Abraham Stuvart, Arun Thesingu Rajan, Hemanth P K Sudhani, Natarajan Raman
The contamination of water bodies by industrial effluents is a growing global concern, especially due to the presence of persistent and bio-accumulative pollutants such as 4-nitrophenol. 4-Nitrophenol is extensively used in pharmaceutical, insecticide, dye and leather industries, resulting in adverse effects on human health and environment. Conventional treatment methods such as adsorption, advanced oxidation, biodegradation and electrochemical reduction have numerous limitations, including incomplete mineralization, elevated operational costs, the generation of secondary pollutants, and challenges related to scalability. Recent studies have shown that biochar-metal composites are promising alternatives, which possess the advantages of the char's physicochemical properties combined with the catalytic activity of metal nanoparticles. The aim of this review is to assess the available literature on the production, adsorption and catalytic properties of biochar-metal composites as well as their application in 4-NP remediation. The influence of feedstock, pyrolysis conditions and metal incorporation on the formation of biochar composites is discussed in detail. This review highlights the importance of life cycle assessment and economic analysis, which can provide an understanding of the potential environmental and economic implications of biochar composites. However, there are several challenges associated with material strength, size constraints, metal leaching potential and commercial availability. This review is an attempt to connect laboratory-scale research with real-world implementation by outlining the important knowledge gaps and proposing future research including integrated studies, novel preparation techniques, mechanistic investigations and policy development. Hence, biochar-metal composites can enhance the conventional water treatment methods and provide effective solutions for mitigating global environmental contamination caused by pollutants like 4-nitrophenol.