Study On Preparation Of Nano-modified Graphene Electrode And Electrochemical Detection Of COD

Chemical oxygen demand(COD)refers to the amount of oxidant consumed by reducing substances in water under certain conditions,expressed in mg / L.Reducing substances are mainly organic substances.If the COD is too high,it will cause anoxic death of aquatic organisms.If irrigation farmland can cause crop growth,benzene and other highly toxic organic matter can cause direct damage to aquatic organisms,and the risk of cancer,mutants and teratology.Therefore,rapid and accurate detection of COD can reflect the degree of water pollution by reducing substances,and then formulate corresponding water treatment processes to protect human health and ecological balance.The national standard method for detecting COD is to oxidize organic matter in water with excess potassium dichromate under strong acid medium and heat to digest for 2h.Titrate the unreacted potassium dichromate with ammonium ferrous sulfate.Calculate the chemical oxygen demand.Although the national standard method is widely used and has good repeatability,it has the problems of long detection time(> 6h),many reagents used,complicated operation,and secondary pollution.The current electrochemical method of COD is used determine the hydroxyl radicals of the electrolytic product,and the hydroxyl radical is extremely oxidized,which can reduce the oxidation of the degrade organic matter in sewage into carbon dioxide and water,causing the change of the response power of the working electrode and calculate the COD value.This method is short(5-30min)and easy to operate,but the general electrode has poor resistance to · OH oxidation corrosion.Although boron-doped diamond(BDD)can resist · OH,BDD is expensive,resulting in the electrochemical detection of COD cannot be industrialized Used in water quality testing.The key to the current electrochemical method is to develop an electrode with a strong resistance to · OH and a reasonable price.In this paper,by studying an electrochemical electrode that can resist the OH oxidation corrosion generated under the condition of high redox voltage,and on this basis,the conditions for electrochemical detection of COD are studied,and finally an innovative method that can replace the national standard method for COD detection is finally formed..The main research contents are as follows:(1)Using petroleum waste as a raw material and a one-step thermal cracking reaction composite substrate material to prepare nano-modified graphene electrodes,which can resist · OH,and optimize the thermal cracking reaction conditions such as:petroleum waste content,reaction time,cooling Time,reaction temperature and other factors make the rearrangement of carbon atoms to form a single layer of graphene to achieve the best adsorption effect of graphene.(2)The electrochemical properties of different substrate materials were studied.By analyzing the cyclic voltammetry behavior,oxygen evolution potential,standard curve slope and linearity,and cycle of four substrate materials of silicon carbide wafers,silicon dioxide wafers,copper sheets,and steel strips Factors such as the number of uses and the effective service life of the electrode,the electrode performance of different base materials was investigated,and finally the silicon dioxide wafer was determined to be the best substrate material for electrochemical detection of COD.(3)The optimization of the conditions for electrochemical detection of COD was studied.Glucose was used as the standard substance.At 2.5V,0.5 mol / L Na2SO4 was used as the supporting electrolyte.Constant potential steady-state polarization was performed for 15 minutes to detect the gradient concentration of glucose solution.Establish a standard curve between the concentration of glucose solution and the amount of electricity,so as to obtain the relationship between COD and the amount of electricity,and calculate the COD value by measuring the amount of electricity in the water sample and substituting the formula.The detection range is 5-60000 mg / L.(4)The established electrochemical method was used to detect real water samples from major lakes,aquaculture plants,food plants,etc.,and compared with the national standard method.The results showed that the relative error range of the two methods for detecting COD was 0.20-Between 7.00%,and the relative error of most water samples is within 5.5%,which meets the requirements within 10% of the national regulations,and can be actually applied to the rapid detection of COD.