, in the case of the cadmium–silver thiosulfate complex, the concentration of silver affects the decomposition rate of cadmium. When the concentration of cadmium was fixed (Cd = 80 mg/L), the rate at which cadmium decomposed decreased as the silver concentration increased. The rate constant of Cd photolysis in the Cd–Ag thiosulfate complex (Cd: 80 mg/L, Ag: 25 mg/L) was 0.00936 min⁻¹. This phenomenon can be explained by apparent rate constant (k _obs) calculation, which has been studied in the kinetics of Ag-thiosulfate photolysis, and the silver ion concentration is inversely proportional to the k _obs. Similarly, when the concentration of cadmium is fixed in this work, the greater the concentration of silver ions, the greater the concentration of Cd–Ag thiosulfate complex ions generated, and the smaller the apparent rate constant.

Figure 2

Rate constant (k) of photolysis of different M-thiosulfate by UV-C (Cd–Ag thiosulfate; Ag–thiosulfate; Cd–thiosulfate).

3.2 Microstructure and chemical composition

To clearly illustrate the microstructure and chemical composition of CdS–Ag₂S nanocomposites, XRD, SEM, FT-IR, and XPS analyses were performed. XRD studies of pure CdS, pure Ag₂S, and photolyzed nanocomposites were conducted. The patterns obtained are shown in Figure 3. Three distinct broad peaks observed in the XRD pattern of the pure CdS (Figure 3b), at approximately 26.7°, 43.9°, and 51.8°, were also detected in the XRD pattern of the nanocomposites (Figure 3a), which are in accordance with the cadmium sulfide phase (PDF:00-002-0454). Similar to the XRD pattern of pure Ag₂S (Figure 3c), several peaks were observed in the nanocomposites (Figure 3a) spectrum at 20° and 80°, some of which are in accordance with peaks obtained from the Argentite phase (PDF:01-089-3840). The result demonstrates that cadmium and silver sulfides were predominantly precipitated via photolysis.

Figure 3

XRD patterns of different samples: (a) nanocomposites; (b) CdS; (c) Ag₂S.

The surface morphology of the CdS–Ag₂S nanocomposites was observed by SEM, and the results are displayed in Figure 4. The precipitates have different shapes, uneven sizes, and poor dispersion and agglomeration. Owing to the limitations of SEM imaging, it is difficult to determine the exact particle size. However, the Tyndall effect observed for the prepared CdS–Ag₂S photocatalyst demonstrated that the particles of the product are in the nanoscale range.

Figure 4

SEM images of the CdS–Ag₂S nanocomposite: (a) ×1,000; (b) ×5,000.

FTIR spectra were collected in the range of 500–4,000 cm⁻¹. The spectra of the CdS–Ag₂S nanocomposites before and after photocatalysis are shown in Figure 5.

Figure 5

FTIR spectra of CdS–Ag₂S nanocomposite: (a) before photocatalysis; (b) after photocatalysis.

The absorption bands observed in the FTIR spectra at 3435.76 and 3435.96 cm⁻¹ (Figure 5a and b) originate from the O–H group of the H₂O present on the surface of the nanocomposites. Figure 5(a) and (b) show absorption bands at 1002.63 and 1013.11 cm⁻¹ that are attributed to sulfate, and the absorption bands at 1631.36 and 1630.66 cm⁻¹ that are attributed to sulfoxide, indicating the presence of the S–O group [26]. Thus, the peaks at 666.01 cm⁻¹ and 618.18 cm⁻¹, which are in the range of 500–750 cm⁻¹, are thus attributed to Ag–S and Cd–S metal-sulfur bonds [17]. No discernible difference was observed in the infrared spectra of the photocatalyst before and after photocatalysis, indicating the stability of the photocatalyst.

The CdS–Ag₂S nanocomposites prepared by photolysis were further analyzed using XPS to determine the valence state of the elements. As shown in Figure 6(a), Cd, Ag, and S were detected in the XPS survey scan. Figure 6(b) shows the XPS profile of Cd 3d, in which two broad peaks are observed. The first peak (411.3 eV) corresponds to Cd 3d_3/2, and the second peak (405.0 eV) corresponds to Cd 3d_5/2 [27,28]. The peaks of Cd 3d peaks were present at the binding energies of 405.0 eV and 411.3 eV. It can be concluded that Cd appeared as cadmium sulfide in the photoproduct, which agrees with the XRD results. Figure 6(c) shows the XPS profile of Ag-3d, in which two peaks with broad features were identified. Based on the NIST XPS database, the first peak (373.9 eV) corresponds to Ag 3d_3/2, and the second peak (367.6 eV) corresponds to Ag 3d_5/2 [29]. Therefore, it was verified that Ag appeared as silver sulfide in the photoproduct, which again agrees with the XRD results. The deconvoluted XPS S-2p spectrum displayed in Figure 6(d) shows two peaks in the narrowed bound energy scope. These S 2p peaks occur as doublets, namely S 2p_3/2 and S 2p_1/2. Makhova et al. [30] and Guo et al. [31,32] reported that the S 2p energy level of CdS and Ag₂S is at 161.5 and 161.0 eV, respectively. Duret-Thual et al. [33] reported that the S 2p energy level of Na₂S₂O₃ is at 162.4 eV, and the S 2p energy level of Na₂SO₄ is at 169.2 eV. It has also been reported that the S 2p energy level of SO 4 2 − which comes from CdSO₄ or Ag₂SO₄ is at 168.0 eV. Therefore, according to the earlier analysis, the obtained nanocomposites primarily comprised cadmium sulfide and silver sulfide. These findings are supported by the XRD results displayed in Figure 3.

Figure 6

Deconvoluted XPS spectra for photoproduct: (a) survey spectrum; (b) Cd-3d spectrum; (c) Ag-3d spectrum; (d) S-2p spectrum.

3.3 Optical and electrochemical properties

To clearly illustrate the optical and electrochemical properties of the CdS–Ag₂S nanocomposites, the UV–Vis DRS, transient photocurrent, and electrochemical impedance spectroscopy (EIS) were conducted, respectively. The UV–Vis DRS and corresponding bandgap energies were applied to scrupulously investigate the optical properties of the CdS–Ag₂S, Ag₂S, and CdS nanocomposites.

The UV–Vis spectra of the photolysis products are shown in Figure 7(a), where excellent absorption is observed in the range 200–1200 nm. The bandgap energies were estimated using a plot of (αhv)² versus photo energy (hv). The intercept of the tangent to this plot provides a good approximation of the indirect bandgap energy. The apparent bandgap can be calculated using the Kubelka–Munk formula, as shown in equation (5).

(5) ( a h v ) 2 = A ( h v − E g ),

where α, h, v, A, and E _g represent the absorbance coefficient, Plank’s constant, incident photon frequency, absorbance, and apparent bandgap, respectively. Figure 7(b) shows that this curve forms the converted Kubelka–Munk formula curve. The intersection of the curve’s tangent and abscissa determines the apparent bandgap energy. Accordingly, the estimated bandgap energies for Ag₂S, CdS, and CdS–Ag₂S, are 0.99, 2.37, and 1.72 eV, respectively. The first two values are in accordance with the theoretical values of silver sulfide and cadmium sulfide. The design and development of CdS–Ag₂S is to reduce the bandgap and enhance visible light absorption by introducing silver components to adjust the position of valence band (VB) or conduction band (CB), and exhibits better photocatalytic activity.

Figure 7

(a) UV-Vis absorbance spectra of Ag₂S, CdS, and CdS–Ag₂S; (b) plots of (αhv)² versus energy (hv) of Ag₂S, CdS, and CdS–Ag₂S.

The transient photocurrent was measured using electrochemical workstations to monitor the migration of photogenerated carriers in the nanocomposites. Figure 8(a) displays the transient photocurrent spectra of the cadmium/silver sulfide prepared via ultrasound-assisted UV photolysis, and cadmium/silver sulfide and cadmium sulfide nanocomposites prepared via UV photolysis. The analysis showed that the current value was observed to increase every 20 s of irradiation time, but when blocked, it rapidly decreased in the subsequent 20 s interval. This indicates that the photogenerated charge carriers were transferred to the electrode, thereby generating a photocurrent. Compared with the CdS–Ag₂S nanocomposites prepared by UV photolysis, the I–t curves of cadmium/silver sulfide synthesized through ultrasound-assisted UV photolysis produced a higher current every 20 s. This demonstrates that the ultrasound treatment improves the dispersion and strengthens the photocatalytic activity. Compared with pure CdS nanocomposites synthesized via pure UV photolysis, the I–t curves of the previously mentioned cadmium/silver sulfide prepared via ultrasound-assisted UV photolysis generated approximately the same or a slightly lower current at every 20 s. This demonstrates that a higher photocurrent improves light absorption and electron extraction, which are in turn beneficial for charge separation [34]. The CdS–Ag₂S EIS Nyquist plots of CdS–Ag₂S are presented in Figure 8(b). The arc radius of CdS–Ag₂S with ultrasound-assisted UV photolysis (presented by the blue line) is smaller than that of CdS–Ag₂S without ultrasound (presented by the red line), indicating that the ultrasound can enhance the charge transfer resistance and the interfacial charge separation. However, the arc radius of CdS–Ag₂S (ultrasound-assisted UV photolysis) is bigger than that of pure CdS (UV-photolysis, black line), which is consistent with the I–t curves.

Figure 8

(a) Transient photocurrent (I–t curves); (b) electrochemical Impedance Spectroscopy (EIS) of different samples.

3.4 Visible light photocatalysis activity of CdS–Ag₂S nanocomposites

Microstructure, chemical composition, optical, and electrochemical properties of the CdS–Ag₂S nanocomposites were compared with the photocatalytic activity of CdS–Ag₂S nanocomposites and pure CdS which are prepared by ultrasound-assisted UV photolysis in the photodegradation of MO under visible light irradiation. The degree of degradation was measured by the characteristic absorption wavelength of 465 nm, and the C/C ₀ vs irradiation time is plotted in Figure 9. In the photocatalytic activity analysis, the adsorption (−60 to 0 min) and the C/C ₀ ratio remained constant, indicating that the MO can hardly adsorb on the surface of the CdS–Ag₂S nanocomposite. During photocatalysis (0 to 90 min), the C/C ₀ of the blank experiment remained constant, indicating that the MO solutions do not exhibit self-degradation. The C/C ₀ of CdS–Ag₂S nanocomposites decreased with time, but it increased under conditions of ultrasonication for 6 h, no ultrasonication, and ultrasonication for 2 h after 90 min. It possessed a photocatalytic efficiency of 87% after 90 min under the condition of ultrasonication for 2 h, which is higher than that of pure CdS with 78% at the same time. The rate constant of the CdS–Ag₂S nanocomposites under different conditions, namely ultrasonication for 6 h, no ultrasonication, and ultrasonication for 2 h, was calculated to be 0.01159, 0.01769, and 0.02148 min⁻¹, respectively. The sample ultrasonicated for 2 h with UV photolysis exhibits a fine degradation rate because the ultrasound can contribute to the dispersion of the system and facilitate the formation of nanocomposites. However, a longer ultrasonic treatment time may damage the structure, causing a decrease in the reaction rate. To objectively evaluate the photocatalytic effect of the nanocomposites prepared by this method, and the capabilities of different components were examined. The results show that the catalytic effect of Ag₂S is very poor, and the rate constant of the pure Ag₂S nanocomposites with UV photolysis was 0.00177 min⁻¹. The rate constant of the pure CdS nanocomposites with UV photolysis was 0.01711 min⁻¹. The rate constant of the synthesized CdS–Ag₂S nanocomposites with UV photolysis was increased to 0.02148 min⁻¹ with the formation of the CdS–Ag₂S nanocomposites, indicating that the ultrasound-assisted UV photolysis method can produce nanocomposites with better properties.

Figure 9

Time-course variation of C/C ₀ toward MO: (a) C/C ₀ vs time; (b) ln(C ₀/C) vs time.

The photocatalytic mechanism of the degradation of MO by CdS–Ag₂S nanocomposites is shown in Figure 10. Under visible light irradiation, CdS undergoes electron band-to-band transition, and electrons (e⁻) transition from valence band (VB) to conduction band (CB), forming photogenerated electron–hole pairs (e⁻/h⁺). Photogenerated electron–hole pairs (e⁻/h⁺) have strong oxidation and reduction properties. The electrons (e⁻) on the conduction band (CB) reduce oxygen to superoxide anion (^• O 2 − ), and the holes (h⁺) on the valence band (VB) oxidize water (H₂O) to hydroxyl radical (^∙OH), generating active oxidizing substances. However, there are defects on the surface of CdS, resulting in the recombination of photogenerated carriers. The CdS–Ag₂S nanocomposite is adopted. The edge potentials of the valence band (VB) and conduction band (CB) of Ag₂S are higher than those of CdS. The electrons (e⁻) on the conduction band (CB) of Ag₂S are transferred to the conduction band (CB) of CdS, and the holes (h⁺) on the valence band (VB) of CdS are transferred to the valence band (VB) of Ag₂S, thus realizing the effective separation of carriers, promoting the degradation of MO to water and carbon dioxide, and improving the photocatalytic activity [35,36].

Figure 10

Degradation mechanism of MO by CdS–Ag₂S nanocomposites under visible light irradiation.

4 Conclusions

In this study, a novel method for synthesizing CdS–Ag₂S nanocomposites from complex solutions is presented. The photochemical co-precipitation of the Cd–Ag thiosulfate complex (Cd: 100 mg/L; Ag: 10 mg/L) produced the CdS–Ag₂S nanocomposites. The XRD and XPS results confirmed that the nanocomposites are chemically composed of CdS and Ag₂S. Based on the Tyndall effect, the size of the CdS–Ag₂S particles is considered to be in the nanoscale. The DRS result indicated that the bandgap energy of CdS–Ag₂S is 1.72 eV. Investigations into the visible-light photocatalytic activity of the CdS–Ag₂S nanocomposites using the I–t curves demonstrated that they can produce a photocurrent under the conditions of stimulated solar irradiation. Investigations into the photocatalytic degradation of MO using the as-synthesized samples revealed that the CdS–Ag₂S nanocomposite possessed a photocatalytic efficiency of 87% after 90 min. According to the kinetic study, which showed that the first-order equation can fit the data, the use of the proposed ultrasound-assisted UV photolysis method can yield nanocomposites with good photocatalytic performance, and the rate constant for the CdS–Ag₂S nanocomposites obtained using this method is 0.02148 min⁻¹.

Funding information: This project was supported by the National Natural Science Foundation of China (Grant No. 52104349), and China Postdoctoral Science Foundation (Grant No. 2021M690915). This project was also funded by The Key Technologies R&D Program of Henan Province (Grant No. 222102320435), and The Key Scientific Research Project of Colleges and Universities in Henan Province (Grant No. 21A450001).
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Conflict of interest: The authors state no conflict of interest.

References

[1] Huang J, Luo Y, Weng M, Yu J, Sun L, Zeng H, et al. Advances and applications of phase change materials (PCMs) and PCMs-based technologies. ES Mater Manuf. 2021;13:23–39.10.30919/esmm5f458Search in Google Scholar

[2] Kadam AN, Salunkhe TT, Kim H, Lee SW. Biogenic synthesis of mesoporous N–S–C tri-doped TiO2 photocatalyst via ultrasonic-assisted derivatization of biotemplate from expired egg white protein. Appl Surf Sci. 2020;518:146194.10.1016/j.apsusc.2020.146194Search in Google Scholar

[3] Mukhopadhyay A, Tripathy BK, Debnath A, Kumar M. Enhanced persulfate activated sono-catalytic degradation of brilliant green dye by magnetic CaFe2O4 nanoparticles: Degradation pathway study, assessment of bio-toxicity and cost analysis. Surf Interfaces. 2021;26:101412.10.1016/j.surfin.2021.101412Search in Google Scholar

[4] Bose S, Tripathy BK, Debnath A, Kumar M. Boosted sono-oxidative catalytic degradation of Brilliant green dye by magnetic MgFe2O4 catalyst: Degradation mechanism, assessment of bio-toxicity and cost analysis. Ultrason Sonochem. 2021;75:105592.10.1016/j.ultsonch.2021.105592Search in Google Scholar PubMed PubMed Central

[5] Tripathy BK, Kumar S, Kumar M, Debnath A. Microwave induced catalytic treatment of brilliant green dye with carbon doped zinc oxide nanoparticles: Central composite design, toxicity assessment and cost analysis. Environ Nanotechnol Monit Manag. 2020;14:100361.10.1016/j.enmm.2020.100361Search in Google Scholar

[6] Liexiao L, Xiaofeng S, Tao X, Huajing G, Shifa W, Zao Y, et al. Template-free synthesis of Bi2O2CO3 hierarchical nanotubes self-assembled from ordered nanoplates for promising photocatalytic applications. Phys Chem Chem Phys. 2022;24:8279–95.10.1039/D1CP05952ASearch in Google Scholar

[7] Supekar A, Kapadnis R, Bansode S, Bhujbal P, Kale S, Jadkar S, et al. Cadmium telluride/cadmium sulfide thin films solar cells:a review. ES Energy Environ. 2020;10:3–12.10.30919/esee8c706Search in Google Scholar

[8] Rahane GK, Jathar SB, Rondiya SR, Jadhav YA, Barma SV, Rokade A, et al. Photoelectrochemical investigation on the cadmium sulfide (CdS) thin films prepared using spin coating technique. ES Mater Manuf. 2020;11:57–64.10.30919/esmm5f1041Search in Google Scholar

[9] Zhao Y, Li L, Zuo Y, He G, Chen Q, Meng Q, et al. Reduced graphene oxide supported ZnO/CdS heterojunction enhances photocatalytic removal efficiency of hexavalent chromium from aqueous solution. Chemosphere. 2022;286:131738.10.1016/j.chemosphere.2021.131738Search in Google Scholar PubMed

[10] Li LL, Yin XL, Sun YQ. Facile synthesized low-cost MoS2/CdS nanodots-on nanorods heterostructures for highly efficient pollution degradation under visible light irradiation. Sep Purif Technol. 2019;212:135–41.10.1016/j.seppur.2018.11.032Search in Google Scholar

[11] Lv T, Li D, Hong Y, Luo B, Xu D, Chen M, et al. Facile synthesis of CdS/Bi4V2O11 photocatalysts with enhanced visible-light photocatalytic activity for degradation of organic pollutants in water. Dalton Trans. 2017;46:12675–82.10.1039/C7DT02151HSearch in Google Scholar PubMed

[12] Liu YP, Shen SJ, Zhang JT, Zhong WW, Huang XH. Cu2xSe/CdS composite photocatalyst with enhanced visible light photocatalysis activity. Appl Surf Sci. 2019;478:762–9.10.1016/j.apsusc.2019.02.010Search in Google Scholar

[13] Tingting C, Huajing G, Guorong L, Zhongsheng P, Shifa W, Zao Y, et al. Preparation of core-shell heterojunction photocatalysts by coating CdS nanoparticles onto Bi4Ti3O12 hierarchical microspheres and their photocatalytic removal of organic pollutants and Cr(VI) ions. Colloids Surf A: Physicochem Eng Aspects. 2022;633:127918.10.1016/j.colsurfa.2021.127918Search in Google Scholar

[14] Yi Z, Ye J, Kikugawa N, Kako T, Ouyang S, Stuart-Williams H, et al. An orthophosphate semiconductor with photooxidation properties under visible-light irradiation. Nat Mater. 2010;9(7):559–64.10.1038/nmat2780Search in Google Scholar PubMed

[15] Lu HD, Wang JX, Du ZY, Liu YP, Li M, Chen P, et al. In-situ anionexchange synthesis AgCl/AgVO3 hybrid nanoribbons with highly photocatalytic activity. Mater Lett. 2015;157:231–4.10.1016/j.matlet.2015.05.135Search in Google Scholar

[16] Wang C, Zhai J, Jiang H, Liu D, Zhang L. CdS/Ag2S nanocomposites photocatalyst with enhanced visible light photocatalysis activity. Solid State Sci. 2019;98:106020.10.1016/j.solidstatesciences.2019.106020Search in Google Scholar

[17] Iqbal T, Ali F, Khalid NR, Bilal Tahir M, IIjaz M. Facile synthesis and antimicrobial activity of CdS-Ag2S nanocomposites. Bioorganic Chem. 2019;90:103064.10.1016/j.bioorg.2019.103064Search in Google Scholar PubMed

[18] Han G, Jin YH, Burgess RA, Dickenson NE, Cao XM, Sun Y. Visible-lightdriven valorization of biomass intermediates integrated with H2 production catalyzed by ultrathin Ni/CdS nanosheets. J Am Chem Soc. 2017;139:15584–7.10.1021/jacs.7b08657Search in Google Scholar PubMed

[19] Di T, Cheng B, Ho W, Yu J, Hua T. Hierarchically CdS-Ag2S nanocomposites for efficient photocatalytic H2 production. Appl Surf Sci. 2019;470:196–204.10.1016/j.apsusc.2018.11.010Search in Google Scholar

[20] El-Nahass MM, Farag AA, Ibrahim EM, Abd-El-Rahman S. Structural, optical and electrical properties of thermally evaporated Ag2S thin films. Vacuum. 2004;72(4):453–60.10.1016/j.vacuum.2003.10.005Search in Google Scholar

[21] Abd-Elkader OH, Shaltout AA. Characterization and antibacterial capabilities of nanocrystalline CdS thin films prepared by chemical bath deposition. Mater Sci Semicond Process. 2015;35:132–8.10.1016/j.mssp.2015.03.003Search in Google Scholar

[22] Sebastián G, Karla G, Ernestode LT, Alicia G. Precious metals recovery from waste printed circuit boards using thiosulfate leaching and ion exchange resin. Hydrometallurgy. 2019;186:1–11.10.1016/j.hydromet.2019.03.004Search in Google Scholar

[23] Wang P, Cheng H, Ding J, Ma J, Jiang J, Huang Z, et al. Cadmium removal with thiosulfate/permanganate (TS/Mn(VII)) system: MnO2 adsorption and/or CdS formation. Chem Eng J. 2020;380:122585.10.1016/j.cej.2019.122585Search in Google Scholar

[24] Egorov NB, Eremin LP, Larionov AM, Usov VF, Tsepenko EA, D’yachenko AS. Products of photolysis of cadmium thiosulfate aqueous solutions. High Energy Chem. 2008;42:119–22.10.1134/S0018143908020100Search in Google Scholar

[25] Han C, Wang G, Cheng C, Shi C, Yang Y, Zou M. A kinetic and mechanism study of silver-thiosulfate complex photolysis by UV-C irradiation. Hydrometallurgy. 2020;191:105212.10.1016/j.hydromet.2019.105212Search in Google Scholar

[26] Zamiri R, Abbastabar Ahangar H, Zakaria A, Zamiri G, Shabani M, Singh B, Ferreira JM. The structural and optical constants of Ag2S semiconductor nanostructure in the Far-Infrared. Chem Cent J. 2015;9(1):28.10.1186/s13065-015-0099-ySearch in Google Scholar PubMed PubMed Central

[27] Di T, Zhu B, Zhang J, Cheng B, Yu J. Enhanced photocatalytic H2 production on CdS nanorod using cobalt-phosphate as oxidation cocatalyst. Appl Surf Sci. 2016;389:775–82.10.1016/j.apsusc.2016.08.002Search in Google Scholar

[28] Yu W, Zhang S, Chen J, Xia P, Richter MH, Chen L, et al. Biomimetic Z-scheme photocatalyst with a tandem solid-state electron flflow catalyzing H2 evolution. J Mater Chem A. 2018;6:15668–74.10.1039/C8TA02922ASearch in Google Scholar

[29] An C, Wang J, Jiang W, Zhang M, Ming X, Wang S, et al. Strongly visiblelight responsive plasmonic shaped AgX: Ag (X = Cl, Br) nanoparticles for reduction of CO2 to methanol. Nanoscale. 2012;4:5646–50.10.1039/c2nr31213aSearch in Google Scholar PubMed

[30] Makhova L, Mikhlin Y, Romanchenko A. A combined XPS, XANES and STM/STS study of gold and silver deposition on metal sulphides. Nucl Instrum Methods Phys Res Sect A: Accel Spectrometers Detect Assoc Equip. 2007;575:75–7.10.1016/j.nima.2007.01.029Search in Google Scholar

[31] Guo J, Liang Y, Liu L, Hu J, Wang H, An W, et al. Core-shell structure of sulphur vacancies-CdS@CuS: Enhanced photocatalytic hydrogen generation activity based on photoinduced interfacial charge transfer. J Colloid Interf Sci. 2021;600:138–49.10.1016/j.jcis.2021.05.013Search in Google Scholar PubMed

[32] Zhang X, Li N, Wu J, Zheng Y, Tao X. Defect-rich O-incorporated 1TMoS2 nanosheets for remarkably enhanced visible-light photocatalytic H2 evolution over CdS: The impact of enriched defects. Appl Catal B. 2018;229:227–36.10.1016/j.apcatb.2018.02.025Search in Google Scholar

[33] Duret-Thual C, Costa D, Yang WP, Marcus P. The role of thiosulfates in the pitting corrosion of Fe-17Cr alloys in neutral chloride solution: Electrochemical and XPS study. Corros Sci. 1997;39(5):913–33.10.1016/S0010-938X(97)81158-4Search in Google Scholar

[34] Yu J, Jin J, Cheng B, Jaroniec M. A noble metal-free reduced graphene oxide–CdS nanorod composite for the enhanced visible-light photocatalytic reduction of CO2 to solar fuel. J Mater Chem A. 2014;2:3407–16.10.1039/c3ta14493cSearch in Google Scholar

[35] Lee J, Lee Y, Bathula C, Kadam AN, Lee SW. A zero-dimensional/two-dimensional Ag-Ag2S-CdS plasmonic nanohybrid for rapid photodegradation of organic pollutant by solar light. Chemosphere. 2022;296:133973.10.1016/j.chemosphere.2022.133973Search in Google Scholar PubMed

[36] Okla M, Janani B, AL-ghamdi AA, Abdel-Maksoud MA, AbdElgawad H, Das A, et al. Facile construction of 3D CdS-Ag2S nanospheres: A combined study of visible light responsive phtotocatalysis, antibacterial and anti-biofilm activity. Colloids Surf A: Physicochem Eng Aspects. 2022;632:127729.10.1016/j.colsurfa.2021.127729Search in Google Scholar

Received: 2022-08-15

Revised: 2022-09-19

Accepted: 2023-01-02

Published Online: 2023-01-25

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/ntrev-2022-0503

Keywords for this article

CdS–Ag2S nanocomposites; UV photolysis; photocatalytic activity

Creative Commons

BY 4.0

Preparation of CdS–Ag2S nanocomposites by ultrasound-assisted UV photolysis treatment and its visible light photocatalysis activity

Article

Abstract

1 Introduction

2 Methods

2.1 Reagents

2.2 Procedure

2.3 Analytical methods

3 Results and discussions

3.1 Investigation of the UV photolysis precipitation

3.2 Microstructure and chemical composition

3.3 Optical and electrochemical properties

3.4 Visible light photocatalysis activity of CdS–Ag2S nanocomposites

4 Conclusions

References

Articles in the same Issue

Articles in the same Issue

Articles in the same Issue

Preparation of CdS–Ag₂S nanocomposites by ultrasound-assisted UV photolysis treatment and its visible light photocatalysis activity

3.4 Visible light photocatalysis activity of CdS–Ag₂S nanocomposites