Application of phosphomolybdate/tungsten disulfide composites in the adsorption and photocatalytic degradation of dyeing wastewater

Water pollution from dye wastewater is a major problem. As an indirect semiconductor, tungsten disulfide has a large specific surface area to adsorb dyes, and can absorb energy to degrade dye molecules under visible light. Furthermore, polyoxometalates reduce the energy gap of the photocatalyst and inhibit the recombination of photogenerated electrons and holes. Here, a novel phosphomolybdate/tungsten disulfide composite was constructed firstly via a solvothermal method to load phosphomolybdic acid onto few-layer-thick disulfide nanosheets. The chemical structure, morphology, porosity, phase, and element composition of the composite phosphomolybdate/tungsten disulfide were characterized. The absorption performance and photocatalysis of the complexes was tested. The adsorption capacity of phosphomolybdate/tungsten composites for dyes has an increasing trend with the increase in phosphomolybdate loading until the loading reaches 80%. The material can selectively adsorb malachite green and methylene blue, with a selectivity factor as high as 4.28 in the mixed solution of methyl orange/malachite green. But it has better photocatalytic effect on methyl orange than malachite green and methylene blue. The material can degrade 98% of methyl orange in 90 min. Our results indicate that the adsorption capacity and photocatalysis of phosphomolybdate/tungsten disulfide composites are significantly enhanced compared with tungsten disulfide. This work creatively combined tungsten disulfide with oxidative polyoxometalates which provide novel insights into the design of low-cost photocatalytic materials and adsorption materials for dyeing wastewater.