Enhanced Photocatalytic Activity of Cu2O Cabbage/RGO Nanocomposites under Visible Light Irradiation

Towards the utilization of Cu2O nanomaterial for the degradation of industrial dye pollutants such as methylene blue and methyl orange, the graphene-incorporated Cu2O nanocomposites (GCC) were developed via a precipitation method. Using Hummers method, the grapheme oxide (GO) was initially synthesized. The varying weight percentages (1–4 wt %) of GO was incorporated along with the precipitation of Cu2O catalyst. Various characterization techniques such as Fourier-transform infra-red (FT-IR), X-ray diffraction (XRD), UV–visible diffused reflectance (UV-DRS), Raman spectroscopy, thermo gravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), and electro chemical impedance (EIS) were followed for characterization. The cabbage-like morphology of the developed Cu2O and its composites were ascertained from field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HR-TEM). In addition, the growth mechanism was also proposed. The results infer that 2 wt % GO-incorporated Cu2O composites shows the highest value of degradation efficiency (97.9% and 96.1%) for MB and MO at 160 and 220 min, respectively. Further, its catalytic performance over visible region (red shift) was also enhanced to an appreciable extent, when compared with that of other samples.


Introduction
The contamination of carcinogenic organic dyes in water bodies is the serious environmental problem in the world. Especially, it is a potential threat to soil, water, plant and human being, when discharging of dyestuffs without proper treatment [1][2][3]. Synthetic dyes play an important role in many industries, but it is hardly difficulty to determine the quantity of dyes discharged in various industrial processes. It is reported that the more than 100,000 synthetic dyes are commercially available in market and their major

RGO/Cu2O Composite Synthesis
The cabbage-like reduced graphene oxide/Cu2O composite (GCC) was synthesized by the precipitation method shown in Scheme 1. A pretreated graphene oxide (30 mg) and copper nitrate trihydrate Cu(NO3)2.3H2O (1 g) were taken and then dissolved in 30 mL distilled water with 30 min ultrasonication at room temperature.

Scheme 1. Synthesis of RGO/Cu2O composite (GCC).
Then, 0.1 M glucose (60 mL) and 0.1 M NaOH (100 mL) solution were added to the above mixture in dropwise under constant stirring at 100 °C. After 3 h, the RGO/Cu2O nanocomposite was formed as a reddish-brown precipitate. Then, it was continuously washed with DI water and ethanol. Further, it was centrifuged and dried (70 °C) in vacuum oven for 6 h to get GCC composite. The procedure was repeated again for the preparation of pure Cu2O without graphene oxide. Difference weight percent (1%, 2%, 3%, and 4%) of GO were utilized for the preparation of various GCC composites as GCC 1, GCC 2, GCC 3, and GCC 4.

Characterization
Different spectral studies were used such as XRD (Xpert-Pro-PAN), Almelo, Netherlands, FT-IR (Thermo Scientific Nicolet iS5), Mumbai, India. UV-DRS (Shimadzu UV-1800) Kyoto, Japan, Raman (RENISHAW inVia), Bangalore, India, FESEM and EDX (Tescan Vega3 (Czech Republic) Horiba HU77 (Japan)), HRTEM (FEI, TECHNAI G2 Then, 0.1 M glucose (60 mL) and 0.1 M NaOH (100 mL) solution were added to the above mixture in dropwise under constant stirring at 100 • C. After 3 h, the RGO/Cu 2 O nanocomposite was formed as a reddish-brown precipitate. Then, it was continuously washed with DI water and ethanol. Further, it was centrifuged and dried (70 • C) in vacuum oven for 6 h to get GCC composite. The procedure was repeated again for the preparation of pure Cu 2 O without graphene oxide. Difference weight percent (1%, 2%, 3%, and 4%) of GO were utilized for the preparation of various GCC composites as GCC 1, GCC 2, GCC 3, and GCC 4.

Photocatalytic evaluation
Photocatalytic study was carried out from visible light irradiation (300 W Xenon lamp) with a 400 nm cutoff filter. A prepared GCC (100 mg) was dispersed in 0.01 g/L concentration of MB and MO dye solutions in 100 mL. Before starting the irradiation, the mixture was kept for 30 min at dark condition with continuous stirring. At room temperature, the photocatalytic behavior of prepared samples was determined with quartz glass photocatalytic reactor. Further, the same method was used for the catalytic behavior of pure Cu 2 O and Degussa P25.

FT-IR Analysis
FT-IR spectral analysis has been used to identify the reduction of oxygen-containing functional groups in GO sheets during reflux process with low temperature. The FT-IR analysis of GO, pure Cu 2 O, and GCC (1-4%) composites is shown in Figure 1. The stretching and bending vibrations of the OH group are attributed from the peaks appeared at 3379 and 1590 cm −1 . The skeletal ring, aromatic carbon, and C=O stretching vibrations in the graphitic domain can be ascribed by the peaks appeared at 1697, 1220, and 1078 cm −1 . The Cu 2 O skeletal vibration is attributed at peak 636 cm −1 . Then, the disappearance of peak at 1220 cm −1 confirmed that glucose could reduce both Cu 2+ and GO to produce GCC during reflux reduction process.

Photocatalytic evaluation
Photocatalytic study was carried out from visible light irradiation (300 W Xenon lamp) with a 400 nm cutoff filter. A prepared GCC (100 mg) was dispersed in 0.01 g/L concentration of MB and MO dye solutions in 100 mL. Before starting the irradiation, the mixture was kept for 30 min at dark condition with continuous stirring. At room temperature, the photocatalytic behavior of prepared samples was determined with quartz glass photocatalytic reactor. Further, the same method was used for the catalytic behavior of pure Cu2O and Degussa P25.

FT-IR Analysis
FT-IR spectral analysis has been used to identify the reduction of oxygen-containing functional groups in GO sheets during reflux process with low temperature. The FT-IR analysis of GO, pure Cu2O, and GCC (1-4%) composites is shown in Figure 1. The stretching and bending vibrations of the OH group are attributed from the peaks appeared at 3379 and 1590 cm −1 . The skeletal ring, aromatic carbon, and C=O stretching vibrations in the graphitic domain can be ascribed by the peaks appeared at 1697, 1220, and 1078 cm −1 . The Cu2O skeletal vibration is attributed at peak 636 cm −1 . Then, the disappearance of peak at 1220 cm −1 confirmed that glucose could reduce both Cu 2+ and GO to produce GCC during reflux reduction process.

Structure Investigation
The crystalline and amorphous nature of GO, Cu2O, and GCC 1, 2, 3, and 4 nanocomposites were examined using XRD patterns as shown in Figure 2a-f. In the case of GO, reflection peak appeared at 10.75° and the interlayer distance between its oxide layers is found to be 0.8133 nm as shown in Figure 2

Structure Investigation
The crystalline and amorphous nature of GO, Cu 2 O, and GCC 1, 2, 3, and 4 nanocomposites were examined using XRD patterns as shown in Figure 2a-f. In the case of GO, reflection peak appeared at 10.75 • and the interlayer distance between its oxide layers is found to be 0.8133 nm as shown in Figure 2a Because of the lower weight percentage of RGO in the composites, the expected peak at 23.9 • has not been observed in the patterns of composites.
(200), (211), (220), (221), (310), (311), and (222) planes for pure Cu2O. The cubic phase of Cu2O structure matched with JCPDS card number 78-2076 from the reflection peaks of Cu2O. The d-spacing was calculated as 0.24 nm with respect to plane (111) in Cu2O. The peaks appeared for GCC also exhibit comparable diffraction peaks and confirm the presence of Cu2O in the composite. Further, the formation of reduced graphene oxide (RGO) has been confirmed by the disappearance of peak 10.75° in XRD patterns of GCC composites. The reduction in Cu2O peak intensities further confirms the formation of RGO in composites. Because of the lower weight percentage of RGO in the composites, the expected peak at 23.9° has not been observed in the patterns of composites.

Raman analysis
The spectra of Raman analysis for GO, Cu2O, and GCC 2 are shown in Figure 3. The obtained D band (1353 cm −1 ) and G-band (1593 cm −1 ) from graphene oxide indicate the presence of sp 2 carbon skeleton in graphene. The shifting values of D and G band indicate the reduction of graphene oxide to graphene and the interaction between the RGO and Cu2O matrix in GCC 2 composite.

Raman analysis
The spectra of Raman analysis for GO, Cu 2 O, and GCC 2 are shown in Figure 3. From the spectrum of Cu2O, four peaks at 293, 338, 626, and 734 cm −1 were exhibited and the same peaks were also found in the GCC 2 but with low intensity. This confirms the anchoring of Cu2O nanoparticles in the RGO. The increase in ratio between the intensity of D and G band from 0.88 in GO to 0.98 in GCC 2 confirms the reduction of oxygen functionalities in composites.

UV-Vis Diffuse Reflectance Spectrum Studies
The UV-DRS spectra of Cu2O and four GCC composites are revealed in Figure 4A. The peak at 650 nm denotes the presence of Cu2O with high crystalline nature. It is noted

UV-Vis Diffuse Reflectance Spectrum Studies
The UV-DRS spectra of Cu 2 O and four GCC composites are revealed in Figure 4A. The peak at 650 nm denotes the presence of Cu 2 O with high crystalline nature. It is noted from the results that the absorbance of visible light region by GCC increases with red shift due the incorporation of graphene on Cu 2 O. This may also significantly influence the optical properties for the enhancement of visible-light absorption. Hence, the improved photocatalytic activity under visible-light is expected. The band-gap energies for pure Cu 2 O, GCC 1, 2, 3, and 4 are calculated to be ( Figure 4B

Thermogravimetric Analysis
The thermogravimetric analysis of GCC 2 nanocomposite is shown in Figure 5. It is clear that there is negligible weight loss observed up to 100 °C for the presence of moisture and solvent. The loss of weight (13.2%) in the region of 100-375 °C is ascribed to the removal of residual functional groups in RGO. The loss of weight up to 14.1% in the region of 375-550 °C is endorsed to the decomposition of carbon skeleton of RGO. The ob-

Thermogravimetric Analysis
The thermogravimetric analysis of GCC 2 nanocomposite is shown in Figure 5. It is clear that there is negligible weight loss observed up to 100 • C for the presence of moisture and solvent. The loss of weight (13.2%) in the region of 100-375 • C is ascribed to the removal of residual functional groups in RGO. The loss of weight up to 14.1% in the region of 375-550 • C is endorsed to the decomposition of carbon skeleton of RGO. The observed weight loss within the particular range of temperature shows that the composite possesses good thermal stability, which also directed to perform the catalytic activity of prepared GCC 2 nanocomposite at below 500 • C.
Polymers 2021, 13, x 9 of 20 possesses good thermal stability, which also directed to perform the catalytic activity of prepared GCC 2 nanocomposite at below 500 °C.

FESEM and EDX Analysis
In order to study about the morphology of Cu2O and GCC 2 composite, the FESEM analysis was carried out. In Figure 6a,b, it is found that a large number of novel cabbage-like structures are obtained from pure Cu2O. Figure 6c,d exhibit the interfacial contact between RGO and Cu2O matrixes. The RGO sheets are attached with the Cu2O material, which may be favorable to generate photoelectrons and thus improve the photocatalytic activity. The chemical composition of the synthesized GCC 2 composite was established from the analysis of EDX spectrum in Figure 7. It shows that the prepared GCC contains C, Cu, and O, and no other impurities were detected.

FESEM and EDX Analysis
In order to study about the morphology of Cu 2 O and GCC 2 composite, the FESEM analysis was carried out. In Figure 6a,b, it is found that a large number of novel cabbagelike structures are obtained from pure Cu 2 O. Figure 6c,d exhibit the interfacial contact between RGO and Cu 2 O matrixes. The RGO sheets are attached with the Cu 2 O material, which may be favorable to generate photoelectrons and thus improve the photocatalytic activity. The chemical composition of the synthesized GCC 2 composite was established from the analysis of EDX spectrum in Figure 7. It shows that the prepared GCC contains C, Cu, and O, and no other impurities were detected.
The growth mechanism of the cabbage-like Cu 2 O architecture under precipitation technique was investigated, and it follows nucleation-dissolution recrystallization mechanism with controlled kinetics, because the nanoparticles were formed in the solution phase system at 100 • C through homogeneous nucleation process [27,28]. Sodium hydroxide (NaOH) acts as a significant role for the development of cabbage-like Cu 2 O architecture. It helps to dissolute the Cu 2 O and forms the intermediate such as Cu(OH) 2 which further leads the formation of nanoparticles via Ostwald ripening process [29]. Moreover, glucose was also considered as an influencing factor for the growth of Cu 2 O nanoparticles. The above factors help to design the structure of nanocomposites with well-defined morphologies.  The growth mechanism of the cabbage-like Cu2O architecture under precipitation technique was investigated, and it follows nucleation-dissolution recrystallization mechanism with controlled kinetics, because the nanoparticles were formed in the solution phase system at 100 °C through homogeneous nucleation process [27,28]. Sodium hydroxide (NaOH) acts as a significant role for the development of cabbage-like Cu2O architecture. It helps to dissolute the Cu2O and forms the intermediate such as Cu(OH)2 which further leads the formation of nanoparticles via Ostwald ripening process [29]. Moreover, glucose was also considered as an influencing factor for the growth of Cu2O nanoparticles. The above factors help to design the structure of nanocomposites with well-defined morphologies.  The growth mechanism of the cabbage-like Cu2O architecture under precipitation technique was investigated, and it follows nucleation-dissolution recrystallization mechanism with controlled kinetics, because the nanoparticles were formed in the solution phase system at 100 °C through homogeneous nucleation process [27,28]. Sodium hydroxide (NaOH) acts as a significant role for the development of cabbage-like Cu2O architecture. It helps to dissolute the Cu2O and forms the intermediate such as Cu(OH)2 which further leads the formation of nanoparticles via Ostwald ripening process [29]. Moreover, glucose was also considered as an influencing factor for the growth of Cu2O nanoparticles. The above factors help to design the structure of nanocomposites with well-defined morphologies.

HR-TEM Analysis
HRTEM images of RGO and the GCC were examined and shown in Figure 8a, which showed that the surface of RGO sheet consists of many wrinkles, which helps to attach the metal particles easily on its surface. The Cu 2 O nanocabbages are anchored on the surface of the RGO sheets as shown in Figure 8b,c. From the HR-TEM images of GCC 2, it is evident that the homogenous deposition is achieved in between RGO and Cu 2 O with no aggregation. The highly dispersed nanocabbage attached on the large surface area of graphene increase the photocatalytic activity. In addition, the SAED pattern of Figure 8d further proved the incorporation of cabbage-like Cu 2 O into RGO composite and confirms the crystalline nature. attach the metal particles easily on its surface. The Cu2O nanocabbages are anchored on the surface of the RGO sheets as shown in Figure 8b,c. From the HR-TEM images of GCC 2, it is evident that the homogenous deposition is achieved in between RGO and Cu2O with no aggregation. The highly dispersed nanocabbage attached on the large surface area of graphene increase the photocatalytic activity. In addition, the SAED pattern of Figure 8d further proved the incorporation of cabbage-like Cu2O into RGO composite and confirms the crystalline nature.

EIS Analysis
It is an important tool for studying the interface surface properties of electrode materials. EIS was employed to examine the fast ion transport within GCC 2 electrode materials. The spectra of bare electrode, pure GO, Cu2O, and GCC 2 were illustrated ( Figure  9) in the range of 0.01 Hz-100 KHz frequency at open circuit potential of 5 mV using 2.5 mM Fe 2+ /Fe 3+ solution. GCC 2 exhibits least internal charge transfer resistance (Rct) and low semicircle arc than pure Cu2O. This may be due to the 2D RGO, which enhance the photocatalytic behavior with conductive nature. Furthermore, this indicates that GCC 2 have decrement of resistance and better ion transport behavior than pure Cu2O.

EIS Analysis
It is an important tool for studying the interface surface properties of electrode materials. EIS was employed to examine the fast ion transport within GCC 2 electrode materials. The spectra of bare electrode, pure GO, Cu 2 O, and GCC 2 were illustrated (Figure 9) in the range of 0.01 Hz-100 KHz frequency at open circuit potential of 5 mV using 2.5 mM Fe 2+ /Fe 3+ solution. GCC 2 exhibits least internal charge transfer resistance (Rct) and low semicircle arc than pure Cu 2 O. This may be due to the 2D RGO, which enhance the photocatalytic behavior with conductive nature. Furthermore, this indicates that GCC 2 have decrement of resistance and better ion transport behavior than pure Cu 2 O.

Photocatalytic Studies
The photocatalytic efficiencies of all GCC composites were explored against methylene blue and methyl orange dyes in aqueous conditions under visible light irradiation. Initially, the GCC is added with the dye solutions with 30 min stirring up to equilibrium attained. Here, the dye concentration should be kept as constant for all experimental conditions. The degradation of MB and MO dyes with respect to time using Cu2O and GCC is shown in Figure 10a,b. The absorption maxima are decreased gradually with respect to time and graphene oxide percentage. Among all composites, the GCC 2 per-

Photocatalytic Studies
The photocatalytic efficiencies of all GCC composites were explored against methylene blue and methyl orange dyes in aqueous conditions under visible light irradiation. Initially, the GCC is added with the dye solutions with 30 min stirring up to equilibrium attained.
Here, the dye concentration should be kept as constant for all experimental conditions. The degradation of MB and MO dyes with respect to time using Cu 2 O and GCC is shown in Figure 10a,b. The absorption maxima are decreased gradually with respect to time and graphene oxide percentage. Among all composites, the GCC 2 performed highest degradation of both dyes for 160 and 220 min, respectively. The reusability of the GCC 2 nanocomposite has been checked several times, and it was observed that the degradation ability is not appreciably reduced up to three times. Owing to the influence of visible light during catalytic process, the chromophore group's elimination was achieved with its structural degradation. The studies of photocatalytic activities for GCC with different graphene oxide (1-4%) loadings were executed. The initial and final concentration (C/C0) change of MB and MO were related to maximum absorbance values. It is identified that the GCC shows highest degradation capacity than that of pure catalyst (Cu2O) and conventional catalyst (Degussa P25) (Figure 11a,b). MB dye degradation with GCC and Cu2O was found to be 97.9% and 59.44%, respectively, after 160 min of visible light irradiation. MO dye degradation with GCC and Cu2O Owing to the influence of visible light during catalytic process, the chromophore group's elimination was achieved with its structural degradation. The studies of photocatalytic activities for GCC with different graphene oxide (1-4%) loadings were executed. The initial and final concentration (C/C 0 ) change of MB and MO were related to maximum absorbance values. It is identified that the GCC shows highest degradation capacity than that of pure catalyst (Cu 2 O) and conventional catalyst (Degussa P25) (Figure 11a,b). MB dye degradation with GCC and Cu 2 O was found to be 97.9% and 59.44%, respectively, after 160 min of visible light irradiation. MO dye degradation with GCC and Cu 2 O was found to be 96.1% and 47.82%, respectively, after 220 min of irradiation under visible light. The percentage of degradation values are presented in Table 1. MB dye degradation with GCC and Cu2O was found to be 97.9% and 59.44%, respectively, after 160 min of visible light irradiation. MO dye degradation with GCC and Cu2O was found to be 96.1% and 47.82%, respectively, after 220 min of irradiation under visible light. The percentage of degradation values are presented in Table 1.  The results of photocatalytic activities prove that amount of graphene plays a major role for the performance of GCC composites against corresponding dyes. Especially, the high surface area of graphene is able to improve the photocatalytic behavior of Cu 2 O than that of its pure form due to the reduction in electron hole pairs recombination by pi-pi* interaction involved in dye molecule. Therefore, the increasing amount of RGO has driven fast the catalytic performance of the composites. However, the degradation capacity was reduced when the GO content goes beyond the limit (i.e.,) above 2% due the shielding effect by excess GO content which confirms the influence of RGO in GCC composites.
It is observed from the degradation results that the GCC composites degrade the dyes effectively when compared to P25 catalyst and pure Cu 2 O. Among the reduced graphene oxide/Cu 2 O composites, 2% GO-loaded (GCC 2) composite reached its maximum degradation ability with 97.9% for MB and 96.1% for MO dyes under visible irradiation because of the reduction rate of recombination in Cu 2 O matrix by RGO, which facilitates the dyes degradation effectively. Furthermore, a comparative account has been made among various graphene-based nanocomposites with prepared RGO/Cu 2 O composites against MB and MO dyes as given in Table 2.

Kinetic Studies
The dye degradation reaction for GCC follows pseudo-first order equation by the analysis of kinetic data as shown in Figure 12a  The various rate constant (k abs ) values are given in Table 3, which exposes that the highest value of GCC 2 further confirms the catalytic efficiency of GCC 2 than other composites.

Total Organic Carbon Analysis
The degradation efficiency of the GCC composites was further confirmed by TOC analysis (Figure 13). Among the results, the higher TOC removal recorded for GCC 2 when compared with other composites, Degussa P25, and pure Cu 2 O materials. Totally, 62% of removal is attained at 160 min and 55% of removal is reached at 220 min for selected organic dyes, which further proves the degradation efficiency for GCC 2 [44][45][46]. The various rate constant (kabs) values are given in Table 3, which exposes that the highest value of GCC 2 further confirms the catalytic efficiency of GCC 2 than other composites.

Total Organic Carbon Analysis
The degradation efficiency of the GCC composites was further confirmed by TOC analysis (Figure 13). Among the results, the higher TOC removal recorded for GCC 2 when compared with other composites, Degussa P25, and pure Cu2O materials. Totally, 62% of removal is attained at 160 min and 55% of removal is reached at 220 min for selected organic dyes, which further proves the degradation efficiency for GCC 2 [44][45][46].

Photocatalytic Mechanism
Graphene material acts a major role in the photocatalytic mechanism of GCC catalyst, which is illustrated in Scheme 2. After the incorporation of RGO with Cu2O, the flow of electrons attained easily in between these two matrixes with the formation of Schottky barriers. In the meantime, the electron hole pairs are also formed for the excitement of electrons from the valence band (VB) to conduction band (CB). Then, the same electrons (e − ) produced oxygen peroxide radicals O2• − by reacting with the dissolved oxygen molecules. Additionally, the hydroxyl radicals OH• is obtained by treating water molecules with positively charged hole (h + ). Finally, the organic dye molecules (MB and MO) were decomposed into CO2 and H2O molecules due the above-said free radicals.

Photocatalytic Mechanism
Graphene material acts a major role in the photocatalytic mechanism of GCC catalyst, which is illustrated in Scheme 2. After the incorporation of RGO with Cu 2 O, the flow of electrons attained easily in between these two matrixes with the formation of Schottky barriers. In the meantime, the electron hole pairs are also formed for the excitement of electrons from the valence band (VB) to conduction band (CB). Then, the same electrons (e − ) produced oxygen peroxide radicals O 2 • − by reacting with the dissolved oxygen molecules. Additionally, the hydroxyl radicals OH• is obtained by treating water molecules with positively charged hole (h + ). Finally, the organic dye molecules (MB and MO) were decomposed into CO 2 and H 2 O molecules due the above-said free radicals. From the mechanism, it is concluded that the RGO is able to reduce the recombination of electrons in between the excited to ground state, which helps to act as a better catalyst in composites for various applications especially in water treatment process.

Conclusions
The properties such as functionality, structural, and thermal and optical properties for the synthesized RGO/Cu2O nanocomposite were characterized by essential spectral techniques. The elemental analysis (C, O, and Cu) and morphological studies were confirmed by transmission and scanning electron microscope with EDX spectra. The RGO sheets exhibit superior interfacial contact with the Cu2O matrix. Further, its catalytic performance over visible region (red shift) was also enhanced to an appreciable extent, when compared with that of other samples. Hence, we can conclude that the effective GCC 2 photocatalyst will be performed as a cost-effective and ecofriendly material for the wastewater treatment in industries. The enhanced properties of the synthesized graphene-based composites will also be recommended to treat the dyes other than MB and MO in textile sector. From the mechanism, it is concluded that the RGO is able to reduce the recombination of electrons in between the excited to ground state, which helps to act as a better catalyst in composites for various applications especially in water treatment process.

Conclusions
The properties such as functionality, structural, and thermal and optical properties for the synthesized RGO/Cu 2 O nanocomposite were characterized by essential spectral techniques. The elemental analysis (C, O, and Cu) and morphological studies were confirmed by transmission and scanning electron microscope with EDX spectra. The RGO sheets exhibit superior interfacial contact with the Cu 2 O matrix. Further, its catalytic performance over visible region (red shift) was also enhanced to an appreciable extent, when compared with that of other samples. Hence, we can conclude that the effective GCC 2 photocatalyst will be performed as a cost-effective and ecofriendly material for the wastewater treatment in industries. The enhanced properties of the synthesized graphene-based composites will also be recommended to treat the dyes other than MB and MO in textile sector.