Ultrasonic-assisted preparation of amidoxime functionalized silica framework via oil-water emulsion method for selective uranium adsorption

The demand for low-cost adsorbent and method for efficient adsorption of metal ions for environmental and energy applications is highly required. The novel amidoxime functionalized silica framework (SiO₂-AO) is prepared through a step by step process including ultrasonic-assisted oil–water emulsion method, surface sulfhydrylation, click reaction and modification of amidoxime. The hexane/water emulsion system in the presence of hexadecyltrimethylammonium bromide (CTAB) gives a large specific surface area of the precursor (SiO₂-OH) and final products. The spectroscopic characterization combined with kinetics and isothermal studies reveals that the interaction between U(VI) and SiO₂-AO is usually through coordination complexation. The adsorption behavior of SiO₂-AO for U(VI) adsorption is explored through various batch methods including the effect of U(VI) concentration, pH, contact time and adsorbent dosage. It is revealed 99.9 ± 0.5% U(VI) adsorption occurs at pH = 8, which is close to the pH of seawater. The highest U(VI) adsorption capacity obtained from the Langmuir adsorption model is 955.8 mg g⁻¹ at room temperature. The high removal rate (above 85%) at low U(VI) initial concentration (3 µg L^-1), excellent selectivity of U(VI) in presence of coexisting ions and high adsorption efficiency of regenerated adsorbent in sixth cycle refer SiO₂-AO as a potential adsorbent for U(VI) adsorption in the practical field.