Catalytic Removal of Aqueous Contaminants on N-Doped Graphitic Biochars: Inherent Roles of Adsorption and Nonradical Mechanisms

Abstract

Environmentally friendly and low-cost catalysts are important for the rapid mineralization of organic contaminants in powerful advanced oxidation processes (AOPs). In this study, we reported N-doped graphitic biochars (N-BCs) as low-cost and efficient catalysts for peroxydisulfate (PDS) activation and the degradation of diverse organic pollutants in water treatment, including Orange G, phenol, sulfamethoxazole, and bisphenol A. The biochars at high annealing temperatures (>700 °C) presented highly graphitic nanosheets, large specific surface areas (SSAs), and rich doped nitrogen. In particular, N-BC derived at 900 °C (N-BC900) exhibited the highest degradation rate, which was 39-fold and 6.5-fold of that on N-BC400 and pristine biochar, respectively, and the N-BC900 surpassed most popular metal or nanocarbon catalysts. Different from the radical-based oxidation in N-BC400/PDS via the persistent free radicals (PFRs), singlet oxygen and nonradical pathways (surface-confined activated persulfate-carbon complexes) were discovered to dominate the oxidation processes in N-BC900/PDS. Moreover, the adsorption of organics was determined to be the key step determining reaction rate, revealing that the pre-adsorption of reactants significantly accelerated the nonradical oxidation pathway. This study not only provides robust and cheap carbonaceous materials for environmental remediation but also enables the first insight into the graphitic biochar-based nonradical catalysis.

Application of biochar-based materials in environmental remediation: from multi-level structures to specific devices

“…The surface chemistry of biochar, including surface functional groups, surface charge, and free radicals, is critical to the behavior of the interface between biochar and organic and inorganic chemicals, for example, it provides important sites for adsorption, and catalytic degradation of pollutants (Chen et al 2015;Fang et al 2015;Lieke et al 2018;Zhong et al 2019;Zhu et al 2018).…”

“…N-doped graphitic biochar can be used as an efficient catalyst for peroxydisulfate (PDS) activation to degrade organic pollutants by two possible reaction pathways. The radical oxidation way was considered to be that electronegative graphitic N induced transfer of electrons from biochar to PDS, which facilitates the generating of free radicals; while, the nonradical oxidation way was put forward as following: PDS was bonded with N-doped sites in biochar to form metastable surface-confined activated persulfate-carbon complexes and then react with adsorbed pollutants in a direct electron-transfer way (Zhu et al 2018).…”

Heterogeneous activation of peroxymonosulfate for bisphenol AF degradation with BiOI0.5Cl0.5

“…20,21 In recent years, lots of researchers have focused their attention on the oxone (potassium peroxymonosulfate, PMS), which is an eco-friendly and promising source to generate $SO 4À c radicals. [22][23][24][25][26][27] On the other hand, bismuth oxyhalides (BiOX, X ¼ Cl, Br and I) have been admitted as excellent adsorbents and photocatalysts for the removal of organic pollutants in the water. [28][29][30][31] The band gaps of BiOX can be within 1.7-3.4 eV by varying the halides and the composition ratios of the two halides (BiOX a -Y 1Àa ).…”

Biochar-based materials and their applications in removal of organic contaminants from wastewater: state-of-the-art review

“…Despite the metal nanoparticles loading and chemical modification, researchers found the multifunctional properties of BCs can be strongly affected by using the different element doping methods (Wang et al 2018d;Liang et al 2018;Wu et al 2017b;Wang et al 2019). On this base, Zhu et al (2018b) fabricated an environment friendly and cost-effective material, N-doped graphitic BCs (N BCs), through the pyrolysis of mixture of wetland plants (reed) and ammonium nitrate (Fig. 3e).…”