摘要
研究了pH值对无定型介孔TiO2表面吸附速率的影响。水中低质量浓度的As(Ⅲ)在介孔TiO2表面的吸附速率可以用表面配合模型来模拟和计算,pH值可通过影响H3AsO3的各级离解形态和TiO2的表面羟基化程度进而影响吸附速率(k)和最大吸附量(Qm)。H3AsO3的各种形态在TiO2羟基化/质子化表面(Ti—OH2+、Ti—OH)的吸附速率常数可以通过非线性回归计算得到。结果表明,在近中性的pH值下(pH=6.3～8.0),表观吸附速率常数为0.034 6～0.037 2L/(mg.min),吸附速率大;在较高或较低的pH值条件下,吸附速率显著降低。当pH值为3.04时,其吸附速率k为0.015 7L/(mg.min);当pH值为9.96时,其吸附速率k为0.017 1 L/(mg.min)。最大吸附速率出现在pH值为8.0左右,而最大吸附容量发生在pH值为9.26左右,与H3AsO3的pKa1(9.22)在数值上非常接近。动力学方程计算得到的Qm为4.415mg/g(pH=9.26),而Langmuir吸附等温式和Dubinin-Radushkevich(D-R)吸附等温式(pH=9.03)计算得到的Qm分别为4.79mg/g和4.57 mg/g,不同方法的计算结果比较接近。由于地下水多为弱碱性环境,最大吸附速率和吸附容量均发生在弱碱性条件下对吸附除砷是有利的。
The article is engaged in tracing the effects of pH value on As（Ⅲ） removing from the drinking water with armorphous mesopawns TiO2. Usually, the apparent adsorption rate of As （III） to meso-porous TiO2 from the water can be simulated and calculated by the surface complexion modeling （SCMs）, the whole adsorption rate constant k can be controlled jointly by the surface active site, the concentration of As （Ⅲ） in solution, the dissociation constants of H3AsO3 and pH value. Since pH value can affect the H3AsO3dissoci- ation morphology and TiO2 surface hydroxylation level, it will be further affecting the adsorption rate and adsorption capacity. In addi- tion, we can also obtain the apparent adsorption rate of the dissocia- tion substance of H3AsO3 to the hydroxyhzed or protonlized surface of meso-pomus TiO2 （Ti-OH2＋ , Ti-OH） by using the non-linear re- gression fit of the experimental data. The constant of the apparent adsorption rate should be located in the range from 0.034 6 to 0.037 2 L/mg min while the pH value is in the nearly neutral condition. However, the rate constant tends to decrease no matter whether the pH value increases or decreases. And, since the rate constant k usually increases with the increase of pH value to the range less than 8.0, further increase of the pH value may result in the decrease of k. For example, the apparent adsorption rate constant was 0.015 7 L/（ mg·min ） at its pH value of 3.04 but 0. 017 1 of L/（mg·min ） at pH 9.96. Derived from pseudo-second order kinetics model, the maximum apparent adsorption rate should be 0.037 2 L/（mg·min） at pH 7.97 and the maximum adsorption capacity 4.415 mg/g at pH 9.26. Therefore, the maximum adsorption pH value at 9.26 proves to be co- incided with the first dissociation constant of pKa1 of H3AsO3 at the pH of 9.22. In the same way,it is also passible to work out the maximum adsorption capacity via the Langmuir or Dubinin-Radushkevich adsorption isotherm, which turns out to be 4.79 mg/g and 4.57 mg/g,respect
出处
《安全与环境学报》
CAS
CSCD
北大核心
2013年第2期17-22,共6页
Journal of Safety and Environment
基金
国家自然科学基金项目(50908001)
安徽省优秀青年科技基金项目(10040606Y29)
安徽省重大科技专项(08010301106)
安徽省国际科技合作项目(09080703035)
