Ordered mesoporous TiO2/activated carbon for adsorption and photocatalysis of Acid Red 18 solution

Ordered mesoporous TiO2, loaded on walnut shell-based activated carbon, was prepared via sol-gel and ultrasonic-assisted technology. The obtained composites (M-TiO2/AC) were characterized via X-ray diffraction, N2 adsorption-desorption isotherms, and Fourier transform infrared spectroscopy. The adsorption–photocatalytic reduction capabilities were calculated using the removal rate of Acid Red 18 solution via UV spectrophotometry. The specific area of M-TiO2/AC increased from 563 m2·g-1 to 881 m2·g-1, compared to TiO2/AC. The removal rate was 92.3% when the Acid Red 18 with a concentration of 80 mg·L-1 was subjected to illumination for 2 h with 0.15 g of M-TiO2/AC. Under this condition the removal rate of Acid Red 18 solution by M-TiO2/AC was higher than that of TiO2/AC (83.7%), or AC (73.1%), which was attributed to the regular mesoporous structure, pore-pore synergistic amplification, and TiO2 photocatalysis. Acid Red 18 might be oxidized and decomposed into small molecular substances, such as CO2 and H2O, by strong oxidizing free hydroxyl radicals provided during the photocatalytic process by M-TiO2. The adsorption and photocatalytic processes followed the pseudo-second-order kinetic model. Internal diffusion and external diffusion processes influenced the adsorption rate.