Effective degradation of Reactive Red 195 via heterogeneous electro-Fenton treatment: theoretical study and optimization

The magnetite (Fe3O4) nanoparticles were synthesized and supported on the reduced graphene oxide. The characterization of the catalyst was performed by FT-IR, VSM, SEM, XRD, and BET techniques. The obtained results indicated that the in situ synthesis of Fe3O4 using coprecipitation method caused the homogenous formation of magnetite nanoparticles on the surface of reduced graphene oxide (average particle size 71.032 nm) with high stability and catalytic activity toward electro-Fenton removal of Reactive Red 195. The effect of various factors (current intensity, initial pollutant concentration, catalyst weight, and pH) was evaluated by response surface methodology using central composite design. The analysis of variance exhibited that the experimental data are in accordance with the quadratic model. At the optimized operation condition (current intensity of 194.96 mA, initial RR195 concentration of 168.43 mg L-1, 2.0 mg catalyst at pH 3.04), the RR195 and COD removals reached 93.34% and 75.27% in 60 min, respectively. The DFT simulation was performed at B3LYP level of theory. The HOMO-LUMO energy gap was reduced from 2.536 to 2.514 eV after supporting of Fe3O4 on the reduced graphene oxide, which demonstrated the higher electrical conductivity. The RR195 removal followed pseudo-first-order kinetics model (k = 0.044 min(-1), R-2 = 0.9938). The stability of the catalyst against leaching was evaluated, and only 2.4% of iron was leached. The catalyst almost remained efficient after six cycles. [GRAPHICS] .