A Study Of Electrochemical Reduction Of Vat Dyes

In textile industry,addition of strong reducing agents is necessary to form the reduced dyestuff which is soluble in alkaline aqueous medium at present.This method produces great economic burden and environmental pollution,because of lots of waste water and high costs.Electrochemical reduction has the features of high security,low cost and less environmental problems,making it a promising alterative to chemical reduction of vat dyes.Therefore,it becomes a research hotspot in the world today.In the study,the indirect electrochemical reduction of Vat Olive T was investigated in detail by cyclic voltammetry and electrolytic experiments.The mechanism of radicals on electrochemical reduction was discussed.In addition,we gave the effects of ultrasound on the electrochemical reduction of indigo and anthraquinone dyes a further study using ultrasound probe and bath technical.And then we got first step conclusion that ultrasonic technical how to play a major role.Finally,we deceloped theoretical studies up to practice and achieved cotton yarn dyeing,which proved this technical can be cycling and controlling costs.The results show that:Firstly:(1)Aside from reducing indigoid dyes and indanthrene dyes,the indirect electrochemical reduction can also reduce anthraquinone dyes,more generally,Fe(III)-TEA complexes have good electrochemical activity in alkaline solution,which are well suited for the indirect electrochemical reduction of VatOlive T and can avoid over-reductiong of Vat Olive T.(2)The test electrode using in cyclic voltammograms(CV)is not SS304 but silver because the redox reaction of dye and media must be achieved on condition that deposited iron on the surface of SS304 electrode.However,the iron deposition may be having an impact.(3)The effects of operating parameters including reaction current density,temperature,concentration of NaOH and Fe(III)-TEA mediator had been studied by L9(34)orthogonal experiments.The results show that high current efficiency(59.09%)can be successfully achieved under optimized conditions and the current density is found to be the main influence factor.Secondly:(1)The effect of electric current density and concentration of media on reduction process was investigated under supersonic condition.The electric current density between 0.4?0.8A·cm-2 should be fine,when it was too low,the action began to decrease because of undercapacity;yet if the electric current densiity was too high,it can be caused by hydrogen evolution.When the concentration of media was between 1:8?9.75,it reached a maximum value,otherwise it may be influenced current efficiency greatly.(2)The temperature influences reduction efficiency of vat dyes greatly.When it ups to 40?,the current efficiency reached a maximum.When it was too much high or too low,the action of reduction began to decrease rapidly.(3)Under certain conditions,deposited iron can be achieved on the surface of electrode by means of cycle voltammentry,which achieved about-1.4V.The iron deposition having an impact during the reduction precesses,especially the first stage.(4)We gave the effects of ultrasound on the electrochemical reduction of indigo a further study using ultrasound probe technical.The results showed that in the ultrasound conditions,the Fe3+/Fe2+ redox process was very significant,which explained ultrasonic technical how to play a major role in the reduction process.Thirdly:in the experiments of dyes middle-system,we concluded the following.(1)Under low concertration of media conditions,the media could recycled four times,the current efficiency of the first recycle was twice as much as other times because of media cost.According to the literature,the media of indirect electrochemical reduction can recycled ten times.(2)It is very essential to complement fresh media liquor for each iteration to make current efficiency stable.(3)Becase of the surface adsorption between dyes and penetrating agent on the suface of electrode,electric double layer structure was changed which increased dyes solubility and enhanced the current efficiency.(4)After cycle dip dyeing several times,the cotton yarn fixation had little difference on naked-eyes observation.The suface color depth(K/S)and crocking test required professional equioment,which provided basis and direction for future development.