Biochar is being increasingly applied for carbon dioxide (CO2) capture to preserve environmental quality. The use of soybean waste, soybean curd residue (SCR) as CO2 adsorbents can help to reduce the uncontrolled disposal of SCR. In this research, SCR-based biochar (Biochar@SCR) was prepared by pyrolysis process. For chemical activation, Biochar@SCR was immersed for 12 hours in 42.5 wt.% H3PO4 solution at 1:1 ratio (g precursor/g H3PO4) to obtain Biochar@SCR-M1. Biochar@SCR-M2 was produced when Biochar@SCR-M1 was pyrolyzed again at 5000C for 2 hours. Elemental and functional groups analyses showed the presence of elemental phosphorus (P) and functional groups of P=O or P=OOH for Biochar@SCR-M1 and Biochar@SCR-M2, suggesting the chemical modification using H3PO4 was successful. Morphological analysis revealed the formation of pores after the pyrolysis process and chemical treatment with H3PO4. Analysis of CO2 adsorption depicted that the adsorption capacities of SCR, Biochar@SCR, Biochar@SCR-M1, and Biochar@SCR-M2 were 3.00 mg/g, 25.21 mg/g, 30.50 mg/g, and 36.00 mg/g, respectively. This result proved the increased CO2 sorption for H3PO4-treated Biochar@SCR, suggesting that phosphoric acid modification is an effective method for preparing biochar with high carbon dioxide adsorption.
