Origins of visible-light emissions in porous silicon

The electronic and optical properties of porous silicon (p-Si) have been theoretically investigated using the minimal sp 3-basis set tight-binding method, with inclusion of second nearest neighbors and spin-orbit interactions. A hypothetical model of p-Si was assumed and calculations of band structures, with focus on bandgap energy E g, oscillator strength (OS) and recombination rate (RR), were carried varying the porosity and the mean distance d between pores. Similar calculations were also performed for other confined silicon nanostructures as hydrogen-passivated silicon nanocrystals (Si:H NCs) and silicon nanowires (Si-NWs). For these two latter systems, the results of E g versus the size d are found to be in excellent agreement with the available measured photoluminescence (PL) data of experimental p-Si samples. On one hand, the results show that sizes in the range d = 1-3 nm are responsible for emission in the visible-light energy window. On the other hand, our results also suggest that the emission properties of p-Si is strongly affected by the 2D and 3D quantum confinement (QC) characters of the involved band edge states. Furthermore, our theoretical values for the RR are found to be larger and closer to the experimental ones in the case of Si:H NCs with respect to the case of Si-NWs. This fact suggests that the intense measured PL features are mainly due to 3D confined nanostructures. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electrocatalytic CO₂ Reduction: From Homogeneous Catalysts to Heterogeneous-Based Reticular Chemistry

CO2, emitted mainly from fossil fuel combustion, is one of the major greenhouse gases. CO2 could be converted into more valuable chemical feedstocks including CO, HCOOH, HCHO, CH3OH, or CH4. To reduce CO2, catalysts were designed and their unique characteristics were utilized based on types of reaction processes, including catalytic hydrogenation, complex metal hydrides, photocatalysis, biological reduction, and electrochemical reduction. Indeed, the electroreduction method has received much consideration lately due to the simple operation, as well as environmentally friendly procedures that need to be optimized by both of the catalysts and the electrochemical process. In the past few decades, we have witnessed an explosion in development in materials science—especially in regards to the porous crystalline materials based on the strong covalent bond of the organic linkers containing light elements (Covalent organic frameworks, COFs), as well as the hybrid materials that possess organic backbones and inorganic metal-oxo clusters (Metal-organic frameworks, MOFs). Owing to the large surface area and high active site density that belong to these tailorable structures, MOFs and COFs can be applied to many practical applications, such as gas storage and separation, drug release, sensing, and catalysis. Beyond those applications, which have been abundantly studied since the 1990s, CO2 reduction catalyzed by reticular and extended structures of MOFs or COFs has been more recently turned to the next step of state-of-the-art application. In this perspective, we highlight the achievement of homogeneous catalysts used for CO2 electrochemical conversion and contrast it with the advances in new porous catalyst-based reticular chemistry. We then discuss the role of new catalytic systems designed in light of reticular chemistry in the heterogeneous-catalyzed reduction of CO2

Investigation of crucial synthesis parameters of rich Al-MTT framework zeolite: Toward more determination for synthesis zone of SSZ-32

Synthesis of zeolite materials using small neutral amines has received more attention recently because of the possibility to produce small crystals and lower price as compared other types of organic structured directing agents (OSDA). For the first time, a precise synthesis zone of SSZ-32 is reported without seeds. Isobutylamine was applied as an OSDA to synthesize SSZ-32 zeolite (MTT framework). The main synthesis parameters such as rotation speed, synthesis time and Si/Al ratio were carefully investigated. The synthesis process was very sensitive to these studied parameters. The SSZ-32 crystals cannot be synthesized in less than 6 days with rotation speed of 35 rpm in a dynamic crystallization. The Si/Al ratio window was narrow as a ratio higher than 27 yielded to form an amorphous powder and quartz crystals. The smallest crystal size produced using isobutylamine was approximately 200 nm, which will be helpful in the elimination of diffusion limitation in the one-dimensional zeolite. (C) 2016 Elsevier Inc. All rights reserved

Soluble silicon nanoparticles–polyaniline capsules for biosensing and imaging

We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications

Highly luminescent PANI-Si nanoparticle capsules using miniemulsion

We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications

Highly luminescent PANI-Si nanoparticle capsules using miniemulsion

We used miniemulsion to synthesize novel water-soluble dispersion of nanocapsules with a polyaniline (PANI) shell and luminescent ultrasmall Si nanoparticle core with diameters of 50–300 nm. The capsules are functionalized with aromatic sulfonic acid. The capsules may be reconstituted in thin films or structured surfaces. The stability of the luminescence and dispersion of the capsules is studied under a wide range of pH conditions. The multiplicity of nanoparticles in the core provides highly amplified and reproducible signal for luminescence-based imaging using standard fluorescence microscopy, while the PANI shell allows a variety of routes for functionalization as well as electrical interrogation, which enables a wide range of biosensing/imaging applications