Selective recovery of copper, zinc and nickel from electroplating wastewater was studied by precipitating the metal sulfides formed by sulfuration treatment. CuSO4, ZnSO4 and NiSO4 involved in model solutions and those of plating wastewater were adjusted to 100-120mg dm−3 of the initial metal concentration. Two kinds of sulfurating agents, sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) of 6.8×10−2 mol dm−3, were employed. As a result, it was found that Na2S was more effective for the separation of the metal sulfides precipitated. The formation of metal sulfides was dependent on the pH value of the solution. In the sulfuration process using Na2S, copper was first separated from the solution as copper sulfide in pH1.4-1.5, followed by the formation of zinc sulfide in pH2.4-2.5. Subsequently, nickel sulfide was precipitated after the formation of copper and zinc sulfides in the residual solution in pH5.5-6.0. The same results of the formation behavior of copper sulfide, zinc sulfide and nickel sulfide in a simulated plating solution were obtained for those in an electroplating solution.
Electroless plating has been extensively applied to electronic devices, since it provides superior throwing power and uniform film formation for complicated geometries. In this study, the formation of a conductive layer in the deep-recessed trenches by using electroless Ni-B plating was investigated. The selection of the complexing agent is important to obtain high uniformity of Ni films in the deep-recessed trenches. Superior uniformity of Ni films in the deep-recessed trenches was obtained by using DL-malic acid as a complexing agent. On the other hand, Ni films from a bath containing glycine were not uniformly deposited, and no deposition was observed at the bottom of the deep-recessed trenches. The influence of the complexing agent on the initial plating reaction was investigated by electrochemical analysis. The deposition reaction obtained from the glycine bath is based on diffusion control. Therefore, nickel ions are mainly reduced at the aperture area of the trenches, and little or no reaction occurred at the bottom area of the trenches in the glycine bath. That is because almost all the Ni ions are consumed at the surface and aperture area. On the other hand, the Ni deposition is not dominated by diffusion control in the DL-malic acid bath. Accordingly, uniform deposition in the trenches can be achieved since the nickel ions reached the bottom of the trenches. In conclusion, it is important to plate uniformly in deep-recessed trenches so that the deposition reaction will not be dominated by the diffusion control state.
The electrochemically effective oxidation of NADH has drawn striking attention because it is widely applicable for fabricating biosensors. The mediators are normally used as electron shuttle molecules between the electrode and enzymes. Phenothiazine compounds deserve as suitable mediators due to theirs negative formal potential and large rate constant. For the practical use, both the enzyme and mediator are required to be co-immobilized on the electrode surface. In this study, gold nano-particles modified with thionine (Th+) were immobilized on the surface of the gold electrode by physical adsorption. Th+ was covalently bound to the surface of the gold nano-particles using 3,3'-dithiobis (succinimidyl propionate) (DSP) as a cross linker. The electrochemistry of Th+ modified on the gold nano-particles was characterized by voltammetry. Th+ molecules on the gold nano-particle modified electrodes showed two redox couples at −30mV and 240mV vs Ag/AgCl at pH7. A well-defined peak for the electrocatalytic oxidation of NADH was observed at 240mV. The nano-particle electrodes modified with glucose dehydrogenase (GDH) and Th+ mediators were fabricated and characterized aiming at fabricating a reagentless glucose biosensor. Upon the addition of glucose to the electrochemical cell, the oxidation current dramatically increased due to an electrocatalytic reaction.