New composite of pecan nutshells biochar-ZnO for sequential removal of acid red 97 by adsorption and photocatalysis

A new composite, biochar derived from pecan nutshell with ZnO (biochar-ZnO) was prepared, in order to obtain a potential catalyst for degradation of Reactive Red 97 (RR97) from aqueous solutions. Composites with different ratio of ZnO supported in the biochar were produced using mechanical mixing and pyrolysis in a reducing atmosphere from N2 at 650 °C. The catalyst composites were characterized by XRD, FT-IR, UV–Vis, FE-SEM, EDS, and BET. The composites presented higher activity compared to ZnO pure. The composite with greater amount of ZnO supported in the biochar (N20Z) degraded 100% of RR97 in only 67 min (30 min biosorption + 37 min photocatalysis). This remarkable performance could be associated to decrease of electron-hole recombination rate, reducing the band gap energy, and increasing the surface area of the photocatalyst. The recycling of the composite N20Z indicated that it can be used for more than 9 cycle and be easily removed from solution. Radical scavenger tests indicated that •OH and h+ were the predominant active species involved on the degradation of RR97. The proposed mechanism indicated that RR97 molecule degrades into lower-mass intermediates Therefore, the composite presented intrinsic properties that become it a promising catalyst for removal of emerging contaminant in water.