Impacts of temperatures and phosphoric-acid modification to the physicochemical properties of biochar for excellent sulfadiazine adsorption

The textural properties and surface chemistry of phosphoric acid-modified biochars (PABCs) prepared at different pyrolysis temperatures (500-700 degrees C) were studied based on the results obtained from XRD, SEM, BET, FT-IR, Raman, XPS and elements analyses. PABCs prepared at higher temperatures tended to possess a bigger proportion of microporous structure. The adsorption capacity and initial rate of PABCs for sulfadiazine (SDZ) were notably improved to 139.2 mg/g and 9.66 mg/(g min) as calculated from the Langmuir model. The adsorption equilibrium time was only one quarter of that without modification. The H3PO4 modification was advantageous to produce phosphate and break functional groups to form disordered carbon structure abundant of micropores. The enhancement in the adsorption of SDZ was due to the confinement effect of hydrophobic cavities from the mircoporous structure and the pi-pi electron-donor-acceptor interaction. Specially, PABCs exhibited stable adsorption capacities at a wide pH range (3.0-9.0) or relatively high concentrations of coexisting ions.

Automated summary

This study investigated the properties of phosphoric acid-modified biochars (PABCs) prepared at different pyrolysis temperatures. PABCs prepared at higher temperatures had a higher proportion of micropores and showed improved adsorption capacity and rate for sulfadiazine (SDZ). The enhancement in adsorption was attributed to the confinement effect of hydrophobic cavities from the microporous structure and the pi-pi electron-donor-acceptor interaction. PABCs exhibited stable adsorption capacities at a wide pH range or high concentrations of coexisting ions.