Preparation Of Heterogenous Photo-Fenton Catalysts And Their Application In The Treatment Of Metronidazole Wastewater

Purification treatment of wastewater from pharmaceutical industry is one of the global research hotspots,which aims to reduce pollution and protects the environment.At present,multiple treatment techniques and methods,such as biological,physical and chemical approaches,have been developed,but no satisfactory treatment effect is achieved due to complex composition,high concentration and difficult degradation of organic pollutants contained in the wastewater.Therefore,developing new techniques has become the key to solve this problem.This paper proposed to develop and modify several catalysts based on the original chemical method,and to verify their effects,so as to provide new technique option and thinking to enhance the purification efficiency of pharmaceutical wastewater.In the present study,the pre-treated coconut shell bio-carbon was used as the vector,and the bio-carbon coated Fe₃O₄?Fe₃O₄@PBC?was first prepared using the Fe?III?-ethanol solution impregnation-calcination method.On the basis of Fe₃O₄@PBC,three iron-containing catalysts were prepared by the impregnation-calcination method,which were MnFe₂O₄@PBC,CuFe₂O₄@PBC and CoFe₂O₄@PBC,respectively.Thereafter,the above-mentioned products were characterized and analyzed by X-ray diffraction?XRD?,scanning electron microscope?SEM?,vibrating sample magnetometer?VSM?,X-ray photoelectron spectroscopy?XPS?,and Brunner-Emmet-Teller?BET?measurements.Subsequently,the Fe₃O₄@PBC and MnFe₂O₄@PBC samples were carried out 120 min of Fenton reaction,while the CuFe₂O₄@PBC sample was subject to 60 min of Fenton reaction,and the CoFe₂O₄@PBC sample was conducted 20 min of Fenton reaction,under the optimal experimental conditions?0.4 g/L catalyst,300 mg/L metronidazole,60 mmol/L H₂O₂,pH 3.0,and adsorption equilibrium in dark environment?,so as to detect the adsorption and decomposition capacities of these 4 samples for metronidazole.In addition,the prepared CuFe₂O₄@PBC catalyst was carried out 120 min of Fenton reaction at pH 7.0.Finally,catalyst products with superior performance were used to degrade the wastewater discharged from pharmaceutical enterprises,so as to detect their effects.The research results were shown below.The first prepared Fe₃O₄@PBC was separated by the applied external magnetic field,and its characterization results were that,the Fe₃O₄ coating was attached onto the bio-carbon surface,with the specific surface area of 1164.5 m²/g;besides,this coating did not change the pore structure of bio-carbon,and maintained the high specific surface area close to bio-carbon?1269.5 m²/g?.Under the optimal conditions,the degradation rate of metronidazole reached as high as 92.2%,and 95.1%metronidazole was removed throughout the whole adsorption catalysis process,thus displaying strong adsorption and catalytic abilities.Fe₃O₄@PBC also possesses favorable stability,which maintained the removal rate of about 92%after 5 repeated uses.Also,our results suggested that,·OH played a leading role in the photo-Fenton system,while O₂·^-and H⁺had weak effects.The iron content in Fe₃O₄@PBC material significantly affected its photo-Fenton degradation and adsorption capacities for metronidazole.The characterization results of the three iron-containing catalysts MnFe₂O₄@PBC,CuFe₂O₄@PBC and CoFe₂O₄@PBC were similar to those of the Fe₃O₄@PBC sample,all of which maintained the original bio-carbon pore structure and high specific surface area,namely,1095.65 m²/g?MnFe₂O₄@PBC?,1097.9 m²/g?CuFe₂O₄@PBC?,and 1153.1 m²/g?CoFe₂O₄@PBC?,respectively.Their metronidazole removal rates under the optimal conditions were 76.6%?MnFe₂O₄@PBC,120 min of photo-catalytic reaction?,96.3%?CuFe₂O₄@PBC,60 min of photo-catalytic reaction?,and 97.7%?CoFe₂O₄@PBC,20 min of photo-catalytic reaction?,respectively.Meanwhile,the metronidazole removal rates after 5repeated uses were maintained at 80.0%?MnFe₂O₄@PBC?,89.1%?CuFe₂O₄@PBC?and 85.1%?CoFe₂O₄@PBC?.At pH 7.0,the metronidazole removal rate of CuFe₂O₄@PBC reached 91.1%after 120 min of photo-catalytic reaction,and the degradation effect was superior to the traditional Fenton reaction or some Fenton-like reactions;besides,the pH value range applicable for Fenton reaction was expanded.At pH 3.0,the CoFe₂O₄@PBC sample had the best catalytic effect,but it still possessed favorable catalytic effect under neutral condition.As a result,the CuFe₂O₄@PBC sample had the best comprehensive heterogeneous photo-Fenton reaction effect.According to the experiment that used the CuFe₂O₄@PBC sample to treat the wastewater from a pharmaceutical factory in Liaoning,the COD content was degraded to below 30 mg/L?average inflow COD,130.28 mg/L?after 2 h of reaction at pH 7.0.The following conclusions are drawn after analyzing the obtained results.1.The Fe₃O₄@PBC prepared in this study has high stability,and strong photo-Fenton catalytic and absorption capacities,which is a promising visible light-driven catalyst used to treat the metronidazole-containing wastewater.In addition,its iron content has significant influence on the photo-Fenton degradation and adsorption capacities.2.Among MnFe₂O₄@PBC,CuFe₂O₄@PBC and CoFe₂O₄@PBC prepared based on Fe₃O₄@PBC,CuFe₂O₄@PBC has the most potent photo-Fenton catalytic and degradation capacities,which is promising to be applied in practice.In this study,the prepared catalysts with bio-carbon as the vector exhibit great superiorities in stability and catalytic efficiency.In particular,CuFe₂O₄@PBC has high efficiency and low operation cost,which provides a possible technique for the upgrading of pharmaceutical wastewater treatment plant.Improve the traditional pharmaceutical wastewater advanced treatment process,combine the traditional activated carbon adsorption unit and the traditional Fenton treatment system into a photo-Fenton treatment system,no need to build a traditional Fenton reaction sedimentation tank,reduce the use of adsorbent and the generation of physical and chemical sludge.Consequently,this study is of important theoretical significance and practical application value.