Application Of Fe-based PBA Materials In Electrochemistry

Prussian Blue Analogues（PBA）is a kind of metal organic framework（MOFs）materials,which is formed by the coordination of metal ions[M^ⅡM^Ⅲ（M=Co,Fe,Ni...）]with cyanoanion（CN-）.PBA has been widely used in electrochemical catalysis,electrochemical detection,photocatalytic degradation,battery electrode materials,and other fields ascribed to stable structure,low density,easy doping and good electrochemical activity.In this thesis,Fe-based PBA,which is composed of Fe-centered atoms(M^Ⅲ),Co（Ⅱ）and Ni（Ⅱ）as coordination metal ions(M^Ⅱ),has unique electronic structure and high coordination stability.M^Ⅱ in PBA was replaced by Co（Ⅱ）and Ni（Ⅱ）to improve its electrochemical properties.Different analytic methods were used to characterize the morphologies,components and electrochemical properties for the electrochemical degradation of anionic and cationic organic dyes,electrochemical detection of hydroquinone isomers and metal corrosion protection under high salt conditions.The details are listed below:（1）Three PBA MOF materials,Co₃^Ⅱ[Fe^Ⅲ（CN）₆]₂,Ni₃^Ⅱ[Fe^Ⅲ（CN）₆]₂ and Ni₃^Ⅱ[Co_0.5^ⅢFe_0.5^Ⅲ（CN）₆]₂ were prepared by coprecipitation method（donated as Co-Fe PBA,Ni-Fe PBA and Ni-Co-Fe PBA）.Meanwhile,Fe₄^Ⅲ[Fe^Ⅱ（CN）₆]₃ PBA（donated as Fe-Fe PBA）was prepared by hydrothermal method.The surface morphologies and crystal structures of the four MOF materials were analyzed by field emission scanning electron microscopy（FE-SEM）,Energy Dispersive Spectrometer（EDS）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FT-IR）.The results showed that Co-Fe PBA and Ni-Fe PBA have regular nanocubic structures in a diameter of about 200 nm,while Ni-Co-Fe PBA and Fe-Fe PBA have irregular cubic structures.These four PBAs all have good crystallinity.（2）Four PBAs were used for electrocatalytic degradation of organic dyes with cationic dye methylene blue（MB）and anionic dye methyl orange（MO）by galvanostatic method.The effects of catalyst,electrolyte solution,current,type and concentration of electrolyte solution were investigated systematically.With 0.1mol·L^-1 NaCl as electrolyte solution,a current of 20 mA,and the highest catalytic activity was achieved from Co-Fe PBA for MB(100 mg·L^-1).The degradation rate was 0.98,much higher than that derived from blank.And for MO(100 mg·L^-1),the degradation rate was 0.96 under the 10 mA constant current for 20 min.The optimum catalyst was Fe-Fe PBA.The optimum catalyst dosage was 30 mg Co-Fe PBA for MB and 20 mg Fe-Fe PBA for MO.Furthermore,the electrolytic products were determined with UPLC-MS.It showed both MB and MO were electrolyzed into small molecules and then degraded into CO₂ and H₂O,which effectively avoided secondary pollution.The results showed that the four PBA materials exhibited high catalytic activity for the degradation of anionic and cationic dyes.Moreover,the degradation rate of MB and MO remained above 0.90after successively used 5 times while the crystal structures kept few changes.（3）One novel electrochemically modified electrode（CME）was prepared for simultaneous detection of hydroquinone（HQ）and catechol（CC）with high sensing.The probe was prepared by"dropping coating"method,in which NiO-NiFe₂O₄doped with graphene oxide（rGO）was immobilized on glassy carbon electrode（GCE）slide with Nafion.The electrochemical properties of the modified electrode were studied by cyclic voltammetry（CV）,differential pulse voltammetry（DPV）and electrochemical impedance spectroscopy（EIS）etc.The results showed that the surface roughness of the modified electrode is greatly increased after coating,the effective active area is2.5 times larger than that of GCE,and the electron mass transfer rate is also significantly enhanced.The electrode showed high sensitivity,wide detection range and low detection limit for HQ and CC.The detection ranges were 10-1000 and10-800μM with detection limits of 2.5μM and 1.9μM for HQ and CC,respectively.Average recoveries were 98.7%-136%with relative standard deviations less than2.58%（n=3）at three spiked levels.The reliability and accuracy of the method were verified by HPLC.（4）Firstly,One polymeric multilayers were assembled on copper slide by layer-by-layer assembly from branched polyethyleneimine（bPEI）and polyacrylic acid（PAA）.It was found the resistance value(R_ct)was significantly increased after coating with（bPEI/PAA）₂₀.After immersed in 500 mM NaCl solution for 15 days,the structure of the coating remained intact.ΔR_ct of Cu coated with（bPEI/PAA）₂₀ was only 58Ω·cm²,which is magnitude smaller than bare copper（736Ω·cm²）.All evidence testified that bPEI/PAA multilayers can effectively protect Cu from corrosion in high salt environment.Moreover,bPEI/PAA can automatically heal the incision with a width of 50μm after immersed in 500 mM NaCl for 1 h.It further showed that the coating had great advantages in metal corrosion protection,which can prolong its service life and reduce cost.Secondly,Ni-Fe PBA was introduced into the multilayers to test the influence of PBA materials for metal corrosion protection.The results indicated that the impedance value increased to as high as 1.12×10¹⁵Ω·cm²after dispersing Ni-Fe PBA into bPEI and PAA solution,while the impedance value of bPEI/PAA coating is only 7.1×10⁵Ω·cm².Importantly,R_ct did not decrease but increased,and the inhibition effect reached 100%and the protection efficiency was over 76.67%after immersed in 500 mM NaCl for 7 days.The results suggested that the introduction of Ni-Fe PBA can further enhance the metal corrosion resistance of bPEI/PAA multilayer coatings.Our finding provided one novel field of PBA materials for metal anti-corrosion.