1 Introduction

In recent few years, the contaminated water due to the dyes, pesticides and other contaminants drugs has gained significant attention owing to their carcinogenic effects on human beings and the environment. Several emerging countries rely heavily on their textile industry for economic growth. Predominantly, the raw materials needed for this sector includes synthetic dyes. There are approximately 10,000 distinct synthetic dyes and more than 700,000 tons of these dyes are produced annually out of which up to 200,000 tons of synthetic dyes are released into the environment without any treatment. The pollution created by the industrial and commercial sectors is rising. Organic dyes are hazardous and non-biodegradable, causing contamination in the textile, cosmetic, and food sectors [1, 2]. The World Bank estimates that the dyeing and finishing of textiles produces between 17 and 20 percent of the industrial wastewater. Therefore, for the sustainability of the environment, treatment of dye polluted water has become a necessity. For this purpose, several conventional and non-conventional methods have been utilized such as nano-filtration, adsorption, coagulation, ozonolysis and photocatalysis. Among these techniques, photocatalysis is used widely due to its efficiency.

The manufacture of highly ordered semiconductor photocatalyst designs has stimulated a lot of attention due to their constant growth with specific shape and accessible usage for energy and sustainability concerns [3]. Degradation rate is an effective parameter for measurement of degradation of organic contaminants from waste water. Since the last several decades, a multitude of active semiconductor photocatalysts such as metal oxide, sulfide, oxynitrides, and graphite carbon nitride have indeed been tried to introduce and used for the organic pollutants are removed in aquatic environments [4,5,6,7]. Generally, most of the metal oxides have band gap in UV region which restricts the utilization of solar spectrum as only 5% of solar light consists of UV wavelength. Tunning the band gap from UV to visible region by doping, co-doping or nano-composites to produce a visible light driven efficient photocatalyst is the main goal of scientists and researchers. It seems essential to push significantly with catalytic materials (in visible region) in order to figure out significant energy concerns [8, 9].

Tungsten oxide (WO3) is a reputable and crucial semiconductor catalyst among all other materials such as ZnO, TiO2, MoS2 etc. due to its highly responsive nature under UV–Visible irradiance, mechanical characteristics, and excellent photostability [10, 11]. Tungsten oxide is utilized in photocatalytic and polarizing filters devices, as well as electrodes. Tungsten oxide photocatalytic performance is still limited due to fast recombination rate of charge carriers and inability of O2 to effectively grab these electrons to produce superoxide radicals which are crucial for the degradation reaction [12]. The location of band gap is reformed by researchers for tungsten oxide through adding low band gap semiconductors to the catalyst to minimize the charge recombination and boosting the photocatalytic activity [13]. The maximum absorbance spectrum is prolonged and charge recombination rate is decreased because of the disparity in conduction and valence band energies between the two semiconductors [14]. Furthermore, it increases the yield of photogenerated electrons located in the conduction band, which aids in photocatalytic degradation. There is very little literature on CuS-WO3 for the degradations of organic contaminants therefore, it is interesting to investigate the photocatalytic performance of said material. Due to its strong optical, electrical, and availability qualities, CuS is utilized to make a nano-composite with WO3.

CuS is an ideal material for renewable power absorption due to its low absorbance in the visible range and strong reflection in the near infrared range [15]. Although, WO3 has a band gap in the range of visible light but its high charge recombination rate makes it a poor photocatalyst for the commercial scale usage. Addition of CuS may vary the band gap of material and provide trapping energy level to reduce the recombination rate which could play a positive role in the degradation of rhodamine B (RhB) dye from wastewater.

In this research work, a facile and efficient hydrothermal approach has been used to synthesize pure CuS and WO3 nanoparticles. Moreover, CuS-WO3 nanocomposites were synthesized for 10%, 12% and 14% CuS concentration. Variation in structural, optical and morphological characteristics were studied by XRD, SEM, EDX, UV, PL etc. Photocatalytic degradation of rhodamine B (RhB) dye was examined in the presence of synthesized nanocomposite. Effect of pH was also investigated on the degradation of RhB dye using the best photocatalyst among all the synthesized sample. Total organic carbon analysis has provided valuable information about the complete mineralization percentage of the dye. To check the photostability of the synthesized nanocomposites, the degradation of RhB dye for 6 cycles has been carried out. RF module of COMSOL Multiphysics 5.3 has been used to mimic a 2D model of the experimental procedure and the effect of concentration of CuS in WO3 on the absorption of visible to near infrared light has been examined over time to estimate the photocatalytic performance of the nanocomposites.

2 Materials and Methods

Copper sulphate pentahydrate (CuSO4.5H2O) sodium thiosulfate 200 mL deionized water, 50 mL isopropanol, CTAB (C19H42BrN) cetrimonium bromide Sodium tungstate dihydrate (Na2WO4⋅2H2O), sodium chloride (NaCl), sulfuric acid (H2SO4), hydrochloric acid (HCL), ethanol, and deionized After processing, all reagents were utilized.

2.1 Synthesis of Photocatalyst CuS, WO3 and Composite

To synthesize copper sulfide, mix 2 g sodium thiosulfate in 100 mL distilled water and agitate for 20 min to create a moisturizer mixture that contains thiosulfate ions (S2O32−), which act as an oxidizing agent. While stirring, 2 g copper sulphate was given to the produced serum, resulting to cupric ions (Cu2+) in the mixture, acted as an oxidant that initiated an oxidation process in the compounds. When copper sulphate was exposed to sodium thiosulfate serum, it became colorless and eventually black. To lower the surface tension of the components, 0.05 g of Cetrimonium bromide was included in the mixture as an agitator. The hydrothermal method has been utilized to create CuS, which entailed putting a solution inside an autoclave at 150 °C Celsius for 6 h. After that, the sample was allowed to recede to ambient temperature. After synthesis let it dry in an 80 °C Muffled oven. Figure 1a depicts the manufacture of pure dried black copper sulfide [16].

Fig. 1
figure 1

a CuS preparation with active Na2S2O3 and copper sulphate. b Preparation of WO3 by sodium chloride and Sodium tungstate di-hydrate reaction. c Preparation of WO3 composite with CuS by Sodium tungstate di-hydrate and NaCl

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Na2WO4⋅2H2O 0.01 mol and 0.06 mol pure sodium chloride were diffused in 30 ml of distilled water in a clean beaker shown in the Fig. 1b. The reaction was taken place using autoclave for 12 h at 180 °C. the reaction mixture is allowed to cool getting yellow precipitates. Pure precipitates are obtained by multiple washing with cold deionized water, ethanol and let it dry in an oven at 120 °C. The weight percentages of CuS added WO3 were calculated: 10, 12 and 14%. Solutions of Tungstic acid (0.008 mol), CTAB (0.002 mol) in water were set into an autoclave machine and the process followed is shown in Fig. 1c. [17].

2.2 Characterization of Photocatalysts

The required samples estimated for the enhancement of photocatalytic properties after they have been synthesized. The structural parameters were determined by the “Bruker D8 X-ray Diffraction technique with Cu-k x-ray source = (1.541874)” range of 20–80 degrees. The morphological analysis of samples has been done with “TESCAN MAIA3 Field emission Scanning Electron Microscopy.” Photoluminescence behavior was observed with photoluminescence (FP-8200 Spectrofluorometer JASCO) giving emission spectra between 420 and 550 nm. At last, the photocatalytic activity was addressed using ‘V-730 Ultraviolet–Visible Spectroscopy’ [18].

3 Results and Discussion

3.1 Morphology and Elemental Analysis

The morphological characteristics and shape of the photocatalysts have been characterized by elemental analysis and SEM data as shown in Fig. 2a & b. In present study, classified flower-shaped CuS and WO3 photocatalysts nanorods are more conductive to photoelectron hole pair expansion and separation. Thus, synthetic flowers such as CuS and WO3 nanorods are considered as optimistic probes for photocatalytic activity. Sharp edges for WO3 nano-rods are observed with 10% concertation of CuS and overall, its morphology is needlelike. Petals of CuS is specific for pronounce and efficient growth of WO3 nanostructures. Geometrical morphology is determined by 14% and it was noticed that the synthesized Nano probes are having sharp edges. The tiny nanoflowers with nano-petals increase the area of absorbance meant for RhB mortification which suggests that 14% CuS sample has an immense surface morphology, supplementary reactive sites and increased photocatalytic behavior [19]. Energy dispersive Xray spectroscopy (EDAX) of 10 and 14% CuS:WO3 nanocomposites in Fig. 2(b) verified the occurrence of peaks corresponding to W, Cu, S and O atoms. The weight and molarity percentage of each species is mentioned in the inset of EDX graphs in Fig. 2b.

Fig. 2
figure 2

a SEM images of pure WO3, flower like CuS and their nanocomposites. b EDX analysis of 10% and 14% WO3 Composites with CuS along with molar and weight percentage

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3.2 X-Ray diffraction (XRD)

XRD helped measuring the phase, dimensions, and morphology of WO3 composite with CuS representatives as shown in Fig. 3. XRD Micrograph manifest that pure WO3 subdue plans (020), (200), (120), (112), (020) (202) (222) (400) and (420.0) with corresponding angles, 25.3°, 25.9°, 28.8°, 33.2°, 36.2°, 37.2°, 45.1°, 42.9° and 57.4° respectively. WO3 sample bearing the monoclinic geometry and its JCPDS no. is 03–1823. The sample showed geometrical parameters α = 90°, β = 89.93° γ = 90o and a, b and c are 7.274 (Å), 7.501 (Å) and 3.824 (Å) respectively while the density is 7.380 g/cm3. Nearly same crystallographic features were observed for pure WO3, 10, 12 and 14% CuS composites [20]. With reference to JCPDS file (06–0464) CuS is hexagonal with a = 3.796 Aͦ and c = 16.209 Aͦ furthermore, composites having 10% CuS are changing the parameters of x-ray for tungsten WO3. (#) and (*) are representation for the peaks of CuS and WO3 planes respectively as shown in Fig. 4. Single WO3 and CuS peaks are identified for the composites of CuS and WO3. Change in concentration of CuS is not affecting the WO3 planes but inversely varying the concentration. 10% composites are giving less intense peaks of CuS than 14%. Furthermore the Scherer’s formula (Eq. 1) was used to verify the size of crystal by (101) peak. [21]. Table 1 shows the lattice parameters and Scherrer size of nanocomposites.

$$D = \frac{0.9\lambda }{{\beta \cos \theta }}$$
(1)
Fig. 3
figure 3

XRD Pattern of pure WO3, CuS and respective nanocomposites

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Fig. 4
figure 4

UV–vis spectrum and Tauc plot of a WO3, b 10% CuS:WO3, c14% CuS:WO3, d CuS, e 12% CuS:WO3 and f the comparison of variation in band gap with increasing concentration of CuS in WO3

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Table 1 Lattice parameters and Scherrer size of fabricated nanocomposites
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Furthermore, the peaks of the diffraction planes (002), (101) and (100) have shifted downwards. The peaks denoted by (*#) describes the mixing of CuS (200) and (202) peaks transferring to lower values increased concentration of copper sulfide.

3.3 Optical Absorption Studies

The light-absorbing properties of copper-sulfide, Tungsten-trioxide and WO3-CuS were inspected by photo-catalysts using UV–Vis analysis, shown in spectroscopy and spectral features Fig. 4. Absorption for synthesized CuS, WO3, 10% and 14% CuS:WO3 were analyzed and the bandgap (BG) values of 1.82, 2.61, 2.47 and 2.25 eV respectively, along with the overview of visible light absorption increasing the ion capacity for CuS:WO3. It was observed that by the addition of copper-sulfide material absorption interchanges in visible range, due to 14% copper-sulfide in the sample of tungsten-trioxide. Its Tauc’s plot demonstrated the decrease in energy by alteration in band gap (BG). This behavior confirms that CuS doped WO3 material is appreciated for the optimized results of optical properties. This decrease in band gap can efficiently enhance the photo-catalysis of prepared samples.

3.4 Photoluminescence Measurements

Further, PL spectroscopy has been utilized to study the optical parameters, reunion rate of electron–hole pairs produced under UV light for pure WO3 and its composites with CuS, shown in Fig. 5. This study was achieved at 400 nm excitation wavelength. It was seen pure WO3 gives the emission at 464 nm and 10% probe shows that the intensity peak shifts downward carrying immense gap with increased wavelength, 464 nm. Introduction of 14% CuS will incorporate new trapping points, decrease of the intensity with bathochromic shift of wavelength [22]. In addition to this, photoluminescence peaks are relevant to the suppression of photo-generated electron–hole pair reunion [23] which is ultimately beneficial for improving photocatalytic performance of nanomaterial.

Fig. 5
figure 5

PL Emission spectrum of WO3 and its composite materials

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4 Photo-Catalytic Degradation Studies

The photo-catalytic degradation of RhB has been characterized in the visible light for RhB contamination to understand the photo catalytic efficiency of synthesized photo catalysts as shown in Fig. 6. A 300W tungsten-halogen lamp was used to provide visible light irradiation. The wavelength extent of light source was greater than 400 nm and usually the distance of 20 cm is kept between the sample and lamp, a 250 ml of dye solution of known amount was added to photo-catalyst. Earlier to light contamination, the magnetically suspension was mixed in the dark to create RhB equilibrium of the photo-catalyst [18]. 4 ml of aliquots were composed at regular intervals and the photo-catalyst was cleared by adaptation through a 0.45 mm membrane Alter (Pall Corporation) during irradiation. A Shimadzu UV-2450 UV–Vis spectrophotometer was used to determine the RhB concentration at dissimilar time intermission at its absorption wavelength characteristic viz., 554 nm [23]. A brief comparison of current work with the recent literature has been shown in Table 2.

Fig. 6
figure 6

a & b Depicting photocatalytic degradation of RhB dye by Pure WO3 and 14% CuS:WO3 composites respectively, c Photocatalytic removal of RhB dye in the presence of fabricated nanomaterial and d rate constant revealing highest rate constant of 0.01870 min−1 for 14% CuS-WO3 nanocomposite

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Table 2 A comparison of present study the relevant work reported in the literature
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4.1 Mechanism of Photo-Catalytic Degradation

Photo-catalytic degradation mechanism of RhB is shown using CuS:WO3 catalyst. The electronegativity of CuS and WO3 is 5.29 and 6.59 eV respectively [30]. The measured valence band (VB) and conduction band (CB) of CuS is 2.46 and 0.64 eV, whereas VB and CB of WO3 is 3.34 and 0.74 eV, respectively. The value of the CB for copper sulfide is more negative as compared to WO3 [30]. Consequently, the photo-induced prompted electron movement from conduction band of CuS to WO3 and simultaneously, there is an exchange of the hole from the valence band of WO3 to CuS. Hence, there is a decrease in electron–hole recombination and it prompts an expansion in the interfacial charge movement responses for the degradation of adsorbed particles of dye. Solution of rhodamine B (RhB) in distilled water, placed in the photo-catalytic reactor and 4 ml of sample was separated out at each 20 min interval obtaining UV–Vis spectra [31]. This study is actually meant to study the deprivation rate of the nano probes as shown in Fig. 6. The adsorption equilibrium of catalyst and dye solution was obtained to study the fabricated samples with RhB solution in dark for half an hour as shown in Fig. 9. In case of pure sample, when the contaminant model has been agitated using catalyst, nearly 1% adsorption was observed and showed bathochromic shift for 10% WO3 and 14% CuS [32]. This increased adsorption is the outcome of the enhanced surface area, more points available for reaction which further enhancing the degrading effectiveness. The photo-catalytic efficiency of the CuS composites with WO3 was investigated through photo degradation of pollutant RhB [33]. The deterioration rate of catalyst seemed to increase with increased portion of CuS in comparison to pure WO3. The absorption of 14 percent CuS mixture clearly revealed the increased degradation depicted in Fig. 6b. The maximum effectiveness was observed for 14% CuS composite. The accessed photo-catalysis is because of more active sites which further affect bandgap and electron‒hole pair reunion rate [34, 35]. For investigation of effectiveness of the samples is determined by following formula (Eq. 2).

$$Degradation \, \left( \% \right) = \, \left( {C/C_{o} } \right) \, \times \, 100$$
(2)

Above mentioned formula, Co and C represents the initial and final concentration of the solution respectively. RhB is merely degraded without catalyst and it manifest that RhB is very stable. However, by adding 10 mg of prepared catalyst (WO3) to aqueous solution, about 38% dye is degraded in 140 min as shown in Fig. 6a & c. Furthermore, proficiency of this process has heightened by increasing in the copper- sulfide ratio in tungsten trioxide. Electrons lying in valance band of photo-catalyst get excited by irradiating with a threshold frequency light and shifted to the CB. Meanwhile, the equal number of holes are there in the VB of WO3 and CuS are the scavengers for electrons and holes, so recombination ratio has decreased [36]. The plausible oxidation reduction processes are show below.

$$WO_{3} - CuS + hv \to WO_{3} - CuS\left( {e^{ - } } \right) + WO_{3} - \left( {h^{ + } } \right)$$
$$WO_{3} - CuS\left( {h^{ + } } \right) + MB \to MB^{ \bullet + } + WO_{3} - CuS$$
$$W{O}_{3}-CuS ({h}^{+}) +{H}_{2}O \to W{O}_{3}-CuS + O{H}^{-} + {H}^{+}$$
$$WO_{3} - CuS\left( {h^{ + } } \right) + OH^{ - } \to WO_{3} - CuS + OH^{ \bullet }$$
$$WO_{3} - CuS\left( {e^{ - } } \right) + O_{2} \to WO_{3} - CuS + O_{2}^{ \bullet - }$$
$$O_{2}^{ \bullet - } - OH^{ \bullet } + MB \to CO_{2} + H_{2} O$$

14% CuS nanoprobe catalyst on reaction with water is generating hydroxyl radicals and H+. Fig. depicts that when catalyst is irradiated, holes are generated and the highly reactive holes are interplaying with RhB [37]. CuS:WO3 (e‾) combining by oxygen (O2) forming superoxide anion radicals, hydroxyl ions while CuS-WO3 (h+) are interacting with one another forming hydroxyl radicals [38]. Superficial rate constant of photo-catalysts can be determined using following formula (Eq. 3):

$$\ln {\mkern 1mu} \left( {{\text{C}}_{{\text{0}}} {\text{/C}}} \right){\mkern 1mu} = {\mkern 1mu} \left( {{\text{k}}_{{{\text{app}}}} } \right)\left( {\text{t}} \right)$$
(3)

where C is preliminary amount of dye and C0 indicating the quantity of dye remaining at time “t”. kapp is apparent rate constant, the linear fitted plot between time t and ln(C0/C) shown in Fig. 7.

Fig. 7
figure 7

Photo-catalytic Mechanism of CuS:WO3 nanocomposites

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4.2 Reusability and Effect of pH

Reusability and photo-stability of 14% CuS:WO3 was measured, an effective parameter to be restrained for an efficiency of catalyst [39]. For determining recycling rate, sample was separated through magnetic field and degraded in six cycles alternatively shown in Fig. 8a. The results revealed that photo-catalytic efficacy was not reduced at the end of six cycles when 87.06% effectively was measured comparing 94.9% of the first cycle. Additionally, the effect of pH on the degradation efficiency of RhB for the best sample (14% CuS:WO3) was investigated. In this experiment, pH of the contaminant solution is adjusted at the start of reaction and was not maintained thorough out the reaction. Results shown in Fig. 8b indicates that moving from acidic to basic pH, the highest degradation efficiency is obtained for 9 pH. Any further increase in pH suppresses the removal efficiency of the catalyst.

Fig. 8
figure 8

a Reusability indicating to high photo-stability of the photo-catalyst for six cycles and b effect of pH for the degradation efficiency of best catalyst

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4.3 Total Organic Carbon (TOC) Analysis

TOC analysis has been conducted to check the complete mineralization of RhB dye when the contaminated dye solution is exposed to light source in the presence of synthesized photocatalyst. The results are shown in Fig. 9. The difference between degradation observed via UV–Visible spectrometer and complete mineralization percentage by TOC is denoted by \(\Delta 1\), \(\Delta 2\), \(\Delta 3\) & \(\Delta 4\) for pure WO3, 10% CuS-WO3, 12% CuS-WO3 and 14% CuS-WO3 respectively. It is observed that with the increase in CuS percentage in the nano-composite, the ability of complete degradation of RhB dye has been enhanced which is evident by the smallest value of \(\Delta 4\) as compare to other values. The difference between degradation percentage and TOC results can be attributed to the fact that, it is possible for an organic dye to lose its characteristic color bond with in first few steps of the degradation reaction. The UV–Visible analysis will count the degradation when the characteristic color peak will be absent irrespective of the fact that complete mineralization is a multistep process and it is possible for the organic contaminant to possess centric benzene ring and also do not show color peak. Therefore, TOC analysis is crucial for the exact confirmation of complete degradation of pollutant. Table 3 provides a review of the critical findings of the photocatalytic performance of synthesized pure WO3 and its nanocomposites with CuS. The percentage mentioned in the table has been round off to the nearest whole number for simplicity.

Fig. 9
figure 9

Total organic carbon analysis to verify the percentage mineralization of RhB dye during photocatalytic treatment of wastewater using pure WO3 and CuS:WO3 composites

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Table 3 Comparison of bandgap energy, degradation percentage and mineralization percentage by TOC for pure WO3 and CuS:WO3 nanocomposites
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4.4 COMOSL Simulation

COMSOL Multiphysics 5.3a is used to simulate the 2D model of experimental work. The schematics are shown in Fig. 10a. Different boundary conditions have been employed to mimic the experimental environment. Input port is used to excite the 2D model with UV–Visible to near infrared radiation (NIR). Scattering boundary condition (SBC) is used to ensure that the radiations are effectively dispersed. Periodic boundary conditions (PBC) are used on the right and left side of the model whereas continuous boundary conditions (CBC) are used on the inner boundaries of the model. The equations of these boundary conditions are given below (Eq. 4–7).

Fig. 10
figure 10

a Schematics of the 2D model, b meshed image of the model, c & d show the y-component and electric field norm respectively

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Periodic boundary condition (PBC)

$${\varvec{E}}_{dst} = {\varvec{E}}_{src} {\text{exp}}\left( { - j{\varvec{k}}.\left( {{\varvec{r}}_{dst} - {\varvec{r}}_{src} } \right)} \right)$$
(4)

Continuous boundary condition (CBC)

$$\left( {n \times \left( {{\varvec{H}}_{1} - {\varvec{H}}_{2} } \right)} \right)_{z} = 0, \left( {n \times \left( {{\varvec{E}}_{1} - {\varvec{E}}_{2} } \right)} \right)_{z} = 0$$
(5)

Scattering boundary condition (SBC)

$$n \times \left( {\nabla \times A_{z} } \right) - jkA_{z} = - jk\left( {1 - {\varvec{k}}.{\varvec{n}}} \right)A_{0z} \exp \left( { - j{\varvec{k}}.{\varvec{r}}} \right), \,A = E \,or \,H$$
(6)

Port

$$s = \smallint \left( {{\varvec{E}} - {\varvec{E}}_{1} } \right).{\varvec{E}}_{1} /\smallint {\varvec{E}}_{1} .{\varvec{E}}_{1}$$
(7)

First, the model is meshed (Fig. 10b) and then normalized (Fig. 11a). The particle size of WO3 used in the simulation was 46 nm (experimental value). The simulation is carried out for 200 min while WO3 NPs were immersed in RhB and water solution. The wavelength is swept from 300 to 1000 nm with the step size of 1 nm for optimal results. TM polarized light has been used for the simulation. The Maxwell equations which govern the light matter interaction are given below (Eq. 8–10).

Fig. 11
figure 11

a Normalization, b shows the improvement in absorption for incorporated samples as compared to pure WO3 and c depicting absorption, reflection and transmission of the model when irradiated by TM polarized light

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$$\nabla \times \left({\upmu }_{r}^{-1}\nabla \times \mathbf{E}\right)-\left({\upvarepsilon }_{r}-\frac{i\sigma }{{\mathrm{\omega \varepsilon }}_{0}}\right){k}_{0}^{2}{\varvec{E}}=0$$
(8)
$$\nabla \times \left( {\left( {\varepsilon _{r} - \frac{{i\sigma }}{{\omega \varepsilon _{0} }}} \right)^{{ - 1}} \nabla \times \user2{H}} \right) - \mu _{r} k_{0}^{2} \user2{H} = 0$$
(9)
$${\varvec{E}}={E}_{z}{{\varvec{e}}}_{z}, {\varvec\,{H}}={H}_{z}{{\varvec{e}}}_{z}, \,{\varepsilon }_{r}={n}^{2}$$
(10)

Absorption, reflection and transmission was analyzed as shown in Fig. 11 c. It is observed that at any given wavelength, the following equation holds true (Eq. 11) which supports the argument that the model has been normalized correctly and no attenuation is present in the model.

$${\text{I}}_{{{\text{reflection}}}} + {\text{ I}}_{{{\text{absorption}}}} + {\text{ I}}_{{{\text{tranmission}}}} = { 1}$$
(11)

After pure WO3, in order to simulate the nano-composites, a few atoms of WO3 were replaced with CuS. Figure 10c & d shows the y-component of electric field and electric field norm for the simulated model. The results shown in Fig. 11b verifies the positive impact due to the presence of CuS for the absorption of light. Improved absorption attributes to the effective generation of photogenerated electron/hole pairs which leads to the higher photocatalytic efficiency. The same trend was obtained from the experiments.

5 Conclusion

The XRD, UV–Vis SEM, EDX and PL Spectroscopic techniques were used to evaluate the structure, composition, morphological and optical parameters of synthesized nanocomposites. Degradation of RhB was used to analyze the photo-catalytic property samples under visible light photo-catalytic reaction. SEM depicted the nanorods morphology of CuS. Blend of Copper Sulfide and WO3 introduces the lower band gap with the increased concertation of copper sulfide. The reduction in band gap from 2.61 to 2.25 eV produced defects and more ratio of copper sulfide decreases the crystalline form. This change would decrease the charge reunion rate and manifest the existence of copper sulfide. Dye degradation inferred that CuS:WO3 nanocomposite manifest efficient photocatalytic behavior than pure WO3. Furthermore, degradation of organic pollutant (RhB) is accompanied by 14% CuS composite with WO3 catalyst. It degrades almost 94.9% of RhB dye in 140 min and it is just because in the composite, band gap and recombination rate is suppressed enhancing the degradation reaction rate of material. TOC analysis revealed that the rate of complete mineralization is less then the values observed by using UV–Visible spectrometer which attributes to the fact that decolorization of RhB dye may occur in initial few steps but complete deterioration of benzene ring is a multi-step reaction. Additionally, COMSOL is used to successfully corelate the experimental observations with simulation. Theoretical analysis verifies the enhanced absorption of light for nanocomposites as compared to pure WO3 indicating the higher photocatalytic activity of nanocomposites for the degradation of organic contaminants. The promising results indicates that CuS: WO3 composite is a potential catalyst for visible-light driven photocatalytic reactions for green energy applications as well as wastewater treatment.