Solvothermal preparation of Ag nanoparticle and graphene co-loaded TiO2 for the photocatalytic degradation of paraoxon pesticide under visible light irradiation

The growing use of organophosphorus compounds such as paraoxon as agriculture pesticides results in their accumulation in soils and groundwater. Therefore there is a high demand for developing efficient methods for removing these materials from contaminated environmental resources. In this study, Ag nanoparticle and graphene co-loaded TiO2 with various contents of Ag and graphene was prepared via a facile surfactant free solvothermal method in a mixture of water and ethanol solvents and was applied, for the first time, for the photocatalytic degradation of paraoxon (as a model organophosphorus compound) under visible light irradiation. In this ternary nanocomposite, the presence of Ag nanoparticles is for narrowing the band gap to the visible region due to its surface plasmon resonance (SPR) effect and the presence of graphene is for diminishing the recombination rate of the photogenerated electron and holes due to its high electrical conductivity. The results of photocatalytic activity tests demonstrate that the nanocomposite with 6% wt Ag and 1% wt graphene content has the best photocatalytic activity among the products. Investigation of the chemical state of the nanocomposites showed that the covering of Ag nanoparticle loaded TiO2 with a high weight ratio of graphene resulted in the formation of Ag-O bonds through bonding of Ag to the oxygen functional groups of graphene which causes a decrease of the SPR effect of Ag and by this way decreases the photocatalytic activity. Gas Chromatography-Mass Spectrometry (GC-MS) was used as analytical tool for determination of the photocatalytic reaction intermediates. GC-MS analysis results show that photodegradation of paraoxon produces 4-nitrophenol, di-ethylphosphate, mono-ethylphosphate, hydroquinone and hydroxyhydroquinone as major intermediates and subsequent photodegradation of these results in complete mineralization of paraoxon.