Noncondensed aromatic carbon of sludge-derived biochar predominated peroxydisulfate activation mechanism for tetracycline degradation via an electron transfer pathway

ABSTRACT

Discrimination of the catalytic ability of heterogeneous biochar components is often challenging. Herein, a sewage sludge-derived biochar (SDBC) was prepared to activate peroxydisulfate (PDS) for tetracycline (TC) degradation. To verify the contribution of different carbon components, SDBC was bleached with NaClO₂ and CH₃COOH to remove noncondensed aromatic carbon (NAC) contained in biochar, which was confirmed by ¹³C Nuclear Magnetic Resonance. The batch degradation experiment revealed that NAC removal decreased TC degradation by SDBC from 84.1% to 33.2% within 2 h, indicating its significant role in PDS activation. The quenching and electron paramagnetic resonance experiments suggested a very minor contribution of radical pathway in TC degradation. Instead, the electron transfer pathway predominated TC degradation mechanism as inferred by electrochemical tests. This is likely ascribed to formation of a biochar-PDS metastable complex, facilitating electron transfer from tetracycline-like compounds. An X-ray photoelectron spectroscopy confirmed that the percent of graphitic N in SDBC decreased after the degradation reaction, which suggested graphitic N is an important active site in biochar. Besides, acid-washed SDBC did not change TC degradation behavior excluding significant contribution of minerals in SDBC to PDS activation. Thus, the roles of biochar components in catalyzing PDS were quantified for the first time, proving insight for selection and manipulation of biochar in catalyzing PDS in environmental application.

GRAPHICAL ABSTRACT

Highlights

• Noncondensed aromatic carbon in biochar is critical for activating peroxydisulfate.

• Direct electron transfer is the primary pathway for biochar to degrade tetracycline.

• The metastable graphitic N-PDS complex was dominant active sites.

• The catalytic ability of biochar is well maintained over a wide pH range.

KEYWORDS:

• Sludge-derived biochar
• noncondensed aromatic carbon (NAC)
• peroxydisulfate (PDS)
• electron transfer
• antibiotic degradation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/26395940.2023.2267755

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [Grant numbers 42277040; 41977117], the National Key Research and Development Program of China [Grant numbers 2021YFD1700800], Qing-Lan Project of Yangzhou University [2020], High-level Talent Support Plan of Yangzhou University [2019], and the Start-up Fund for Introduced Scholar of Jiangsu University [5501370018].