Fenton oxidation of synthetic food dyes by Fe-embedded coffee biochar catalysts prepared at different pyrolysis temperatures: A mechanism study

초록

Fe-embedded biochar catalysts originating from waste coffee grounds (Fe@HCBCs) were developed at different pyrolysis temperatures (500, 600, and 700 degrees C) for the Fenton oxidation of synthetic food dyes: amaranth (AM) and sunset yellow (SY). Increasing the pyrolysis temperature significantly improved the physicochemical properties of the Fe@HCBCs (i.e., surface area, total pore volume, and Fe content), which led to the highest AM and SY removal in the Fe@HCBC700/H2O2 system. The Fe@HCBC700/H2O2 system showed 19.0 and 14.6 mg (dyes)/g(catalysts).h of catalytic reaction rate for AM and SY, respectively. The results of the scavenging experiment and electron spin resonance revealed that hydroxyl radicals (center dot OH) were the dominant reactive oxygen species for the oxidation of AM and SY by the Fe@HCBCs/H2O2 system. The heterogeneous Fenton-like reaction between the Fe content of the Fe@HCBC surfaces and H2O2 was the main contributor to the oxidation of AM and SY compared with the homogeneous Fenton reaction caused by aqueous Fe with H2O2. The effects of catalyst dosage (0.1-0.5 g/L), H2O2 concentration (0.0-12.5 mM), pH (3.0-9.0), and solution temperature (15-35 degrees C) on the oxidation of AM and SY by the Fe@HCBCs/H2O2 systems at pH 3.0 were also investigated. The opposite result was obtained in a suspension with pH > 5.0; that is, the removal efficiency gradually increased as the pyrolysis temperature decreased (500 degrees C > 600 degrees C > 700 degrees C) because of the abundance of O-containing functional groups on the surface of the Fe@HCBC500. These observations imply that pyrolysis temperatures might have a strong impact on the catalytic degradation of synthetic food dyes using the Fe@HCBCs/H2O2 systems.

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