The direct synthesis of metal−organic frameworks (MOFs) with strong Brønsted acidity is challenging because the functional groups exhibiting Brønsted acidity (e.g., sulfonic acid groups) often jeopardize the framework integrity. Herein, we report the direct synthesis of two hierarchically porous MOFs named NUS-6 composed of either zirconium (Zr) or hafnium (Hf) clusters with high stability and strong Brønsted acidity. Via the modulated hydrothermal (MHT) synthesis, these two MOFs can be easily synthesized at a low temperature (80 °C) with high throughput. They exhibit BET surface areas of 550 and 530 m 2 g −1 for Zr and Hf one, respectively, and a unique hierarchically porous structure of coexisting micropores (∼0.5, ∼0.7, and ∼1.4 nm) and mesopores (∼4.0 nm) with dangling sulfonic acid groups. Structural analysis reveals that the hierarchical porosity of NUS-6 is a result of missing linkers and clusters of the parental UiO-66 framework. These unique features make NUS-6 highly efficient and selective solid acid catalysts for dehydration of fructose to 5hydroxymethylfurfural (HMF), in which NUS-6(Hf) demonstrates a superior performance versus that of NUS-6(Zr) because of the stronger Brønsted acidity contributed from Hf-μ 3 -OH groups as well as smaller pore sizes suitable for the restriction of unwanted side reactions. Our results have demonstrated for the first time the unique attributes of Hf-MOFs featured by superior stability and Brønsted acidity that can be applied as heterogeneous catalysts in biobased chemical synthesis.

Fluorescent porous materials have been under intensive investigation recently, because of their wide applications in molecular recognition and chemical sensing. However, it is a great challenge to achieve size selectivity and sensing linearity for molecular recognition. Herein, we report a series of porous organic frameworks (POFs) containing flexible tetraphenylethylene (TPE) moieties as molecular rotors with responsive fluorescent behavior. These fluorescent POFs exhibit size-selective turn-on fluorescence for the effective chemical sensing of volatile organic compounds (VOCs), which can be attributed to the different degrees of motion restriction of flexible TPE rotors by various VOCs, leading to the partially freezing of rotors in more fluorescent conformations. Significantly, a linear aggregation-induced emission (AIE) relationship is observed between the fluorescent POFs and the VOCs over a wide range of concentrations, which is highly beneficial for quantitative sensing applications. The gas-phase detection of arene vapors using POFs is also proven with unprecedentedly high sensitivity, selectively, and recyclability. The mechanism of responsive fluorescence in POFs is further investigated using molecular simulations and density functional theory (DFT) calculations.

Although many studies on luminescent metal–organic frameworks (MOFs) have been reported for chemical sensing applications, it has yet to be realized in MOFs the precise linearity control over photophysical characteristics and sensing sensitivity at the molecular level for a fundamental understanding of the structure–property relationships. Here we demonstrate the first example of aggregation-induced emission (AIE)-responsive MOFs with precise linearity control of photophysics and chemical sensing. We employ a multivariate strategy to tune the number of AIE molecular rotors (dynamic phenyl rings) in a MOF system by varying the ratio of tetraphenylethylene (TPE)-based organic linker, leading to highly tunable photophysical characteristics (e.g., maximum emission peak, quantum yield, and optical band gap) featuring linear correlations with linker content. Importantly, the sensing sensitivity of these dynamic MOFs can be enhanced by increasing the number of AIE molecular rotors with perfect linearity control, as systematically investigated by fluorescence responsive to temperature, viscosity, guest molecular size, as well as theoretical calculations. Our study shows that the sensing sensitivity of the AIE-responsive MOF in this study (termed as NUS-13-100%) is better than those of our previously reported materials. Significantly, the observed linear relationship between emission intensity and molecular weight of polystyrene as the analyte suggests that such AIE-responsive MOFs could be used as molecular sensors for fluorescence-based determination of polymer molecular weight. Eventually, the optical sensing device containing NUS-13-100% shows a perfect linearity response with high sensitivity for the detection of trace toxic benzene vapor. In short, our work paves the way toward porous MOFs containing AIE molecular rotors with a versatile responsive emission mechanism and suitable pore size/geometry for broad applications in chemical sensing and environmental monitoring.

We report the intergrowth of ZIF-8 crystals on ultrathin graphene oxide (GO) membranes, which helps to reduce the non-selective pores of pristine GO membranes leading to gas selectivities as high as 406, 155, and 335 for H2/CO2, H2/N2, and H2/CH4 mixtures, respectively.

Two new yttrium sulfate tellurites, namely, Y3(TeO3)2(SO4)2(OH)(H2O) and Y2(Te4O10)(SO4), were achieved in our exploration of new sulfates with large birefringence in Y3+-Te4+-SO42- system. The two compounds exhibit two new three...