Reduction effect of pore wall and formation of Au nanowires inside monolithic mesoporous silica

Triggering gold nanoparticles formation on a quartz surface by nanosecond pulsed laser irradiation

A new direct and straightforward method is proposed to synthesize bare Au nanoparticles (Au NPs) on a quartz surface by nanosecond 532 nm pulsed laser irradiation of a quartz surface in contact with Au(iii) precursor solution. The characterisation by XPS, UV-Vis, SEM and AFM measurements demonstrate the formation of bare Au NPs anchored on the quartz surface with a mean height of 27 ± 10 nm localized in the laser irradiation area. The main features of this approach are their simplicity, quick fabrication and the large surface area covered by Au NPs. The absence of ligands/stabilizing agents on the Au NPs makes this substrate very suitable for its direct surface modification opening the range of applications in biology, medicine, sensing, catalysis, among others. As a proof of concept, the capabilities and advantages of this substrate as Surface Enhanced Raman Spectroscopy (SERS) platform were tested demonstrating the absence of any Raman signal overlapping with the analyte in the whole spectral range.

Removal of Heavy Metals from Wastewaters: A Challenge from Current Treatment Methods to Nanotechnology Applications

Removing heavy metals from wastewaters is a challenging process that requires constant attention and monitoring, as heavy metals are major wastewater pollutants that are not biodegradable and thus accumulate in the ecosystem. In addition, the persistent nature, toxicity and accumulation of heavy metal ions in the human body have become the driving force for searching new and more efficient water treatment technologies to reduce the concentration of heavy metal in waters. Because the conventional techniques will not be able to keep up with the growing demand for lower heavy metals levels in drinking water and wastewaters, it is becoming increasingly challenging to implement technologically advanced alternative water treatments. Nanotechnology offers a number of advantages compared to other methods. Nanomaterials are more efficient in terms of cost and volume, and many process mechanisms are better and faster at nanoscale. Although nanomaterials have already proved themselves in water technology, there are specific challenges related to their stability, toxicity and recovery, which led to innovations to counteract them. Taking into account the multidisciplinary research of water treatment for the removal of heavy metals, the present review provides an updated report on the main technologies and materials used for the removal of heavy metals with an emphasis on nanoscale materials and processes involved in the heavy metals removal and detection.

Bipolar electrochemical method for dynamic in situ control of single metal nanowire growth

Fabrication plays a key role in determining the unique electrical, optical, and catalytic properties of metal nanowires. Here we present a bipolar electrochemical method for dynamically monitoring and controlling the rate of single metal nanowire growth in situ without a direct electrical connection. Solutions of a metal precursor and a reducing agent are placed on either side of a silica nanochannel, and a pair of electrodes is used to apply a tunable electric potential across the channel. Metal nanowire growth is initiated by chemical reduction when the two solutions meet and continues until the nanochannel is blocked by the formation of a short metal wire segment. Further growth is driven by a bipolar electrochemical mechanism which enables the reduction of metal precursor ions at one end of the nanowire and the oxidation of the reducing agent at the other. The growth rate is monitored in real time by simultaneously recording both the faradaic current and optical microscope video and can be adjusted accordingly by changing the applied electric potential. The resulting nanowire is solid, electrically insulated, and can be used as a bipolar nanoelectrode. This technique can be extended to other electrochemical systems, as well, and provides a confined reaction space for studying the dynamics of any process that can be optically or electrically monitored.

Comparison of surface plasmon resonance responses to dry/wet air for Ag, Cu, and Au/SiO2

We investigated the optical absorption spectra of Ag-, Cu-, and Au-mesoporous SiO(2) systems, respectively, after the samples were heated in dry air and in wet air. As expected, dry air at high temperature leads to the surface plasmon resonance (SPR) disappearance of Ag-SiO(2) and Cu-SiO(2) and a slight SPR increase of Au-SiO(2). However, a small amount of water vapor in air induces a strong SPR appearance for both Ag- and Au-containing samples, indicating that water vapor plays an abnormal reduction effect on both Ag and Au species in mesoporous SiO(2), despite the fact that it usually plays an oxidation role on Pt-group metals, but it cannot induce the SPR appearance for the Cu-containing sample under the same condition.

Gold and gold-iron modified zeolites--towards the adsorptive deodourisation

Zeolites exhibiting different structures (Y, Beta, and ZSM-5) were modified with gold and iron and applied for odour adsorption from the air containing dibutyl sulphide (Bu(2)S) used as a representative odour producing compound. The structure of the zeolites used determines the rate of adsorption (higher on Y type zeolites and smaller on two other zeolites), whereas hydrophilicity affects the selectivity towards Bu(2)S adsorption increasing in the order: Y<Beta<ZSM-5. For the same zeolite structure, Bu(2)S adsorption selectivity depends on the total acidity of zeolites which increases after iron modification. The texture and surface properties of the modified zeolites were studied by XRD, XPS, UV-vis, TEM, pyridine adsorption and FTIR, test reactions (acetonylacetone cyclisation, isopropanol decomposition).