Hayes Patrick L, Malin Jessica N, Konek Christopher T, Geiger Franz M
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA.
J Phys Chem A. 2008 Jan 31;112(4):660-8. doi: 10.1021/jp076976g. Epub 2008 Jan 9.
Inorganic anions and cations are ubiquitous in environmental chemistry. Here, we use second harmonic generation to track the interaction of the environmentally important metal cations barium, strontium, and cadmium and the nitrate anion with fused quartz/water interfaces at pH 7. Using a dynamic flow system, we assess the extent of reversibility in the binding process and report the absolute number density of adsorbed cations, their charge densities, and their free energies of adsorption. We also present resonantly enhanced second harmonic generation experiments that show that nitrate is surface active and report the free energies and binding constants for the adsorption process. The second harmonic generation spectrum of surface-bound nitrate shows a new adsorption band that cuts further into the solar spectrum than nitrate in the aqueous or solid state. The results that we obtain for all four inorganic ions and the implications for tropospheric and aquatic chemistry as well as geochemistry are discussed in the context of fundamental science as well as pollutant transport models.
无机阴离子和阳离子在环境化学中无处不在。在此，我们利用二次谐波产生技术来追踪环境中重要的金属阳离子钡、锶和镉以及硝酸根阴离子在pH值为7时与熔融石英/水界面的相互作用。使用动态流动系统，我们评估了结合过程中的可逆程度，并报告了吸附阳离子的绝对数密度、它们的电荷密度以及吸附自由能。我们还展示了共振增强二次谐波产生实验，该实验表明硝酸根具有表面活性，并报告了吸附过程的自由能和结合常数。表面结合硝酸根的二次谐波产生光谱显示出一个新的吸附带，该吸附带比水溶液或固态中的硝酸根更深入地切入太阳光谱。我们针对所有四种无机离子所获得的结果，以及它们对对流层和水生化学以及地球化学的影响，将在基础科学以及污染物传输模型的背景下进行讨论。
