Department of Physics, 225 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556, USA.
Department of Civil and Environmental Engineering and Earth Sciences, 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556, USA.
J Colloid Interface Sci. 2017 Dec 15;508:75-86. doi: 10.1016/j.jcis.2017.08.040. Epub 2017 Aug 14.
Remediation and prevention of environmental contamination by toxic metals is an ongoing issue. Additionally, improving water filtration systems is necessary to prevent toxic metals from circulating through the water supply. Graphene oxide (GO) is a highly sorptive material for a variety of heavy metals under different ionic strength conditions over a wide pH range, making it a promising candidate for use in metal adsorption from contaminated sites or in filtration systems. We present X-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Cd (II), U(VI) and Pb(II) ions onto multi-layered graphene oxide (MLGO). This study shows that the binding environment of each metal onto the MLGO is unique, with different behaviors governing the sorption as a function of pH. For Cd sorption to MLGO, the same mechanism of electrostatic attraction between the MLGO and the Cd ions surrounded by water molecules prevails over the entire pH range studied. The U(VI), present in solution as the uranyl ion, shows only subtle changes as a function of pH, likely due to the varied speciation of uranium in solution. The adsorption of the U to the MLGO is through a covalent, inner-sphere bond. The only metal from this study where the dominant adsorption mechanism to the MLGO changes with pH is Pb. In this case, under lower pH conditions, Pb is bound onto the MLGO through dominantly outer-sphere, electrostatic adsorption, while under higher pH conditions, the bonding changes to be dominated by inner-sphere, covalent adsorption. Since each of the metals in this study show unique binding properties, it is possible that MLGO could be engineered to effectively adsorb specific metal ions from solution and optimize environmental remediation or filtration for each metal.
有毒金属造成的环境污染的修复和预防是一个持续存在的问题。此外，有必要改进水过滤系统，以防止有毒金属在供水系统中循环。氧化石墨烯（GO）是一种在不同离子强度条件下、宽 pH 范围内对多种重金属都具有高吸附能力的材料，因此它是一种很有前途的候选材料，可用于从受污染的地点或过滤系统中吸附金属。我们提出了 X 射线吸收精细结构（XAFS）光谱研究结果，探讨了 Cd(II)、U(VI)和 Pb(II)离子在多层氧化石墨烯（MLGO）上的结合环境。这项研究表明，每种金属在 MLGO 上的结合环境是独特的，不同的行为控制着吸附作用随 pH 的变化。对于 Cd 在 MLGO 上的吸附，MLGO 和水分子包围的 Cd 离子之间的静电吸引力在整个研究的 pH 范围内占主导地位。溶液中以铀酰离子形式存在的 U(VI)，其行为随 pH 仅略有变化，可能是由于溶液中铀的形态变化。铀与 MLGO 的吸附是通过共价的内球键进行的。在这项研究中，唯一一种吸附机制随 pH 变化的金属是 Pb。在这种情况下，在较低的 pH 条件下，Pb 通过主要的外层静电吸附键合到 MLGO 上，而在较高的 pH 条件下，键合方式变为主要的内层共价吸附。由于这项研究中的每种金属都表现出独特的结合特性，因此有可能设计 MLGO 以有效地从溶液中吸附特定的金属离子，并针对每种金属优化环境修复或过滤。
