Synthesis, physicochemical properties and photocatalytic activity of zirconia-titania heterostructured nanocomposite for degradation of paraquat dichloride

Abstract

The advanced oxidation process using heterogeneous photocatalyst has been proven as a promising technique for the wide range of organic pollutants degradation in aquatic environment. Paraquat dichloride is a highly toxic organic pollutant that is still being widely used in agricultural sectors. This could cause malicious effects to living things and should be treated immediately. In this study, nanocomposite TiO2 based photocatalysts incorporated with transition metal oxides were synthesized using modified sol-gel and hydrothermal methods. The photocatalytic activity of the prepared catalysts was examined for the paraquat dichloride degradation in aqueous solution under UV lamp ( and fluorescence visible lamp ( 400 nm, Philips, 36 watts) for four hours. The photodegradation of paraquat dichloride was monitored using ultraviolet-visible spectrophotometer. The potential catalysts were further accomplished for several optimization studies inclusive of co-catalyst ratio, calcination temperature and catalyst dosage. From the screening results, ZrO2/TiO2 photo activity for both methods. The characterization analyses showed the presence of crystalline heterostructure ZrTiO4/Ti2ZrO6/TiO2 species with particle size in the range of 8-25 nm and band gap energy of 3.1 - 3.38 eV. The obtained species were confirmed by X-ray photoelectron spectroscopy and high resolution-transmission electron microscopy. The nano irregular morphology was observed with mesoporous mixtures of Type III and IV isotherms and H2 (b) type hysteresis loop with surface area of 49 m2g-1. The highest photodegradation of 98.45% was obtained using 0.3 g of ZrO2/TiO2 (40:60) prepared by hydrothermal method with 100% mineralization after irradiated for four hours. Meanwhile, for sol-gel method, only 84.51% of degradation was obtained over 0.3 g of ZrO2/TiO2 (20:80) catalyst. Response surface methodology with Box-Behnken design suggested that 0.3 g of ZrO2/TiO2 catalyst with 40:60 Zr to Ti dichloride degradation. Under this condition, the paraquat dichloride photodegradation achieved 98.87%, higher than the recommended value. Furthermore, the advance optimization on the effect of pH, addition of H2O2, sonication treatment, hydrogenation process and immobilization on the support material were also studied but no significant increment was observed for the photodegradation. The suggested active species from the radical scavenger studies were in the order of e- > O2 - > OH > h+. From the mechanistic study, the paraquat cation was adsorbed on the ZrO2/TiO2 (40:60) photocatalyst surface while intermediates of monopyridone, C12H16N2O4 ion, 4-carboxyl-1-methylpyridium ion were validated by Gaussian 16 software. The mechanism was confirmed following the first-order kinetic in accordance to Langmuir-Hinshelwood model.