Ni-doped FeC2O4 for efficient photo-Fenton simultaneous degradation of organic pollutants and reduction of Cr(VI): Accelerated Fe(III)/Fe(II) cycle, enhanced stability and mechanism insight

Fenton system was generally employed only for organic pollutants degradation due to the strong oxidizability, while few study focused on treating the combination pollutants of organic compounds and heavy metals in Fenton process. The Ni-doped FeC2O4 (NiFeOx) photo-Fenton catalyst was prepared for the simultaneous degradation of rhodamine B (RhB) and reduction of Cr(VI). Ni doping could accelerate the Fe(III)/Fe(II) cycle on the catalyst, and also enhance the structural stability which was verified by density functional theory (DFT) calculation. The removal efficiency of RhB/Cr(VI) mixture almost reached 100% within 10 min in the 10-NiFeOx photo-Fenton system. The 10-NiFeOx showed a high efficiency for RhB/Cr(VI) removal in wide pH range (2.9–10.1), and displayed excellent recyclability. In photo-Fenton system, ·OH, ·O2− and h+ played vital roles for RhB degradation, and e−, ·O2−, Fe2+ and ·CO2− were responsible for Cr(VI) reduction. Moreover, 30 L of pilot-scale experiments for the degradation of various organic dyes and toxicity assessment of the degradation intermediates demonstrated that 10-NiFeOx Fenton system had great applicability. This study provides a new insight to design an effective and sustainable photo-Fenton catalyst for treating organic wastewater containing Cr(VI).