Immobilization of uranium(VI) by niobate/titanate nanoflakes heterojunction through combined adsorption and solar-light-driven photocatalytic reduction
Immobilization of uranium(VI) by niobate/titanate nanoflakes heterojunction through combined adsorption and solar-light-driven photocatalytic reduction
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DOI：
10.1016/j.apcatb.2018.02.062
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Xiaona Liu;Penghui Du;Weiyi Pan;Chenyuan Dang;Tianwei Qian;Hong-fang Liu;Wen Liu;Dongye Zhao
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文献类型：
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作者：
Xiaona Liu;Penghui Du;Weiyi Pan;Chenyuan Dang;Tianwei Qian;Hong-fang Liu;Wen Liu;Dongye Zhao
采用一步水热法制备了铌酸盐/钛酸盐纳米片（Nb/TiNFs）复合材料。Nb/TiNFs显示出异质结结构，这是由于在三钛酸盐纳米片上沉积了一小部分钛酸盐。三钛酸盐（Na1.6H0.4Ti3O7自由基·1.7H2O）是主晶相，并且钛酸盐（Na 2Nb 2 O 6自由基·H2O）与钛酸盐的摩尔比被确定为1：15.9。Nb/TiNFs对U（VI）具有快速的吸附动力学和较高的吸附容量（LangmuirQmax= 298.5mg/g）。离子交换和表面络合是吸附U（VI）的主要机制，异质结独特的隧道晶格结构进一步增强了吸附。此外，Nb/TiNFs能够在太阳光下通过光催化还原将U（VI）转化为其固定形式UO 2（s）。在初始U（VI）= 20 mg/L，pH = 5.0的条件下，经4 h太阳辐射后，89.3%以上的（VI）转化为U（IV）。漫反射UV-vis吸收光谱和Mott-Schottky图表明，与纯TNT相比，Nb/TiNF的带隙能量变窄。密度泛函理论（DFT）能带结构和态密度的计算进一步证实了钛酸盐和钛酸盐的异质结结构，导致复合材料中两相的导带偏移。因此，光激发电子从钛酸盐转移到钛酸盐导致电子-空穴对的复合被抑制。此外，铀在钛酸盐和钛酸盐异质结的隧道晶格中的捕获防止了U（IV）再氧化为U（VI），从而实现了铀的长期固定。再动员试验表明，只有18.7%的U（VI）被再氧化为U（VI），几乎没有U溶解到水相暴露90天。这种新材料有望用于水中高强度放射性核素的分离和安全处置。
A niobate/titanate nanoflakes (Nb/TiNFs) composite was synthesized through a one-step hydrothermal method. Nb/TiNFs displayed a heterojunction structure owing to deposition of a small fraction of niobate onto tri-titanate nanoflakes. Tri-titanate (Na1.6H0.4Ti3O7radical dot1.7H2O) was the primary crystal phase, and the molar ratio of niobate (Na2Nb2O6radical dotH2O) to titanate was determined to be 1:15.9. Nb/TiNFs showed rapid adsorption kinetics and high adsorption capacity for U(VI) (LangmuirQmax= 298.5 mg/g). Ion-exchange and surface complexation were the key mechanisms for U(VI) uptake, and the adsorption was further enhanced by the unique tunnel lattice structure of the heterojunction. Moreover, Nb/TiNFs were able to convert U(VI) into its immobile form, UO2(s) under solar light through photocatalytic reduction. More than 89.3% of (VI) was transformed into U(IV) after 4 h of solar irradiation (initial U(VI) = 20 mg/L, pH = 5.0). Diffuse reflectance UV–vis absorption spectra and Mott-Schottky plots indicated a narrowed band gap energy of Nb/TiNFs compared to neat TNTs. Density functional theory (DFT) calculation on band structure and density of states further confirmed the heterojunction architecture of niobate and titanate, resulting in offset of the conduction bands for the two phases in the composite material. Therefore, transfer of photo-excited electrons from titanate to niobate leads to inhibition of recombination of the electron-hole pairs. In addition, the trapping of uranium in the tunnel lattice of titanate and niobate heterojunction prevents re-oxidation of U(IV) to U(VI), thus achieving long-term immobilization of uranium. Remobilization tests indicated that only 18.7% of U(VI) was re-oxidized to U(VI) and almost no U dissolved into the aqueous phase when exposed air for 90 days. The new material is promising for separation and safe disposal of high strength radionuclides in water.