Treatment Of Emerging Contaminants In Water Through Activation Of Persulfate By Bimetallic Spinel/Nanocarbon Composites

In recent years,the pollution of drug PPCPs in water has aroused widespread concern,and the accumulation of trace pollution will bring threats to life,health and ecosystem.Antibiotic drugs and non steroidal anti-inflammatory drugs are widely used in PPCPs,and they are detected to some extent in groundwater,river and traditional sewage treatment plants.In this study,levofloxacin,sulfamethoxazole and nimesulide,the non steroidal anti-inflammatory drugs,were selected as the target pollutants to assess the degradation ability of sulfated radical based advanced oxidation technology?SR-AOPs?.Two bimetal spinel/nano carbon composites,NiFe₂O₄/CS and NiCo₂S₄/CS,Cu-Fe LDH/CMK bimetal spinel precursor/nano carbon composite,were prepared and used to activate PS to degrade target pollutants.The catalytic activity of the catalysts was evaluated by optimizing the degradation conditions and exploring the degradation mechanism,and then they were used for the degradation of hospital wastewater.This paper mainly carried out the following work:In order to explore the catalytic effect of bimetal oxide spinel and bimetal sulfide spinel after being connected witb nanocarbon,NiFe₂O₄/CS and NiCo₂S₄/CS composite were prepared by hydrothermal method,with the physicochemical properties being characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microcopy?TEM?,Brunauer-Emmett-Teller?BET?and Fourier Transform infrared spectroscopy?FT-IR?.Meanwhile,NiFe₂O₄/CS was also applied to activate persulfate?PS?for elimination of levofloxacin,The result showed that NiFe₂O₄/CS composite owned stronger capacity for PS activation than pure NiFe₂O₄ and CS.Furthermore,the influence factors,such as the dosage of catalyst,the concentration of PS and the initial pH,were optimized and analyzed.Also,when the levofloxacin degradation carried out under the optimized condition,with 0.6 g/L NiFe₂O₄/CS composite and 1.8 g/L persulfate being added and the initial pH being adjusting to 5,67%levofloxacin was degraded within 1 hour.In addition,the possible mechanism of NiFe₂O₄/CS nanocomposite activating PS was proposed through the radical scavengers and the result of XPS.More importantly,the repeated experiment was conducted for several times,which proved that the NiFe₂O₄/CS composite owned retrieveablity and reusability,providing a potentially useful catalyst for contaminants removal in water/wastewater treatment.After that,novel NiCo₂S₄/CS composite acted as catalyst to activate PS for nimesulide degradation.The results showed that NiCo₂S₄/CS composite owned the highest activity compared with pure NiCo₂S₄ and carbon sphere?CS?,achieving 92%nimesulide degradation in10 min with 0.1 g/L catalyst and 0.4 g/L persulfate.Furthermore,the NiCo₂S₄/CS membrane was fabricated by vacuum filtration,and 94%and 80%above nimesulide degradation were realized for the first time and after six times repeated experiment,which demonstrated that the catalyst was convenient to achieve recovery and reusability.In addition,the radical quenching experiment,XPS and the electrochemical methods?LSV and EIS?were measured to investigate the possible mechanism pathway,the results of which showed that both the non-radical pathway and radical pathway might attribute to nimesulide degradation,while the SO₄·^-remained the dominant species.This research provided a novel sulfide NiCo₂S₄/CS membrane for the oxidative technique for emerging organic contaminants in water treatment.In order to further explore the effect of bimetallic spinel precursor/nano carbon composite,Cu-Fe LDH was synthesized and calcined at different temperature ranged from 400 to 600?to form into metal oxides.Then,the CMK/LDH,CMK/CLDH-400,CMK/CLDH-500 and CMK/CLDH-600 composites were fabricated by co-precipitation and sonic treatment,respectively.Furthermore,the prepared samples were used to activate PS for sulfamethoxazole degradation.Based on the several characterizations and degradation experiments,a comparative study of different catalysts was conducted and the results reached the following factors:i The prepared samples were connected firmly via chemical bond instead of just physical connection both two different methods.ii CMK/LDH owned the best capacity of PS activation on sulfamethoxazole decomposition,84.9%SMX of 25 mg/L was degraded with less dosage of persulfate?0.5 g/L?and catalyst?0.15 g/L?being added.iii CMK/CLDH-600 owned the better adaptability of initial pH value compared with CMK/LDH and CMK/CLDH-400.After that,the several repeated degradation experiments demonstrated that CMK/LDH could be regenerated by a facile acetone cleaning method.Lastly,based on scavenger quenching experiment and chronoamperometric,the existence of both radical and non-radical pathway in CMK/LDH composite/PS/SMX system was induced.It was interesting to find that the SO₄·^-and HO·were mainly generated by LDH and CMK part for PS activation,respectively.However,the non-radical pathway for SMX decomposition was only ascribed to the electron bridge effect that the CMK owned.This study might provide a theoretical support for further studies on comparison about LDH and the metal oxides originating from calcination of LDH for PS activation.In order to explore the effect of NiFe₂O₄/CS,NiCo₂S₄/CS and Cu-Fe LDH/CMK composite on the practical wastewater treatment,the sewage from a hospital in Gansu Province was sampled and the degradation experiments of PS activation were carried out with prepared catalysts.The results show that Cu-Fe LDH/CMK owned the best effect on COD removal of hospital wastewater among the above three catalysts.After that,the dosage of PS and Cu-Fe LDH/CMK composite were optimized by adding50mL of hospital wastewater into the conical flask in the constant temperature shaker.The 70.8%COD removal of hospital wastewater could be achieved by adding 1.8g/L PS and 0.8g/L catalyst.Finally,according to the optimized ratio of catalyst and PS,the treatment scale of hospital wastewater was expanded to 10L,and 78.9%COD removel of wastewater was realized within 6h.Compared with the small-scale experiment,the treatment effect is slightly reduced but the change is not significant.The results show that this experiment provides a feasible and effective technology for PS activation.