(716d) Preparation and Characterization of Sulfonated Biochar and Its Application As a Photo-Fenton Catalyst in Water Treatment and Biomass Valorization

Lignocellulosic biomass can be converted to biochar (BC), a material that possess excellent visible light absorption capacity and plenty of sp²-hybridisation structures. In particular, BC-based catalysts provide access to innovative materials design owing to excellent surface properties, crystallinity, chemical stability, recoverability, and higher photocatalytic activities than pristine semiconductor photocatalysts. Recent studies providing evidence of resonance-stabilised free radicals (PFRs) on BC surface have highlighted the need to exploit the oxidative stress induced by PFRs for ecologically beneficial applications. Here, we report the synthesis and characterisation of H₂SO₄-modified BC-TiO₂ nanocomposite (SBC) as a solid acid to activate H₂O₂ at circumneutral pH under visible light radiation. In the prepared material, H₂SO₄ modification leads to removal of ash and improves surface area of BC, while TiO₂ acts as Lewis acid sites. We found under solar-simulating light that SBCs have a remarkable capability of activating H₂O₂ under Fe-free conditions, that can be exploited to drive oxidation reactions. Results showed that a complete MO removal and a TOC reduction of 70.2% can be achieved with SBC pyrolyzed at 500 ^oC. The catalytic activity of SBC depended on the pyrolysis temperature and correlated well with the surface acidity and persistent free radical (PFR) concentration. A combination of acid-site poisoning and EPR studies revealed that •OH is the key transient formed upon H₂O₂ activation, followed by •O₂^- and ¹O₂. Our results demonstrate how a cheap, metal-free alternative heterogeneous catalyst could be developed from waste biomass to drive chemical reactions that are of industrial and environmental significance. We anticipate our carbon catalysts to be a starting point for more sophisticated materials design, leading to cheaper and robust nanomaterials, that can harvest light energy to drive oxidation reactions. For example, the activity of the SBCs could be expanded to biomass conversion, leading to a closed-loop photo-biorefinery for the valorisation of biomass into commercially valuable fine chemicals. Furthermore, this work offers a window into integrating biochar as a versatile, niche catalytic material in addition to its well known role as an adsorbent.