Hybrid adsorption-photocatalysis of organic pollutants with bifunctional TiO₂/AC composite under solar light: Prospective applications in water treatment and reclamation

Several recently synthesized composites of nitrogen-doped TiO₂ supported on activated carbon (N-TiO₂/AC) were investigated for adsorption of recalcitrant organics and photocatalysis under the simulated solar light. Synergistic adsorption-photocatalysis was observed due to high adsorptive properties of the AC (see Figure 1). The synthesis could be tailored to produce a range of N-TiO₂/AC with different loadings of N-TiO₂ on AC, which demonstrated varying bifunctionalities of adsorption and photocatalysis. Bisphenol-A (BPA), acid red, and atrazine have been investigated. Adsorption of the pollutants (in dark) by N-TiO₂/AC achieved equilibrium within 1 h. The adsorption capacity as determined by Langmuir equation was only marginally reduced due to partial blockage of AC surface by the deposited N-TiO₂, as compared to the virgin AC. The results of BPA adsorption and photocatalysis are shown in Figure 2. Up to 95% of BPA in the bulk solution could be degraded by N-TiO₂/AC within 8 h of irradiation. The BPA photocatalysis was more favorable under acidic condition. The bifunctionality of N-TiO₂/AC permits self-regeneration of the exhausted AC under solar irradiation, and thus continual use in the flow-through system operating under repeating day-night cycle of alternating solar photocatalysis and adsorption processes, for effective removal of most organics.