Enhanced photocatalytic performance of rGO/UiO-66(Zr)/Ag3PO4 composite for degradation of methyl orange (MO) under visible light irradiation

Industries like textile, plastic, pulp, and paper produce dye-containing waste waters that have harmful effect on the environment as well as human health. This work presents a series of binary and ternary composites formed by reduced graphene oxide (rGO), silver phosphate (Ag3PO4) and the nanocrystalline MOF, UiO-66(Zr). The composites exhibit the best of their catalytic features to achieve efficient photocatalysis to remove the model dye methyl orange (MO) from aqueous solution as well as dyes from a real industrial wastewater effluent. The composites were prepared under sustainable conditions, at room temperature. XRD characterization shows that the prepared MOF is one of the most nanocrystalline reported UiO-66(Zr), becoming even more nanocrystalline in the composite formation. Different physicochemical characterization techniques indicated the existence of such interaction. Thus, DRS-UV-vis spectroscopy makes clear the reduction of the band-gap of the composites compared with the individual components; the band intensity of the photoluminescence (PL) spectra is substantially reduced in composites, confirming the diminution of electron-hole recombination; and electrochemical impedance spectroscopy (EIS) shows that the electrodes modified with ternary composites present faster electron transfer ability. The selected composite rGO/UiO-66(Zr)/Ag3PO4 exhibits high efficiency on the photodegradation of the model MO dye compared to the binary and single counterparts. It could be attributed to its high surface area, enhanced visible light absorption, efficient charge transfer process, as well as the synergetic effect between its components. A degradation mechanism is proposed based on the estimated band-gaps and on the scavenging study with strategically-chosen species.