Degradation of p-Nitrophenol on Biochars: Role of Persistent Free Radicals

Abstract

Generation of environmentally persistent free radicals (EPFRs) on solid particles has recently attracted increasing research interest. EPFRs potentially have high reactivity and toxicity. However, the impact of EPFRs on organic contaminant behavior is unclear. We hypothesized that EPFRs in biochars can degrade organic contaminants and play an important role in organic contaminant behavior. We observed obvious degradation of p-nitrophenol (PNP) in the presence of biochars, through the detection of NO3(-) as well as organic byproducts. The extent of PNP degradation was correlated to the intensity of EPR signals of biochar particles. tert-Butanol (a •OH scavenger) did not completely inhibit PNP degradation, indicating that •OH could not fully explain PNP degradation. The decreased PNP degradation after tert-butanol addition was better correlated with reduced PNP sorption on biochars. PNP degradation through the direct contact with EPFRs in biochar particles could be an important contribution to the PNP concentration reduction in the aqueous phase. The coating of natural organic matter analogue (tannic acid) on biochars did not considerably inhibit PNP degradation, suggesting the ability of biochars to degrade PNP in soil and natural water. Similar EPFR-promoted degradation was observed for five different types of biochars and one activated carbon, as well as one additional chemical (p-aminophenol). Therefore, organic chemical degradation by EPFRs in biochars can be a common process in the environment and should be incorporated in organic chemical fate and risk studies.

Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin

“…The relatively higher reactivity of FeS/Fe3O4@BC500 and FeS/Fe3O4@BC600 composites in catalyzing the degradation of ciprofloxacin (Figure 8a) should be related to the higher aromaticity of biochar prepared at higher pyrolysis temperature. Because more aromatic structure in biochar favors the resonance stabilization of free radicals [40,54]. The results indicate the biochar-supported composite is more stable than the unsupported one, which is beneficial for reusability of the biochar-supported catalyst.…”

“…The relatively higher reactivity of FeS/Fe 3 O 4 @BC500 and FeS/Fe 3 O 4 @BC600 composites in catalyzing the degradation of ciprofloxacin (Figure 8a) should be related to the higher aromaticity of biochar prepared at higher pyrolysis temperature. Because more aromatic structure in biochar favors the resonance stabilization of free radicals [40,54]. In general, the biochars prepared at temperatures other than 500 °C were also applicable as support of iron compounds for enhancing their catalytic activity, while the reasons for the different performance of biochar prepared at different temperatures deserve further investigations.…”

A scientometric review of biochar research in the past 20 years (1998–2018)

“…More importantly, the degradation of organic pollutants by biochar deserved increasing attention because it could completely remove organic pollutants. The persistent free radicals could directly degrade (Chen et al 2017a;Fang et al 2017;Qin et al 2017a;Yang et al 2016bYang et al , 2017 or activate H 2 O 2 /persulfate (Ouyang et al 2017;Wang et al 2017b;Yang et al 2017) to degrade organic pollutants. Modified biochar was also effective in the degradation of organic pollutants.…”

Catalytic degradation of the soil fumigant 1,3-dichloropropene in aqueous biochar slurry

“…The results showed that the degradation rate were 49.47%, 54.51%, 32.17%, and 30.57% on dry C-300, C-700, R-300, and R-700, respectively. Therefore, we assumed that biochar itself can also directly catalyze the degradation of 1,3-D (Tuazon et al, 1984;Yang et al, 2016).…”

“…EPFRs in biochar particles can contribute to contaminant degradation (Fang et al, 2014(Fang et al, , 2015Yang et al, 2016). The standard curve of DPPH is shown Fig.…”