Janusz W, Matysek M
Department of Radiochemistry and Colloid Chemistry, Maria Curie Skłodowska University, pl. M.C. Skłodowskiej 3, 20-031 Lublin, Poland.
J Colloid Interface Sci. 2006 Apr 1;296(1):22-9. doi: 10.1016/j.jcis.2005.08.067. Epub 2005 Oct 5.
The study of the adsorptions of cadmium and oxalate ions at the titania/electrolyte interface and the changes of the electrical double layer (edl) structure in this system are presented. The adsorption of cadmium or oxalate ions was calculated from an uptake of their concentration from the solution. The concentration of Cd(II) or oxalate ions in the solution was determined by radiotracer method. For labeling the solution 14C and 115Cd isotopes were used. Coadsorption of Cd(II) and oxalic ions was determined simultaneously. Besides, the main properties of the edl, i.e., surface charge density and zeta potential were determined by potentiometer titration and electrophoresis measurements, respectively. The adsorption of cadmium ions increases with pH increase and shifts with an increase of the initial concentration of Cd(II) ions towards higher pH values. The adsorption process causes an increase of negatively charged sites on anatase and a decrease of the zeta potential with an increase of initial concentration of these ions. The adsorption of oxalate anions at the titania/electrolyte interface proceeds through the exchange with hydroxyl groups. A decrease of pH produces an increase of adsorption of oxalate ions. The processes of anion adsorption lead to increase the number of the positively charged sites at the titania surface. However, specific adsorption of bidenate ligand as oxalate on one surface hydroxyl group may form inner sphere complexes on the metal oxide surface and may overcharge the compact part of the edl. The presence of oxalate ions in the system affects the adsorption of Cd(II) ions on TiO2, increasing the adsorption at low pH range and decreasing the adsorption at high pH range. Using adsorption as a function of pH data, some characteristic parameters of adsorption envelope were calculated.
本文介绍了镉离子和草酸根离子在二氧化钛/电解质界面的吸附研究以及该体系中双电层（EDL）结构的变化。镉离子或草酸根离子的吸附量是通过溶液中其浓度的变化来计算的。溶液中Cd(II)或草酸根离子的浓度采用放射性示踪法测定。为标记溶液，使用了(^{14}C)和(^{115}Cd)同位素。同时测定了Cd(II)和草酸根离子的共吸附情况。此外，分别通过电位滴定和电泳测量确定了双电层的主要性质，即表面电荷密度和zeta电位。镉离子的吸附量随pH值升高而增加，并随着Cd(II)离子初始浓度的增加向更高pH值方向移动。吸附过程导致锐钛矿上带负电的位点增加，并且随着这些离子初始浓度的增加，zeta电位降低。草酸根阴离子在二氧化钛/电解质界面的吸附是通过与羟基交换进行的。pH值降低会导致草酸根离子吸附量增加。阴离子吸附过程导致二氧化钛表面带正电的位点数量增加。然而，草酸根等双齿配体在一个表面羟基上的特异性吸附可能会在金属氧化物表面形成内球络合物，并可能使双电层的紧密部分带过量电荷。体系中草酸根离子的存在会影响Cd(II)离子在TiO₂上的吸附，在低pH范围内增加吸附，在高pH范围内降低吸附。利用吸附量随pH值变化的数据，计算了吸附包络的一些特征参数。
