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A facile method of synthesizing ammonia modified graphene oxide for efficient removal of uranyl ions from aqueous medium

机译：合成氨改性氧化石墨烯以从水性介质中有效去除铀酰离子的简便方法

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Graphene oxide has recently emerged as an efficient adsorbent for removal of heavy metals including radionuclides from contaminated ground water. Here we demonstrate very high adsorption capacity (q(e) = 72.2 mg g(-1)) of graphene oxide for adsorption of uranyl ions. However, in the presence of common interfering cations (Ca2+, Mg2+, K+, Na+, Pb2+, Fe2+ and Zn2+) and anions (CO32-, HCO3-, Cl- and SO42-) that are expected in ground water, the adsorption capacity of uranyl ions on graphene oxide decreased drastically owing to poor selectivity. Here we also report a strategy for significantly improving selective adsorption of uranyl ions in the presence of the above interfering species. The graphene oxide is modified by liquid ammonia in the presence of a dehydrating agent (the material obtained is referred to as NH3-GO adsorbent) and thoroughly characterized by zeta potential measurement, Raman spectroscopy, Fourier transformed infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The suitability of NH3-GO as an adsorbent of uranyl ions has been studied in batch mode as a function of pH, temperature, adsorbent dose and initial concentration of uranyl ions. The maximum experimental adsorption capacity at equilibrium conditions is found to be 40.1 mg g(-1) at pH 6 at 298 K, which is not affected by the presence of most of the cations and anions. This marked improvement in the selectivity of uranyl ion adsorption is attributed to amidation of graphene oxide, rendering improved selectivity as compared to carboxylic acid groups. The maximum monolayer coverage (q(max)) was deduced as 80.13 mg g(-1), indicating it to be an excellent adsorbent. The mechanism of adsorption is studied in terms of adsorption isotherm models, kinetic models and thermodynamic studies, which indicated a dual mechanism of chemisorption and physisorption owing to more than one type of binding site in NH3-GO. It is concluded that the ammonia modified graphene oxide exhibited a highly selective adsorption property for uranyl ions at neutral pH.
机译：氧化石墨烯最近成为一种有效的吸附剂，用于从受污染的地下水中去除重金属，包括放射性核素。在这里，我们证明了非常高的石墨烯氧化物吸附能力（q（e）= 72.2 mg g（-1））对铀酰离子的吸附。但是，在地下水中存在常见干扰阳离子（Ca2 +，Mg2 +，K +，Na +，Pb2 +，Fe2 +和Zn2 +）和阴离子（CO32-，HCO3-，Cl-和SO42-）的情况下，其吸附能力由于选择性差，氧化石墨烯上的铀酰离子急剧减少。在这里，我们还报告了在上述干扰物质存在下，显着提高铀酰离子选择性吸附的策略。氧化石墨烯在脱水剂（获得的材料称为NH3-GO吸附剂）存在下通过液氨进行改性，并通过zeta电位测量，拉曼光谱，傅立叶变换红外光谱，透射电子显微镜和扫描电子进行彻底表征显微镜检查。 NH3-GO作为铀酰离子吸附剂的适用性已分批研究，取决于pH，温度，吸附剂剂量和铀酰离子初始浓度的函数。发现在平衡条件下的最大实验吸附容量是在298 K的pH 6下为40.1 mg g（-1），这不受大多数​​阳离子和阴离子的存在的影响。铀酰离子吸附选择性的显着提高归因于氧化石墨烯的酰胺化，与羧酸基团相比，选择性提高。得出最大单层覆盖率（q（max））为80.13 mg g（-1），表明它是极好的吸附剂。从吸附等温线模型，动力学模型和热力学研究等方面研究了吸附机理，这表明由于NH3-GO中存在多种结合位点，化学吸附和物理吸附具有双重作用。结论是，氨改性的氧化石墨烯在中性pH下对铀酰离子具有高度选择性的吸附性能。

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