Controlled oxidative decomposition of rice husk to induce formation of hierarchically meso-macroporous carbon foams with unprecedented porosity

Carbon materials with large interconnected pores are desired because of their excellent diffusion performance, but their synthesis is often cumbersome and costly. In this study, we systematically removed cellulose and hemicellulose from rice husk (RH) through oxidative decomposition and subsequently converted the residual material into rice husk carbon (RHC) with an interconnected mesoporous-macroporous structure via NaOH activation. After activation, the resulting RHC exhibits a foam-like morphology with exceptional porosity (S external  = 970 cm 2 /g), which has not been previously reported in the literature. The meso-macroporous structure of RHC is highly correlated with the decomposition degree of RH, indicating that the pore structure originates from the oxidative decomposition process. Furthermore, due to the presence of abundant oxygen-containing functional groups on oxidatively decomposed RH, the consumption of NaOH for subsequent activation is significantly lower than that reported in previous studies (NaOH/char mass ratio of 1.17 for this work, compared to approximately 2–7 in traditional methods). The interconnected meso-macroporous channels of RHC materials result in the exceptional capacity for methyl orange adsorption capacity and fast diffusion rate (Adsorption capacity = 158 mg/g, K 1  = 0.115), exceeding CMK-3 (Adsorption capacity = 98 mg/g, K 1  = 0.063), a typical mesoporous carbon material.