Stabilization and Decomposition of Organic Matters by Nano-porous Metals

Nanoporous (np-) metals affect chemical stability of various organic matters much more than their bulk counterparts. Self-assembly monolayers (SAMs) of 4-aminothiophenol are more stable on np-Au fabricated by dealloying Ag-Au alloy than on flat Au, which were elucidated by cyclic voltammetry (CV). The first-principles calculations indicate that atomic defect of Au surface, which is characteristic of ligament surface of np-Au, reduce the binding energy of thiol molecule.The stabilized SAMs on np-Au are also effective for enzyme immobilization. When laccase was immobilized on np-Au surface, its thermal stability was improved compared with nonfixed laccase. The higher stability of immobilized laccase is due to the synergistic effect of reduced conformational flexibility of the enzyme in nanopores and SAMs stability. CV with the working electrode of enzyme-immobilized np-Au revealed that the electron transfer between enzyme and electrode is successfully enhanced by SAMs. These aspects of enzyme-immobilized and SAMs-decorated np-Au can be applied to the electrodes of biofuel cell.Np-metals such as np-Au, np-Pd and np-Ni, on the other hand, remarkably decompose methyl orange (MO, a typical stable azo dye in the textile industry) in an aqueous solution, while MO is highly stable in aqueous solutions which include their bulk counterparts. Ultraviolet-visible light spectroscopy and high-performance liquid chromatography demonstrated that np-Au breaks the azo bond (–N=N–) in MO molecules. Defective surface of ligaments in np-metals plays an important role in this catalytic decomposition of MO.