Showing papers on "Mesoporous material published in 2019"

Versatile Nanoemulsion Assembly Approach to Synthesize Functional Mesoporous Carbon Nanospheres with Tunable Pore Sizes and Architectures

Abstract: Functional mesoporous carbons have attracted significant scientific and technological interest owning to their fascinating and excellent properties. However, controlled synthesis of functional mesoporous carbons with large tunable pore sizes, small particle size, well-designed functionalities, and uniform morphology is still a great challenge. Herein, we report a versatile nanoemulsion assembly approach to prepare N-doped mesoporous carbon nanospheres with high uniformity and large tunable pore sizes (5-37 nm). We show that the organic molecules (e.g., 1,3,5-trimethylbenzene, TMB) not only play an important role in the evolution of pore sizes but also significantly affect the interfacial interaction between soft templates and carbon precursors. As a result, a well-defined Pluronic F127/TMB/dopamine nanoemulsion can be facilely obtained in the ethanol/water system, which directs the polymerization of dopamine into highly uniform polymer nanospheres and their derived N-doped carbon nanospheres with diversely novel structures such as smooth, golf ball, multichambered, and dendritic nanospheres. The resultant uniform dendritic mesoporous carbon nanospheres show an ultralarge pore size (∼37 nm), small particle size (∼128 nm), high surface area (∼635 m2 g-1), and abundant N content (∼6.8 wt %), which deliver high current density and excellent durability toward oxygen reduction reaction in alkaline solution.

High-performance bifunctional oxygen electrocatalysts for zinc-air batteries over mesoporous Fe/Co-N-C nanofibers with embedding FeCo alloy nanoparticles

Abstract: Mesoporous Fe/Co-N-C nanofibers with embedding FeCo nanoparticles (denote as FeCo@MNC) have been prepared from electrospun Fe/Co-N coordination compounds with bicomponent polymers consisting of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN). The as-fabricated hybrid nanofibers exhibited one-dimensional mesoporous morphology, a large BET surface area and uniformly distributed active sites (e.g FeCo alloy, Fe/Co-N). It elucidated that the co-existence of FeCo alloy and Fe/Co-N active sites could promote the catalytic activity of ORR and OER simultaneously. Essentially, the unique one-dimensional of nanofiber with observable porous morphology has indispensable contribution to charge transportation and exposure of active sites to O2 adsorption when assembled into a rechargeable zinc-air battery. As a result, FeCo@MNC exhibited a low discharge-charge voltage gap (e.g. 0.9 V, discharge-charge at 20 mA cm−2), higher power density (e.g. 115 mW cm−2, at 143 mA cm−2) and stability.

Implanting Atomic Cobalt within Mesoporous Carbon toward Highly Stable Lithium–Sulfur Batteries

Abstract: Lithium-sulfur (Li-S) batteries hold great promise to serve as next-generation energy storage devices. However, the practical performances of Li-S batteries are severely limited by the sulfur cathode regarding its low conductivity, huge volume change, and the polysulfide shuttle effect. The first two issues have been well addressed by introducing mesoporous carbon hosts to the sulfur cathode. Unfortunately, the nonpolar nature of carbon materials renders poor affinity to polar polysulfides, leaving the shuttling issue unaddressed. In this contribution, atomic cobalt is implanted within the skeleton of mesoporous carbon via a supramolecular self-templating strategy, which simultaneously improves the interaction with polysulfides and maintains the mesoporous structure. Moreover, the atomic cobalt dopants serve as active sites to improve the kinetics of the sulfur redox reactions. With the atomic-cobalt-decorated mesoporous carbon host, a high capacity of 1130 mAh gS-1 at 0.5 C and a high stability with a retention of 74.1% after 300 cycles are realized. Implanting atomic metal in mesoporous carbon demonstrates a feasible strategy to endow nanomaterials with targeted functions for Li-S batteries and broad applications.

A Mesoporous Nanoenzyme Derived from Metal-Organic Frameworks with Endogenous Oxygen Generation to Alleviate Tumor Hypoxia for Significantly Enhanced Photodynamic Therapy.

Abstract: Tumor hypoxia compromises the therapeutic efficiency of photodynamic therapy (PDT) as the local oxygen concentration plays an important role in the generation of cytotoxic singlet oxygen (1 O2 ). Herein, a versatile mesoporous nanoenzyme (NE) derived from metal-organic frameworks (MOFs) is presented for in situ generation of endogenous O2 to enhance the PDT efficacy under bioimaging guidance. The mesoporous NE is constructed by first coating a manganese-based MOFs with mesoporous silica, followed by a facile annealing process under the ambient atmosphere. After removing the mesoporous silica shell and post-modifying with polydopamine and poly(ethylene glycol) for improving the biocompatibility, the obtained mesoporous NE is loaded with chlorin e6 (Ce6), a commonly used photosensitizer in PDT, with a high loading capacity. Upon the O2 generation through the catalytic reaction between the catalytic amount NE and the endogenous H2 O2 , the hypoxic tumor microenvironment is relieved. Thus, Ce6-loaded NE serves as a H2 O2 -activated oxygen supplier to increase the local O2 concentration for significantly enhanced antitumor PDT efficacy in vitro and in vivo. In addition, the NE also shows T2 -weighted magnetic resonance imaging ability for its in vivo tracking. This work presents an interesting biomedical use of MOF-derived mesoporous NE as a multifunctional theranostic agent in cancer therapy.

Three-dimensional ordered porous electrode materials for electrochemical energy storage

Abstract: The past decade has witnessed substantial advances in the synthesis of various electrode materials with three-dimensional (3D) ordered macroporous or mesoporous structures (the so-called “inverse opals”) for applications in electrochemical energy storage devices. This review summarizes recent advancements in 3D ordered porous (3DOP) electrode materials and their unusual electrochemical properties endowed by their intrinsic and geometric structures. The 3DOP electrode materials discussed here mainly include carbon materials, transition metal oxides (such as TiO2, SnO2, Co3O4, NiO, Fe2O3, V2O5, Cu2O, MnO2, and GeO2), transition metal dichalcogenides (such as MoS2 and WS2), elementary substances (such as Si, Ge, and Au), intercalation compounds (such as Li4Ti5O12, LiCoO2, LiMn2O4, LiFePO4), and conductive polymers (polypyrrole and polyaniline). Representative applications of these materials in Li ion batteries, aqueous rechargeable lithium batteries, Li-S batteries, Li-O2 batteries, and supercapacitors are presented. Particular focus is placed on how ordered porous structures influence the electrochemical performance of electrode materials. Additionally, we discuss research opportunities as well as the current challenges to facilitate further contributions to this emerging research frontier. Three-dimensional ordered porous materials can improve the electrochemical storage of energy. Jing Wang and Yuping Wu from Nanjing Tech University, China and co-workers review the development of these materials for use as electrodes in devices such as batteries and supercapacitors. Three-dimensional ordered porous materials are created by inserting the desired raw material into a template made from an array of spheres. The spheres are removed to leave a hole-filled material ideal for storage. The authors describe how this ordered porous structure influences the electrochemical performance of electrodes made from elementary materials, transition metal oxides, conductive polymers, or carbon-based materials, among others. The challenges for the future are discussed, including developing a better fundamental understanding of charge transport, improving efficiency, scaling-up production, and lowering production costs. The past decade has witnessed substantial advances in the synthesis of various electrode materials with three-dimensional (3D) ordered macroporous or mesoporous structures (the so-called “inverse opals”) for applications in electrochemical energy storage devices. Yuping Wu from Nanjing Tech University anchored recent advancements in 3D ordered porous (3DOP) electrode materials and their unusual electrochemical properties bound by their intrinsic and geometric structures. The team introduces various 3DOP electrode materials and their representative applications as electrode materials. Additionally, the team also provides research opportunities as well as the challenges to facilitate further contributions to this emerging research frontier.

High-Lithium-Affinity Chemically Exfoliated 2D Covalent Organic Frameworks.

Abstract: Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium-ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB-COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few-layered COF nanosheets (E-TFPB-COF), whose restacking is prevented by the in situ formed MnO2 nanoparticles. Compared with the bulk TFPB-COF, the exfoliated TFPB-COF exhibits new active Li-storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E-TFPB-COF/MnO2 and E-TFPB-COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g-1 after 300 cycles with good high-rate capability.

Mesoporous carbon hollow microspheres with tunable pore size and shell thickness as efficient electromagnetic wave absorbers

Abstract: Carbon hollow microspheres with a uniform mesoporous shell (PCHMs) were designed and fabricated using a template-assistant method followed by a pyrolysis-etching process. Through tuning the pyrolysis temperature, PCHMs with various pore size and shell thickness can be obtained. In particular, the PCHMs carbonized at 650 °C (PCHMs-650) are composed of a mesoporous shell (thickness: 52 nm) and an interior void of 153 nm, endowing the materials with large surface area of 925.9 m2/g. The unique core-shell structure generated by carbon shell and void core is critical for the attenuation capability of EM energy. The composites containing 20 wt% PCHMs-650 exhibit favorable microwave absorbing performance with the minimum reflection loss (RLmin) of −39.4 dB at 3.6 mm. The broadest effective absorption bandwidth (EAB) can extend to 5.28 GHz (9.68–14.96 GHz) at only 2.6 mm. It is believed that PCHMs can be used as a promising absorber with lightweight, impressive bandwidth and strong absorption efficiency.

Efficient photo-Fenton activity in mesoporous MIL-100(Fe) decorated with ZnO nanosphere for pollutants degradation

Abstract: Metal-organic frameworks (MOFs) have received significant interest as a promising photocatalyst for environmental remediation due to its high surface area and porous nature. The small pores ( 2 nm) and open pore cavities that can provide right pathways for ingoing and outgoing of molecules during catalysis. Herein, we successfully report stable mesoporous MIL-100(Fe) loaded with ZnO NS by an in situ self-assembly method. The prepared samples were characterized by Brunauer–Emmett–Teller (BET) and N2 adsorption-desorption isotherm to study their surface area and porosity. The catalytic performance of mesoporous MIL-100(Fe) was approximately 2–3 order of magnitude more than that of microporous MIL-100(Fe). Such higher catalytic activity in mesoporous MIL-100(Fe) can be ascribed to its mesocellular structure which can improve the molecular diffusion and accessibility inside MOF channels. The charge separation efficiency and photo-Fenton activity of mesoporous MIL-100(Fe) can further be increased by introduction of certain amount of ZnO NS and H2O2. Moreover, the as synthesized sample shows higher photo-Fenton degradation efficiency at lower pH value with certain amount of H2O2. Lastly, the possible catalytic mechanism has been tentatively proposed. This study not only used for the pollutants degradation but also provide useful platform for the application of mesoporous MOFs as an efficient photo-Fenton activity to various other fields.

Pore-tuning to boost the electrocatalytic activity of polymeric micelle-templated mesoporous Pd nanoparticles

Abstract: Understanding how mesoporous noble metal architectures affect electrocatalytic performance is very important for the rational design and preparation of high-performance electrocatalysts. Herein, by using polymeric micelle-assembled structures as templates, mesoporous Pd nanoparticles with tunable porous constructions are synthesized by simply tuning the solvent compositions. The effect of porous Pd nanoparticles on the electrocatalytic performance is thoroughly studied. Their superior electrocatalytic activity can be attributed to the mass transport efficiency and open porous structures.

Enhanced low-temperature performance of CO2 methanation over mesoporous Ni/Al2O3-ZrO2 catalysts

Abstract: Converting carbon dioxide to value-added chemicals has been attracted much attention, whereas direct hydrogenation of CO2 to synthetic natural gas (SNG) at a lower temperature remains a big challenge. Mesoporous Al2O3-ZrO2 modified Ni catalysts were prepared via a single-step epoxide-driven sol-gel method for CO2 methanation. Almost 100% selectivity of CH4 with 77% CO2 conversion were obtained at a lower temperature of 300 °C, and no catalyst deactivation was observed in 100 h. Different characterization methods including N2 adsorption-desorption, H2-TPR, H2-TPD, XRD, XPS, and TEM were combined together to explore the interaction of Ni-ZrO2 and Al2O3-ZrO2. Incorporation of ZrO2 into Ni/Al2O3 weakened the Ni-Al2O3 interaction via the combination of Al2O3-ZrO2 solid solution, promoting the reduction and dispersion of NiO phase. The adding of higher Zr loading increased the amount of active metallic nickel sites and oxygen vacancies on the composite support, improving obviously the lower temperature catalytic activity and CH4 selectivity. Higher Ni species loading further resulted in the formation of active Ni sites and improved the low-temperature CO2 methanation performance. Moreover, the enhanced stability of the Al2O3-ZrO2 support and oxygen vacancies provided by the ZrO2 promoter could help to promote the catalytic stability.

Three-dimensionally ordered mesoporous iron oxide-supported single-atom platinum: Highly active catalysts for benzene combustion

Abstract: Single-atom catalysts are a kind of promising catalytic materials that can use the precious metal more efficiently. The KIT-6-templaing method was adopted to obtain three-dimensionally ordered mesoporous iron oxide (meso-Fe2O3). The meso-Fe2O3-supported single-atom Pt with a loading of x wt% (xPt1/meso-Fe2O3, x = 0.08, 0.15, and 0.25) catalysts were synthesized via a polyvinyl alcohol-protected reduction route. The 0.25 Pt1/meso-Fe2O3 sample showed much better catalytic activity than the meso-Fe2O3-supported Pt nanoparticle (0.25 PtNP/meso-Fe2O3) sample for benzene combustion, with the temperatures T10%, T50%, and T90% (corresponding to benzene conversions of 10, 50, and 90%) were 164, 186, and 198 °C at a space velocity of 20,000 mL/(g h), respectively. The TOFPt (2.69 s−1) obtained over 0.25 Pt1/meso-Fe2O3 at 160 °C was much higher than that (1.16 s−1) obtained over the 0.25 PtNP/meso-Fe2O3 sample at 160 °C. Furthermore, the 0.25 Pt1/meso-Fe2O3 and 0.15Pt1/meso-Fe2O3 samples exhibited better water-resistant ability than the 0.25 PtNP/meso-Fe2O3 sample, which was possibly due to formation of the active radicals and decomposition of carbonates in the presence of moisture. In situ DRIFTS results demonstrate that the phenolate and benzoquinone as well as cyclohexanone and maleate were the main intermediates in the oxidation of benzene. The good stability of the 0.15Pt1/meso-Fe2O3 and 0.25 Pt1/meso-Fe2O3 samples was associated with the strong interaction between Pt and meso-Fe2O3.

A Cation-Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells

Abstract: Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn2+ to Sn4+ . Now a chemical route is developed for fabrication of high-quality methylammonium tin iodide perovskite (MASnI3 ) films: hydrazinium tin iodide (HASnI3 ) perovskite film is first solution-deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI2 ), and then transformed into MASnI3 via a cation displacement approach. With the two-step process, a dense and uniform MASnI3 film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI3 as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.

High-quality mesoporous graphene particles as high-energy and fast-charging anodes for lithium-ion batteries

Abstract: The application of graphene for electrochemical energy storage has received tremendous attention; however, challenges remain in synthesis and other aspects. Here we report the synthesis of high-quality, nitrogen-doped, mesoporous graphene particles through chemical vapor deposition with magnesium-oxide particles as the catalyst and template. Such particles possess excellent structural and electrochemical stability, electronic and ionic conductivity, enabling their use as high-performance anodes with high reversible capacity, outstanding rate performance (e.g., 1,138 mA h g-1 at 0.2 C or 440 mA h g-1 at 60 C with a mass loading of 1 mg cm-2), and excellent cycling stability (e.g., >99% capacity retention for 500 cycles at 2 C with a mass loading of 1 mg cm-2). Interestingly, thick electrodes could be fabricated with high areal capacity and current density (e.g., 6.1 mA h cm-2 at 0.9 mA cm-2), providing an intriguing class of materials for lithium-ion batteries with high energy and power performance.

Epitaxial growth of oriented prussian blue analogue derived well-aligned CoFe2O4 thin film for efficient oxygen evolution reaction

Abstract: The development of cost-effective, high-efficiency, and non-noble metal based electrocatalysts for oxygen evolution reaction (OER) is considered to be the most pivotal portion for electrochemical water splitting to generate renewable energy. Herein, well-aligned mesoporous CoFe2O4 thin film is first developed from surface epitaxial growth of oriented CoFe-based prussian blue analogue thin film (CoFe-PBA thin film) for efficient electrocatalytic OER. CoFe-PBA thin film with preferred [100] orientation is first prepared on the substrate surface by employing liquid phase epitaxial method without any structure-directing surfactants. After thermal pyrolysis, such CoFe-PBA thin film was transformed into well-aligned mesoporous CoFe2O4 thin film. Interestingly, the self-support CoFe2O4 thin film electrode with the mass loading of 1.6 mg cm−2 delivers an oxygen evolution current density of 10 mA cm−2 at an overpotential of 266 mV and exhibits durable stability in 1 M KOH aqueous solution. The remarkable and stable catalytic performance of the CoFe2O4 thin film can be mainly owing to the mesoporous structure of CoFe2O4, efficient charge/electron transfer, the numerous exposed active sites, and the well-structured configuration of the electrode. Hence, this work provides an effective paradigm for preparing binder-free, self-support, and low-cost spinel oxide electrocatalyst for efficient OER derived from surface epitaxial growth of oriented PBA thin film.

Synthesis of uniform ordered mesoporous TiO2 microspheres with controllable phase junctions for efficient solar water splitting

Abstract: As a benchmark photocatalyst, commercial P25–TiO2 has been widely used for various photocatalytic applications. However, the low surface area and poorly porous structure greatly limit its performance. Herein, uniform ordered mesoporous TiO2 microspheres (denoted as Meso-TiO2-X; X represents the rutile percentage in the resultant microspheres) with controllable anatase/rutile phase junctions and radially oriented mesochannels are synthesized by a coordination-mediated self-assembly approach. The anatase/rutile ratio in the resultant microspheres can be facilely adjusted as desired (rutile percentage: 0–100) by changing the concentration of hydrochloric acid. As a typical one, the as-prepared Meso-TiO2-25 microspheres have a similar anatase/rutile ratio to commercial P25. But the surface area (78.6 m2 g−1) and pore volume (0.39 cm3 g−1) of the resultant microspheres are larger than those of commercial P25. When used as the photocatalyst for H2 generation, the Meso-TiO2-25 delivers high solar-driven H2 evolution rates under air mass 1.5 global (AM 1.5 G) and visible-light (λ > 400 nm), respectively, which are significantly larger than those of commercial P25. This coordination-mediated self-assembly method paves a new way toward the design and synthesis of high performance mesoporous photocatalysts.