Adsorption characteristics and mechanisms of phenol and bisphenol A by nitrogen-modified mask-based biochar

Enhancing the waste use of renewable resources is an important initiative for promoting carbon peaking and carbon neutrality. In this study, common waste masks and herbal dregs were used as raw materials to prepare mask-based biochar through co-pyrolysis, and nitrogen-modified mask-based biochar (NMC) was synthesized hydrothermally using urea as a nitrogen source for the batch adsorption of phenol and BPA. In this paper, the adsorption characteristics of NMC on phenol and bisphenol A were explored using three adsorption kinetic models (pseudo-first-order kinetic, pseudo-second-order kinetic, and Elovich model) and three isothermal adsorption models (Langmuir, Freundlich, and D-R model). The mechanism of NMC adsorption for phenol and bisphenol A was investigated by combining experimental data with characterization results. The results showed that the adsorption process of NMC on phenol and bisphenol A was consistent with the pseudo-second-order kinetic model and the Langmuir model, indicating that the adsorption process was mainly a chemically dominated near-monolayer adsorption. The theoretical maximum adsorption capacities of phenol and bisphenol A by NMC calculated using Langmuir model to be 56.56 mg·g−1 and 48.29 mg·g−1, respectively. In the binary component system, subject to a combination of chemical and physical adsorption, phenol is more competitive due to its high hydrophilicity and small molecular size, and in the process of adsorption, it will form a multilayer substructure of “adsorbent-bisphenol A- bisphenol A/phenol”, which promotes the adsorption of phenol by NMC. The adsorption mechanisms of NMC for phenol and bisphenol A include hydrogen bond, π-π interactions, electrostatic interactions, and pore filling. This study aimed to develop low-cost, efficient adsorbents for the removal of phenolic pollutants.