Promotion Effect Of Easily Degradable Organics On Refractory Organics In PEC And Its Application In COD Determination

Photoelectrocatalytic（PEC）is a kind of advanced oxidation process with high efficient and clean performance in the treatment of refractory organics,and thus has drawn widespread concerns.Our team has built a PEC chemical oxygen demand（COD）method based on the TiO₂ nanotube arrays by taking advantages of the designed thin layer reactor which with the thin liquid layer and fast mass transfer.However,some refractory organics such as dye wastewater could hardly be exhaustedly oxidized,resulting the difficulty of the accurate COD determination of these refractory organics.Therefore this work suggested the COD determination method of the refractory organics based on the study of the promotion effect of easily degradable organics.Meanwhile,to realize the real-time online COD determination and the visible light response COD determination,this work combined the flow injection technology and prepared a WO₃ COD sensor,respectively.Additionally,this work studied the effect mechanism of TBA which is a kind of hydroxyl radical scavenger in the PEC process.The promotion mechanism of easily degradable organics on PEC degradation of refractory dye.This work took the methyl orange（MO）as the typical refractory azo dye,and TiO₂ nanotube arrays as the photoanode.This work studied the effect of different easily degradable organics including those with hydroxyl groups（such as methanol）and methanoic acid on the PEC degradation of MO by taking use of the thin layer reactor.Results showed that the all of easily degradable organics could realize exhausted oxidation,while the refractory oraganic such as MO could not,the degradation rate was 39.59%for 50 mg·L^-1 MO.Fortunately,the degradation of refractory orgnaics could be promoted by adding easily degradable organics.For illustration,the PEC degradation of MO could be promoted by adding some easily degradable organics.MO was difficult to be exhausted oxidized when existing alone,for example.While adding easily degradable organics with hydroxyl groups into MO could elevate the degradation rate,the promotion effect of different organics were in the order:glycerol>glycol≈fructose≈glucose>methanol.The exhausted mineralization could be achieved by adding 150 mg·L^-1 glycerol into 50 mg·L^-1 MO.It was found that this promotion performance was positively correlated with the number of hydroxyl group contained in easily degradable organics,indicating that the hydroxyl group may convert into hydroxyl radicals and then promote the PEC degradation of refractory organics.Methanoic acid（MA）showed more excellent promotion effect on the PEC degradation of MO,even a small amount of MA could obviously promote the PEC degradation of MO,and this effect magnified with the increasing of MA.When the amount of MA was up to as twice as MO within a certain concentrations range,the total organics in the reactor could be oxidized.The promotion effect ofeasily degradable organics may related to the active radicals generated in the PEC process.This phenomenon illustrated that all of these above-mentioned easily degradable organics above-mentioned are good active radical promotion agents in PEC process.COD determination of refractory orgnaics by PEC method.This work detect the COD values of refractory organics by the standard recovery method based on the promotion of easily degradable organics.Dye wastewater such as methyl orange,congo red,methylene blue and pharmaceutical wastewater such as berberine,tetracycline hydrochloride were chosen as the typical refractory organics.Easily degradable organics such as methanoic acid,glycerol,and glucose were chosen as the additive substance in this work.The results showed that the accurate determination of refractory organics could be realized by adding the easily degradable organics of obvious promotion effect.This work investigated the light intensity,applied bias and electrolyte concentrations and determined the optimum condition of the standard recovery method.Photoelectrocatalytic-flow injection COD quick online detection method.This work combined the photoelectrocatalytic COD determination method with the flow injection technology to set up a quick COD online detection method.In this work,the influence factors such as the light intensity,the applied bias,the concentration of electrolyte,the flow rate and the injection volume of sample were studied to optimize the COD detect condition.Results showed that all of the detected COD values of these analytical organics including glucose,sucrose,KHP,glutamic acid and even the refractory isonicotinic acid were closed to the corresponding theoretical values and showed good linar relationship.The detected COD values of real samples such as top water,ground water and pharmaceutical wastewater also showed good accuracy.Visible light response WO₃ COD sensor and its COD detection.The existing COD sensor could only respond to the UV light.To deal with this disadvantage,this work developed a WO₃ nanoporous COD sensor which could response to the visible light and applied the sensor to the COD determination.Results showed that the WO₃ sensor could meet the requirement of different organics including glucose,maleic acid,glycine,methanol and sodium acetate,and showed good linear relationship.This work studied the influence factors on COD determination such as the electrolyte species and concentrations,the light intensity,the applied bias and determined the optimum conditions.The inhibite effect of Tert-Butyl Alcohol（TBA）on PEC degradation of organics.In this work TiO₂ nanotube arrays was used as the PEC photoanode,glucose and potassium hydrogen phthalate（KHP）were used as the typical organics.This work investigated the inhibite effect of TBA which is a kind of hydroxyl radical scavenger on the PEC degradation of different organics by taking use of the designed thin layer reactor.It was found that TBA could obviously affect the PEC degradation of organics.For illustration,glucose and KHP could be exhaustedly oxidized in the thin layer reactor,respectively.However,the degradation rate of both organics decreased after adding TBA,even decreased with the increasing of TBA.Moreover,it was found that the effect of TBA on glucose was more obvious than KHP.The reason may relate to the capture of hydroxyl radical by TBA on the surface of the TiO₂ nanotube arrays,and the strong adsorption ability of KHP could avoid the over capture of hydroxyl radical by TBA.