Titanium-immobilized Layered HUS-7 Silicate as a Catalyst for Photocatalytic CO2 Reduction.

Utilizing photocatalytic CO2 reduction presents a promising avenue for combating climate change and curbing greenhouse gas emissions. However, maximizing its potential hinges on the development of materials that not only enhance efficiency but also ensure process stability. Here, we introduce Hiroshima University Silicate-7 (HUS-7) with immobilized Ti species as a standout contender. Our study demonstrates the remarkable photocatalytic activity of HUS-7 in CO2 reduction, yielding substantially higher carbonaceous product yields compared to conventional titanium-based catalysts TS-1 and P25. Through thorough characterization, we elucidate that their boosted photocatalytic performance is attributed to the incorporation of isolated Ti species within the silica-based precursor, serving as potent photoinduced active sites. Moreover, our findings underscore the crucial role of the Ligand-to-Metal Charge Transfer (LMCT) process in facilitating the photoactivation of CO2 molecules, shedding new light on key mechanisms underlying photocatalytic CO2 reduction.

Electrochemical characterization of leached steel-making sludge.

In this work, the electrochemical properties of the leached sludge, magnetite and zinc ferrite were studied. Acetic acid was used as a leaching reagent because, in recent years, there has been a surge of interest in using zinc-containing materials as photocatalysts, with acetic acid finding application in their preparation. Various methodological approaches were used, but the best results were achieved with a combination of 1-3 h leaching in 0.01 M acetic acid with a solid/liquid ratio of 500. In this arrangement, zincite was almost completely removed from the sludge, while zinc ferrite and magnetite remained in the solid residue. Ex situ analyses of the main leaching products were performed by X-ray diffraction, infrared spectroscopy, and thermogravimetry. The electrochemical behaviour of solid residue and model systems, that are micromagnetite and zinc ferrite, was studied in alkaline media by means of modified carbon paste electrodes, cyclic voltammetry, and chronocoulometry, with a suitable potential window ranging from 0 to 1.5 V. In summary, a linear dependence of the anodic and cathodic peak height on the square root of the scan rate was found. The position of the anodic and cathodic peaks shifted slightly with scan rate, only at low rates, up to 25 mV/s, the individual peaks coincided. The electrochemical response suggested a quasireversible process.

Hematites Precipitated in Alkaline Precursors: Comparison of Structural and Textural Properties for Methane Oxidation.

Hematite (α-Fe2O3) catalysts prepared using the precipitation methods was found to be highly effective, and therefore, it was studied with methane (CH4), showing an excellent stable performance below 500 °C. This study investigates hematite nanoparticles (NPs) obtained by precipitation in water from the precursor of ferric chloride hexahydrate using precipitating agents NaOH or NH4OH at maintained pH 11 and calcined up to 500 °C for the catalytic oxidation of low concentrations of CH4 (5% by volume in air) at 500 °C to compare their structural state in a CH4 reducing environment. The conversion (%) of CH4 values decreasing with time was discussed according to the course of different transformation of goethite and hydrohematites NPs precursors to magnetite and the structural state of the calcined hydrohematites. The phase composition, the size and morphology of nanocrystallites, thermal transformation of precipitates and the specific surface area of the NPs were characterized in detail by X-ray powder diffraction, transmission electron microscopy, infrared spectroscopy, thermal TG/DTA analysis and nitrogen physisorption measurements. The results support the finding that after goethite dehydration, transformation to hydrohematite due to structurally incorporated water and vacancies is different from hydrohematite α-Fe2O3. The surface area SBET of Fe2O3_NH-70 precipitate composed of protohematite was larger by about 53 m2/g in comparison with Fe2O3_Na-70 precipitate composed of goethite. The oxidation of methane was positively influenced by the hydrohematites of the smaller particle size and the largest lattice volume containing structurally incorporated water and vacancies.

Characterization of Montmorillonites by Infrared and Raman Spectroscopy for Preparation of Polymer-Clay Nanocomposites.

The detailed structural chemistry of clay minerals is an important aspect of polymer-clay nanocomposite research. A variety of analytical methods are currently available for material characterization. Keep in mind, however, that each method has some limitations. The best results are usually achieved by a combination of several analytical methods. The contribution demonstrates the potential and applicability of infrared and Raman spectroscopy in identification and structural characterization of montmorillonites. The vibrational spectra of montmorillonites (SAz-2, STx-1, SWy-2 and Kunipia-F), obtained by Fourier Transform infrared spectroscopy in the near infrared region (8000-4000 cm-1) and in the middle infrared region (4000-400 cm-1) together with Fourier Transform Raman measurements in the region from 4000-50 cm-1, are presented. The aim of the experimental study was to compare the spectral data of both analytical techniques in terms of their sensitivity to chemical composition, isomorphic substitution of central atoms, and layer stacking order of the clay minerals. The results confirmed that Fourier Transform infrared spectroscopy through middle infrared and near infrared spectral regions provided the most comprehensive information about octahedral, tetrahedral and hydroxyl structure units of montmorillonites.

Synthesis and Antimicrobial Activity of Polyethylene/Chlorhexidine/Vermiculite Nanocomposites.

The set of polyethylene/clay nanocomposites with increasing amount of antimicrobial nanofiller (3, 6 and 10 wt%) was prepared by melt compounding procedure. The antimicrobial drug chlorhexidine diacetate was loaded into natural clay mineral vermiculite and also to its monoionic sodium form and then these organoclay nanofillers were incorporated into polymeric matrix. The structure of prepared organoclays and nanocomposites was studied by X-ray diffraction analysis and Fourier transforms infrared spectroscopy. Further thermal properties of polyethylene/clay nanocomposites were investigated by thermogravimetric analysis and the surface roughness was evaluated by atomic force microscopy. Finally, organoclays and polyethylene/clay nanocomposites were tested for antimicrobial activity against bacterial strains Staphylococcus aureus, Escherichia coli and yeast Candida albicans. Prepared samples showed a very good antimicrobial activity with long lasting effect. In the case of polyethylene/clay nanocomposites we observed some differences in antimicrobial action between two used antimicrobial nanofillers. These results suggested great potential of using the polymer/clay nanocomposites in the wide range of antimicrobial applications.

Hybrid Antibacterial Nanocomposites Based on the Vermiculite/Zinc Oxide-Chlorhexidine.

The hybrid nanocomposite materials based on the vermiculite/zinc oxide-chlorhexidine were prepared in two steps. In the first step the vermiculite/zinc oxide nanocomposite was prepared by the mechanochemical method followed by a heat treatment at 650 °C for 90 min. In the second step the chlorhexidine dihydrochloride was intercalated to the vermiculite/zinc oxide nanocomposite in weight ratio 1:1, 1:2, 1:4, 2:1 and 4:1 (wt%) thereby vermiculite/zinc oxide-chlorhexidine nanocomposites were prepared. Phase analysis, crystal structure, phase transformation, chemical composition and particle size of the prepared hybrid nanocomposite materials were using X-ray diffraction methods, energy dispersive X-ray fluorescence spectroscopy, carbon phase analysis, Fourier transforms infrared spectroscopy and particle size analysis. Antibacterial activity of hybrid nanocomposite materials was investigated on Gram negative (E. coli, P. aeruginos.) and the Gram positive (S. aureus, E. faecalis) bacterial strain and against yeast Candida a. by finding the minimum inhibitory concentration. The hybrid nanocomposite materials exhibit high antibacterial activity after 30 minutes with a long-lasting effect persisting up to 5 days. Dependence of the zinc oxide and chlorhexidine concentration in vermiculite structure on the antibacterial activity was observed.

Infrared and Raman spectroscopy of three commercial vermiculites doped with cerium dioxide nanoparticles.

Three commercial vermiculites and these vermiculites doped with cerium dioxide nanoparticles were investigated by infrared and Raman spectroscopy. Infrared spectroscopy in middle infrared region (4000-400 cm-1) was supplemented by separation of overlapped spectral bands in the region of stretching vibration of hydroxyl groups. Detailed structural properties of vermiculites were completed based on the Raman spectroscopy in the spectral region between 800 and 100 cm-1 and X-ray diffraction analysis. Raman spectroscopy provided evidence of trioctahedral-dioctahedral vermiculite-mica in original vermiculite and trioctahedral phyllosilicate structures in vermiculites after precipitation procedure of cerium dioxide nanoparticles. The wavenumber shifts of the Raman bands at about 670 cm-1 and 190 cm-1 in spectra of vermiculites showed strong trend with increasing Fe3+ and Al substitution in tetrahedra and octahedra, respectively.

Novel TiO2/C3N4 Photocatalysts for Photocatalytic Reduction of CO2 and for Photocatalytic Decomposition of N2O.

TiO2/g-C3N4 photocatalysts with the ratio of TiO2 to g-C3N4 ranging from 0.3/1 to 2/1 were prepared by simple mechanical mixing of pure g-C3N4 and commercial TiO2 Evonik P25. All the nanocomposites were characterized by X-ray powder diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, transmission electron microscopy, photoelectrochemical measurements, and nitrogen physisorption. The prepared mixtures along with pure TiO2 and g-C3N4 were tested for the photocatalytic reduction of carbon dioxide and photocatalytic decomposition of nitrous oxide. The pure g-C3N4 exhibited the lowest photocatalytic activity in both cases, pointing to a very high recombination rate of charge carriers. On the other hand, the most active photocatalyst toward all the products was (0.3/1)TiO2/g-C3N4. The highest activity is achieved by combination of a number of factors: (i) specific surface area, (ii) adsorption edge energy, (iii) crystallite size, and (iv) efficient separation of the charge carriers, where the efficient charge separation is the most decisive parameter.

Identification of clay minerals by infrared spectroscopy and discriminant analysis.

Identification of clay minerals based on chemometric analysis of measured infrared (IR) spectra was suggested. IR spectra were collected using the diffuse reflection technique. Discriminant analysis and principal component analysis were used as chemometric methods. Four statistical models were created for separation and identification of clay minerals. More than 50 samples of various clay mineral standards from different localities were used for the creation of statistical models. The results of this study confirm that the discriminant analysis of IR spectra of clay minerals could provide a powerful tool for identification of clay minerals. Differentiation of muscovite from illite and identification of mixed structures of illite-smectite were achieved.

Study of cetyltrimethylammonium and cetylpyridinium adsorption on montmorillonite.

Adsorption of cetyltrimethylammonium (CTA) and cetylpyridinium (CP) onto Na-rich montmorillonite (MMT) was studied. For this purpose, the adsorption isotherms of CTA and CP, along with desorption curves of metal cations (Na+, K+, Ca2+, Mg2+), were obtained by means of capillary isotachophoresis and atomic absorption spectrometry. Infrared, X-ray diffraction pattern, specific surface area, porosity, and moisture adsorption measurements of montmorillonite revealed that CTA and CP were adsorbed in monolayer arrangements. CTA is assumed to be attached to the negatively charged MMT surface mainly by electrostatic forces. On the other hand, CP, adsorbed in higher amounts, can be additionally bound via other interactions of pyridinium rings, such as induced and pi-pi interactions. By the surfactant adsorption, the montmorillonite surface became hydrophobic and its micro- and mesopores were significantly diminished. Using scanning electron microscopy, aggregation of such organically modified MMT particles was observed.