Role of the surface characteristics of hyper-crosslinked polymers on the transformation of adsorbed trichlorophenol: Implications for understanding the surface reactivity of biochar derived from waste biomass

The surface reactivity of biochar derived from waste biomass has not been well understood due to its complex composition and heterogeneity. Therefore, this study synthesized a series of biochar-like hyper-crosslinked polymers (HCPs) with different amounts of phenolic hydroxyl groups on the surface as an indicative tool to investigate the roles of key surface properties of biochar on transforming pollutants being adsorbed. Characterization of HCPs suggested that electron donating capacity (EDC) of different HCPs was positively correlated with increasing amounts of phenol hydroxyl groups, whereas specific surface area, degree of aromatization and graphitization were negatively correlated. It was found that greater amounts of hydroxyl radicals were produced with increasing amounts of hydroxyl groups on the synthesized HCPs. Batch degradation experiments with trichlorophenols (TCPs) suggested that all HCPs could decompose TCP molecules upon contact. The degree of TCP degradation (~45 %) was highest for HCP made from benzene monomer with the lowest amounts of hydroxyl groups, which was likely driven by its greater specific surface area and reactive sites for TCP degradation. Conversely, the degree of TCP degradation (~25 %) by HCPs with the highest hydroxyl group abundance was the lowest, probably because the lower surface area of HCPs had limited TCP adsorption, which led to lower interaction between HCP surface and TCP molecules. The results concluded from the contact of HCPs and TCP suggested both EDC and adsorption capacity of biochar played critical roles in transforming organic pollutants.