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Hierarchically porous MOFs (HP-MOFs) present advantageous synergism of micro- and mesopore but challenging in synthetic control at molecular scale. Herein, we present the first example of reversible and controllable mesopore generation and renovation in a microporous MOF of HKUST-1 via synthetic manipulation at molecular scale. An ammonia-gas etching strategy is proposed to create mesopores in carboxylate-based microporous MOFs and thus produce HP-MOFs. Gas-phase etching ensures uniform mesopore formation inside the MOF crystals via plane-oriented cutting the carboxylate-metal bonds off without affecting the crystal size and morphology. The mesopore size is controlled by the etching temperature, while the mesopore volume could be tuned by adjusting etchant pressure. The generated mesopores could be renovated using MOF precursors solutions so that to achieve controllable mesopore generation/closure, and encapsulation of the adsorbed molecules. This work demonstrates a powerful protocol for precisely tailoring and tuning the properties of MOF materials at molecular scale.

Adsorption of guest molecules by porous materials proceeds in a spontaneous exothermic way, whereas desorption usually requires external energy input as an endothermic process. Reducing such energy consumption makes great sense in practice. Here we report the reversible and automatic methanol (MeOH) adsorption/release in an ionic hydrogen-bonded organic framework (iHOF) constructed from guanidinium cation and borate anion ([B(OCH3)4]3[C(NH2)3]4Cl•4CH3OH, termed Gd-B) at ambient condition. The metastable Gd-B automatically releases all sixteen MeOH molecules (63.4 wt%) via desorption and tetra-methyl borate hydrolysis at ambient atmosphere and the structure can be recovered when re-exposed to MeOH vapor or liquid, mimicking combustible ice behavior but at ambient condition. Reversible capture/release of four guest MeOH molecules is also realized without destroying its crystal structure. The combustible Gd-B paves a way for exploring metastable iHOF materials as carrier for alternative energy source and drug delivery etc., Porous materials function as sorbents for gas storage but release of guest molecules often needs extra energy. Here the authors report reversible methanol adsorption and release in a hydrogen-bonded organic framework, which mimics combustible ice behavior but under ambient condition.

The photoreduction of toxic Cr(VI) to environmental Cr(III) driven by visible-light is highly desired. Metal-organic frameworks (MOFs), as one class of outstanding porous materials, had been utilized for photoreduction of Cr(VI). Current methods modulated the photoreduction of Cr(VI) mainly by selection of suitable metal ions or organic ligands in single component MOFs. However, most of them still exhibit limited photoreduction performance due to low Cr(VI) adsorption rate/capacity, weak light harvesting efficiency, and/or poor electronic utilization efficiency. Multivariate metal-organic frameworks with highly visible-light photosensitive unit and strong Cr(VI) adsorption strut into one single phase is therefore expected to be an effective strategy to improve the photoreduction of Cr(VI), but remains unexplored. Herein, intense visible-light absorption porphyrin unit and strong toxic anions adsorption strut were integrated into one single MOF simultaneously via a sequential mixed-ligand and ionization method, which strongly improve the photoreduction performance of Cr(VI). The synergistic effect of strong adsorption of Cr2O72− and efficient utilization of light endowed H2TCPP⊂(I-)Meim-UiO-66 with highly efficient photoreduction activity toward toxic Cr2O72− under visible light in a rate of 13.3 mgCr(VI)/gcatalyst/min, much higher than the reported MOF-based photocatalysts including typical NH2-UiO-66 (0.2 mgCr(VI)/gcatalyst/min) and NH2-MIL-125 (1.6 mgCr(VI)/gcatalyst/min). As far as we know, this is the best catalyst among all the reported MOF-based photocatalysts for Cr(VI) photoreduction, in which the I- in our imidazolium functionalized MOF acts as sacrificial agent. Based on the results from time-resolved photoluminescence spectra, electron spin resonance, and theoretical calculation etc., a photoreduction mechanism of Cr2O72- over H2TCPP⊂(I-)Meim-UiO-66 was also well proposed. This general and facial strategy, combining the advantages of adsorption and photosensitivity in a multivariate MOF, paves the way to design of higher efficient photocatalytic materials.

Inductively coupled plasma reactive-ion etching (ICP-RIE) is first applied to decrease the thickness of a Si substrate for light-addressable potentiometric sensor (LAPS) characterization. A simple and reliable process flow with the self-aligned Al layer as a hard mask layer in ICP-RIE is used to fabricate a thin semiconductor substrate with Al back-side contact. A single-side polished P-type Si wafer with a thickness of 350 μm is decreased to 100 μm by ICP-RIE from the polished side. The thickness of the thin Si substrate and the dimensions of the designed patterns determined by ICP-RIE are verified using scanning electron microscopy (SEM) and an optical microscope (OM). A selective high-dielectric constant insulator, niobium oxide (NbOx), is directly deposited on the unpolished side of the thin Si substrate as the sensing membrane of a LAPS by reactive ratio frequency (rf) sputtering. A high photocurrent was found in the ICP-RIE LAPS sample under back-side illumination, particularly in high-frequency operation. Compared to an Si substrate without ICP-RIE, 3-fold and 6.5-fold higher photocurrents were achieved by the proposed LAPS with ICP-RIE measured at 1 and 50 kHz of light modulated frequency, respectively. The highest modulated frequency of illumination was 50 kHz for an acceptable photocurrent in the LAPS with ICP-RIE, which is sufficient for two-dimensional (2D) images acquired with high-speed scanning. The NbOx layer deposited on the unpolished Si surface could automatically generate higher pH sensitivity than conventional polished Si surfaces because of the higher surface roughness. The calculated pH sensitivity and linearity were 55.8 mV/pH and 99.6%, respectively, in a pH range from 2 to 12. No clear degradation of hysteresis was found for the LAPS with ICP-RIE. For the designed patterns of the Al hard mask layer, the spatial resolution of the 2D image of the LAPS with ICP-RIE could be obtained by the difference between dimensions observed by OM and the dimensions calculated from the photocurrent versus scanning length controlled by the X-Y stage. A pattern with a length of 250 μm generated by ICP-RIE was measured as 255 μm in the LAPS with scanning step of 5 μm. ICP-RIE is demonstrated to achieve a spatial resolution of 5 μm in the Si-based LAPS. Further reduction of the thickness of an Si substrate by ICP-RIE controlling and its ability to create a dynamic 2D image are suggested for future investigation in spatial resolution optimization.

Fast and highly selective detection of trace amounts of metal ions has become one of the most urgent issues concerning public security and living systems. However, developing a highly efficient fluorescent sensor for metal ions still remains a great challenge. Metal–organic frameworks (MOFs) are a promising class of porous fluorescent sensors towards ion detection. Herein, the anionic MOF FJI-C8 based on the π-conjugated aromatic ligand H6TDPAT (2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) containing uncoordinated nitrogen and carboxylate oxygen atoms was chosen as highly efficient sensor for selective detection of Fe3+. Due to the strong interaction between Fe3+ and Lewis base sites (uncoordinated nitrogen and carboxylate oxygen atoms), the high overlap between the emission spectrum of the anionic FJI-C8 and the absorption spectrum of Fe3+, and the good overlap of the excitation spectrum of the host material FJI-C8 with the absorption spectrum of Fe3+, FJI-C8 exhibited a high sensitivity (0.0233 mM of Fe3+) and extra selectivity (Ksv = 8245 M−1) for the rapid detection (less than 30 s) of Fe3+ with low usage (0.04 mg mL−1 of FJI-C8 suspension). To the best of our knowledge, this is the first example of a luminescent MOF chemosensor based on a trefoil ligand with the highest density of uncoordinated N and carboxylate O atoms for the highly selective detection of Fe3+. It is also crucial to note that this is a first time detection of Fe3+ using both FJI-C8 suspension and solid after filtration, and the results indicate that the detection of Fe3+ using the FJI-C8 suspension is better. This study will pave the way for designing luminescent MOF chemosensors for the detection of Fe3+ ion.

Graphitic carbon nitride quantum dots (g‐CNQDs) are highly promising photoresponsive materials. However, synthesis of monodispersed g‐CNQDs remains challenging. Here we report the dual function of MOF [Cu3BTC2] (HKUST‐1) as a catalyst and template simultaneously to prepare g‐CNQDs under mild conditions. Cyanamide (CA), a graphitic carbon nitride precursor, catalytically dimerized inside the larger MOF cavities at 90 °C and condensed into g‐CNQDs at 120 °C in a controlled fashion. The HKUST‐1 template was stable under the reaction conditions, leading to uniform g‐CNQDs with a particle size of 2.22±0.68 nm. The as prepared g‐CNQDs showed photoluminescence emission with a quantum yield of 3.1 %. This concept (MOF dual functionality) for catalyzing CA polycondensation (open metal sites (OMSs) effect) and controlling the produced particle size (pore‐templating effect), together with the tunable MOF porosity, is expected to produce unique g‐CNQDs with controllable size, morphology, and surface functionality., The first example of a MOF as a dual‐function material for templating and catalyzing the formation of monodispersed graphitic carbon nitride quantum dots (g‐CNQDs) under very mild conditions is reported. g‐CNQDs with tailorable sizes and properties can be prepared using this synthetic protocol, taking the advantages of the huge MOF family with tunable pore structures.

A fully integrated system and user interface, named Mirror-LAPS, was established for chemical imaging of diffusion-based reactions and bioimaging, e.g., cellular metabolism imaging in situ, with advantages of portability, real-time monitoring and flexible control. By means of a field programmable gate array (FPGA), a minimized drive circuit and an illumination path integrated into the hardware, the volume and cost of this Mirror-LAPS system are only 11 % and 75 %, respectively, those of the conventional LAPS system. 2D images can be easily constructed based on the combination of the measured photocurrent with automatic digitization and recorded coordinates for each pixel in the frame. The time to image one pixel under the optimized parameters with a periods per pixel (PPP) of 64 is approximately 6.6 ms. The location, area, and resolution of pixels can be easily, quickly and flexibly adjusted in the user interface to obtain 2D images and a real-time video. The cellular metabolism of HK2 cellsfor different cell numbers and glucose concentrations is virtually demonstrated by this Mirror-LAPS system by the color changes in 2D images for the first time, which could provide a reliable platform in a cell culturing space for cell-based research.

Amorphous silicon (a-Si) has been approved for use as the semiconductor layer in a light-addressable potentiometric sensor (LAPS). A new device structure of niobium oxide (NbOx)/P-I-N amorphous silicon (a-Si) on ITO/glass is proposed for a thin film LAPS with the advantage of a high photovoltage. P-type, intrinsic and N-type a-Si layers are fabricated by plasma enhanced chemical vapor deposition (PECVD) with selective gas dopants on ITO/glass. A single NbOx layer is directly sputtered onto an a-Si substrate and is used as the pH sensing membrane. The temperatures for all of the processes used to manufacture this device are lower than 300 °C, including the rapid thermal anneal (RTA) treatment, which is compatible with conventional fabrication processes for glass substrates in solar cells and thin film transistors. Based on the photovoltage versus gate bias characteristics in standard buffer solutions, the calculated pH sensitivity and linearity from pH 2 to 10 is 40 mV/pH and 99.4% for the P-I-N a-Si LAPS with RTA treatment at 300 °C. Compared with an intrinsic a-Si structure, a 50% higher photovoltage is achieved in the P-I-N a-Si LAPS. Furthermore, XRD and SIMS are used to verify the properties of the a-Si film. A high frequency ac laser signal of up to 20 kHz was obtained with the P-I-N a-Si LAPS while maintaining the same spatial resolution, which is important for two-dimensional images acquired by high-speed scanning with an analog micromirror.

An In–Ga–Zn oxide (IGZO) layer is applied, for the first time, as the semiconductor layer of a light-addressable potentiometric sensor (LAPS). The IGZO layer sputtered on the commercial ITO/glass substrate could be used as the active layer of an LAPS illuminated by a ultraviolet light-emitting diode (UV LED). In the operation of LAPS, an IGZO/ITO glass substrate with a higher photocurrent and less interference of the ambient light compared with a conventional n-type silicon wafer is obtained. A sensing membrane of sputtered niobium oxide directly on the IGZO layer, with a substrate temperature of 250 °C, is verified to have a pH sensitivity of 61.8 mV/pH according to photocurrent versus gate bias curves measured in various pH buffer solutions. The ac signal applied to the UV LED can be increased to 30 kHz for IGZO LAPS pH sensing. This improvement is beneficial for the sensor’s use in high-speed 2-D chemical image applications.

Indium Gallium Zinc Oxide (IGZO) on Indium Tin Oxide (ITO) glass has been applied as the semiconductor substrate of a light-addressable potentiometric sensor (LAPS) with the advantages of immunity to room light inference and high photocurrent. For the first time, investigations into this IGZO LAPS including two-dimensional (2D) chemical imaging and reduction of the potential biorelative damage induced by the requirement of an ultraviolet (UV) light source are presented in this study. For the spatial resolution, a smaller aperture for the light spot provided by a light emitting diode (LED) makes the photocurrent decrease. To overcome this natural limitation, the type of AC modulation of light source is changed from a sine wave to a square wave with different duty cycles. The photocurrent and power consumption of a 365 nm LED with square wave and a duty cycle of 40 % are 42.2 % higher and 16.2 % lower than those of the conventional setup of a sine wave, respectively. The pH sensitivity, linearity, hysteresis and drift are comparable. The illumination wavelengths of 365, 405 and 435 nm are studied for photoresponse. 405 nm illumination with acceptable pH sensing performance can be suggested for IGZO LAPS for less bio damage concern. Additionally, a laser with a wavelength of 405 nm with spot size of 25 μm and scanning step of 2 μm is proven to have a clear pattern recognition down to 50 μm in 2D image. Further optimization of the spot size of the laser, thickness and composition of IGZO are suggested for better spatial resolution.

It is highly desired but challenging to achieve highly active single-atom Fe sites from iron-based metal-organic frameworks (MOFs) for efficient oxygen reduction reaction (ORR) due to the easy aggregation of iron species and formation of the inactive Fe-based particles during pyrolysis. Herein, a facile migration-prevention strategy is developed involving the incorporation of polyaniline (PANI) into the pores of iron porphyrinic-based MOF PCN-224(Fe) and followed by pyrolysis to obtain the single-atom Fe implanted N-doped porous carbons material PANI@PCN-224(Fe)-900. The introduced PANI inside the pores of PCN-224(Fe) not only served as protective fences to prevent the aggregation of the iron species during thermal annealing, but also acted as nitrogen sources to increase the nitrogen content and form Fe- N x -C active sites. Compared with the pristine PCN-224(Fe) derived carbonization sample containing Fe-based particles, the carbonaceous material PANI@PCN-224(Fe)-900 without inactive Fe-based particles exhibited superb ORR electrocatalytic activity with a more positive half-wave potential, significantly improved stability in both alkaline media, and more challenging acidic condition. The migration-prevention strategy provides a new way to fabricate atomically dispersed metal active sites via pyrolysis approach for promoting catalysis.

Highly dispersed ultrafine defective Pt nanoparticles (NPs) encapsulated in the mesopores of MIL-101 were successfully achieved for the first time through a facile chemical dealloying approach. PtCo alloy NPs inside the mesoporous MIL-101 were firstly formed via a double-solvent method and the Co species were subsequently selectively etched by diluted nitric acid to achieve the defective Pt NPs. Compared with PtCo alloy NPs, the as-prepared defective Pt NPs showed an improved catalytic activity towards the hydrogenation of nitroarenes under mild conditions.

The thickness effect of In-Ga-Zn oxide (IGZO) semiconductor layer is investigated for pH sensing in light-addressable potentiometric sensor (LAPS). pH sensing membrane is 45 nm-thick NbOx, which is directly on IGZO/ITO/glass substrate. The thickness of IGZO layer is determined by time-mode control in reactive rf sputtering. The highest photovoltage and operation frequency can be obtained in the IGZO thickness of 300 nm. pH sensitivity is about 65 mV/pH with ac signal frequency at 1 kHz. For better stability in hysteresis, further investigations on sensing membrane optimization are suggested.