Say Chye Joachim Loo

Imparting functionality to a metal–organic framework material by controlled nanoparticle encapsulation

Microporous metal-organic frameworks (MOFs) that display permanent porosity show great promise for a myriad of purposes. The potential applications of MOFs can be developed further and extended by encapsulating various functional species (for example, nanoparticles) within the frameworks. However, despite increasing numbers of reports of nanoparticle/MOF composites, simultaneously to control the size, composition, dispersed nature, spatial distribution and confinement of the incorporated nanoparticles within MOF matrices remains a significant challenge. Here, we report a controlled encapsulation strategy that enables surfactant-capped nanostructured objects of various sizes, shapes and compositions to be enshrouded by a zeolitic imidazolate framework (ZIF-8). The incorporated nanoparticles are well dispersed and fully confined within the ZIF-8 crystals. This strategy also allows the controlled incorporation of multiple nanoparticles within each ZIF-8 crystallite. The as-prepared nanoparticle/ZIF-8 composites exhibit active (catalytic, magnetic and optical) properties that derive from the nanoparticles as well as molecular sieving and orientation effects that originate from the framework material.

Hetero-nanostructured suspended photocatalysts for solar-to-fuel conversion

Converting solar energy into valuable hydrogen and hydrocarbon fuels through photocatalytic water splitting and CO2 photo-reduction is highly promising in addressing the growing demand for renewable and clean energy resources. Developing efficient photocatalysts for solar-driven H2 production and CO2 reduction is the most essential part in achieving this goal. For the purpose of attaining high photocatalytic efficiency, hetero-nanostructures formed by multiple material components have been demonstrated as an effective strategy. Within this heterostructure, its interface is a critical consideration, whereby it determines the principle of charge transfer across the heterojunctions and consequent surface reactions. This article reviews the recent developments of hetero-nanostructures for photocatalytic H2 production and CO2 reduction based on material compositions that form heterojunctions.

A cuprous oxide–reduced graphene oxide (Cu2O–rGO) composite photocatalyst for hydrogen generation : employing rGO as an electron acceptor to enhance the photocatalytic activity and stability of Cu2O

Photocorrosion, that causes rapid deactivation of Cu(2)O photocatalysts, was addressed by incorporating this oxide in a composite with reduced graphene oxide which acts as an electron acceptor to extract photogenerated electrons from Cu(2)O. Cu(2)O-rGO composite engineering also allows enhancing significantly photocatalytic activities of Cu(2)O for H(2) generation.

Preparation of Au-BiVO4 heterogeneous nanostructures as highly efficient visible-light photocatalysts

Au-BiVO(4) heterogeneous nanostructures have been successfully prepared through in situ growth of gold nanoparticles on BiVO(4) microtubes and nanosheets via a cysteine-linking strategy. The experimental results reveal that these Au-BiVO(4) heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO(4) microtubes and nanosheets for both dye degradation and water oxidation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from BiVO(4) to the attached gold nanoparticles as well as their surface plasmon resonance (SPR) absorption. These new heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.

Radiation effects on poly(lactide-co-glycolide) (PLGA) and poly(l-lactide) (PLLA)

The purpose of this study is to examine the effects of electron beam (e-beam) radiation on the thermal and morphological properties of biodegradable polymers (PLGA and PLLA), and to understand the radiation-induced degradation that these materials experience. PLGA(80:20) and PLLA polymer films were prepared by solvent casting, and were e-beam irradiated at doses of 5, 10, 20, 30 and 50 Mrad. The degradation of the films was studied by measuring the changes in their molecular weights, FTIR spectra thermal and morphological properties. The dominant effect of e-beam irradiation, in the presence of air, on both PLGA and PLLA is believed to be chain scission. The average molecular weight of PLGA decreases rapidly at low radiation dosage and remains relatively unchanged at high radiation dose (above 20 Mrad). Crystallinity increases with radiation dose for the non-irradiated amorphous PLGA. PLLA also undergoes chain scission upon irradiation but to a lesser degree compared to PLGA. The higher crystallinity of PLLA is the key factor in its greater stability to e-beam radiation compared to PLGA. The glass-transition temperatures (Tg) and melting temperatures (Tm) of both PLGA and PLLA decrease with increasing radiation dosage. Chain scission, though responsible for the reduction in the average molecular weight, Tg and Tm of both polymers, encourages crystallization. E-beam radiation enhances polymer degradation of PLGA and PLLA.

A novel strategy for surface treatment on hematite photoanode for efficient water oxidation

In this paper, we report a novel strategy for surface treatment of hematite nanorods for efficient photo-driven water oxidation. This is the first report describing the growth of Sn treated hematite from α-FeOOH nanorod arrays in one step without substantially altering morphologies. With this treatment the photocurrent density increased from 1.24 for pristine hematite nanorods to 2.25 mA cm−2 at 1.23 V vs. RHE (i.e. 81% improvement). The increase in photocurrent density was also accompanied by improved incident-photon-to-current efficiencies and oxygen evolution. The photocurrent improvement is mainly attributed to a reduced electron–hole recombination at the hematite–electrolyte interface through the formation of FexSn1−xO4 layer at the hematite nanorod surface as shown by XPS, HRTEM, EDAX line scan analyses and PEC measurements.

Synthesis of high surface area mesostructured calcium phosphate particles

High surface area mesostructured calcium phosphate (MCP) particles were synthesized using surfactants (F127 and P123) and the textural properties were optimized in this study. The synthesized MCP samples subsequently underwent surfactant washing for surfactant removal, which achieved surface areas of > 200 m(2) g(-1). It was found that both F127 and P123 gave similar surface areas (S(BET)), but differing pore diameters (D(pore)). Other synthesis parameters, such as synthesis temperature, surfactant concentration and pH, were also studied to further optimize the textural properties of MCP. It was found that the highest surface area MCP was synthesized at 25 degrees C and pH 12, with 80 wt.% surfactant concentration. Further, in vitro loading and delivery tests on optimized MCP showed an enhanced loading efficiency of bovine serum albumin and lysozyme as compared with non-mesostructured calcium phosphate.

The role of PEG architecture and molecular weight in the gene transfection performance of PEGylated poly(dimethylaminoethyl methacrylate) based cationic polymers.

In this study, we report the synthesis of well-defined model PEGylated poly(dimethylaminoethyl methacrylate) based cationic polymers composed of different PEG architecture with controlled PEG and nitrogen content via reversible addition-fragmentation chain transfer (RAFT) polymerization, and study the effects of PEG architecture and polymer molecular weight on gene delivery and cytotoxicity. Investigation of the physico-chemical interactions of these model cationic polymers with DNA demonstrated that all these polymers effectively complexed with DNA, and PEG topology did not significantly affect the abilities of the polymers to complex and release DNA. However the size and zeta potential of the complexes were found to be influenced by PEG architecture. The polymers with the block-like configurations formed nanosized DNA complexes. In contrast, considerably higher molecular weight was necessary for the copolymer with the statistical configuration of short PEG chains to form such a small complex. Cell line-dependent influence of PEG architecture on cellular uptake, gene expression efficiency and cell viability of the polymer-DNA complexes was observed. The diblock copolymer-DNA complexes induced higher gene expression than the brush-like block copolymer-DNA complexes, and the statistical copolymer-DNA complexes mediated much lower gene expression than the block-like copolymers-DNA complexes. Increasing the molecular weight of statistical polymer to some extent improved gene expression efficiency. The statistical copolymer was less cytotoxic as compared to the block-like copolymers. These findings provide important insights into the effect of PEGylation nature on gene expression, which will be useful for the design of PEGylated gene delivery polymers.

Nanoporous Thermochromic VO2 (M) Thin Films: Controlled Porosity, Largely Enhanced Luminous Transmittance and Solar Modulating Ability

Vanadium dioxide is the most widely researched thermochromic material with a phase transition temperature (τ(c)) of around 68 °C, and its thermochromic performance can be enhanced by adding nanoporosity. Freeze-drying has been employed to fabricate nanostructures with different porosities from 16 to 45% by varying the prefreezing temperature and precursor concentration. The luminous transmittance (Tlum) and solar modulating ability (ΔTsol) are greatly enhanced as a result of increasing pore size and pore density. The freeze-dried sample with 7.5 mL of H2O2 precursor dip-coated at 300 mm/min gives the best combination of thermochromic properties (Tlum ≈ 50%, ΔTsol = 14.7%), which surpasses the best combined thermochromic performance reported to date that we are aware of (Tlum ≈ 41%, ΔTsol = 14.1%).

Artificial photosynthetic hydrogen evolution over g-C3N4 nanosheets coupled with cobaloxime

We report an economic and noble-metal-free artificial photosynthetic system, consisting of g-C3N4 as a photosensitizer and a photocatalyst, and cobaloxime as a co-catalyst, for H2 generation. This system allows for effective electron transfer from excited g-C3N4 to Co(III)(dmgH)2pyCl to generate reduced cobaloxime intermediate species for efficient H2 evolution. Transient fluorescence studies reveal that the presence of cobaloxime and TEOA promotes the population of excited electrons to transfer from g-C3N4, which is responsible for the high photocatalytic activity of this g-C3N4-cobaloxime conjugation system.