Enhanced removal efficiency of toluene over activated carbon under visible light.

Toluene removal rates using activated carbon (AC) at various relative humidity (RH) levels (0%, 30%, 60%) were compared under dark and visible-light conditions. Light exposure significantly increased toluene-removal efficiency independent of RH. When AC was pre-treated with an optimal concentration of HNO, its toluene-removal efficiency was enhanced further with light, an effect that can be attributed to increased surface-area and porosity. Fourier-transform infrared analysis confirmed that exposure of HNO-modified AC to light induced partial oxidation of toluene. Within visible-light range (380-650 nm), shorter wavelengths were more effective for toluene-removal compared with longer wavelengths. This suggests that hydroxyl groups formed on AC-surface under light strongly interact with aromatic rings of toluene, allowing for greater uptake of toluene. Moreover, AC can sustain its photo-activity when mixed with cement and cured, suggesting its potential applications in air-purifying building materials. An efficient and practical method for regeneration of spent AC is also demonstrated.