Tailored Mesoporous Silicas: From Confinement Effects to Catalysis

2009 ◽  
Vol 1217 ◽  
Author(s):  
A. C. Buchanan, III ◽  
Michelle K. Kidder
Keyword(s):  
Chemical Reactivity ◽  
High Surface ◽  
High Surface Area ◽  
Mesoporous Silicas ◽  
Surface Immobilization ◽  
Product Selectivity ◽  
Aryl Ether ◽  
Ether Linkage ◽  
Synthetic Methodologies ◽  
The Impact

AbstractOrdered mesoporous silicas continue to find widespread use as supports for diverse applications such as catalysis, separations, and sensors. They provide a versatile platform for these studies because of their high surface area and the ability to control pore size, topology, and surface properties over wide ranges. Furthermore, there is a diverse array of synthetic methodologies for tailoring the pore surface with organic, organometallic, and inorganic functional groups. In this paper, we will discuss two examples of tailored mesoporous silicas and the resultant impact on chemical reactivity. First, we explore the impact of pore confinement on the thermochemical reactivity of phenethyl phenyl ether (PhCH2CH2OPh, PPE), which is a model of the dominant β-aryl ether linkage present in lignin derived from woody biomass. The influence of PPE surface immobilization, grafting density, silica pore diameter, and presence of a second surface-grafted inert “spacer” molecule on the product selectivity has been examined. We will show that the product selectivity can be substantially altered compared with the inherent gas-phase selectivity. Second, we have recently initiated an investigation of mesoporous silica supported, heterobimetallic oxide materials for photocatalytic conversion of carbon dioxide. Through surface organometallic chemistry, isolated M-O-M’ species can be generated on mesoporous silicas that, upon irradiation, form metal to metal charge transfer bands capable of converting CO2 into CO. Initial results from studies of Ti(IV)-O-Sn(II) on SBA-15 will be presented.

Gold nanoparticles grown on hydrophobic and texturally-tunable PDMS-like framework

2021 ◽  
Author(s):  
Marieme Kacem ◽  
Nadia Katir ◽  
Jamal El Haskouri ◽  
Abdellatif Essoumhi ◽  
Abdelkrim El Kadib
Keyword(s):  
Gold Nanoparticles ◽  
Surface Area ◽  
Metal Clusters ◽  
High Surface ◽  
High Surface Area ◽  
Mesoporous Silicas

Mesoporous silicas are among the most suitable high-surface area solids to support small-sized metal clusters and nanoparticles. Unfortunately, the instability of silica in water constitutes a serious impedement for its...

Influence of nanoparticles on the polymer-conditioned dewatering of wastewater sludges

2013 ◽  
Vol 67 (9) ◽  
pp. 2117-2123
Author(s):  
N. J. Boyle ◽  
G. M. Evans
Keyword(s):  
Activated Sludge ◽  
Titanium Dioxide Nanoparticles ◽  
Low Cost ◽  
High Surface ◽  
High Surface Area ◽  
Wastewater Sludge ◽  
Small Scale ◽  
Sludge Dewatering ◽  
Solids Content ◽  
The Impact

The effect of using small-scale, high surface area, nanoparticles to supplement polymer-conditioned wastewater sludge dewatering was investigated. Aerobically digested sludge and waste activated sludge sourced from the Hunter Valley, NSW, Australia, were tested with titanium dioxide nanoparticles. The sludge samples were dosed with the nanoparticles in an attempt to adsorb a component of the charged biopolymer surfactants present naturally in sludge. The sludge was conditioned with a cationic polymer. The dewatering characteristics were assessed by measuring the specific resistance to filtration through a modified time-to-filter testing apparatus. The solids content of the dosed samples was determined by a mass balance and compared to the original solids content in the activated sludge. Test results indicated that nanoparticle addition modified the structure of the sludge and provided benefits in terms of the dewatering rate. The samples dosed with nanoparticles exhibited faster water removal, indicating a more permeable filter cake and hence more permeable sludge. A concentration of 2–4% nanoparticles was required to achieve a noticeable benefit. As a comparison, the sludge samples were also tested with a larger particle size, powdered activated carbon (PAC). It was found that the PAC did provide some minor benefits to sludge dewatering but was outperformed by the nanoparticles. The solids content of the final sludge was increased by a maximum of up to 0.6%. The impact of the order sequence of particles and polymer was also investigated. It was found that nanoparticles added before polymer addition provided the best dewatering performance. This outcome was consistent with current theories and previous research through the literature. An economic analysis was undertaken to confirm the viability of the technology for implementation at a full-scale plant. It was found that, currently, this technology is unlikely to be favourable unless the nanoparticles can be sourced for a low cost.

scholarly journals Darcy–Forchheimer Radiative Flow of Micropoler CNT Nanofluid in Rotating Frame with Convective Heat Generation/Consumption

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 666 ◽  
Author(s):  
Ebraheem O. Alzahrani ◽  
Zahir Shah ◽  
Wajdi Alghamdi ◽  
Malik Zaka Ullah
Keyword(s):  
Heat Generation ◽  
High Surface ◽  
High Surface Area ◽  
Numerical Results ◽  
Coupled Equations ◽  
Analysis Technique ◽  
Homotopy Analysis ◽  
Material Energy ◽  
The Impact ◽  
Thermal Radiation Effect

Since 1991, from the beginning of the carbon nanotube era, this has been a focus point for investigation due to its synthetic and simple nature. Unique properties like good stiffness, high surface area, and resilience of carbon nanotubes (CNTs) have been investigated in many engineering applications such as hydrogen storage, composite material, energy storage, electrochemical super-capacitors, transistors, sensors, and field-emitting devices. Keeping in view these applications, we investigate single and multi-walled CNTs nanofluid flow having water as the base fluid between parallel and horizontal rotating plates with microstructure and inertial properties. The thermal radiation effect is considered for variable phenomenon of heat generation/consumption. The principal equations are first symmetrically transformed to a system of nonlinear coupled ordinary differential equations (ODEs), and then, Homotopy Analysis Technique (HAM) and numerical method are employed for solving these coupled equations. The obtained analytical and numerical results are explained graphically and through different tables. The HAM and numerical results show an excellent agreement. The Skin friction and the Nusselt number are numerically calculated and then analyzed with the already published results, and these results are found to be in agreement with one another. The impact of important parameters are shown graphically.

Concluding remarks: there's nowt so queer as carbon electrodes

2014 ◽  
Vol 172 ◽  
pp. 521-532 ◽  
Author(s):  
Patrick R. Unwin
Keyword(s):  
Carbon Materials ◽  
Local Density ◽  
High Surface ◽  
High Surface Area ◽  
Carbon Electrodes ◽  
Key Points ◽  
Recent Developments ◽  
History Of ◽  
History Of Use ◽  
The Impact

This contribution provides a personal overview and summary of Faraday Discussion 172 on “Carbon in Electrochemistry”, covering some of the key points made at the meeting within the broader context of other recent developments on carbon materials for electrochemical applications. Although carbon electrodes have a long history of use in electrochemistry, methods and techniques are only just becoming available that can test long-established models and identify key features for further exploration. This Discussion has highlighted the need for a better understanding of the impact of surface structure, defects, local density of electronic states, and surface functionality and contamination, in order to advance fundamental knowledge of various electrochemical processes and phenomena at carbon electrodes. These developments cut across important materials such as graphene, carbon nanotubes, conducting diamond and high surface area carbon materials. With more detailed pictures of structural and electronic controls of electrochemistry at carbon electrodes (and electrodes generally), will come rational advances in various technological applications, from sensors to energy technology (particularly batteries, supercapacitors and fuel cells), that have been well-illustrated at this Discussion.

scholarly journals Adequacy of the ASTM C1240 Specifications for Nanosilica Pozzolans

2019 ◽  
Vol 13 (1) ◽  
pp. 42-49 ◽  
Author(s):  
Maan S. Hassan
Keyword(s):  
Compressive Strength ◽  
Activity Index ◽  
Chemical Reactivity ◽  
Standard Procedure ◽  
High Surface ◽  
False Negative ◽  
High Surface Area ◽  
Particle Sizes ◽  
Nano Silica ◽  
Pozzolanic Reactivity

Background: Nano-silica is a new pozzolan that is boosting the field of nanomaterials and can be used effectively in the concrete industry. ASTM C1240 is used to qualify silica fume pozzolans for use in concrete and for marketing purposes. Objective: The present study aims to assess the adequacy of ASTM C1240 in qualifying nanosilica for use in concrete and to introduce a modified procedure to measure the pozzolanic activity of nanosilica used with cementitious composites. Methods: The effects of various particle sizes and dosages on the compressive strength of blends in standard mortar were investigated. The correlation between the chemical reactivity and the compressive strength were also investigated using TGA and XRD analyses. The criterion conceived was validated at two ages: 7 days and 28 days. Results and Conclusion: The strength activity index results revealed that the following standard procedure ASTM C1240 is not applicable for nanosilica due to the high surface area and great pozzolanic reactivity of SiO2 nanoparticles, so a lower cement replacement percentage should be used. This study suggests that it be no more than 7%. The pozzolanicity testing results confirm that a nanosilica replacement level of more than 7% could not be effective in transforming further Portlandite into a C-S-H or other major cementing compound, leading to a “false negative” for nanosilica pozzolans.

scholarly journals Li2O-Based Cathode Additives Enabling Prelithiation of Si Anodes

2021 ◽  
Vol 11 (24) ◽  
pp. 12027
Author(s):  
Yeyoung Ha ◽  
Maxwell C. Schulze ◽  
Sarah Frisco ◽  
Stephen E. Trask ◽  
Glenn Teeter ◽  
...  
Keyword(s):  
Coulombic Efficiency ◽  
High Surface ◽  
Solid Electrolyte Interphase ◽  
Active Material ◽  
High Surface Area ◽  
Lithium Ion ◽  
Particle Morphology ◽  
Lithium Oxide ◽  
Si Anodes ◽  
The Impact

Low first-cycle Coulombic efficiency is especially poor for silicon (Si)-based anodes due to the high surface area of the Si-active material and extensive electrolyte decomposition during the initial cycles forming the solid electrolyte interphase (SEI). Therefore, developing successful prelithiation methods will greatly benefit the development of lithium-ion batteries (LiBs) utilizing Si anodes. In pursuit of this goal, in this study, lithium oxide (Li2O) was added to a LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode using a scalable ball-milling approach to compensate for the initial Li loss at the anode. Different milling conditions were tested to evaluate the impact of particle morphology on the additive performance. In addition, Co3O4, a well-known oxygen evolution reaction catalyst, was introduced to facilitate the activation of Li2O. The Li2O + Co3O4 additives successfully delivered an additional capacity of 1116 mAh/gLi2O when charged up to 4.3 V in half cells and 1035 mAh/gLi2O when charged up to 4.1 V in full cells using Si anodes.

scholarly journals In-Situ Synthesis of Nb2O5/g-C3N4 Heterostructures as Highly Efficient Photocatalysts for Molecular H2 Evolution under Solar Illumination

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 169 ◽  
Author(s):  
Faryal Idrees ◽  
Ralf Dillert ◽  
Detlef Bahnemann ◽  
Faheem Butt ◽  
Muhammad Tahir
Keyword(s):  
Photocatalytic Activity ◽  
Charge Carrier ◽  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Photogenerated Electron ◽  
Band Alignment ◽  
Solar Irradiation ◽  
Electron Hole ◽  
The Impact

This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H2). In particular, 3-dimensional Nb2O5/g-C3N4 heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb2O5 with a low charge carrier recombination rate and a g-C3N4 exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb2O5 to g-C3N4 on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co-catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron-hole pairs is found to increase significantly as compared to that of pure Nb2O5 and g-C3N4, respectively, with the highest molecular H2 production of 110 mmol/g·h being obtained for 10 wt % of g-C3N4 over Nb2O5 as compared with that of g-C3N4 (33.46 mmol/g·h) and Nb2O5 (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron-hole pairs at the Nb2O5/g-C3N4 interface through a direct Z-scheme.

Transition of magnetism in graphene coated with metal nanoparticles

2017 ◽  
Vol 10 (04) ◽  
pp. 1750037 ◽  
Author(s):  
Dongju Lee ◽  
Kee Sun Lee ◽  
Nam Chul Kim ◽  
Changbin Song ◽  
Sung Ho Song
Keyword(s):  
Graphene Oxide ◽  
Metal Nanoparticles ◽  
Electromagnetic Interference ◽  
Chemical Reactivity ◽  
High Surface ◽  
High Surface Area ◽  
Dimensional Structure ◽  
Exfoliated Graphene ◽  
Novel Approach ◽  
Very High

The unique two-dimensional structure and very high surface area of graphene results in amazing properties and makes it an ideal substrate for the chemical adsorption of many types of metal nanoparticles (NPs). Here, we demonstrate a novel approach for synthesizing multi-functional graphene-magnetic nanoparticles (GNPs) hybrids. The hybrids exhibit a combination of features, including excellent processability, superparamagnetism, electrical conductivity and high chemical reactivity. The synthesis of graphene by Cu or Ni reduction of exfoliated graphene oxide results in the removal of oxygen functionalities of the graphene oxide. The process is scalable, green and efficiently enables the controllable production of GNPs. The GNPs have great potential for a variety of applications, including as materials for magnetic resonance imaging, microwave absorption and electromagnetic interference shielding.

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