Preparation Of AlCrFeMn Based High Entropy Alloys And Their Degradation Behavior Of Azo Dyes

With the rapid development of the modern textile industry,there are more and more synthetic organic dyes.As organic synthetic dye,azo dyes have accounted for more than 80 %of the total amount of artificial organic dyes.During the production and use of azo dyes,a lot of dye wastewater is generated,and the physical and chemical properties of azo dyes wastewater are particularly stable,low biodegradability,and direct discharge will cause great harm to the environment and human health.Therefore,the treatment of azo dyes wastewater has always been the focus and difficulty of the wastewater treatment industry,and it is also a research hotspot at home and abroad.Traditional methods for treating azo dye wastewater include physical methods,chemical methods,and biological methods.Many of these three methods have the disadvantages of high cost,low efficiency and harsh reaction conditions,so they need to be further improved.High entropy alloys(HEAs)are new type of alloys with many excellent properties developed in recent decades,and research has shown that HEAs have excellent ability to degrade azo dyes.However,there are few studies on the mechanism of HEAs to degrade azo dyes,and few reports have been made on alloys design of HEAs for degrading azo dyes.The main purpose of this work is to further expand the HEAs systems used to degrade azo dyes wastewater,to widen their scope of application,especiaily broaden the application of their excellent functional characteristics.This work focuses on the design and preparation of HEAs systems,the behavior and mechanism of azo dye degraded by HEAs systems.At the same time,XRD,OM,SEM,TEM,UV-Vis,FTIR,BET,XPS and other testing methods are used for characterization and analysis.The degradation object is the typical azo dye direct blue 6(DB6).In this work,under the same experimental conditions,the degradation efficiency of DB6 by AlCrFeMn HEA powders is 3000 times higher than that of commercially available pure iron powders,and the degradation efficiencies of DB6 by AlCrFeMn with the addition of Mg,Ti,S,P and C have been increased to 2 times,1.2 times,42 times,6.6 times and 3.8 times,respectively.This can fully explain that the AlCrFeMn based HEAs reported in this work show excellent ability to degrade azo dyes.The first step is to design HEAs with three atomic ratios: AlCrFeMn,AlCrFeNi and Fe Cr Ni Mn,and these three types of HEAs are prepared by mechanical alloying.Through comprehensive comparative analysis of phase composition,alloy composition and degradation performance,AlCrFeMn HEA is determined as the basic alloy in this work.In order to further improve its degradation ability,on the basis of AlCrFeMn HEA,the effect of adding different elements on the degradation of DB6 dye solution by AlCrFeMn alloy is also studied.The added elements are mainly divided into two categories: one group is metal elements,that are three metal elements of Mg,Ti and Ni;the other group are non-metal elements,that are three non-metal elements of S,P and C.In addition,three representative HEAs(AlCrFeMn,AlCrFeMn Mg and AlCrFeMn S)with relatively good degradation ability are selected from AlCrFeMn-based HEAs.The three types of HEAs at different alloy powder concentrations(0.125 g/L-6 g/L),different solution p H values(p H = 3,7,10),different dye concentrations(50 mg/L-200 mg/L),different reaction temperatures(25 °C-55 °C),etc.are further studied.The degradation behavior of the three representative HEAs under various experimental conditions are analyzed in-depth.Powder-based HEAs have better ability to degrade azo dyes than bulk HEAs of the same quality.In this work,mechanical alloying method is selected to prepare the designed HEAs.However,the HEAs in powder state also have disadvantages in the process of degrading azo dyes.That are,when treating dye wastewater,the HEAs in powder state have a certain loss rate,which is not easy to recover,and sometimes the degradation rate is too fast to control and other issues.In order to solve these problems,a new method for degrading azo dyes after entrapping HEAs powders with calcium alginate beads(CABs)is also proposed in this work.A certain decrease,but it can greatly reduce the loss rate of the HEAs powders during the degradation reaction.At the same time,the HEAs entrapped by CABs can be easily filtered from the dye solution for recycle and reuse.This method has not been reported in the existing public literature,and the idea is particularly novel.Bare HEAs powders and HEAs entrapped by CABs have their advantages and disadvantages when degrading azo dye solutions.In practical applications,alloy samples in different states can be selected according to needs to give full play to their respective advantages.The ability of powder HEAs to degrade azo dyes is closely related to their elemental composition,physical properties,chemical properties,lattice distortion,residual stress,specific surface area,active sites,defects and other factors.This work has important enlightening effects on the use of HEAs for water resources protection and is a very meaningful research work.