Autoreduction Process Research Articles

Carboxymethyl cellulose nanocolloids anchored Pd(0) nanoparticles (CMC@Pd NPs): synthesis, characterization, and catalytic application in transfer hydrogenation.

Herein, we report on the preparation of novel colloidal system based on carboxymethyl cellulose (CMC) and Pd nanoparticles (CMC@Pd NPs) via an ecofriendly auto-reduction process under mild conditions. In the first step, the follow-up of reduction and preparation of CMC anchored palladium nanoparticles (Pd NPs) in aqueous solution was carried out using UV-Vis spectroscopy. Thereafter, the monodispersed colloids were fully characterized by advanced analytical, structural, and morphological techniques. Based on Scherrer equation, the as-synthesized CMC@Pd NPs crystallite size was about 10.88nm. Accordingly, the detailed microscopic study revealed CMC nanocolloids anchored uniform distribution of Pd NPs and the presence of CMC nanofilm as protective monolayer. To the best of our knowledge, the observed nanoscale properties are reported for the first time for CMC-M system. The performance of the as-synthesized CMC@Pd nanocolloids was first investigated in the reduction of 4-nitrophenol, as a model substrate, to 4-aminophenol using NaBH4 as a hydrogen source. Moreover, the catalytic reduction of various nitroarenes bearing electron withdrawing or donating substituents was carried out and monitored by UV-Vis spectroscopy. The chemo- and regioselectivity of the catalytic reduction in presence of CMC@Pd NPs were also studied. Consequently, the prepared CMC@Pd nanocolloids exhibit remarkable activity, good heterogeneity, and higher reusability and stability for the catalytic reduction reaction under mild conditions.

Solid-state synthesized hyperbranched polyamides as hosts for antimicrobial silver nanoparticles

Silver nanoparticles (AgNPs) are versatile materials that offer interesting perspectives in biomedical, catalytic, and electronic fields, which certainly prompted research for sustainable synthetic routes with low cost since it meets both industrial requirements and minimize environmental damage. In fact, some hyperbranched polymers (HBPs) can be used to produce AgNPs through green processes resulting in colloids with great stability. HBPs are commonly synthesized by simple methods, supporting their large-scale production. At the present work, hyperbranched polyamide (HBPA) was used to prepare AgNPs within a hyperbranched network with narrow size distribution and average diameter of ca. 2–5 nm. Such AgNPs were synthesized by the chemical reduction method using NaBH4 and by auto-reduction (AR) process. Microbiological assays performed with the resulting hybrid hyperbranched HBP-AgNPs network (HBPENs) by AR presented antimicrobial activity against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Candida albicans with minimum inhibitory concentration (MIC) values ranging from 9.1 ± 0.2 to 56.6 ± 0.2 μg/ml. AgNPs synthesized using NaBH4 also showed good antimicrobial activity against the microorganisms tested. However, the MIC values were considerably higher than AgNPs by AR process, showing the AR method is a good alternative to obtain nanoparticles with better antimicrobial activity and smaller size.

Determination and Optimization of the Luminescence External Quantum Efficiency of Silver-Clusters Zeolite Composites

We have measured for the first time the external quantum efficiency (EQE) of silver clusters containing zeolites (henceforth referred to as silver-clusters zeolite composites). These materials, fabricated by silver cation exchange followed by a thermal autoreduction process, have EQEs up to 69%. Because of their unique spectral features such as large Stokes shift and high EQE, these materials could be potentially used as phosphors for the fabrication of fluorescent lamps and as wavelength convertors in solar cells. An EQE comparison between less pure commercial silver-loaded zeolites and self-synthesized silver-zeolites showed the importance of the chemical and optical purity of the starting host material. Besides this, the zeolite topology and silver content play an important role on the luminescent performance of such materials. The ability to reliably measure the EQE enabled us to further optimize the synthesis of silver-zeolite composites. A new reduction–oxidation cycle is demonstrated not only to im...

Behaviour of Thin Magnetic Films at Low Temperatures

The problem of the analysis of low temperature magnetization is exposed in detail. The application of exact Bose representation of spin operators to the bulk ferromagnets is justified. By means of this representation the magnetization of ultrathin films was analysed. It turned out that thin films magnetization contains exponentially small terms characterized by Dyson’s functions even in harmonical approximation. The main conclusions of this work are that magnetic lattice of thin film is more rigid than the macroscopic lattice and that the autoreduction process (the three layer film divides onto three two layer subfilms) takes place in the film.

Oligosaccharide-modified dendrimers for templating gold nanoparticles: Tailoring the particle size as a function of dendrimer generation and -molecular structure

Dendrimer-stabilized nanoparticles are promising candidates for the application of functional nanoparticles in bio- and physiological environments. Herein, a new class of glycodendrimers, 2nd–5th generation poly(propyleneimine) (PPI) dendrimers with dense maltose shell, is used to guide the formation of colloidal gold nanoparticles in aqueous solution at room temperature. The nanoparticles are synthesized by complexing metal ions to the maltose-modified PPI dendrimers followed by chemical reduction or by auto-reduction in the presence of glycodendrimers. In the auto-reduction process, the dendrimer simultaneously serves as effective reducing- and stabilizing agent. The particle size and -size distribution can be controlled directly as a function of dendrimer's generation with formation of smaller particles at higher dendrimer generations. The results also suggest that different mechanisms (interfacial uptake and dendritic box) are responsible for the stabilization of the nanoparticles in the presence of the glycodendrimers.

Low-temperature magnetization in nanofilms

The low-temperature magnetization of a film was analyzed by the use of exact Bose representation of spin operators that does not suffer from the presence of unphysical states. The magnetization of thin films has exponentially small temperature correctness, so that Dyson’s proof about exponentially small correction coming from two bosons at ideal lattice point cannot be used in film analyses. The main conclusions of this work are that magnetic lattice of a thin film is more rigid than the macroscopic lattice and that the autoreduction process (the three layer film divides into two layer subfilms) takes place in the film.

Platinum species in the pores of NaX, NaY and NaA zeolites studied using EPR, XAS and FTIR spectroscopies

The results of X-band EPR, X-ray absorption and Fourier transform infrared spectroscopy on Pt(NH(3))(4)(2+) exchanged NaX, NaY and NaA zeolites reveal after oxygen calcination at 573 K that diamagnetic Pt(2+) is not the only product. Calcination provides Pt(3+) cations, but depending on the heating rate, the decomposition of amino groups during calcination also produces hydrogen that reduces Pt(3+) to Pt(2+) and Pt(+). NaX (Si/Al = 1.23) has a more negative framework charge than NaY (Si/Al = 2.31), so Pt(3+) can be stabilized only in NaX, whereas lower oxidation states of Pt such as Pt(+) can be stabilized in both, NaX and NaY, and neither of the paramagnetic Pt cations are stabilized in NaUSY (Si/Al = 3). The autoreduction process allows controlling the number of Pt(3+) and Pt(+) in the NaX zeolite by changing the calcination heating rate: a heating rate of 1.25 K min(-1) gives only Pt(+), but 0.5 K min(-1) gives a Pt(3+)/Pt(+) ratio close to 1. The structure of the support is also important for the synthesis of Pt species. While isolated paramagnetic Pt ions were stabilized in faujasite zeolites (NaX and NaY), a paramagnetic Pt dimer was obtained in a Linde type A zeolite (LTA, Si/Al = 1) by applying the same preparation methods. The fraction of paramagnetic Pt species which were characterized by X-band EPR spectroscopy amounts to 2-18% of the total Pt in the zeolites, the remaining Pt must be diamagnetic.

Intra- and Intermolecular Transfers of Protein Radicals in the Reactions of Sperm Whale Myoglobin with Hydrogen Peroxide

Reaction of sperm whale metmyoglobin (SwMb) with H2O2 produces a ferryl (MbFeIV=O) species and a protein radical and leads to the formation of oligomeric products. The ferryl species is maximally formed with one equivalent of H2O2, and the maximum yields of the dimer (28%) and trimer (17%) with 1 or 2 eq. Co-incubation of the SwMb Y151F mutant with native apoSwMb and H2O2 produced dimeric products, which requires radical transfer from the nondimerizing Y151F mutant to apoSwMb. Autoreduction of ferryl SwMb to the ferric state is biphasic with t = 3.4 and 25.9 min. An intramolecular autoreduction process is implicated at low protein concentrations, but oligomerization decreases the lifetime of the ferryl species at high protein concentrations. A fraction of the protein remained monomeric. This dimerization-resistant protein was in the ferryl state, but after autoreduction it underwent normal dimerization with H2O2. Proteolytic digestion established the presence of both dityrosine and isodityrosine cross-links in the oligomeric proteins, with the isodityrosine links primarily forged by Tyr151-Tyr151 coupling. The tyrosine content decreased by 47% in the dimer and 14% in the recovered monomer, but the yields of isodityrosine and dityrosine in the dimer were only 15.2 and 6.8% of the original tyrosine content. Approximately 23% of the lost tyrosines therefore have an alternative but unknown fate. The results clearly demonstrate the concurrence of intra- and intermolecular electron transfer processes involving Mb protein radicals. Intermolecular electron transfers that generate protein radicals on bystander proteins are likely to propagate the cellular damage initiated by the reaction of metalloproteins with H2O2.

Effect of water on the autoreduction level of copper in excessively ion-exchanged [formula omitted]. An FTIR study

Thermal treatment of a calcined Cu ZSM-5 in inert gas (or in vacuum) is known as an aprotic autoreduction process when some of the Cu 2+ species are reduced to Cu + ions. If, however, an excessively ion-exchanged, calcined 3.1% w/w Cu ZSM-5 ( Si Al = 20 , Cu Al = 0.75 ) sample was heated in Ar flow up to 773K, the intensity of the OH band at 3611 cm −1, A OH(3611), increased relatively by 5.9 to 41.6% depending on the heating period and the amount of H 2O added into the Ar line. On the other hand, it was not possible to go below 5–6% increase of A OH(3611) even under the most careful experimental conditions. An extended period of outgassing did not cause reduction to Cu 0, i.e. the Ar line was practically free from any reducing agent (H 2 or hydrocarbon). The framework vibrations revealed the autoreduction; the increasing sharp band at 2294 cm −1 was attributed to the first overtone of superoxide anion in an asymmetrical complex as Cu 2+ O − 2t Cu +. CO dose at 293 K about doubled the amount of Cu + ions at the expense of superoxide while a strong CO band formed at 2157 cm −1 ( A co = 1.764).

Local Spin Density Functional Theory Study of Copper Ion-Exchanged ZSM-5

We have used local spin density functional theory to investigate the electronic and structural properties of Cu species (Cu+, Cu2+O-, and Cu2+OH-) interacting with isolated ⋮Al−O-−Si⋮ sites CuZSM-5. We have also evaluated the thermodynamic stability of these species and the thermodynamics of a proposed scheme for the autoreduction of Cu2+ to Cu+. We have found all of the species studied to be thermodynamically stable and the proposed autoreduction process to be thermodynamically feasible at temperatures normally encountered in the pretreatment of as-exchanged CuZSM-5. In addition, we have investigated the interactions of Cu2+ cations with both 6-T site and 5-T site ring structures containing two Al atoms. We have found that Cu2+ in a 6-T site ring structure is thermodynamically unstable, while that in a 5-T site ring structure is thermodynamically stable.

Textural variations in CeO 2 on thermal treatment in various atmospheres

The products of the thermal treatment of precipitated CeO 2 (pH 8.75) were obtained by heating in a reducing (hydrogen), an oxidizing (oxygen) or an inert (nitrogen) atmosphere in the temperature range 150–550 °C. Surface area measurements of the samples were carried out using nitrogen adsorption at 77 K. Structural characterizations were performed by using X-ray diffraction (wide angle), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The lattice parameter measurements were achieved by means of the X-ray diffractometer technique. X-ray analysis showed that the samples are well-crystallized f.c.c. CeO 2. DTA and TGA showed only physically adsorbed water. A small exothermic peak at about 290 °C and a broad exothermic peak at about 520 °C result from a small autoreduction process and a sintering process respectively. Both processes are accompanied by a decrease in the lattice parameter, the autoreduction process in a hydrogen atmosphere only, whereas the sintering process is independent of the prevailing atmosphere. Heating the samples at 150 °C in any atmosphere increases the surface area. At higher temperatures, the surface area is a function of the variations in the solid texture imposed by the prevailing atmosphere. Oxygen is strongly adsorbed onto the surface, probably in a dissociated state. Pore structure analysis showed that the original sample and the products obtained in the various atmospheres possess both mesopores and micropores. At 550 °C oxygen facilitated the production of a product with a large surface area and an average pore radius of 13.2 Å, whereas a hydrogen atmosphere enhanced sintering and gave a product with a wider average pore size.

Chemical evolution of the terrestrial planets

Chemical evolution of the terrestrial planets