Electrocatalytic Hydrogenation Of Vat Dyes With Nickel-sulfur Alloy Electrode

The traditional reducing method of vat dye is using sodium hydrosulfite in the alkaline solution,but the stability of sodium hydrosulfite is poor,the practical amount usually three times of that of theoretical amount and cannot be recycled.What's more,it will produce high concentrations of sulfites and sulfates,which not only cause environmental pollution,but also increase the cost of sewage treatment.Therefore,the use of electrochemical reducing method to replace the traditional method has become an important research direction.At present,there are many studies on indirect electrochemical reduction,and direct electrochemistry is only limited in indigo dyes reduction,while the study of electrocatalytic hydrogenation reduction is seldom.Electrocatalytic hydrogenation reduction not only needn't any medium and a large number of chemical additives,but also the dye solution can be recycled.This method has a huge application prospect.In this study,the electrode of self-made Nickel-Sulphur alloy was selected as the cathode electrode in the electrochemical reduction system.The surface morphology and the electrochemical behavior of the electrode in the electrochemical reduction system was analyzed by cyclic voltammetry and SEM,the cotton fabric was dyed after the reduction of the dye,then the K/S value and the rubbing fastness of the fabric were tested.It is found that nickel sulfur alloy electrode has certain reduction ability to vat dyes.The main contents and conclusions are as follows.Firstly,by comparing the cathodic polarization curves of nickel,platinum,titanium,and nickel foams and the reduction of the vat dyes.it was found that Ni can electrochemical reduce vat dyes.Nickel foam has a better reduction effect than nickel flakes.Then,to obtain higher catalytic activity,nickel sulfur plating formulations of two different sulfur sources are selected for discussion,and surface morphology and other properties of the two electrodes were analyzed by SEM,EDS,and other tests.The results indicated that the sulfur-sourced nickel thiosulfate electrode is the most effective one for dye reduction.After studying the electroplating substrate,it was found that the graphite felt had a large specific surface area and had a good adsorption of the nickel-sulfur alloy.Finally,the graphite felt was selected as the substrate.In addition,the influence of various factors on the overpotential of hydrogen evolution was analyzed by orthogonal test,and the best formula for preparing the nickel-sulfur electrode was obtained: Ni SO4 0.75mol/L,Ni Cl2 0.1 mol/L and H3BO3 0.6 mol/L,Na2S2O3 0.75 mol/L,C18H30O3 S 0.0036 mol/L.Under this process recipe,the nickel sulfur alloy electrode was prepared under the condition of current density 20 m A/cm2,plating time 50 min,and plating temperature 40?.The vat dye was electrochemically reduced with a reduction rate of 85% and current efficiency is 7.12%.Finally,the pure cotton fabric was dyed with reduced yellow G and compared with the samples dyed by traditional insurance powder reduction.It was found that the K/S values,the dry and wet rubbing fastness,and the soap fastness of the dyed fabrics by these two methods are close but electrocatalytic hydrogenation reduction still needs improvement in the further study.