Preparation Of Nano-carbon-based Catalyst Materials And The Treatments And Mechanisms Applied For Polluted Water

It is a hot topic for domestic and foreign scholars to seek economical,effective,green and safe catalytic degradation materials for environmental pollutants and solve the current problem of refractory organic pollutants in po lluted water.Chlorinated olefin-contaminated groundwater and dye wastewater are two kind of typical environmental pollution water.Electrochemical hydrodechlorination is an effective method for the degradation of chlorinated olefin in groundwater.But,the cathode catalyst materials which have been reported so far usually exist some disadvantages such as low dechlorination efficiency,incomplete dechlorination and high dechlorination voltage.Photo-Fenton is a common technology for dye wastewater treatment,and it is urgent to prepare an efficient and stable photocatalyst for photo-Fenton technology.In recent years,nano-carbon materials have been widely used in the field of photocatalytic and electrocatalytic degradation of environmental organic pollutants,but there have been few reports on the electrochemical hydrodechlorination of chlorinated olefin in groundwater and the treatment of dye wastewater by photo Fenton.In addition,New methods for preparation of new nano-carbon materials and catalyst materials are also research hotspots in the field.Therefore,this paper carried out the following three aspects of research:?1?Preparation of nickel-doped graphene?Graphene/Nickel,GR/Ni?cathode catalyst material and its application in electrochemical hydrodechlorination of perchloroethylene?PCE?in groundwater.?2?Preparation of ND/Layered Double Hydroxide?ND/LDH?photo-Fenton catalyst and its application in methylene blue?MB?degradation.?3?Preparation of nanodiamond?ND?based on pulsed laser bombardment of graphene suspension.The following innovative results were obtained:1.This study prepared GR/Ni cathode catalyst,which was composed of nano-nickel particles and graphene.The phase structure and electrochemical property of GR/Ni were characterised.The electrochemical hydrodechlorination of PCE in groundwater was driven by microbial fuel cell?MFC?with GR/Ni as the cathode.The hydrodechlorination characteristics and mechanism were investigated.The results showed that the reduction of PCE in water can happen at the potential of-0.24 V?vs.Ag/AgCl?.MFC can effectively drive PCE electrochemical hydrodechlorination reaction on GR/Ni cathode in groundwater.When the reaction time was 96 hours and the initial PCE concentration was 15 mg/L,the removal rate of PCE by GR/Ni cathode was 46.3%,while the removal rate of PCE by bare nickel and bare graphene cathode were only 23.6%and 17.1%,respectively.Within the initial PCE concentration range of 1¹5 mg/L,the higher the PCE concentration,the higher the removal rate.When the pH of groundwater was in the range of 5⁹,pH had no significant effect on the removal rate of PCE.During the electrochemical hydrodechlorination process,the dechlorination intermediate products such as trichloroethene?TCE?,cis-Dichloroethylene?cDCE?and vinyl chloride?VC?were all detected.However,when the reaction time was 22 days,only ethylene?ETH?and chloridion?Cl^-?were detected in the experimental groundwater.During the whole experiment,the open circuit voltage of MFC was always kept between 0.460⁰.389 V,and the corresponding circuit current was kept between 0.257⁰.221 mA.These results demonstrated that the GR/Ni cathode can electrochemically dechlorinate the PCE into ETH effectively in the groundwater under low voltage and neutral environment,and no dechlorination intermediate product was accumulated.Therefore,it is feasible for MFC to drive the in-situ electrochemical hydrodechlorination remediation for actual chlorinated olefin-contaminated groundwater with GR/Ni as the cathode.2.This study combined ND and CuFe-LDH together to prepare a novel photo-Fenton catalyst ND/LDH.The crystal structure,chemical state and the optical absorption property were characterised.Take the degradation of MB dye as an example,the photo-Fenton catalytic degradation characteristics,photocatalytic stability and photo-Fenton mechanism were investigated with ND/LDH as the photo-Fenton catalyst.The results showed that ND/LDH had hydrotalcite-like structure and good crystallinity.When the photo-Fenton reactions were conducted under visible-light???420 nm?irradiation for 120 min,the removal rate of MB with ND/LDH was 93.5%,significantly higher than LDH's?78.3%?.The optimal dose of ND/LDH for photo-Fenton reaction was 0.0667 g/L.After five cycles,the removal rate of MB remain above 93.2%,and the removal rate of TOC?Total Organic Carbon?in MB solution was 89.7%,higher than other photo-Fenton catalysts reported so far.Free radical quenching experiments proved that hydroxyl radical?·OH?was the main active-species in the ND/LDH photo-Fenton system.ND/LDH exhibits excellent UV-visible absorption performance.The optical band-gap of ND/LDH was 0.94 eV,the maximum of Valence Band?VB?was 1.48 eV?vs.NHE?,and the bottom of CB?Conduction Band?was 0.54 eV?vs.NHE?.The photo-Fenton catalytic mechanism of ND/LDH can be described as follow:ND can rapidly capture the photo-generated electrons of LDH and extend their lifetime.Then,the photo-generated electrons on the CB of ND had sufficient time to accelerate the redox cycles of Cu³⁺/Cu²⁺and Fe³⁺/Fe²⁺to photoactivate H₂O₂ to produce·OH,resulting in excellent photo-Fenton efficiency on MB degradation.These results demonstrated that ND/LDH is a novel photo-Fenton catalyst with the advantages of high efficiency,high stability and visible-light response,and has a broad application prospect and practical value in the treatment of refractory organic polluted water.3.The products and phase transition pressure of the pulse laser laser was analyzed by building the experimental system of the laser bombardment of graphene water.The phase transition mechanism of graphene to the nano-diamond was explored.The results showed that the strong pulse laser bombarded?230 Mj,130mJ?gaphene suspension,and the nano-diamond particles were found in the suspension.Under the 230 mj pulse laser bombardment,the maximum pressure of water was 18GPa.ND and Amorphous carbon are found in the product.Under the 130 mJ pulse laser bombardment,the maximum pressure of water was 10 GPa.Graphene nanobelts were shown in products.In high temperature and high pressure environment,graphene was vaporized and liquefied.In the experiment,the process of the preparation was infered"solid-plasma-steam-liquid-solid"The hydrogen and oxygen of water in the plasma were also the main causes of ND stability.This paper expounds the preparation method of GR/Ni cathode material and the ND/LDH photo-Fenton material,and realizes its application in the field of environmental photo/electrocatalytic degradation of organic polluta nts.This paper used the pulse laser bombardment method to prepare the ND from raw materials.The phase transition mechanism of ND was explored in this method.This work provides a theoretical and experimental basis for further development and development of carbon materials and the application of environmental fields.