Coupling adsorption and degradation in p-nitrophenol removal by biochars

Biochar is an attractive class of materials because of its various feedstock and wide application potential in agricultural and environmental remediation activities. Recent studies have suggested that biochar may both adsorb and degrade organic contaminants; however, the properties of biochar that control its apparent interactions with organic contaminants are still unknown. In this study, p-nitrophenol was chosen as a model organic pollutant. Its adsorption and degradation by biochar were investigated with a special focus on correlations with the biochar properties. The apparent removal of p-nitrophenol by biochars increased with the increase of pyrolysis temperature. After acetonitrile extraction of the biochars, p-nitrophenol adsorption increased while degradation decreased. Thus, there was no significant change in the apparent removal of p-nitrophenol across eight reaction cycles. An analysis of the physicochemical properties of biochar showed that p-nitrophenol adsorption was determined by the biochar surface area, while the degradation may be because of the varying compositions of biochars, including free radicals, functional groups determining its redox activities, and transition metals. The relative importance of these compositions varied with the pyrolysis temperature. More extensive study is warranted on the relationship between biochar properties and reactivity for targeted biochar production and application. The results of this study provide fundamental information on biochar preparation and its application in organic pollutant removal.