Upcycling citrus waste into porous carbon and aerogel materials: State-of-the-art and prospects

Abstract

Advanced porous carbon and aerogel materials are widely applied in water treatment, catalysis, energy storage, and biomedical engineering. With increasing focus on sustainability, renewable biomass sources have emerged as promising feedstocks due to their rich cellulose and lignin content. This review provides the first integrated analysis of both synthesis and post-pyrolysis activation methods specifically tailored to citrus waste-derived porous materials, highlighting how processing conditions impact structure and functionality. We examine state-of-the-art techniques, including microwave-assisted hydrothermal synthesis, dual-axis freezing, and template-directed activation, and compare their effects on surface area, porosity, and scalability. Moreover, this review uniquely explores emerging strategies such as AI-based optimization and low-temperature solvent-free activation, which offer pathways toward large-scale implementation. We also discuss current limitations and propose targeted future directions. Upcycling citrus waste into multifunctional porous materials not only addresses biomass waste management, but also opens up new avenues for designing cost-effective, high-performance materials for green technology applications.