| In order to adsorb iodine ions from water efficiently, we prepared a visible-light response photocatalytic adsorbent 3D Ag2O-Ag/TiO2 and studied its iodine adsorption performance and mechanism. The main contents were:Firstly, the 3D Ag2O-Ag/TiO2 composites were synthetized and characterized. The composites were synthesized through a photochemical deposition process loading Ag2O and Ag nanoparticles simultaneously on the surface of TiO2 microspheres, which had been prepared beforehand by TiCl4 hydrolysis and self-assembly. The as-prepared 3D Ag2O-Ag/TiO2 spheres were characterized using SEM, EDX, TEM, BET, XRD, XPS and UV-Vis DRS techniques to determine the morphology, microstructure, chemical compositions and optical properties. XRD and XPS analyses showed that Ag atoms in the composites existed in two chemical states, namely Ag2O and Ag. High-resolution TEM images presented Ag2O and Ag nanoparticles were independent with an average size of 3.26 ± 0.04 and 2.67 ± 0.01 nm, respectively. And the content of Ag2O and Ag were 4.192 % and 1.917 % respectively calculated by EDX and XPS. UV-Vis DRS showed the composites had a good visible light absorption.Secondly, the iodine adsorption performance of 3D Ag2O-Ag/TiO2 composites was investigated. The adsorption process of I- reached equilibrium within 300 min with the adsorption capacity of 207 mg/g, and the adsorption process was non-reversible chemical adsorption. Ag2O and Ag nanoparticles played a crucial role in the removal process of iodine, and the adsorption capacity of the composites for Iis greatly enhanced under visible light. The composites have a high selectivity, even in simulated salt lake water where the concentration of Cl- is up to 4.3×105 times that of I-. The composites possess outstanding adsorption ability of trace amount of I-, and the concentration of I- ether in deionized water or Saline Lake can be brought down below 20 ppb. The composites also feature good reusability, as they still performed well through a simple regeneration after five cycles.Finally, the iodine adsorption mechanism of 3D Ag2O-Ag/TiO2 composite was explored. A series of characterization analyses and experiments showed the high efficient removal process of iodine from water occurred through three steps by the cooperative effects between Ag2O and Ag/TiO2, namely the adsorption of Ag2O for I-, the photocatalysis of Ag/TiO2 for oxidation of I- to I2 in visible light and the re-adsorption of AgI for I2. Additionally, the value of n from AgI2n+1 is 1.7 through calculations, which means the adsorption capacity of Ag2O for I- is enlarged 4.4 times by the photooxidation of Ag/TiO2 under visible light. |
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