Two-step hydrothermal synthetic method of niobium-tungsten complex oxide and its adsorption of methylene blue

Niobium-tungsten oxide Nb18W16O9 was successfully synthesized by a two-step hydrothermal process and heat treatment. The structural and characteristics of samples and their adsorption of methylene blue (MB) have been investigated by XRD, SEM and UV–Vis spectrometer. Structural results indicated that the sample obtained through heat-treatment in the case of pH = 3 is a niobium-tungsten oxide (Nb18W16O93) with Pbam space group. Meanwhile, adsorption of methylene blue on niobium-tungsten complex oxide showed that the calcined sample with nanobar-shape synthesized by a two-step hydrothermal process in pH range of 3 adsorbed above 97% methylene blue with the concentration of 10 mg/L in 5 min at room temperature. Also, it has been showed that its adsorption is superior to an as-hydrothermal prepared sample.