Resource utilization of agricultural residues: one-step preparation of biochar derived from Pennisetum giganteum for efficiently removing chromium from water in a wide pH range.

Biochars derived from agricultural residues, Pennisetum giganteum, were prepared by a one-step activation method after impregnated with HPO. The effects of activation temperature and the HPO impregnation method on the structure and performance of biochar were investigated. The characterization results of XPS, FTIR, and N adsorption-desorption showed that the P-containing biochar prepared by the one-step method had a large specific surface area, large pores, and abundant surface functional groups. And, the groups including C-P, O-P, and C-O participated in the adsorption of Cr(VI). Moreover, the target adsorbent has a good removal effect on Cr (VI) in a wide range of pH. The Cr(VI) removal efficiency was more than 55.92% at pH≤9. Interestingly, the adsorption results also showed that the adsorbent could offer acid groups for regulating the pH of the bulk solution and thus keep the adsorption surroundings in a narrow pH range. In addition, the target adsorbent has been proved to have good selective removal of Cr(VI). Even after repeated use for 5 times, the removal capacity of Cr(VI) is still 77.4%. This work provides a simple scheme for the high-value utilization of Pennisetum agricultural solid waste, and also confirms that the biochar activated by phosphoric acid can effectively remove Cr(VI) in the solution with wide pH range.