Heterogeneous activation of peroxymonocarbonate by chalcopyrite (CuFeS2) for efficient degradation of 2,4-dichlorophenol in simulated groundwater

Recently, increasing attention has been paid to the activated peroxymonocarbonate (APMC) process, because it is envisioned to be engineered for the chemical oxidation remediation of groundwater in karstic regions with elevated levels of naturally occurring bicarbonate. In the present study, we explored the feasibility of using metal sulfides (CuFeS2, CuS, and FeS2) as the catalysts for heterogeneous APMC (H-APMC) processes. Among the three synthesized metal sulfides, the CuFeS2 catalyst exhibited reversible redox properties, thereby it had the best performance to activate peroxymonocarbonate (PMC) for the degradation of 2,4-dichlorophenol (2,4-DCP). The X-ray photoelectron spectroscopy analysis and density-functional-theory calculations both revealed that, for the CuFeS2-catalyzed APMC process, iron sites of CuFeS2 acted as the catalytic active sites. Electron spin resonance and chemical quenching experiments revealed that the intermediated reactive species for a CuFeS2-catalyzed APMC process included hydroxyl radicals ((OH)-O-center dot), singlet oxygen (O-1(2)), superoxide radicals (O-center dot(2)-), and carbonate radicals ((CO3-)-C-center dot). It was also found that, under a low bicarbonate condition (<= 25 mM), the concentration of H2O2 was not the limiting factor that controlled the degradation rate of 2,4-DCP. Instead, bicarbonate concentration and catalyst dosage significantly influenced the performance of CuFeS2-catalyzed APMC process. Al2O3-supported CuFeS2 catalyst (Al2O3@CuFeS2) was prepared and tested as fillers for practical application. The flowing experiment using fixed-bed reactor showed that the Al2O3@CuFeS2 fillers could effectively activate PMC and thereby degraded the 2,4-DCP. Runoff of the coated CuFeS2 component occurred during the experiment, but the leached copper and iron species from the fillers were constantly at a low and safe level (< 1.5 mg/L). The CuFeS2-catalyzed APMC process showed a good prospect for groundwater remediation in karstic regions.