ATR-FTIR and XPS study on the structure of complexes formed upon the adsorption of simple organic acids on aluminum hydroxide |
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Authors: | GUAN Xiao-hong CHEN Guang-hao and SHANG Chii |
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Institution: | 1. Department of Environmental Engineering,Jiangsu Polytechnic University,Changzhou 213164,China 2. Department of Civil Engineering,Hong Kong University of Science and Technology,Hong Kong,China |
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Abstract: | Information on the binding of organic ligands to metal (hydr)oxide surfaces is useful for understanding the adsorption behaviour of natural organic matter (NOM) on metal (hydr)oxide. In this study, benzoate and salicylate were employed as the model organic ligands and aluminum hydroxide as the metal hydroxide. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra revealed that the ligands benzoate and salicylate do coordinate directly with the surface of hydrous aluminum hydroxide, thereby forming inner-sphere surface complexes. It is concluded that when the initial pH is acidic or neutral, monodentate and bridging complexes are to be formed between benzoate and aluminum hydroxide while bridging complexes predominate when the initial pH is alkalic. Monodentate and bridging complexes can be formed at pH 5 while precipitate and bridging complexes are formed at pH 7 when salicylate anions are adsorbed on aluminum hydroxide. The X-ray photoelectron (XP) spectra demonstrated the variation of C 1s binding energy in the salicyate and phenolic groups before and after adsorption. It implied that the benzoate ligands are adsorbed through the complexation between carboxylate moieties and the aluminum hydroxide surface, while both carboxylate group and phenolic group are involved in the complexation reaction when salicylate is adsorbed onto aluminum hydroxide. The information offered by the XPS confirmed the findings obtained with ATR-FTIR. |
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Keywords: | Adsorption aluminum hydroxide benzoic acid complexation natural organic matter salicylic acid aluminum hydroxide organic acids simple adsorption complexes structure groups complexation reaction carboxylate variation binding energy photoelectron precipitate anions bridging initial acidic neutral forming spectra |
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