Preparation of oxygen-deficient 2D WO3-x nanoplates and their adsorption behaviors for organic pollutants: equilibrium and kinetics modeling

A novel oxygen defect-rich WO3-x nanoplates were synthesized using a solvothermal method followed by an annealing treatment under Ar-H-2 gas mixture atmosphere. WO3-x nanoplates possess large numbers of oxygen defects systematically demonstrated by the elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The adsorption capacity of defect-rich 2D WO3-x nanoplates was evaluated by removal of methyl orange (MO) and the adsorption capacity could reach to 63.7 mu gmg(-1) with good stability and reusability after. Their adsorption performance at the temperature of 298K, 308K and 318K is carried out and proved to fit Langmuir isotherm model very well, suggestive of a monolayer adsorption on the materials surface sites. In addition, adsorption kinetics studies show that the adsorption process conforms to the pseudo-second-order equation model very well demonstrating a chemical process for MO adsorption. Compared to pure WO3 with annealing treatment at N-2 and air atmospheres, the one treated under Ar-H-2 gas mixture atmosphere (WO3-x) shows higher adsorption capacity and fast adsorption kinetics toward MO, which was attributed to deprivation of lattice oxygen of WO3 at the reducing atmosphere. Meanwhile, the 2D defect-rich WO3-x nanoplates also exhibit excellent adsorption properties toward methylene blue and rhodamine B, and they can be made into thin film by vacuum suction filtration for dynamically removing the organic pollutants. Our study shows that the as-synthesized defect-rich 2D WO3-x nanoplates have potential applications in real-time wastewater treatment.