Enhancing the yield of hydrogen peroxide and phenol degradation via a synergistic effect of photoelectrocatalysis using a g-C3N4/ACF electrode

Abstract

In this work, a new activated carbon fiber (ACF) cathode modified with graphitic carbon nitride (g-C3N4) was developed, which enables the substantially improved production of H2O2 (up to 32.8 mg L−1) with relatively low energy consumption (10.9 kWh kg−1) compared to generation without g-C3N4 (4.09 mg L−1). The cathode was analyzed and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction, and it was proved that the synthesized g-C3N4 is a thin layer sheet with a large number of carbon particles and low defect porosity. The cathode manufacturing parameters were optimized, and the influences of H2O2 production including the cathode potential, pH value, aeration rate and performance stability were studied. These features improved the production of H2O2 by about more than 7 folds when optimized ratio of g-C3N4 was used, and the modified cathode kept stable performance of H2O2 generation in 5 cycles. Further discussed by linear sweep voltammetry, rotating disk electrode and contact angle analysis, the existence of g-C3N4 were found to accelerate the electron transfer rate, is advantageous to the surface of the oxygen reaction, but will not change the two electronic number of oxygen reduction reaction activities, and this leads to enhanced performance of hydrogen peroxide production and the possible mechanism was suggested. Finally, the cathode improve by g-C3N4 proved the degradation effect of phenol by photoelectric-Fenton process. Phenol was degraded completely, and 93.8% of the organic carbon was removed, which is more than 1.5 and 5 times the amount achieved using electro-Fenton and photo-Fenton degradation only. In the degradation process of phenol, electrocatalysis and photocatalysis, they were optimized to produce substantial synergistic effect, proving the great potential practical application of organic wastewater treatment.