N-doped graphitic biochars from C-phycocyanin extracted Spirulina residue for catalytic persulfate activation toward nonradical disinfection and organic oxidation

• Published in: Water research (Oxford) Vol. 159; pp. 77 - 86
• Main Authors: Ho, Shih-Hsin, Chen, Yi-di, Li, Ruixiang, Zhang, Chaofan, Ge, Yiming, Cao, Guoliang, Ma, Ming, Duan, Xiaoguang, Wang, Shaobin, Ren, Nan-qi
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-08-2019
• Subjects: Bacteria inactivation; Biochar; Carbocatalysis; Nonradical; Peroxydisulfate; Bacteria inactivation; Nonradical; Peroxydisulfate; Carbocatalysis; Biochar
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2019.05.008

Biochars are low-cost and environmental-friendly materials, which are promising in wastewater treatment. In this study, biochars were manufactured from C-phycocyanin extracted (C-CP) Spirulina residue (SDBC) via thermal pyrolysis. Simultaneously, N-doping was also achieved from the protein in the algae for obtaining a high-performance carbocatalyst for peroxydisulfate (PDS) activation. The SDBC yielded large specific surface areas, nitrogen loading, and good conductivity, which demonstrated excellent oxidation efficiencies toward a wide array of aqueous microcontaminants. An in-depth mechanistic study was performed by integrating selective radical scavenging, solvent exchange (H2O to D2O), diverse organic probes, and electrochemical measurement, unveiling that SDBC/PDS did not rely on free radicals or singlet oxygen but a nonradical pathway. PDS intimately was bonded with a biochar (SDBC 900-acid, pyrolysis at 900 °C) to form a surface reactive complex that subsequently attacked an organic sulfamethoxazole (SMX) adsorbed on the biochar via an electron-transfer regime. During this process, the SDBC 900-acid played versatile roles in PDS activation, organic accumulation and mediating the electron shuttle from SMX to PDS. This nonradical system can maintain a superior oxidation efficiency in complicated water matrix and long-term stable operation. More importantly, the nonradical species in SDBC 900-acid/PDS system were capable of inactivating the bacteria (Escherichia coli) in wastewater. Therefore, the biochar based nonradical system can provide a mild and high-efficiency strategy for disinfection in waste and drinking water by green carbocatalysis. This study provides not only a value-added biochar catalyst for wastewater purification but also the first insight into the bacteria inactivation via nonradical oxidation.
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•N-doped graphitic biochar (SDBC) was fabricated from Spirulina residue after C-phycocyanin extraction.•The protein in Spirulina residue works as natural nitrogen precursors.•The residual inorganic salts can function as pore forming agents.•SDBC were effective in persulfate activation for sulfamethoxazole degradation.•Carbon based nonradical oxidation can effectively inactivate bacteria in wastewater.