Photodegradation of 2,4-DCP in biochar-related environments: impacts of dissolved organic matter and its molecular weight

The widespread application of biochar has inevitably led to the release of various amounts of biochar-derived dissolved organic matter (BDOM) and gradual formation of a biochar-related environment, which significantly influences the environmental behaviors of contaminants. However, the impacts of BDOM on chlorophenol photodegradation remain unknown. In this study, we prepared BDOM from crop residue biochar to evaluate its effects on 2,4-DCP photodegradation. The results showed that 2,4-DCP undergoes self-sensitized photodegradation <i>via</i> the self-production of ¹O₂ and ˙OH in the absence of BDOM. The BDOM enhanced 2,4-DCP photodegradation owing to the production of ³BDOM*, ¹O₂ and ˙OH, contributing 60%, 22.2% and 4.4%, respectively. Nevertheless, this facilitation effect was weakened with increasing BDOM content because of the enhanced light screening and quenching effects. Low molecular weight (MW, <1 kDa) fractions predominated in BDOM, with a contribution of 62.7%; moreover, these fractions had a higher potential to produce ³BDOM* and ¹O₂ and played more important roles in 2,4-DCP indirect photodegradation than high MW fractions. The high MW fractions (MW > 1 kDa) exhibited a stronger light screening effect that decelerated the photodegradation of 2,4-DCP. Furthermore, the degradation of 2,4-DCP by ³BDOM* occurred <i>via</i> both energy and electron transfer pathways, in which low MW fractions of BDOM were predominantly formed <i>via</i> the energy transfer pathway, while high MW fractions were mainly formed through the electron transfer pathway. These results suggest that the low MW fractions of BDOM have stronger photoactivity and may play more significant roles in influencing the environmental behaviors of refractory pollutants.