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Colloids and Surfaces A: Physicochemical and Engineering Aspects
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Item-typ:Veröffentlichung, On thermal stability and decomposition mechanisms of aromatic diamines employed as links in novel Pt nanoparticle network catalysts(Elsevier, 2023-01-05); ; ; The thermal stability of microporous networks of Pt nanoparticles interlinked by p-Phenylenediamine (PDA) was investigated by temperature-programmed desorption spectroscopy (TPD) and transmission electron microscopy (TEM). The detection of aniline, benzene, and NH3 as major desorbing fragments in TPD revealed cleavage of the C-N bonds in PDA as a major route of thermally induced decomposition, probably via hydrogenolysis assisted by dehydrogenation reactions of PDA running alongside. Varying the Pt:PDA ratio in the networks demonstrated that the Pt nanoparticles catalytically promote the decomposition of their PDA links. A quantitative analysis of the TPD spectra indicated that the thermal stability of PDA strongly correlates with the number of bonds (0, 1 or 2) formed by the amino groups of an individual PDA molecule with Pt. Only the most stable PDA species appears to be of relevance for the structural stability of the nanoparticle network, as heating experiments with in situ TEM showed. The results have strong implications for the application of PDA-linked Pt nanoparticles as heterogeneous catalysts in hydrogen gas microsensors where the choice of operating temperature has to balance maximization of signal-to-noise ratio and maintenance of structural stability. An anealing step up to 450–500 K after synthesis of the catalyst is suggested in order to optimize its catalytic activity by removing PDA species that are not essential for structural stabilty.Wissenschaftlicher ArtikelBand:656, Part A57 52 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Preparation of novel adsorbents based on combinations of polysiloxanes and sewage sludge to remove pharmaceuticals from aqueous solutions(Elsevier {BV}, 2016-03-19); ; ; Novel adsorbents were developed by varying the ratios of polysiloxanes and sewage sludge. The adsorbents were synthesized by mixing various polysiloxanes with methyl (MK), methyl/phenyl (H44) or without functional groups with sewage sludge in a solvent and pyrolyzed under an inert atmosphere. The adsorbents were characterized using several analytical and functional techniques, and used for adsorption of diclofenac (DCF) and nimesulide (NM) from aqueous solutions. Nitrogen adsorption/desorption measurements showed type I isotherms, which are typically for microporous materials, and the specific surface areas (SBET) were found to be in the range of 48 m2 g−1 and 631 m2 g−1. The sludge content was the major determinant for a decrease in SBET and hydrophobicity, as compared with pure polysiloxane samples. Among the composite materials, H67S33-500 (sample with 67% of polysiloxane H44 and 33% of sludge pyrolyzed at 500◦C) had the highest SBET value of 487 m2 g−1 while M40T60-600 (sample with 40% of polysiloxane MK and 60% of TEOS and pyrolyzed at 600◦C) exhibited the highest SBET value of 631 m2 g−1 among the hybrid materials. Experimental variables such as initial pH of the adsorbate solutions was optimized for adsorptive characteristics of the novel adsorbents. The optimum pH for adsorption of DCF and NM onto the adsorbents were 7.0 and 9.0, respectively. The equilibrium of adsorption was investigated using Langmuir, Freundlich and Sips models. Sips isotherm model gave the best fit of the equilibrium data. DCF showed better affinity for adsorbents than NM—suggesting that hydrophobic sites on the surfaces played a key role in the adsorption process.Wissenschaftlicher ArtikelBand:49793 174 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Hierarchical emulsion based hybrid ceramics synthesized with different siloxane precursor and with embedded nickel nanoparticlesAn emulsion-based synthesis route for the generation of organo-silica-based monolithic hybrid ceramics with a high content of different organic groups and embedded nickel nanoparticles is presented. By this route hybrid ceramics with a hierarchical pore size distribution and tailorable surface characteristics can be obtained. Mixtures of methyl polysiloxane (MK), tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) with varying ratios are selected as precursors, cross-linked, and subsequently pyrolyzed at 500 or 600 °C. In this way monolithic emulsion based hybrid ceramics with three different organo-functionalized siloxane precursor can be synthesized. Additionally, by adding the metal precursor NiCl2, metal-containing emulsion-based hybrid ceramics can be achieved. By adjusting the oil/water ratio and using high- or low internal phase emulsions (HIPEs or LIPEs), controlled micro-, meso-, and macropore distributions are obtained. After pyrolysis, materials achieve specific BET surface areas of up to 550 m2/g. Adjustable surface characteristics in terms of hydrophobicity and hydrophilicity of the material surface by thermal decomposition behavior of precursors is demonstrated. Nickel is incorporated through the formation of complexes with APTES, resulting in well-distributed metal nanoparticles with average particle sizes between 35 and 69 nm. The material properties are pivotal features for catalysis and gas separation applications.Wissenschaftlicher ArtikelBand:49292 101