Engineered electronic band structure of titanium carbide (TiC)-based fibrous silica catalyst for balanced simultaneous removal of hexavalent chromium and tetracycline

Abstract

Simultaneous removal of tetracycline (TC) and hexavalent chromium (Cr(VI)) from wastewater is limited by low photocatalytic efficiency and complex catalyst recovery. This study investigates titanium carbide (TiC)-based fibrous silica KAUST Catalysis Centre (KCC-1) composites for the visible-light-driven removal of TC and Cr(VI), focusing on the effects of calcination, TiC loading (1–5 wt%), and synthesis method. Uncalcined TiC/KCC-1 outperformed the calcined catalyst due to its higher surface area, anatase content, and stronger TiC–support interaction. Among loadings, 3TiC/KCC-1 achieved the highest removal (68 % Cr(VI), 66 % TC), while one-pot synthesized TiC/KCC-1 (1P) showed superior performance (73 % Cr(VI), 72 % TC), lower energy demand (731 kWh/m³), and cost (USD 36.7) compared to the impregnated catalyst (TiC/KCC-1 (IM)). Enhanced activity is attributed to its narrow band gap (1.7 eV), efficient charge separation, and favorable band positions. Electrochemical studies revealed TiC/KCC-1 (1P) improved charge transfer and reduced resistance. Mechanistically, TiC/KCC-1 (1P) directs photogenerated electrons toward Cr(VI) reduction via its +0.70 eV conduction band, while its +2.4 eV valence band supports TC oxidation through hydroxyl radical formation. In contrast, TiC/KCC-1 (IM) suffers from electron competition and insufficient oxidative potential due to its less favorable band positions. These findings underscore TiC/KCC-1 (1P) as a promising, green, energy-efficient photocatalyst for multi-contaminant wastewater treatment.