Bisphenol A promotes tannins adsorption by increasing heterogeneity and hydrophilicity of porous carbons: evidence from site energy distribution

The coexistence of phenolics is ubiquitous in real environments. However, competitive and complementary adsorptions between phenolics, including tannins and bisphenol A (BPA), remain unclear because of the different adsorption preferences of the adsorbent surface. In this study, novel H₃PO₄/NaOH modified porous carbons derived from corn were synthesized. The objective was to investigate the effect of the adsorption site availability on phenolics adsorption determined by pore size. Results showed that BPA and GA (gallic acid) exhibited high adsorption on H₃PO₄-modified porous carbon (220.74, 144.52 mg·g⁻¹, respectively). TA (tannic acid) demonstrated high adsorption on NaOH-modified porous carbon (201.38 mg·g⁻¹). The adsorption of BPA, GA and TA involved multiple interactions, including hydrogen bond, π-π interactions, hydrophobic interactions and pore filling. Analysis of approximate energy distribution indicated that H₃PO₄/NaOH activation increased the number of adsorption sites of porous carbons. The energy distributions of BPA were overlapped with that of GA, which further verified that BPA competed for adsorption to GA more than to TA. Although BPA occupied adsorption sites on porous carbon over GA and TA, it modified the heterogeneity and hydrophilicity of porous carbons, and promoted the adsorption of GA (126%-200%) and TA (121%-320%). This suggests a complex co-adsorption mechanism where competition is counterbalanced by surface modification effects.