Biochar Derived from Mild Temperature Carbonization of Alkali-Treated Sugarcane Bagasse for Efficient Adsorption to Organic and Metallic Pollutants in Water

Persistent organic pollutants (POPs) and metals are harmful pollutants; thus, their emission and diffusion need to be controlled. Biochar derived from biomass shows potential application in pollutant adsorption. Sugarcane bagasse raw (SCR) is a major by-product of the sugar industry, and its added value will be well exploited by a proper carbonization process with a mild temperature. In this work, biochar samples were prepared using simple and cost-effective carbonization to the SCR at 300 and 400 °C (roughly corresponding to the complete volatilization of hemicellulose and cellulose, respectively). The alkali (NaOH) pretreatment was employed, and their activation process was investigated at these temperatures. It was found that alkali pretreatment resulted in significant changes in specific surface area (SSA) and total pore volume (TPV) significantly as compared to those without alkali activation. The changes in surface morphology and oxygen-containing functional groups (mainly C–OH) were observed, especially on the activated one at 400 °C, where the samples showed a pore structure and cracks with uneven distribution. Thus, RhB and Cr(III) which were selected as the represented contaminants were efficiently adsorbed by the samples with alkali pretreatment. Moreover, an excellent monolayer coverage adsorption per unit specific surface area (0.82–57.79 mg/m2) was observed. The adsorption process of RhB on alkali-biochar could be dominated by physisorption, while chemisorption was for Cr(III). In addition, competitive adsorption behavior was speculated to exist between the sodium oxide embedded in alkali-pretreated biochar and Cr (III) in the aqueous phase. Therefore, with a simple alkali pretreatment and a mild temperature carbonization, SCR could be transferred to biochar with adsorption to both POPs and metal ions. This method will be suitable to mass production of biochar for environmental protecting application.