Key Role of Persistent Free Radicals in Hydrogen Peroxide Activation by Biochar: Implications to Organic Contaminant Degradation

Abstract

We investigated the activation of hydrogen peroxide (H2O2) by biochars (produced from pine needles, wheat, and maize straw) for 2-chlorobiphenyl (2-CB) degradation in the present study. It was found that H2O2 can be effectively activated by biochar, which produces hydroxyl radical ((•)OH) to degrade 2-CB. Furthermore, the activation mechanism was elucidated by electron paramagnetic resonance (EPR) and salicylic acid (SA) trapping techniques. The results showed that biochar contains persistent free radicals (PFRs), typically ∼ 10(18) unpaired spins/gram. Higher trapped [(•)OH] concentrations were observed with larger decreases in PFRs concentration, when H2O2 was added to biochar, indicating that PFRs were the main contributor to the formation of (•)OH. This hypothesis was supported by the linear correlations between PFRs concentration and trapped [(•)OH], as well as kobs of 2-CB degradation. The correlation coefficients (R(2)) were 0.723 and 0.668 for PFRs concentration vs trapped [(•)OH], and PFRs concentration vs kobs, respectively, when all biochars pyrolyzed at different temperatures were included. For the same biochar washed by different organic solvents (methanol, hexane, dichloromethane, and toluene), the correlation coefficients markedly increased to 0.818-0.907. Single-electron transfer from PFRs to H2O2 was a possible mechanism for H2O2 activation by biochars, which was supported by free radical quenching studies. The findings of this study provide a new pathway for biochar implication and insight into the mechanism of H2O2 activation by carbonaceous materials (e.g., activated carbon and graphite).

Competitive adsorption of cadmium and aluminum onto fresh and oxidized biochars during aging processes

“…Biochar is a carbon-rich material produced during the pyrolysis of biomass, and its application as in situ heavy metal immobilization has received considerable interests in recent years (Chen and Yuan 2011;Chen et al 2012;Downie et al 2012;Fang et al 2014;Lehmann 2007;Woolf et al 2010;Xu and Chen 2015). Biochar was shown to be a promising amendment agent for the immobilization of heavy metal, and both inorganic matter (such as P and Si) and organic functional groups in biochars affected the immobilization and bioavailability of heavy metal (Angelo et al 2014;Cao et al 2009a;Luo et al 2014;Uchimiya et al 2012a;Zhang et al 2013a;Xu and Chen 2015).…”

Effect of H2O2 concentrations on copper removal using the modified hydrothermal biochar

“…3 implied that the hydroxyl group on HLG was close to increase lineally with the increase of H 2 O 2 concentrations. On the other hand, Fang et al (2014) claimed that persistent free radicals (PFRs) were contained on biochar surface and could produce carboxylic groups when H 2 O 2 was added. However, carbon loss was also very obvious with the increase of H 2 O 2 concentrations (Guo and Chen, 2014), which could mainly be due to aromatic carbons decomposed by H 2 O 2 (Heard and Senftle, 1984).…”

Biochar – Ecological Product and Its Application in Environmental Protection

“…For this reason, a physicochemical modification is often considered both in proper biomass pyrolysis and after pyrolysis performed. A modification (change in functional groups) can be carried out by oxidation [7][8][9], amination [10], sulfonation [11] and esterification [12].…”