Hydrothermal processing of lignocellulosic biomass generates aqueous streams enriched in phenolic and furanic intermediates, but these dissolved carbon species are commonly lost through oxidative degradation. Here, we developed an organic radical-mediated humification strategy driven by thermally activated persulfate, which redirects dissolved carbon into humic acid-like substances (HALs) with cross-linked aromatic−heterocyclic structures through phenol−furan coupling rather than oxidative mineralization to CO 2 . Under acid-alkaline pretreatment that enhances precursor release, the HAL yield reached 61.43%, significantly higher than the 6.32−7.78% obtained from single-condition pretreatments. This pathway retained 81.1% of biomass carbon in products, including 75.9% in HALs and 5.2% in coproducts, while only 18.9% was released as CO 2 . The process simultaneously enabled detoxification and carbon retention, removing 88−100% of benzenoid aromatics and 98−100% of furanic compounds while preserving 48.3−87.2% of bioavailable substrates. Ultrahigh-performance liquid chromatography−electrospray ionization−mass spectrometry resolved oligomer series indicative of chain-growth incorporation, and pyrolysis−gas chromatography−mass spectrometry confirmed aryl-furan connectivity, supporting the formation of π-conjugated, redox-active aromatic−heterocyclic networks. Density functional theory calculations showed that phenol−furan radical coupling lowers the activation barrier from 96.5 to 10.1 kcal mol −1, enabling efficient C−C/C−O bond formation and polymer growth. Process simulation at a biomass feed rate of 10,000 kg/h projected a HAL production of 6143 kg/h; technoeconomic analysis further indicated favorable economic performance, with an internal rate of return of 53.6%, a discounted payback period of 3.9 years, and a net present value of 15.0 billion CNY. These findings establish a carbon-retentive pathway that transforms hydrothermal wastewater from a waste stream into a precursor platform for functional carbon materials in circular biorefineries.
Wang et al. (Mon,) studied this question.