Enhanced uranium self-photocatalytic extraction via adsorption effect of acid-modified SiO2

Uranium photocatalytic extraction has been regarded as a promising way for nuclear wastewater management. Lots of studies showed the enhanced adsorption capacity of photocatalyst can improve the uranium extraction capacity. However, the mechanism of synergistic effect between adsorption and photocatalytic is still unclear. Herein, we proposed a novel adsorption trigger uranium self-photocatalytic extraction strategy which can enhance the transition from soluble uranyl ions to insoluble metastudtite. Silica (SiO2) with different amounts of surface silicon hydroxyl groups were utilized as both adsorbent and photocatalyst, and they were obtained by modifying with H2SO4, HCl and HNO3, respectively. The SiO2 equipped different specific surface area with an order of SiO2(H2SO4) (350.12 m2 g-1) > SiO2(HNO3) (286.80 m2 g-1) > SiO2(HCl) (264.85 m2 g-1) > SiO2 (9.70 m2 g-1). The adsorption capacity of U(VI) on SiO2(H2SO4) was highest as 137.95 mg g-1, which was 7 times higher than that of the unmodified SiO2. The improvement of adsorption performance with acid-modified SiO2 enhanced the aggregation of uranyl ions, thereby accelerating the self-photocatalytic extraction of uranyl ions. Additionally, the modification of SiO2 with H3PO4 introduces phosphate groups that significantly diminish the photocatalytic activity of uranyl ions, sequentially effectively halting the self-photocatalytic degradation of uranium. Furthermore, SiO2(H2SO4) showed the good reusability and stability after being recycled and reused five times as well as good selectivity for U(VI). The work delivers a further understanding of the effect of catalyst adsorption on photocatalytic reactions, serving as a guide for the development and synthesis of advanced photocatalysts in future studies.