Adsorption-photocatalytic degradation of Acid Red 88 by supported TiO2: Effect of activated carbon support and aqueous anions

TiO₂ nanoparticles supported on activated carbons (TiO₂/AC) were synthesized for the synergistic removal of Acid Red 88 (AR) via photocatalytic degradation and adsorption. Great enhancement of photocatalytic efficiency was achieved by supporting TiO₂ on two ACs, Darco-G60 and Norit SA UF. The surface hydrophilic properties and pore size distribution of ACs have significant influences on TiO₂ deposition on the supports, resulting in remarkable different performances of the two TiO₂/AC composites in the degradation of AR. TiO₂ loaded on Norit SA UF (TiO₂/AC-N) had a more dispersed coverage on the AC support but lower AR adsorption capacity due to larger degree of pores blockage by the TiO₂ nanoparticles which were also shielded from incident UV. In comparison, TiO₂ loaded on Darco-G60 (TiO₂/AC-D) showed higher photocatalytic activity and better durability in cyclic reuse. The synergistic adsorption-photocatalysis was observed, and the optimal TiO₂-to-AC mass ratio was 80-20 for the highest photocatalytic activity. Inorganic anions exhibited varying impacts on the performance of TiO₂/AC. In general, the AC support could greatly abate TiO₂ deactivation by inorganic anions. Sulfate promoted the AR degradation over both TiO₂/AC-D and TiO₂/AC-N while chloride and nitrate exhibited no influence on TiO₂/AC-D but positive effect on TiO₂/AC-N. Phosphate and bicarbonate could deactivate the TiO₂/AC composites but to a less extent compared to their effects on the TiO₂ without AC support.