IR Peak Research Articles

Characterization and Nanofluid Stability of CoFe2O4-APTES and CoFe2O4-PVA Nanoparticles

Nanofluid contains nanoparticles that enhanced the property of the base fluid. However, the separating layer between the nanoparticles and base fluids may interfere the nanofluids performance. Studies have been made that surface modification of nanoparticles may improve the dispersion of nanoparticles in base fluids. This paper reports the study of the colloidal stability of surface modified nanoparticles using a polymer and an amino-silane. The nanoparticles were prepared by one-step and two-step methods using cobalt iron oxide nanoparticles with brine solution and deionized water as the base fluids. Functionalization by surface modification of the nanoparticles to enhance the nanofluids stability was carried out using (3-aminopropyl) triethoxysilane (APTES) and polyvinyl alcohol (PVA). Characterization using Fourier Transform Infrared (FTIR), Field Emission Scanning Electron Microscope (FESEM) and X-ray Powder Diffraction (XRD) were performed to study the functionality and morphology of the synthesized nanoparticles. The extra IR peaks such as Si-O-Si at 1063 cm-1 for CoFe2O4-APTES and C=O at 1742 cm-1 for CoFe2O4-PVA showed that there are additional elements in the cobalt ferrite due to functionalization. The size of synthesized CoFe2O4-APTES ranged between 15.99 nm to 26.89 nm while CoFe2O4-PVA is from 25.70 nm to 54.16 nm. The stability of the nanofluid were determined via zeta potential measurements. CoFe2O4-APTES nanofluid has zeta potential of -35.7 mV compared to CoFe2O4-PVA at -15.5 mV.

First-principles study of solid hydrogen: Comparison among four exchange-correlation functionals

The structures of solid hydrogen under high pressures have been revisited by using first-principles electronic structure calculations. Focusing on the stability, the intramolecular bond strength of hydrogen molecules in solid hydrogen, and the cell volume, we made a comparison study on seven structures including $P21/c\text{\ensuremath{-}}24$, $C2/c\text{\ensuremath{-}}24$, $P6122\text{\ensuremath{-}}36$, $Pc\text{\ensuremath{-}}48$, $Pca21\text{\ensuremath{-}}48$, $Cmca\text{\ensuremath{-}}4$, and $Cmca\text{\ensuremath{-}}12$ with the recently proposed strongly constrained and appropriately normed (SCAN) functional and three conventional exchange-correlation functionals, namely Perdew-Burke-Ernzerhof (PBE), Becke-Lee-Yang-Parr (BLYP), and van der Waals-density functional (vdW-DF). On one hand, with the SCAN functional the $C2/c$ structure takes the minimum static lattice enthalpies in the pressure range from 150 to 450 GPa, which agrees with the recent synchrotron infrared spectroscopic study and is similar to the result of the BLYP functional. On the other hand, the vibration frequencies of hydrogen molecules calculated by the SCAN functional match well with the experimental characteristic IR and Raman peaks, which indicates that the SCAN functional gives a reasonable estimation of the bond strength or bond length of hydrogen molecules in solid hydrogen, while the BLYP and vdW-DF functionals overestimate the bond strength. All SCAN, PBE, BLYP, and vdW-DF functionals give a good estimation of the unit cell volumes. Thus, the structures optimized with the SCAN functional can be an excellent starting point for advanced works on solid hydrogen.

Comparative antibacterial potential of silver nanoparticles prepared via chemical and biological synthesis

New and improved approaches are urgently needed to fight the increasing number of multi-drug resistant bacteria. The antibacterial effect of silver nanoparticles (AgNPs) prepared by standardized chemical and biological syntheses is compered here. Biological systems included extracts of Opuntia ficus-indica mucilage and extracellular growth broth of Aspergillus niger and Bacillus megaterium. The nanoparticles were characterized by infrared spectroscopy, IR, and transmission electron microscopy. All of the AgNPs shared characteristic IR peaks and had an average size of 20–60 nm. The AgNPs were mainly spherical regardless of synthetic path. The synthesis based on the extracellular broth of the fungus, due to the highest biomass and active compounds concentration, resulted in a high yield of nanoparticle formation. These AgNPs also exhibited the highest inhibition zone against Salmonella typhimurium and Staphylococcus aureus. The syntheses reported here have no significant influence on AgNPs physical characteristics, as compared to literature, but represent processes with shorter reaction time. Additionally, the fungal based nanoparticles have superior antibacterial characteristics.

Synthesis, characterization and toxicity profiling of graphene oxide-metformin hydrogel as a sustained release system for metformin in-vitro

We report here a sustained release system of metformin hydrochloride (MH) for its application in-vitro. Metformin hydrochloride (MH) conjugated graphene oxide (GO) hydrogel was synthesized and well-characterized by spectroscopic techniques like UV–Visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR). UV–Vis spectra showed a characteristic peak of GO at 232 nm and a shoulder at 315 nm, similarly FTIR-spectra showed characteristic peaks of GO at 1614.09 cm−1, 1374.93 cm-1and 1106.55 cm−1 and OH vibrations peak at 3377 cm−1. The GO + MH hydrogel showed broad characteristic IR peak at 3009 cm−1 which attributed to the cumulative vibrations of O–H and N–H stretching. The microscopic techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) was also done for characterization of the hydrogel. Zeta potential was also monitored of GO (−42 mV) before and after its gelation with metformin (-4 mV). All biophysical techniques validated the successful synthesis of GO and its conjugation with metformin through hydrogen and electrostatic interactions. The release behaviour of metformin from GO + MH hydrogel (1:10 ratio) was also investigated over a period of 24 h in a simulated pH environment of in-vitro experiments and nearly 66% cumulative release was determined. This data indicates that the effective utilization of synthesized GO + MH hydrogel can be done for therapeutics studies in the in-vitro condition. Toxicity profiling of GO was also done on the HepG2 cell line using MTT assay after 24 h incubation and found out the biocompatible nature of GO even at 100 μg/ml dose concentration.

Dose rate effects on shape memory epoxy resin during 1 MeV electron irradiation in air

The effects of 1 MeV electron irradiation in air at a fixed accumulated dose and dose rates of 393.8, 196.9, 78.8, and 39.4 Gy s−1 on a shape memory epoxy (SMEP) resin were studied. Under low-dose-rate irradiation, accelerated degradation of the shape memory performance was observed; specifically, the shape recovery ratio decreased exponentially with increasing irradiation time (that is, with decreasing dose rate). In addition, the glass transition temperature of the SMEP, as measured by dynamic mechanical analysis, decreased overall with decreasing dose rate. The dose rate effects of 1 MeV electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance (EPR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time. Moreover, the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm-1, which are attributed to stretching vibrations of amide CO and ketone/acid CO, at lower dose rates. The intensities of the IR peaks at 1660 and 1720 cm-1 increased exponentially with increasing irradiation time, and the relative intensity of the IR peak at 2926 cm-1 decreased exponentially with increasing irradiation time. The solid-state 13C nuclear magnetic resonance (NMR) spectra of the SMEP before and after 1 MeV electron irradiation at a dose of 1970 kGy and a dose rate of 78.8 Gy s-1 indicated damage to the CH2–N groups and aliphatic isopropanol segment. This result is consistent with the detection of nitrogenous free radicals, a phenoxy-type free radical, and several types of pyrolytic carbon radicals by EPR. During the subsequent propagation process, the free radicals produced at lower dose rates were more likely to react with oxygen, which was present at higher concentrations, and form the more destructive peroxy free radicals and oxidation products such as acids, amides, and ketones. The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.

Structural and Electrochemical Studies of La2O3 Coated LiCoO2 Particles

Nanocrystalline LiCoO2 particles have been surface modified with La2O3 by a simple and cost effective resin coating process. The synthesized pure and La2O3 coated samples were characterized by thermogravimetric analysis / differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. XRD studies revealed that the presence of La2O3 coating over LiCoO2 particles did not affect the original layer structure of pure LiCoO2. Also, no extra peak was detected for La2O3 phase. FTIR results confirmed the structural co-ordination of the samples. Also, the shifting and broadening of IR peaks corresponding to LiCoO2 confirmed the presence of IR peaks of La2O3. TEM image showed the formation of interconnected small nanoparticle subunits structure for LiCoO2. TEM image also showed the presence of thin La2O3 layer over LiCoO2 particles. The cyclic voltammetry studies revealed that the La2O3 coated LiCoO2 particles exhibited reversible redox peaks with slight increase in peak intensity and peak area compared to pure LiCoO2. It indicates an improved charge storage capacity of La2O3 coated LiCoO2 sample compared to pure LiCoO2 sample.

Goethite enhanced the Cr(VI) reduction by gallic acid through the stabilisation of free radicals: spectroscopic evidences and implication for transformation of Cr(VI) in an Oxisol

ABSTRACT Produced from root exudation activities and the decomposition of organic matter, gallic acid (GA) has been shown to be widely involved in the electron transfer reactions in soils as well as the transformation of redox-sensitive pollutants, while which was subject to the mediation of solid surfaces with the unknown mechanisms. This study aimed to investigate the catalytic effect of goethite on the Cr(VI) reduction by GA and explore the implication for the transformation of Cr(VI) in an oxisol. The results have shown that the adsorption of GA by goethite followed pseudo-second-order model. The GA was very stable at pH 4.0 in solution, whereas its oxidation by O2wasaccelerated in the presence of goethite as evidenced by the rapid appearance of IR peak of quinones. Similarly, the reduction of Cr(VI) by GA proceeded slowly with semi-quinonic species as the intermediate oxidation products of GA, while which would be significantly enhanced with the addition of goethite or oxisol. The mechanism was ascribed to that surface adsorption promoted the dissociation of –OH groups of GA and the subsequent formation of semiquinone radicals. Most importantly, these free radicals could be stabilised on the goethite surfaces, which was believed to be favourable for the reduction of Cr(VI). The catalysis of aqueous Fe(III) was excluded in this study due to its low concentration in the reaction systems. Furthermore, the majority of produced Cr(III) was adsorbed on the surfaces as the form of octahedron. The findings above indicated the environmental risk of Cr(VI)-polluted acidicsoilswould be alleviated when GA was present.

The Use of Silane-Aniline as Coupling Agent between Titanium (IV) Oxide Core and Polyaniline Emeraldine Salt Shell

Stable electronic configuration between the interface of an n-type oxide semiconductor core and a p-type polymer shell is necessary in order to guarantee a consistent functioning core-shell structure. This research aims to use silane-aniline to link between an n-type Titanium (IV) oxide (TiO2) core and p-type polyaniline emeraldine salt (PANI-ES) shell. Core-shell structure was created by functionalizing TiO2 powders with silane aniline molecules using simple soaking technique and then polymerizing the attached aniline molecules using an oxidative technique. Infrared spectroscopy reveals the presence of Si-O bonds signifying the presence of linkage between the inorganic core and polymeric shell. Polymerization of the attached aniline molecules may have led to coupling of aromatic rings to form long polymeric structures which caused widening and shifting of aromatic rings’ IR peak to lower wavenumber. In conclusion, silane-aniline was successfully utilized to connect the n-type TiO2 core and p-type PANI-ES shell.

IR Features of Hydrous Mg2SiO4-Ringwoodite, Unannealed and Annealed at 200–600 °C and 1 atm, with Implications to Hydrogen Defects and Water-Coupled Cation Disorder

Three batches of Mg2SiO4-ringwoodites (Mg-Rw) with different water contents (CH2O = ~1019(238), 5500(229) and 16,307(1219) ppm) were synthesized by using conventional high-P experimental techniques. Thirteen thin sections with different thicknesses (~14–113 μm) were prepared from them and examined for water-related IR peaks using unpolarized infrared spectra at ambient P-T conditions, leading to the observation of 15 IR peaks at ~3682, 3407, 3348, 3278, 3100, 2849, 2660, 2556, 2448, 1352, 1347, 1307, 1282, 1194 and 1186 cm−1. These IR peaks suggest multiple types of hydrogen defects in hydrous Mg-Rw. We have attributed the IR peaks at ~3680, 3650–3000 and 3000–2000 cm−1, respectively, to the hydrogen defects [VSi(OH)4], [VMg(OH)2MgSiSiMg] and [VMg(OH)2]. Combining these IR features with the chemical characteristics of hydrous Rw, we have revealed that the hydrogen defects [VMg(OH)2MgSiSiMg] are dominant in hydrous Rw at high P-T conditions, and the defects [VSi(OH)4] and [VMg(OH)2] play negligible roles. Extensive IR measurements were performed on seven thin sections annealed for several times at T of 200–600 °C and quickly quenched to room T. They display many significant variations, including an absorption enhancement of the peak at ~3680 cm−1, two new peaks occurring at ~3510 and 3461 cm−1, remarkable intensifications of the peaks at ~3405 and 3345 cm−1 and significant absorption reductions of the peaks at ~2500 cm−1. These phenomena imply significant hydrogen migration among different crystallographic sites and rearrangement of the O-H dipoles in hydrous Mg-Rw at high T. From the IR spectra obtained for hydrous Rw both unannealed and annealed at high T, we further infer that substantial amounts of cation disorder should be present in hydrous Rw at the P-T conditions of the mantle transition zone, as required by the formation of the hydrogen defects [VMg(OH)2MgSiSiMg]. The Mg-Si disorder may have very large effects on the physical and chemical properties of Rw, as exampled by its disproportional effects on the unit-cell volume and thermal expansivity.

Effect of the electronic state on low-rank coals with Ca2+ ion exchange

Ca2+-exchanged coal prepared from calcium hydroxide is a good catalyst for steam gasification of low-rank coal with a fixed-bed quartz reactor. However, it is difficult to clarify the effect of Ca2+ ion exchange on low-rank coal by experiment. To investigate the effect of Ca2+ ions on low-rank coals, this study determined the electronic states between Ca2+-exchanged and raw coal models and compared them by B3LYP/6-31G∗ and HF/6-311G∗ calculations. The experiments revealed that the Ca2+ ion exchange method significantly affects gasification of low-rank coal. It is considered that the molecular structure of low-rank coal presents significant changes in the electronic state before and after Ca exchange, even with a simple molecular structure. Therefore, a molecular model was created in which a COOH/OH H+ ion was exchanged with one Ca2+ ion, and quantum chemical calculations were subsequently performed. The results revealed that the –COOCa1/2 IR peak calculated from B3LYP/6-31G∗ appeared at approximately the same position as the experimental IR peak in low-rank coal after Ca exchange. The Ca structure was more stable following interaction with the O in the benzene OH group than with that in the OH group of the tetralin ring containing Ca. Furthermore, the increased negative charge of the benzene ring following Ca interaction was presumed to improve the reactivity between the low-rank coal and steam. In addition, weak bonds in the Ca2+-exchanged coal molecules were investigated by calculating the difference between the values of the Löwdin and Mulliken bond orders before and after Ca2+ exchange. The results indicated that the binding in the molecule was weakened by Ca coordination. From these facts, it is presumed that H+/Ca2+ ion exchange promotes the decomposition of low-rank coal.

Chlorpyrifos-degrading cyanobacterium – Coleofasciculus chthonoplastes isolated from paddy field

ABSTRACTCyanobacterial strains were isolated from different locations of Kerala, India and grown in BG 11 medium. Cultures were tested for their pesticide degradation capability by growing them in chlorpyrifos containing media. The strain showing better growth in chlorpyrifos containing medium, Coleofasciculus chthonoplastes was chosen for further studies. The supernatant of its culture was analysed for the degraded products of chlorpyrifos. Extracted fractions were spotted on thin-layer chromatography (TLC) plates along with the standard compounds. TLC of the supernatant showed additional bands. These were not caused by the inputs. Fourier Transform Infrared Spectroscopy (FTIR) of the additional bands showed a difference in IR peak values which indicated the degradation of chlorpyrifos. Biodegradation products of the pesticide were identified by GC-MS and LC-MS analyses. A new compound 1,1,2,3,3 pentachloro propane, considered as derived from chlorpyrifos, was also found as a metabolite in the medium.

On the SN2 reactions modified in vibrational strong coupling experiments: reaction mechanisms and vibrational mode assignments.

Recent experiments have reported modified chemical reactivity under vibrational strong coupling (VSC) in microfluidic Fabry-Pérot cavities. In particular, the reaction rate of nucleophilic substitution reactions at silicon centers (SN2@Si) has been altered when a vibrational mode of the reactant was coupled to a confined light mode in the strong coupling regime. In this situation, hybrid light-matter states known as polaritons are formed and seem to be responsible for the modified chemical kinetics. These results are very encouraging for future applications of polaritonic chemistry to catalyze chemical reactions, with the ability to manipulate chemical phenomena without any external excitation of the system. Still, there is no theory capable of explaining the mechanism behind these results. In this work we address two points that are crucial for the interpretation of these experiments. Firstly, by means of electronic structure calculations we report the reaction mechanism in normal conditions of the two recently modified SN2@Si reactions, obtaining in both cases a triple-well PES where the rate-determining step is due to the Si-C and Si-O bond cleavage. Secondly, we characterize in detail the normal modes of vibration of the reactants. In the VSC experiments, reaction rates were modified only when specific vibrations of the reactants were coupled to a cavity mode. We find that these vibrations are highly mixed among the different fragments of the reactants leading to a completely new assignment of the IR peaks coupled to cavity modes in the original experimental works. Our results are fundamental for the interpretation of the VSC experiments given that in the absence of a theory explaining these results, the current phenomenological understanding relies on the assignment of the character of the vibrational IR peaks.

Evolution Process and Controlled Synthesis of Humins with 5-Hydroxymethylfurfural (HMF) as Model Molecule.

Elucidation of the chemical structure and formation mechanism of humins is a requisite to further improve the efficiency of acid-catalyzed biomass conversion. Through a low-temperature approach, the key intermediates resulting in the formation of 5-hydroxymethylfurfural (HMF)-derived humins were captured, revealing multiple elementary reactions such as etherification, esterification, aldol condensation, and acetalization. Through humin characterization, it was found out that the aldol condensation moiety between aldehyde group and levulinic acid is critical to justify the characteristic IR peaks (1620 and 1710 cm-1 ) and aromatic fragments from pyrolysis GC-MS. Based on the investigations by means of HPLC-MS/MS, IR, pyrolysis GC-MS, and SEM, the structural models of humins at different temperatures were proposed, which are comprised of the elementary reaction types confirmed by the key intermediates. Humin structures with varying content of aldol condensation could be controllably synthesized under different reaction conditions (temperature and time), demonstrating the evolution process of HMF-derived humins.

Structural and ionic conductivity characterization of PEO:MC-NH4I proton-conducting polymer blend electrolytes based films

In the present work, series of proton-conducting polymer electrolyte films based on polyethylene oxide/methylcellulose complexed with different concentrations of ammonium iodide (NH4I) as doping salt were prepared by solution cast technique. The produced films were characterized by X-ray diffraction (XRD), Polarized optical microscope (POM), Fourier transform infrared (FTIR), and electrical impedance spectroscopy (EIS). The XRD and POM results reveal that the sample with 30 wt% NH4I (PBE-30) has the lowest degree of crystallinity. The observed shift in the IR peak position of the N–H stretching band at regions 3000–3300 cm−1 as a function of NH4I concentration suggested clear evidence of an interaction between host polymers and NH4I. The highest value of electrical conductivity was found to be 7.62×10-5S.cm-1 at 303K for PBE-30. The temperature-dependent of electrical conductivity and ion transport properties was described using both the Arrhenius and Vogel-Tammann-Fulcher (VTF) relations. The activation energy values decrease with increasing DC conductivity and vice-versa.

PH dependent drug release from drug conjugated PEGylated CdSe/ZnS nanoparticles

Stimuli-responsive nanoparticles (NPs) are very useful for drug delivery applications. This manuscript presents PEGylated CdSe/ZnS core/shell NPs (PEGylated NPs) for the pH-dependent delivery of anticancer drug doxorubicin (DOX). DOX is conjugated chemically to end group of PEGylated NPs (‒NH2) by an acid cleavable hydrogen bond. DOX is conjugated to PEGylated NPs by two methods (i) without crosslinker and (ii) with crosslinker. TEM studies showed increase in size of NPs (from 25 to 40 nm) on DOX conjugation which is later confirmed by dynamic light scattering (100–260 nm). Zeta studies revealed that NPs exhibits neutral (~0 mV) surface charge. Shifts of peaks in FT‒IR, a shift towards longer wavelength region in UV–vis absorption spectra and quenching of fluorescence intensity in emission spectra confirms the conjugation of DOX to PEGylated NPs. Conjugation of DOX to PEGylated NPs and release profiles are strongly affected by the pH conditions. In vitro, drug release profiles showed maximum release of DOX from PEGylated NPs at acidic pH ~41% for DOX conjugated PEGylated NPs with crosslinker, whereas for DOX conjugated PEGylated NPs without crosslinker the maximum release is ~22%. The approach of conjugating DOX to PEGylated NPs has been proven useful for targeting cancerous cells and controlled release at the target site.

PECULIARITIES OF DOPPEROMETRIC INDICATORS OF FETOPLACENTAL COMPLEX IN WOMEN WITH THREATEN PREMATURE BIRTHS USING METABOLIC THERAPY

Premature birth is one of the leading problems of modern obstetrics, because, despite the efforts of scientists and practitioners, has no tendency to decrease. The stability of hemodynamic processes in the mother-placenta-fetus system is one of the basic conditions that ensures the normal course of pregnancy, growth and development of the fetus. Circulatory disorders in it leads to many complications of pregnancy. It has been established that using metabolic therapy in the form of omega-3 polyunsaturated fatty acids (PUFAs) in pregnant women helps to improve blood circulation in the mother-placenta-fetus system, improves the rheological properties of blood, prevents the development of preeclampsia and affects the reduction of perinatal complications. The introduction of Doppler studies of the blood flow of the placental complex (PC) into practical obstetrics allows not only to assess the condition of the fetus, but also to predict the development of possible complications.The aim of the study was to investigate the Doppler parameters of the state of the placental complex (PC) of pregnant women with the threat of preterm labor who received metabolic therapy.Material and methods of the study. The analysis of Doppler parameters of the state of the PC 60 pregnant women with the threat of preterm labor in the period of gestation 28-34 weeks was carried out. Pregnant women were divided into 2 groups: 1 group (n = 30) - pregnant women with the threat of preterm labor, who received standard complex basic therapy in combination with metabolic therapy in the form of 300 mg of omega-3 PUFAs per day, group 2 (n = 30) pregnant women with the threat of preterm labor, who received only standard complex basic therapy. The control group (CG) consisted of 30 practically healthy women with physiological pregnancy.The results of the study and their discussion. According to the Doppler study of PC, it was found that in 1 and 2 groups there was an increase in resistance index (IR) and systolic-diastolic ratio (SD) in the umbilical arteries (UA) (group 1: IR-0.87,80.05 and SD -3.57±0.2; group 2: IR-0.88±0.05 and SD-3.56±0.1) compared with pregnant CG (IR-0.62±0.07 and SD- 2.85±0.3). At the same time, indicators of IR, SD, pulse index (PI) and systolic peak velocity (SPV) in the middle cerebral artery (MCA) corresponded to thenorm, while in the fetal aorta (FA) an increase in IR and a decrease in PI (group 1: II- 1.05±0.2 and PI-0.9±0.2, group 2: IP-1.05±0.1 and PI-1.0±0.2) with unchanged indices of the SD and the average blood flow velocity (ABV). After the received treatment, in pregnant women of group 1, there were changes in Doppler hemodynamic parameters in UA and FA, namely: a decrease in IR and SD (II-0.69±0.2 and SD-2,98±0.2) in the UA and a decrease in IR and an increase in PI (IR-0.78±0.1 and PI-1.9±0.2) in FA compared with reliably higher data of Dopplerometric indicators of PC in pregnant women of group 2 (p±0.05).Conclusions. The use of metabolic therapy in the complex treatment of the threat of preterm labor has a positive effect on the change in the hemodynamic parameters of PC and can be used to improve blood flow in the mother-placenta-fetus system.

A Supramolecular View on the Cooperative Role of Brønsted and Lewis Acid Sites in Zeolites for Methanol Conversion.

A systematic molecular level and spectroscopic investigation is presented to show the cooperative role of Brønsted acid and Lewis acid sites in zeolites for the conversion of methanol. Extra-framework alkaline-earth metal containing species and aluminum species decrease the number of Brønsted acid sites, as protonated metal clusters are formed. A combined experimental and theoretical effort shows that postsynthetically modified ZSM-5 zeolites, by incorporation of extra-framework alkaline-earth metals or by demetalation with dealuminating agents, contain both mononuclear [MOH]+ and double protonated binuclear metal clusters [M(μ-OH)2M]2+ (M = Mg, Ca, Sr, Ba, and HOAl). The metal in the extra-framework clusters has a Lewis acid character, which is confirmed experimentally and theoretically by IR spectra of adsorbed pyridine. The strength of the Lewis acid sites (Mg > Ca > Sr > Ba) was characterized by a blue shift of characteristic IR peaks, thus offering a tool to sample Lewis acidity experimentally. The incorporation of extra-framework Lewis acid sites has a substantial influence on the reactivity of propene and benzene methylations. Alkaline-earth Lewis acid sites yield increased benzene methylation barriers and destabilization of typical aromatic intermediates, whereas propene methylation routes are less affected. The effect on the catalytic function is especially induced by the double protonated binuclear species. Overall, the extra-framework metal clusters have a dual effect on the catalytic function. By reducing the number of Brønsted acid sites and suppressing typical catalytic reactions in which aromatics are involved, an optimal propene selectivity and increased lifetime for methanol conversion over zeolites is obtained. The combined experimental and theoretical approach gives a unique insight into the nature of the supramolecular zeolite catalyst for methanol conversion which can be meticulously tuned by subtle interplay of Brønsted and Lewis acid sites.

In situ studies on ceria promoted cobalt oxide for CO oxidation

In situ studies of catalysts play valuable roles in observing phase transformation, understanding the corresponding surface chemistry and the mechanism of the reaction. In this paper, ceria promoted cobalt oxide was prepared by the calcination method and investigated for the CO oxidation. The microstructure and morphology of CeO2-Co3O4 were investigated by the Scanning Electron Microscope, High-resolution transmission electron microscopy, Raman and X-ray photoelectron spectroscopy characterization. The effect of CeO2 doping on Co3O4 for CO oxidation was characterized by in situ X-ray Diffraction (in situ XRD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). In situ XRD was carried out under H2 atmosphere to evaluate the redox property of catalysts. The results indicated that the ceria doping can enhance the reducibility of Co2+ and promote the Co3+—Co2+—Co3+ cycle, owing to the oxygen replenish property of CeO2. Furthermore, adsorbed carbonate species on the surface of CeO2-Co3O4 were investigated by in situ-DRIFTS experiment. It was turned out that carbonate species on ceria promoted cobalt oxide catalysts showed different IR peaks compared with pure cobalt oxide. The carbonate species on ceria promoted catalyst are more active, and similar to free state carbonate species with weak bonding to catalyst surface, which can effectively inhibit catalyst inactivation. This study revealed the mechanism of ceria promoting CO oxidation over cobalt oxide, which will provide theoretical support for the design of efficient CO oxidation catalysts.

Spectroscopic properties and activated mechanism of NO on isolated cationic tantalum clusters: A first-principles study.

The adsorption and dissociation of NO on the cationic Ta15+ cluster were investigated using the density-functional theory (DFT) calculations, and the Ta-centered bicapped hexagonal antiprism (BHA) structure of cationic Ta15+ cluster can be identified as the global minimum, which reproduces well the infrared multiple photo dissociation (IR-MPD) spectrum. Our results show that the cationic BHATa15+ cluster provides the hollow region for NO to interact effectively, and possess larger adsorption strength on the region than other sites. The density of states, charge density differences and frontier molecular orbitals were analyzed to understand the electronic properties of the stable NO-adsorbed isomers. The characteristic IR peaks of the firstly two low-lying isomers are properly assigned, in which the strongest IR peak originates from the N - O stretching vibration. For the dissociation of NO on the BHATa15+ cluster, it is found that the reaction path II easily occurs rather than path I due to small reaction barrier, and the cluster may possess the great catalytic behavior to dissociate NO molecule. The present results will inevitably stimulate future theoretical and experimental studies for the design of novel Ta-based catalytic materials for the NO dissociation.

Synthesis and study of the efficacies of Tetraaza macrocyclic ligand for the adsorption of heavy metals from wastewater

Condensation of Ethyl 2-methylacetoacetate and ethylenediamine yield 88.7% of Dimethyl-7,14-Diphenyl-1,4,8,11-Tetraazacyclotetradeca-4,7,11,14-Tetraene with a condense chemical formula as C 18 H 32 N 4 O 2 , and a molecular weight of 336.47. The complexes were prepared by the adsorption of heavy metals (Fe, Cu, Cd, Co and, Pb) from wastewater samples obtained from Kofar sauri, Lambun Dan Lawal and Youth craft village. The compounds were investigated by solubility, conductivity, melting/decomposition point, Atomic Absorption Spectroscopy, Infrared spectroscopy and Uv-visible spectroscopy. The Ligand 003 shows IR peak of υ(C=N) at 1633cm -1 , and a shift was observed to a lower peak as a result of adsorption of the heavy metals by the ligand, which is signifying the formation of the complexes. AAS results indicates high concentration of Cu in each case when compared, the rest of the metals varying at different level of concentration in the compounds. Cu may best fit the center of the ligand cavity having a concentration beyond computing with the rest of the metals. Key words : Schiff base, wastewater, heavy metals