The inherent nature of N/P heteroatoms in Sargassum fusiforme seaweed biochar enhanced the nonradical activation of peroxymonosulfate for acetaminophen degradation in aquatic environments

Abstract

This study investigated the catalytic activity of biochar materials derived from algal biomass Sargassum fusiforme (S. fusiforme) for groundwater remediation. A facile single-step pyrolysis process was used to prepare S. fusiforme biochar (SFBC_X), where x denotes pyrolysis temperatures (600 °C-900 °C). The surface characterization revealed that SFBC₈₀₀ possesses intrinsic N and P heteroatoms. The optimum experimental condition for acetaminophen (AAP) degradation (>98.70%) was achieved in 60 min using 1.0 mM peroxymonosulfate (PMS), 100 mg L^-1 SFBC₈₀₀, and pH 5.8 (unadjusted). Moreover, the degradation rate constant (k) was evaluated by the pseudo-first-order kinetic model. The maximum degradation (>98.70%) of AAP was achieved within 60 min of oxidation. Subsequently, the k value was calculated to be 6.7 × 10^-2 min^-1. The scavenger tests showed that radical and nonradical processes are involved in the SFBC₈₀₀/PMS system. Moreover, the formation of reactive oxygen species (ROS) in the SFBC₈₀₀/PMS system was confirmed using electron spin resonance (ESR) spectroscopy. Intriguingly, both radical (O₂^•-, ^•OH, and SO₄^•-) and nonradical (¹O₂) ROS were formed in the SFBC₈₀₀/PMS system. In addition, electrochemical studies were conducted to verify the electron transfer process of the nonradical mechanism in the SFBC₈₀₀/PMS system. The scavenger and electron spin resonance (ESR) spectroscopy showed that singlet oxygen (¹O₂) is the predominant component in AAP degradation. Under optimal condition, the SFBC₈₀₀/PMS system reached ∼81% mineralization of AAP within 5 min and continued to ∼85% achieved over 60 min of oxidation. Coexisting ions and different aqueous matrices were investigated to examine the feasibility of the catalyst system, and the SFBC₈₀₀/PMS system was found to be effective in the remediation of AAP-contaminated groundwater, river water, and effluent water obtained from wastewater treatment plants. Moreover, the SFBC₈₀₀-activated PMS system demonstrated reusability. Our findings indicate that the SFBC₈₀₀ catalyst has excellent catalytic activity for AAP degradation in aquatic environments.

Keywords: Acetaminophen; Biochar; Electron transfer; Nonradical pathway; Peroxymonosulfate.