Anisotropic silicon-modified loofah carbon aerogels for synergistic solar-environmental energy harvesting in interfacial evaporation

Abstract

Carbon aerogels derived from biomaterials enable highly efficient solar steam generation. However, simultaneously achieving high evaporation efficiency while ensuring salt resistance, long-term stability, and multi-pollutant removal remains a significant challenge. Herein, we present a sustainable platform fabricated from abundant loofah biomass that integrates photothermal conversion with passive radiative cooling. Hybrid carbon/silica (C-PT) aerogels are synthesized via alkaline-TEMPO oxidation, polyvinyltrimethoxysilane (PVTMS) cross-linking, and pyrolysis at 800 °C. This process preserves the loofah's innate vascular channels while embedding cristobalite SiO₂ nanoparticles within a turbostratic carbon matrix. The resulting hierarchical structure possesses a dual function: its anisotropic thermal insulation localizes solar heat at the surface, while its high thermal emissivity within the atmospheric window facilitates radiative cooling. This cooling effect lowers the evaporator's temperature below ambient, thereby enhancing convective heat transfer from the environment. This synergistic energy harvesting strategy enables the optimized C-P₃T aerogel to achieve an evaporation rate of 1.95 kg m⁻² h⁻¹ and a remarkable apparent efficiency of 108.1% under 1-sun irradiation, with 13.1% of the energy input originating from the captured environmental heat. Critically, the aerogel resists salt fouling, maintaining a stable evaporation rate in 3.5 wt% NaCl over 100 h without salt accumulation, enabled by synergistic electrostatic repulsion and rapid ion diffusion through its anisotropic channels. It concurrently addresses water contamination, removing >99.9% of heavy metal ions and achieving near-complete rejection of organic dyes. Integrated with robust mechanical properties, this work establishes a versatile platform for high-performance water purification by demonstrating a rational design that synergistically combines solar heating with radiative cooling.