Mechanistic insight into Photocatalytic mineralization of dyes using metal oxide- Parametric and kinetic study

doi:10.21203/rs.3.rs-4161362/v1

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Mechanistic insight into Photocatalytic mineralization of dyes using metal oxide- Parametric and kinetic study

https://doi.org/10.21203/rs.3.rs-4161362/v1

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In the present study, the photocatalytic degradation of Rhodamine-B dye was carried out. bismuth oxide (α − Bi₂O₃) and copper oxide (CuO) photo catalyst was prepared for the degradation analysis. During the photocatalysis of Rhodamine-B degradation, the order of removal with different semiconductors was followed in the following order: α − Bi₂O₃ > CuO. The effect of operating parameters, including solution pH (3–8), catalysts dose (0.2–1.5 g/L), temperature change (5–20 ^oC), and initial Rhodamine B dye concentration (10–25 mg/L), were systematically examined using α − Bi₂O₃ photocatalyst under UV-light irradiation. The Rhodamine-B dyes showed the best removal efficiency of 97% at operating conditions of natural pH = 7.0, catalyst dose = 1.5 g/L, temperature = 20 ^◦C, and Rh-B concentration = 10 mg/L under control conditions. As − prepared semiconductor materials such as α − Bi₂O₃ and CuO were characterized by using many techniques like scanning electron microscope, energy dispersive X-ray, Fourier Transmission Infrared spectroscopy, and X − ray diffraction technique. A degradation pathway was also suggested by the identification of reaction intermediates. The reusability test analysis of bismuth oxide confirmed that photocatalysts can be separated after degradation and reused many times, and there were no other changes in structure and morphologies. This study confirmed the simple synthesis approach of semiconductor materials and their uses for the treatment of Rhodamine-B dye.

Rhodamine-B

α−Bi2O3

and CuO Photo catalyst

Mineralization

Photocatalytic activity

Since the last two decades, global water pollution has continuously increased on a very large scale. The increase in water pollution is caused by the industrialization and commercialization of the different types of manufacturing industries, chemical laboratories, etc. [1]. These industries produce different types of recalcitrant organic pollutants such as dyes [2], pesticides [3], insecticides [4], pharmaceutical compounds [5], many personal care compounds [5], etc. These pollutants are very dangerous for humans and the nature of aquatic life [6]. Some industries, such as printing, leather, and textile industries, use organic dyes, which require 700,000 tons of dyes each year [7] and produce huge amounts of wastewater; therefore, textile dyes are considered a significant pollutant in water [8]. In the last few years, about 20% of the world's production of water effluents has contained dyes in their discharge from the textile industry. This effluent produces detrimental effects on the kidneys, liver, reproductive functions, and immune systems, and it is a probable carcinogen. Therefore, the degradation of dyes from wastewater is necessary.

Further, dyes are stable, recalcitrant in nature, and non − biodegradable compounds, which are difficult to remove from conventional treatment technology [9]. The presence of dyes in water affects aquatic life in many ways, such as reducing the penetration of sunlight in water [10], which affects the photosynthesis process and produces several diseases, such as eye irritation and carcinogenic and mutagenic problem [11]. Therefore, effective treatment of the dyes before the discharge of wastewater is very necessary to attract scientists all over the world.

There are several methods for the degradation of dyes from wastewater, including adsorption [12], coagulation [13], photocatalytic treatment [14], and biological process [15]. Advanced oxidation processes such as sonolysis [16], electrochemical [17], photocatalytic [18], and Fenton process [19], Sonophotolysis [20] have gained much attention for the degradation of dyes from wastewater.

Most of the AOPs generate the ^● O.H. radicals. These radicals, by virtue, non-selectively degraded the pollutants present in wastewater. However, each method has its own limitations and disadvantages. Photocatalysis with semiconductors is a process in which a photocatalyst is used in the presence of UV light for the degradation of pollutants [21]. H₂O₂ was used as an oxidant during the photocatalysis process. The photocatalysis process has the advantage of being simple, with no secondary pollutant, no discharge requirement, and complete mineralization of pollutants in CO₂ and H₂O. [21]. Even though many studies are available on the degradation of the dyes however, comparative studies of the degradation of dyes using different photocatalysts, such as α − Bi₂O₃ and CuO, are not reported in the literature. Further, these catalysts have significantly low cost, are non-toxic, and are environmentally friendly. Bi₂O₃ is a Bi − based material with a small band gap. Due to its non-toxic effect and good visible photocatalytic effect, it is widely used in the environment.

In the present study, comparative degradation analysis of the dyes was carried out using different photocatalysis, such as α − Bi₂O₃ and CuO. Characterization of these photocatalysts was carried out using X − ray diffraction, scanning electron microscopy, and Electron Dispersion X − ray analysis. The photocatalytic activity of these materials was studied by using Rhodamine B (RhB) dye as an organic pollutant. A parametric study was carried out using different parameters such as initial dye concentration, pH, catalyst dose, and temperature. A degradation pathway of the dyes was suggested, along with a reusability analysis of the photocatalyst. Kinetics of degradation of pollutants was also reported.

2.1. Chemicals

All the chemicals used are of the analytical grade. Rhodamine B dye (RhB) was purchased for the Yogesh dye stuff product Ltd., India. Reagents copper sulfate pentahydrate (CuSO₄.5H₂O) and ferrous sulfate heptahydrate (FeSO₄.7H₂O) were obtained from S.D. Fine Chemicals, India. Bismuth nitrate pentahydrate [Bi (NO₃)₃.5H₂O] zinc sulfate heptahydrate (ZnSO₄. 7H₂O) was obtained from Himedia laboratories, India. Sodium hydroxide (NaOH), dichloromethane (CH₂Cl₂), and acetone (C₃H₆O) were purchased from Ranbaxy Chemicals Ltd., India. Pure distillates were purchased from Earthman Services Pvt Ltd., India.

2.2 Experimental Procedure

The degradation of Rh-B dye is observed under ultraviolet light irradiation. α − Bi₂O₃ particles are used in the photocatalytic reduction of the dyes containing wastewater. The initial concentration of the Rh-B dye was 20 mg/L. The solution of Rh-B was irradiated using UV irradiation light in a closed chamber in the presence of hydrogen peroxide. The solution was kept inside a beaker and stirred using a magnetic stirrer. The magnetic stirrer RPM (run per minute) is maintained at approximately 150 − 200. Samples were withdrawn at regular intervals of time. The intensity and color of the solution are measured by the UV − visible spectrophotometer. The range of the UV visible spectrophotometer is 200 to 800 nm. The maximum absorbance of Rhodamine B dye was measured at 546 nm. Adsorption-desorption equilibrium was also carried out before the Rh-B degradation experiments.

2.3. Preparation and Characterization of Nanocatalyst

The precipitation method was used for the preparation of the CuO and α − Bi₂O₃ photocatalyst. In the formation of the copper sulfate pentahydrate, firstly, we took 150 mL water in a washed beaker and put the beaker on the magnetic stirrer. The temperature of the system is maintained at 40⁰C during the water heating. After that, 4 g reagent was added in the slightly hot water and maintained the RPM of the magnetic stirrer at 150 − 200. Then, the temperature of the solution was increased from 40 to 80⁰C. To maintain the basic pH of the solution, the freshly prepared solution of NaOH (2 g in the 100 mL distilled water) was mixed dropwise. The process of mixing the solution was continuing for about 15 − 20 minutes by maintaining the temperature of the solution at 80⁰C. After that, the temperature of the solution, was dropped by stopping the process of heating, and the temperature of the mixture fell to 30⁰C, and the process of stirring was continuous for 90 min. After that, sample solution was kept in the chamber to cool down and stelled down the prepared particles. Prepared particles take 2 hours to settle down. After 2 hours, separated layer of prepared particles and water can be seen. At this stage, the size of the particles is less than nano size, so to collect the particles from the solution, we use the centrifuge process. In this process, we take the solution in the centrifuge tubes. These tubes are placed in the centrifuge machine for rotation, and the machine's RPM is set at 5000 RPM for 15 minutes. The process of centrifuging proceeded for coagulation of the particles so that we could easily collect the particles and proceed to further application part. The coagulated particles are collected in the crucible, and then we put this crucible in the oven at 800 ⁰C for 12 hours, where the extra moisture is heated up and starts to evaporate. Then, this crucible is placed in the muffle furnace at a temperature of 400⁰C for about 3 hours. Then, to cool down the temperature, it is placed in the designator. After this complete procedure, the required particles are prepared. Then, these particles undergo many characterizations.

3.1. Characterization of Materials

3.1.1. X − ray diffraction analysis:

XRD results have been used to analyze the crystallinity of the mesosphere semiconductors. The XRD patterns of the α-Bi₂O₃ and CuO are illustrated in Fig. 1. For bismuth-based compounds, the order of intense and strong diffraction peaks consisted of the monoclinic α-phase of Bi₂O₃ along with O₂-deficient Bi₂O₃. The standard JCPDS data files (Monoclinic-Bi₂O₃: card no.76-1730) were satisfied with the corresponding (hkl) values of different peaks that are indexed in Fig. 1. The highest peak intensity at ~ 27.55^o corresponds to (hkl) value (120) for pure Bi₂O₃ monoclinic [22], as shown in Fig. 1. The existence of new peaks in significant proportions superbly matches oxygen-deficient Bi₂O₃. The perfect peaks at 79.72^o (312), 75.1^o (211), 61.08^o (111), 56.29^o (006), 45.92^o (101), 44.02^o (006), 42.18^o (320), 40.02^o (311), 29.6^o (107), 28.1^o (101), 25.13^o (210), 23.6^o (101) equivalent to tetragonal, and hexagonal, respectively. Higher O₂ deficient phases favour the higher donor density or n-type carrier concentrations and superb photocatalytic activity of as-prepared semiconductors. For the crystalline size and phase of CuO mesosphere, the diffraction peaks at Bragg angle (2θ) values and corresponding crystal plane indices of 32.53° (110), 35.58° (002), 38.76° (111), 48.81° (202), 53.45° (002), 58.24° (202), 61.56° (113), 66.14° (022), and 75.22° (222) revealed the presence of monoclinic crystalline phase (β = 99.5° and α = γ = 90^o) of CuO (JCPDS no. 98-008-7124, space group C12/C1) [23] & [24]. The XRD results showed the as-prepared CuO mesosphere has a pure monoclinic crystal phase. Moreover, the crystallinity of the sample shows the positions of different atoms or molecules. The SEM analysis was used to confirm the surface morphology of the as-synthesized products. The Bi₂O₃ powder in Figure. 2 (a-b) shows the SEM images of mixed-phase α-Bi₂O₃ at different magnifications. It can be realized that the α-Bi₂O₃ contains the combination of nanosphere approximately the average breadths and lengths 40 nm and 126 nm with the range of 44 nm diameter, respectively. The agglomerate nature of the particles from the images (Figure. 2a-b) was confirmed by the nearly invisible boundaries of the inter-particle. Spherical particles of an average diameter of 48 nm display α-Bi₂O₃ nano sphere-like structures and display the hallow spherical type morphology [25]. To know the morphology of the CuO sample, SEM images (Fig. 2d and e). The porous CuO morphology showed the collection of uncertain or thread spheres with different shapes and sizes (∼125 − 175 nm) and average lengths with about 58 nm thickness. The CuO mesosphere formation was started by the nucleation of the sample, followed by the build-up or growth of different CuO threads via self-assembly action [26]. In the elemental dispersion X-ray analysis (EDX), the elemental analyses of the as-synthesized metal oxide samples determined the chemical composition by using the EDS. Figure 2c illustrates the EDS spectrum of some parts of the α-Bi₂O₃ sample and approves the creation of α-Bi₂O₃ during the photocatalysts as 49.9% Bi and 42.1% O atoms have existed in the 1: 1.2 ratio. From the results of the analysis, it is found that the comparative content of Bi is somewhat lesser than consistent oxygen in α-Bi₂O₃ [27]. However, there is an even 1:1 ratio of Bi and O, signifying a rise in the comparative trend. While there was no noticeable number of additional elements, the varied changes in the surface morphology and crystalline pattern support the above results. EDX profile of the CuO mesosphere shows the actual elements composition (Figure.2f). The EDS spectrum of some parts of the CuO sample approves the creation of CuO during the photocatalysts as 60.1% Cu and 39.9% O atom have existed in the 1: 1 ratio. From the results of the analysis, it is found that the relative content of Bi is almost equal.

3.1.2. FT − IR analysis: After calcinating at 400^oC for three h, the FT − IR spectra of as − synthesized materials are shown in Fig. 3. A strong absorption peak at below 400 cm^− 1 illustrates the occurrence of metal oxide nanoparticles, which assistances in the inference of the α − Bi₂O₃ and CuO. For both the α − Bi₂O₃ and CuO samples, a wide peak noticed between 3200 and 3500 cm^− 1 is expected to O–H stretching vibration frequency of water adsorbed on the material surface, and the bending vibration peak frequency at 1635 cm^− 1 can be signified by the H–O–H bond [28]. The FT − IR spectra of α − Bi₂O_{3 are} illustrated in Fig. 3. The main peak of Bi–O stretching frequency occurs at 400–1600 cm^− 1. The peak ~ 3500 and 1630 cm^− 1 can give the appearance of both − O–H stretching and bending vibrations, respectively [29]. The peak at 845.6 cm^− 1 and 443.9 cm^− 1 are given to stretching vibration of Bi–O bonds and Bi − O−Bi bonds in the α − Bi₂O₃. FTIR and XRD analysis results show the final products as α − Bi₂O₃. The peak frequency at 3449 cm^− 1, 1699 cm^− 1, and 1581 cm^− 1 are recognized as the residual hydroxyl groups (O–H) stretching, C − O and C − C stretching vibrations, respectively. Figure 3 shows the FTIR spectra of the CuO mesosphere. A strong transmittance peak at 3573 cm^− 1 and 1114 cm^− 1 showed the O − H stretching and O − H stretching for alkyl. The strong and very intense characteristic peak of CuO positioned ranges from 968 cm^− 1 to 463 cm^− 1. The peak position at 606 cm^− 1, 525 cm^− 1, and 432 cm^− 1 was detected owing to Cu − O stretching frequency [30]. The occurrence of CO₂ molecules in the air was also detected in the peaks at 2332 and 2360 cm^− 1 [31]. A weak vibrational band at 3500 cm^− 1 and 1040 cm^− 1 shows the O − H stretching frequency of water in the KBr matrix.

4.1. Comparative Photocatalytic Activity of Bi₂O₃ and CuO Nanocomposite

Comparative analysis of the photocatalyst, namely commercial Bi₂O₃, spherical Bi₂O_3, spherical α- Bi₂O₃/H₂O_2, and spherical CuO, was carried out using ultra visible light. Rh-B was selected as a pollutant for degradation analysis. As shown in Fig. 4. About 95% removal was obtained using a spherical α- Bi₂O₃/H₂O₂ photocatalyst as compared to the spherical CuO, i.e., only 75% removal was obtained under identical treatment conditions. These results of Rh-B degradation show that Bi₂O₃ can effectively degrade the pollutants as compared to the CuO.

Figure 4 shows that the α-Bi₂O₃/H₂O₂ system totally degraded the pollutant in 105 min of treatment time at pH = 7. These show that there is a synergistic effect between the α-Bi₂O₃ and the H₂O₂ system, which leads to greater degradation of the pollutants. Results of α-Bi₂O₃ and H₂O₂ systems were also compared using commercial α-Bi₂O₃ and H₂O₂ systems, which show that comparatively lower degradation of the Rh-B using commercial α-Bi₂O₃ and H₂O₂ systems indicating higher catalytic activity of α-Bi₂O₃ and H₂O₂ system. Further, it was also seen that Rh-B degradation using α-Bi₂O₃/H₂O₂ system shows pseudo-first-order Kinetics with rate constant value = 3.1×10^− 2 min^− 1. Therefore, the Bi₂O₃ photocatalyst was selected for further optimization of the parameter.

4.2. Effect of Operating Parameters

The degradation study of Rh-B dyes was systematically analyzed using Bi₂O₃ photocatalyst, as discussed below.

4.2.1. Effect of Initial Dye Concentration

The influence of the initial concentration of the dye was studied using the Rh-B dye concentration in the range of 10–25 mgL^− 1. Other conditions of parameter were fixed, i.e., α-Bi₂O₃, catalysts dose concentration = 0.20 g L^− 1, pH = 7, Temperature = 20⁰C. It is observed that the degradation efficiency was decreased when dye concentrations increased from 10 − 25 mgL^− 1. The dye degradation efficiency decreased from 97–62% for α-Bi₂O₃, photo catalyst when the concentration of dyes was increased from 10–25 mgL^− 1, as shown in Fig. 5a.

This may be due to the fact that when the initial dye concentration was enhanced, extra dye molecules were adsorbed on the photocatalyst surface, which reduced the penetration of the light and, therefore, the interaction of the oxidant with dye molecules. Because the dye molecules are occupied and many active sites are blocked by dye concentration, the O.H. radical's formation rate also decreases, and therefore, dye degradation decreases. The adsorption of OH⁻ and O₂ on the photocatalysts was reduced, resulting in a less radical generation. Further, photons were prohibited prior to the appearance of the photocatalysts' surface as an outcome of photon adsorption being reduced by the photocatalysts.

At higher initial dye concentrations, the pollutants in the solution increase, and enough catalyst surfaces are not available for pollutants; therefore, the interaction of pollutants with the catalyst decreases, and therefore, removal decreases. Further, at higher dye concentrations, repulsion between particles of dyes takes place, which leads to more dispersion of the pollutant, and therefore, removal of dyes decreases. In the above as − synthesized catalysts, the best dye removal performance was using the α-Bi₂O₃ catalyst system, which shows the best performance of more than 97% RhB degradation within 105 min of treatment time at Rh-B = 10 mg/L. Therefore, for further analysis, an Rh-B = 10 mg/L concentration of dye was selected.

4.2.2. Effect of pH

Initial solution pH is an important factor of solution that has a significant impact on the effectiveness of photocatalysts and is thus regarded as a critical parameter in dye effluent treatment. As a result, analysis of different pH from the range between 3 to 8 was studied (Fig. 5b). An initial dye concentration of Rhoda mine B was fixed at about 10 mgL^− 1 in the presence of UV irradiation, and the catalyst dose was set to 1.0 g/L. The pH of the dye solution was fixed by the addition of hydrochloric acid (HCl) and sodium hydroxide (NaOH). It clearly indicates that the greatest results were achieved in a neutral solution (pH = 7). A zero point charge shows catalysts on the surface that are outwardly positively charged in an acidic medium and negatively charged in a basic medium. The Rhodamine B is an amphoteric dye. A pH lower than the zero point charge improves the adsorption of Rhodamine B dye molecules onto the surface of photocatalysts, which results in better RhB dye degradation in neutral conditions and much less acidic conditions. These two conditions are favorable for the dye degradation because the Rhoda mine dye has a neutral charge due to the presence of a negative charge containing two groups, namely, an amino group (NH₂) and one carboxylic group (COOH). The acidic phase encourages dye adsorbing on the catalyst's surface and increases photo-degradation competence. The photocatalytic degradation of the Rhodamine dye in an acidic medium favored the formation of hydroxy radicals, as can be assumed from the following reaction.

O₂ (ads) + e ^̶ CB → O₂ ^{• ̶} (ads) (1)

H⁺ + •O ^̶_{2 (ads)} → HO^•₂ (2)

2HO → O + HO (3)

O⁻ ₂ + H₂O^• → ^•OH + OH⁻ + O₂ (4)

The maximum RhB removal with α-Bi₂O₃, at different pH of 3, 5, and 7, was found to be around 48–96% (Fig. 5b). Therefore, for further analysis, pH = 7 was selected.

4.2.3 Effect of Catalysts Dose

Another important factor is the effect of catalyst dose on dye degradation, which was studied during the treatment. It is observed thatAs the catalyst dose increased, the dye degradation efficiency successively increased. The effect of catalyst dose was tested from 0.2, 0.5, 1, and 1.5 gL^− 1 in a dye solution of 10 mgL^− 1 concentration and neutral pH = 7 of Rhoda mine B dye (Fig. 5c). It was found that although the dye could be removed by α -Bi₂O₃, dye removal was meaningfully improved by enhancing the dose of each α -Bi₂O₃ from 0.2 − 1.5 gL^− 1. As shown in Fig. 5c, 28–42% RhB was degraded at 105 min when each α − Bi₂O₃ dosage was 0.2 gL^− 1, though a small modification in elimination was attained at the catalyst dose and was enhanced at about 1.5 gL^− 1. This improvement has happened since increased α -Bi₂O₃ dosages could offer additional active sites for H₂O₂ activation. In view of the above, α-Bi₂O₃ was selected as the best catalyst, and the catalyst dosage of 1.5 gL^− 1 was designated as the best quantity in the present study. This really is owing to the greater concentration of catalysts, which limits optimal light absorption and, therefore, reduces the photocatalytic degradation of dye. As a result, an optimal catalyst dosage of 1.5 g/L was used for further analysis.

4.2.4 Effect of Temperature

Temperature is an important parameter in the degradation study of Rh-B dye. The Rh-B degradation was found to be increased with an increase in temperature from 5 to 20^oC as shown in Fig. 5d. A maximum 72% Rh-B degradation after 80 minutes at 20°C was found while the complete Rh-B degradation occurred within 105 minutes at 20°C. This might depend upon the activation energy (E_a) of the molecules.

Further, Chen et al. [34] suggested that higher temperatures show higher removal efficiency of the pollutant under photocatalytic activity. This may be due to the electron-hole recombination system. The oxidation rate of the adsorptive capacities also decreases; therefore, pollutant removal increases at higher temperatures.

4.3. Kinetic study for Photocatalytic Degradation of BPA

Kinetic analysis of the degradation of Rh-B dye was also carried out for the different operating factors of the reactor, such as Rh-B concentration, catalyst dose, initial pH, and temperature. The nth-order kinetics analysis was performed using the power law model [35]. The following equation was used for the analysis.

n^th order: $- \frac{{{\text{d}}{{\text{C}}_{{\text{BPA}}}}}}{{{\text{dt}}}}{\text{=}}{{\text{k}}_{\text{n}}}{{\text{(}}{{\text{C}}_{{\text{BPA}}}}{\text{)}}^{\text{n}}}{\text{ }} \Rightarrow {\text{ }}\frac{1}{{{{{\text{(C}}_{{{\text{BPA}}}}^{{\text{t}}})}^{{\text{n}} - 1}}}} - \frac{1}{{{{{\text{(C}}_{{{\text{BPA}}}}^{{\text{o}}})}^{{\text{n}} - 1}}}}=({\text{n}} - 1){{\text{k}}_{\text{n}}}{\text{t}}$ (5)

where n^th = kinetic rate constant (mol L^− 1) ⁽¹⁻ⁿ⁾ min^− 1, respectively. Errors were reduced using the nonlinear regression analysis method by using average relative error (ARE), which was calculated as follows:

$${\text{ARE(\% )=}}\frac{{{\text{100}}}}{{\text{n}}}{\sum {\left| {\frac{{{{{\text{(C}}_{{{\text{BPA}}}}^{{\text{t}}})}_{{\text{exp}}}} - {{({\text{C}}_{{{\text{BPA}}}}^{{\text{t}}})}_{{\text{cal}}}}}}{{{{{\text{(C}}_{{{\text{BPA}}}}^{{\text{t}}})}_{{\text{exp}}}}}}} \right|} _{\text{i}}}$$

Where ${{\text{(C}}_{{{\text{BPA}}}}^{{\text{t}}})_{{\text{exp}}}}$and ${({\text{C}}_{{{\text{BPA}}}}^{{\text{t}}})_{{\text{cal}}}}$ are the concentration values, experimental and calculated, respectively? Table 1 represents the n^th-order rate constant (k_n) and the order of reaction (n) (Power − law model); it was observed that Rh-B dye degradation best fits the n^th-order kinetics model. Figure 6 shows the fitting of kinetic data by the power law model for the BPA removal with time. The nth order of reaction was found to be 0.1, 0.1, 0.5, and 1.0 for different operating parameters, i.e., catalyst dose, initial pH, temperature, and initial BPA concentration. The kinetics of the degradation was found to be 3.6×10^− 3(mol L^− 1) ⁽¹⁻ⁿ⁾ min^− 1

Table 1

Study of the Pseudo first order, Pseudo second-order, and n^th-order kinetics parameter for the photocatalytic treatment of Rh-B under different range of the operating parameter.
Parameter	n^th-Order Kinetics
	n	k_n	R²	ARE (%)
Catalyst dose (g L^− 1)	Other conditions: (Rh-B)_o =20 mg/L, pH_o=7.0
0.2	0.5	4.6×10^− 2	0.98	1.2
0.5	0.2	4.0×10^− 2	0.99	0.3
1	0.4	4.6×10^− 2	0.98	0.2
1.5	0.6	4.9×10^− 2	0.99	0.5
Initial Rh-B Concentration (mg L^− 1)	Other conditions: (Bi₂O₃)_o= 1.5 g/L, pH_o=7.0
10	0.6	4.8×10^− 2	0.97	0.5
15	0.2	3.6×10^− 3	0.98	0.9
20	0.1	2.5×10^− 3	0.99	0.9
25	0.1	4.6×10^− 3	0.98	2.7
Initial pH_o	Other conditions: (Rh-B)_o=10 mg/L, (Bi₂O₃)_o =1.5 g/L pHo = 7.0
4	0.1	2.6×10^− 2	0.96	1.3
5	0.1	5.6×10^− 2	0.99	3.7
7	0.3	3.6×10^− 3	0.97	2.1
8	0.5	3.7×10^− 3	0.98	0.5
Temperature (^oC)	Other conditions: (Rh-B)_o=10 mg/L, (Bi₂O₃)_o= 1.5 g/L, pH_o=7.0
10	0.5	5.2×10^− 2	0.99	0.2
15	0.8	3.8×10^− 2	0.99	0.06
20	1.0	3.1×10^− 2	0.98	1.2
25	1.0	3.3×10^− 2	0.97	1.5
k_n is nth order kinetic constant ((mg L^− 1) (1^− n) min^− 1). d: ARE is Average relative error (%).

4.4. UV–Visible Analysis of Rhodamine B dye

The UV–visible analysis (200–800 nm) of Rhodamine B dye at the optimal treatment condition with spherical shaped α -Bi₂O₃ was studied, and the obtained results were reported in Fig. 7a. Rhodamine B dye is an amphoteric dye that has maximum absorbance (𝜆_𝑚𝑎𝑥) of RhB at 554 nm at extinction coefficient (E_max=10⁵ M^–1cm^–1). As the treatment time increased, the intensity of the peak at 𝜆_𝑚𝑎𝑥 = 554 nm decreased. After 80 min photo catalysis, the absorption at 554 nm became almost zero representing the auxochrome groups –N(CH₃) nonappearance, which is responsible for the color of the dye (32). The 𝜆_𝑚𝑎𝑥 peaks at 253 nm shift near 209 and 185 nm, a lower wavelength representing the mono aromatic ring's presence in the treatment solution after 80 min of photo catalysis. There are no new absorption wavelengths in the spectrum that provide evidence that triphenylmethane poly-conjugated aromatic ring degradation decreases with time (33). The change in the spectral peak position from higher to shorter wavelength, usually named a hypochromic shift, is owing to the N–de–methylating process. Solvatochromic parameters such as solvent polarity may also be the cause of this shift.

4.5. Reusability of α − Bi₂O₃ Mesosphere

Reusability analysis of photocatalysts is important from an economic and application point of view. After photocatalytic degradation of the pollutant, centrifugation, and filtration took place for the reusability analysis. Four successive Rh-B degradation analyses were carried out using Bi₂O₃ for evaluation of reusability, as shown in Fig. 7b. After each experiment, the solution was centrifuged and filtered, then washed with ethanol and dried at 90 ^oC for 120 min. The reusability analysis of the photocatalyst is shown in Fig. 7b. It is observed that photocatalytic degradation was significantly reduced after 5th run. This may be due to the fact that during washing, some loss of the α-Bi₂O₃ mesosphere from the support surface takes place. Further accumulation of the pollutant on the surface of the photocatalyst reduces the active site available for the interaction of the molecules. Therefore, photocatalytic activity gets reduced after five cycles. After five cycles, the photocatalyst was recovered and calcined at 600^oC for three hours and then reused. The obtained results prove that thermal regeneration of the photocatalyst is more effective. Therefore, it can be said that thermal treatment is an essential process for the used catalyst to regenerate its activity.

4.6. XRD Pattern of α-Bi₂O₃ After Rhoda mine B Dye Removal

Figure 8 shows the XRD pattern of recovered catalysts that are collected after the last cycle of the experimental test. The XRD pattern showed no impurity peaks of the reused catalyst, which shows no photo-corrosion and leaching of the catalyst through the dye reduction. The crystallinity of the post-degradation catalyst is still almost reserved and shows the excellent stability and robustness of the catalyst under the reaction condition.

4.7. Proposed Degradation Mechanism of Rh-B dye:

During the photocatalytic degradation of the pollutant, many intermediate compounds are generated during the reaction. These intermediate compounds help to propose the degradation pathway of the pollutants during UV light is irradiated. Electrospray ionization mass spectra (ESI-MS) were used for the by-product analysis of the product. ESI mass spectrum analysis was carried out at different time intervals during the irradiation process. Based on the m/z values, a degradation pathway was suggested, as shown in Fig. 9. [36]. In the proposed degradation pathway, Rh-B dyes were broken down in m/z = 415, which further produced m/z = 282. This is because when the photo catalyst is exposed to UV light, • O.H. radicals and holes are formed, which attack the central carbon of the RhB, leading to the degradation of the dyes. Following intermediates were formed: N, N-diethyl-N-ethyl rhodamine, N, N-diethyl rhodamine, N-ethyl-N-ethyl rhodamine, and N-ethyl rhodamine, with m/z values of 443, 415, 387, and 359 respectively. Their intermediates were further degraded in other m/z values. [37]. Another pathway involved N-demethylation followed by carboxylation, leading to the generation of an isomerized intermediate with m/z values of 282. These intermediates were then degraded into possible intermediates with m/z values of 268 and 254. Based on the mass results, a fragmentation pathway and intermediates were proposed for the UV-LED light-induced photocatalytic degradation of RhB dye [32].

The resulting intermediates were further oxidized into various products, including glutaric acid (17), adipic acid (18), butane-1,3-diol (19), 3,4-dihydroxybenzoic acid (20), phthalic acid (21) and benzoic acid (22). These products were similar to those reported in previous literature on the degradation of RhB dye using conventional irradiation sources. The oxidized products were ultimately mineralized into CO₂, H₂O, NO₃⁻, and NH₄⁺. This suggests that the photocatalytic degradation under UV-LED light was confirmed by–M.S. analysis and that UV-LED sources can be used as an alternative to conventional UV sources for the development of photocatalytic reactors [38].

In the present study, the chemical precipitation method for the synthesis of α − Bi₂O₃, semiconductor photo catalysts, was used for the degradation analysis of Rh-B dyes. It is found that α − Bi₂O₃ provides higher degradation efficiency for Rh-B degradation compared to the CuO photocatalyst. At the optimum conditions of catalyst dose = 1.5 g/L, pH = 7, RhB concentration = 10 mg/L, temperature = 20⁰C, 97% of Rh-B was removed using α − Bi₂O₃, semiconductor photo catalysts. The X-ray diffraction patterns show that the α -Bi₂O₃ sample has a tetragonal and hexagonal structure, and the CuO sample shows a monoclinic structure. An SEM image of α − Bi₂O₃ particle shows spherical particles of average diameter 48 nm displays. The porous CuO morphology showed the collection of uncertain or thread spheres with different shapes and sizes (∼125 − 175 nm) and average lengths with about 58 nm thickness. The highest 94% degradation of α-Bi₂O₃ in the neutral pH = 7. In a comparison of as − synthesized catalysts, namely CuO, the α-Bi₂O₃ was selected as the good photocatalytic action for the Rhodamine B dye degradation.

Conflict of Interest

All author of the manuscript declare that there is no conflict of interest for the manuscripts.

Suhan MBK, Shuchi SB, Anis A, Haque Z, Islam MS. Comparative degradation study of remazol black B dye using electro – coagulation and electro – Fenton process: Kinetics and cost analysis. Environ Nanatechnol Monit Manage. 2020;14:100335.
Liu Y, Yan A, Ding L, Wei J, Liu Y, Niu Y, Qu R. (2024). Simultaneous and ultrafast removal of anionic and cationic dyes from aqueous solution by Zr-based MOFs hybridized by attapulgite and adsorption performance research. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 680, p.132643.
Zhao J, Duan G, Zhu D, Li J, Zhu Y. (2024). Microbial-influenced pesticide removal co-occurs with antibiotic resistance gene variation in soil-earthworm-maize systems. Environmental Pollution, 342, p.123010.
Wang R, Wang F, Lu Y, Zhang S, Cai M, Guo D, Zheng H. (2024). Spatial distribution and risk assessment of pyrethroid insecticides in surface waters of East China Sea estuaries. Environ Pollut, 123302.
Li J, Yin M, Wang Y, Wang L. Improvement of the conventional flat plate electrode: Application of filtered Pd@ Ti electrode in the removal of toxic chlorinated PPCPs. Sep Purif Technol. 2024;329:125120.
Singh S, Patidar R, Srivastava VC, Kumar P, Singh A, Lo SL. Ellipsoid-shaped copper oxide as an effective peroxymonosulfate activator for perfluorooctanoic acid decomposition. Mater Today Commun. 2023;34:105107.
Batra V, Kaur I, Pathania D, Chaudhary V. Efficient dye degradation strategies using green synthesized ZnO – based nanoplatforms: A review. Appl Surf Sci Adv. 2022;11:100314.
Lanjwani MF, Tuzen M, Khuhawar MY, Saleh TA. (2024). Trends in photocatalytic degradation of organic dye pollutants using nanoparticles: a review. Inorganic Chemistry Communications, 159, p.111613.
Waghchaure RH, Adole VA, Jagdale BS. (2022). Photocatalytic degradation of methylene blue, rhodamine B, methyl orange and Eriochrome black T dyes by modified ZnO nanocatalysts: A concise review. Inorg Chem Commun, 109764.
Patidar R, Srivastava VC. Mechanistic and kinetic insights of synergistic mineralization of ofloxacin using a sono-photo hybrid process. Chem Eng J. 2021;403:125736.
Alavi M, Karimi N, Salimikia I. Photosynthesis of zinc oxide nanoparticles and its antibacterial, anti-quorum sensing, antimotility, and antioxidant capacities against multidrug-resistant bacteria. J Ind Eng Chem. 2019;72:457–73.
Molla A, Li Y, Mandal B, Kang SG, Hur SH, Chung JS. Selective adsorption of organic dyes on graphene oxide: Theoretical and experimental analysis. Appl Surf Sci. 2019;464:170–7.
Gan Y, Ding C, Xu B, Liu Z, Zhang S, Cui Y, Wu B, Huang W, Song X. Antimony (Sb) pollution control by coagulation and membrane filtration in water/wastewater treatment: A comprehensive review. J Hazard Mater. 2023;442:130072.
Anisuzzaman SM, Joseph CG, Pang CK, Affandi NA, Maruja SN, Vijayan V. Current Trends in the Utilization of Photolysis and Photocatalysis Treatment Processes for the Remediation of Dye Wastewater: A Short Review. ChemEngineering. 2022;6(4):58.
Palanisamy S, Nachimuthu P, Awasthi MK, Ravindran B, Chang SW, Palanichamy M, Nguyen DD. Application of electrochemical treatment for the removal of triazine dye using aluminum electrodes. J Water Supply: Res Technol – Aqua. 2020;69(4):345–54.
Dehane A, Merouani S. Dyes Sonolysis: An Industrial View of Process Intensification Using Carbon Tetrachloride. Advanced Oxidation Processes in Dye – Containing Wastewater. Singapore: Springer; 2022. (115 – 145).
Sarfo DK, Kaur A, Marshall DL, O'Mullane AP. (2023). Electrochemical degradation and mineralisation of organic dyes in aqueous nitrate solutions. Chemosphere, 316, p.137821.
Wen Y, Chen J, Gao X, Che H, Wang P, Liu B, Ao Y. Piezo – enhanced photocatalytic performance of ZnO nanorod array for pollutants degradation in dynamic water: Insight into the effect of velocity and inner flow field. Nano Energy. 2022;101:107614.
Seror SB, Shamir D, Albo Y, Kornweitz H, Burg A. (2022). Elucidation of a mechanism for the heterogeneous electro – fenton process and its application in the green treatment of azo dyes. Chemosphere, 286, p.131832.
Rizwan K, Bilal M, Slimani Y, Show PL, Rtimi S, Roy A, Iqbal HM. Hydrogen-based sono-hybrid catalytic degradation and mitigation of industrially-originated dye-based pollutants. Int J Hydrog Energy. 2023;48(17):6597–612.
Patidar R, Srivastava VC. Mechanistic insight into ultrasound-induced enhancement of electrochemical oxidation of ofloxacin: Multi-response optimization and cost analysis. Chemosphere. 2020;257:127121.
Bera KK, Chakraborty M, Mondal M, Banik S, Bhattacharya SK. Synthesis of α-β Bi2O3 heterojunction photocatalyst and evaluation of reaction mechanism for degradation of RhB dye under natural sunlight. Ceram Int. 2020;46(6):7667–80.
Xu D, Ma H. Degradation of rhodamine B in water by ultrasound-assisted TiO₂ photocatalysis. J Clean Prod. 2021;313:127758.
Qin Q, Qiao N, Liu Y. Spongelike porous CuO as an efficient peroxymonosulfate activator for degradation of Acid Orange 7. Appl Surf Sci. 2020;521:146479.
Hajra S, Oh Y, Sahu M, Lee K, Kim HG, Panigrahi BK, Mistewicz K, Kim HJ. Piezoelectric nanogenerator based on flexible PDMS–BiMgFeCeO₆ composites for sound detection and biomechanical energy harvesting. Sustainable Energy Fuels. 2021;5(23):6049–58.
Molkenova A, Sarsenov S, Atabaev S, Khamkhash L, Atabaev TS. (2021). Hierarchically-structured hollow CuO microparticles for efficient photo-degradation of a model pollutant dye under the solar light illumination. Environmental Nanotechnology, Monitoring & Management, 16, p.100507.
Ali O, Alkanad K, Shekar GS, Hezam A, Lokanath NK. (2023). Synthesis, structural and morphological characterization of α-Bi2O3 nanostructure for photocatalytic hydrogen production and degradation of organic pollutants. Materials Today: Proceedings.
Parvaz S, Rabbani M, Rahimi R. (2021). Fabrication of novel magnetic ZnO hollow spheres/pumice nanocomposites for photo-degradation of Rhodamine B under visible light irradiation. Materials Science and Engineering: B, 263, p.114863.
Wahba MA, Yakout SM, Abdel-Monem YK, Hammood AAA. (2023). Simple and Easy Control-Synthesis of Pure α-Bi2O3 and Bi2O2CO3: Morphological, Optical and Solar Photon-Energy Photocatalytic Studies. Chemistry Africa,1–13.
Mushtaq Q, Joly N, Martin P, Qazi JI. Optimization of Alkali Treatment for Production of Fermentable Sugars and Phenolic Compounds from Potato Peel Waste Using Topographical Characterization and FTIR Spectroscopy. Molecules. 2023;28(21):7250.
Singh G, Dwivedi SK. (2020). Decolorization and degradation of Direct Blue-1 (Azo dye) by newly isolated fungus Aspergillus terreus GS28, from sludge of carpet industry. Environmental Technology & Innovation, 18, p.100751.
Singh S, Srivastava VC, Lo S, Mandal TK, Naresh G. Morphology-controlled green approach for synthesizing the hierarchical self-assembled 3D porous ZnO superstructure with excellent catalytic activity. Microporous Mesoporous Mater. 2017;239:296–309.
Singh S, Srivastava VC, Lo S, Mandal TK, Naresh G. Morphology-controlled green approach for synthesizing the hierarchical self-assembled 3D porous ZnO superstructure with excellent catalytic activity. Microporous Mesoporous Mater. 2017;239:296–309.
Chen D, Cheng Y, Zhou N, Chen P, Wang Y, Li K, Huo S, Cheng P, Peng P, Zhang R, Wang L. Photocatalytic degradation of organic pollutants using TiO2-based photocatalysts: A review. J Clean Prod. 2020;268:121725.
Patidar R, Srivastava VC. (2020). Mechanistic insight into ultrasound-induced enhancement of electrochemical oxidation of ofloxacin: Multi-response optimization and cost analysis. Chemosphere, 257, p.127121.
He Z, Sun C, Yang S, Ding Y, He H, Wang Z. Photocatalytic degradation of rhodamine B by Bi2WO6 with electron accepting agent under microwave irradiation: mechanism and pathway. J Hazard Mater. 2009;162(2–3):1477–86.
Natarajan TS, Thomas M, Natarajan K, Bajaj HC, Tayade RJ. Study on UV-LED/TiO₂ process for degradation of Rhodamine B dye. Chem Eng. 2011;169:126–34.
Pinheiro LRS, Gradíssimo DG, Xavier LP, Santos AV. Degradation of Azo Dyes: bacterial potential for bioremediation. Sustainability. 2022;14(3):1510.

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Mechanistic insight into Photocatalytic mineralization of dyes using metal oxide- Parametric and kinetic study

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material and Methods

2.1. Chemicals

2.2 Experimental Procedure

2.3. Preparation and Characterization of Nanocatalyst

3. Results and Discussion

3.1. Characterization of Materials

3.1.1. X − ray diffraction analysis:

4. Photocatalytic Activity

4.1. Comparative Photocatalytic Activity of Bi₂O₃ and CuO Nanocomposite

4.2. Effect of Operating Parameters

4.2.1. Effect of Initial Dye Concentration

4.2.2. Effect of pH

2HO → O + HO (3)

4.2.3 Effect of Catalysts Dose

4.2.4 Effect of Temperature

4.3. Kinetic study for Photocatalytic Degradation of BPA

4.4. UV–Visible Analysis of Rhodamine B dye

4.5. Reusability of α − Bi₂O₃ Mesosphere

4.6. XRD Pattern of α-Bi₂O₃ After Rhoda mine B Dye Removal

4.7. Proposed Degradation Mechanism of Rh-B dye:

Conclusions

Declarations

Conflict of Interest

References

Status:

Version 1

Mechanistic insight into Photocatalytic mineralization of dyes using metal oxide- Parametric and kinetic study

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material and Methods

2.1. Chemicals

2.2 Experimental Procedure

2.3. Preparation and Characterization of Nanocatalyst

3. Results and Discussion

3.1. Characterization of Materials

3.1.1. X − ray diffraction analysis:

4. Photocatalytic Activity

4.1. Comparative Photocatalytic Activity of Bi2O3 and CuO Nanocomposite

4.2. Effect of Operating Parameters

4.2.1. Effect of Initial Dye Concentration

4.2.2. Effect of pH

2HO → O + HO (3)

4.2.3 Effect of Catalysts Dose

4.2.4 Effect of Temperature

4.3. Kinetic study for Photocatalytic Degradation of BPA

4.4. UV–Visible Analysis of Rhodamine B dye

4.5. Reusability of α − Bi2O3 Mesosphere

4.6. XRD Pattern of α-Bi2O3 After Rhoda mine B Dye Removal

4.7. Proposed Degradation Mechanism of Rh-B dye:

Conclusions

Declarations

Conflict of Interest

References

Status:

Version 1

4.1. Comparative Photocatalytic Activity of Bi₂O₃ and CuO Nanocomposite

4.5. Reusability of α − Bi₂O₃ Mesosphere

4.6. XRD Pattern of α-Bi₂O₃ After Rhoda mine B Dye Removal