Post-synthetic Methods Research Articles

Luminescent CdTe and CdSe Semiconductor Nanocrystals: Preparation, Optical Properties and Applications

The novel optical and electrical properties of luminescent semiconductor nanocrystals are appealing for ultrasensitive multiplexing and multicolor applications in a variety of fields, such as biotechnology, nanoscale electronics, and opto-electronics. Luminescent CdSe and CdTe nanocrystals are archetypes for this dynamic research area and have gained interest from diverse research communities. In this review, we first describe the advances in preparation of size- and shape-controlled CdSe and CdTe semiconductor nanocrystals with the organometallic approach. This article gives particular focus to water soluble nanocrystals due to the increasing interest of using semiconductor nanocrystals for biological applications. Post-synthetic methods to obtain water solubility, the direct synthesis routes in aqueous medium, and the strategies to improve the photoluminescence efficiency in both organic and aqueous phase are discussed. The shape evolution in aqueous medium via self-organization of preformed nanoparticles is a versatile and powerful method for production of nanocrystals with different geometries, and some recent advances in this field are presented with a qualitative discussion on the mechanism. Some examples of CdSe and CdTe nanocrystals that have been applied successfully to problems in biosensing and bioimaging are introduced, which may profoundly impact biological and biomedical research. Finally we present the research on the use of luminescent semiconductor nanocrystals for construction of light emitting diodes, solar cells, and chemical sensors, which demonstrate that they are promising building blocks for next generation electronics.

Synthesis, Characterization, and Oxygen Sensing Properties of Functionalized Mesoporous SBA-15 and MCM-41 with a Covalently Linked Ruthenium(II) Complex

Novel oxygen sensing materials consisting of the [Ru(dpp)2Phen]2+ (dpp = 4, 7-diphenyl-1,10-phenanthroline, Phen = 1,10-phenanthroline) portion covalently grafted to the ordered functionalized mesoporous SBA-15 and MCM-41 backbones are prepared by co-condensation of tetraethoxysilane (TEOS) and the functionalized Ru(II) complex [Ru(dpp)2Phen-Si]2+ (Phen-Si = 2-[4‘-{3-(Triethoxysilyl)propyl}phenyl]imidazo [4,5-f]-1,10-phenanthroline) in the presence of Pluronic P123 or cetyltrimethylammoniumbromide (CTAB) surfactant as template, respectively. 1,10-Phenanthroline covalently grafted to 3-(triethoxysilyl)propyl isocyanate is used not only as the precursors but also as the second ligand of the Ru(dpp)2Cl2·2H2O complex to prepare the functionalized mesoporous materials for oxygen sensors. For comparative purposes, two different synthesis procedures, including the one-pot synthesis and the postsynthetic treatment methods, are used to prepare the covalently grafted samples. Furthermore, the oxygen sensing materia...

Biomolecular sensor based on fluorescence-labeled aptamer

Fluorescent DNA probes for l-argininamide were developed by a combination of DNA aptamers and fluorophore–quencher pairs. These molecules were synthesized by a combination of pre- and post-synthetic modification methods. The fluorescence-labeled aptamer could detect l-argininamide specifically. The binding affinities were defined by the binding affinity of the original aptamer to indicate that the end labeling of the aptamer did not influence the affinities.

NiMo catalysts supported on titania-modified SBA-16 for 4,6-dimethyldibenzothiophene hydrodesulfurization

A series of Ti-containing mesoporous SBA-16 supports and the respective NiMo catalysts were prepared to study the effect of the method for support preparation and TiO 2 loading on the dispersion of titania, characteristics of Ni and Mo surface species and their catalytic activities in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS). The solids prepared were characterized by N 2 physisorption, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), FT–Raman spectroscopy, temperature-programmed reduction (TPR), chemical analysis and HRTEM. Titania was incorporated to purely siliceous SBA-16 support by two post-synthetic methods: chemical grafting and incipient wetness impregnation. The results show that Ti-SBA-16 supports with different TiO 2 content and dispersion can be obtained without substantial loss of SBA-16 characteristics. The best dispersion of TiO 2 in the SBA-16 pore channels was obtained by the grafting method (DRS, FT–Raman). However, titania loading in this case was limited to 15.1 wt.% TiO 2. Samples prepared by impregnation show the presence of different Ti species: isolated Ti species and small anatase clusters (inside the mesopore channels of SBA-16) and anatase crystallites (on the external surface), even for low titania loadings (XRD). Crystal size of anatase phase increased with titania loading. It was found that TiO 2 incorporation in the SBA-16 support leads to stronger interaction of Mo and Ni oxidic species with the support (TPR) providing better dispersion to the sulfided metal species (HRTEM). NiMo catalysts supported on Ti-modified SBA-16 showed high activity in 4,6-dimethyldibenzothiophene HDS. It can be concluded, therefore, that Ti-SBA-16 materials prepared by post-synthetic routes show promising features as supports for Mo-based hydrotreating catalysts.

New NiMo catalysts supported on Al-containing SBA-16 for 4,6-DMDBT hydrodesulfurizationEffect of the alumination method

Abstract A series of Al-containing mesoporous molecular sieves SBA-16 was prepared by synthetic and post-synthetic methods using different Al sources. NiMo catalysts supported on Al-SBA-16 were prepared and tested in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS) reaction. The synthesized solids were characterized by N2 physisorption, XRD, ammonia TPD, Py FT-IR, 27Al MAS–NMR, temperature programmed reduction, chemical analysis and HRTEM. It was found that the characteristics of the Al-SBA-16-supports strongly depend on the used Al source and the method selected for Al incorporation into the SBA structure. Post-synthetic alumination of SBA-16 by reacting with AlCl3 or Al(i-PrO)3 has a number of advantages in comparison with the incorporation of Al by grafting with NaAlO2 or direct synthesis, among them, (i) a good control of Al content in the sample; (ii) little influence on the mesoporous structure of the parent SBA-16; (iii) creation of Bronsted acid sites; and (iv) stronger interaction with deposited Ni and Mo species providing them better dispersion. NiMo catalysts supported on Al-SBA-16, which were prepared by grafting with AlCl3 or Al(i-PrO)3, show high activity in 4,6-DMDBT HDS; this can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of these catalysts, namely, to the participation of both types of sites, coordinatively unsaturated sites (CUS) of NiMoS active phase and Bronsted acid sites of the support, in the catalytic transformations of 4,6-DMDBT.

New NiMo catalysts supported on Al-containing SBA-16 for 4,6-DMDBT hydrodesulfurization: Effect of the alumination method

A series of Al-containing mesoporous molecular sieves SBA-16 was prepared by synthetic and post-synthetic methods using different Al sources. NiMo catalysts supported on Al-SBA-16 were prepared and tested in the 4,6-dimethyldibenzothiophene hydrodesulfurization (HDS) reaction. The synthesized solids were characterized by N 2 physisorption, XRD, ammonia TPD, Py FT-IR, 27Al MAS–NMR, temperature programmed reduction, chemical analysis and HRTEM. It was found that the characteristics of the Al-SBA-16-supports strongly depend on the used Al source and the method selected for Al incorporation into the SBA structure. Post-synthetic alumination of SBA-16 by reacting with AlCl 3 or Al(i-PrO) 3 has a number of advantages in comparison with the incorporation of Al by grafting with NaAlO 2 or direct synthesis, among them, (i) a good control of Al content in the sample; (ii) little influence on the mesoporous structure of the parent SBA-16; (iii) creation of Brönsted acid sites; and (iv) stronger interaction with deposited Ni and Mo species providing them better dispersion. NiMo catalysts supported on Al-SBA-16, which were prepared by grafting with AlCl 3 or Al(i-PrO) 3, show high activity in 4,6-DMDBT HDS; this can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of these catalysts, namely, to the participation of both types of sites, coordinatively unsaturated sites (CUS) of NiMoS active phase and Brönsted acid sites of the support, in the catalytic transformations of 4,6-DMDBT.

Synthesis and characterization of hydrotreating Mo catalysts supported on titania-modified MCM-41

A series of Ti modified MCM-41 supports and their respective Mo catalysts were prepared and characterized to study the effect of support preparation method on the dispersion of titania and on the characteristics of Mo surface species. Two methods of post-synthetic incorporation of titania were tested: chemical grafting and incipient wetness impregnation. The characterization results were compared to those obtained with Ti-MCM-41 supports where Ti was incorporated during the hydrothermal synthesis of MCM-41 (synthetic route). The results show that supports with different TiO2 content and dispersion, can be obtained. The synthetic route allows to prepare mesoporous supports with ordered structure and high surface area only if the titania content is low (less than 10 wt.%). On the contrary, the post-synthetic methods allow to achieve higher titania loadings without substantial loss of MCM-41 characteristics. The best dispersion of TiO2 in the MCM-41 channels was obtained by the grafting method. Clear differences in the characteristics of Mo species were observed (Raman and XRD) for catalysts supported on Si-MCM-41, Ti-MCM-41 and Si-MCM-41 covered with titania. The latter materials, prepared via post-synthetic route, show promising features as supports for Mo based hydrotreating catalysts.

Silica-Based, Cubic Mesostructures: Synthesis, Characterization and Relevance for Catalysis

We review the formation mechanism, synthetic history and catalytic applications of the cubic phases of mesoporous silica. MCM-48 and SBA-1, analogous to surfactant lyotropic liquid crystal phases, possess a three-dimensional pore array, a 15–30 A pore aperture and a narrow pore size distribution. Evidence for intermediate range order within the silicate walls based on PAS-FTIR spectra will be discussed. Isomorphic heteroatom substitution of aluminum and a number of transition metals has been achieved by both hydrothermal and post-synthetic methods in order to modify the surface activity of these materials. Modified materials containing fully oxidized, early transition metals were found to be catalytically active for photocatalytic reduction of CO2 with water as well as peroxidative oxidation and halogenation of large organic substrates.