A series of copper(II), nickel(II) and zinc(II) dimetallic complexes were prepared and their affinities towards arsenate investigated. Indicator displacement assays (IDAs) were carried out to establish the complexes with best affinities towards arsenate. A di-zinc complex (3) was selected and its arsenate-binding abilities investigated by isothermal titration calorimetry (ITC). The X-ray crystal structure of this metallo-receptor bound to arsenate is also reported, which allowed us to establish the binding mode between 3 and this oxyanion. Immobilising 3 onto HypoGel resin yielded a novel adsorbent (Zn–HypoGel) with high affinity for arsenate. Adsorption of arsenate from competitive solutions and natural groundwater was greater than that of the commercially used iron oxide Bayoxide E33. Zn–HypoGel could be efficiently and simply regenerated by washing with sodium acetate solution.
Synthesizing and testing bicomposite adsorbents for the removal of environmentally problematic oxy-anions is high on the agenda of research-led universities.Here we present a laboratory module successfully developed at Imperial College London that introduces the advanced undergraduate student in engineering (chemical, civil, earth) and science (chemistry, materials, earth science) to several fundamental principles associated with this research area in a simple, engaging and safe way. This includes (i) the synthesis of inorganic bicomposite sorbents, (ii) the evaluation of the adsorption−removal process, and (iii) the analysis of the sorbate; all underpinned by theory. We devise an experiment using phosphate oxyanions and an iron−titanium oxide bicomposite sorbent, which is simple to synthesize. The adsorption of phosphate solutions of varying concentration is tested and assessed at pH 5 and 9. Phosphate concentrations at equilibrium are analyzed using UV−vis spectroscopy to plot adsorption isotherms and compare the Langmuir and Freundlich models. This topical introduction to environmental engineering is an excellent opportunity to investigate adsorption processes. The complexity of data interpretation can be tailored to a range of abilities, and the topics addressed in the experiment are relevant starting points for further exploration of environmental geochemistry, pollution control, element transport, and adsorption. We present ready-to-use spreadsheets for the students to facilitate data analysis.
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