Luxton Todd P, Eick Matthew J, Scheckel Kirk G
US Environmental Protection Agency, National Risk Management Research Laboratory, Land Remediation and Pollution Control Division, 5995 Center Hill Ave, Cincinnati, OH 45224, USA.
J Colloid Interface Sci. 2008 Sep 1;325(1):23-30. doi: 10.1016/j.jcis.2008.05.022. Epub 2008 May 16.
Arsenate adsorption on amorphous (RuO(2)1.1H(2)O) and crystalline (RuO(2)) ruthenium oxides was evaluated using spectroscopic and kinetic methods to elucidate the adsorption mechanism. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local coordination environment of adsorbed arsenate. Additionally, pressure-jump (p-jump) relaxation spectroscopy was used to investigate the kinetics of arsenate adsorption/desorption on ruthenium oxides. Chemical relaxations resulting from the induced pressure change were monitored via electrical conductivity detection. EXAFS data were collected for two initial arsenate solution concentrations, 3 and 33 mM at pH 5. The collected spectra indicated a similar coordination environment for arsenate adsorbed to RuO(2)1.1H(2)O for both arsenate concentrations. In contrast the EXAFS spectra of RuO(2) indicated differences in the local coordination environments for the crystalline material with increasing arsenate concentration. Data analysis indicated that both mono- and bidentate surfaces complexes were present on both RuO(2)1.1H(2)O and RuO(2). Relaxation spectra from the pressure-jump experiments of both ruthenium oxides resulted in a double relaxation event. Based on the relaxation spectra, a two step reaction mechanism for arsenate adsorption is proposed resulting in the formation of a bidentate surface complex. Analysis of the kinetic and spectroscopic data suggested that while there were two relaxation events, arsenate adsorbed to ruthenium oxide surfaces through both mono- and bidentate surface complexes.
采用光谱和动力学方法评估了砷酸盐在非晶态（RuO(2)·1.1H(2)O）和晶态（RuO(2)）钌氧化物上的吸附情况，以阐明吸附机制。利用扩展X射线吸收精细结构光谱（EXAFS）确定吸附砷酸盐的局部配位环境。此外，采用压力跃变（p-jump）弛豫光谱研究砷酸盐在钌氧化物上的吸附/解吸动力学。通过电导率检测监测由诱导压力变化引起的化学弛豫。在pH值为5时，针对两种初始砷酸盐溶液浓度（3 mM和33 mM）收集了EXAFS数据。收集到的光谱表明，对于两种砷酸盐浓度，吸附在RuO(2)·1.1H(2)O上的砷酸盐具有相似的配位环境。相比之下，RuO(2)的EXAFS光谱表明，随着砷酸盐浓度的增加，晶态材料的局部配位环境存在差异。数据分析表明，RuO(2)·1.1H(2)O和RuO(2)上均存在单齿和双齿表面络合物。两种钌氧化物的压力跃变实验得到的弛豫光谱均导致双弛豫事件。基于弛豫光谱，提出了砷酸盐吸附的两步反应机制，导致形成双齿表面络合物。动力学和光谱数据分析表明，虽然存在两个弛豫事件，但砷酸盐通过单齿和双齿表面络合物吸附在钌氧化物表面。
