Agrowaste derived biochars impregnated with ZnO for removal of arsenic and lead in water

[Display omitted] •Characterization of biochar derived from ZnO impregnation on residual biomass using precipitation method.•ZnO impregnation improved As and Pb adsorption capacities of biochars.•ZnO impregnation improved the microstructure of the biochar based on corncob and increased the number of active sites.•ZnO impregnated corncob biochar showed the greatest adsorption properties.•Adsorption of As(V) over biochar-ZnO based on corncob and coffee husk adsorbents is reported for the first time. Using residual biomass for biochar production to be applied for water treatment is a cost effective and environmental-friendly alternative to activated carbon. However, biochars are materials with low textural properties (total specific area and total pore volume) and hence lower adsorption capacity compared to activated carbon. In that sense, this study aimed to impregnate ZnO on biochar derived from agricultural residual biomass to improve its As(V) and Pb(II) adsorption capacity. Biochars derived from corn cob and coffee husk were prepared by carbonization in mild conditions and then impregnated with ZnO using precipitation method. The resulting materials were comprehensively characterised describing their textural, chemical, surface, morphological and structural properties. Adsorption capacity of the produced materials was tested with As(V) and Pb(II) in kinetic and equilibrium experiments. The ZnO impregnation of the biochars derived from both precursors improves their adsorption capacities and, in most cases, accelerates the rate of adsorption of both pollutants. The best results were obtained by corncob derived ZnO impregnated biochar (CC-ZnO) reaching a maximum equilibrium adsorption capacity of 25.9 mg of As(V)/g and at least 25.8 mg of Pb(II)/g. The corncob derived ZnO impregnated biochar is a suitable adsorbent candidate for the use in the removal of As and Pb from polluted water.