Ce-doped hollow In2O3 nanoboxes derived from metal–organic frameworks with excellent formaldehyde-sensing performance

In recent years, metal oxides derived from metal organic frameworks (MOFs) have been widely used in the gas-sensing direction due to their regular framework structure and large porosity. At the same time, rare earth ion doping can also effectively improve the gas-sensing properties of metal oxide semiconductors. Herein, we report the synthesis of MOFs-drived Ce-doped In₂O₃ samples by calcining precursors prepared by a simple oil bath method. The experimental characterization results show that the as-prepared samples exhibit uniform hollow nanoboxes with high surface area (48.5 m²/g) and abundant oxygen vacancies. Owing to the unique structures, the 1 wt% Ce-doped In₂O₃ nanobox-based gas sensor shows a fast response (1 s), quick recovery (1 s), and an ultralow detection limit (response of 13.4 for 1 ppm of formaldehyde) at the low operating temperature (140 °C). The excellent gas-sensing performance is mainly attributed to hollow structure and the incorporation of Ce, increasing the number of oxygen vacancies and adsorbed oxygen in improving formaldehyde sensing performance of In₂O₃ sensors. This kind of rare earth ion-doped hollow nanoboxes derived from MOFs provides a strategy for the design and development of high performance gas sensor.

     

Mitochondria-targeted metal–organic frameworks for cancer treatment

Much of the progress in subcellular targeted therapy of cancer over the past years has been driven by attacking disease cell’s mitochondria. A paradigm, central to cancer biology is that mitochondrial dysfunction controls a series of the point-of-no-return metabolic changes including variation of redox status, production of reactive oxygen species, safeguarding of calcium levels, initiation of programmed cell death and the formation of mitochondria permeability transition pores. Mitochondria are also related to tumor invasion, proliferation, tumorigenesis, and metastasis and are therefore, considered as one of the most central therapeutic targets in cancer. Very recently, it has been shown that supramolecular metal–organic frameworks (MOFs) could be targeted to the tumor’s mitochondria selectively using the triphenylphosphonium (TPP⁺) conjugation approach or exploiting the intrinsic cationic nature of the MOFs. Mitochondria-targeted MOFs (mitoMOFs) can significantly disrupt the metabolic processes in cancer cells either by releasing ‘classic’ chemotherapeutic drugs or by facilitating photodynamic inactivation, microwave thermal therapy and other pathways. This review discusses the design and development of novel MOF-based platforms for applications in mitochondria-targeted therapeutics and provides key insights into their mechanistic roles in achieving optimal therapeutic outcomes with minimal side-effects. Overall, mitoMOFs have a great potential to propel the field of targeted therapy and could likely change the conventional pharmacological interventions scientifically and clinically.     

Microstructural evolution of N–O–S self-doped porous carbons based on heteroatomic migration for supercapacitor electrodes

Journal of Materials Science: Materials in Electronics - N?O?S self-doped porous carbons (FAKC-T), possessing considerable specific surface areas (SSA,...     

Hollow porous nanocuboids cobalt-based metal–organic frameworks with coordination defects as anode for enhanced lithium storage

Journal of Materials Science - Controlling the morphology of metal–organic frameworks to improve their application in energy storage remains a particular challenge. In this work, hollow...     

Ultrafast room-temperature synthesis of hierarchically porous metal–organic frameworks by a versatile cooperative template strategy

Hierarchically porous MOFs (HP-MOFs) are commonly prepared by means of hydrothermal synthesis. Nonetheless, its relatively long crystallization time and harsh synthesis conditions have strongly obstructed the enhancement of HP-MOFs space–time yields (STYs) and the decrease in energy consumption. Herein, a simple and versatile method for preparing various HP-MOFs at room temperature was demonstrated, which had introduced surfactant as the template, whereas zinc oxide (ZnO) has been used as an accelerant. The resulting HP-MOFs showed multimodal hierarchical porous structures and excellent thermal stability. More importantly, the synthesis time was reduced dramatically to 11 min, with a maximal HP-MOFs STY of as high as 2575 kg m^?3 d^?1. Furthermore, the rapid formation process of HP-MOFs was examined through quantum chemistry calculation, and a feasible synthesis mechanism was also proposed. Notably, our synthesis strategy had shown a versatility, since other surfactants could also be used as the templates for the rapid room-temperature fabrication of diverse stable HP-MOFs. Importantly, the porosity of the HP-MOFs could be readily tuned through controlling the type of template. Moreover, gas adsorption measurement of HP-MOFs revealed high CH₄ uptake capacity at 298 K due to the increase in surface area and pore volume. Our findings suggest that such method is applicable for the rapid synthesis of a wide variety of HP-MOFs on an industrial scale.     

3D-assembled graphene–LiFePO4 frameworks with enhanced electrochemical performance

In the on-going development of power sources and energy-storage devices, achieving both high power and large energy capacity with a high discharge rate is still a great challenge. In this paper, three dimension assembled graphene–LiFePO₄ (G–LFP) composites were prepared by one-step hydrothermal method. LiFePO₄ (LFP) particles became smaller and were dispersed uniformly on the graphene sheets after compositing with graphene. Compared to the pristine LFP, the electrochemical properties of the G–LFP are greatly improved, especially the rate capability and the cyclic performance. At 10 C, the G–LFP holds nearly 80 % of the initial capacity and has a flat voltage platform, while for the LFP, its capacity drops down to 65 % and its voltage platform is not noticeable. After 600 cycles at 10 C, the specific capacity of the G–LFP decreases from 135 to 125 mA hg^?1 with a capacity loss of 5.1 %, while it drops from 105  to 86  mA hg^?1 with a capacity loss of 30 % for the LFP. The reason for the improvement of the electrochemical performances could be ascribed to the introduction of graphene which enhances the conductivity and diminishes the LFP size which improves the diffusion of lithium ions.     

Current trends in stimuli-responsive nanotheranostics based on metal–organic frameworks for cancer therapy

In the biomedical field, stimuli-responsive systems comprising smart nanoplatforms based on metal–organic frameworks (MOFs) have garnered immense attention in view of their high surface area, biocompatibility, facile synthesis, tunable structural features, adjustable pore size, and highly versatile composition. Interestingly, stimuli-responsive MOFs are excellent nanoplatforms for biomedical applications as they are designed to specifically change their properties upon interior stimuli in target tissues (e.g., pH and redox reaction triggering agents) or exposure to exterior stimuli like temperature, various wavelengths of light and magnetic fields. Compared to other single-imaging techniques either alone or in combination with each other, synergistic therapy based on multimodal imaging-guided strategies deliver high diagnostic accuracy, as well as superior therapeutic efficiency. In order to fully comprehend the field of stimuli-responsive MOFs, herein, the basic mechanistic chemistry of stimuli-responsive MOFs along with the latest progress in the development of cell imaging and theranostic nanoplatforms for biomedical imaging, phototherapy and cancer chemotherapy is elaborated.     

Cobalt–carbon derived from zeolitic imidazolate framework on Ni foam as high-performance supercapacitor electrode material

ZIF-67 (Co(MeIM)₂, MeIM = 2-methylimidazole) was selected as a precursor to synthesize the metallic cobalt/carbon composites on Ni foam directly and intimately. The results show that ZIF-67 forms a uniform membrane and densely covers the Ni foam substrate. Besides, the cobalt/carbon composites obtained are composed of cobalt nanoparticles with a diameter up to around 2.6 nm, which are anchored on carbon homogeneously. The specific capacitance of the composites material is up to 512 F g⁻¹ at a current density of 1 A g⁻¹ in 1.0 M KOH electrolyte. Furthermore, the specific capacitance loss is ∼46.4% with increase at the current density from 1 to 20 A g⁻¹. More significantly, the specific capacitance retention rate is 87.5% at a current density of 5 A g⁻¹ after 1000 cycles. These results suggest that the electrochemical performance can be greatly enhanced by the well-controlled size and distribution of the cobalt nanoparticles, which is mainly attributed to the unique structure and composition of ZIF-67.     

Growth of cobalt–nickel layered double hydroxide on nitrogen-doped graphene by simple co-precipitation method for supercapacitor electrodes

Nitrogen-doped graphene/Co–Ni layered double hydroxide (RGN/Co–Ni LDH) is synthesized by a facile co-precipitation method. Transmission electron microscopy images indicated that the formation of Co–Ni(OH)₂ nanoflakes with the good dispersion anchored on the surfaces of the nitrogen-doped graphene sheets. The nitrogen-doped graphene composites delivered the enhanced electrochemical performances compared to the pure Co–Ni LDH due to the improved electronic conductivity and its hierarchical layer structures. The high specific capacitance of 2092 F g^?1 at current density of 5 mA cm^?2 and the rate retention of 86.5% at current density of 5–50 mA cm^?2 are achieved by RGN/Co–Ni LDH, higher than that of pure Co–Ni LDH (1479 F g^?1 and 76.5%). Moreover, the two-electrode asymmetric supercapacitor, with the RGN/Co–Ni LDH composites as the positive electrode and active carbon as the negative electrode material, exhibits energy density of 49.4 Wh kg^?1 and power density of 101.97 W kg^?1 at the current density of 5 mA cm^?2, indicating the composite has better capacitive behavior.     

Synthesis of porous Mn3O4 microparticles by the KMnO4–AC reduction and combustion system

A direct method to synthesize porous hausmannite (Mn₃O₄) microparticles by the KMnO₄–AC reaction and combustion system is reported in this paper. In order to synthesize the manganese oxide, four experimental factors were considered: pH (3.0, 4.5 and 6.0), AC content (2.08 × 10^?2 and 8.33 × 10^?2 M), initial Mn(VII) content (4.55 × 10^?4 and 9.1 × 10^?4 M) and stirring velocity (300 and 500 rpm). The AC was added to the Mn(VII) aqueous solution and stirred for 2 h. For different pH levels, the Mn(VII) content in the solution was measured by UV/Vis spectrometry at 540 nm in order to evaluate the Mn reduction. Later, the manganese-loaded AC was calcined at 700°C in dry air at 1900 sccm during 60 min, indicating that the Mn₃O₄ content is directly proportional to the acidity of the solution. Spongy and porous Mn₃O₄ microparticles were synthesized considering the following levels: pH (3.0), an AC content (8.33 × 10^?2 M) and an initial Mn(VII) content (9.1 × 10^?4 M) with 500 rpm.     

Layered Co–Mn hydroxide nanoflakes grown on carbon cloth as binder-free flexible electrodes for supercapacitors

The layered Co–Mn hydroxide nanoflakes grown on carbon cloth (CC) have been successfully fabricated via a facile solvothermal method in a mixed solvent of water and methanol. The structure and morphology of final products could be readily tuned in a wide range by tuning volume ratios of methanol and water. The electrochemical measurements revealed that layered Co–Mn hydroxide nanoflakes grown on CC, exhibit a high-specific capacitance and remarkable cycling stability, which is of great importance for their practical applications in high-performance supercapacitor. Moreover, the specific capacitances of layered hydroxides would be enhanced with the expansion of interlayer spacing.     

Solid ion transition route to 3D S–N-codoped hollow carbon nanosphere/graphene aerogel as a metal-free handheld nanocatalyst for organic reactions

A novel metal-free bulk nanocatalyst,S-N-codoped hollow carbon nanosphere/graphene aerogel (SNC-GA-1000),has been successfully fabricated using a facile and clean solid ion transition route.In this method,ZnS is used as the hard template and S source,while polydopamine acts as a reducing agent and carbon source.At a high annealing temperature,Zn metal is reduced and evaporates,leaving only free S vapor to diffuse into the carbon layer.Interestingly,the as-obtained SNC-GA-1000 exhibits much higher catalytic activity in an organic reduction reaction than unloaded bare S-N-codoped carbon nanospheres.Hydrothermal reduction of the graphene oxide sheets loaded with ZnS@polydopamine core-shell nanospheres (ZnS@PDA) affords a three-dimensional bulk graphene aerogel.Although nanosized catalysts exhibit high catalytic activities,their subsequent separation is not always satisfactory,making post-treatment difficult.This approach achieves a trade-off between activity and separability.More importantly,due to the 3D structural nature,such bulk and handheld nanocatalysts can be easily separated and recycled.     

Rational design of graphene @ nitrogen and phosphorous dual-doped porous carbon sandwich-type layer for advanced lithium–sulfur batteries

Lithium sulfur (Li–S) batteries show great prospect as a next generation high energy density rechargeable battery systems. However, the practical utilization of Li–S batteries is still obstructed by the shuttle effects which inducing the fast capacity fading and the loss of active sulfur. Herein, a special graphene @ nitrogen and phosphorous dual-doped porous carbon (N–P–PC/G) is presented to modify a commercial separator for an advanced Li–S battery. The N–P–PC/G nanosheet employs graphene layer as an excellent conductive framework covered with uniform layers of N, P dual-doped porous carbon on both sides which possessing massive interconnected meso-/micropores. It is demonstrated that the N–P–PC/G-modified separator can suppress the shuttle effects by coupling interactions including physical absorption, chemical adsorption and interfacial interaction. With the aid of the N–P–PC/G-modified separator, the pure sulfur cathode with high-sulfur loading of 3 mg cm^?2 offers a high initial discharge capacity of 1207 mA h g^?1 at 0.5 C (1 C = 1675 mA h g^?1), and a maintained capacity of 635 mA h g^?1 (fading rate of only 0.095% per cycle), after 500 cycles. This work suggests that combining hybrid nanocarbon with multi-heteroatom doping to modify the commercial separator is an effective approach to obtain high electrochemical performance Li–S batteries.     

Deposition of Cu–Mn alloy film from supercritical carbon dioxide for advanced interconnects

Cu–Mn alloy films for microelectronic interconnects were deposited by H₂ reduction of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)-copper(II) [Cu(tmhd)₂] and bis(penta-methylcyclopentadienyl)-manganese [Mn(pmcp)₂] in supercritical carbon dioxide (scCO₂). 20-nm thick and continuous Cu–Mn films with a smooth surface were deposited at the temperature of 210 °C. Manganese was found to be segregated to film surface and its content on the surface increased with increasing Mn precursor concentration in scCO₂. Mn addition by supercritical fluid deposition could improve surface quality of the Cu film. And electrical resistivity of the Cu–Mn films increased with the Mn contents in the film.     

Nonlinear current–voltage behavior of CaCu3Ti4O12 thin films derived from sol–gel method

CaCu₃Ti₄O₁₂ (CCTO) thin films were synthesized by a sol–gel method followed with spin-coating and sintering process in order to investigate the effects of sintering temperature and thickness of CCTO thin films on the electrical properties as a varistor. The phase identification and morphology of the films have been characterized using X-ray diffractometer and field emission scanning electron microscope. A semiconductor parameter analyzer was used to determine the non-Ohmic (I–V) behaviors. The results showed that the breakdown voltage firstly decreased and then increased with the rising of sintering temperature and was directly proportional to the thickness of the film. Furthermore, the threshold voltage of each sample exhibited nearly twofold relationship as functions of two different measuring mode, surface-to-surface and surface-to-substrate. The lowest leakage current (I _L) and the highest nonlinear coefficient (α) of CCTO thin films were found in the sample sintered at 700 °C. A double Schottky barrier model composed of a depletion layer and a negative charge sheet was employed to explained the non-Ohmic behaviors. A linear relationship between ln(J) and E ^1/2 indicated that a Schottky barrier should exist at the grain boundary.     

MgAl2O4–LaCr0.5Mn0.5O3 composite ceramics for high temperature NTC thermistors

New negative temperature coefficient (NTC) ceramics based on xMgAl₂O₄–(1 ? x)LaCr_0.5Mn_0.5O₃ (x = 0, 0.4, 0.6, 0.8) composition were investigated. The composite ceramics (x = 0.4, 0.6, 0.8) consisted of two phases: a cubic spinel MgAl₂O₄ phase and an orthorhombic perovskite LaCr_0.5Mn_0.5O₃ phase isomorphic to LaCrO₃. The brighter regions were the LaCr_0.5Mn_0.5O₃ and the darker was the MgAl₂O_4. There was ion diffusion between these two phases. X-ray photoelectron spectroscopy analysis corroborated the presence of Cr³⁺, Cr⁴⁺, Mn³⁺ and Mn⁴⁺ ions on lattice sites, which may result in the hopping conduction. The ρ ₃₀₀ and B _400/800 constant increased with increasing MgAl₂O₄ content. The values of ρ ₃₀₀, B _400/800 and activation energy of NTC thermistors were in the range 1.76–1.22 × 10⁸ Ωcm, 2,646–8,711 K, 0.228–0.746 eV, respectively. This means the electrical properties can be adjusted to desired values, depending on the MgAl₂O₄ content.     

Ordered mesoporous α-Fe2O3 (hematite) thin-film electrodes for application in high rate rechargeable lithium batteries

Herein is reported the synthesis of ordered mesoporous α-Fe(2)O(3) thin films produced through coassembly strategies using a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent and hydrated ferric nitrate as the molecular precursor. The sol-gel derived α-Fe(2)O(3) materials are highly crystalline after removal of the organic template and the nanoscale porosity can be retained up to annealing temperatures of 600 °C. While this paper focuses on the characterization of these materials using various state-of-the-art techniques, including grazing-incidence small-angle X-ray scattering, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and UV-vis and Raman spectroscopy, the electrochemical properties are also examined and it is demonstrated that mesoporous α-Fe(2)O(3) thin-film electrodes not only exhibit enhanced lithium-ion storage capabilities compared to bulk materials but also show excellent cycling stabilities by suppressing the irreversible phase transformations that are observed in microcrystalline α-Fe(2)O(3).