Research on non-cyanide electroless gold plating reactions for sustainable use

为了建立可持续利用的无氰化学镀金反应，我研究了以亚硫酸盐（SO_3^<2->）和硫代硫酸盐作为Au(I)离子配体、硫脲（TU）作为还原剂和对苯二酚（HQ）的电镀溶液中的氧化还原反应。得到以下结果：1)在电镀过程中，Au(I)配合物与TU反应，HQ被巯基自由基氧化为苯醌(Q), S0_3^<2->与Q反应生成对苯二酚磺酸（HQSA）， HQSA进一步磺化，反应机理与HQ2相似。发现TU能够加速Au(I)配合物的还原。这种加速是在金电极表面特别观察到的，而不是在玻璃碳（GC）电极上。3)使用Au、GC、Pt和Au汞合金电极评估了HQSA在水缓冲液（pH 5、8）和有机溶剂（DMSO、DMF）中电化学脱硫的可能性。在这些溶剂-电极体系的电位窗口内不发生脱硫反应4)在电镀过程中，建议以[Au(SO_3^<2->)_2]^<3->的形式供应Au(I)配合物，因为[Au(SO_3^<2->)_2]^<3->的供应导致镀液中SO_3^<2->的浓度增加。对Au(I)络合物的还原没有显著影响5)提出了一种以二甲基二磺酰对苯二酚代替苯基络合物建立可持续利用的无氰化学镀金反应的新方法

Aiming to establish non-cyanide electroless gold plating reactions for sustainable use, I have investigated redox reactions in the plating solution containing sulfite (SO_3^<2->) and thiosulfate as ligands for Au(I) ion, thiourea (TU) as a reducing agent, and hydroquinone (HQ). The following results were obtained1) In the course of the plating reaction, HQ is oxidized to benzoquinone (Q) by thiyl radical which is a product of the reaction between Au(I) complex and TU, followed by the formation of hydroquinone sulfonic acid (HQSA) through the reaction between S0_3^<2-> and Q.HQSA is further sulfonated according to a similar reaction mechanism to that of HQ2) It was found that TU is able to accelerate the reduction of Au(I) complexes. This acceleration is specifically observed on the gold electrode surface, not on glassy carbon (GC) electrodes3) The possibility of the electrochemical desulfonation of HQSA was assessed in aqueous buffers (pH 5, 8) and organic solvents (DMSO, DMF) using Au, GC, Pt, and Au amalgam electrodes. The desulfonation reaction did not occur within the potential windows of these solvent-electrode systems4) The supply of Au(I) complex as [Au(SO_3^<2->)_2]^<3-> during the plating was recommended, since the increase in the concentration of SO_3^<2-> in the plating solution, which is caused by the supply of [Au(SO_3^<2->)_2]^<3->, does not significantly affect the reduction of Au(I) complex5) I proposed a new approach toward the establishment of the non-cyanide electroless gold plating reaction for sustainable use, in which dimethyl disulfonyl hydroquinone is used instead of HQ