Effects of Chemical Activation Conditions on Hierarchical Porous Carbon via Oxytetracycline Adsorption

Abstract

This study investigated the characteristics and oxytetracycline (OTC) adsorption of hierarchical porous carbons (HPCs) synthesized under different activation conditions using biomass wheat flour (WF) and NaHCO3 as an activator. It was found that the characteristics of the HPCs, such as specific surface area, total and mesopore volume, defects, and crystallinity, were highly dependent on the activation temperature, the dose of the activator, and activation time. In particular, the adsorption mechanisms and adsorption capacity were dominantly governed by the degree of defects in graphitic structures and mesoporosity, which are largely determined by the dose of the activator and the activation temperature. The best OTC adsorption was achieved with the HPC of the most abundant mesopores, which was prepared at 900 °C, a WF:NaHCO3 mass ratio of 1:1, and a duration of 2 h (HPC900_R1.0_2H). Based on the results of the experiments concerning adsorption kinetics, equilibrium adsorption, and the effects of pH, OTC adsorption onto HPC900_R1.0_2H was monolayer in type, homogeneous, governed by the combination of diffusion and chemisorption, and largely attributed to π–π electron–donor–acceptor interactions and electrostatic interactions. The thermodynamic parameters suggest that it is spontaneous and endothermic. These findings provide valuable information about the design and synthesis of HPCs from biomass, which exhibit optimized properties for the adsorption of refractory organic pollutants.