Surface-enhanced Raman scattering (SERS) spectroscopy is an analytical method for the detection of low amounts of analytes adsorbed on an appropriate coinage metal (Au, Ag, Cu) surface. Generally, the values of the enhancement factor are the highest on silver, lower on gold and relatively very low on copper. In this study, we have focused on the estimation of the enhancement factors of copper surface/substrates formed by different preparation procedures. The SERS activity of large electrochemically prepared substrates and colloidal systems is compared. The surface morphology of the large substrates was studied using scanning electron microscopy and atomic force microscopy. The size distribution of colloidal nanoparticles was monitored by dynamic light scattering. The values of enhancement factor are in both cases more than 10 5 for the FT-SERS spectra, demonstrating the fundamental role of nanostructured copper as a substrate material at the excitation wavelength (1064 nm) used.
The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu.
The initially very promising transport properties of glassy high free volume polymers deteriorate rapidly over time. In this work, we focused on this aging phenomenon in two polymers of intrinsic microporosity (PIMs), namely PIM-1 and PIM-EA-TB. To identify the main mechanisms involved, we studied the time-declines of permeability and diffusivity of methanol vapours in flat membranes with approximately equal thicknesses. The permeation measurements were carried out using a continuous flow permeation method with carrier gas, where the methanol vapours were held at constant activity 0.2 at 25°C. Two different experimental modes were used: (i) continuous experiments that consisted of one long experiment with a duration of over 650 hours for each polymer and (ii) momentary experiments that consisted of a vast number of short (ca. 6 hours) consecutive measurements of transient permeation. The observed decreases of methanol permeability due to aging were more intense in the case of continuous mode for both polymers. In other words, the aging was ca.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.