Morphogenesis of Metal–Organic Mesocrystals Mediated by Double Hydrophilic Block Copolymers

Mesocrystalssuperstructures of crystalline nanoparticles that are aligned in a crystallographic fashionare of increasing interest for formation of inorganic materials with complex and sophisticated morphologies to tailor properties without changing chemical composition. Here we report morphogenesis of a novel mesocrystal consisting of nanoscale metal–organic frameworks (MOF) by using double hydrophilic block copolymer (DHBC) as a crystal modulator. DHBC selectively prefers the metastable hexagonal kinetic polymorph and promotes anisotropic crystal growth to generate hexagonal rod mesocrystals via oriented attachment and mesoscale assembly. The metastable nature of hexagonal mesocrystals enables further hierarchical morphogenesis by a solvent-mediated polymorphic transformation toward stable tetragonal mesocrystals that retain the outer hexagonal particle morphology. Furthermore, synthesis of hybrid MOFs, where hexagonal mesocrystals are vertically aligned on specific surfaces of cubic MOFs, is demonstrated. The present strategy opens a new avenue to create MOF mesocrystals and their hybrids with controlled size and morphology that can be designed for various potential applications

Direct Access to Hierarchically Porous Inorganic Oxide Materials with Three-Dimensionally Interconnected Networks

Hierarchically porous oxide materials have immense potential for applications in catalysis, separation, and energy devices, but the synthesis of these materials is hampered by the need to use multiple templates and the associated complicated steps and uncontrollable mixing behavior. Here we report a simple one-pot strategy for the synthesis of inorganic oxide materials with multiscale porosity. The inorganic precursor and block copolymer are coassembled into an ordered mesostructure (microphase separation), while the in situ-polymerized organic precursor forms organic-rich macrodomains (macrophase separation) around which the mesostructure grows. Calcination generates hierarchical meso/macroporous SiO₂ and TiO₂ with three-dimensionally interconnected pore networks. The continuous 3D macrostructures were clearly visualized by nanoscale X-ray computed tomography. The resulting TiO₂ was used as the anode in a lithium ion battery and showed excellent rate capability compared with mesoporous TiO₂. This work is of particular importance because it (i) expands the base of BCP self-assembly from mesostructures to complex porous structures, (ii) shows that the interplay of micro- and macrophase separation can be fully exploited for the design of hierarchically porous inorganic materials, and therefore (iii) provides strategies for researchers in materials science and polymer science

Block Copolymer Directed Ordered Mesostructured TiNb₂O₇ Multimetallic Oxide Constructed of Nanocrystals as High Power Li-Ion Battery Anodes

In order to achieve high-power and -energy anodes operating above 1.0 V (vs Li/Li⁺), titanium-based materials have been investigated for a long time. However, theoretically low lithium charge capacities of titanium-anodes have required new types of high-capacity anode materials. As a candidate, TiNb₂O₇ has attracted much attention due to the high theoretical capacity of 387.6 mA h g^–1. However, the high formation temperature of the TiNb₂O₇ phase resulted in large-sized TiNb₂O₇ crystals, thus resulting in poor rate capability. Herein, ordered mesoporous TiNb₂O₇ (denoted as m-TNO) was synthesized by block copolymer assisted self-assembly, and the resulting binary metal oxide was applied as an anode in a lithium ion battery. The nanocrystals (∼15 nm) developed inside the confined pore walls and large pores (∼40 nm) of m-TNO resulted in a short diffusion length for lithium ions/electrons and fast penetration of electrolyte. As a stable anode, the m-TNO electrode exhibited a high capacity of 289 mA h g^–1 (at 0.1 C) and an excellent rate performance of 162 mA h g^–1 at 20 C and 116 mA h g^–1 at 50 C (= 19.35 A g^–1) within a potential range of 1.0–3.0 V (vs Li/Li⁺), which clearly surpasses other Ti-and Nb-based anode materials (TiO₂, Li₄Ti₅O₁₂, Nb₂O₅, etc.) and previously reported TiNb₂O₇ materials. The m-TNO and carbon coated m-TNO electrodes also demonstrated stable cycle performances of 48 and 81% retention during 2,000 cycles at 10 C rate, respectively

One-Pot Synthesis of Tin-Embedded Carbon/Silica Nanocomposites for Anode Materials in Lithium-Ion Batteries

We report a facile “one-pot” method for the synthesis of Sn-embedded carbon–silica (CS) mesostructured (nanostructured) composites through the selective interaction of resol (carbon precursor), tetraethylorthosilicate (TEOS), and tributylphenyltin (Sn precursor) with an amphiphilic diblock copolymer, poly(ethylene oxide-<i>b</i>-styrene), PEO-<i>b</i>-PS. A unique morphology transition from Sn nanowires to spherical Sn nanoparticles embedded in CS framework has been obtained. Metallic Sn species are homogeneously embedded in a rigid CS framework and are effectively confined within the nanostructures. The resulting composites are used as anode materials for lithium-ion batteries and exhibit high specific capacities (600 mA h g ^–1 at a current density of 45 mA g^–1, and 440 mA h g^–1 at a current density of 300 mA g^–1) and an excellent cyclability of over 100 cycles with high Coulombic efficiency. Most of all, the novel method developed in this work for synthesizing functional hybrid materials can be extended to the preparation of various functional nanocomposites owing to its versatility and facileness

Toward Ultimate Control of Radical Polymerization: Functionalized Metal–Organic Frameworks as a Robust Environment for Metal-Catalyzed Polymerizations

Herein, an approach via combination of confined porous textures and reversible deactivation radical polymerization techniques is proposed to advance synthetic polymer chemistry, i.e., a connection of metal–organic frameworks (MOFs) and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). Zn₂(benzene-1,4-dicarboxylate)₂(1,4-diazabicyclo­[2.2.2]­octane) [Zn₂(bdc)₂(dabco)] is utilized as a reaction environment for polymerization of various methacrylate monomers (methyl, ethyl, benzyl, and isobornyl methacrylate) in a confined nanochannel, resulting in polymers with control over dispersity, end functionalities, and tacticity with respect to distinct molecular size. To refine and reconsolidate the compartmentation effect on polymer regularity, initiator-functionalized Zn MOF was synthesized via cocrystallization with an initiator-functionalized ligand, 2-(2-bromo-2-methylpropanamido)-1,4-benzenedicarboxylate (Brbdc), in different ratios (10%, 20%, and 50%). Through the embedded initiator, surface-initiated ARGET ATRP was directly initiated from the walls of the nanochannels. The obtained polymers had a high molecular weight up to 392 000. Moreover, a significant improvement in end-group functionality and stereocontrol was observed, entailing polymers with obvious increments in isotacticity. The results highlight a combination of MOFs and ATRP that is a promising and universal methodology to prepare various polymers with high molecular weight exhibiting well-defined uniformity in chain length and microstructure as well as the preserved chain-end functionality

Toward Ultimate Control of Radical Polymerization: Functionalized Metal–Organic Frameworks as a Robust Environment for Metal-Catalyzed Polymerizations

Herein, an approach via combination of confined porous textures and reversible deactivation radical polymerization techniques is proposed to advance synthetic polymer chemistry, i.e., a connection of metal–organic frameworks (MOFs) and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). Zn₂(benzene-1,4-dicarboxylate)₂(1,4-diazabicyclo­[2.2.2]­octane) [Zn₂(bdc)₂(dabco)] is utilized as a reaction environment for polymerization of various methacrylate monomers (methyl, ethyl, benzyl, and isobornyl methacrylate) in a confined nanochannel, resulting in polymers with control over dispersity, end functionalities, and tacticity with respect to distinct molecular size. To refine and reconsolidate the compartmentation effect on polymer regularity, initiator-functionalized Zn MOF was synthesized via cocrystallization with an initiator-functionalized ligand, 2-(2-bromo-2-methylpropanamido)-1,4-benzenedicarboxylate (Brbdc), in different ratios (10%, 20%, and 50%). Through the embedded initiator, surface-initiated ARGET ATRP was directly initiated from the walls of the nanochannels. The obtained polymers had a high molecular weight up to 392 000. Moreover, a significant improvement in end-group functionality and stereocontrol was observed, entailing polymers with obvious increments in isotacticity. The results highlight a combination of MOFs and ATRP that is a promising and universal methodology to prepare various polymers with high molecular weight exhibiting well-defined uniformity in chain length and microstructure as well as the preserved chain-end functionality

Preparation Method of Co₃O₄ Nanoparticles Using Ordered Mesoporous Carbons as a Template and Their Application for Fischer–Tropsch Synthesis

Co₃O₄ nanoparticles (NPs) with a narrow particle size distribution were fabricated via a facile and novel method using mesoporous carbon materials (CMK-3, MSU-F-C) as sacrificial templates. The particle size distribution of the Co₃O₄ NPs varied depending on the pore size of the templates. Synthesis of the NPs with concurrent complete removal of the templates was achieved at 593 K, which is lower than the temperatures utilized in previous reports. It was verified that the carbon template was decomposed by catalytic oxidation with cobalt and NO_<i>x</i> species generated by thermal decomposition of the cobalt nitrate precursor in air. The prepared NPs, and particularly the Co₃O₄ NPs synthesized from CMK-3, acted as excellent catalysts for the Fischer–Tropsch synthesis (FTS). The high catalytic performance was associated with the optimum particle size (6–10 nm) of the nanoparticles for FTS and enhanced reducibility

One-Pot Synthesis of Intermetallic Electrocatalysts in Ordered, Large-Pore Mesoporous Carbon/Silica toward Formic Acid Oxidation

This study describes the one-pot synthesis and single-cell characterization of ordered, large-pore (>30 nm) mesoporous carbon/silica (OMCS) composites with well-dispersed intermetallic PtPb nanoparticles on pore wall surfaces as anode catalysts for direct formic acid fuel cells (DFAFCs). Lab-synthesized amphiphilic diblock copolymers coassemble hydrophobic metal precursors as well as hydrophilic carbon and silica precursors. The final materials have a two-dimensional hexagonal-type structure. Uniform and large pores, in which intermetallic PtPb nanocrystals are significantly smaller than the pore size and highly dispersed, enable pore backfilling with ionomers and formation of the desired triple-phase boundary in single cells. The materials show more than 10 times higher mass activity and significantly lower onset potential for formic acid oxidation as compared with commercial Pt/C, as well as high stability due to better resistivity toward CO poisoning. In single cells, the maximum power density was higher than that of commercial Pt/C, and the stability highly improved, compared with commercial Pd/C. The results suggest that PtPb-based catalysts on large-pore OMCSs may be practically applied as real fuel cell catalysts for DFAFC

Mesoporous Ge/GeO₂/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility

We report mesoporous composite materials (m-GeO₂, m-GeO₂/C, and m-Ge-GeO₂/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO₂/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g^–1), and stable cycle life compared with the other mesoporous and bulk GeO₂ electrodes. m-Ge/GeO₂/C exhibits one of the highest areal capacities (1.65 mA h cm^–2) among previously reported Ge- and GeO₂-based anodes. The superior electrochemical performance in m-Ge/GeO₂/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge

Facile Synthesis of Nb₂O₅@Carbon Core–Shell Nanocrystals with Controlled Crystalline Structure for High-Power Anodes in Hybrid Supercapacitors

Hybrid supercapacitors (battery-supercapacitor hybrid devices, HSCs) deliver high energy within seconds (excellent rate capability) with stable cyclability. One of the key limitations in developing high-performance HSCs is imbalance in power capability between the sluggish Faradaic lithium-intercalation anode and rapid non-Faradaic capacitive cathode. To solve this problem, we synthesize Nb₂O₅@carbon core–shell nanocyrstals (Nb₂O₅@C NCs) as high-power anode materials with controlled crystalline phases (orthorhombic (<i>T</i>) and pseudohexagonal (<i>TT</i>)) <i>via</i> a facile one-pot synthesis method based on a water-in-oil microemulsion system. The synthesis of ideal <i>T</i>-Nb₂O₅ for fast Li⁺ diffusion is simply achieved by controlling the microemulsion parameter (<i>e.g.,</i> pH control). The <i>T</i>-Nb₂O₅@C NCs shows a reversible specific capacity of ∼180 mA h g^–1 at 0.05 A g^–1 (1.1–3.0 V <i>vs</i> Li/Li⁺) with rapid rate capability compared to that of <i>TT</i>-Nb₂O₅@C and carbon shell-free Nb₂O₅ NCs, mainly due to synergistic effects of (i) the structural merit of <i>T</i>-Nb₂O₅ and (ii) the conductive carbon shell for high electron mobility. The highest energy (∼63 W h kg^–1) and power (16 528 W kg^–1 achieved at ∼5 W h kg^–1) densities within the voltage range of 1.0–3.5 V of the HSC using <i>T</i>-Nb₂O₅@C anode and MSP-20 cathode are remarkable