جستجوی مقالات مرتبط با کلیدواژه "structure" در نشریات گروه "شیمی"

We studied the reaction in which carbon monoxide is converted to hydrocarbons, and investigated the behaviors and the combination system of catalysts exchanged with platinum and ammonium ions. Experiments were conducted at 1.2 MPa, 523K, and CO/H2=1 ratio. The structure and the texture of the catalysts, assessed by XRD, BET/BJH, and SEM, exhibited a microporosity for ZSM-5/11 and a micro/mesoporosity for AlMCM-41, which implies a direct effect on the catalytic properties of these materials. The conversions obtained were 60%, 55%, and 50% for Ptn+/H+-catalysts, Ptn+-catalysts, and H+-catalysts respectively. Such conversions could be attributed to the good acidity resulting from the simultaneous presence of Ptn+/H+ at different oxidation states of platinum, which was revealed by XANES PtLIII analysis, and their uniform dispersion within the inner surface and its grain size average conducted by the titration of adsorbed H2-O2. FTIR analysis showed a better distribution of acid sites for bi-exchanged catalysts over mono-exchanged ones, which resulted in a good catalytic activity. These results suggest a strong correlation between the high selectivity of light hydrocarbon products, the ions, and the catalyst types. These differences depended mainly on the facility of forming different products, such as n/iso-alkanes and alkenes. Skeletal isomerization was the main transformation observed on exchanged catalysts, particularly those with Ptn+/H+ ions. A deactivation process of catalysts, versus time-on-stream, begins after 70 minutes, especially for combined exchanged materials.

X-ray absorption fine structure (XAFS) denotes the details of how X-ray is absorbed by an atom at energies near and above the core-level binding energies of that atom. Specifically, XAFS is the modulation of an atom’s X-ray absorption probability because of the chemical and physical state of the atom. XAFS spectra are especially sensitive to the formal oxidation state, the coordination chemistry,, and the distances, coordination number, and the species of the atoms instantly surrounding the selected element. Because of this dependency, XAFS provides a useful, and pretty simple way to determine the chemical state and the local atomic structure for a certain atomic species. XAFS can be used in a variety of systems and bulk physical environment. XAFS is normally used in a wide range of scientific fields, including biology, environmental science, catalysts research, and material science. Herein, the structures of a few inorganic compounds are investigated by XAFS.

Recently, nanoparticles have attracted much attention owing to their potential in biomedical applications, such as drug delivery systems, sustained release and controlled release. Various nanocarriers have been employed to ameliorate the efficacy and cytotoxicity of drugs, reducing their side effects through changing their pharmacokinetic properties. A simple and well-known model of pharmaceutical carriers is the layered zinc hydroxide (LZH) compound. In the present research, salicylic acid (Sal)-loaded LZH was synthesized using the ion-exchange method. The resulted nanohybrid (Sal-LZH) was characterized using the PXRD, FT-IR spectroscopy, STA analysis, BET, and SEM. Sal anions were intercalated into the interlayer gallery space of LZH, leading to different drug releases at pH 4.8 and 7.4. It was found that, the release of Sal anions from the synthetic nanohybrid occurred in a controlled manner, and the resulting material is suitable for use as a controlled-release formulation for various kinds of anti-inflammatory agent.

The coordination compounds of Fe (II) and Fe(III) with phthalic acid were synthesized. The compounds were studied by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), and IR spectroscopy. It has been established that, regardless of the oxidative number of iron, the synthesis products have the same chemical composition and chemical formula - [Fe2(o-C6H4(COO)2)3]. It also found that the carboxyl groups of phthalate dianion have a monodentate and bridging function and the complex itself is a polymer-layered structure. Based on the obtained results, a schematic structure of the complex was proposed. Also were studied the thermal stability of the complex in the temperature range 20-660 °С and the supramolecular interaction of this substance with the rheological properties of heavy commercial oils. This significantly reduces the viscosity of heavy oil during transportation. Coordination polymer-based composites have been developed and tested. The use of composite solves several technological problems associated with the transport of high-viscosity oil.

The synthesis of some new cobalt (III) complexes: [Co (5-Xsalen) (PEt3)] ClO4.H2O (where X= H, NO2, Br, OMe) were synthesized and characterized using elemental analysis, 1HNMR, IR and UV-vis spectroscopy. The summarized results of these spectral evidences are in conformity with the structure of the synthesized complexes. In this study, we synthesized four novel complexes of Co (III) by the reaction of the metal ions with the salen ligands. The ligands coordinated with the metal ions through N- and O-donors. The complexes exhibited a geometry based on the coordination number 5. The results showed 1HNMR spectra of these complexes are consistent with the suggest formulation and show that the cobalt in these complexes is low spin. Its structure was established by 1HNMR, IR, and UV-visible spectroscopy.

The importance of natural products in the pharmaceutical industry cannot be abated because it plays a vital role in the prevention and treatments of diseases such as cancer, malaria, pile etc. These natural products e.g. alkaloid, flavonoid, phenol, saponin, and tannin are bioactive compounds in a plant which are essential in plant metabolic activities. All of these including alkaloids has been tested for their huge medicinal properties hence, serves as an alternative medicine. Although, through the modern-day technologies, these bioactive compounds are separated from the plants and synthesized into capsules and tablets for easy administration, usage, and storage. The manner of poisoning with plants can be due to unintentional ingestion, affordability, and availability, excess ingestion, improper methods of extraction and purification of plant materials. In some cases, the resultant effect(s) of these poisoning may cause serious illness, injury or even death. Thus, this review gives an overview of the pharmacological importance of named alkaloids, toxicology and methods of extraction and purification of alkaloids in the plant. Furthermore, this review will provide information to researchers to further investigate the medicinal potentials of these alkaloids, help in the development of new drugs for the treatment of various diseases, creates awareness on the side-effects of excess or abuse of medicinal plants and finally encourages rational use of natural resources for sustainability.

Theoretical study of the electronic structure using, Density Functional Theory (DFT) calculations at the B3PW91/6-31G (d) level of theory have been employed to the TM@C34 (TM =Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) in order to investigate the geometries, electronic structures, binding energies, linear polarizability ⟨Δ𝛼⟩, first order hyperpolarizability ⟨𝛽⟩, natural bonding orbital (NBO), was studied based on the ''C34'' fullerene. The results found that the most stable structure is e(C2). Minimal energy structures of each endohedral metallofullerene were obtained. Hybridizations were found between the Ti, V, Cr, Fe, Co, and Ni, 3d valence orbitals and the ''C34'' cage orbitals, while none was found between the Mn and Cu orbitals and the ''C34'' cage orbitals. These findings were obtained with the preferential position of the metal atom inside the fullerene cage, i.e. these results are found suitable for the metal Mn and Cu orbitals present inside the fullerene cage. Natural bonding orbital (NBO) shows that the charges always transfer from the TM atoms to the ''C34'' cage. In going from isolated TM atom to TM@C34, the occupation of the 4s orbital is strongly reduced. The introduction to TM to the empty ''C34''leads to more active NLO performance. The TM@C34 (TM =Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) interactions are characterized in terms of several theoretical parameters such as density of states (DOS), molecular electrostatic potentials (MEPs), non-linear optical (NLO) properties and electrophilicity and thermodynamic properties were also performed at B3PW91/6-31G (d) level of theory.

This paper reviews some progressive studies and innovations in cement and concrete materials in nano field. Due to the widespread acceptance of the special properties of nano materials and using them for engineering concrete performance, understanding and directing their properties are not achievable without instructing concepts and investigating interactions among components. Due to achievement of different properties of matters at the nanoscale, evaluating their physical and chemical effects on micro and macro scales in concrete and understanding the mechanisms that govern the interactions of nanoscale materials with appropriate characterization are essential. Advanced characterization techniques should be used for concrete to distinguish components of concrete multiphase composite. The other aim of this study was to better understand the importance of probably future advanced techniques and how they can be used as valuable tools to study the nanostructure and microstructure of cement and cement hydration products.

Ru/Al2O3 catalysts were prepared by conventional incipient wetness impregnation as well as colloid deposition of RuCl3 precursor via in situ reduction with ethylene glycol (polyol) method on alumina support. The samples were characterized by TEM, XRD and TPR techniques. The catalytic performance tests were carried out in a fixed-bed micro-reactor under different operating conditions. Ethylene glycol as the reducing agent in the polyol methodproduced well-dispersed and uniform ruthenium nanoparticles with an average diameter of 7 nm supported on Al2O3. In conventional method, however, reduction by hydrogen resulted in considerably larger particles with average size of 12 nm.The Ru/Al2O3 catalyst prepared by polyol method exhibited three-fold higher activity in ammonia synthesis compared to the catalyst prepared by conventional method. The turnover frequency ratio of ammonia synthesis of polyol to conventional catalyst was estimated to be 2.1 at 450°C implying the reaction is structure-sensitive over Ru-based catalysts.

Substitution of two or four carbon atoms by nitrogen in the corannulene molecule as a carbon nanostructure was done and the obtained structures were optimized at MP2/6-31G(d) level of theory. Calculations of the nucleus-independent chemical shift (NICS) were performed to analyze the aromaticity of the corannulene rings and its derivatives upon doping with N at B3LYP/6-31G(d) level of theory. Results showed NICS values in six-membered and five-membered rings of two and four N atoms doped corannulene are different and very dependent to number and position of the N atoms. The values of the mean NICS of all N-doped structures are more positive than intact corannulene that show insertion of N atom to the structures causes to decreasing aromaticity of them.

A new nano-sized cobalt(II) coordination polymer, (CoL1).0.5DMF. 1.5CH3OH (1); [H2L1 = 5-(4-Carboxy phenyl azo) salicyilic acid] has been synthesized by a sonochemical method. The thermal stability of compound 1 was studied by thermo- gravimetric and differential thermal analyses. Nano-structure of this coordination polymer was characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction and scanning electron microscopy. Nanoparticles of Co3O4 were obtained by calcination of compound 1 at 550°C. The Co3O4 nano-particles were characterized by powder Xray diffraction and scanning electron microscopy.

Nano-zeolite CoAPO-5 as a member of AFI family, was synthesized via a hydrothermal treatment, and structurally characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray analysis (EDAX). The effects of crystallization temperature and time on the structure of these powder products were studied. XRD patterns of the synthesized powders revealed a high-crystallinity and pure phase of AFI. SEM images and Scherrer equation showed the nano-size of the obtained CoAPO-5. Also, SEM images showed nano-wires as small as 30-50 nm in CoAPO-5 structures. According to EDAX analysis, P/Al ratio of the prepared CoAPO-5 powder was about 1.5. Crystal sizes and the crystallinity of CoAPO-5 reduced at higher temperatures of hydrothermal treatment. On the other hand, the larger crystals grew by increasing the crystallization time from 24 to 48 h.

The stabilized zirconia with different Cu contents synthesized via solgel method. The samples were prepared by hydrolysis and condensation of orgnomatelic sol. After that the result gels were dried at 80 °C and then calcined at various temperatures. Tِhe differential thermal analysis (DTA), X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM) and transmission electronic microscopy (TEM) were used to determine the characteristics of nanoparticles. Unlike the stable pure ZrO2 that has monoclinic structure at room temperature, the synthesized pure ZrO2 and ZrO2-CuO powders have been cubic and tetragonal structure at room temperature after calcinations. Moreover, it is obtained those changes in the crystallite size affect the stabilization of tetragonal or cubic structure at room temperature, and increase in content of dopant favored decrease of the crystallite size and metastabilization of both tetragonal and cubic polymorphs.

In recent years there has been considerable interest in the structures, energies and thermodynamics of(GaN)4 clusters and it is the subject of many experimental and theoretical studies because of theirfundamental importance in chemical and physical process. All calculation of this study is carried outby Gaussian 98. Geometry optimization for (GaN)4 nanocluster are be fulfilled at B3LYP, B1LYPand LSDA levels of theory with LANL2DZ basis set. Calculated are accomplished at 298 K. Thestructures, energetic and thermodynamic properties and vibrational spectra will be discussed.

DFT and QTAIM computations have been performed on numbers of pure nitrogen cluster speciesi.e. Nn (n = 4, 6) for investigating the structure and bonding. This study is critical since thesemolecules have been nominated as the good synthetic targets of High Energy Materials (HEM).0nthe other hand the decomposition mechanism is closely depends on the bonding pattern. Thislatter concept was searched via modem theory of Atoms in molecules (QTAIM) since theconventional methods were found to be incapable for describing the structure and bond in theseatomic clusters.

The intermolecular forces between water molecules are of great importance in many areas of chemistry including solvation, solution chemistry, and biochemistry. As a result of this (H2O)n systems have received a great significant of attention, both experimental and theoretical. All calculation of this study are carried out by Gaussian 98 soft ware. Geometry optimization for each cluster were be performed at HF/6-311++G(2df,2p), single point vibration energy B3LYP/6-311++G (2df,2p) and MP2/6-31+G(2df,p). IR frequencies and intensity were calculated at B3LYP/6-311++G (2df,2p) level of theory.
All calculation was accomplished at 298 k and 0 k. The structures, energies and thermodynamic properties will be discussed.