A Study On The Degradation Of Acid Red 73 And Norfloxacin By Persulfate In The Presence Of RGO-Fe₃O₄ Composite

Sulfate radical-based advanced oxidation processes?AOPs?have been received increasing attention due to its simple operation,high efficiency,and no secondary pollution.It utilizes highly reactive sulfate radical(SO₄^-·)generating from persulfate?PS?and peroxymonosulfate?PMS?to oxidize organic contaminants.However,there are still some key issues that need to be addressed.Activation of PS by ultraviolet light,thermal energy,and ultrasound require external energy supply,high cost and high requirements for the device,which make them difficult to large-scale wastewater treatment.Transition metal ions can effectively activate the PS and PMS,but it has some shortcomings such as unwanted reaction,difficulty in controlling the ion concentration in the solution,narrow pH range,and inability to recycle and sludge generation.Therefore,the development of heterogeneous catalyst to activate persulfate is of great importance.A reduced graphene oxide nanosheet-iron oxide composite?rGO-Fe₃O₄?was synthesized using coprecipitation method,and its performance in activating persulfate to oxide organic pollutants was investigated.We selected Acid Red 73?AR73?and norfloxacin?NOF?as target pollutants.Techniques such as X-ray powder diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Vibrating sample magnetometer?VSM?and transmission electron microscopy?TEM?were applied to characterize the catalyst.The effects of reaction parameters were investigated.As shown in XRD spectra of rGO-Fe₃O₄,Fe₃O₄ particles were successfully embedded in the rGO layer.The XPS indicates a new peak at 531.2 eV corresponding to the Fe-O-C bond in the O1s spectra,which confirms the strong interfacial interactions between rGO and Fe₃O₄.The TEM shows that Fe₃O₄ is uniformly distributed in rGO sheet,thus can effectively prevent the aggregation of Fe₃O₄.The magnetic saturation of rGO-Fe₃O₄ is 73.8 emu/g,indicating that rGO-Fe₃O₄ can be easily separated from solution by an applied magnetic field.N₂ adsorption/desorption isotherms on rGO-Fe₃O₄ is a type IV hysteresis loop.The calculated BET surface area and pore volume were 54.62 m²/g and 0.067 cm³/g.The experimental results of the degradation of acid red 73 by rGO-Fe₃O₄activated persulfate showed that under the conditions of a catalyst dosage of 1.0 g/L,persulfate concentration of 1.0 g/L,and pH of 6.9,the 50 mg/L AR73 was totally removed in 10 min at room temperature.The rGO-Fe₃O₄ exhibited excellent activity towards AR73 degradation at different pH values?3-9?.Increasing the temperature can speed up the reaction.The AR73 degradation by the rGO-Fe₃O₄/PS followed the first-order kinetics,and the activation energy was 33.91 kJ/mol.Quenching tests showed that SO₄^-·,·OH and¹O₂ were all generated in rGO-Fe₃O₄/PS system,in which¹O₂ was the major reactive species for the degradation of AR73.Cycling experiment showed the AR73 degradation efficiency remained high catalytic activity after four times of reuse.The composite of rGO-Fe₃O₄ also exhibited excellent catalytic activity towards the degradation of norfloxacin?NOF?.The results showed that under the conditions of the addition of 0.5 g/L catalyst,persulfate concentration of 1.0 g/L,the degradation rate of 20 mg/L NOF was 89.69%and TOC removal rate was 45.69%in 75 min.The rGO-Fe₃O₄ catalyst exhibited excellent adsorption effect on NOF and the adsorption rate of NOF in 60 min reached 42.87%.The increase in initial pH values led to a slight decrease in removal efficiency of NOF.Cycling experiments showed the NOF degradation efficiency remained 74.99%after four times of reuse.The comparison of XRD patterns between fresh catalyst and the used showed that no obvious changes of characteristic peaks were observed,indicating that the rGO-Fe₃O₄ catalyst had good structure stability.According to the results of HPLC-MS,the degradation intermediates were identified and the possible transformation pathways were proposed.