Porous materials are of great interest because of their interesting structural, optical and surface properties, leading to a wide range of applications. [1,2] Among the various properties of porous materials, their high specific surface area, low density, and cost-effectiveness are particularly notable and make them attractive candidates for catalysis, [3] sensing [4] and actuation [5] applications. Nanoporous particles in particular are attractive candidates for these applications, because of their higher surface-to-volume ratio in comparison with bulk counterparts. There have been numerous efforts towards the solution-based synthesis of porous and hollow metal nanoparticles, [6][7][8][9][10] however their applicability is limited as the assembly of individual nanoparticles present in solution is still a major challenge. There have also been limited efforts towards the creation of porosity in thin films. [11] Most of the efforts in this direction have been limited to the de-alloying process, in which one of the components of an alloy is selectively dissolved using an acid, leaving behind a porous network/channel of the more noble metal component. [11,12] However, the acid-mediated de-alloying process requires the cumbersome task of alloy formation and has limited applicability to those metal alloy systems wherein both of the metal components dissolve into the de-alloying solution (acid). This therefore necessitates the use of a different approach for the creation of porosity in supported metal thin films and/or metal foils, which can be universally applied to all the metallic systems. Recently, galvanic replacement reactions (transmetallation reactions) involving sacrificial metal nanoparticles and suitable metal ions have been employed by various groups [13][14][15][16][17][18] for the synthesis of hollow/porous metal [13,14] and metal alloy [15,16] nanostructures in aqueous [14][15][16][17] and organic environments. [18] Galvanic replacement reactions are single-step reactions that utilize the differences in the standard electrode potentials of various elements, leading to deposition of the more noble element and dissolution of the less noble component. The electroless nature of galvanic replacement reactions provides them the unique and significant advantage of simplicity. Very recently, the potential of galvanic replacement reactions was also explored for the epitaxial growth of thin films. [19] In this study, we have investigated the scope of galvanic replacement reactions as a versatile tool for the creation of nanoscale porosity in metal foils as a representative of bulk metal surfaces. More specifically, the reaction of Cu 2+ ions with nickel foil results in a Cu-Ni nanoporous surface. The Cu-Ni nanoporous material has been characterized by using various microscopy tools including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Auger microscopy in addition to X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) analysis. Recognizing that such nanoporous surfa...

We demonstrate a facile localized reduction approach to synthesizing a Au nanoparticle-decorated Keggin ion/TiO(2) photococatalyst for improved solar light photocatalysis application. This has been achieved by exploiting the ability of TiO(2)-bound Keggin ions to act as a UV-switchable, highly localized reducing agent. Notably, the approach proposed here does not lead to contamination of the resultant cocatalyst with free metal nanoparticles during aqueous solution-based synthesis. The study shows that for Keggin ions (phosphotungstic acid, PTA), being photoactive molecules, the presence of both Au nanoparticles and PTA on the TiO(2) surface in a cocatalytic system can have a dramatic effect on increasing the photocatalytic performance of the composite system, as opposed to a TiO(2) surface directly decorated with metal nanoparticles without a sandwiched PTA layer. The remarkable increase in the photocatalytic performance of these materials toward the degradation of a model organic Congo red dye correlates to an increase of 2.7-fold over that of anatase TiO(2) after adding Au to it and 4.3-fold after introducing PTA along with Au to it. The generalized localized reduction approach to preparing TiO(2)-PTA-Au cocatalysts reported here can be further extended to other similar systems, wherein a range of metal nanoparticles in the presence of different Keggin ions can be utilized. The composites reported here may have wide potential implications toward the degradation of organic species and solar cell applications.

Catalytic wet oxidation (CWO) of ferulic acid (a model lignin compound) was investigated at low temperature and pressure (100 °C, 172 kPa P O2). Nine homogeneous catalysts were screened at three different catalyst loadings. Homogeneous copper ions were observed to be the most active catalysts; various copper based heterogeneous catalysts were also prepared and tested. The most active catalyst was Cu−Ni−Ce−Al2O3; however, this catalyst also exhibited the highest extent of copper leaching. Cu−Mn−Al2O3 was the most stable catalyst tested and was second only to Cu−Ni−Ce−Al2O3 in terms of activity among nine heterogeneous catalysts studied. Heterogeneous catalytic activity compared with the activity due to leached metal ions was observed to be dominant for both of the above-mentioned catalysts.