Tailoring the microstructure and permeation properties of bridged organosilica membranes via control of the bond angles

Novel Silica Hybrid Xerogels Prepared by Co-Condensation of TEOS and ClPhTEOS: A Chemical and Morphological Study

The search for new materials with improved properties for advanced applications is, nowadays, one of the most relevant and booming fields for scientists due to the environmental and technological needs of our society. Within this demand, hybrid siliceous materials, made out of organic and inorganic species (ORMOSILs), have emerged as an alternative with endless chemical and textural possibilities by incorporating in their structure the properties of inorganic compounds (i.e., mechanical, thermal, and structural stability) in synergy with those of organic compounds (functionality and flexibility), and thus, bestowing the material with unique properties, which allow access to multiple applications. In this work, synthesis using the sol-gel method of a series of new hybrid materials prepared by the co-condensation of tetraethoxysilane (TEOS) and 4-chlorophenyltriethoxysilane (ClPhTEOS) in different molar ratios is described. The aim of the study is not only the preparation of new materials but also their characterization by means of different techniques (FT-IR, ²⁹Si NMR, X-ray Diffraction, and N₂/CO₂ adsorption, among others) to obtain information on their chemical behavior and porous structure. Understanding how the chemical and textural properties of these materials are modulated with respect to the molar percentage of organic precursor will help to envisage their possible applications: From the most conventional such as catalysis, adsorption, or separation, to the most advanced in nanotechnology such as microelectronics, photoluminescence, non-linear optics, or sensorics.

Network Structure Engineering of Organosilica Membranes for Enhanced CO2 Capture Performance

The membrane separation process for targeted CO2 capture application has attracted much attention due to the significant advantages of saving energy and reducing consumption. High-performance separation membranes are a key factor in the membrane separation system. In the present study, we conducted a detailed examination of the effect of calcination temperatures on the network structures of organosilica membranes. Bis(triethoxysilyl)acetylene (BTESA) was selected as a precursor for membrane fabrication via the sol-gel strategy. Calcination temperatures affected the silanol density and the membrane pore size, which was evidenced by the characterization of FT-IR, TG, N2 sorption, and molecular size dependent gas permeance. BTESA membrane fabricated at 500 °C showed a loose structure attributed to the decomposed acetylene bridges and featured an ultrahigh CO2 permeance around 15,531 GPU, but low CO2/N2 selectivity of 3.8. BTESA membrane calcined at 100 °C exhibited satisfactory CO2 permeance of 3434 GPU and the CO2/N2 selectivity of 22, displaying great potential for practical CO2 capture application.

Recent Progress in a Membrane-Based Technique for Propylene/Propane Separation

The similar physico-chemical properties of propylene and propane molecules have made the separation process of propylene/propane challenging. Membrane separation techniques show substantial prospects in propylene/propane separation due to their low energy consumption and investment costs, and they have been proposed to replace or to be combined with the conventional cryogenic distillation process. Over the past decade, organosilica membranes have attracted considerable attention due to their significant features, such as their good molecular sieving properties and high hydrothermal stability. In the present review, holistic insight is provided to summarize the recent progress in propylene/propane separation using polymeric, inorganic, and hybrid membranes, and a particular inspection of organosilica membranes is conducted. The importance of the pore subnano-environment of organosilica membranes is highlighted, and future directions and perspectives for propylene/propane separation are also provided.

Impacts of Green Synthesis Process on Asymmetric Hybrid PDMS Membrane for Efficient CO2/N2 Separation

The effects of green processes in hybrid polydimethylsiloxane (PDMS) membranes on CO₂ separation have received little attention to date. The effective CO₂ separation of the membranes is believed to be controlled by the reaction and curing process. In this study, hybrid PDMS membranes were fabricated on ceramic substrates using the water-in-emulsion method and evaluated for their gas transport properties. The effects of the tetraethylorthosilicate (TEOS) concentration and curing temperature on the morphology and CO₂ separation performance were investigated. The viscosity measurement showed that, at specific reaction times, it is benefit beneficial to fabricate the symmetric hybrid PDMS membranes with a uniform and dense selective layer on the substrate. Moreover, the a high TEOS concentration can decrease the reaction time and obtain create the a fully crosslinked structure, allowing more efficient CO₂/N₂ separation. The separation performance was furtherly improved with in the membrane prepared at a high curing temperature of 120 °C. The developed membrane shows excellent CO₂/N₂ separation with a CO₂ permeance of 27.7 ± 1.3 GPU and a CO₂/N₂ selectivity of 10.3 ± 0.3. Moreover, the membrane shows a stable gas separation performance of up to 5 bar of pressure.

Microporous framework membranes for precise molecule/ion separations

Microporous framework membranes such as metal-organic framework (MOF) membranes and covalent organic framework (COF) membranes are constructed by the controlled growth of small building blocks with large porosity and permanent well-defined micropore structures, which can overcome the ubiquitous tradeoff between membrane permeability and selectivity; they hold great promise for the enormous challenging separations in energy and environment fields. Therefore, microporous framework membranes are endowed with great expectations as next-generation membranes, and have evolved into a booming research field. Numerous novel membrane materials, versatile manipulation strategies of membrane structures, and fascinating applications have erupted in the last five years. First, this review summarizes and categorizes the microporous framework membranes with pore sizes lower than 2 nm based on their chemistry: inorganic microporous framework membranes, organic-inorganic microporous framework membranes, and organic microporous framework membranes, where the chemistry, fabrications, and differences among these membranes have been highlighted. Special attention is paid to the membrane structures and their corresponding modifications, including pore architecture, intercrystalline grain boundary, as well as their diverse control strategies. Then, the separation mechanisms of membranes are covered, such as diffusion-selectivity separation, adsorption-selectivity separation, and synergetic adsorption-diffusion-selectivity separation. Meanwhile, intricate membrane design to realize synergistic separation and some emerging mechanisms are highlighted. Finally, the applications of microporous framework membranes for precise gas separation, liquid molecule separation, and ion sieving are summarized. The remaining challenges and future perspectives in this field are discussed. This timely review may provide genuine guidance on the manipulation of membrane structures and inspire creative designs of novel membranes, promoting the sustainable development and steadily increasing prosperity of this field.

Role of the Plasma Activation Degree on Densification of Organosilicon Films

The possibility of controlling the density of organosilicon films was investigated by tuning the plasma activation degree without providing extra energy to the structure, as usually reported in the literature. For this purpose, thin films were deposited in plasmas fed with hexamethyldisiloxane/Ar mixtures at a total pressure of 9.5 Pa. The power of the radiofrequency excitation signal, P, ranged from 50 to 300 W to alter the average energy of the plasma species while the electrical configuration was chosen to avoid direct ion bombardment of the growing films. In this way, it was possible to evaluate the effect of P on the film properties. Thickness and deposition rate were derived from profilometry data. X-ray energy dispersive and infrared spectroscopies were, respectively, applied to analyze the chemical composition and molecular structure of the layers. Surface topography and roughness were determined by atomic force microscopy while nanoindentation was used to evaluate the mechanical properties of the films. From electrochemical impedance spectroscopy the total resistance to the flow of electrolyte species was derived. The main alteration observed in the structure with changing P is related to the proportion of the methyl functional which remains connected to the Si backbone. Chain crosslinking and film density are affected by this structural modification induced by homogeneous and heterogeneous plasma reactions. The density increase resulted in a film with hardness comparable to that of the silica and more resistant to the permeation of oxidative species, but preserving the organosilicon nature of the structure.

Organosilica-Based Membranes in Gas and Liquid-Phase Separation

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with steam or a liquid-phase under high temperature. These attributes make them outperform pure silica membranes. In this review, types of precursors, preparation method, and synthesis factors for the construction of organosilica membranes are covered. The effects that these factors exert on characteristics and performance of these membranes are also discussed. The incorporation of metals, alkoxysilanes, or other functional materials into organosilica membranes is an effective and simple way to improve their hydrothermal stability and achieve preferable chemical properties. These hybrid organosilica membranes have demonstrated effective performance in gas and liquid-phase separation.