Hard Template Method Research Articles

Optimizing Ni–Fe Oxide Electrocatalysts for Oxygen Evolution Reaction by Using Hard Templating as a Toolbox

A specific investigation was carried out to study the influence of the Ni/Fe ratio for oxygen evolution reaction (OER) by using the hard templating method as a toolbox. Various compositions of homogeneously blended Ni–Fe oxide nanoparticles with a primary particle size of around 8 nm were simply prepared by using pore confinement of the tea leaves template. Based on the similar physical properties, including particle size and surface area, for all samples, it was verified that the OER activity in alkali electrolyte was mainly governed by the metal stoichiometry, where a maximum current density was obtained with a Ni/Fe ratio of 32/1. The higher catalytic performance of Ni32Fe oxide was attributed to lower reaction resistance and higher intrinsic activity, which are confirmed by electrochemical impedance spectroscopy and surface area analysis, respectively. The lowest overpotential (0.291 VRHE at 10 mA/cm2) as well as the highest current density (over 600 mA/cm2 at 1.7 VRHE) was achieved with Ni/Fe = 32/1 ...

Mesoporous MnCo2O4 spinel oxide for a highly active and stable air electrode for Zn-air rechargeable battery

Large-capacity rechargeable batteries for mobile devices are strongly required now, and the metal-air battery is currently considered as one of the most promising rechargeable batteries with a large capacity. In this study, oxygen reduction (ORR) and oxygen evolution reaction (OER) on mesoporous MnCo2O4 spinel was studied for rechargeable Zn-air battery. Comparing the prepared spinel oxides containing Fe, it was found that the ORR/OER activity of MnCo2O4 was reasonably high and stably cycled. Mesoporous MnCo2O4 was successfully prepared by using a hard template method with mesoporous silica (SBA-15) for an inorganic template. The obtained mesoporous MnCo2O4 showed the BET surface area of 108 m2/g and the average pore size of 2 nm. By increasing the surface area with mesoporous structure, overpotential of MnCo2O4 to ORR/OER was much decreased. Zn-air battery was prepared by using mesoporous MnCo2O4 as air electrode and 4 M KOH aqueous electrolyte, the stable discharge potential and capacity were exhibited at 1.05 V and 700 mAh/g-Zn, respectively. In addition, stable charge/discharge cycles were also sustained more than 200 cycles.

Recent Advances on Controlled Synthesis and Engineering of Hollow Alloyed Nanotubes for Electrocatalysis.

The past decade has witnessed great progress in the synthesis and electrocatalytic applications of 1D hollow alloy nanotubes with controllable compositions and fine structures. Hollow nanotubes have been explored as promising electrocatalysts in the fuel cell reactions due to their well-controlled surface structure, size, porosity, and compositions. In addition, owing to the self-supporting ability of 1D structure, hollow nanotubes are capable of avoiding catalyst aggregation and carbon corrosion during the catalytic process, which are two other issues for the widely investigated carbon-supported nanoparticle catalysts. It is currently a great challenge to achieve high activity and stability at a relatively low cost to realize commercialization of these catalysts. An overview of the structural and compositional properties of 1D hollow alloy nanotubes, which provide a large number of accessible active sites, void spaces for electrolytes/reactants impregnation, and structural stability for suppressing aggregation, is presented. The latest advances on several strategies such as hard template and self-templating methods for controllable synthesis of hollow alloyed nanotubes with controllable structures and compositions are then summarized. Benefiting from the advantages of the unique properties and facile synthesis approaches, the capability of 1D hollow nanotubes is then highlighted by discussing examples of their applications in fuel-cell-related electrocatalysis. Finally, the remaining challenges and potential solutions in the field are summarized to provide some useful clues for the future development of 1D hollow alloy nanotube materials.

Photonic titanium dioxide film obtained from hard template with chiral nematic structure for environmental application

In the present work, mesoporous TiO2 with a photonic structure was elaborated using cellulose nanocrystals (CNCs) as a biotemplate by two-step hard template methods. This strategy enables to replicate the chiral nematic (CN) structure of the photonic films (biotemplate) in TiO2 films. A series of iridescent CNCs films with different weight ratios of silica/CNCs composite photonic films were prepared via evaporation induced self-assembly (EISA) method. The films showed iridescent color and tuneable Bragg reflection wavelengths by solely changing the ratio between the silica and the CNCs biotemplate. Polarized optical microscopy (POM) performed on hydride SiO2/CNCs films showed a birefringence and typical fingerprint of chiral nematic structure. This birefringence was also observed for TiO2 films obtained using SiO2 films as a hard template, which suggested the transfer of the chiral nematic structure in TiO2 materials. Afterwards, their optical, morphological and electronic properties were studied by scanning electron microscope (SEM), POM, energy-dispersive X-ray spectroscope (EDX) and time resolved microwave conductivity (TRMC). The photocatalytic activities were evaluated by following the phenol degradation using high performance liquid chromatography (HPLC). The results showed that the structuration of the TiO2 film using a chiral nematic SiO2 film as hard template enhances the photocatalytic performance compared to non-structured mesoporous TiO2.

Rational design of MgF2 catalysts with long-term stability for the dehydrofluorination of 1,1-difluoroethane (HFC-152a).

In this study, three different approaches, i.e. the sol–gel method, precipitation method and hard-template method, were applied to synthesize MgF2 catalysts with improved stability towards the dehydrofluorination of hydrofluorocarbons (HFCs); the in situ XRD technique was employed to investigate the relationship between the calcination temperature and the crystallite size of precursors to determine optimal calcination temperature for the preparation of the MgF2 catalysts. Moreover, the physicochemical properties of MgF2 catalysts were examined via BET, XRD, EDS and TPD of NH3 and compared. Undoubtedly, the application of different methods had a significant influence on the surface properties and catalytic performances of MgF2 catalysts. The surface areas of the catalysts prepared by the precipitation method, sol–gel method and template method were 120, 215 and 304 m2 g−1, respectively, upon calcination at 200 °C. However, the surface area of the MgF2 catalysts decreased significantly when the calcination temperatures of 300 and 350 °C were applied. The catalytic performance of these catalysts was evaluated via the dehydrofluorination of 1,1-difluoroethane (HFC-152a). The MgF2 catalyst prepared by the precipitation method showed the lowest catalytic activity among all the MgF2 catalysts. When the calcination temperature was above 300 °C, the MgF2 catalysts prepared via the template method demonstrated the highest catalytic conversion rate with catalytic activity following the order: MgF2-T (template method) > MgF2-S (sol–gel method) > MgF2-P (precipitation method). The conversion rate generally agreed with the total amount of acid on the surface of the catalysts, which was measured by the NH3-TPD technique. The MgF2-T catalysts were further examined for the dehydrofluorination of HFC-152a for 600 hours, and a conversion rate greater than 45% was maintained, demonstrating superior long-term stability of these catalysts.

Lignin-Derived Nitrogen-Doped Porous Carbon as a High-Rate Anode Material for Sodium Ion Batteries

Nitrogen-doped carbon anode materials have been prepared by a hard-template (SiO2 nanoparticles) method, in which alkali lignin-derived azo polymer (AL-azo-NO2) was used as a low-cost carbon precursor. The as-prepared N-doped carbon materials show a honeycomb-like morphology with uniform nanopores. These materials are able to reversibly insert Na+ ions and show promising cycling performance. In particular, the porous carbon material with larger surface area and pore volume delivers a higher initial capacity of 205 mAh g−1 in the voltage range of 0.01–2 V at 50 mA g−1, compared to the material with lower surface area and pore volume (only 155 mAh g−1). The former also exhibits much better rate capability than the latter. Even at a high current density of 1 A g−1, it shows a high specific capacity of 101 mAh g−1 after 1100 cycles, which retains 92% of its initial capacity. Electrochemical impedance spectroscopy (EIS) results prove that the enhanced electrochemical performance is attributed to the improved Na+-ions kinetics in this material. This work presents an alternative approach for the synthesis of high-rate carbonaceous anode materials for sodium ion batteries from low cost and sustainable feedstock.

Crackled nanocapsules: the "imperfect" structure for enzyme immobilization.

Herein, the first example of crackled organosilica nanocapsules (CONs) is reported to directly immobilize enzymes without any further chemical modification. Enzymes are adsorbed on both the exterior and interior surfaces of CONs, integrating the merits of adsorption and encapsulation. When used for Candida rugosa lipase (CRL) immobilization, the CONs displayed higher enzyme loading, lower enzyme leaching, and elevated enzyme activity, compared to the conventional non-crackled nanocapsules/particles.

3D Gold-Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation.

A hard template method is used to prepare porous gold-doped cerium and cobalt oxide (Au-Cex Coy ) materials. A series of 3D Au-Ce x Coy /graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well-defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au-Cex Coy catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross-linker to form 3D Au-Cex Coy /GA composites. In addition, the resulting catalyst of 3 wt% Au-Ce3 Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO2 and Co3 O4 promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au-Ce3 Co/GA catalyst make it potentially applicable in HCHO removal.

Facile synthesis of nitrogen-enriched nanoporous carbon materials for high performance supercapacitors

Mesoporous carbons with ultrahigh nitrogen content were prepared for supercapacitors through the hard template method. Silica nanoparticles were used as the hard template, and ethylenediamine and CCl4 served as precursor. Large amount of mesopores were generated through removing the silica nanoparticles with HF. The effect of carbonization temperature on the pore structure and nitrogen content and thus on the capacitive performance of supercapacitors were investigated. It was found that the higher carbonization temperature leads to an initial increase and then decrease of specific surface area and a continuous decrease in N content. The sample carbonized at 700 °C (NC700) shows the highest capacitance (306 F g−1) due to the higher surface area (533 m2 g−1) and ultrahigh N content (18.06%). The increase in specific surface area results in improvement of double-layer capacitance, while the N element increases the pseudocapacitance and the wettability of the carbons. In addition, NC700 shows excellent stability with 96.6% capacitance retention even after 10,000 cycles at a current density of 3 A g−1.

Hollow Polypyrrole Nanospindles for Highly Effective Cancer Therapy.

Polypyrrole (PPy) hollow nanostructures continue to attract the interest researchers because of their good biocompatibility, high photothermal conversion efficiency, and excellent stability. The preparation of PPy hollow nanostructures by the hard templating method without complicated post-synthetic treatment and additional oxidizing agents remains a challenge. In this work, we report a facile and novel hard templating method to fabricate hollow PPy nanospindles in which MIL-88(Fe) serves as the template. Fe3+ centers in MIL-88(Fe) could induce the polymerization of pyrrole to construct the shell, and MIL-88(Fe) would be decomposed by solvent water. This method did not require any extra oxidizing agents and post-synthetic treatment. Hollow PPy nanospindles exhibit excellent photothermal and drug loading ability, and the therapy effect of cancer was significant. This method provides a new hard templating approach for the synthesis of polymer hollow nanostructures.

Mixed matrix membranes containing well-designed composite microcapsules for CO2 separation

Hollow fillers with tailored nanostructures and functionalities have become promising candidates for advanced mixed matrix membranes (MMMs). Herein, polydopamine/poly (ethylene glycol) (PEG) composite microcapsules are synthesized by hard template method and embedded into the Pebax matrix to fabricate MMMs for CO2 capture. As a well-known biomimetic adhesive, polydopamine in the capsule wall renders adequate polymer-filler interfacial adhesion. The template removal process produces through-wall mesopores, which allow rapid gas diffusion into the lumen, further significantly reducing the trans-membrane mass transfer resistance. The remaining PEG in the capsule wall not only increases CO2 affinity, but also avoids excessive chain rigidification at polymer-filler interface. In this way, the composite capsules, compared with those without PEG, confer significantly enhanced separation performance on membranes. The optimal gas transport property of the resultant membranes is obtained with a CO2 permeability of 510 Barrer and an ideal selectivity of 84.6 for CO2/N2 at humidified state, i.e., 108%, 98% higher than those of neat Pebax membrane, respectively. In addition, owing to dopamine-enabled strong adhesion, the MMMs exhibit better stability than Pebax membrane in the long-term test at 85 °C.

One-step Synthesis of N-Doped Mesoporous Carbon as Highly Efficient Support of Pd Catalyst for Hydrodechlorination of 2,4-Dichlorophenol

Although the hard template method is often employed to prepare N-doped mesoporous carbon(N-MC), the removal of the silica template commonly involves the use of highly toxic HF or repeated treatment with NaOH solution. Herein, we report a polyvinylidene fluoride-assisted one-step method for synthesis of N-MC, namely the silica-free N-MC can be prepared via temperature-programmed thermal treatment of a slurry obtained by dispersing nano-silica into a solution containing sucrose, urea, oxalic acid, polyvinylidene fluoride and dimethylacetamide. The resulting N-MC, which owns 3.47%(mass fraction) nitrogen and a surface area of 929 m2/g, is a highly suitable support of Pd catalyst used in hydrodechlorination of 2,4-dichlorophenol, with its performance being much better than those of MC and activated carbon. The excellent catalytic hydrodechlorination activity of the Pd/N-MC catalyst can be attributed to its strong metal-support interaction which results in a good Pd dispersion and high resistance to the growth of nanosized Pd under reaction conditions.

Large surface and pore structure of mesoporous WS2 and RGO nanosheets with small amount of Pt as a highly efficient electrocatalyst for hydrogen evolution

In this work, mesoporous WS2 with high surface area was prepared by hard template method. First, a one-step nanocasting generates metal precursor@mesoporous silica SBA-15 composites. A hydrothermal method is subsequently adopted to convert the precursors to sulfides in the confined nanochannels. After etching silica SBA-15, mesoporous layered metal sulfide crystals were obtained as the products. Then, we have put forward a new catalyst based on mesoporous WS2, RGO nanosheets and Pt nanoparticles as a highly efficient electrocatalyst for hydrogen evolution. The Pt/WG-2 nanostructure electrocatalyst in this report exhibits excellent performance with a small Tafel slope of 47 mV dec−1, long-term durability and an overpotential of 95 mV in 0.5 M H2SO4 for the hydrogen evolution reaction (HER).

CO2 Sorption Properties over Ordered Mesoporous Carbon CMK-3 in the Presence of MDEA Solution

By using the hard template method, CMK-3 can be synthesized. The large Brunauer–Emmett–Teller surface area and total pore volume of CMK-3 were 1134 m2/g and 1.128 cm3/g, respectively. The sorption isotherms of CO2 on CMK-3 in the presence of MDEA solutions were measured. It was shown that the CO2 sorption capacity at low pressure was enhanced by chemical absorption and was higher than that of CMK-3 in the presence of water. However, the formation of the CO2 hydrate was inhibited. When the concentration of the MDEA solution exceeded 1.4 mol/L, no hydrate was formed, and the sorption capacity was only 13 mmol/g at approximately 3.5 MPa, which was significantly lower than that of the water under the same pressure. The inhibitory effect of MDEA on hydrate formation was reduced at a low solution concentration. When the concentration of the MDEA solution was 0.52 mol/L, the gas hydrate was formed at approximately 1.88 MPa; the sorption capacity was approximately 28.7 mmol/g at 3.58 MPa, which was close to the h...

Textural properties dependent supercapacitive performances of mesoporous graphitic carbon nitride

In this article, the tunable capacitance properties of mesoporous graphitic carbon nitride (MGCN) by tailoring its textural properties are reported. MGCN with different textural properties is synthesized by a hard template method using two different templates namely, SBA-15 and KIT-6. The formation of graphitic layers in the as-synthesized samples is confirmed by X-ray diffraction studies and successful replication of morphology and mesoporosity of the templates into the as-synthesized samples is confirmed by microscopic and nitrogen adsorption-desorption studies. The bulk and surface chemical composition of the as-synthesized samples are analyzed using Fourier transform infrared spectroscopy, CHNS/O analysis and X-ray photoelectron spectroscopic studies. The specific capacitance values of 322 and 245 F g−1 are obtained at a current density of 0.5 A g−1 for MGCN synthesized using SBA-15 and KIT-6, respectively. Although, MGCN synthesized using SBA-15 (MGCN-SBA-15) exhibits higher specific capacitance than MGCN synthesized using KIT-6 (MGCN-KIT-6), its rate performance is slightly lower than that of MGCN-KIT-6. The higher specific capacitance of MGCN-SBA-15 is attributed to its high surface area, more number of mesopores and large pore volume, whereas the presence of highly ordered mesopores in MGCN-KIT-6 results in higher rate performance. Both MGCN-SBA-15 and MGCN-KIT-6 electrodes demonstrate excellent cycling stability over 15,000 cycles. These results demonstrate that the supercapacitive performances of MGCN can be improved by tailoring its textural properties.

Preparation of palladium-doped mesoporous WO3 for hydrogen gas sensors

This study presents a hydrogen gas sensor using Pd-loaded mesoporous WO3 (Pd/M-WO3) as the sensing material. Pd/M-WO3 was synthesized through the hard-template method. The surface morphology, microstructure, and composition of Pd/M-WO3 were characterized through X-ray diffraction, transmission electron microscopy, energy-dispersive spectrometry, and the Brunner–Emmet–Teller model. Sensing responses using commercial WO3 powder and synthetic mesoporous WO3 (M-WO3) were compared with that using Pd/M-WO3 as the sensing materials for hydrogen sensors. Pd/M-WO3 exhibited the highest hydrogen sensing ability. Comparison of hydrogen sensing performances of WO3, M-WO3, and Pd/M-WO3 at room temperature showed that the sensing performance of M-WO3 is superior to that of commercial WO3 powder, but doping of M-WO3 with Pd can effectively improve the sensing efficiency (from 1.07 to 11.78). The Pd/M-WO3-based gas sensor exhibits promising hydrogen gas sensing characteristics, such as fast response, highly selective detection, good reproducibility, and extremely short recovery time (10 s). Therefore, this sensor is an ideal candidate for application in high-performance hydrogen gas sensing.

Stable Voltage Cutoff Cycle Cathode with Tunable and Ordered Porous Structure for Li-O2 Batteries.

Ordered porous RuO2 materials with various pore structure parameters are prepared via a hard-template method and are used as the carbon-free cathodes for Li-O2 batteries under the voltage cutoff cycle mode. The influences of pore structure parameters of porous RuO2 on electrochemical performance are systematically studied. Results indicate that specific surface area and pore size determine the specific capacity and round-trip efficiency of Li-O2 batteries. Too small pores cause pore blockage and hinder the diffusion pathways of Li+ and O2 , thereby causing small specific capacity and high overpotentials. Too large pores weaken the mechanical property of porous RuO2 , thereby causing the rapid decrease in capacity during electrochemical reaction. The Li-O2 battery based on the RuO2 cathode with an average pore size of 16 nm (RuO2 -16) exhibits a high round-trip efficiency of ≈75.6% and an excellent cycling stability of up to 70 cycles at 100 mA g-1 with a voltage window of 2.5-4.0 V. The superior performance of RuO2 -16 can be attributed to its optimal pore structure parameters. Furthermore, the in situ differential electrochemical mass spectrometry test demonstrates that RuO2 can effectively reduce parasitic reactions compared with carbon materials.

Nanorod carbon nitride as a carbo catalyst for selective oxidation of hydrogen sulfide to sulfur.

Two-dimensional mesoporous carbon nitride and its highly efficient nanorod framework were prepared via hard-templating method. The obtained materials were fully characterized. The results showed that the samples structural ordering and morphology were similar to those of the parent silica templates; they had large pore volumes as well as high surface area structures. Carbon nitride carbocatalysts were used for H2S selective oxidation. The catalytic tests were carried out at 190, 210 and 230 °C in a fixed bed reactor. The obtained selectivity values for mesoporous carbon nitride rod and mesoporous carbon nitride toward elemental sulfur at 190 °C were 88.8% and 83%, respectively. Both samples were highly active due to their alkaline surface, appropriate pore size distribution and structure. In comparison with other carbon-based materials used for this process, mesoporous carbon nitride rod is the first carbonaceous material reported so far that could yield high levels of both conversion and selectivity at 190 °C. This superiority could be caused by the narrow pore size distribution (<3 nm), incorporation of nitrogen into the carbon matrix and its appropriate morphology. Nitrogen species act as electron donors in H2S oxidation. Rod-like particles might have acted as nanoreactors that facilitated the reaction progress.

Catalytic decomposition of ammonium perchlorate on hollow mesoporous CuO microspheres

Hollow mesoporous CuO microspheres (CuO-HM) have been prepared by a hard-template method and their structure properties as well as catalytic performance in ammonium perchlorate (AP) decomposition were fully investigated by XRD, SEM, XPS, TG/DSC and TG/F-TIR methods. The results indicated that CuO-HM could be described as CuO micro-sized spheres composed of self-assembled nanoparticles, possessing hollow and mesoporous structure. Compared with CuO nanoparticles and CuO microspheres, CuO-HM has significantly improved catalytic efficiency in AP decomposition due to large surface area, easily accessible porous and hollow structure. Typically, CuO-HM could decrease the AP decomposition temperature by 105.7 °C and enhance the heat production by 735 J/g. TG/FT-IR results indicated that CuO-HM accelerated the thermal decomposition of AP mainly at the high temperature decomposition stage with the releasing of N2O, NO, NH3, H2O, HCl, O2 et al. This study demonstrated that hollow and mesoporous CuO was a promising catalyst for the application in solid fuel rockets propellants.

Advanced Functional Carbons and Their Hybrid Nanoarchitectures towards Supercapacitor Applications.

Porous carbons have attracted much attention as electrode materials for supercapacitors due to their enormous surface area, high electrical conductivity, excellent corrosion resistance, high temperature stability, and relatively low cost. The design of porous architectures is considered key for determining electrochemical performance. Pore size distribution, pore size, and pore connectivity strongly affect electrochemical performance. Various carbon materials with pore size ranging from micro- to macropores were extensively studied. Herein, various types of porous carbon-based and hybrid materials from different approaches and their electrochemical applications are summarized. Appropriate tuning of the pore size of carbon materials is essential for ensuring good transport of ions with different sizes throughout the electrolyte, so that the electrode materials can be fully utilized. Many carbon materials were produced from a series of carbonization and activation processes that possess controllable pore structures, including activated carbons, graphite, carbon nanotubes, carbon aerogels, and templated porous carbons. Templated carbon materials were prepared by various approaches, such as direct carbonization from carbon precursors and soft- and hard-template methods. To enhance the electrochemical performance of the electrode materials, heteroatoms, such as nitrogen, sulfur, and boron, were doped into porous carbons. In addition, to optimize the overall capacitance without destroying the stability and morphology of electrode materials, pseudocapacitive materials, such as transition-metal oxides, were introduced into the carbon frameworks. In this review, recent advances in the fabrication of nanoarchitectured porous carbons and metal oxides through various approaches for supercapacitor applications are summarized.