Synergistic Photothermal–Photocatalytic H ₂ O ₂ Production and Seawater Desalination over Donor–Acceptor Structured Mesoporous Hydrothermal Carbon Microspheres

Photocatalytic hydrogen peroxide (H2O2) production is a sustainable alternative to the energy-intensive and waste-generating industrial anthraquinone process. However, its efficiency is traditionally limited by rapid charge recombination and sluggish reaction kinetics. In this work, we developed metal-free hydrothermal carbon (HTC) via a facile one-step carbonization of dextran. The results demonstrate that D-HTC possesses well-defined microspherical morphology with a mesoporous nanostructure and a unique donor–acceptor electronic architecture. These nanoscale porous features provide abundant accessible active sites and facilitate efficient mass transport, contributing to the enhanced photocatalytic performance. Crucially, the material exhibits a profound in situ photothermal effect, converting broadband solar energy into localized heat (Tsurf ≈ 65 °C), which accelerates surface reaction kinetics and mass transport according to Arrhenius-type behavior. Furthermore, we identified a seawater cation-promoted ″electron sink″ effect, where ions such as Na+ and Mg2+ suppress charge recombination, enhancing catalytic activity in natural seawater. Under simulated solar irradiation, D-HTC achieves a robust H2O2 evolution rate of 0.283 mmol g–1 h–1 without sacrificial agents. By deploying this material in a bifunctional platform, we demonstrate the concurrent production of H2O2 and freshwater via seawater desalination with a salt rejection rate exceeding 99%. This work establishes a paradigm for utilizing biomass-derived hydrothermal carbon spheres in high-efficiency solar-to-chemical energy conversion and water purification.