Effects and mechanism of bridging ligands on the adsorption performance for arsenic and antimony removal by titanium xerogel
To clarity the relationship between the structure of bridging ligands and the adsorption performance,a series of titanium xerogels were synthesized with 11 ligands(organic carboxylic acids,alcohol-amines,and diketones)and their performance for arsenic and antimony removal was investigated.The titanium xerogel synthesized with acetylacetone(AcAc)as a bridging ligand showed an excellent adsorption performance:the adsorption capacities to As(Ⅲ),As(Ⅴ),Sb(Ⅲ),and Sb(Ⅴ)were 329,461,584 and 805 mg·g-1(in titanium),respectively,and the adsorption rates were 10.1,8.1,11.5 and 1.9 times higher than that of the xerogel without organic ligand.All the tested ligands had comparable effects on the adsorption capacity,but led to significant differences in the adsorption rate.The xerogels with organic carboxylic acid ligands adsorbed As and Sb at rates of only 30％—60％of that with AcAc,while weak ligand,such as butanedione,had negligible effect on the adsorption rate.Compared with other ligands,AcAc had a moderate coordination capacity between butanedione and strong ligands(e.g.,tartaric acid and triethanolamine),which balanced the inhibition of rapid hydrolysis of titanium during synthesis and the quick release of new active sites during adsorption.When the hydrogen at the central or terminal carbon of AcAc was substituted by methyl groups,the content of the enolic form and consequently the coordination ability were reduced,which in turn weakened the adsorption performance.
heavy metal pollutiontitanium xerogel adsorbentacetylacetoneligandssol-gel
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