Investigation of phenol adsorption performance and mechanism using Na2EDTA-modified activated biochars produced from a fluidized bed pyrolysis system

Abstract

The study investigated the characteristics and mechanisms of phenol adsorption in three types of modified activated biochars (rice straw, rice husk, and sawdust) obtained through fluidized bed pyrolysis system, particularly focusing on biochars activated with KOH and modified with Na2EDTA. The experimental comprehensively analyzed the morphology of biochars through nitrogen adsorption-desorption (BET), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), while employed mathematical descriptions with isotherm, adsorption kinetics, and thermodynamics models. The adsorption process could be better described by the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the spontaneous and exothermic reaction. After being activated by KOH, results showed that KOH could generate potassium vapor for etching carbon layers at high temperatures, forming a microporous structure. With the KOH activation and Na2EDTA modification, the amino (-NH2) and carboxyl (-COOH) groups were effectively loaded on the adsorbents. Especially, after Na2EDTA modification, an N1s peak appeared in the XPS spectrum, the peak area ratios of pyrrolic-N and graphitic-N drop from 54.20 % to 21.45%–49.15% and 16.62%, while that of pyridinic-N and nitrogen oxides correspondingly increased, indicating the presence and alteration of nitrogen-containing functional groups, promoting the formation of π-π bonds, and strengthening of π-π dispersion effects. Meanwhile, the specific surface area reaches 1143.60 m2/g to 1337.20 m2/g, the maximum adsorption capacities reach 156.29 mg/g to 195.17 mg/g, which outperform the commercial activated biochars. This finding suggests that Na2EDTA -modified biochars by fluidized bed could enhance the adsorption capacity for phenol, and offer economic feasibility and high production technical for the environmental protection and wastewater treatment.