Degradation Of Phenol With Persulfate Activated By Surface Modified Activated Carbon

Coal is the main energy for China due to its characteristic energy structure.As the leading industry of coal chemical industry,coal gasification process generates a great amount of wastewater and causes a noticeable problems for environment,phenolic compounds are important refractory pollutants for coal gasification wastewater with high biotoxicity.Therefore,it is of great significance to explore an efficient method for phenolic pollutants removal and eliminate pollutions of coal chemical industry.The advanced oxidation process with persulfate?PS?as oxidants has attracted much attentions for wastewater treatment.Sulfate radicals?SO₄^-·?,forming through persulfate activation,are of with the strong oxidizing properties?standard oxidation-reduction potential E0 = + 2.5 + 3.1 V/NHE standard hydrogen electrode?,and can degrade organics rapidly and efficiently.its,the advanced oxidation process basing on SO₄^-· shows a wide application prospect owing to its strong oxidizing property,good stability,long life and wide p H applicability.PS could be activated bythermal treatment,photo,alkali,transition metal ion and carbon material.PS activation by carbon materialcan effectively avoid the high energy consumption of photo activation and thermal activation,corrosion equipment of alkali activation,and secondary pollution of transition metal ions activation.Controlling the surface functional groups of carbon material by surface modification can effectively improve its adsorption capacity and catalytic performance.In this paper,activated carbon?AC0?was surface modified by using nitric acid oxidation combined thermal treatment in nitrogen and urea treatment.The surface modified activated carbons were used for K2S2O8 activation to form SO₄^-·with phenol as target pollutant.The influences of the modification condition and the operating conditions on the phenol degradation were investigated.And the effects of modified functional groups on the catalytic activation of PS were also investigated.In addition,a new method was developed for eliminating the effect of residual PS on the solution COD measurement of the the persulfate based advanced oxidation process.The main research results are as following:?1?The disturbance of PS on the COD determination could be effectively eliminated through Na₂SO₃ heat treatment.The research results showed that the remaining PS of wastewater would lead to a positive error for COD determination.When,the remaining PS in wastewater can be effectively removed without COD changing under the Na₂SO₃/PS molar ratio > 2,the temperature of 90 ?,and reaction time of 60 min.?2?Activated carbon was modified by nitric acid oxidation combined with thermal treatment,and the obtained activated carbon ACNH was used to activate PS for phenol degradation.The results showed that the activated carbon catalytic activity for PS activation significantly increased after the modification.In the ACNH/PS system,the oxidation rate of phenol was 5 times higher than that of AC0/PS system.The optimum PS/phenol molar ratio,ACNH dosage for the phenol degradation was 3: 1and 0.4 g/L,respectively.And the ACNH was of wide p H range of application.?3?Two kinds of nitrogen-doped activated carbon?UAC and UACN?were obtained through by urea treatment and nitric acid-urea treatment,respectively.And the two kinds of carbon were used to activate PS to degrade phenol.The results showed that the doping of nitrogen atom could improve the catalytic performance of activated carbon for PS activation.The oxidation rate of phenol degradation in UAC/PS system and UACN/PS system were 1.5 times and 2 times higher than that of AC0/PS system,respectively.In UACN/PS system,the optimal PS/phenol ratio,UACN dosage are 2: 1 and 0.4 g/L,respectively.Acidic and neutral solution benefits the PS activation by UACN.?4?The surface chemical properties of activated carbon before and after the modification were analyzed by N₂ isothermal adsorption,elemental analysis,X-ray photoelectron spectroscopy,and scanning electron microscopy.It was found that the increase of basic functional groups?such as quinone,pyrone,pyridine nitrogen?N-6?and pyrrole nitrogen?N-5??,the delocalized ? electron,and surface defects can effectively promote the activation ability while-COOH and-NO₂ and other electron-withdrawing groups have a passive effect on the PS activation.?5?The mechanism of phenol degradation in AC/PS system was proposed.PS and phenol were adsorbed on on the near surface of the activated carbon,the basic functional groups,delocalized ? electrons provided electrons as the Lewis base sites to the PS for SO₄^-·formation.Basing on the data of COD,p H,and intermediates concentrations,it was concluded that phenol was firstly oxidized to benzoquinone,and benzoquinone continued to be oxidized to small molecule carboxylic acid,then mineralized to CO₂ and H₂O.