A sustainable solution for removal of glutaraldehyde in saline water with visible light photocatalysis

Unique effect of bromide ion on intensification of advanced oxidation processes for pollutants removal: A systematic review

Advanced oxidation processes (AOPs) have been developed to decompose toxic pollutants to protect the aquatic environment. AOP has been considered an alternative treatment method for wastewater treatment. Bromine is present in natural waters posing toxic effects on human health and hence, its removal from drinking water sources is necessary. Of the many techniques advanced oxidation is covered in this review. This review systematically examines literature published from 1997 to April 2024, sourced from Scopus, PubMed, Science Direct, and Web of Science databases, focusing on the efficacy of AOPs for pollutant removal from aqueous solutions containing bromide ions to investigate the impact of bromide ions on AOPs. Data and information extracted from each article eligible for inclusion in the review include the type of AOP, type of pollutants, and removal efficiency of AOP under the presence and absence of bromide ion. Of the 1784 documents screened, 90 studies met inclusion criteria, providing insights into various AOPs, including UV/chlorine, UV/PS, UV/H2O2, UV/catalyst, and visible light/catalyst processes. The observed impact of bromide ion presence on the efficacy of AOP processes, alongside the AOP method under scrutiny, is contingent upon various factors such as the nature of the target pollutant, catalyst type, and bromide ion concentration. These considerations are crucial in selecting the best method for removing specific pollutants under defined conditions. Challenges were encountered during result analysis included variations in experimental setups, disparities in pollutant types and concentrations, and inconsistencies in reporting AOP performance metrics. Addressing these parameters in research reports will enhance the coherence and utility of subsequent systematic reviews.

Electrostatic self-assembled layered polymers form supramolecular heterojunction catalyst for photocatalytic reduction of high-stability nitrate in water

In this work, two polymers are connected by electrostatic self-assembly method to form a supramolecular heterojunction to remove pollutants. g-C₃N₄-Cl/PANI catalyst can be used for photocatalytic reduction of nitrate in water, and the nitrogen selectivity reaches 98.2%. Specially, charge density analysis and comparative experiments showed that the introduction of covalent chlorine increased in electron transfer conduction between layers. In addition, differential charge density and solid EPR tests reveal high electron density and electron transfer pathways for supramolecular heterostructures. The results of the work function give direct evidence for the high catalytic performance of the supramolecular heterojunction. The reasons and active species of photocatalytic reduction of nitrate by g-C₃N₄-Cl and g-C₃N₄-Cl/PANI are compared. The catalyst exhibits the performance of highly reducing nitrate to harmless nitrogen with the contribution of supramolecular heterojunction and covalent chlorine. In short, a new idea of constructing a supramolecular photocatalyst is proposed, which can be applied to efficiency reduce nitrate in water.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

Effective blockage of chloride ion quenching and chlorinated by-product generation in photocatalytic wastewater treatment

Photocatalytic degradation of pollutants in high salinity wastewater usually shows extremely low activities and produces highly toxic by-products, often related to the presence of excess chloride ion (Cl^-). Herein, we report for the first time that involvement of Cl^- (quenching active species and generating chlorinated by-products) could be effectively blocked during photocatalytic processes. Based on a comprehensive investigation of its mechanism, we found that Cl^- could quench superoxide radicals (O₂^-) through a cyclic indirect quenching model with holes (h⁺) and hydroxyl radicals (OH) quenching as "initiators". Thus, scavenging h⁺ and OH could successfully block the chain reactions between Cl^- and O₂^-, and photocatalytic degradation of methyl orange (a refractory dye, with O₂^- as dominant attacking species) could be enhanced by nearly 50 times, even when Cl^- content was up to 10 wt%. More importantly, both HPLC-MS analyses and DFT calculation validated that, by blocking its quenching effect, Cl^- could be successfully excluded from the pollutant degradation processes, thus preventing the generation of toxic chlorinated by-products. This work provides new insights into control of chlorinated by-products and proposes feasible strategies to extend photocatalytic technology in high salinity wastewater.

Study of the Digestate as an Innovative and Low-Cost Adsorbent for the Removal of Dyes in Wastewater

Digestate, as an urban solid waste, was considered as an innovative adsorbent for colorant polluted wastewater. Batch adsorption experiments were carried out using digestate as an adsorbent material to remove various dyes belonging to different categories. The removal rate and adsorption capacity of dyes were evaluated and the dose of digestate, contact time, and initial dye concentration were studied. The maximum removal rate was approximately 96% for Methylene Blue. The equilibrium time for the Methylene Blue was 4 h, while for other dyes, a longer contact time was required to reach the equilibrium. The suspicion of colloidal matter release into the solution from solid fraction of the digestate led to the investigation of the consequence of a washing step of the digestate adsorbent upstream the adsorption experiment. Washed and not washed adsorbents were tested and the differences between them in terms of dye removal were compared. Moreover, experimental data were fitted by pseudo-first order, pseudo-second order, and intra-partial diffusion kinetic models as well as Langmuir, Freundlich, and Sips isotherm models. The results from fitted models showed that the adsorption of various dyes onto the digestate was mostly well fitted by the Langmuir isotherm and pseudo-second-order kinetic model.