Co-precipitation strategy for engineering pH-tolerant and durable ZnO@MgO nanospheres for efficient, room-temperature, chemisorptive removal of Pb(II) from water

Due to high surface area and large pore volume, nanostructure zinc oxides/its composites have gained a lot of research interests for heavy metal removal from water. Low stability of the ZnO at low and high pH is however a problem. In this work, ZnO@MgO, ZnO and MgO are synthesized via co-precipitation, followed by calcinations. The samples show remarkable removal of Pb(II) from water when compared to commercial samples; the best results is obtained using ZnO@MgO which exhibit adsorption capacity of 250 mg g −1 equivalent to 100% removal capacity. The optimum removal capacity is retained in a wide range of pH (i.e. pH 6–9) at temperature 30 °C. Low adsorption capacity coupled with low stability in acidic condition; a problem associated with ZnO-based adsorbents when it is being used for the removal of heavy metals from water/wastewater; often prevents this system from being practically used; is overcome here. The ZnO@MgO adsorbent shows chemical stability over wide range of pH(2–9). The adsorption is chemisorptive in nature, endothermic and evidently aided by high surface heterogeneity (△H° ˜25 kJ mol-1 and △S°˜110.6 J mol −1  K −1 ). Appreciable adsorption capacity over wide range of pH-value, high recovery and reusability results from nanosphere morphology of the composite sample; all these novel properties are attributed to the strong electronic coupling effect between MgO and ZnO. This work is expected to spur further research on ZnO-based composite materials in allied areas, including (i) mitigation of atmospheric pollution and (ii) water treatment processes.