Removal Of Silica Template Research Articles

Lanthanum oxide-based nanomaterials synthesized by using carbon aerogel template for efficient phosphate capture

Phosphate is a chemical compound that contains phosphorus, an essential nutrient for the growth of all organisms on Earth. However, the overuse of fertilizers has created a serious environmental problem worldwide, because the discharge of wastewater containing excess phosphate leads to eutrophication. Therefore, proper management of phosphate from wastewater is very important. In this study, lanthanum oxide-based nanomaterials (LONs) were synthesized by a hard-template method using porous carbon aerogels, and their potential as adsorbents for efficient phosphate removal was evaluated. The use of carbon aerogels offers facile production of porous adsorbents because simple calcination under air can remove the template, which is more suitable for environmental and industrial applications than the use of toxic chemicals for conventional silica template removal. The morphology and porosity of the LONs were controlled by adjusting the synthesis conditions, including calcination and oxidation. The phosphate removal capacity of LONs strongly depends on the porous structure and surface area because the adsorption process is governed by monolayer adsorption of phosphate-forming lanthanum phosphate. LONs with an optimized structure exhibited a high adsorption capacity of 135.14 mg P g−1 at 28 °C (qm by the Langmuir isotherm model). LON adsorbents have great potential for efficient phosphate removal to meet increasingly stringent discharge standards and to prevent the pollution of water resources.

Nitrogen and sulfur co-doped hierarchical porous carbon as functional sulfur host for lithium-sulfur batteries

Nitrogen and sulfur co-doped hierarchical porous carbon (N,S-HPC) is synthesized by using polyaniline and poly(3,4-ethylenedioxythiophene) as doping sources and polytetrafluoroethylene as the silica template removal agent for lithium-sulfur batteries. N,S-HPC shows the interconnected hierarchical porous network, which enables sulfur to be uniformly dispersed in the carbon matrix thus accelerating the transport of electrons and lithium ions. The S@N,S-HPC composite cathode exhibits a high capacity utilization of 1106 mA h/g at 0.2 C, together with excellent rate capacity of 600 mA h/g at 2 C, and also superior cycle life over 500 cycles with a capacity decay of 0.08 % per cycle at 1 C. The outstanding electrochemical performances for S@N,S-HPC cathode are mainly ascribed to the hierarchical porous structure of carbon and N/S co-doping, which offers sufficient interface for the deposition of solid discharge products and impedes the diffusion of polysulfides due to both physical confinement and chemical interaction by porous carbon matrix and N/S atoms.

Synthesis of ordered mesoporous carbons by Teflon-assisted removal of silica template in tri-constituent co-assembly for supercapacitors

The synthesis of mesoporous carbon through tri-constituent co-assembly by introduction of silica as supporting is amenable to improve the surface area and porosity. However, this is a multistep process along with contamination from the use of toxic HF solution to remove the silica template. Herein, a “green” and one-pot method is demonstrated to prepare ordered mesoporous carbon with high surface area (1160 m2 g−1) by direct addition of Teflon into tri-constituent phases (including soft template, carbon, and silica source) for co-assembly and followed by pyrolysis. During the high-temperature treatment, the removal of soft template and silica support (can fast reacts with Teflon) and carbonization process are simultaneously accomplished to yield the carbon product with hierarchically porous structure including bimodal mesopores centered at 2.4 and 4.5 nm and abundant micropores. The resulting mesoporous carbon demonstrates an excellent electrochemical performance of 186 F g−1 at a discharge current of 1 A g−1 in 6 M NaOH. It can be attributed to both the hierarchically microporous/mesoporous structure and high surface area allowing the efficient transportation of ions into the carbon matrix. This mesoporous carbon also exhibits a good cycling stability with capacitance retention of ~ 97% over 5000 cycles.

Synthesis of centimeter-scale monolithic SiC nanofoams and pore size effect on mechanical properties

By pressure infiltrating pre-ceramic polymer polycarbosilane (PCS) into thermally and mechanically stable silica nanofoam, followed by PCS pyrolysis and silica template removal, synthesis of large-scale monolithic SiC nanofoams has been accomplished. Tailoring of the porosity and cell size of the SiC nanofoam has been realized by dissociating the porosity and pore size of the silica nanofoam. Because of the surface hardening and increased surface volume ratio of deformable nanopores, with the same porosity, the decrease of nanopore size has led to an increase in the quasi-static and dynamic indentation resistance for SiC nanofoams.

Mesoporous silica templated-albumin nanoparticles with high doxorubicin payload for drug delivery assessed with a 3-D tumor cell model

Human serum albumin (HSA) nanoparticles emerge as promising carriers for drug delivery. Among challenges, one important issue is the design of HSA nanoparticles with a low mean size of ca. 50 nm and having a high drug payload. The original strategy developed here is to use sacrificial mesoporous nanosilica templates having a diameter close to 30 nm to drive the protein nanocapsule formation. This new approach ensures first an efficient high drug loading (ca. 30%) of Doxorubicin (DOX) in the porous silica by functionalizing silica with an aminosiloxane layer and then allows the one-step adsorption and the physical cross-linking of HSA by modifying the silica surface with isobutyramide (IBAM) groups. After silica template removal, homogenous DOX-loaded HSA nanocapsules (30–60 nm size) with high drug loading capacity (ca. 88%) are thus formed. Such nanocapsules are shown efficient in multicellular tumor spheroid models (MCTS) of human hepatocarcinoma cells by their significant growth inhibition with respect to controls. Such a new synthesis approach paves the way toward new protein based nanocarriers for drug delivery.

A Cathodic Electro-Fenton Catalyst Derived from Ionic-Liquid: Peroxide Generation and Di-Valent Iron Regeneration

The highly nitrogen-doped porous carbon materials for peroxide generation and di-valent iron regeneration were synthesized by the pyrolysis of ionic-liquid, which are precursor of carbon and nitrogen, using a silica nanoparticle template. In acidic solution, both of two/four electron oxygen reduction reaction (ORR) activities of ionic-liquid derived nitrogen-doped carbon catalyst increased significantly with pyridinic/graphitic N ratio in their structure. From the cyclic voltammogram, we confirmed that di-valent/tri-valent iron redox property enhanced with increasing surface carbonyl functional group, formed during removal of silica template. The degradation experiments of azo-dye and trace pharmaceutical compounds showed that the Fenton reaction (hydroxyl radical formation) drastically increased when double working electrodes (electrode 1: peroxide generation, electrode 2: di-valent iron regeneration) were used at the same time, and as a result, the removal efficiency was drastically increased. Based on the physical/electrochemical analysis, the ionic-liquid is a candidate precursor of highly nitrogen-doped carbon as energy effective electro-Fenton catalyst. Acknowledgements This work was supported by the Korea Ministry of Environment as a “Global Top Project” (Project No. 2016002190003).

Nitrogen and Sulfur Co–Doped Hollow Carbon Nanospheres Derived from Surface‐Attached Polyelectrolyte Monolayers

AbstractNitrogen, sulfur co‐doped hollow carbon nanospheres are synthesized by simple pyrolysis of surface‐attached 2‐thiophene acetic acid neutralized poly(4‐vinylpyridine) monolayers on silica nanoparticles, followed by removal of silica templates. The covalently grafted polymer chains prevent the aggregation of silica templates during pyrolysis process, resulting in well‐distributed mesopores. The formed materials exhibit an improved electrocatalytic performance for oxygen reduction reactions under basic conditions compared to nitrogen doped hollow carbon nanospheres in terms of the positive shift of half‐wave potential. The best catalytic activity is observed for the material with surface area of 489 m2g−1 derived from 15 nm silica templated modified with polymers, which is comparable to commercial 20 wt.% Pt/C catalysts (half‐wave potential negatively shifts by 10 mV with similar limiting current density compared with Pt/C catalysts). Although the dual doping can improve the catalytic activity, the increase in sulfur concentration of the formed materials has little effect on the electrocatalytic performance for oxygen reduction reactions. This development offers a new synthetic strategy to synthesize heteroatoms co‐doped or multi‐doped spherical hollow carbon materials not only for application in electrochemical devices, but also as model materials for fundamental understanding of properties of carbon‐based materials.

Hard-template preparation of Au/CeO2 mesostructured catalysts and their activity for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Ordered mesoporous CeO2 has been prepared via a hard-template method using SBA-15 as a structure-directing agent. Leaching with NaOH and thermal treatment at 500 °C enabled the removal of the inorganic template, thus resulting in the formation of long-range ordered CeO2. Nevertheless, small amounts of silica were present in the final oxides. The resulting CeO2 samples were used as supports for Au nanoparticles and the prepared catalysts were tested in the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). Fine tuning of the silica template removal process was necessary to prepare active materials, by maximizing the close contact between the metal and the support, and thus confirming the important role of ceria defects in 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid.

Magnetically separated and N, S co-doped mesoporous carbon microspheres for the removal of mercury ions

Abstract Magnetically separated and N, S co-doped mesoporous carbon microspheres (N/S-MCMs/Fe 3 O 4 ) are fabricated by encapsulating SiO 2 nanoparticles within N, S-containing polymer microspheres which were prepared using resorcinol/formaldehyde as the carbon source and cysteine as the nitrogen and sulfur co-precursors, followed by the carbonization process, silica template removal, and the introduction of Fe 3 O 4 into the carbon mesopores. N/S-MCMs/Fe 3 O 4 exhibits an enhanced Hg 2+ adsorption capacity of 74.5 mg/g, and the adsorbent can be conveniently and rapidly separated from wastewater using an external magnetic field. This study opens up new opportunities to synthesize well-developed, carbon-based materials as an adsorbent for potential applications in the removal of mercury ions from wastewater.

No More HF: Teflon-Assisted Ultrafast Removal of Silica to Generate High-Surface-Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance.

An innovative technique to obtain high-surface-area mesostructured carbon (2545 m(2) g(-1)) with significant microporosity uses Teflon as the silica template removal agent. This method not only shortens synthesis time by combining silica removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained carbon material (JNC-1) displays excellent CO2 capture ability (ca. 26.2 wt % at 0 °C under 0.88 bar CO2 pressure), which is twice that of CMK-3 obtained by the HF etching method (13.0 wt %). JNC-1 demonstrated higher H2 adsorption capacity (2.8 wt %) compared to CMK-3 (1.2 wt %) at -196 °C under 1.0 bar H2 pressure. The bimodal pore architecture of JNC-1 led to superior supercapacitor performance, with a specific capacitance of 292 F g(-1) and 182 F g(-1) at a drain rate of 1 A g(-1) and 50 A g(-1) , respectively, in 1 m H2 SO4 compared to CMK-3 and activated carbon.

No More HF: Teflon‐Assisted Ultrafast Removal of Silica to Generate High‐Surface‐Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance

AbstractAn innovative technique to obtain high‐surface‐area mesostructured carbon (2545 m2 g−1) with significant microporosity uses Teflon as the silica template removal agent. This method not only shortens synthesis time by combining silica removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained carbon material (JNC‐1) displays excellent CO2 capture ability (ca. 26.2 wt % at 0 °C under 0.88 bar CO2 pressure), which is twice that of CMK‐3 obtained by the HF etching method (13.0 wt %). JNC‐1 demonstrated higher H2 adsorption capacity (2.8 wt %) compared to CMK‐3 (1.2 wt %) at −196 °C under 1.0 bar H2 pressure. The bimodal pore architecture of JNC‐1 led to superior supercapacitor performance, with a specific capacitance of 292 F g−1 and 182 F g−1 at a drain rate of 1 A g−1 and 50 A g−1, respectively, in 1 m H2SO4 compared to CMK‐3 and activated carbon.

Fabrication of hollow spheres of Co3O4 for catalytic oxidation of carbon monoxide

In this study, hollow Co3O4 spheres for the oxidation of carbon monoxide were fabricated using silica templates. The shells were formed by the precipitation of carbonate species on silica templates, and then leached in an aqueous sodium hydroxide solution for the removal of silica templates followed by calcination process. The effects of preparation conditions such as pH (=7–10) and calcination conditions were investigated. Homogeneous hollow Co3O4 spheres were obtained at pH value of 7.09, and high-purity hollow Co3O4 spheres were obtained at calcination temperatures greater than 623 K. The samples calcined at temperatures less than 623 K included cobalt carbonate species, and the carbonate species converted into catalytically inactive cobalt oxyhydroxide after leaching in an aqueous sodium hydroxide solution. The samples calcined at temperatures greater than 623 K included pure Co3O4 phase even after leaching. In the samples calcined at temperatures greater than 623 K, the amount of surface Co3+ species decreased with calcination temperature, while those of surface Co2+ species increased with calcination temperature. The activity of the catalyst for the oxidation of carbon monoxide was found to depend on calcination temperature, and the highest activity was obtained over the hollow spheres calcined at 623 K. The results indicate that high purity of Co3O4 phase and the surface Co3+ species plays an important role for high activity. The hollow spheres also exhibited activity higher than those exhibited by Co3O4 coated on silica templates and Co3O4 nanoparticles, indicating that the hollow spheres are an effective catalyst compared with the supported catalyst and nanoparticle catalyst.

Photomechanically Controlled Encapsulation and Release from pH-Responsive and Photoresponsive Microcapsules.

Poly(acrylic acid)/azobenzene microcapsules were obtained through distillation precipitation polymerization and the selective removal of silica templates by hydrofluoric acid etching. The uniform, robust, and monodisperse microcapsules, confirmed by transmission electron microscopy and scanning electron microscopy, had reversible photoisomerization under ultraviolet (UV) and visible light. Under UV irradiation, azobenzene cross-linking sites in the main chain transformed from the trans to cis isomer, which induced the shrinkage of microcapsules. These photomechanical effects of azobenzene moieties were applied to the encapsulation and release of model molecules. After loading with rhodamine B (RhB), the release behaviors were completely distinct. Under steady UV irradiation, the shrinkage adjusted the permeability of the capsule, providing a novel way to encapsulate RhB molecules. Under alternate UV/visible light irradiation, a maximal release amount was reached due to the continual movement of shell networks by cyclic trans-cis photoisomerization. Also, microcapsules had absolute pH responsiveness. The diffusion rate and the final release percentage of RhB both increased with pH. The release behaviors under different irradiation modes and pH values were in excellent agreement with the Baker-Lonsdale model, indicating a diffusion-controlled release behavior. Important applications are expected in the development of photocontrolled encapsulation and release systems as well as in pH-sensitive materials and membranes.

An Approach for Highly Porous Non-Precious Metal Catalyst Synthesis for Polymer Electrolyte Fuel Cell Cathodes

Polymer electrolyte fuel cells (PEFCs) are electrochemical devices that convert chemical energy into electricity for a variety of applications, the most notable of which is transportation. The integration of PEFCs at scale for transportation applications however has been hindered due to the high price of platinum (Pt) that is the state-of-the-art catalyst for the oxygen reduction reaction (ORR) on the cathode. Replacing Pt with non-precious metal catalysts (NPMCs) synthesized from earth abundant elements (C, N, Fe, etc.) is therefore essential to deploy PEFCs for transportation applications. Recently, many advances have been realized towards the development of NPMCs. One of the most important advances is the synthesis of highly porous (HP)-NPMCs. HP-NPMCs allow for improved active site accessibility as well as facilitated mass transport. This is especially important as the relatively low volumetric activity of NPMCs leads to a significantly larger electrode thickness for NPMCs in comparison to Pt/C catalysts, i.e., ca. 70 μm vs. 10 μm, respectively. Two main strategies that have been employed to achieve HP-NPMCs are the use of: (i) metal-organic frameworks (MOFs) [1] and (ii) template agents such as silica [2]. MOFs however are generally very expensive, with only very few commercially available, and a silica template approach requires using highly corrosive and hazardous reagents such as hydrofluoric acid for a silica template removal. These approaches are therefore far from ideal for efficient catalyst production. In this work, we adopted a more proficient technique that uses combined nitrogen precursors. With this method, a lower decomposition temperature nitrogen precursor, cyanamide (CM), and higher decomposition temperature nitrogen precursor, polyanniline (PANI), are concurrently used. Under this circumstance, during heat-treatment, CM works as an efficient foaming agent. Indeed, we can synthesize HP-NPMCs with a microporous surface area of 1585 m2/g, and demonstrate record H2-air fuel cell performance (Fig. 1). In this talk, more detailed microscopic features and electrochemical and fuel cell performances of these HP-MPMCs will be presented. Acknowledgements Financial support for this has been provided by the DOE-EERE through the Fuel Cells Technologies Office. References Proietti et al., Nat. Commun. 2, 416 (2011).Serov et al., Appl. Catal. B: Environmental, 127, 300 (2012). Figure 1

Nanocasting hierarchical carbide-derived carbons in nanostructured opal assemblies for high-performance cathodes in lithium-sulfur batteries.

Silica nanospheres are used as templates for the generation of carbide-derived carbons with monodisperse spherical mesopores (d=20-40 nm) and microporous walls. The nanocasting approach with a polycarbosilane precursor and subsequent pyrolysis, followed by silica template removal and chlorine treatment, results in carbide-derived carbons DUT-86 (DUT=Dresden University of Technology) with remarkable textural characteristics, monodisperse, spherical mesopores tunable in diameter, and very high pore volumes up to 5.0 cm3 g(-1). Morphology replication allows these nanopores to be arranged in a nanostructured inverse opal-like structure. Specific surface areas are very high (2450 m2 g(-1)) due to the simultaneous presence of micropores. Testing DUT-86 samples as cathode materials in Li-S batteries reveals excellent performance, and tailoring of the pore size allows optimization of cell performance, especially the active center accessibility and sulfur utilization. The outstanding pore volumes allow sulfur loadings of 80 wt %, a value seldom achieved in composite cathodes, and initial capacities of 1165 mAh gsulfur(-1) are reached. After 100 cycle capacities of 860 mAh gsulfur(-1) are retained, rendering DUT-86 a high-performance sulfur host material.

Highly nitrogen-doped mesoscopic carbons as efficient metal-free electrocatalysts for oxygen reduction reactions

A facile method was developed for the synthesis of metal-free, highly N-doped (>7 wt%) mesoscopic carbons (NMCs), which were fabricated by first preparing carbon–silicate (C–Si) composites by co-condensation method using a melamine-formaldehyde resin oligomer as the primary nitrogen and carbon source, and P123 triblock copolymer surfactant and sodium silicate as the soft and hard template, respectively, under microwave irradiation conditions, followed by carbonization and silica-template removal. The NMCs were found to exhibit superior electrocatalytic activity, long-term stability, and excellent tolerance over methanol crossover effect. Such NMCs derived from organic–inorganic hybrids assisted by microwave heating not only possess high surface areas and active quaternary and pyridinic-N species that are favourable for ORR, as verified by DFT calculations, but also render large-scale production and practical applications as cost-effective electrode materials.

High performance supercapacitor prepared from hollow mesoporous carbon capsules with hierarchical nanoarchitecture

Hollow core mesoporous shell carbon (HCMSC) capsules are prepared by nano-casting method which involves surfactant-assisted synthesis of silica spheres with mesoporous shell as template and impregnation of carbon precursor into mesoporous shell of the silica, followed by carbonization and silica template removal. The resulting HCMSC capsules possess 3D-interconnected nanoarchitecture with unique hierarchical meso/macro-porosity along with high surface area and large mesopore volume. The HCMSC capsules are tested for electrochemical double layer capacitor in a standard two electrode flat cell using non-aqueous electrolyte. The specific capacitance measured by galvanostatic charge-discharge at 0.3 A g−1 current density is found to be 162 F g-1, which is among the highest values reported so far for mesoporous carbon materials in a practical two electrode symmetric system using organic electrolyte. The cyclic performance tested at high current density of 1.0 A g−1 is found to retain 88% of initial capacity up to 2000 charge-discharge cycles. High capacitance performance of the HCMSC is attributed to the well-developed hierarchical 3D open network of macropores and interstitial void open to mesopores in the mesoporous shell, which not only facilitate fast charge transfer, but also facile electrolyte movement to access the active sites.

Simple Cocasting Method to Prepare Magnetic Mesoporous FePt/C Composites and Their Protein Adsorption Property

A simple cocasting method has been developed to prepare magnetic mesoporous FePt/C composites with superparamagnetic FePt nanoparticles embedded in carbon walls. Furfuryl alcohol, iron(III) acetylacetonate (Fe(acac)3), and platinum(II) acetylacetonate (Pt(acac)2) were used as the carbon and FePt nanoparticle precursors to be simultaneously incorporated into the channels of mesoporous silica SBA‐15 template by the incipient wetness impregnation technique. After the polymerization of furfuryl alcohol, the carbonization in argon, and the removal of silica template, magnetic mesoporous FePt/C composites were finally obtained. Magnetic mesoporous FePt/C composites have high surface area of 1244 m2/g and narrow mesopore size distribution peaked at 4.93 nm. FePt nanoparticles were well embedded in mesoporous carbon walls, and mesoporous FePt/C composites exhibit superparamagnetic behavior. Using cytochrome c (Cyt c), myoglobin (Mb), and bovine serum albumin (BSA) as model proteins, the adsorption capacities of Cyt c, Mb, and BSA on magnetic mesoporous FePt/C composites can reach ca. 200, 162, and 121 μg/mg, respectively. These results indicated that mesoporous FePt/C composites have potential as magnetically separable adsorbent for biomolecules separation.

Mesoporous tungsten oxides as photocatalysts for O2 evolution under irradiation of visible light

Three-dimensionally ordered mesoporous WO3 was successfully synthesized by a hydrothermal method using mesoporous silica KIT-6 as a hard template and phosphotungstic acid as a precursor. The tungsten oxide after removal of silica template was characterized by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Investigations of optical and photoelectrochemical properties showed that the mesoporous WO3 was a n-type semiconductor with a band gap of 2.6eV and demonstrated prompt, steady, and reproducible photocurrent responses during repeated on/off cycles of visible light illumination (λ>420nm). The mesoporous WO3 modified by platinum nanoparticles could be used as a stable photocatalyst for photoinducing O2 evolution. Under visible light irradiation, the average O2 evolution rate is 34.5μmolg−1h−1 in the presence of an electron acceptor IO3−. This work demonstrated a potential application of using mesoporous WO3 modified by platinum nanoparticles as a novel photocatalyst in the field of solar energy conversion.

Surface‐Confined Atom Transfer Radical Polymerization from Sacrificial Mesoporous Silica Nanospheres for Preparing Mesoporous Polymer/Carbon Nanospheres with Faithful Shape Replication: Functional Mesoporous Materials

AbstractA facile approach for the preparation of mesoporous polymer nanospheres (MPN) and mesoporous carbon nanospheres (MCN) with complete shape retention based on surface‐confined atom transfer radical polymerization of various methacrylate monomers from in situ generated initiator‐modified hard silica nanospheres template is developed. This approach yields mesoporous silica‐polymer hybrid nanospheres (MSPN) with mesopores that are uniformly filled with covalently attached well‐defined poly(methacrylate)s. The silica frameworks are subsequently etched, resulting in MPN. Pyrolysis of MSPN and subsequent removal of silica template resulted in the production of MCN. They retain the size, shape, and mesoporous ordering of the silica template nanospheres. Gel permeation chromatography analysis of the silica free polymers reveals that they have controlled molecular weights and low polydispersities (PDIs). Kinetics studies reveal that the molecular weight of the grafted polymer increases linearly with time, maintaining low PDIs, indicating the living nature of the polymerization. The mesoporous polymer material is found to have low dielectric constant, which paves the way for their use as low‐dielectric constant materials in microelectronics. This approach allows fabrication of functional MPN using functional comonomers, which are successfully used for the synthesis of “clickable” mesoporous polymer nanospheres, removal of ionic contaminates through anion exchange, and glucose sensing.