Biochars produced from different feedstocks via pyrolytic carbonization and ultraviolet (UV) modification were used as alternative adsorbents for aqueous hexavalent chromium (Cr(VI)) remediation. Structural and morphological analysis showed that UV irradiation increased the surface area of biochar and added a large amount of oxygen-containing functional groups on biochar's surface, resulting in about 2–5 times increase of Cr(VI) removing capacity (14.39–20.04 mg/g) compared to that of unmodified biochars (3.60–8.43 mg/g). The sorption ability among different feedstocks after modification was as following: corn stack > sawdust > wheat straw. The adsorption kinetics and adsorption isotherm data agreed well with the pseudo-second-order model and Freundlich model, respectively. Experimental and modeling results suggested that the oxygen-containing functional groups and surface areas of biochars were notably increased after UV irradiation, which was mainly governed by surface complexation. X-ray photoelectron spectroscopy (XPS) analysis showed that reduction occurred during Cr(VI) adsorption. In addition, UV irradiation can significantly increased the concentration of dissolved organic matter (DOM) in biochars. The collected outcomes showed that UV-modified biochar was a good material for the exclusion of hexavalent chromium from aqueous medium. The excellent adsorption capacity, environmental-friendly and low cost properties made the novel material an auspicious candidate for environmental remediation.

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