Laser printing of optically resonant hollow crystalline carbon nanostructures from 1D and 2D metal-organic frameworks

FeAu mixing for high-temperature control of light scattering at the nanometer scale

Control of the optical properties of a nanoparticle (NP) through its structural changes underlies optical data processing, dynamic coloring, and smart sensing at the nanometer scale. Here, we report on the concept of controlling the light scattering by a NP through mixing of weakly miscible chemical elements (Fe and Au), supporting a thermal-induced phase transformation. The transformation corresponds to the transition from a homogeneous metastable solid solution phase of the (Fe,Au) NP towards an equilibrium biphasic Janus-type NP. We demonstrate that the phase transformation is thermally activated by laser heating up to a threshold of 800 °C (for NPs with a size of hundreds of nm), leading to the associated changes in the light scattering and color of the NP. The results thereby pave the way for the implementation of optical sensors triggered by a high temperature at the nanometer scale via NPs based on metal alloys.

Recent Advances in Laser-Induced Synthesis of MOF Derivatives

Metal-organic frameworks (MOFs) are crystalline materials with permanent pores constructed by the self-assembly of organic ligands and metal clusters through coordination bonds. Due to their diversity and tunability, MOFs are used as precursors to be converted into other types of functional materials by pyrolytic recrystallization. Laser-induced synthesis is proven to be a powerful pyrolytic processing technique with fast and accurate laser irradiation, low loss, high efficiency, selectivity, and programmability, which endow MOF derivatives with new features. Laser-induced MOF derivatives exhibit high versatility in multidisciplinary research fields. In this review, first, the basic principles of laser smelting and the types of materials for laser preparation of MOF derivatives are briefly introduced. Subsequently, it is focused on the peculiarity of the engineering of structural defects and their applications in catalysis, environmental protection, and energy fields. Finally, the challenges and opportunities at the current stage are highlighted with the aim of elucidating the future direction of the rapidly growing field of laser-induced synthesis of MOF derivatives.

Laser-Assisted Design of MOF-Derivative Platforms from Nano- to Centimeter Scales for Photonic and Catalytic Applications

Laser conversion of metal-organic frameworks (MOFs) has recently emerged as a fast and low-energy consumptive approach to create scalable MOF derivatives for catalysis, energy, and optics. However, due to the virtually unlimited MOF structures and tunable laser parameters, the results of their interaction are unpredictable and poorly controlled. Here, we experimentally base a general approach to create nano- to centimeter-scale MOF derivatives with the desired nonlinear optical and catalytic properties. Five three- and two-dimensional MOFs, differing in chemical composition, topology, and thermal resistance, have been selected as precursors. Tuning the laser parameters (i.e., pulse duration from fs to ns and repetition rate from kHz to MHz), we switch between ultrafast nonthermal destruction and thermal decomposition of MOFs. We have established that regardless of the chemical composition and MOF topology, the tuning of the laser parameters allows obtaining a series of structurally different derivatives, and the transition from femtosecond to nanosecond laser regimes ensures the scaling of the derivatives from nano- to centimeter scales. Herein, the thermal resistance of MOFs affects the structure and chemical composition of the resulting derivatives. Finally, we outline the "laser parameters versus MOF structure" space, in which one can create the desired and scalable platforms with nonlinear optical properties from photoluminescence to light control and enhanced catalytic activity.

Insights into Solid-To-Solid Transformation of MOF Amorphous Phases

Metal-organic frameworks (MOFs) have been recently explored as crystalline solids for conversion into amorphous phases demonstrating non-specific mechanical, catalytic, and optical properties. The real-time control of such structural transformations and their outcomes still remain a challenge. Here, we use in situ high-resolution transmission electron microscopy with 0.01 s time resolution to explore non-thermal (electron induced) amorphization of a MOF single crystal, followed by transformation into an amorphous nanomaterial. By comparing a series of M-BTC (M: Fe³⁺, Co³⁺, Co²⁺, Ni²⁺, and Cu²⁺; BTC: 1,3,5-benzentricarboxylic acid), we demonstrate that the topology of a metal cluster of the parent MOFs determines the rate of formation and the chemistry of the resulting phases containing an intact ligand and metal or metal oxide nanoparticles. Confocal Raman and photoluminescence spectroscopies further confirm the integrity of the BTC ligand and coordination bond breaking, while high-resolution imaging with chemical and structural analysis over time allows for tracking the dynamics of solid-to-solid transformations. The revealed relationship between the initial and resulting structures and the stability of the obtained phase and its photoluminescence over time contribute to the design of new amorphous MOF-based optical nanomaterials.

Lipase immobilization on a novel class of Zr-MOF/electrospun nanofibrous polymers: Biochemical characterization and efficient biodiesel production

In this study, due to the favorable properties of MOF compounds and fibrous materials, new nanostructures of Zr-MOF/PVP nanofibrous composites were synthesized by electrospinning procedure. The related features of these samples were characterized by relevant analyzes, including SEM, BET surface area analysis, XRD, and FTIR spectroscopy. The final product showed significant properties such as small particle size distribution, large surface area, and high crystallinity. This strategy for producing these nanostructures could lead to new compounds as novel alternative materials for biological applications. Lipase MG10 was successfully immobilized on the mentioned nanofibrous composites and biochemically characterized. The lipase activity of free and immobilized lipases was considered by measuring the absorbance of pNPP (500 μM in 40 mM Tris/HCl buffer, pH 7.8, and 0.01% Triton X100) at 37 °C for 30 min. Different concentrations of glutaraldehyde, different crosslinking times, different times of immobilization, different enzyme loading, and different pH values have been optimized. Results showed that the optimized immobilization condition was achieved in 2.5% glutaraldehyde, after 2 h of crosslinking time, after 6 h immobilization time, using 180 mg protein/g support at pH 9.0. The immobilized enzyme was also totally stable after 180 min incubation at 60 °C. The free enzyme showed the maximum activity at pH 9.0, but the optimal pH of the immobilized lipase was shifted about 1.5 pH units to the alkaline area. The immobilized lipase showed about 2.7 folds (78%) higher stability than the free enzyme at 50 °C. Some divalent metal ions, including Cu²⁺ (22%), Co²⁺ (37%), Mg²⁺ (12%), Hg²⁺ (11%), and Mn²⁺ (17%) enhanced the enzyme activity of immobilized enzyme. The maximum biodiesel production (27%) from R. communis oil was obtained after 18 h of incubation by lipase MG10. The immobilized lipase displayed high potency in biodiesel production, about 83% after 12 h of incubation. These results indicated the high potency of Zr-MOF/PVP nanofibrous composites for efficient lipase immobilization.

Metal-Organic Frameworks in Modern Physics: Highlights and Perspectives

Owing to the synergistic combination of a hybrid organic-inorganic nature and a chemically active porous structure, metal-organic frameworks have emerged as a new class of crystalline materials. The current trend in the chemical industry is to utilize such crystals as flexible hosting elements for applications as diverse as gas and energy storage, filtration, catalysis, and sensing. From the physical point of view, metal-organic frameworks are considered molecular crystals with hierarchical structures providing the structure-related physical properties crucial for future applications of energy transfer, data processing and storage, high-energy physics, and light manipulation. Here, the perspectives of metal-organic frameworks as a new family of functional materials in modern physics are discussed: from porous metals and superconductors, topological insulators, and classical and quantum memory elements, to optical superstructures, materials for particle physics, and even molecular scale mechanical metamaterials. Based on complementary properties of crystallinity, softness, organic-inorganic nature, and complex hierarchy, a description of how such artificial materials have extended their impact on applied physics to become the mainstream in material science is offered.