Structural dependent persulfate activation by coke powder for aniline degradation

Abstract

• Structural dependent PS activation by CP is investigated. • CP holds excellent activity for PS activation over a wide pH range. • Dissolved oxygen plays an insignificant role in ROS generation. • The carbonaceous component on CP involves in PS activation but ash does not. • PFRs, OFGs, sp 2 -hybridized carbon and defects contribute to persulfate activation. Coke powder (CP), the by-product of coal carbonization, its activity of persulfate (PS) activation was systematically investigated. Structural dependent organic pollutant degradation performances and the related mechanisms were discussed in detail. The structural characteristics of CP were studied using X-ray diffraction, Raman, Fourier transform infrared spectra, X-ray photoelectron spectra, and electron paramagnetic resonance (EPR) etc. Characterization results indicate that CP contains ∼ 78% carbon and presents highly disordered amorphous structures with abundant oxygenated functional groups (OFGs) and persistent free radicals (PRFs). The catalytic application reveals that CP held excellent activity for PS activation across a wide pH range from 3 − 11. In the presence of 0.5 g/L CP, 0.25 mM PS and 0.021 mM aniline (pH 7 ± 0.2), >99% aniline was degraded within 40 min. Under the interference of inorganic anions (Cl − , HCO 3 − and SO 4 2− ), 98% aniline degradation efficiency still could be achieved. Meanwhile, quenching tests and EPR demonstrated that the superoxide anion radical (O 2 − ) was responsible for aniline degradation in CP/PS system, and its generation was independent of dissolved oxygen. The outstanding performance of aniline degradation and ROS generation were attributed to the existence of PRFs, sp 2 -hybridized carbon, OFGs and defects on CP inducing O–O bonding homolytic cleavage of PS into sulfate radicals. Besides, the OFGs including C–OH and –COOH as electron donors facilitated PS decomposition to generate O 2 − . The findings imply that CP is an excellent PS activator, and clarify the development of remediation materials by using by-products of coking process for wastewater treatment.