Zinc vanadium oxide coupled carbon nitride nanocomposite for photocatalytic carbon dioxide reduction to methanol

Photocatalytic reduction of carbon dioxide (CO2) with water (H2O) into solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. The main objective of this study was to design and fabricate photoreactor system and to synthesize Z-scheme assembly of reduced graphene oxide (RGO) and protonated carbon nitride (pCN) based zinc vanadium oxide (ZnV2O6) nanocomposite for selective photoreduction of CO2 to solar fuels. The pure ZnV2O6, ZnV2O6/RGO, ZnV2O6/pCN and ZnV2O6/RGO/pCN nanocomposites were synthesized by a single step solvothermal method. The performance of nanocomposite catalysts was investigated in a liquid and gas phase photocatalytic systems under UV and visible light irradiations. The most effective catalyst in liquid phase system was ZnV2O6/RGO/pCN which gave a maximum methanol yield of 3726.7 µmol g-cat-1 using photoreactor without reflector and 5207.2 µmol g-cat-1 using photoreactor with reflector. Performance comparison revealed 1.4 times higher yield rate in photoreactor with reflector compared to photoreactor without reflector. Besides, weight percent ratio, effect of time and stability contributed significantly to enhance reactor performances. Using gas phase system, ZnV2O6/RGO/pCN nanocomposite demonstrated excellent photoactivity in the reduction of CO2 into carbon monoxide (CO), hydrogen (H2), methane (CH4) and methanol (CH3OH) under visible light irradiation. The CO evolution rate as a main product over ZnV2O6/RGO/pCN nanocomposite of 3756 µmol g-cat-1 was obtained. The quantum efficiency of 14.2 % was achieved for CH3OH production in a photoreactor with reflector, followed by 10.4 % and 0.25 % in photoreactor without reflector and fixed-bed photoreactor, respectively under visible light irradiation. Finally, Langmuir-Hinshelwood kinetic model was developed to investigate adsorption behaviors and photocatalytic oxidation and reduction process. In conclusion, solar photoreactor with reflector and modified ZnV2O6 nanocatalysts could make markedly higher CO2 reduction to fuels

Well-designed ZNV2O6/G-C3N4 2D/2D nanosheets heterojunction with faster charges separation via pcn as mediator towards enhanced photocatalytic reduction of CO2 to fuels

Fabrication of well-designed 2D/2D heterojunction composite with effective interfacial contact by incorporating zinc vanadium oxide (ZnV2O6) and protonated g-C3N4 (pCN) for enhanced photocatalytic CO2 reduction has been investigated. The 2D/2D ZnV2O6/pCN samples, synthesized by a one-pot solvothermal method, were analysed using XRD, SEM, EDX-mapping, TEM, N2 sorption, XPS, UV–vis, RAMAN and PL characterization techniques. It was observed that surface charge modification through protonation of graphitic carbon nitride serves as a mediator and trapped photo-excited electrons. The performance of composite catalysts was investigated in a liquid and gas phase photocatalytic systems under UV and visible light irradiations. Using slurry system, CH3OH production rate enhanced up to 3742 μmol g-cat−1 over ZnV2O6/pCN, 1.15 and 5 times higher than the pure ZnV2O6 (3254 μmol g-cat−1) and pCN (753 μmol g-cat−1) samples, respectively. Instead, the CO evolution rate as a main product over ZnV2O6/pCN nanosheets of 3237 μmol g-cat−1 was obtained using gas phase system. This enhanced activity can be mainly ascribed to the addition of pCN with ZnV2O6 in a controlled ratio as well as synergistic effect of ZnV2O6/pCN nanosheet heterojunctions. Besides, hierarchical structure, higher interfacial interaction, abundant 2D coupling interfaces and efficient separation of charges could efficiently promote both the photo-activity and products selectivity. The obtained ZnV2O6/pCN 2D/2D nanosheets heterojunction with a mediator exhibited excellent photocatalytic stability, which prevailed even after 32 h of operation time for continuous CH3OH production. The possible reaction mechanism anticipated to understand the movement of electrons and holes for CO2 reduction over the ZnV2O6/pCN photocatalyst

Indirect Z-scheme assembly of 2D ZnV2O6/RGO/g-C3N4 nanosheets with RGO/pCN as solid-state electron mediators toward visible-light enhanced CO2 reduction

Indirect Z-scheme assembly of graphene-bridged 2D ZnV2O6/pCN nanosheets composite has been fabricated by one-step solvothermal process and tested for photoinduced CO2 conversion under visible-light irradiations. The highest CH3OH production of 3488 μmol g-cat−1 was obtained over ZnV2O6/RGO/g-C3N4 composite, 1.02 and 1.25 times higher comparing to ZnV2O6/RGO and ZnV2O6/g-C3N4 samples, respectively. This enhanced efficiency can be ascribed to well-designed ternary heterojunction with hierarchical structure and efficient charges separation by RGO. More importantly, CH3OH yield was further improved by introducing RGO/pCN as an electron sink, which led to a 1.07 times higher yield than using only RGO. This reveals that ternary 2D ZnV2O6/RGO/pCN nanostructure has higher visible-light absorption, improved charge separation, and enhanced photocatalytic efficiency due to RGO/pCN as multiple mediators. The stability of composite catalyst also prevailed for 32 h for continuous CH3OH production. Therefore, structured Z-scheme composite with multiple electron mediators enables efficient CO2 conversion under visible-light irradiation

Development of Ag-Doped ZnO Thin Films and Thermoluminescence (TLD) Characteristics for Radiation Technology

This work examined the thermoluminescence dosimetry characteristics of Ag-doped ZnO thin films. The hydrothermal method was employed to synthesize Ag-doped ZnO thin films with variant molarity of Ag (0, 0.5, 1.0, 3.0, and 5.0 mol%). The structure, morphology, and optical characteristics were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and UV–vis spectrophotometers. The thermoluminescence characteristics were examined by exposing the samples to X-ray radiation. It was obtained that the highest TL intensity for Ag-doped ZnO thin films appeared to correspond to 0.5 mol% of Ag, when the films were exposed to X-ray radiation. The results further showed that the glow curve has a single peak at 240–325 °C, with its maximum at 270 °C, which corresponded to the heating rate of 5 °C/s. The results of the annealing procedures showed the best TL response was found at 400 °C and 30 min. The dose–response revealed a good linear up to 4 Gy. The proposed sensitivity was 1.8 times higher than the TLD 100 chips. The thermal fading was recorded at 8% for 1 Gy and 20% for 4 Gy in the first hour. After 45 days of irradiation, the signal loss was recorded at 32% and 40% for the cases of 1 Gy and 4 Gy, respectively. The obtained optical fading results confirmed that all samples’ stored signals were affected by the exposure to sunlight, which decreased up to 70% after 6 h. This new dosimeter exhibits good properties for radiation measurement, given its overgrowth (in terms of the glow curve) within 30 s (similar to the TLD 100 case), simple annealing procedure, and high sensitivity (two times that of the TLD 100)

Fabricating 2D/2D/2D heterojunction of graphene oxide mediated g-C3N4 and ZnV2O6 composite with kinetic modelling for photocatalytic CO2 reduction to fuels under UV and visible light

Two dimensional (2D) reduced-graphene-oxide/g-C3N4 modified 2D ZnV2O6 heterojunction for enhanced photocatalytic CO2 reduction has been investigated. The catalysts were fabricated using one-pot solvothermal method and were tested in a fixed-bed reactor under visible and UV-light. The ZnV2O6/RGO/g-C3N4 composite catalyst demonstrated excellent photoactivity for CO2 reduction to CO and hydrocarbons under visible light. The maximum CO yield rate of 2802.9 µmol g-1 h-1 was obtained over the composite, which is 7.4 and 1.7 times higher than using g-C3N4 and ZnV2O6, respectively. The improved activity attributing to synergistic effect of 2D layer heterojunction with enhanced charges separation by RGO mediator under visible light. Comparatively, 2 times lower productivity was obtained under UV-light than visible-light due to higher visible-light absorption. The time-dependent kinetic-model was further developed to understand the influence of photocatalytic oxidation and reduction processes on the reaction chemistry. The model is based on Langmuir–Hinshelwood (L–H) mechanism to understand the formation rates of products during photocatalytic CO2 conversion with water vapours. Kinetic reveals surface reaction is a rate limiting step, which depends on the generation of charge carrier with higher light absorption. The findings from the experimental and kinetic-model would be useful to understand photo-catalytic reaction engineering in solar energy applications. Graphical abstract: [Figure not available: see fulltext.

Optimization of As(V) Removal by Dried Bacterial Biomass: Nonlinear and Linear Regression Analysis for Isotherm and Kinetic Modelling

Arsenic occurrence and toxicity records in various industrial effluents have prompted researchers to find cost-effective, quick, and efficient methods for removing arsenic from the environment. Adsorption of As(V) onto dried bacterial biomass is proposed in the current work, which continues a line of previous research. Dried bacterial biomass of WS3 (DBB) has been examined for its potential to remove As(V) ions from aqueous solutions under various conditions. Under optimal conditions, an initial concentration of 7.5 ppm, pH 7, adsorbent dose of 0.5 mg, and contact period of 8 h at 37 °C results in maximum removal of 94%. Similarly, amine, amide, and hydroxyl groups were shown to contribute to As(V) removal by Fourier transform infrared spectroscopy (FTIR), and the adsorption of As(V) in the cell wall of DBB was verified by FESEM-EDX. In addition, equilibrium adsorption findings were analyzed using nonlinear and linear isotherms and kinetics models. The predicted best-fit model was selected by calculating the coefficient of determination (R2). Adsorption parameters representative of the adsorption of As(V) ions onto DBB at R2 values were found to be more easily attained using the nonlinear Langmuir isotherm model (0.95). Moreover, it was discovered that the nonlinear pseudo-second-order rate model using a nonlinear regression technique better predicted experimental data with R2 than the linear model (0.98). The current study verified the nonlinear approach as a suitable way to forecast the optimal adsorption isotherm and kinetic data

Optimization of As(V) Removal by Dried Bacterial Biomass: Nonlinear and Linear Regression Analysis for Isotherm and Kinetic Modelling

Arsenic occurrence and toxicity records in various industrial effluents have prompted researchers to find cost-effective, quick, and efficient methods for removing arsenic from the environment. Adsorption of As(V) onto dried bacterial biomass is proposed in the current work, which continues a line of previous research. Dried bacterial biomass of WS3 (DBB) has been examined for its potential to remove As(V) ions from aqueous solutions under various conditions. Under optimal conditions, an initial concentration of 7.5 ppm, pH 7, adsorbent dose of 0.5 mg, and contact period of 8 h at 37 °C results in maximum removal of 94%. Similarly, amine, amide, and hydroxyl groups were shown to contribute to As(V) removal by Fourier transform infrared spectroscopy (FTIR), and the adsorption of As(V) in the cell wall of DBB was verified by FESEM-EDX. In addition, equilibrium adsorption findings were analyzed using nonlinear and linear isotherms and kinetics models. The predicted best-fit model was selected by calculating the coefficient of determination (R2). Adsorption parameters representative of the adsorption of As(V) ions onto DBB at R2 values were found to be more easily attained using the nonlinear Langmuir isotherm model (0.95). Moreover, it was discovered that the nonlinear pseudo-second-order rate model using a nonlinear regression technique better predicted experimental data with R2 than the linear model (0.98). The current study verified the nonlinear approach as a suitable way to forecast the optimal adsorption isotherm and kinetic data

Suitability of treated wastewater for irrigation and its impact on groundwater resources in arid coastal regions: Insights for water resources sustainability

Water scarcity threatens agriculture and food security in arid regions like Saudi Arabia. The nation produces significant quantities of municipal wastewater, which, with adequate treatment, could serve as an alternative water source for irrigation, thereby reducing reliance on fossil and non-renewable groundwater. This study assessed the appropriateness of using treated wastewater (TWW) for irrigation in a dry coastal agricultural region in Eastern Saudi Arabia and its impact on groundwater resources. Field investigations were conducted in Qatif to collect water samples and field measurements. A multi-criteria approach was applied to evaluate the TWW's suitability for irrigation, including complying with Saudi Standards, the Irrigation Water Quality Index (IWQI), the National Sanitation Foundation water quality index (NSFWQI), and the individual irrigation indices. In addition, the impact of TWW on groundwater was assessed through hydrogeological and isotope approaches. The results indicate that the use of TWW in the study area complied with the Saudi reuse guidelines except for nitrate, aluminum, and molybdenum. However, irrigation water quality indices classify TWW as having limitations that necessitate the use for salt-tolerant crops on permeable and well-drained soils. Stable isotopic analysis (δ2H, δ18O) revealed that long-term irrigation with TWW affected the shallow aquifer, while deep aquifers were minimally impacted due to the presence of aquitard layer. The application of TWW irrigation has successfully maintained groundwater sustainability in the study area, as evidenced by increased groundwater levels up to 2.3 m. Although TWW contributes to crop productivity, long term agricultural sustainability could be enhanced by improving effluent quality, regulating irrigation practices, implementing buffer zones, and monitoring shallow groundwater. An integrated approach that combines advanced wastewater treatment methods, community involvement, regulatory oversight, and targeted monitoring is recommended to be implemented