Rapid reduction of chloramphenicol by sodium bicarbonate-activated biochar loaded with nano zero-valent iron: Influence of pyrolysis parameters and the key role of graphitic carbon structure

Abstract

In this study, sodium bicarbonate (NaHCO₃)-modified biochar (mBC) obtained at a modification ratio of 2:1 was used to load nano zero-valent iron (nZVI) for the removal of chloramphenicol (CAP). nZVI@mBC removed 98.7% of CAP within 60 min, much higher than naked nZVI (45.0%) and unmodified biochar-loaded nZVI (nZVI@BC) (50.7%). The effects of pyrolysis parameters (modification ratio (m[NaHCO₃]/m[biomass]), pyrolysis temperature, heating rate, and holding time) on the ability of biochar to load nZVI were systematically investigated. The results showed that the modification ratio and pyrolysis temperature had a large influence on the loading property of mBC. The mechanism of nZVI@mBC for efficient CAP removal was explored. NaHCO₃-modification promoted the formation of pore and graphite structures of biochar, and facilitated the uniform loading of nZVI. Electrochemical analysis showed that nZVI@mBC reduced CAP by direct electron transfer pathway (DET). The key graphitic carbon structure of mBC promoted the formation of iron-carbon galvanic cell, which favored electron transfer and led to better decontamination performance of nZVI@mBC. In addition, nitro reduction and dechlorination were identified as the main pathways for CAP degradation. Finally, the performance of nZVI@mBC for CAP removal in complex environments was explored to determine its environmental suitability. This study comprehensively analyzed the effects of different pyrolysis conditions on the loading capacity of modified biochar, and also elucidated the key graphitic structure of modified biochar to promote pollutant removal, which can provide a reference for the structural design of biochar-based carriers.