LAUSR

In this study, a series of quaternary ammonium-modified hydrochars was fabricated using rice straw as raw material. The physicochemical properties of the hydrochars before and after modification were characterized by FTIR, XPS and CHN element analysis, and an adsorption mechanism was proposed. Results showed the quaternary ammonium groups were successfully grafted onto the hydrochar. The modified hydrochar showed favorable capacity for methyl orange (MO) elimination from aqueous solution with a maximum value of 849 mg/g, which was an order of magnitude higher than that of pristine hydrochar (49 mg/g). Besides, the MO adsorption of all the adsorbents fitted well with the pseudo-second-order and Langmuir models, and the adsorption process was exothermal. Analysis of the adsorption mechanism showed that the decontamination process was primarily controlled by electrostatic attractions and ion exchange.Graphical abstractUtilization of rice straw to produce quaternary ammonium-functionalized hydrochars for the efficient removal of methyl orange.