Kevin C.-W. Wu

Hierarchically porous carbon derived from polymers and biomass: effect of interconnected pores on energy applications

Hierarchically porous carbons (HPCs) with 1D to 3D network are attracting vast interest due to their potential technological application profile ranging from electrochemical capacitors, lithium ion batteries, solar cells, hydrogen storage systems, photonic material, fuel cells, sorbent for toxic gas separation and so on. Natural raw-materials such as biomass-biopolymer derived hierarchical nanostructured carbons are especially attractive for their uniform pore dimensions which can be adjustable over a wide range of length scales. Good electrical conductivity, high surface area, and excellent chemical stability are unique physicochemical properties which are responsible for micro/nanostructured porous carbon to be highly trusted candidate for emerging nanotechnologies. This review focuses on the ‘out-of-the-box’ synthetic techniques capable of deriving HPC with superior application profiles. The article presents the promising scope of accessing HPCs from (1) hard-templating, soft-templating, and non-templating routes, (2) biopolymers with a major focus on non-templating strategies. Subsequently, emerging strategies of hetero-atom doping in porous carbon nanostructures are discussed. The review will highlight the contribution of synergistic effect of macro–meso–micropores on a range of emerging applications such as CO2 capture, carbon photonic crystal sensors, Li–S batteries, and supercapacitor. Mechanism of ion transport and buffering, electrical double layer enhancement have been discussed in the context of pore structure and shapes. We will also show the differences of HPC and ordered mesoporous carbon (OMC) in terms of their synthesis strategies and choices of template for self-assembly. How the remarkable mechanical strength of the HPCs can be achieved by selecting self-assembling template, whereas collapse of mesostructure via decomposition of framework occurs due to poor thermal stability or high N-content of the carbon source will be discussed.

Imparting Functionality to Biocatalysts via Embedding Enzymes into Nanoporous Materials by a de Novo Approach: Size-Selective Sheltering of Catalase in Metal–Organic Framework Microcrystals

We develop a new concept to impart new functions to biocatalysts by combining enzymes and metal-organic frameworks (MOFs). The proof-of-concept design is demonstrated by embedding catalase molecules into uniformly sized ZIF-90 crystals via a de novo approach. We have carried out electron microscopy, X-ray diffraction, nitrogen sorption, electrophoresis, thermogravimetric analysis, and confocal microscopy to confirm that the ~10 nm catalase molecules are embedded in 2 μm single-crystalline ZIF-90 crystals with ~5 wt % loading. Because catalase is immobilized and sheltered by the ZIF-90 crystals, the composites show activity in hydrogen peroxide degradation even in the presence of protease proteinase K.

Nanoarchitectured Design of Porous Materials and Nanocomposites from Metal‐Organic Frameworks

The emergence of metal-organic frameworks (MOFs) as a new class of crystalline porous materials is attracting considerable attention in many fields such as catalysis, energy storage and conversion, sensors, and environmental remediation due to their controllable composition, structure and pore size. MOFs are versatile precursors for the preparation of various forms of nanomaterials as well as new multifunctional nanocomposites/hybrids, which exhibit superior functional properties compared to the individual components assembling the composites. This review provides an overview of recent developments achieved in the fabrication of porous MOF-derived nanostructures including carbons, metal oxides, metal chalcogenides (metal sulfides and selenides), metal carbides, metal phosphides and their composites. Finally, the challenges and future trends and prospects associated with the development of MOF-derived nanomaterials are also examined.

Nanoarchitectures for Mesoporous Metals.

The field of mesoporous metal nanoarchitectonics offers several advantages which cannot be found elsewhere. These materials have been showcasing impressive enhancements of their electrochemical properties for further implementation, compared to their micro- and macroporous counterparts. Since the last few decades, various methods have been developed to achieve narrow pore size distribution with a tunable porosity and particle morphology. While hard templates offer a reliable and intuitive approach to synthesize mesoporous metals, the complexity of the technique and the use of harmful chemicals pushed several research groups to focus in other directions. For example, soft templates (e.g., lyotropic crystals, micelles assemblies) and solution phase methods (requiring to control reduction reactions) offer more and more possibilities in terms of available compositions and morphologies. Indeed, various metal (Pt, Pd, Au, Ru, etc.) can now be synthesized as dendritic, core@shell, hollow or polyhedral nanoparticles, with single- or multicomponents, alloyed or not, with unprecedented electrochemical activity.

Recent progress in mesoporous titania materials: adjusting morphology for innovative applications

Abstract This review article summarizes recent developments in mesoporous titania materials, particularly in the fields of morphology control and applications. We first briefly introduce the history of mesoporous titania materials and then review several synthesis approaches. Currently, mesoporous titania nanoparticles (MTNs) have attracted much attention in various fields, such as medicine, catalysis, separation and optics. Compared with bulk mesoporous titania materials, which are above a micrometer in size, nanometer-sized MTNs have additional properties, such as fast mass transport, strong adhesion to substrates and good dispersion in solution. However, it has generally been known that the successful synthesis of MTNs is very difficult owing to the rapid hydrolysis of titanium-containing precursors and the crystallization of titania upon thermal treatment. Finally, we review four emerging fields including photocatalysis, photovoltaic devices, sensing and biomedical applications of mesoporous titania materials. Because of its high surface area, controlled porous structure, suitable morphology and semiconducting behavior, mesoporous titania is expected to be used in innovative applications.

Controlling physical features of mesoporous silica nanoparticles (MSNs) for emerging applications

Mesoporous silica nanoparticles (MSNs) with particle sizes less than 100 nm and desired properties have been synthesized using various methods for several promising applications in the fields of biomedicine and catalysis. In this Highlight article, we briefly review the recent advances in this emerging nanomaterial. Some general aspects including control of particle size, mesostructure and morphology, mechanism of formation, and future challenges are introduced and discussed.

Large‐Scale Synthesis of Reduced Graphene Oxides with Uniformly Coated Polyaniline for Supercapacitor Applications

We report an effective route for the preparation of layered reduced graphene oxide (rGO) with uniformly coated polyaniline (PANI) layers. These nanocomposites are synthesized by chemical oxidative polymerization of aniline monomer in the presence of layered rGO. SEM, TEM, X-ray photoelectron spectroscopy (XPS), FTIR, and Raman spectroscopy analysis results demonstrated that reduced graphene oxide-polyaniline (rGO-PANI) nanocomposites are successfully synthesized. Because of synergistic effects, rGO-PANI nanocomposites prepared by this approach exhibit excellent capacitive performance with a high specific capacitance of 286 F g(-1) and high cycle reversibility of 94 % after 2000 cycles.

Cellulose-to-HMF conversion using crystalline mesoporous titania and zirconia nanocatalysts in ionic liquid systems

Mesoporous titania and zirconia nanoparticles (MTN and MZrN, respectively) exhibiting a desired specific surface area and porous structure, different acidity, and different crystallinity were successfully synthesized through a controlled hydrolysis method and different post-treatments without the utilization of surfactants. The catalytic activities of the synthesized MTN and MZrN were investigated for the conversion of cellulose to glucose and 5-hydroxymethylfurfural (HMF) in an ionic liquid (i.e., 1-ethyl-3-methylimidazolium chloride, [EMIM]Cl) system. The amount of the catalyst (4.0 mg) and reaction time (3 h) were optimized for cellulosic conversion over the HT-MTN catalyst, resulting in maximum 12.9% glucose and 18.2% HMF yields at 120 °C reaction temperature. HT-MZrN exhibited superior HMF yield (i.e., 29.2%) to HT-MTN (i.e., 18.2%) because of the appearance of relatively strong acidity at 450 °C. In addition, we studied the effect of different crystallinity (i.e., amorphous, tetragonal, and monoclinic phases) of the same MZrN material on the conversion yields of glucose and HMF. Crystalline MZrN materials (i.e., either tetragonal or monoclinic phase) exhibited higher HMF yields than amorphous MZrN because of the existence of relatively strong acidity. The tetragonal MZrN catalyst presented better performance than monoclinic and amorphous MZrN catalysts because its acidity at higher temperature (i.e., over 450 °C) was higher than that of the other two, which shows great potential in one-pot cellulose-to-HMF conversion.

Biocompatible, surface functionalized mesoporous titania nanoparticles for intracellular imaging and anticancer drug delivery

Mesoporous titania nanoparticles (MTNs) with excellent biocompatibility (LC(50)≈ 400 μg mL(-1)) and a large surface area (ca. 237.3 m(2) g(-1)) were synthesized and further functionalized with a phosphate-containing fluorescent molecule (i.e. flavin mononucleotide; FMN) and loaded with an anticancer drug (i.e. Doxorubicin) for successful intracellular bioimaging and drug delivery, respectively, in human breast cancer cells BT-20.

Hollow mesoporous hydroxyapatite nanoparticles (hmHANPs) with enhanced drug loading and pH-responsive release properties for intracellular drug delivery

Biocompatible and biodegradable hydroxyapatite nanoparticles with a hollow core and mesoporous shell structure (denoted as hmHANPs) are synthesized by an opposite ion core/shell strategy and applied to pH-responsive intracellular drug delivery systems (DDS). The synthesized hmHANPs have several advantages over solid hydroxyapatite nanoparticles (HANPs), where the hollow and mesoporous structure enhances drug-loading capacity, and the thin hydroxyapatite shell structure reduces burst release of drug and provides pH-responsive release. Doxorubicin (DOX), a therapeutic anticancer drug, was loaded in hmHANPs and HANPs for intracellular drug delivery systems (DDS). Compared to HANPs having a low drug-loading efficacy (17.9%), hmHANPs exhibited an excellent drug-loading efficacy (93.7%). In addition, the release amount of DOX from hmHANPs was 2.5-fold the amount from HANPs. Compared with free DOX, the anticancer efficacy of DOX-loaded hmHANPs was greatly enhanced, as evidenced by the results of MTT assays and confocal laser scanning microscopy using breast cancer cells (BT-20). The synthesized hmHANPs show great potential as drug nanovehicles with high biocompatibility, enhanced drug loading, and pH-responsive features for future intracellular DDS.