Oxidation Removal Of Sweetener Acesulfame From Water By Persulfate Activated With Iron-Loaded Activated Coke

Artificial sweeteners（ASs）,as emerging pollutants,are being applied the production of food,beverage,medicine and personal care products on the basis of their superior taste and low heat.However,artificial sweeteners are hardly degraded by human metabolism.Conventional water and wastewater treatment process cannot remove them effectively and safely,It is necessary to select appropriate processes for ASs treatment.Activated coke（ACO）has low production cost,good pore structure,large specific surface area,rich surface groups,high chemical stability and mechanical strength.As such,ACO has strong adsorption capacity and has been applied in practical water and wastewater treatment.In this study,nanometer zero-valent（n ZVI）and Fe₃O₄,which belong to two kinds of iron species,were immobilized onto ACO.The n ZVI supported ACO（n ZVI-ACO）was synthesized by liquid-phase reduction method while Fe₃O₄-supported ACO（Fe₃O₄-ACO）by chemical coprecipitation method.The common ASs acesulfame potassium（ACE）was selected as the target pollutant.Both n ZVI-ACO and Fe₃O₄-ACO were used to activate peroxydisulfate（PDS）for the catalytic oxidation of ACE.The effects of the dosage of iron-loaded activated coke,PDS dosage,ACE concentration,initial solution p H and reaction temperature were investigated,while the activation performance of the two catalysts and the catalytic oxidation mechanism were compared.The main research conclusions are presented as follows:It was observed that there was an optimal load of zero-valent iron and Fe₃O₄ on ACO.The highest PDS activation performance was noted while the mass ratio of n ZVI or Fe₃O₄ on ACO with iron-carbon was at 1:5,which was significantly higher than that of ACO/PDS system.The pseudo-first-order kinetics K_app value of the combined process of n ZVI-ACO or Fe₃O₄-ACO with PDS was 14.87 and 5.13 times that of the sum of the separate adsorption and PDS oxidation,respectively.A significant synergy was observed in the combined process.SEM and BET results showed that there are a large number of small spherical particles on the surface of n ZVI-ACO and the surface is rough and porous.There were irregular substances on the surface of Fe₃O₄-ACO,and the interior of iron-loaded activated coke is mainly mesoporous（2～50 nm）.EDS spectrum show that the contents of C,O and Fe in n ZVI-ACO are 77.5%,16.5%and6.1%respectively.The contents of C,O and Fe in Fe₃O₄-ACO were 87.7%,10.3%and2.0%respectively.The analysis of FTIR,XRD,XPS and Raman spectra showed that ACO was successfully loaded with n ZVI and Fe₃O₄,and the surface was rich in functional groups,forming more defect sites.An increase in the dosage of iron-loaded activated coke enhanced the degradation of ACE,while an optimal PDS dosage was found for both catalysts.Both n ZVI-ACO and Fe₃O₄-ACO can effectively activate PDS to remove ACE in the p H range of3.0～9.0.In the n ZVI-ACO/PDS system,when the dosage of n ZVI-ACO is 0.5 g/L,the concentration of PDS is 0.4 m M,and the initial p H is 5.0,the removal rate of ACE can reach 97.0%;In the Fe₃O₄-ACO/PDS system,the dosage of Fe₃O₄-ACO is 0.5 g/L,the concentration of PDS is 0.1 m M,and 89.3%of ACE can be removed without adjusting the initial p H（p H=4.5）.Through Box-Behnken experiment,the optimum reaction conditions for the maximum ACE removal efficiency of n ZVI-ACO/PDS and Fe₃O₄-ACO/PDS systems were determined as follows:the dosage of n ZVI-ACO was 0.45 g/L,the concentration of PDS was 0.35 m M,and the initial p H of the solution was 5.3;The dosage of Fe₃O₄-ACO is 0.49 g/L,the concentration of PDS is 0.14 m M,and the initial p H of the solution is 4.9,which has been verified by actual experiments.In addition,both free radical and non-free radical oxidation mechanisms were involved in both n ZVI-ACO/PDS and Fe₃O₄-ACO/PDS systems.The main oxidizing species include SO₄·^-,·OH and·O₂^-（the contribution of ¹O₂ and hole（h⁺）to the oxidation system cannot be calculated through quenching experiment due to the experimental limitations）.In ACO/PDS system,the contribution rates of SO₄·^-,·OH and·O₂^-to ACE degradation are 4.1%,7.7%and 75.1%,respectively.In n ZVI-ACO/PDS system,the contribution rates are 66.0%,71.5%and 71.8%,respectively.In Fe₃O₄-ACO/PDS system,the contribution rates to ACE degradation are 20.0%,28.6%and 61.9%,respectively.After ACO was loaded with iron species,the contribution rate of SO₄·^-and·OH radicals was significantly increased,and the effect of n ZVI load was more significant than that of Fe₃O₄ load.At the same time,the surface active site of the iron-loaded active coke can form metastable complexes with PDS（n ZVI-ACO-PDS*or Fe₃O₄-ACO-PDS*）,which induces the occurrence of electron transfer and oxidizing removal of ACE.Both n ZVI-ACO and Fe₃O₄-ACO have good reusability,indicating their potential application in actual water treatment.