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Hypochlorite (ClO-) is widely used as a disinfectant, whose residue content in water should be strictly controlled due to the potential threat to human health in an inappropriate concentration. Herein, dual-emissive metal-organic frameworks with a UiO-66 prototype structure, PDA/Eu/PDA-UiO-66-NH2(x), were elegantly designed and prepared by a mixed ligand assembly and sequential post-synthesis strategy. Since blue emission is sensitive to ClO-, PDA/Eu/PDA-UiO-66-NH2(40) was selected as a model nanosensor for ratiometric and turn-on sensing of ClO- while red emission acts as a reference signal. Remarkably, PDA/Eu/PDA-UiO-66-NH2(40) shows high efficiency and specificity toward ClO- detection, as verified by a very short response time of 15 s, a wide linear range of 0.1-60 μM, a low detection limit of 0.10 μM, and excellent selectivity toward common competing ions. The recovery experiments show that the recoveries of spiking ClO- in tap water range from 96 to 103%. The rigidification of the coordinated H2N-BDC2- ligands should be responsible for the turn-on fluorescence of PDA/Eu/PDA-UiO-66-NH2(40). This work not only shows a highly efficient and specific fluorescent nanosensor for ClO- detection but also presents the first MOF-based fluorescent probe for turn-on and ratiometric sensing of ClO-.

It is mandatory to decontaminate Cr(VI) species from water streams due to their high toxicity. The photoreduction of hazardous Cr(VI) to nontoxic Cr(III) is a very promising approach to control Cr(VI) pollution. Although some MOFs and their composites have been employed as photocatalysts to reduce toxic Cr(VI), their catalytic activities are always limited by inefficient visible light absorption and inferior Cr(VI) adsorption performances. Herein, cationic Ru-UiO-dmbpy(1) that is decorated with a high density of cationic charges and also embedded with catalytically competent and visible light harvesting moieties (i.e. Ru(bpy)3) was successfully synthesized by a sequential mix-and-match and ionization process. The presence of Ru(bpy)3 moieties makes Ru-UiO-dmbpy(1) an excellent visible-light harvester, extending the absorption edge from 420 nm for pristine UiO-bpy to about 780 nm for Ru-UiO-bpy/Ru-UiO-dmbpy(1). Driven by ion exchange, Ru-UiO-dmbpy(1) shows a large adsorption rate constant (k2) of 1.33 × 10−2 g mg−1 min−1 in the adsorption of Cr2O72−, which is 8.26 times that of pristine UiO-bpy and 6.27 times that of the non-ionization counterpart Ru-UiO-bpy(1) under the same adsorption conditions. The equilibrium Cr2O72− uptake capacity of Ru-UiO-dmbpy(1) reaches 101.8 mg g−1, which is about 1.98 and 1.81 times that of UiO-bpy and Ru-UiO-bpy(1), respectively. With an efficient visible light absorption ability and superior Cr(VI) adsorption performance, Ru-UiO-dmbpy(1) shows a reaction rate constant (k1) of 0.011 min−1 in the photoreduction of Cr(VI) without any sacrificial agents under visible light illumination, which is much larger than those of pristine UiO-bpy (0.003 min−1) and its non-ionization counterpart Ru-UiO-bpy(1) (0.007 min−1) under the same conditions. The result unambiguously demonstrates that the Cr(VI) photoreduction activity could be largely enhanced by photosensitiser introduction and framework ionization. To further evaluate the catalytic performance of Ru-UiO-dmbpy(1), Cr(VI) reduction was also investigated in the presence of various sacrificial agents. Remarkably, a high Cr(VI) photoreduction rate of 6.4 mgCr(VI) gcatalyst−1 min−1 was obtained when benzyl alcohol was used as a sacrificial agent, which is a record value among those reported for MOF-based photocatalysts.

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H2O2 as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol-1) and an extraordinarily high TOF value (42.7 h-1) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH(H2O) catalytic sites decorated in MOF-808. The superoxide radicals (•O2-) and hydroxyl radicals (•OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Bronsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH(H2O) groups promoting the H2O2 decomposion in to both •O2- and •OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.

The detection of hypochlorite (ClO-) content in tap water is extremely important because excess amounts of hypochlorite can convert into highly toxic species and inadequate amounts of hypochlorite cannot fully kill bacteria and viruses. Although several metal-organic frameworks (MOFs) have been successfully employed as fluorescent sensors for hypochlorite detection, all these sensors are based on single emission that responds to the dose of hypochlorite. Ratiometric sensors are highly desirable, which can improve the sensitivity, accuracy, and reliability via self-calibration. Herein, a nanoscale dual-emission multivariate 5-5-Eu/BPyDC@MOF-253-NH2 was synthesized by sequential mixed-ligand self-assembly and postsynthesis method. Among the two emission bands of 5-5-Eu/BPyDC@MOF-253-NH2, the strong blue emitting derived from ligands is sensitive to hypochlorite, while the red emitting derived from Eu(III) almost keeps invariable. Therefore, 5-5-Eu/BPyDC@MOF-253-NH2 was exploited as a fluorescent ratiometric nanosensor for "on-off" sensing of hypochlorite. Notably, the proposed sensing system showed an excellent performance including fast response (within 15 s), relative high specificity, wide linear range (0.1-30 μM), and low detection limit (0.094 μM). Besides, the suppressed blue emitting was recovered after the addition of ascorbic acid (AA) that consumes ClO- via the redox reaction. Therefore, 5-5-Eu/BPyDC@MOF-253-NH2 was further employed as a fluorescent ratiometric nanosensor for the "on-off-on" sensing of AA. This work represents the first MOF-based fluorescent "switch" for the ratiometric sensing of hypochlorite and the second for ratiometric sensing of AA.

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H

Carbon dots doped with nitrogen and copper have been synthesized via a hydrothermal method. They possess favorable peroxidase-like catalytic activity over a wide range of pH values and temperatures. Specifically, they were used to catalyze the oxidation of ortho- and para-phenylenediamine (OPD and PPD) by H2O2. The resulting products possess different colors (yellow for OPD and brown for PPD), which can be visually discriminated. The corresponding typical absorption peaks of oxidized products for OPD and PPD are at 413 nm and 500 nm, respectively. The method displays excellent discrimination ability and selectivity over potential interferents. The detection limits are 1.1 μM for OPD and 1.9 μM for PPD. The respective linear ranges are from 5 to 200 μM for OPD and from 2.5 to 700 μM for PPD. The method was applied to the quantification of OPD and PPD in spiked natural waters.

It is imperative to remove organicarsenic acids (OAAs) from water because they can convert into highly toxic inorganic arsenic compounds in natural environment via biotic and abiotic degradation routes. Herein, seven Zr-based metal-organic frameworks (Zr-MOFs) including DUT-67, UiO-66, UiO-67, MOF-808, MOF-808F, NU-1000, NU-1000B with various structures were screened for the adsorptive removal of representative OAAs including p-arsanilic acid (ASA) and roxarsone (ROX) in water media. Initial screening found that MOF-808 and MOF-808F have the largest adsorption capacities. Therefore, their adsorption behaviors including adsorption kinetics, isotherms, specificity and effects of pH were fully investigated. Remarkably, MOF-808F had the second largest maximum adsorption capacities of ASA (621.1 mg g−1) and ROX (709.2 mg g−1) among the reported MOF-based adsorbents. In addition, MOF-808F showed excellent selectivity and reusability and no observable drop of adsorption efficiency was found in the presence of equimolar competing ions (Cl−, OAc− or SO42−) or after three successive adsorptive runs. By contrast, MOF-808 had inferior adsorption specificity and reusability in spite of the very similar structure with MOF-808F. The structure-dependent adsorption performances can be explained by the distinct adsorptive mechanisms, which were revealed by zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation etc. The dominant interaction between MOF-808 and ASA was coordination interactions, while ASA adsorption over MOF-808F was governed by the synergistic effect of π-π stacking, hydrogen bonding, and electrostatic interactions. This work no only presented an excellent adsorbent (MOF-808F) toward OAAs, but also revealed the structure dependent adsorption performances/mechanisms.

The components of urban surface cover are diversified, and component temperature has greater physical significance and application values in the studies on urban thermal environment. Although the multi-angle retrieval algorithm of component temperature has been matured gradually, its application in the studies on urban thermal environment is restricted due to the difficulty in acquiring urban-scale multi-angle thermal infrared data. Therefore, based on the existing multi-source multi-band remote sensing data, access to appropriate urban-scale component temperature is an urgent issue to be solved in current studies on urban thermal infrared remote sensing. Then, a retrieval algorithm of urban component temperature by multi-source multi-band remote sensing data on the basis of MODIS and Landsat TM images was proposed with expectations achieved in this work, which was finally validated by the experiment on urban images of Changsha, China. The results show that: 1) Mean temperatures of impervious surface components and vegetation components are the maximum and minimum, respectively, which are in accordance with the distribution laws of actual surface temperature; 2) High-accuracy retrieval results are obtained in vegetation component temperature. Moreover, through a contrast between retrieval results and measured data, it is found that the retrieval temperature of impervious surface component has the maximum deviation from measured temperature and its deviation is greater than 1 °C, while the deviation in vegetation component temperature is relatively low at 0.5 °C.

The main disadvantage of Land surface temperature (LST) retrieval methods from Landsat TM thermal channel images is that atmospheric profile parameters are needed, and MODIS has several near infrared bands that can be used to estimate atmospheric profile parameters. Two methods that could be used to retrieve the LST from Landsat TM and MODIS data were compared in this paper, the first of them is the mono-window algorithm developed by Qin et al. and the second is the single-channel algorithm developed by Jimenez-Munoz and Sobrino. Atmospheric profile parameters such as atmospheric moisture content, atmospheric transmittance and average atmospheric temperature have been estimated from MODIS data, and the land surface emissivity values have been estimated from a methodology based on spectral mixture analysis. Finally, a comparison between the LST measured in situ and retrieved by the algorithms over urban area of Changsha city in China is present. Result indicates that the two LST retrieval algorithms can get high-precision results in support of atmospheric parameters from MODIS images, the average deviation of mono-window algorithm is 0.76K, and the deviation of generalized single-channel algorithm is 1.23k.