Fe₃O₄@PDA-Cu???core/shell Complexe Catalysts:Study On The Preparation,modification And Properties

Water pollution has become a global concern.Effective treatment of organic pollutants in water has become a research hotspot.Dye wastewater treatment has become one of the important topics in water treatment based on its high chroma,high COD,high toxicity and biological refractory.With the implementation of the new law in 2013,it is difficult for the processing requirements to be met by traditional biological method,physical method,chemitrical method and combined technologies.Therefore,novel treatment methods and technologies is urgented to develop.Advanced oxidation technologies and biomimetic catalysts have drawn attention in wastewater treatment.The common research focus of both is to develop effective catalysts to active hydrogen peroxide and molecular oxygen for dyes degradation.The transition metal oxides and their complexes have been used to active hydrogen peroxide to generate the hydroxyl radical for the treatment of refractory organic.But these catalysts are easily lost and difficult to reuse.The study of magnetic core-shell catalysts Fe₃O₄@CAS provides a way to solve these problems.Therefore,the transition metal/PDA is loaded on the magnetic nano-Fe₃O₄ to obtain the core-shell catalyst,then cross-link by PEI to improve the alkali resistance of the catalyst,and last catalytic activity for the degradation of different structures of dyes in this thesis.The detailed results were summarized as follows:1)The core-shell catalyst Fe₃O₄@PDA-Cu?II?was prepared by in-situ polymerization from Fe₃O₄ and dopamine.And its composition and structure were characterized by FT-IR spectra,DRS,UV-Vis spectra,TGA method,XRD,N₂ adsorption-desorption and XPS.The catalytic effect was invetigated by spectrophotometer.And found that the catalyst can activate hydrogen peroxide to degrade methyl orange effectively.The catalytic effect was investigated by the temperature,the p H value,the dosage of hydrogen peroxide and the substrate concentration.It was found that the increase of the temperature and the increase of the amount of hydrogen peroxide were beneficial to the methyl orange degradation.It was favorable for the degradation of methyl orange at pH=8¹0.The balance of the degradation speed and degradation rate of methyl orange was reached at 30 mg/L.The optimal condition of the degradation is determined:30 mg/L of substrate concentration,10 mg/L of the catalyst dosage,40?of temperature,pH=9.0,27 mmol/L of the dosage of hydrogen peroxide.Under the optimum conditions,the structure and the active center of catalyst was stable in presence of salt with pH=2¹0.The catalyst was inactivated and the active center is destroyed in presence of strong alkali conditions.And the catalyst can be recycled for more than 5 times with the active center of catalyst lost slowly.2)The core-shell catalyst Fe₃O₄@PDA/PEI-Cu?II?was prepared by in-situ polymerization from Fe₃O₄,DA and PEI.Its composition and structure were characterized by FT-IR spectra,DRS,UV-Vis spectra,TGA method,XRD,N₂ adsorption-desorption,XPS.The catalytic effect was investigated by spectrophotometer.And found that the catalyst can activate hydrogen peroxide to degrade methyl orange effectively.The catalytic effect was investigated by the temperature,the pH value,the amount of hydrogen peroxide and the substrate concentration.It was found that the increase of temperature and the increase of the amount of hydrogen peroxide were beneficial to the methyl orange degradation.It was favorable for the catalytic degradation of methyl orange at pH=7¹0.The balance of the degradation speed and degradation rate of methyl orange was reached at 30 mg/L.The optimal condition of the degradation is determined:30 mg/L of substrate concentration,10 mg/L of the catalyst dosage,40?of temperature,pH=9.0,27 mmol/L of the amount of hydrogen peroxide.Under the optimum conditions,the structure and the active center of the catalyst was stable in presence of salt with pH=2¹2.The alkali resistance is increased for the PEI containing.The catalyst can be recycled for more than 4 times with the active center of catalyst lost slowly.3)The core-shell catalyst Fe₃O₄@PDA/APTES-Cu?II?was prepared by in-situ polymerization from Fe₃O₄,DA and APTES.Its composition and structure were characterized by FT-IR spectra,DRS,UV-Vis spectra,TGA method,XRD,N₂ adsorption-desorption,XPS.The catalytic effect was investigated by spectrophotometer.And it was found that the catalyst can activate hydrogen peroxide to degrade methyl orange effectively.The catalytic effect was investigated by the temperature,the pH value,the amount of hydrogen peroxide and the substrate concentration.It was found that the increase of temperature and the increase of the amount of hydrogen peroxide were beneficial to the degradation of methyl orange.It was favorable for the degradation of methyl orange at pH=8¹0.The balance of the degradation speed and degradation rate of methyl orange was reached at 30 mg/L.The optimal condition of the degradation is determined:30 mg/L of substrate concentration,10 mg/L of the catalyst dosage,25?of temperature,pH=9.0,27 mmol/L of the dosage of hydrogen peroxide.Under the optimum conditions,the structure and active center of the catalyst was stable in the presence of salt with pH=2¹0.The catalyst was inactivated and the active center is destroyed in presence of strong alkali conditions.And the catalyst can be recycled for more than 4 times with the active center of catalyst lost slowly.4)The catalyst stability was studied in presence of HCl or NaOH,salt with recycling.It was found that the structure and active centers of the catalyst Fe₃O₄@PDA-Cu???and Fe₃O₄@PDA/APTES-Cu???were stable at pH=2¹0,and their structure and active centers were destroyed under strong alkaline conditions.The structure and active centers of the catalyst Fe₃O₄@PDA/PEI-Cu???was stable at pH=2¹2,which shows that the PEI containing is favorable to the alkali resistance of the catalyst.Moreover,the catalyst can be recycled by magnetic recycling with good mechanical properties and the chemical properties.5)The degradation effect of eight kinds of different dye substrates,methyl orange,rhodamine B,alizarin red,R,O,B,E and acid red dyeing wastewater were studied.It was found that the degradation rate of methyl orange,rhodamine B,alizarin red and acid red dyeing wastewater was 100%after 2 h.However,the degradation rate of R,O,B,E with nitro and bromine groups was 40-80%after 24 h in presence of Fe₃O₄@PDA-Cu?II?or Fe₃O₄@PDA/PEI-Cu?II?,80-100%after 24 h in presence of Fe₃O₄@PDA/APTES-Cu?II?,which show that the catalyst has certain substrate selectivity,and the APTES containing in Fe₃O₄@PDA/APTES-Cu?II?could improve catalitic activity with wider substrate.6)The degradation products were determined by high performance liquid chromatography,the COD of degradation solution was determined by Mn method,the absorption of degradation gas was carried out by saturated calcium hydroxide solution.Found that the products of degradation have p-hydroxy phenol,o-hydroxy phenol,oxalic acid and CO₂.The COD decreased with dyes degradation.All these show that the treatment is not dyes decolorization,but degradation and mineralization.7)The mechanism of the hydrogen peroxide activated for dyes degradation was investigated by free radical capture experiments and free radical inhibition experiments.Found that 2,5-dihydroxybenzoic acid was obtained with salicylic acid capturing hydroxyl.And the degradation of methyl orange was inhibited in presence of t-butanol,which was deduced the reaction of the methyl orange with the hydroxyl radical and the reaction of the t-butanol with the hydroxyl radical occurred simultaneously and competitively.All these show that the H₂O₂activated by the catalysts with the hydroxyl radical.The methyl orange was attacked and degradated by the hydroxyl radical.8)The dye degradation progress was investigated by Grap HPad Prism 7 software.Found that the degradation process of methyl orange was accorded with the Michaelis-Menten equation,which show that tha catalysts should be used as enzyme model and the degradation process of methyl orange is an enzymatic mechanism.9)The catalyst with PEI containing has better alkaline resistance.The catalyst with APTES containg has better catalytic activity and wider substrates.These are indicated that the nonpolar polymer is good to the alkali resistance of the catalyst and the multifunctional block is beneficial to the substrate expansion,which provides the theoretical and practical basis for the preparation of highly efficient catalysts with alkali resistant.