钼Ⅵ-、钨Ⅵ-溴代苯羟乙酸络合吸附电流在催化体系中的增敏研究和应用Ⅱ.络合物化学组分,电极反应过程和增敏机理

Study on the Enhancement of the Complex Current of Mo(Ⅵ)-,W(Ⅵ)-Br-BHA in the Catalytic System and ApplicationⅡ. Stoichiometry of Complexes, Electrode Reaction Process and Mechanism of Enhancement

由前文〔1〕已知 ,Mo -、W -BrBHA -NaClO3体系的平行催化电流 ,可被质子化有机染料或阳离子表面活性剂进一步增敏 ,其中以亚甲蓝 (MB)为最佳 ,并提出它们的增敏顺序和可能的规律。本文研究了Mo 、W 和Br -BHA络合物的形成和摩尔比 ,均为 1∶2 ,求算了它们的表观稳定常数 (Ks) ,分别为 2× 1 0 9和 5 7× 1 0 6 ,电极反应均为 1个电子转移的准可逆过程 ;详细研究了该体系加入MB后 ,Mo -、W -BrBHA在电极表面的化学反应和电极反应的变化 ,包括 :Ep 移动和ip″的增敏程度、峰形改变的大小、温度系数以及吸附等温类型的变化等。结果表明 :预先吸附在电极表面上的MB与Mo -BrBHA不形成络合物 ,它们之间只产生静电吸引的诱导吸附 ,而MB对W -BrBHA则诱导吸引形成缔合物。无论那种情况 ,Mo ,W 在电极表面的浓度都得到增大 。

As known in the previous work 〔1〕 , the parallel catalytic current of Mo(Ⅵ)-,W(Ⅵ)-BrBHA-NaClO 3 system could be further increased by the protonated organic dyes and cationic surfactants, among them the methylene blue(MB) was the best one, and the enhancemcnt order and the possible regularity have been suggested. In this paper, the formation and the molar ratio (1∶2) of the complex of molybdenum (Ⅵ) and/or tungsten (Ⅵ) with Br BHA were studied, and the apparent stability constants (K s) were evaluated to be 2.1×10 9 and 5.7×10 6 respectively. The investigated results demonstrated that the electrode reaction both for Mo(Ⅵ) and W(Ⅵ) in the system studied was a quasi-reversible process involved one electron transferred. After adding MB, the varying of the chemical and/or electrode reaction of Mo(Ⅵ)-, W(Ⅵ)-BrBHA including the scale of E p shifted and that of i p″ increased the size of peak shape changed, the temperature coefficient and the disparity of the adsorption isotherm etc. were studied in detail. The results indicated that the MB adsorbed on the electrode surface in advance, did not form the comlex with Mo(Ⅵ)-BrBHA, but between them produced an inductive adsorption attracted by static electricity of both adsorbed species loaded opposite charge only; However MB inductively attracted the W?-BrBHA to form an association complex. In spite of which situation, anyway, the concentration of Mo(Ⅵ) and W(Ⅵ) on the electrode surface both were increased, and their parallel catalytic currents were enhanced in the different level.