The unavailability of clean drinking water is one of the significant health issues in modern times. Industrial dyes are one of the dominant chemicals that make water unfit for drinking. Among these dyes, methylene blue (MB) is toxic, carcinogenic, and non-biodegradable and can cause a severe threat to human health and environmental safety. It is usually released in natural water sources, which becomes a health threat to human beings and living organisms. Hence, there is a need to develop an environmentally friendly, efficient technology for removing MB from wastewater. Photodegradation is an advanced oxidation process widely used for MB removal. It has the advantages of complete mineralization of dye into simple and nontoxic species with the potential to decrease the processing cost. This review provides a tutorial basis for the readers working in the dye degradation research area. We not only covered the basic principles of the process but also provided a wide range of previously published work on advanced photocatalytic systems (single-component and multi-component photocatalysts). Our study has focused on critical parameters that can affect the photodegradation rate of MB, such as photocatalyst type and loading, irradiation reaction time, pH of reaction media, initial concentration of dye, radical scavengers and oxidising agents. The photodegradation mechanism, reaction pathways, intermediate products, and final products of MB are also summarized. An overview of the future perspectives to utilize MB at an industrial scale is also provided. This paper identifies strategies for the development of effective MB photodegradation systems.

Efficient and excellent nanoparticles are required for the degradation of organic dyes in photocatalysis. In this study, silver–manganese oxide nanoparticles (Ag-Mn-NPs) were synthesized through a wet chemical precipitation method and characterized as an advanced catalyst that has enhanced photocatalytic activity under sunlight irradiation. The nanoparticles were characterized using scanning electron microscopy (SEM), XRD, UV–vis light spectra, and energy-dispersive X-ray (EDX) spectroscopy, revealing their spherical and agglomerated form. The EDX spectra confirmed the composition of the nanoparticles, indicating their presence in oxide form. These bimetallic oxide nanoparticles were employed as photocatalysts for the degradation of malachite green (MG) dye under sunlight irradiation in an aqueous medium. The study investigated the effects of various parameters, such as irradiation time, catalyst dosage, recovered catalyst dosage, dye concentration, and pH, on the dye’s photodegradation. The results showed that Ag-Mn oxide nanoparticles exhibited high photocatalytic activity, degrading 92% of the dye in 100 min. A longer irradiation time led to increased dye degradation. Moreover, a higher catalyst dosage resulted in a higher dye degradation percentage, with 91% degradation achieved using 0.0017 g of the photocatalyst in 60 min. Increasing the pH of the medium also enhanced the dye degradation, with 99% degradation achieved at pH 10 in 60 min. However, the photodegradation rate decreased with increasing dye concentration. The Ag-Mn oxide nanoparticles demonstrate excellent potential as a reliable visible-light-responsive photocatalyst for the efficient degradation of organic pollutants in wastewater treatment.

The contamination of industrial water sources with synthetic dyes, such as methylene blue (MB), remains a persistent environmental concern, demanding effective remediation techniques. In response, this research centers on the utilization of trimetallic nanoparticles (TMNPs) composed of Fe-Ni-Cr, Fe-Ni-Cd and Fe-Ni-Cu as a promising solution to address color-related pollution in aquatic ecosystems. These nanoparticles were synthesized using the wet chemical precipitation method and rigorously characterized using Fourier transform infrared (FT-IR), energy-dispersive X-rays (EDX), and scanning electron microscopy (SEM). Armed with these trimetallic nanoparticles, our primary objective was to harness their photocatalytic prowess when exposed to direct sunlight in aqueous environments for the degradation of MB. The progress of photodegradation was meticulously monitored using a reliable visible spectrophotometer, providing insights into the degradation kinetics. Remarkably, within just six hours of solar irradiation, the TMNPs exhibited a remarkable capacity to degrade MB, achieving an impressive degradation rate ranging from 77.5% to 79.4%. In our relentless pursuit of optimization, we conducted a comprehensive examination of various parameters including catalyst dosage, dye dosage, and pH levels, focusing specifically on the Fe-Ni-Cr TMNPs. Through systematic experimentation, a trifecta of optimal conditions emerged: a pH level of 10 (resulting in a 79.35% degradation after 1.5 h), a catalyst amount of 0.005 g (yielding 43.5% degradation after 1.5 h), and a dye concentration of 40.0 ppm (culminating in a 42.54% degradation after 1.5 h). The study also extended its scope to explore the regeneration potential of the catalyst, shedding light on its sustainability in long-term applications. Amidst the vibrant interplay of color and water, TMNPs emerged as a symbol of optimism, offering a promising avenue for the removal of synthetic dyes from the water system. With each experiment and investigation, we inch closer to realizing clearer waters and brighter environmental horizons.

The Sustainable Development Goals (SDGs) play key role in propelling transformative changes, and highlighting burning issues to be addressed to achieve successful global developmental initiative. Zinc oxide (ZnO) and reduced graphene oxide (rGO) are helpful in achieving various SDGs. However, both materials have some limitations. To overcome the drawbacks of individual ZnO and rGO nanomaterials, ZnO/rGO nanocomposites are designed. This review aims to highlight issues being faced by ZnO and graphene oxide and their resolution through the development of ZnO/rGO nanocomposite. Various characterization techniques are discussed to explore physio-chemical properties. As the composite materials exhibit enhanced charge carrier separation, and extended lifetime of photoinduced charge carriers, making them a promising agent for improved photocatalytic degradation of pollutants, biosensors, and energy conversion and storage devices such as solar cells, and lithium batteries etc. Morphological relationship with various activities and potential applications in numerous fields, including controlling environmental pollution, biomedical, bio-sensing, energy etc., have also been discussed to explore their importance. Additionally, for further advancement to design next generation material several recommendations have been given. The knowledge gained from this review is the way for the development of next-generation nanomaterials, capable of addressing global challenges in energy and environmental sustainability etc.