Performance and mechanism into TiO2/Zeolite composites for sulfadiazine adsorption and photodegradation

The composite material based on natural Zeolite coated with TiO2 (TiO2/ZEO) synthesized by sol-gel method was used as a photocatalyst to rapidly degrade Sulfadiazine (SDZ). The adsorption-degradation behavior and mechanism of SDZ on TiO2/ZEO were investigated for revealing the role of adsorption and degradation under UV light. TiO2/ZEO was easier to be separated than the bare TiO2 powders in aqueous media. Compared with bare Zeolite, TiO2/ZEO markedly improved the efficiency in photocatalytic degradation of SDZ: more than 90% of SDZ could be removed within 120 min of both adsorption and degradation by TiO2/ZEO dosage of 1 g·L−1 at neutral pH, whereas less than 15% was removed by Zeolite alone. The Langmuir-Hinshelwood first-order linear transform with k = 0.0212 min−1 was observed for the photocatalytic degradation reaction of SDZ. The parameters such as loaded amount of TiO2, initial SDZ concentration, solution pH value, humic acid (HA) concentration, and recycle numbers on removal efficiency were also studied. The enhancement in removal efficiency was not attributed to the simple adsorption of SDZ on zeolite but also the synergistic effect obtained through the combined use of TiO2 photocatalyst and zeolite adsorbent in the composite material, which can accelerate the SDZ photodegradation in water. The photocatalytic mechanism, as characterized using ESR and trapping experiments of reactive species, indicates that the synergism effect between radOH, h+, radO2− and 1O2 all play a role in photocatalytic oxidation of SDZ.