From agricultural waste to device: Corncob-derived biocarbon for coupled solar evaporation and photocatalysis

Solar interfacial steam generation can deliver freshwater with minimal energy input, but most evaporators remain single-function devices that concentrate organics in the residual brine and rely on costly substrates. We report a waste-to-device platform, reduced TiO₂@corncob biochar (r-TiO₂@CCB), that integrates interfacial evaporation and photocatalysis in a single recoverable monolith. Corncob biowaste is carbonized to a mechanically robust, low-conductivity scaffold with aligned macro-mesopores; oxygen-vacancy-rich TiO₂ nanodomains are then anchored throughout the pore walls, forming intimate semiconductor-carbon contacts. Textural and spectroscopic analyses confirm the design logic: a hierarchical pore network that sustains capillary water supply, preserved anatase crystallinity, and ∼15% Ti³⁺ associated with oxygen vacancies that extend spectral response and facilitate interfacial charge transfer. Under one-sun irradiation (1 kW m^-2), the optimized monolith carbonized at 700 °C achieves an evaporation rate of 2.18 kg m^-2 h^-1 in pure water and 2.40 kg m^-2 h^-1 in 5 ppm Rhodamine B (RhB), with solar-to-vapor efficiency up to ∼90 %. Concurrently, it removes over 90% of RhB within 3 h, and retains >75 % removal after five reuse cycles. The synergy arises from heat localization and solute concentration in thin interfacial films that accelerate catalysis, while pollutant mineralization diminishes optical screening and interfacial resistance to enhance evaporation. By converting abundant biowaste into a dual-functional, powder-free device, this work provides general design rules for scalable, solar-driven purification that couples energy-lean evaporation with on-site contaminant destruction.