Sewage sludge-derived TiO₂/Fe/Fe₃C-biochar composite as an efficient heterogeneous catalyst for degradation of...

Novel TiO₂/Fe/Fe₃C-biochar composite, as a heterogeneous catalyst, has been synthesized by a single-step route, where sewage sludge (SS) and different ratios of nanoparticles (NPs: Fe and Ti) impregnated with chitosan using coagulation and flocculation techniques for subsequent thermal decomposition at 800 °C. The physiochemical properties of samples have been characterized thoroughly and employed in methylene blue (MB) degradation tests. It was found that NPs ratio and chitosan support have significant influences on the properties and catalytic activity of catalysts. Chitosan inclusion successfully improves the surface area and mesoporosity of composites, while high contents of Fe integration reduce surface area and active site (Fe₃C) due to Fe⁰ agglomeration. Though, Ti incorporation produces Ti³⁺ that activated photosensitivity. Catalyst with the high mesoporous surface, Ti³⁺, selective Fe₃C, and small Fe⁰ shows superior MB removal competency through concurrent adsorption, photodegradation, and H₂O₂ activation. Primarily OH and some O₂^- radicles participating in the degradation reactions evident from scavenging experiments. The maximum MB removal capacity evaluated as 376.9 mg L^-1 in neutral pH. Moreover, the catalyst exhibits excellent material stability, recyclability, easy separability, and low Fe-ion leaching (0.11 mg L^-1) after catalysis. This study provided new insight into a low-cost and environmentally friendly route of catalyst synthesis using SS, NPs, and chitosan, which concurrently advantageous to SS disposal and wastewater treatment.