Microporous Organosilica Research Articles

Laminar MoS2 Nanosheets Embedded into Organosilica Membranes for Efficient H2 Separation

Two-dimensional (2D) molybdenum disulfide (MoS2) with a unique action on H2 was incorporated into 1,2-bis(triethoxysilyl)ethane (BTESE)-derived bridged microporous organosilica networks to form a composite membrane for H2 separation by a sol–gel method. Due to their opposite ζ-potentials, a continuous surface without lamellar boundary defects was formed between BTESE sols derived by the hydrolysis–polymerization reaction and MoS2 nanosheets. When the MoS2 content increased in BTESE networks, the H2 permeance showed an overall increasing trend in the range of 1.85–2.89 × 10–7 mol·m–2 s–1 Pa–1 (552–864 GPU), which was higher than that of pristine BTESE membrane with the H2 permeance of 491 GPU. In addition, optimized MoS2/BTESE membranes showed a much higher H2/N2 permselectivity of 129 than that of the pristine BTESE membrane of 17 at 100 °C. The synergistic effect of BTESE and MoS2 nanosheets plays an important role. Through adsorption isotherm test and diffusivity as well as energy calculation, BTESE networks became denser by nonporous MoS2 addition that prevented N2 from passing, while H2 was promoted with excellent adsorption on charged edges of MoS2, resulting in improved H2 separation performance both in permeance and selectivity. This provides an attractive mechanism for hydrogen separation.

Reverse osmosis and pervaporation of organic liquids using organosilica membranes: Performance analysis and predictions

AbstractThis study systematically investigated and modeled the organic solvent reverse osmosis (OSRO) and pervaporation (PV) performances of bis(triethoxysiyl)acetylene (BTESA)‐derived microporous organosilica membranes with different microstructures and permeation properties. BTESA membranes calcined at a low temperature of 100°C exhibited great promise for utility in the challenging OSRO separation of methanol/organic azeotropes such as methanol/toluene and methanol/methyl tert‐butyl ether and demonstrated ultrahigh values for both permeating flux and rejection together with good operation stability. In addition, a generalized solution‐diffusion model enabled a suitable description of the permeation behaviors of organic solvent molecules through the BTESA membranes irrespective of the use of either OSRO or PV modalities, which allowed us to predict the OSRO performance via PV, and vice versa.

Tuning the Pore Structures of Organosilica Membranes for Enhanced Desalination Performance via the Control of Calcination Temperatures.

Microporous organosilica membranes based on 1,2-bis(triethoxylsilyl)ethane (BTESE) were fabricated via an acid-catalyzed sol-gel technique. In the preparation process, the calcination temperature plays a significant role in structural and surface properties of the organosilica networks. With an increase in calcination temperature, the surface hydrophilicity decreased due to the enhanced condensation of Si-OH groups in the networks. N2 adsorption results suggest that the pore structures of BTESE membranes was clearly dependent on the calcination temperature. The pore sizes of the membranes were quantitatively determined by using the Normalized Knudsen-based permeance (NKP) model. In pervaporation tests, the membranes with higher calcination temperatures showed higher salt rejections and lower water permeances, which was attributed to the changes in pore size and surface chemistry of pore walls. The BTESE membranes calcined at 200 °C exhibited superior hydrothermal stability in temperature cycles up to 70 °C and high reproducibility in concentration cycles with NaCl concentrations of 0.2–13 wt%, showing great promise for desalination applications of high-salinity water.

One-pot synthesis of a microporous organosilica-coated cisplatin nanoplatform for HIF-1-targeted combination cancer therapy.

Nanoparticle formulations have proven effective for cisplatin delivery. However, the development of a versatile nanoplatform for cisplatin-based combination cancer therapies still remains a great challenge.Methods: In this study, we developed a one-pot synthesis method for a microporous organosilica shell-coated cisplatin nanoplatform using a reverse microemulsion method, and explored its application in co-delivering acriflavine (ACF) for inhibiting hypoxia-inducible factor-1 (HIF-1).Results: The resulting nanoparticles were tunable, and they could be optimized to a monodisperse population of particles in the desired size range (40-50 nm). In addition, organic mPEG2000-silane and tetrasulfide bond-bridged organosilica were integrated into the surface and silica matrix of nanoparticles for prolonged blood circulation and tumor-selective glutathione-responsive degradation, respectively. After reaching the tumor sites, cisplatin induced cancer cell death and activated HIF-1 pathways, resulting in acquired drug resistance and tumor metastasis. To address this issue, ACF was co-loaded with cisplatin to prevent the formation of HIF-1α/β dimers and suppress HIF-1 function. Hence, the efficacy of cisplatin was improved, and cancer metastasis was inhibited.Conclusion: Both in vitro and in vivo results suggested that this core-shell nanostructured cisplatin delivery system represented a highly efficacious and promising nanoplatform for the synergistic delivery of combination therapies involving cisplatin.

Fabrication of La/Y-codoped microporous organosilica membranes for high-performance pervaporation desalination

La/Y-codoped microporous organosilica membranes were successfully fabricated by sol-gel procedure with 1,2-bis(triethoxysilyl)ethane (BTESE) as silica precursor for efficient desalination. The rare earth elements were confirmed to be doped into silica frameworks during the sol-gel procedure by various characterizations, which would decrease particles size and size distribution of BTESE-derived sols and form hydrothermally stable Si–O–RE (RE for La and Y) bonds. It could significantly influence membrane surface morphology, microstructure properties and hydrophilcity of La/Y-codoped membranes, and then improve their desalination performance. Under the optimized preparation conditions, La25Y75-SiO2 (La:Y = 25:75, mol%) membranes exhibited the highest water flux of 10.3 kg m−2 h−1 and NaCl rejection of nearly 100% towards 3.5 wt% NaCl feed solution even at room temperature of 25 °C. It was attributed to strongest hydrophilcity, finest microstructure, and lowest mass resistance of water permeation for La25Y75-SiO2 membranes. Moreover, such these organosilica membranes demonstrated good stability for 200 h simulated seawater desalination tests without any significant changes of separation performance and promising hydrothermal durability under various salts solutions with different concentrations at 25–60 °C.

Removal of S-metolachlor herbicide from aqueous solutions by meso and microporous organosilica materials

Abstract The adsorption of S-metolachlor herbicide from aqueous solution by benzenesilica materials was studied. The materials were synthesized with 1,4-bis(triethoxysilyl)benzene as organosilica precursor and Brij 76 and Pluronic P123 as surfactants. Additionally, 1,3,5-triisopropylbenzene (TPB) was used as porogen to produce microporosity. Those materials obtained by Brij-76 and P123 showed well-structured ordering. However, a disordered microporous benzenesilica material was obtained in presence of P123 and TPB. All materials proved to be efficient adsorbents for S-metolachlor. Among them, the material synthesized with Brij 76 showed the highest adsorption capacity due to its ordered structure and, mainly, to its higher proportion of mesopores.

Fluorine Doping of Microporous Organosilica Membranes for Pore Size Control and Enhanced Hydrophobic Properties.

Fluorine-doped organosilica membranes for gas and pervaporation (PV) separation were fabricated using a sol–gel method. NH4F and bis(triethoxysilyl)methane (BTESM) were selected as the dopant and Si precursor, respectively, for the fabrication of fluorine-doped organosilica membranes. Doping with fluorine was evaluated for its effect on the physicochemical properties of organosilica (hydrophobicity/hydrophilicity and network size). Fluorine doping dramatically eliminated the formation of Si–OH groups in the sol, so that the condensation of Si–OH groups during the calcination process was suppressed. It is possible that fluorine doping enlarged the network pore sizes in organosilica, because the F-BTESM (F/Si = 1/9) membrane showed superior He and H2 permeance with a low H2/N2 permeance ratio that corresponded to the network pore size by comparison with an undoped BTESM membrane. The F-BTESM (F/Si = 1/9) membranes clearly showed a high level of C3H6 permeance (>3.0 × 10–7 mol m–2 s–1 Pa–1) with a high C3H6/SF6 permeance ratio (∼250), which suggests that the network pore size of F-BTESM is suitable for the separation of large molecules such as hydrocarbon gases (C3/C4, C4 isomer, etc.). Organosilica membranes both with and without fluorine doping showed stable PV performance because of the fact that H2O permeance and each permeance ratio under different separation systems was approximately constant over 10 h at 70 °C. Fluorine doping enhanced the hydrophobic nature of the organosilica, which was confirmed by the H2O adsorption and PV properties.

Diethylenedioxane-bridged microporous organosilica membrane for gas and water separation

Abstract A new dioxane-bridged alkoxysilane, 2,5-bis[2-(triethoxysilyl)ethyl]-1,4-dioxane (BTES-ED), was synthesized as a precursor of organically bridged silica membrane to investigate the effects of the 1,4-dioxane ring as a rigid and polar spacer. The monomer was polymerized by the sol-gel process to give the gels in film, powder, and membrane forms. Nitrogen adsorption measurement of the gel powder showed the type-I adsorption/desorption isotherm, suggesting that the gel possessed a microporous structure with pore size distribution ranging from approximately 0.8 to 1.6 nm. Reflecting microporosity, the membrane exhibited selective gas permeation properties (H2/SF6 permeance ratio = ca. 1900) based on molecular sieving effects. Reverse osmosis experiments were conducted using a 2000 ppm NaCl aqueous solution at an operation pressure of 1.0 MPa, revealing water desalination properties with the water permeance of 1.84 × 10−13 m3/m2·s·Pa and the NaCl rejection of 98.5%. These results are discussed in comparison with the results of other bridged silica membranes reported previously. The 2,5-diethylene-1,4-dioxane bridging unit is rigid and polar, thereby contributing to improving gas and water separation performance.

Long-term flexibility-based structural evolution and condensation in microporous organosilica membranes for gas separation

Long-term ongoing consolidation is unravelled for microporous hybrid organosilica membranes, showing chemical, structural and micropore evolution.

Tailoring the Separation Behavior of Polymer-Supported Organosilica Layered-Hybrid Membranes via Facile Post-Treatment Using HCl and HN3 Vapors.

A promising layered-hybrid membrane consisting of a microporous organosilica active layer deposited onto a porous polymer support was prepared via a facile sol-gel spin-coating process. Subsequently, the pore sizes and structures of the organosilica top layers on the membrane surface were tuned at mild temperature combined with vapor treatment from either hydrochloric acid (HVT) or ammonia (AVT), thereby tailoring the desalination performance of the membranes during reverse osmosis (RO) processing. The effects of HVT and AVT on the pore size, structure, and morphology of organosilica layers and on the separation performances of membranes were investigated in detail. We confirmed that both HVT and AVT processes accelerated the condensation of silanol (Si-OH) in the organosilica layer, which led to dense silica networks. The layered-hybrid membranes after HVT showed an improved salt rejection and reduced water flux, while membranes after AVT exhibited a decrease in both salt rejection and water permeability. We found that HVT gave rise to smoother and denser organosilica layers, while AVT produced large voids and formed pinholes due to Ostwald ripening. These conclusions were supported by a comparative analysis of the results obtained via FTIR, TG-MS, SPM, and RO desalination.

Structure–property tuning in hydrothermally stable sol–gel-processed hybrid organosilica molecular sieving membranes

Supported microporous organosilica membranes made from bridged silsesquioxane precursors by an acid-catalyzed sol–gel process have demonstrated a remarkable hydrothermal stability in pervaporation and gas separation processes, making them the first generation of ceramic molecular sieving membranes with sufficient performance under industrially relevant conditions. The commercial availability of various α,ω-bis(trialkoxysilyl)alkane and 1,4-bis(trialkoxysilyl)benzene precursors facilitates the tailoring of membrane properties like pore size and surface chemistry via the choice of precursor(s) and process variables. Here, we describe the engineering of sols for making supported microporous thin films, discuss the thermal and hydrothermal stability of microporous organosilicas and give a short overview of the developments and applications of these membranes in liquid and gas separation processes since their first report in 2008.

Modified gas‐translation model for prediction of gas permeation through microporous organosilica membranes

A modified gas‐translation (GT) model was applied for the theoretical analysis of gas permeation through microporous organosilica membranes derived from bis(triethoxysilyl)ethane (BTESE) via a sol–gel method using different water/alkoxide molar ratios. The pore sizes of BTESE‐derived membranes were quantitatively determined by normalized Knudsen‐based permeance analysis, which was based on a modified‐GT model, using experimentally obtained permeances of He, H2, N2, C3H8, and SF6. The pore sizes of BTESE‐derived membranes were successfully controlled from 0.65 to 0.46 nm by increasing the H2O/BTESE ratio from 6 to 240. Furthermore, theoretical correlations of all possible pairs of permeance ratios were calculated based on the modified‐GT model. The experimental data were in good agreement with the theoretical correlation curves, indicating that the modified‐GT model can clearly explain gas permeation mechanisms through microporous membranes, and, thus, can be used to predict the gas permeation properties for these membranes. © 2014 American Institute of Chemical Engineers AIChE J 60: 4199–4210, 2014

Modeling water flux and salt rejection of mesoporous γ-alumina and microporous organosilica membranes

The water and ion transport through a mesoporous γ-alumina membrane and a microporous organosilica membrane was simulated using the extended Nernst–Planck equation combined with models for Donnan, steric and dielectric interfacial exclusion mechanisms. Due to the surface charge within the pore, the electroviscous effect was introduced in the model. The modified model fits well the rejection and permeability data for both membranes. The organosilica membrane shows a higher selectivity compared to the γ-alumina membrane, but the permeate flux is lower. At low ionic strength the electroviscous effect lowers the water flux through the γ-alumina membrane. The electroviscous effect is negligible for the organosilica membrane because its absolute surface potential (~20mV) is low compared to the γ-alumina membrane (~60mV). The simulation shows that the electroviscous effect should be included for the membranes with high surface potential (>20mV) and a pore size below 2–5 times of the electroviscous double layer thickness.

New insights into the microstructure-separation properties of organosilica membranes with ethane, ethylene, and acetylene bridges.

Microporous organosilica membranes with ethane, ethylene, and acetylene bridges have been developed and the extensive microstructural characterization has been discussed in relation with separation properties of the membrane. The organosilica network structure and the membrane performances can be controlled by adjusting the flexibility, size, and electronic structure of the bridging groups. A relatively narrow size distribution was obtained for the novel acetylene-bridged sol by optimizing the sol synthesis. Incorporation of larger rigid bridges into organosilica networks resulted in a looser microstructure of the membrane, which was quantitatively evaluated by N2 sorption and positron annihilation lifetime (PAL) measurements. Molecular weight cutoff (MWCO) measurements indicated that the acetylene-bridged membrane had a larger effective separation pore size than ethane- and ethylene-bridged membranes, leading to a relatively low NaCl rejection in reverse osmosis. In quantum chemical calculations, a more open pore structure and increased polarization was observed for the acetylene-bridged networks, which led to a significant improvement in water permeability. The present study will offer new insight into design of high-performance molecular separation membranes.

Tailoring the Affinity of Organosilica Membranes by Introducing Polarizable Ethenylene Bridges and Aqueous Ozone Modification

Bis(triethoxysilyl)ethylene (BTESEthy) was used as a novel precursor to develop a microporous organosilica membrane via the sol-gel technique. Water sorption measurements confirmed that ethenylene-bridged BTESEthy networks had a higher affinity for water than that of ethane-bridged organosilica materials. High permeance of CO2 with high CO2/N2 selectivity was explained relative to the strong CO2 adsorption on the network with π-bond electrons. The introduction of polarizable and rigid ethenylene bridges in the network structure led to improved water permeability and high NaCl rejection (>98.5%) in reverse osmosis (RO). Moreover, the aqueous ozone modification promoted significant improvement in the water permeability of the membrane. After 60 min of ozone exposure, the water permeability reached 1.1 × 10(-12) m(3)/(m(2) s Pa), which is close to that of a commercial seawater RO membrane. Meanwhile, molecular weight cutoff measurements indicated a gradual increase in the effective pore size with ozone modification, which may present new options for fine-tuning of membrane pore sizes.

Influence of sol–gel process parameters on the micro-structure and performance of hybrid silica membranes

A facile, versatile and reproducible sol–gel process to make microporous organosilica membranes by using 1,2-bis (triethoxysilyl) ethane (BTESE) as a precursor is reported. The influence of process parameters on sol particle size and rheology of BETSE-derived sols was investigated to produce defect-free composite membranes by a single dipping procedure and subsequent calcination. The microporous structure of a BTESE layer on mesoporous alumina supports enabled selective molecular sieving of gas molecules. Single gas permeation (SGP) experiments, performed at 200°C, showed that a H2/CH4 permselectivity of 24 was reproducibly achieved. No SF6 gas permeance through these membranes proof the presence of a defect-free microstructure. SEM cross-section analysis showed a hybrid selective layer with a thickness dependent on the sol precursor concentration.

Development of Robust Organosilica Membranes for Reverse Osmosis

Hybrid organically bridged silica membranes have attracted considerable attention because of their high performances in a variety of applications. Development of robust reverse osmosis (RO) membranes to withstand aggressive operating conditions is still a major challenge. Here, a new type of microporous organosilica membrane has been developed and applied in reverse osmosis. Sol-gel derived organosilica RO membranes reject isopropanol with rejection higher than 95%, demonstrating superior molecular sieving ability for neutral solutes of low molecular weight. Due to the introduction of an inherently stable hybrid network structure, the membrane withstands higher temperatures in comparison with commercial polyamide RO membranes, and is resistant to water to at least 90 °C with no obvious changes in filtration performance. Furthermore, both an accelerated chlorine-resistance test and Fourier transform infrared analysis confirm excellent chlorine stability in this material, which demonstrates promise for a new generation of chlorine-resistant RO membrane materials.

New organic–inorganic hybrid microporous organosilica having high metal ion adsorption capacity

A new microporous organic-inorganic hybrid organosilica LHMM-2 containing a bis(propyliminomethyl)benzene moiety inside the framework has been synthesized hydrothermally without using any template or structure-directing agent. Powder XRD and TEM image analyses suggest a new disordered microporous structure with pores of dimension ca. 0.54 nm, and (13)C and (29)Si MAS NMR and spectroscopic results indicate the presence of bridging organic bis(propyliminomethyl)benzene moiety in this framework. TPD-NH(3) results suggested that nearly 5 times as much bis(propyliminomethyl)benzene moiety is located inside the micropore walls (matrix) than in the surface of the pores. LHMM-2 shows very high adsorption capacity for metal cations like Fe(3+), Cu(2+) and Zn(2+).

Acidic Character and Catalytic Activity of Sulpho-Functionalized Porous Silica with an Ordered Structure

Microporous organosilica incorporating various amounts of sulpho groups (MS-SO3H) was prepared by hydrolysis and the co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS), followed by oxidation of the thiol group. The resulting microporous silica had a regular porous structure similar to that of the mesoporous silica MCM-41, as shown by X-ray diffraction and nitrogen adsorption measurements. Ammonia adsorption microcalorimetry indicated that a large number of sulpho groups were successfully incorporated into the microporous silica framework. The sulpho group-incorporating microporous silica (MS-SO3H) exhibited catalytic activity towards the isomerization of but-1-ene to cis- and trans-but-2-ene via an acid catalysis mechanism.