Search NASA⌕ Search

SEARCH · Search NASA

Results for “mesoporous material”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Creation of discrete active site domains via mesoporous silica poly(styrene) composite materials for incompatible acid–base cascade reactions

This work highlights the design and synthesis of bifunctional mesoporous silicate – polymer composite dual acid–base supported cascade catalysts. Compartmentalization of the two incompatible active sites is sought by segregating acid sites on the silica surface, and base sites within polymer chains and/or polymer domains. The ability to isolate and segregate active sites via control of the mesoporous silica pore size and polymer molecular weight is probed with silica samples functionalized by a grafting-to process. Supplemental activator and reducing agent (SARA) atom transfer radical polymerization is used to synthesize random copolymers containing protected primary amines. Thiol–ene ‘click’ chemistry facilitates silica functionalization via a convergent approach, with the ene-functionalized polymer end group and silica-grafted thiols forming SBA/MCM-SH-poly(styrene-co-2-(4-vinylbenzyl)isoindoline-1,3-dione). Polymer deprotection and thiol oxidation produces primary amine/sulfonic acid containing composite catalysts. With the polymer supported Lewis base and silica grafted Brønsted acid, the two-step deacetalization – Knoevenagel condensation cascade is explored to assess the ability of these polymer/silica hybrids to segregate active sites, allowing both acid and base site accessibility. Six composite catalysts are synthesized and tested in individual and cascade reactions with kinetic results demonstrating that lower molecular weight SBA-15-P1 and MCM-41-P1 catalysts outperform (higher turnover frequencies and initial rates) their higher molecular weight analogues, as well as a polymer-free system containing molecular active sites dispersed on the silica surface. Higher molecular weight composite catalysts perform more poorly due to limited chain solubility, mass transfer limitations, and poor catalyst accessibility. In many cases, the polymer chains effectively thread into the mesopores, with higher molecular weight polymers leading to pore blockage and inhibited mass transfer.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Medium controlled aggregative growth as a key step in mesoporous silica nanoparticle formation

Near monodisperse mesoporous silica nanoparticles (MSN) represent a promising and rapidly developing type of mesoporous silica materials; however, the vast data on their synthesis remains unorganized and ill-understood. We systematically studied the formation of MSN under basic and neutral conditions using various temperatures, CTAB concentrations, hydrolyzing agents (triethanolamine, ammonia, phosphate buffers), and media with different colloidal stabilization properties (with ethanol as a cosolvent and monovalent salts). In the typical conditions for the preparation of stable MSN colloids, the particle size was controlled by colloidal stabilization by the medium (solvent type, ionic strength, and surfactant concentration) in agreement with the “aggregative growth” mechanism, rather than by solely the hydrolysis and condensation rates conventionally used for data interpretation in the classical nucleation theory. Medium properties (pH, ion types and concentration, polarity) also defined the efficiency of silica-surfactant cooperative self-assembly, which directly affected the porosity, mesopore size and pore wall thickness. Interestingly, this traditional silica-surfactant route showed a limited effect on the particle size, emphasizing the dominating role of colloidal stabilization in the studied reaction conditions. In situ pH measurements showed that every reaction medium has unique pH evolution profiles depending on the buffer capacity, hydrolysis and condensation rates. Reaction systems that fail to maintain the working pH can lead to non-porous products or undesired particle morphology and size distribution. The established particle formation mechanism allowed us to formulate comprehensive guidelines for preparing relatively concentrated colloids of near monodisperse (PDI 5–15%) mesoporous 30–700 nm silica spheres with variable porosity and mesopore size. Here, these findings will be particularly useful in designing new mesoporous silica-containing materials for biomedical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Mesoporous Crystalline Niobium Oxide with a High Surface Area: A Solid Acid Catalyst for Alkyne Hydration

A mesoporous crystalline niobium oxide with tunable pore sizes was synthesized via the sol–gel-based inverse micelle method. The material shows a surface area of 127 m 2 /g, which is the highest surface area reported so far for crystalline niobium oxide synthesized by soft template methods. The material also has a monomodal pore size distribution with an average pore diameter of 5.6 nm. A comprehensive characterization of niobium oxide was performed using powder X-ray diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, UV–vis, and X-ray photoelectron spectroscopy. The material acts as an environmentally friendly, solid acid catalyst toward hydration of alkynes under with excellent catalytic activity (99% conversion, 99% selectivity, and 4.39 h –1 TOF). Brønsted acid sites present in the catalyst were found to be responsible for the high catalytic activity. Lastly, the catalyst was reusable up to five cycles without a significant loss of the activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mesoporous metal titanates as multifunctional catalysts

The present disclosure relates to mesoporous metal titanate materials composition. Specifically, the present disclosure relates to a mesoporous metal titanate material composition that is active for multiple reactions, including aromatic alkylation, alkene coupling, alkene cyclization, alkyne oxidation, alcohol dehydrogenation reactions.

Suib, Steven L.↗
DOE OSTI2021

Simulations of the IR and Raman spectra of water confined in amorphous silica slit pores

Water in nano-scale confining environments is a key element in many biological, material, and geological systems. The structure and dynamics of the liquid can be dramatically modified under these conditions. Probing these changes can be challenging, but vibrational spectroscopy has emerged as a powerful tool for investigating their behavior. A critical, evolving component of this approach is a detailed understanding of the connection between spectroscopic features and molecular-level details. In this paper, this issue is addressed by using molecular dynamics simulations to simulate the linear infrared (IR) and Raman spectra for isotopically dilute HOD in D 2 O confined in hydroxylated amorphous silica slit pores. The effect of slit-pore width and hydroxyl density on the silica surface on the vibrational spectra is also investigated. The primary effect of confinement is a blueshift in the frequency of OH groups donating a hydrogen bond to the silica surface. This appears as a slight shift in the total (measurable) spectra but is clearly seen in the distance-based IR and Raman spectra. Analysis indicates that these changes upon confinement are associated with the weaker hydrogen-bond accepting properties of silica oxygens compared to water molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Probing electrolyte–silica interactions through simulations of the infrared spectroscopy of nanoscale pores

The structural and dynamical properties of nanoconfined solutions can differ dramatically from those of the corresponding bulk systems. Understanding the changes induced by confinement is central to controlling the behavior of synthetic nanostructured materials and predicting the characteristics of biological and geochemical systems. A key outstanding issue is how the molecular-level behavior of nanoconfined electrolyte solutions is reflected in different experimental, particularly spectroscopic, measurements. This is addressed here through molecular dynamics simulations of the OH stretching infrared (IR) spectroscopy of NaCl, NaBr, and NaI solutions in isotopically dilute HOD/D 2 O confined in hydroxylated amorphous silica slit pores of width 1–6 nm and pH ~2. In addition, the water reorientation dynamics and spectral diffusion, accessible by pump–probe anisotropy and two-dimensional IR measurements, are investigated. In this work, the aim is to elucidate the effect of salt identity, confinement, and salt concentration on the vibrational spectra. It is found that the IR spectra of the electrolyte solutions are only modestly blue-shifted upon confinement in amorphous silica slit pores, with both the size of the shift and linewidth increasing with the halide size, but these effects are suppressed as the salt concentration is increased. This indicates the limitations of linear IR spectroscopy as a probe of confined water. However, the OH reorientational and spectral diffusion dynamics are significantly slowed by confinement even at the lowest concentrations. The retardation of the dynamics eases with increasing salt concentration and pore width, but it exhibits a more complex behavior as a function of halide.

Mesoporous material↗
DOE OSTI2020

Regulating the Catalytic Activity of Pd Nanoparticles by Confinement in Ordered Mesoporous Supports

Studying structure-sensitive reactions requires the synthesis of catalytic nanoparticles with precisely controlled sizes. Here we demonstrate the facile production of size controlled Pd nanoparticles by confinement in the pores of mesoporous silica nanoparticles (MSN). We show that Pd particles 2.1 nm in size have a higher catalytic activity than larger nanoparticles for the Suzuki-Miyaura cross coupling between 4’-bromoacteophenone and phenyl boronic acid and for the hydrogenation of phenol in aqueous phase. The enhanced activity can be explained in terms of increased number of coordinatively unsaturated sites and higher back donation capacity of the small nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enhanced visible-light-assisted peroxymonosulfate activation on cobalt-doped mesoporous iron oxide for orange II degradation

Sulfate radical-based advanced oxidation processes (SR-AOP) attracted a lot of attention due to their capability and adaptability in wastewater treatment. Although heterogeneous cobalt-based catalysts have been extensively studied and have emerged superior for peroxymonosulfate (PMS) activation, leaching of cobalt is still a major concern. Herein, we report a photo-assisted PMS activation approach using cobalt doped mesoporous iron oxide with exceptional activity and stability up to 7 cycles with very low cobalt leaching (0.5 ppm). The highest activity was obtained by 1 mol % cobalt doped mesoporous iron oxide. Orange II dye was completely degraded by the reactive oxygen species (ROS) generated under visible light irradiation within 1 min. ROS were evaluated using two distinct techniques (Fluorescence probes and Electron Paramagnetic Resonance (EPR). ROS quenching experiments were also used to highlight the dominant pathway. This study correlates the structural and electronic changes induced with cobalt doping to the exceptional activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Adsorption and Catalytic Activity of Gold Nanoparticles in Mesoporous Silica: Effect of Pore Size and Dispersion Salinity

The assembled state of nanoparticles (NPs) within porous matrices plays a governing role in directing their biological, electronic, and catalytic properties. However, the effects of the spatial confinement and environmental factors, such as salinity, on the NP assemblies within the pores are poorly understood. In this study, we use adsorption isotherms, spectrophotometry, and small-angle neutron scattering to develop a better understanding of the effect of spatial confinement on the assembled state and catalytic performance of gold (Au) NPs in propylamine-functionalized SBA-15 and MCM-41 mesoporous silica materials (mSiO 2 ). We carry out a detailed investigation of the effect of pore diameter and ionic strength on the packing and spatial distribution of AuNPs within mSiO 2 to get a comprehensive insight into the structure, functioning, and activity of these NPs. We demonstrate the ability of the adsorbed AuNPs to withstand aggregation under high salinity conditions. We attribute the observed preservation of the adsorbed state of AuNPs to the strong electrostatic attraction between oppositely charged pore walls and AuNPs. The preservation of the structure allows the AuNPs to retain their catalytic activity for a model reaction in high salinity aqueous solution, here, the reduction of p-nitrophenol to p-aminophenol, which otherwise is significantly diminished due to bulk aggregation of the AuNPs. This fundamental study demonstrates the critical role of confinement and dispersion salinity on the adsorption and catalytic performance of NPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cobalt–niobium co-doping of indium oxide: structural and adsorption/catalytic properties for CO 2 valorization

The co-doping of the indium oxide structure with cobalt and niobium is attempted using a microemulsion method to produce high-surface-area, mesoporous, functional materials. The co-doping leads to a major nanometric bixbyite oxide phase, with both cations occupying cation positions and affecting the size and shape of the oxide entities. For specific cobalt to niobium atomic ratios, the presence of a second surface phase is encountered. Such a surface phase corresponds to an ill-defined indium hydroxide-type phase. The coexistence of the two phases is a unique phenomenon associated with the presence of both cations, which play a decisive role in promoting the CO 2 adsorption capability of the solids, as well as the valorization of the molecule under dual heat–light excitation. The co-doping of indium oxide thus appears to be a unique way to intensify the analogous thermal (classical) catalytic process for the elimination/valorization of carbon dioxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effects of pore size on water dynamics in mesoporous silica

Water confined in mesoporous silica plays a central role in its many uses ranging from gas sorption to nanoconfined chemical reactions. Here in this paper, the influence of pore diameter (2.5–5.4 nm) on water hydrogen bond (H-bond) dynamics in MCM41 and SBA15 mesoporous silicas is investigated using femtosecond infrared vibrational spectroscopy and molecular dynamics simulations on selenocyanate (SeCN-) anions dissolved in the pores. As shown recently, SeCN- spectral diffusion is a reliable probe of surrounding water H-bond structural motions. Additionally, the long CN stretch vibrational lifetime facilitates measurement of the full range of confined dynamics, which are much slower than in bulk water. The simulations shed light on quantitative details that are inaccessible from the spatially averaged observables. The dependence of SeCN- orientational relaxation and that of spectral diffusion on the distance from the silica interface are quantitatively described with an exponential decay and a smoothed step-function, respectively. The distance-dependence of both quantities is found to be independent of the diameter of the pores, and the spatial distribution of SeCN- is markedly non-uniform, reaching a maximum between the interface and the pore center. The results indicate that the commonly invoked two-state, or core–shell, model is a more appropriate description of spectral diffusion. Using these insights, we model the full time-dependence of the measured dynamics for all pore sizes and extract the “core” and “shell” dynamical correlation functions and SeCN- spatial probability distributions. The results are critically compared to those for water confined in reverse micelles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Surface structure of linear nanopores in amorphous silica: Comparison of properties for different pore generation algorithms

In this work, we compare the surface structure of linear nanopores in amorphous silica (a-SiO 2 ) for different versions of “pore drilling” algorithms (where the pores are generated by the removal of atoms from the preformed bulk a-SiO 2 ) and for “cylindrical resist” algorithms (where a-SiO 2 is formed around a cylindrical exclusion region). After adding H to non-bridging O, the former often results in a moderate to high density of surface silanol groups, whereas the latter produces a low density. The silanol surface density for pore drilling can be lowered by a final dehydroxylation step, and that for the cylindrical resist approach can be increased by a final hydroxylation step. In this respect, the two classes of algorithms are complementary. We focus on the characterization of the chemical structure of the pore surface, decomposing the total silanol density into components corresponding to isolated and vicinal mono silanols and geminal silanols. The final dehyroxylation and hydroxylation steps can also be tuned to better align some of these populations with the target experimental values.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Prototype equation of state for phase transition of confined fluids based on the generalized van der Waals partition function

A simple self-consistent prototype equation of state (EOS) based on the Generalized van der Waals (vdW) partition function has been demonstrated to describe the phase transition of simple fluids in nanopores with uniform size. Different from those commonly presented in the literature, the new EOS does not need an auxiliary equation that is conventionally applied to provide the capillary pressure derived from surface tension. Lastly, the encouraging performance of the EOS calls for further extension to applications with more complex fluids and porous media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Fluid Behavior in Nanoporous Silica

We investigate dynamics of water (H 2 O) and methanol (CH 3 OH and CH 3 OD) inside mesoporous silica materials with pore diameters of 4.0, 2.5, and 1.5 nm using low-field (LF) nuclear magnetic resonance (NMR) relaxometry. Experiments were conducted to test the effects of pore size, pore volume, type of fluid, fluid/solid ratio, and temperature on fluid dynamics. Longitudinal relaxation times (T 1 ) and transverse relaxation times (T 2 ) were obtained for the above systems. We observe an increasing deviation in confined fluid behavior compared to that of bulk fluid with decreasing fluid-to-solid ratio. Our results show that the surface area-to-volume ratio is a critical parameter compared to pore diameter in the relaxation dynamics of confined water. An increase in temperature for the range between 25 and 50°C studied did not influence T 2 times of confined water significantly. However, when the temperature was increased, T 1 times of water confined in both silica-2.5 nm and silica-1.5 nm increased, while those of water in silica-4.0 nm did not change. Reductions in both T 1 and T 2 values as a function of fluid-to-solid ratio were independent of confined fluid species studied here. The parameter T 1 /T 2 indicates that H 2 O interacts more strongly with the pore walls of silica-4.0 nm than CH 3 OH and CH 3 OD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Synthesis and Characterization of Mesoporous Silica Nanoparticles Loaded with Pt Catalysts

Coating the catalyst with a nanoporous layer has been demonstrated to be an effective approach to improve catalyst stability. Herein, we systematically investigate two types of core-shell mesoporous silica nanoparticles with a platinum nanocatalyst using a variety of characterization methods. One of the mesoporous particles has a unique amine ring structure in the middle of a shell (Ring-mSiO 2 /Pt-5.0/SiO 2 ), and the other one has no ring structure (mSiO 2 /Pt-5.0/SiO 2 ). Brunauer–Emmett–Teller/Barrett–Joyner–Halenda (BET/BJH) presented a similar surface area for both particles, and the pore size was 2.4 nm. Ultra-Small-Angle X-ray Scattering (USAXS)/ Small-Angle X-ray Scattering (SAXS) showed the size of mSiO 2 /Pt-5.0/SiO 2 and Ring-mSiO 2 /Pt-5.0/SiO 2 were 420 nm and 272 nm, respectively. It also showed that the ring structure was 30 nm above the silica core. Using high-resolution Transmission Electron Microscopy (TEM), it was found that the platinum nanoparticles are loaded evenly on the surface of the silica. In situ SAXS heating experiments and Thermogravimetric Analysis (TGA) indicated that the mSiO 2 /Pt-5.0/SiO 2 were more stable during the high temperature, while the Ring-mSiO 2 /Pt-5.0/SiO 2 had more change in the particle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A mechanistic study of mesoporous TiO 2 nanoparticle negative electrode materials with varying crystallinity for lithium ion batteries

Nanoscale oxide-based negative electrodes are of great interest for lithium ion batteries due to their high energy density, power density and enhanced safety. In this work, we conducted a case study on mesoporous TiO 2 nanoparticle negative electrodes with uniform size and varying crystallinity in order to investigate the trend in the electrochemical properties of oxide-based nanoscale negative electrodes with varying crystallinity. Furthermore, mesoporous solid spherical TiO 2 nanoparticles with a uniform particle size and varying crystallinity, i.e. , amorphous TiO 2 (A-TiO 2 ), partially crystalline TiO 2 (PC-TiO 2 ) and fully crystalline TiO 2 (FC-TiO 2 ) nanoparticles were studied. At low current rate (quasi steady-state), the specific capacity of the samples drops with the decrease of crystallinity. Ex situ synchrotron pair distribution function analysis reveals that the 1D zigzag Li ion diffusion pathway becomes expanded with the increase of crystallinity, which promotes ion mobility and charge storage. At high current rates (away from equilibrium states), however, the A-TiO 2 sample demonstrates slightly larger capacity than the FC-TiO 2 sample, both of which show larger capacities than that of the PC-TiO 2 sample. Both A-TiO 2 and FC-TiO 2 samples exhibit higher capacitive contribution to the charge storage and larger Li + diffusivity than those of the PC-TiO 2 sample, which explains their better rate capability. Moreover, the larger Li + diffusivity of the A-TiO 2 sample leads to the slightly larger specific capacity than the FC-TiO 2 sample at the highest current rate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗