Catalytic behavior of surfactant-containing-MCM-41 mesoporous materials for cycloaddition of 4-nitrophenyl azide

International audienceSi-MCM-41, Ga-MCM-41 and Al-MCM-41 mesoporous catalysts (with Si/Al = 80 and Si/Ga = 80) were prepared by direct synthesis under hydrothermal crystallization method using sodium aluminate or gallium sulfate and tetraethyl orthosilicate (TEOS) as aluminum or gallium and silica sources, respectively. The structural features of the materials were determined by various physico-chemical techniques such as X-ray diffraction (XRD), nitrogen sorption at 77 K, Fourier transform infrared spectroscopy (FTIR), scanning and transmission electronic microscopy (SEM, TEM) and thermogravimetric analysis ATG. The catalytic activity of the calcined and as-synthesized catalyst was evaluated through the cycloaddition reaction of 4-nitrophenyl azide with activated alkenes at room temperature under liquid-phase conditions. High yields of 1,2,3-triazole were obtained. For comparison purpose, mixtures of homogeneous and heterogeneous catalyst Et3N/M-MCM-41 (M = Al or Ga) are also tested. The catalyst was used in five consecutive experiments without important loss of activity, confirming its stability. Finally, a new method for preparing triazoles in short reaction times was developed

Comparison of Lewis Acidity between Al-MCM-41 Pure Chemicals and Al-MCM-41 Synthesized from Bentonite

This study focused on the Lewis acidity of Al-MCM-41 prepared from bentonite (Al-MCM-bentonite) as silica and aluminum source simultaneously. This acidity was compared with Al-MCM-41 synthesized from pure chemicals reagents (Al-MCM-standard). Structural analysis showed that the substitution of the silicon atom by the aluminum atom decreases the structural order of Al-MCM-standard, whereas Al-MCM-bentonite has a better structural organization. The Lewis acidity of the Al-MCM-bentonite was evaluated in allylation reaction of benzaldehyde with allyltrimethylsilane and pyridine adsorption experiments. The results showed that the difference in acidity between Al-MCM-standard and Al-MCM-bentonite is due to the amount of aluminum incorporated into the framework of our mesoporous materials. According to the EDX analysis, the incorporation of aluminum in Al-MCM-standard (Si/Al = 13.47) is more important than in Al-MCM-bentonite (Si/Al = 43.64). This explains the low acidity of Al-MCM-bentonite, and the moderate yields in the allylation reactions of benzaldehyde with allyltrimethylsilane. Copyright © 2019 BCREC Group. All rights reserve

Catalytic reduction of organic pollutants, antibacterial and antifungal activities of AgNPs@CuO nanoparticles–loaded mesoporous silica

In this work, the mesoporous silica MCM-41 was prepared by a hydrothermal method and then modified using silver and copper. The obtained samples were used as antibacterial/antifungal agents and as catalysts for the reduction of the following dyes: Methylene Blue (MB), Congo Red (CR), Methyl Orange (MO), and Orange G (OG). Several parameters affecting the reduction of dyes were investigated and discussed such as the catalyst nature, the initial concentration of the dye, the dye nature, the selectivity of the catalyst in a binary system as well as the catalyst reuse. The catalysts were characterized using XRD, nitrogen sorption measurements, XRF, FTIR, XPS, SEM/EDS, and TEM. XRD, XPS, and TEM analysis clearly showed that the calcination of copper- and silver-modified silica leads to the formation of well-dispersed CuO and AgNPs having sizes between 5 and 10 nm. As determined by XRF analysis, the content of silver nanoparticles was higher compared to CuO in all samples. It has been shown that the dye reduction is influenced by the size and the content of nanoparticles as well as by their dispersions. The catalytic activity was shown to be the highest for the Ag–Cu-MCM(0.05) catalyst with a rate constant of 0.114, 0.102, 0.093, and 0.056 s−1 for MO, MB, CR, and OG dyes in the single-dye system, respectively. In the binary system containing MB/OG or MB/MO, the catalyst Ag–Cu-MCM(0.05) was more selective toward the MB dye. The reuse of the catalyst for three consecutive cycles showed higher MB conversion in a single system with an increase in reaction time. For antifungal and antibacterial properties, the application of calcined and uncalcined materials toward six different strains showed good results, but uncalcined materials showed the best results due to the synergistic effect between CuO and unreduced species Ag+ which are considered responsible for the antibacterial and antifungal action

Mesoporous silica supported amine and amine-copper complex for CO2 adsorption: Detailed reaction mechanism of hydrophilic character and CO2 retention

International audienceMesoporous silica SBA-15 was functionalized with various amines and then doped with copper II cation (Cu2+). The modified materials were tested for the retention of CO2 at room temperature using temperature-programmed desorption (CO2-TPD). Several parameters affecting the CO2 retention capacity (CRC) such as the nature of amine groups, repetitive adsorption-desorption cycles and dispersion of copper were investigated. CO2-TPD and H2O-TPD allowed correlating the hydrophilic character with the CO2 retention capacity. The obtained results showed that amine-functionalized mesoporous materials containing their own moisture exhibit higher effectiveness in the retention of CO2. Triamine-functionalized SBA-15 displayed the highest CRC value as a result of the increase of the number of adsorption sites. Material reuse in three adsorption/desorption cycles revealed high stability with a slight decrease in CRC. The dispersion of copper induced a progressive decrease in the CRC value. The CRC decreased with increasing Cu2+ content due to competitive complexation of Cu2+ by the amino groups

M (M: Cu, Co, Cr or Fe) nanoparticles-loaded metal-organic framework MIL-101(Cr) material by sonication process: Catalytic activity and antibacterial properties

The current study deals with the preparation and development of nanomaterials based on iron, copper, chromium or cobalt to study their antibacterial and catalytic properties. To achieve this, the different metals were dispersed in the material MIL-101(Cr) by an ultrasonic-assisted method and then treated by chemical reduction in order to produce corresponding metal nanoparticles (MNPs). The obtained nanocatalysts MIL-101(Cr)/MNPs were characterized by various techniques such as XRD, XPS, SEM, TEM, FTIR; TGA, XRF, Adsorption-desoprtion of nitrogen at 77 K and UV–vis DR. The results showed that the nanocatalysts consist of a mixture of metal phases and oxides. All the prepared nanocatalysts were evaluated based on their performance in reducing the methylene blue (MB) dye in the presence of NaBH4 as reducing agent, for selection of the optimal catalyst. The best catalytic activity was obtained by the MIL-101 (Cr)/CuNPs nanocatalyst in which 6 min was sufficient to reduce the MB dye and the recorded rate constant kapp was 0.503 min−1. The performance of this catalyst was evaluated by varying the effects of three important parameters such as catalyst loading and the concentration of NaBH4 and MB dye. The study of the effects of these three parameters on the reduction process reveals that more than 99% of MB dye was reduced using 0.6 mM of MB dye, 6.8 mM of NaBH4 and 3 mg of nanocatalyst. The kinetic study shows that the reduction of MB dye by the MOF-101(Cr)/CuNPs nanocatalyst follows pseudo-first order kinetics. In addition, the MIL-101(Cr)/CoNPs and MIL-101(Cr)/CuNPs samples demonstrated efficacy at inhibiting bacterial and fungal growth. Hence, it is concluded through this work that the nature, size and concentration of nanoparticles present in the MOF matrix are the key parameters that can influence the catalytic and antibacterial properties of these MNP-loaded MIL-101(Cr) systems

Amélioration du comportement en cyclage thermique d'un dépôt plasma métallique par compression isostatique à chaud.

International audienceA HIP post-treatment applied on LLPS FeCrAlY coatings improved resistance under thermal cycling (high coating densification, strong adherence to substrate). Observation of the oxide scale using SEM, enabled us to explain such an improvement of the behaviour of post-hipped coatings when submitted to both oxidation and thermal stresses

Etude cinétique et thermodynamique d'adsorption de Composés phénoliques sur un matériau mesoporeux hybride organique-inorganique

International audienceThe objective of this work is thus to study the kinetics, thermodynamics and adsorption isotherms of two phenolic compounds phenol (PhOH) and P-hydroxy benzoic acid (4AHB) on a mesoporous material type MCM- 48 functionalized with an organosilane type trimethylchlorosilane (TMCS) (MCM-48-G). At first, the study of the kinetics, thermodynamics and adsorption isotherms of phenolic compounds in each single solution was performed. In a second step, a similar study was performed on a mixture of these two molecules. Several kinetic models (pseudo-first order, pseudo-second order) were used to determine the kinetic parameters of adsorption. Several adsorption models (Langmuir, Freundlich) were also used to determine the thermodynamic parameters of adsorption isotherms. The effect of three-dimensional pores of MCM-48 and comparison of adsorption of PhOH and 4AHB was examined. It was found that MCM-48-G to a significant adsorption capacity for PhOH and 4AHB, this may be related to the hydrophobicity created by the organic function of TMCS in the MCM-48-G.The results of adsorption and PhOH 4AHB were analyzed using the Freundlich and Langmuir models. It was observed that the adsorption of 4AHB was higher than PhOH. Thermodynamics of adsorption showed that the values obtained for our sample confirm well the interactions with phenol and 4AHB are physical in nature. The adsorption of pollutants on our MCM-48 (G) is a spontaneous and exothermic process.L'objectif de ces travaux est ainsi d'étudier la cinétique, la thermodynamique et les isothermes d'adsorption de deux composés phénoliques le phénol (PhOH) et l'acide P-hydroxy benzoïque (4AHB) sur un matériau mesoporeux de type MCM-48 fonctionnalisée par un organosilane de type Trimethylchlorosilane (TMCS) (MCM-48-G). Dans un premier temps, l'étude de la cinétique, la thermodynamique et les isothermes d'adsorption de chacun des composés phénoliques en mono solution a été réalisée. Dans un second temps, une étude similaire a été effectuée sur un mélange de ces deux molécules. Plusieurs modèles cinétiques (pseudo-premier ordre, pseudo-second ordre) ont été utilisés afin de déterminer les paramètres cinétiques d'adsorption. Plusieurs modèles d'adsorption (Langmuir, Freundlich) ont également été utilisés afin de déterminer les paramètres thermodynamiques des isothermes d'adsorption. L'effet de pores tridimensionnels du MCM-48 et la comparaison d'adsorption du PhOH et 4AHB a été examiné. Il a été trouvé que MCM-48-G à une grande capacité adsorption significative pour PhOH et 4AHB; ceci peut être lié à l' hydrophobicité créé par la fonction organique du TMCS dans le MCM-48-G. Les résultats d'adsorption pour PhOH et 4AHB ont été analysés en utilisant les modèles Freundlich et Langmuir. Il a été observé que l'adsorption du 4AHB était plus haute que PhOH. La thermodynamique d'adsorption a montré que les valeurs obtenues pour notre échantillon confirment bien que les interactions avec le phénol et 4AHB sont de nature physique. L'adsorption de nos polluants sur la MCM-48 (G) est un processus spontané et exothermique

Textural properties of ZSM-5 nanocrystals prepared in alkaline potassium fluoride medium

International audienceIn this paper, we optimized the fluorine route in hydrothermal conditions under atmospheric pressurefor the synthesis of ZSM-5 crystals of controlled size. Several experimental parameters were varied forobtaining particles in the nanoscale range in the shortest time with the highest crystalline as well astextural properties. The 100% crystalline ZSM-5 crystals were obtained for a temperature of reaction of100◦C and a crystallization time of 7 days. The concentration of the organic template was found to greatlyinfluence the crystallization process. XRD showed that the best result was obtained for a TPABr/SiO2ratioof 0.4. Below this ratio, a slowdown of the crystallization process was observed. The increase of the molarratio template/silica above 0.4 induced an unfavourable increase of the alkalinity of the mixture. Thisresulted in a decrease of the crystal growth and consequently a decrease of the size of the zeolite crystals.In these conditions, the average diameter of the crystals was extended from 20 to 47 nm. Beyond 20 h, the ageing time had a little effect on the crystallinity of the final products, whereas the crystal size wasconsiderably reduced from 52 nm to less than 25 nm when the ageing time was increased from 20 to 44 h

Key factor affecting the basicity of mesoporous silicas MCM-41: effect of surfactant extraction time and Si/Al ratio

International audienc