Removal Of Diclofenac From Wastewater By Graphene Oxide Loading Cuprous Oxide

Diclofenac（DCF）is an emerging pollutant,which has easily been detected in surface water,sewage treatment plants,sediment of sewage treatment plants,soil and even biota.DCF is one of the typical drugs that bringing ahout drug-specific liver injury.Long-term and extensive exposure of DCF can lead to acute liver failure or even death.Since DCF is a bioactive substance,its biological activity may adversely affect non-target organisms when it enters the environment.DCF is hard to degrade naturally,and the removal rate in traditional sewage treatment plants is only 21-40%,which causing a potential ecological hazard.Nowadays,persulfate activation technology shows a broad prospect in the water treatment field.Compared with traditional oxidants,persulfate（PDS）is stable and easy to store and transport during practical applications.PDS hardly decompose at room temperature,but it can produce sulfate radical(SO₄^·-)with high oxidation potential after activation and decomposition by means of external energy or transition metal.It has unique advantages in the remediation of groundwater and soil contaminated by organic matter.Although PDS activation technology has been widely used in wastewater treatment,it still has some disadvantages such as high energy consumption,side reactions and narrow p H applicability.Cuprous oxide（Cu₂O）has been proved to have high activation effect on PDS.Because the different particle size and morphology of nano Cu₂O directly affect its catalytic activation performance of PDS,researchers are currently focused on exploring the control of particle size and morphology of nano Cu₂O.Therefore,controllable preparation of nano Cu₂O with good morphology based on simple and green process is extremely important.Nanoparticles generally tend to agglomerate in aqueous solution,which reduces their specific surface area and leads to a reduction in stability and catalytic efficiency.Due to its high surface area and chemical stability,Graphene oxide（GO）can be used as a benign carrier for nanoparticles,preventing the agglomeration of nanoparticles.In addition,the catalytic activity of nanoparticles can be improved through the synergy between catalysis and adsorption.In this paper,DCF was used as the target pollutant,and the morphology of controllable nano Cu₂O was prepared by simple green ionic liquid[BMIM]Br assisted chemical precipitation method,then it was further combined with GO.The removal effect of activated persulfate on DCF degradation by nano Cu₂O and GO/Cu₂O nanocomposites was systematically studied.The different environmental factors,degradation products and reaction mechanism were also discussed in detail.The conclusions are as follows:（1）By adjusting the concentration of ionic liquid（[BMIM]Br）（0.4 wt.%,0.6 wt.%,0.8wt.%）,different morphology of Cu₂O nanoparticles,including smooth regular octahedron,truncated octahedron and spherical were obtained.The optimal reaction conditions of DCF degradation using PDS activated with nano Cu₂O were as follows:Cu₂O dosage was 1.00 g/L,C_PDS:C_DCF was 25:1.After 240 minutes,the maximum DCF degradation rate reached 89.0%.Under different initial p H,the resulted Cu₂O nanoparticles with controllable morphology can all activate PDS effectively.After degradation of DCF by activation of PDS for 3 times,nano Cu₂O showed good catalytic stability and degradation rate only decreased by 12.9%.Electron paramagnetic resonance spin capture experiment showed that the sulfate radical(SO₄^·-)and hydroxyl radical（·OH）played a leading role in the degradation of DCF.SO₄^·-and·OH do not be consumed with HCO₃^-and Cl^-co-existing in the reaction system.As a result,the concentration of free radicals does not fall and the degradation rate of the reaction keeps constant.（2）GO/Cu₂O nano-composites with different mass ratios of m（GO）:m（Cu₂O）（1:2,1:5,1:10,1:25）were prepared.The degradation rate of DCF using activated PDS was compared between nano Cu₂O and GO/Cu₂O nanocomposites.It is found that when the amount of catalyst was 1.00 g/L and C_PDS:C_DCF was 15:1,the catalytic degradation rate of GO/Cu₂O nanocomposites was up to 89.5%,while the catalytic degradation rate of nano Cu₂O was only59.2%.Catalyst not only reduced the amount of PDS,but also improved the catalytic activity.The valence states of copper and carbon elements on the surface of GO/Cu₂O nanocomposites did not change significantly before and after catalytic degradation reaction.The degradation rate of DCF only decreased 5.4%after 3 cyclic degradation.Compared with nano Cu₂O（12.9%）,GO/Cu₂O nanocomposites showed better catalyst stability.GO/Cu₂O nanocomposites are liable to generate SO₄^·-and·OH radicals in DCF degradation.Intermediates were formed during DCF degradation,which resulting in lower mineralization rate if compared with degradation rate.Through intermediates identification,DCF degradation process includes hydroxylation and C-N bond cleavage.In conclusion,nano Cu₂O with controllable morphology and GO/Cu₂O nanocomposites were successfully prepared based on simple green ionic liquid[BMIM]Br assisted chemical precipitation method.The resulted sample has the advantages of low energy consumption,wide range of p H application and recyclable.They are expected to be used for large-scale treatment of DCF wastewater which is the organic pollutants hard to be biodegraded.