Preparation And Dye Degradation Performance Of Ni-based High-entropy Alloy Catalyst

Water is the source of life,but also the source of world development.However,dye wastewater pollution is becoming a serious environmental problem in modern industry.In order to develop excellent catalysts for the degradation of dye wastewater,high-performance photocatalysts with different systems have always been a hot topic research in the field of materials and chemistry.High-entropy alloys（HEAs）have attracted extensive attention and research interest due to their unique composition design concept,simple phase structure and excellent physical and chemical properties.In this study,(Ni₄₀Fe₃₀Co₂₀Al₁₀)₉₀Ti₁₀HEA powders and ribbon catalysts were prepared by mechanical alloying（MA）and single roller melt-spinning technique respectively.The excellent HEA catalysts with stable cycle and excellent performances have been acquired.Using XRD,SEM,TEM,laser particle size analyzer,XPS and electrochemical workstation,the phase components and microstructural evolution of HEA powders under different ball milling times have been studied.The effects of fabrication processing and different catalytic conditions on the dye degradation ability of HEA powders have been explored in detail.And,the corresponding catalytic mechanisms are discussed.In addition,the phase composition,microstructure,catalytic performance and corrosion resistance of HEA ribbon were systematically investigated.The main conclusions are as follows:The HEA powder catalysts were obtained after different MA milling times of 30,60 and90 h.The HEA powder after ball milling for 30 h(A₃₀)has a single face-centered cubic（FCC）solid solution.With the milling time extends from 60 h(A₆₀)to 90 h(A₉₀),the as-milled products of HEA powders consist of the mixed structures of FCC solid solution and amorphous phase.Three powders are all in the shape of flaky stacking with a thickness of about 1μm,and show the low degree of crystallinity.Under the visible light condition,HEA powder catalysts effectively degrade malachite green（MG）and methyl blue（MB）solutions without producing new organic substances.The A₃₀has the best catalytic performance for MB solution with the degradation rate reaching86.75%.It is found that the metal elements change from atomic state to ionic state with the phenomenon of oxidation and grain growth in the catalytic process.It provides more electrons for the degradation of MB and improves the crystallinity degree of the catalyst powders.The activation characteristics of twins and stacking fault on the surface of A₆₀catalyst are beneficial to improve the cycle stability.The grow-up of crystals are induced by homogenization annealing treatment of the A₆₀powders(H-A₆₀).Moreover,the homogenization treatment weakens the lattice strain and heterogeneity,further leads to the reduction of the numbers of defects and nano-galvanic cells,which increases the resistance of electron transport at grain boundary.Those make the lower catalytic degradation effect than that of A₆₀powders.Cryogenic treatment of A₆₀powders(C-A₆₀)have higher physical adsorption capacity.The catalytic performance is improved in the initial reaction stage.It presents that the maximum degradation rate of C-A₆₀is the better than H-A₆₀,but the lower than A₆₀.A small amount of H⁺（p H=6）and a higher contents（0.7g/L）improve the degradation effect of A₆₀.The(Ni₄₀Fe₃₀Co₂₀Al₁₀)₉₀Ti₁₀HEA ribbons with good plasticity were prepared by single roller melt-spinning technique.The phase components of the ribbon catalyst consist of（Ni,Fe）-rich FCC and Al-rich BCC solid solution phases.The FCC solid solution shows the fine equiaxed grains with a size of about 1 um,and the BCC intergranular phase has a size of about 200 nm.The degradation rate of MG is up to 93.45%,exhibiting the best catalytic performance of HEA ribbon.Moreover,the degradation rate of MB is better,but the catalytic performance of brilliant yellow solution becomes weak.The catalytic degradation of ribbon can be divided into two reaction processes:first fast-then slow.This is due to the fact that Ti and Al distributed in the ribbon surface tend to form dense oxide film in the air,which inhibits electron transport and leads to slow catalytic degradation.When the passive film is broken down,there is a potential difference between the newly exposed grains and passive film,which forms a galvanic cell in the solution and promotes the faster catalytic reaction.In addition,the ribbon catalyst has excellent cycling stability for the degradation of MG and MB.The degradation of MB is cycled more than 5 times,and the degradation rate is not lower than the first time.The degradation rate of MG is still as high as 86.15%after 8 times cycles of experiments,which is only 9%lower than that of the first catalysis.The catalytic effect is far better than that of the Fe₇₈Si₉B₁₃amorphous ribbon（74.34%）.