Zinc oxide - mesoporous silica nanocomposite: preparation, characterisation and application in water treatment for lead, cadmium and chromium removal

Applications of nanomaterials in water and wastewater treatment and in environmental clean-up operations depend on the adsorption capacity of the materials for contaminants such as potentially toxic elements (PTEs). However, on their own nanoparticles can lose effectiveness as contaminant sorbents because of flocculation and aggregation. Embedding nanoparticles within a silica matrix offers one potential solution to the problem; hence, in this study, zinc oxide nanoparticles (ZnO-NP) were embedded in a mesoporous silica (MCM-41) matrix to create a composite material with potential for contaminants removal from water. The composite material (ZnO-mSiO(2)) and original ZnO-NP were characterised via UV-Vis, FTIR, XRD, TGA/DTA, BET, and SEM techniques, and were then evaluated for their capacities to remove cadmium (Cd), chromium (Cr) and lead (Pb) from water samples across varying conditions (pH, initial contaminant concentration, contact time and adsorbent mass: solution volume ratios). Langmuir and Freundlich adsorption isotherms were fit to the data to describe the adsorption observed. The ZnO-mSiO(2) composite material proved highly effective at removing the PTEs (particularly Pb) across a wide range of conditions, with optimum removal rates achieved at pH 7 and above and 90 minutes contact time.