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Jin-Chong Tan

Publications and source records attributed to Jin-Chong Tan.

At least 37 records · Page 2Linked to original sources
arXiv2021

High rate nanofluidic energy absorption in porous zeolitic frameworks

Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and ex-trusion mechanisms under realistic, high-rate deformation conditions. Herein, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate depend-ence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable, and reusable impact energy absorbers for challenging new applications.

cond-mat.mtrl-sci↗
arXiv2021

Broadband dielectric behavior of MIL-100 metal-organic framework as a function of structural amorphization

The performance of modern electronics is associated with the multi-layered interconnects, encouraging the development of a low-k dielectrics. Herein, we studied the effects of phase transition from crystalline to amorphous on dielectric, optical and electrical properties of MIL-100 (Fe) and Basolite F300 metal-organic framework (MOF) obtained using different synthesis techniques in both the radio (4-1.5 MHz) and infrared (1.2-150 THz) frequency regimes, which are important for the microelectronics, infrared optical sensors, and high-frequency telecommunications. The impact of amorphization on broadband dielectric response was established based on: (1) The comparison in the dielectric characteristics of a commercially available amorphous Basolite F300 versus a mechanochemically synthesized crystalline MIL-100 in the MHz region. (2) By tracking the frequency shifts in the vibrational modes of MIL-100 structure in the far-IR (phonons) and mid-IR regions. We showed that various parameters such as pelleting pressure, temperature, frequency, density, and degree of amorphization greatly affect the dielectric properties of the framework. We also investigated the influence of temperature (20-100 °C) on the electric and dielectric response in the MHz region, crucial for all electronic devices.

cond-mat.soft↗
arXiv2021

Facile and Fast Transformation of Non-Luminescent to Highly Luminescent MOFs: Acetone Sensing for Diabetes Diagnosis and Lead Capture from Polluted Water

Metal-organic frameworks (MOFs) stand as one of the most promising materials for the development of advanced technologies owing to their unique combination of properties. The conventional synthesis of MOFs involves a direct reaction of the organic linkers and metal salts, however, their post-synthetic modification is a sophisticated route to produce new materials or to confer novel properties that cannot be attained through traditional methods. This work describes the post-synthetic MOF-to-MOF transformation of a non-luminescent MOF (Zn-based OX-1) into a highly luminescent framework (Ag-based OX-2) by a simple immersion of the former in a silver salt solution. The conversion mechanism exploits the uncoordinated oxygen atoms of terephthalate linkers found in OX-1, instead of the unsaturated metal sites commonly employed, making the reaction much faster. The materials derived from the OX-1 to OX-2 transformation are highly luminescent and exhibit a selective response to acetone, turning them into a promising candidate for manufacturing fluorometric sensors for the diagnosis and monitoring of diabetes mellitus. Our methodology can be extended to other metals such as lead (Pb). The fabrication of a polymer mixed-matrix membrane containing OX-1 is used as a proof-of-concept for capturing Pb ions (as pollutants) from water. This research instigates the exploration of alternative methodologies to confer MOFs with special aptitudes for photochemical sensing or for environmental applications such as water purification.

physics.app-ph↗
arXiv2021

Highly luminescent silver-based MOFs: Scalable eco-friendly synthesis paving the way for photonics sensors and electroluminescent devices

Luminescent multifunctional nanomaterials are important because of their potential impact on the development of key technologies such as smart luminescent sensors and solid-state lightings. To be technologically viable, the luminescent material needs to fulfil a number of requirements such as facile and cost-effective fabrication, a high quantum yield, structural robustness, and long-term material stability. To achieve these requirements, an eco-friendly and scalable synthesis of a highly photoluminescent, multistimuli responsive and electroluminescent silver-based metal-organic framework (Ag-MOF), termed "OX-2" was developed. Its exceptional photophysical and mechanically resilient properties that can be reversibly switched by temperature and pressure make this material stood out over other competing luminescent materials. The potential use of OX-2 MOF as a good electroluminescent material was tested by constructing a proof-of-concept MOF-LED (light emitting diode) device, further contributing to the rare examples of electroluminescent MOFs. The results reveal the huge potential for exploiting the Ag MOF as a multitasking platform to engineer innovative photonic technologies.

cond-mat.mtrl-sci↗
arXiv2021

MOF-Based Polymeric Nanocomposite Films as Potential Materials for Drug Delivery Devices in Ocular Therapeutics

Novel MOF-based polymer nanocomposite films were successfully prepared using Zr-based UiO-67 as a metal-organic framework (MOF) and polyurethane (PU) as a polymeric matrix. Synchrotron X-ray powder diffraction (SXRPD) analysis confirms the improved stability of the UiO-67 embedded nanocrystals and scanning electron microscopy images confirm their homogeneous distribution (average crystal size ~100-200 nm) within the 50-um thick film. Accessibility to the inner porous structure of the embedded MOFs was completely suppressed for N2 at cryogenic temperatures. However, ethylene adsorption measurements at 25°C confirm that at least 45% of the MOF crystals are fully accessible for gas phase adsorption of non-polar molecules. Although this partial blockage limits the adsorption performance of the embedded MOFs for ocular drugs (e.g., brimonidine tartrate) compared to the pure MOF, an almost 60-fold improvement in the adsorption capacity was observed for PU matrix after incorporation of the UiO-67 nanocrystals. UiO-67@PU nanocomposite exhibits a prolonged release of brimonidine (up to 14 days were quantified). Finally, the combined use of SXRPD, thermogravimetric analysis (TGA) and FTIR analysis confirmed the presence of the drug in the nanocomposite film, the stability of the MOF framework and the drug upon loading, and the presence of brimonidine in an amorphous phase once adsorbed. These results open the gate towards the application of these polymeric nanocomposite films for drug delivery in optical therapeutics, either as a component of contact lens, in the composition of lacrimal stoppers (e.g., punctal plugs) or in sub-tenon inserts.

cond-mat.mtrl-sci↗
arXiv2021

Green reconstruction of MIL-100 (Fe) in water for high crystallinity and enhanced guest encapsulation

MIL-100 (Fe) is a highly porous metal-organic framework (MOF), considered as a promising carrier for drug delivery, and for gas separation and capture applications. However, this functional material suffers from elaborated and toxic synthesis that may hinder its biomedical use and large-scale production to afford commercial applications. Herein, we report a green mechanochemical water immersion approach to yield highly crystalline MIL100 (Fe) material. Subsequently, we have harnessed this strategy for facile fabrication of drug@MOF composite systems, comprising (guests) 5-fluorouracil, caffeine, or aspirin encapsulated in the pores of (host) MIL-100 (Fe). Inelastic neutron scattering was uniquely used to probe the guest host interactions arising from pore confinement of the drug molecules, giving additional insights into the reconstruction mechanism. Our results pave the way to the green production of MIL type materials and bespoke guest-encapsulated composites by minimizing the use of toxic chemicals, whilst enhancing energy efficiency and material's life cycle central to biotechnological applications.

cond-mat.mtrl-sci↗
arXiv2021

Dual-Guest Functionalised ZIF-8 Framework for 3D Printing White Light-Emitting Composites

Metal-organic frameworks (MOFs) stand as a promising chemically-active host scaffold for the encapsulation of functional guests, because they could enhance luminescent properties by molecular separation of fluorophores in the nanoscale pores of the MOF crystals. Herein, we show simultaneous nanoconfinement of two fluorophores viz. (A) Fluorescein and (B) Rhodamine B in the sodalite cages of ZIF-8, constructed under ambient conditions through a simple one-pot reaction. We report a novel dual-guest@MOF system, termed: A+B@ZIF-8, which overcomes the intrinsic problem of aggregation caused quenching in the solid-state to gain bright yellow emission under UV irradiation. Subsequently, we combine this yellow emitter with a blue-emitting photopolymer resin, to yield a 3D printable luminescent composite material. We design a number of 3D printable composite objects for converting UV into warm white light emission, achieving a high quantum yield of ~44% in the solid-state 3D printed form. This research instigates the bespoke application of a vast range of 3D printable Guest@MOF designer composites targeting energy-saving lighting devices, smart sensors and future optoelectronics.

cond-mat.soft↗
arXiv2021

Near-field infrared nanospectroscopy reveals guest confinement in metal-organic framework single crystals

Metal-organic frameworks (MOFs) can provide exceptional porosity for molecular guest encapsulation useful for emergent applications in sensing, gas storage, drug delivery and optoelectronics. Central to the realisation of such applications however is the successful incorporation of a functional guest confined within the host framework. Here we demonstrate, for the first time, the feasibility of scattering-type scanning near-field optical microscopy (s-SNOM) and nano-Fourier transform infrared (nanoFTIR) spectroscopy, in concert with density functional theory (DFT) calculations to reveal the vibrational characteristics of the Guest@MOF systems. Probing individual MOF crystals, we pinpoint the local molecular vibrations and thus, shed new light on the host-guest interactions at the nanoscale. Our strategy not only confirms the successful encapsulation of luminescent guest molecules in the porous host framework in single crystals, but further provides a new methodology for nanoscale-resolved physical and chemical identification of wide-ranging framework materials and designer porous systems for advanced applications.

cond-mat.soft↗
arXiv2021

Dye-Encapsulated Zeolitic Imidazolate Framework (ZIF-71) for Fluorochromic Sensing of Pressure, Temperature, and Volatile Solvents

Luminescent metal-organic frameworks (MOFs) offer a multifunctional platform for creating non-invasive sensors and tuneable optoelectronics. However, fluorochromic materials that are photophysically resilient and show high sensitivity towards different physical and chemical stimuli are scarce. We report a facile host-guest nanoconfinement strategy to construct a fluorescent hybrid material with multiple sensing capabilities. We design and fabricate a new Guest@MOF material: comprising a zeolitic MOF (ZIF-71) as a nanoporous host for encapsulating rhodamine B (RhB dye) guest molecules, resulting in the RhB@ZIF-71 system with mechanochromic, thermochromic, and solvatochromic sensing response. The fluorochromic sensing properties stem from the nanoconfinement effect that ZIF-71 imposes on RhB monomers, yielding the H- or J-type aggregates with tuneable photophysical and photochemical properties. For mechanochromism, the external pressure causes an emission red shift in a linear fashion, switching RhB guests from H-type to J-type aggregates through a shear deformation. For thermochromism, we demonstrate a linear scaling as a function of temperature due to the spatial restriction imposed on J-type aggregates incarcerated in ZIF-71 pores. Harnessing the solvatochromism of RhB@ZIF-71, we identified three diverse groups of volatile organic compounds. The multimodal sensing response pave the way to smart applications like photonic pressure sensors, non-invasive thermometers, and ultrasensitive chemosensors.

cond-mat.mtrl-sci↗
arXiv2020

Guest-Tunable Dielectric Sensing Using a Single Crystal of HKUST-1

There is rising interest on low-k dielectric materials based on porous metal-organic frameworks (MOFs) for improved electrical insulation in microelectronics. Herein, we demonstrate the concept of MOF dielectric sensor built from a single crystal of HKUST-1. We study guest encapsulation effects of polar and non-polar molecules, by monitoring the transient dielectric response and AC conductivity of the crystal exposed to different vapors (water, I2, methanol, ethanol). The dielectric properties were measured along the <100> crystal direction in the frequency range of 100 Hz to 2 MHz. The dielectric data show the efficacy of MOF dielectric sensor for discriminating the guest analytes. The time-dependent transient response reveals dynamics of the molecular inclusion and exclusion processes in the nanoscale pores. Since dielectric response is ubiquitous to all MOF materials (unlike DC conductivity and fluorescence), our results demonstrate the potential of dielectric MOF sensors compared to resistive sensors and luminescence-based approaches.

cond-mat.soft↗
arXiv2019

Impact of pressure and temperature on the broadband dielectric response of the HKUST-1 metal-organic framework

Herein we employed high-resolution spectroscopic techniques in combination with periodic ab initio density functional theory (DFT) calculations to establish the different polarization processes for a porous copper-based MOF, termed HKUST-1. We used alternating current measurements to determine its dielectric response between 4 Hz and 1.5 MHz where orientational polarization is predominant, while synchrotron infrared (IR) reflectance was used to probe the far-IR, mid-IR, and near-IR dielectric response across the 1.2 THz to 150 THz range (ca. 40 - 5000 cm^-1) where vibrational and optical polarizations are principal contributors to its dielectric permittivity. We demonstrate the role of pressure on the evolution of broadband dielectric response, where THz vibrations reveal distinct blue and red shifts of phonon modes from structural deformation of the copper paddle-wheel and the organic linker, respectively. We also investigated the effect of temperature on dielectric constants in the MHz region pertinent to microelectronics, to study temperature-dependent dielectric losses via dissipation in an alternating electric field. The DFT calculations offer insights into the physical mechanisms responsible for dielectric transitions observed in the experiments and enable us to explain the frequency shifts phenomenon detected under pressure. Together, the experiments and theory have enabled us to glimpse into the complex dielectric response and mechanisms underpinning a prototypical MOF subject to pressure, temperature, and vast frequencies.

cond-mat.mtrl-sci↗
arXiv2018

Dielectric Properties of Metal-Organic Frameworks Probed via Synchrotron Infrared Reflectivity

We present the frequency-dependant (dynamic) dielectric response of a group of topical polycrystalline zeolitic imidazolate-based metal-organic framework (MOF) materials in the extended infrared spectral region. Using synchrotron-based FTIR spectroscopy in specular reflectance, in conjunction with density functional theory (DFT) calculations, we have revealed detailed structure-property trends linking the THz region dielectric response to framework porosity and structural density. The work demonstrates that MOFs are promising candidate materials not only for low-\k{appa} electronics applications but could also be pioneering for terahertz (THz) applications, such as next-generation broadband communications technologies.

cond-mat.mtrl-sci↗
arXiv2017

Mechanoluminescent MOF nanoplates: spatial molecular isolation of light-emitting guests in a sodalite framework structure

Mechanoluminescent materials have a wide range of promising nanotechnological applications, such as photonics based sensors and smart optoelectronics. Examples of mechanoluminescent metal-organic framework (MOF) materials, however, are relatively scarce in the literature. Herein, we present a previously undescribed Guest@MOF system, comprising Perylene@ZIF-8 nanoplates which will undergo a reversible 442 nm <->502 nm photoemission switching when subject to a moderate level of mechanically induced pressure (~10s MPa). The nanoplates were synthesized via a high-concentration reaction (HCR) strategy at ambient conditions, to yield a crystalline ZIF-8 framework hosting the highly luminous Perylene guests; the latter confined within the porous sodalite cages of ZIF-8. Remarkably, we show that in a solid-state condition, it is the spatial isolation and nano-partitioning of the luminescent guests that bestow a unique solution-like optical properties measured in the host-guest assembly. We elucidate how the switchable red- or blue-shifts of the visible emission can be accomplished by mechanically modifying the nanoscale packing of the underlying nanoplates. Theoretical calculations suggest that the elasticity of the host sodalite cage coupled with the intermolecular weak interactions of the confined guest are underpinning the unique mechanoluminescent behavior observed.

cond-mat.mtrl-sci↗
arXiv2017

Detecting Molecular Rotational Dynamics Complementing the Low-Frequency Terahertz Vibrations in a Zirconium-Based Metal-Organic Framework

We show clear experimental evidence of co-operative terahertz (THz) dynamics observed below 3 THz (~100 cm-1), for a low-symmetry Zr-based metal-organic framework (MOF) structure, termed MIL-140A [ZrO(O2C-C6H4-CO2)]. Utilizing a combination of high-resolution inelastic neutron scattering and synchrotron radiation far-infrared spectroscopy, we measured low-energy vibrations originating from the hindered rotations of organic linkers, whose energy barriers and detailed dynamics have been elucidated via ab initio density functional theory (DFT) calculations. For completeness, we obtained Raman spectra and characterized the alterations to the complex pore architecture caused by the THz rotations. We discovered an array of soft modes with trampoline-like motions, which could potentially be the source of anomalous mechanical phenomena, such as negative linear compressibility and negative thermal expansion. Our results also demonstrate coordinated shear dynamics (~2.5 THz), a mechanism which we have shown to destabilize MOF crystals, in the exact crystallographic direction of the minimum shear modulus (Gmin).

cond-mat.mtrl-sci↗
arXiv2017

Optochemically Responsive 2D Nanosheets of a 3D Metal-Organic Framework Material

Outstanding functional tunability underpinning metal-organic framework (MOF) confers a versatile platform to contrive next-generation chemical sensors, optoelectronics, energy harvesters and converters. We report a rare exemplar of a porous 2D nanosheet material, constructed from an extended 3D MOF structure. We develop a rapid supramolecular self-assembly methodology at ambient conditions, to synthesize readily-exfoliatable MOF nanosheets, functionalized in situ by adopting the Guest@MOF (Host) strategy. Nanoscale confinement of light-emitting molecules (as functional guest) inside the MOF pores generates unusual combination of optical, electronic, and chemical properties, arising from the strong host-guest coupling effects. We show highly promising photonics based chemical sensing opened up by the new Guest@MOF composite systems. By harnessing host-guest optochemical interactions of functionalized MOF nanosheets, we have accomplished detection of an extensive range of volatile organic compounds (VOCs) and small molecules important for many practical applications.

cond-mat.mtrl-sci↗
arXiv2017

Large elastic recovery of zinc dicyanoaurate

We report the mechanical properties of the `giant' negative compressibility material zinc(II) dicyanoaurate, as determined using a combination of single-crystal nanoindentation measurements and \emph{ab initio} density functional theory calculations. While the elastic response of zinc dicyanoaurate is found to be intermediate to the behaviour of dense and open framework structures, we discover the material to exhibit a particularly strong elastic recovery, which is advantageous for a range of practical applications. We attribute this response to the existence of supramolecular helices that function as atomic-scale springs, storing mechanical energy during compressive stress and hence inhibiting plastic deformation. Our results are consistent with the relationship noted in [Cheng \& Cheng, \textit{Appl. Phys. Lett.}, 1998, {\textbf{73}}, 614] between the magnitude of elastic recovery, on the one hand, and the ratio of material hardness to Young's modulus, on the other hand. Drawing on comparisons with other metal--organic frameworks containing helical structure motifs, we suggest helices as an attractive supramolecular motif for imparting resistance to plastic deformation in the design of functional materials.

cond-mat.mtrl-sci↗
arXiv2014

Perfect and Stable Hybrid Glasses from Strong and Fragile Metal-Organic Framework Liquids

Hybrid glasses connect emerging fields of metal-organic frameworks (MOFs) with the glass-formation, amorphization, and melting processes of these structurally diverse and chemically versatile systems. Most zeolites, including MOFs, amorphize around the glass transition, devitrifying and then melting at much higher temperatures. The relationship between the two processes has so far not been investigated. Herein we show how heating first results in a low density perfect glass, following an order-order transition, leading to a super-strong liquid of low fragility that dynamically controls MOF collapse. A subsequent order-disorder transition creates a high density liquid of greater fragility. After crystallization and melting, subsequent cooling results in a stable glass virtually identical to the high density phase. Furthermore, the wide-ranging melting temperatures of different MOFs suggest these can be differentiated by topology. Our research provides new insight into the stability and functionality of these novel ductile crystalline materials, including the possibility of melt-casting MOFs.

cond-mat.mtrl-sci↗