Unravelling superior photodegradation ability and key photoactive structures of hydrochar particle to typical emerging contaminant than corresponding bulk hydrochar from food waste

Abstract

Hydrochar from waste biomass is a promising material for removing emerging contaminants (e.g., antibiotics) in water/soil environment. Abundant small-sized hydrochar particles (HPs) with a high content of reactive functional groups and high mobility are easily released into ecosystems through hydrochar applications. However, the photodegradation ability and corresponding structures of HPs are largely unknown, which hinder accurate estimation of the remediation effect of hydrochar in ecosystems. Herein, photodegradation performance of HP towards targeted norfloxacin (NOR, a typical antibiotic) under light irradiation (visible and UV light) were investigated after adsorption processes upon release into soil/water, and its reactive species and photoactive structures were clarified and compared with those of residual bulk hydrochar (BH) comprehensively. The results showed that: (1) photodegradation percentages of HPs were 4.02 and 4.48 times higher than those of BHs under UV and visible light, in which reactive species of both HPs and BHs were ·OH and ·O₂ ⁻; (2) density functional theory (DFT) results identified that the main photoactive structure of graphitic-N decreased the energy gap (Eg) of HPs, and C=O, COOH groups improved electron donating ability of BHs; (3) well-developed graphitization structure of HP resulted from higher polymerization reaction was an significant photoactive structure involving its superior photodegradation ability relative to that of BH. The distinct heterogeneities of photodegradation ability in HP and BH and underlying photoactive structures provide an in-depth understanding of hydrochar application for removing emerging contaminants in soil/water environment. Identifying photoactive structures is helpful to predict photodegradation ability of hydrochar according to their abundance.

Highlights

•	Photodegradation percentage of HP from hydrochar application was ~4 times superior to that of BH in degradation of NOR.
•	Major reactive species of HPs and BHs (·OH and ·O2 −) were generated from graphitic-N and C=O/COOH groups, respectively.
•	Photoactivity of HPs superior to BHs was mainly generated from well-developed graphitization structure of former.

Keywords

Hydrochar / Norfloxacin / Electron–hole / Graphitic-N / Density functional theory

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Funding

National Natural Science Foundation of China(42207276); National Key Research and Development Program of China(2021YFD1700805)