Preparation and Characterization of Phosphoric Acid-Modified Biochar Nanomaterials with Highly Efficient Adsorption and Photodegradation Ability

Phosphoric acid-modified biochar (PMBC) was prepared using biochar (BC) as the carbon source and phosphoric acid as the activating agent. The PMBC exhibited an ordered vessel structure after deashing treatment, but the sidewalls became much rougher, the polarity (O/C atomic ratio of BC = 0.2320 and O/C atomic ratio of PMBC = 0.1604) decreased, and the isoelectric points (PI of BC = 5.22 and PI of PMBC = 5.51) and specific surface area (SSA of BC = 55.322 m²/g and SSA of PMBC = 62.285 m²/g) increased. The adsorption characterization of the removal of sulfadiazine (SDZ) from PMBC was studied. The adsorption of SDZ by PMBC was in accordance with the Langmuir isotherm model and the pseudo-second-order kinetics model, and the adsorption thermodynamics were shown as Gibbs free energy < 0, an enthalpy change of 19.157 kJ/mol, and an entropy change of 0.0718 kJ/(K·mol). The adsorption of SDZ by PMBC was a complicated monolayer adsorption that was spontaneous, irreversible, and endothermic, and physical adsorption and chemical adsorption occurred simultaneously. The adsorption process was controlled by microporous capture, electrostatic interactions, hydrogen-bond interactions, and π-π interactions. PMBC@TiO₂ photocatalysts with different mass ratios between TiO₂ and PMBC were prepared via the in situ sol-gel method. PMBC@TiO₂ exhibited both an ordered vessel structure (PMBC) and irregular particles (TiO₂), and it was linked via Ti-O-C bonds. The optimal mass ratio between TiO₂ and PMBC was 3:1. The removal of SDZ via PMBC@TiO₂ was dependent on the coupling of adsorption and photocatalysis. The PMBC-enhanced photocatalytic performance of PMBC@TiO₂ resulted in a higher absorption of UV and visible light, greater generation of reactive oxygen species, high levels of adsorption of SDZ on PMBC, and the conjugated structure and oxygen-containing functional groups that promoted the separation efficiency of the hole-electron pairs.