Efficient photodegradation of paraquat herbicide over TiO₂-WO₃ heterojunction embedded in diatomite matrix and...

Photodegradation of paraquat herbicide was assessed over several TiO₂-WO₃ heterojunctions embedded in the diatomite matrix. The characterization results indicated that WO₃ embedding in the TiO₂ decorated-diatomite matrix could not only enhance the adsorption capacity, visible-light response, and distribution of semiconductor species but also lessen the recombination rate and band gap energy. These characteristics were more noticeable as 5 wt.% of WO₃ was embedded. Despite better optical properties of immobilized TiO₂-WO₃ nanocomposites, overloading WO₃ generally alleviates the synergetic effect of tungsten due to surface coverage of diatomite matrix and, subsequently, the significant attenuation of textural properties, more formation of agglomerations and defects as trapping centers in the oxidation sites of heterostructures, and also, less likely of forming TiO₂-WO₃ heterojunction. In accordance with characterization results, the highest UV-photodegradation of paraquat was attained over heterostructured nanocomposite containing 5 wt.% WO₃ (T25-W5/Di). The effects of significant operating parameters were also investigated, modeled, and optimized using response surface methodology (RSM)-central composite design (CCD). Under optimized operation conditions, the experimental removal efficiency of paraquat reached 97.1 and 80% using UV and simulated solar light, respectively. Moreover, the reusability results confirm the sustained activity of the T25-W5/Di nanocomposite.