Step-scheme BiVO4/WO3 heterojunction photocatalyst under visible LED light irradiation removing 4-chlorophenol in aqueous solutions

Degradation of organic Pollutant by Using of BiVO4-NiFe2O4 Heterostructure Photocatalyst under Visible Light Irradiation: Assessment of Detoxicity Study Using Cirrhinus mrigala

The current study mainly concentrates on the photocatalytic activity of composite nanomaterial of BiVO4 (BVO), NiFe2O4 (NFO), and BiVO4-NiFe2O4 (BVO-NFO) under visible light. Among these, BVO-NFO composite degrades crystal violet dye within 60 min with a percentage degradation of 95.65% under visible light illumination. The BVO-NFO composite exhibits better photodegradation performance, which can be attributed to the effective light absorption and reduced recombination of the photoexcited charge carriers. Additionally, by applying a magnetic field, the BVO-NFO composite can be magnetically recovered by using the magnet for subsequent recycling. The synthesized composite was characterized using optical techniques like X-ray diffraction, ultraviolet diffuse reflectance spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, and energy dispersive X-ray analysis. The effect of dye, before and after degradation, on vital organs of fish species was examined such as fish gill (pulmonary-toxicity), fish liver (hepato-toxicity), fish kidney (renal toxicity), fish brain (neural toxicity), and fish muscle (myopathy). This work offers a clear and practical method for designing a highly crystalline semiconductor photocatalyst for dye degradation and the remediation of industrial wastewater.

Degradation of 2,4-dinitrotoluene in aqueous solution by dielectric barrier discharge plasma combined with Fe-RGO-BiVO4 nanocomposite

2,4-Dinitrotoluene (2,4-DNT) as a priority and hazardous pollutant, is widely used in industrial and military activities. In this study the synergistic effect of Fe-RGO-BiVO4 nanocomposite in a non-thermal dielectric barrier discharge plasma reactor (NTP-DBD) for degrading 2,4-DNT was evaluated. Preparation of the Fe-RGO-BiVO4 nanocomposite was done by a stepwise chemical method depositing Fe and reduced graphene oxide (RGO) on BiVO4. Field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), UV-vis diffuse reflectance spectra (DRS), and energy-dispersive X-ray spectroscopy mapping (EDS-mapping) validated the satisfactory synthesis of Fe-RGO-BiVO4. To find the optimal conditions and to determine the interaction of model parameters, a central composite design (RSM-CCD) had been employed. 2,4 DNT can be completely degraded at: initial 2,4-DNT concentration of 40 mg L-1, Fe-RGO-BiVO4 dosage of 0.75 g L-1, applied voltage of 21kV, reaction time of 30 min and pH equal to 7, while the single plasma process reached a degradation efficiency of 67%. The removal efficiency of chemical oxygen demand (COD) and total organic carbon (TOC) were 90.62% and 88.02% at 30 min contact time, respectively. Results also indicated that average oxidation state (AOS) and carbon oxidation state (COS) were enhanced in the catalytic NTP-DBD process, which demonstrate the effectiveness of proposed process for facilitating biodegradability of 2,4-DNT.

Enhanced hydroxyl radical generation for micropollutant degradation in the In2O3/Vis-LED process through the addition of periodate

Periodate (PI) as an oxidant has been extensively studied for organic foulants removal in advanced oxidation processes. Here PI was introduced into In2O3/Vis-LED process to enhance the formation of ·OH for promoting the degradation of organic foulants. Results showed that the addition of PI would significantly promote the removal of sulfamethoxazole (SMX) in the In2O3/Vis-LED process (from 9.26% to 100%), and ·OH was proved to be the dominant species in the system. Besides, the process exhibited non-selectivity in the removal of different organic foulants. Comparatively, various oxidants (e.g., peroxymonosulfate, peroxydisulfate, and hydrogen peroxide) did not markedly promote the removal of SMX in the In2O3/Vis-LED process. Electrochemical analyses demonstrated that PI could effectively receive photoelectrons, thus inhibiting the recombination of photogenerated electron-hole (e-/h+) pairs. The holes then oxidized the adsorbed H2O to generate ·OH, and the PI converted to iodate at the same time. Additionally, the removal rate of SMX reduced from 100% to 17.2% as Vis-LED wavelengths increased from 440 to 560 nm, because of the low energy of photons produced at longer wavelengths. Notably, the species of PI do not affect its ability to accept electrons, resulting in the degradation efficiency of SMX irrespective of pH (4.0-10.0). The coexistence of inorganic cations and anions (such as Cl-, CO32-/HCO3-, SO42-, Ca2+, and Mg2+) also had an insignificant effect on SMX degradation. Furthermore, the process also showed excellent degradation potential in real water. The proposed strategy provides a new insight for visible light-catalyzed activation of PI and guidance to explore green catalytic processes for high-efficiency removal of various organic foulants.

Impact of alternate Mn doping in ternary nanocomposites on their structural, optical and antimicrobial properties: Comparative analysis of photocatalytic degradation and antibacterial activity

The present study was done to investigate and compare the photocatalytic and antibacterial activity of two in situ Manganese doped ternary nanocomposites. The dual ternary hybrid systems comprised Mn-doped Ag₂WO₄ coupled with MoS₂-GO and Mn-doped MoS₂ coupled with Ag₂WO₄-GO. Both hierarchical alternate Mn-doped ternary heterojunctions formed efficient plasmonic catalysts for wastewater treatment. The novel nanocomposites were well-characterized using XRD, FTIR, SEM-EDS, HR-TEM, XPS, UV-VIS DRS, and PL techniques confirming the successful insertion of Mn⁺² ions in respective host substrates. The bandgap of the ternary nanocomposites evaluated by the tauc plot showed them visible light-active nanocomposites. The photocatalytic ability of both Mn-doped coupled nanocomposites was investigated against the dye methylene blue. Both ternary nanocomposites showed excellent sunlight harvesting ability for dye degradation in 60 min. The maximum catalytic efficiency of both photocatalysts was obtained at a solution pH value of 8, photocatalyst dose and oxidant dose of 30 mg/100 mL and 1 mM for Mn-Ag₂WO₄/MoS₂-GO, 50 mg/100 mL, 3 mM for Mn-MoS₂/Ag₂WO₄-GO keeping IDC of 10 ppm for all photocatalysts. The nanocomposites showed excellent photocatalytic stability after five successive cycles. The response surface methodology was used as a statistical tool for the evaluation of the photocatalytic response of several interacting parameters for dye degradation by ternary composites. The antibacterial activity was determined by the inactivation of gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria by support-based doped ternary hybrids.

Kinetic studies of dexamethasone degradation in aqueous solution via a photocatalytic UV/H2O2/MgO process

Wastewaters discharged from different industries and hospitals may contain pharmaceuticals, especially dexamethasone (DEX). Thus, we applied the UV/H₂O₂ photocatalytic method in the presence of the MgO nanoparticles to remove dexamethasone from synthetic wastewater. Moreover, the effects of parameters such as pH (3-11), hydrogen peroxide concentration (1-8 mM), initial DEX concentration (5-30 mg/L), and catalyst dosage (0.01-0.2 g/L) during the reaction times (0-30 min) were investigated. Furthermore, the efficiency of UV/H₂O₂ in the presence and absence of catalysts was investigated. The photocatalyst is characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and Fourier-transform infrared spectroscopy (FTIR) techniques. It was found that the removal rate was enhanced by decreasing pH and the initial dexamethasone concentration. The removal rate was enhanced somewhat with concentrations of hydrogen peroxide and MgO. In the case of UV/H₂O₂/MgO, 87% removal efficiency was achieved, under the optimal conditions: pH 3, contact time of 30 min, dexamethasone concentration of 20 mg/L, H₂O₂ of 0.5 mM, and UV radiation of 55 watts. The kinetic data indicated that the reaction followed the second-order kinetic model. The results showed that the UV/H₂O₂ photochemical process can efficiently remove dexamethasone from aqueous in the presence of a MgO catalyst, and the mineralization efficiency was reached at about 98%.

Enhanced synchronous photocatalytic 4-chlorophenol degradation and Cr(VI) reduction by novel magnetic separable visible-light-driven Z-scheme CoFe2O4/P-doped BiOBr heterojunction nanocomposites

The co-existence of organic contaminants and heavy metals including 4-chlorophenol (4-CP) and Cr(VI) in aquatic system have become a challenging task in the wastewater treatment. Herein, the synchronous photocatalytic decomposition of 4-CP and Cr(VI) over new Z-scheme CoFe₂O₄/P-BiOBr heterojunction nanocomposites were revealed. In this work, the nanocomposites were successfully developed via a surfactant-free hydrothermal method. The heterojunction interface was created by decorating magnetic CoFe₂O₄ nanoparticles onto P-BiOBr nanosheets. The as-fabricated CoFe₂O₄/P-BiOBr nanocomposites substantially improved the synchronous decomposition of 4-CP and Cr(VI) compared to the single-phase component samples under visible light irradiation. Particularly, the 30-CoFe₂O₄/P-BiOBr nanocomposite displayed the best photocatalytic performance, which decomposed 95.6% 4-CP and 100% Cr(VI) within 75 min. The photocatalytic improvement was assigned to the Z-scheme heterojunction assisted charge migration between CoFe₂O₄ and P-BiOBr, and the acceleration of charge carrier separation was validated by the findings of charge dynamics measurements. The harmful 4-CP was photodegraded into smaller organics whereas the Cr(VI) was photoreduced into Cr(III) after 30-CoFe₂O₄/P-BiOBr photocatalysis, and the good recyclability of fabricated nanocomposite in photocatalytic reaction also showed promising potential for practical applications in environmental remediation. Finally, the radical quenching tests confirmed that there existed the Z-scheme path of charge migration in CoFe₂O₄/P-BiOBr nanocomposite, which was the mechanism responsible for its high photoactivity.

Emerging S-Scheme Photocatalyst

Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S-scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state-of-the-art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type-II and Z-scheme heterojunctions, S-scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S-scheme heterojunction are proposed and four types of S-scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S-scheme heterojunction are presented. Finally, different photocatalytic applications of S-scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S-scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S-scheme heterojunction photocatalyst are critically discussed.