Effect of aging on surface chemistry of rice husk‐derived biochar

Herein, we aimed to determine the physicochemical properties of biochar produced from rice husk at 350 and 550°C, to characterize changes in the biochar properties during aging and to identify the effect of aging time on these changes. To simulate different stages in the aging process, samples were incubated at a constant temperature in the dark and maintained at 60% water holding capacity for 100–300 d. The transformation and morphology of the biochar particles were monitored by diffuse‐reflectance Fourier transform infrared spectroscopy (DRIFTS), scanning electron microscopy (SEM) coupled with energy X‐ray dispersive spectroscopy, and X‐ray photoelectron spectroscopy (XPS). During aging, a layer formed on the surface and the content of easily oxidized substances increased with increased aging time. In addition, SEM indicated that oxidation occurred close to the biochar surface rather than in the biochar particle interior. Furthermore, the DRIFTS and XPS results indicated that the biochar surface produced at 550°C underwent decarboxylation and hydroxylation, while for the 350°C biochar, the increase in surface oxygen content was associated with the presence of hydroxyl moieties. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 410–417, 2018