Ag and Cu nanoparticles supported in mordenite structure have been formed applying reduction temperatures in the range 100-400 C and varying Ag/Cu atomic ratios. Absorbance spectra of samples exhibit signature features consistent with absorption via localized surface plasmons propagating in metallic nanoparticles. The formation of binary Ag-Cu nanoparticles is inferred. Theoretical calculations within an average field Maxwell-Garnett model modified for a three component composite system are used to interpret resonance shifts and relative intensities of plasmon peaks in the experimental findings. Within the applied model the relative volume occupied by each metallic species can be changed. This permits the simulation of experimental conditions of the samples. It is experimentally found that the simultaneous presence of two metal species during the synthesis affects reduction temperatures, stability and relative concentration of embedded nanoparticles. Furthermore the observed optical spectra of the supported bimetallic nanoparticles is contrasted with that of single metal nanoparticles studied previously. Our study represents a contribution to the possibility of optical monitoring of synthetic pathways in zeolite + metal nanoparticle systems.
Systems for optical analysis use vacuum chambers, where low pressures are reached. Remaining water molecules are the prevalent contaminant in high vacuum chambers. For this reason measurement of water levels is an important task that allows correct equipment operation. In this work, a different approach is presented for detecting and quantifying the water molecules inside a the vacuum chamber used in optical systems. A zeolite coated quartz crystal microbalance is used for detecting the water molecules, and the change in the resonance frequency is measured using a novel technique known as the principle of rational approximations. Theoretical results show how nanograms of adsorbed molecules are measured, and the number of molecules are quantified.
Optical spectra of noble metal nano-particles supported on different types of zeolites are studied and compared. The absorbance spectra of Cu, Ag and Au nanoparticles supported on mordenite, β-zeolite, Na/Y and H/Y zeolites respectively are reported. Spectra for pre-exchanged Au-Cu/Na/Y, Au-Ni/Na/Y and Au-Fe/Na/Y are also studied. A simple effective medium approach (Maxwell-Garnett) is used to obtain a theoretical complex effective dielectric function of the composite and to asses the sensibility of the plasmon resonance to the sample characteristics. The knowledge of these properties can hopefully be applied to the development of optical tools to monitor the synthetic path.
Successful preparation of the Ce-Zr-Al oxide thin films and glassy products by a newly developed organic-free modification of the sol-gel technique is reported. The structural composition and some properties of the samples obtained were investigated by TEM, XRD, FTIR, ESR, UV-Vis, PL and XPS. The optical investigation of the obtained films together with ESR data indicate the appearance of the bulk Ce3+-defects (g⊥ = 1.962-1.967, g// = 1.938-1.940, assigned to 4f1 state, with concentration ~2•1018spin/g). The significant PL intensity rising at elevated temperature was related to spontaneous increasing of Ce3+ concentration in sol-gel samples under thermal dehydration. Also, an unexpected formation of intra-band gap states during thermal treatment of xerogels was manifested in UV-Vis spectra. This intra-band-gap states was attributed to the oxygen related defects that contribute to PL signal.
Copper incorporation into zeolites by the ion-exchange from Cu(II) solutions followed by different heat treatments results in a production of a number of species. Redistribution among different sites after dehydration, spontaneous and forced reduction, cluster and particle aggregation, etc. can occur, and a final copper state depends on type of zeolite, SiO2/Al2O3 molar ratio and processing conditions. Various species where observed: copper ions Cu2+ and Cu+, small particles and clusters Cun. We concentrate on the appearance of small copper clusters feasible in zeolites with size of cavities those match the cluster size. The clusters were simulated with ab initio quantum chemical calculations in the range of sizes 5 < n < 10 those are probable within zeolites cavities. Experimental data available on optical absorption of the reduced copper in the three types of zeolites can argue on the occurrence of the clusters stabilized within channels under mild reduction conditions while the larger copper nanoparticles appear under the harder reduction. The model calculation proposes some few-atomic copper clusters (Cun) as the candidates to fit the zeolite cavities with correspondence of the calculated absorption bands with the experimental spectra.
Cu-mordenites catalysts are among the most active available for de-NOx at moderate temperatures. Silica-alumina molar ratio of mordenite supports strongly affects conversion efficiency for NOx. Copper mordenites' rapid deactivation by water has led us to investigate the effects of adsorbed water on framework and extra-framework ions, mainly using NMR of 27Al and 1H. Adsorbed water content has been monitored and controlled in mordenite samples via TGA, as well as by vacuum calcination. Several NMR measurements have been performed to aid in the interpretation of spectra, including variable pulse-delay spin echo and 1H-27Al TRAPDOR. A number of surface characterization techniques have been applied to both H- and Cu-mordenites. Catalytic experiments showed that the reduction of NOx to N2 and O2 by hydrocarbons reach 95-98 % depending on the catalyst composition.
The most recent approach to the development of novel antimicrobial and antifungal agents is based on the application of synthetic and natural zeolites, because zeolites are known to be the carrier and slow releaser of the heavy metals with olygodynamic properties. The microbiological activity of the ion-exchanged zeolites is attributed to the ionic state of the metal sreleased from the zeolites by ion re-exchange. In the present work we used low cost natural clinoptilolite (Cli) as a substrate for copper and silver in different states. The state of oxidation of the exchanged metal in zeolite with supported Cu and Ag species (in the form of cations, small clusters, sub-coloidal particles, large particles) in order to fit them to fulfill the following criteria: to demonstrate their high protective abilities against fungi and long-term stability. The study of structure of samples with XRD, UV-visible spectroscopy, FTIR, their stability with temperature and during storage was carried out for obtaining the correct correlation with microbiological activity.
Copper nanoparticles were produced within the protonated and alkaline forms of several zeolites by the hydrogen reduction of corresponding Cu-exchanged forms. Variation of zeolite structure, reduction temperature and acidity of zeolites were the main factors influencing metal reducibility and appearance of copper reduced forms. They were detected by means of optical absorption using diffuse reflectance spectroscopy technique. The effect of zeolite type upon the plasmon resonance band associated with the reduced copper clusters was investigated experimentally and discussed with eh Mie theory simulation results. The type of this spectral appearance is associated with size of copper nanoparticles formed as the result of reduction and secondary aggregation and dielectric properties of zeolite micro crystals being a matrix for the nanoparticle stabilization.
Small copper particles within zeolite (mordenite) matrix produced by copper ion reduction were studied. Variation of SiO2/Al2O3 molar ratio of mordenite does not change crystal structure, but results in different ionic properties. A change of SiO2/Al2O3 ratio leads to transformation of the plasmon resonance from a classical peak to a shoulder in the same wavelength range. These features were simulated by the Mie theory, and calculations outlined additional absorption bands those consistent with the experiment.
Change the reduction temperature from 293 to 873 K permitted to prepare Ag-(natural clinoptilolite) samples with varying contribution of the different states of silver. At temperatures <EQ 473 K small Agnm+ clusters (n < 10) and Agn subcolloidal particles (n approximately equals 10) are formed. Reduction at temperatures >= 573 K leads to disappearance of silver clusters and subcolloidal particles and formation of large silver particles on external zeolite surface. Prepared samples are stable in air.
Clusters of CdS were prepared inside the framework voids of zeolites NaX and chabazite by multistage ion exchange chemical reaction. It was observed that each stage of reaction affects the structure of zeolites crystals. Aluminum atoms change their coordination state at the first stage because of hydrolytic decomposition of some Al-O tetrahedral bonds. Partially reversible relaxation of aluminum atoms of zeolite framework occurs during the second stage of chemical reaction. This spontaneous transition of the coordination number of aluminum atoms took place without changing of their positions of framework atoms. Such kind of the interaction between framework atoms of alumosilicates and doping ions, which are precursors of the clusters in the zeolite hosts, give indirect information about mechanism of the `ship-in-the-bottle' synthesis of semiconductor materials.
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