Waste-derived nanocomposites as dual-function materials for water and energy sustainability

The growing world crisis of waste, water shortage, and energy insecurity which needs sustainable and permanent solutions. Traditional nanocomposites, which are usually prepared by using high purity starting materials through energy intensive methods, are increasingly incompatible with environmental objectives. This review uniquely integrates dual functionality waste-based nanocomposites and their role in circular economy principles. The current approach highlighted in this review is the emerging waste-based nanocomposites as dual-purpose materials that can be used to meet the requirements of water purification and energy storage/conversion at the same time. We methodically explore the conversion of multiple waste streams (agricultural residues, plastic waste, industrial sludge, and biomass) into functional nanocomposites using thermal, biological, and hybrid synthesis pyrolysis, hydrothermal carbonization (HTC), microbial reduction, and artificial intelligence (AI)-directed design. Particular attention is given to multipurpose systems in which one material is used in the environmental and energy fields such as SiO 2 /biochar composites made of rice husk in heavy metal adsorption and super capacitor electrode, or N-doped carbon made of textile waste in the dye degradation and hydrogen evolution catalysis. Besides these, some other nanomaterials have also been highlighted in this review. We critically assess synthesis pathways through life cycle assessment (LCA) and techno economic analysis (TEA) alongside structure property relationships, performance indexes, and the environmental impact of these materials. All critical issues, including the control of impurities, batch variability, and scaling, are addressed, along with innovative directions such as modular reactors, decentralized production, and their integration with wastewater energy systems. In the future, we proposed a circular nanotechnology economy in which urban waste can serve as a strategic asset to the next generation of sustainable technologies. This review offers a pathway toward the realization of high performance, low cost, and environmentally-friendly nanocomposites by sensitizing waste valorization, materials science, and system-level sustainability at the nexus of water and energy.