A quantitative prediction model for the phosphate adsorption capacity of carbon materials based on pore size distribution

Abstract Capacitive deionization (CDI) is an emerging technology with high efficiency, energy-saving and environmentally friendly, which adsorbs charged ions by polarized electrodes. In this study, the effect of the pore size distribution (PSD) on the electrosorption of phosphate was studied by using five carbon electrodes composed of carbon aerogel (CA) and activated carbon (AC) with different pore structures. Based on the PSD, we developed a quantitative prediction model for the adsorption capacity of carbon materials for phosphate. The results show that the adsorption capacity of carbon materials for phosphate is not directly related to typical pore structure indexes, such as specific surface area (SSA), micropore volume, mesoporous volume, and total pore volume. The adsorption capacity of phosphate is highly positively correlated with the pore volume and BETSSA in 1.1–3.5 nm range, which indicates that pores in 1.1–3.5 nm range are the key to achieving a high phosphate adsorption capacity. Pores may be the main sites where phosphate ions are adsorbed in carbon particles. We developed a quantitative prediction model based on the contributions of pores of different sizes to the adsorption capacity, verified by PSD and the adsorption behavior of eight other carbon materials. This study emphasized the importance of PSD to the electrosorption capacity of carbon electrodes. The developed model provides the possibility for accurate prediction of the phosphate removal capacity of carbon materials applied to CDI electrodes and theoretical guidance for the selection of electrode materials.