A porous sponge-like TiO2/ZnO composite catalyst for photocatalytic degradation of methyl orange

Abstract

TiO₂-based photocatalyst holds great prospect in degrading organic dyes in wastewater, but it still confronts a series of challenges in terms of inadequate dye adsorption and mineralization capability during the degradation process. Here, a TiO₂/ZnO composite photocatalyst with sponge-like porous structure was prepared by employing sol-gel method with activated carbon (AC) as template. The microstructure and properties of the as-prepared catalyst were characterized by UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray fluorescence spectroscopy, elemental analysis, nitrogen adsorption and photoluminescence spectroscopy. The influences of catalyst composition ratio, initial dye concentration and pH values of solution on the degradation efficiency of methyl orange (MO) in water were mainly investigated. The results indicate that the proportions Zn(NO₃)₂ and AC over Tetrabutyl titanate (TBT) in raw materials significantly impact the microstructural formation of ultimate photocatalysts. Moreover, it is favorable for creating more porous structure in resultant catalysts by increasing the AC usage in starting materials. In addition, the catalyst surface morphology tends to become more compact when increasing the proportion of Zn(NO₃)₂. In comparison to single TiO₂ catalyst, the band gap of composite photocatalyst notably decreases from 3.03 eV to 2.67 eV. Specifically, a nearly complete degradation of MO is achieved within 25 min for the catalyst made by the mass ratio of 1:1:0.1 (TBT:Zn(NO₃)₂:AC) in raw materials. More importantly, the catalyst maintains an excellent reactive activity by keeping the degradation efficiency above 93.6 % even after six times of degradation recycles.