Ammonium tungsten bronze nanocrystalline can be synthesized by a one-step hydrothermal method using ammonium tungstate as the tungsten source, citric acid as the stabilizer, HCl as the reducing agent, and hydrochloric acid as the precipitating agent. It is reported that some experts have prepared ammonium tungsten bronze nanocrystalline by the abovementioned method and studied the effect of HCl concentration on the nanocrystals.
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The results show that when the HCl concentration is lower than 7.67 mg/mL, the product is a pure hexagonal (NH4) xWO3 nanorod, which grows in the [001] orientation; when the HCl concentration increases (9.86 and 12.05 mg/mL), the impurity phases of WO3·H2O and (NH4) 10W12O41 were formed. The adsorption experiments show that (NH4) xWO3 nanocrystals have excellent adsorption performance for methylene blue: the average value of cyclic adsorption removal rate for methylene blue in a 10 mg/L aqueous solution can reach ~ 85%; and the adsorption removal rate for methylene blue in a 40 mg/L aqueous solution reach ~ 80%. In addition, the methylene blue dye adsorbed on the surface of (NH4) xWO3 can be removed by heating at 250 °C for 2 hours under air conditions. The nanocrystals after heat treatment still have good adsorption performance for methylene blue. For methylene blue in a 10 mg/L aqueous solution, the average adsorption removal rate can reach ~ 90%.
