Nitrogen-doped carbon material NCM-T heterogeneously catalyzed liquid-phase hydrogenation of nitrobenzene to aniline.

As an important chemical intermediate, aniline is primarily produced industrially through catalytic hydrogenation of nitrobenzene. Herein, a series of nitrogen-doped carbon materials (referred to as NCM-T, with T denoting the roasting temperature (°C)) were prepared through high-temperature roasting of sucrose and melamine for the heterogeneous catalytic liquid-phase hydrogenation of nitrobenzene to aniline. A preliminary study of the involved reaction mechanism was performed by combining the results of material characterisation and catalyst evaluation. Experimental results showed that the graphitic N content and the defective sites simultaneously affected the performance of NCM-T in catalysing the hydrazine hydrate reduction in the nitrobenzene hydrogenation reaction. The catalyst NCM-800 was reacted in an ethanol solution with hydrazine hydrate as the reducing agent at 80 °C for 5 h. Notably, the nitrobenzene conversion rate was up to 94%, and the aniline selectivity was 100%. The turnover frequency (TOF) could reach up to 7.9 mol g-1 h-1, and after five recycling cycles, only a small loss of catalytic activity was observed. This shows that the prepared catalyst is a recyclable catalyst that can be used for reducing the nitrobenzene from hydrazine hydrate to aniline.

Source profile study of VOCs unorganized emissions from typical aromatic devices in petrochemical industry.

Volatile organic compounds (VOCs) are significant pollutants generated during the processes of petroleum refining and chemical production. Aromatic hydrocarbons, in particular, pose a great risk to human health. Nevertheless, unorganized emissions of VOCs from typical aromatics units remain poorly studied and reported. Therefore, it is vital to achieve precise control over aromatic hydrocarbons while managing VOCs. In this study, two typical aromatics production devices in petrochemical enterprises, namely aromatics extraction devices and ethylbenzene devices, were selected. The fugitive emissions of VOCs from the process pipelines in the units were investigated. Samples were collected and transferred using the EPA bag sampling method and HJ 644 and analyzed using gas chromatography-mass spectrometry. The results indicated that a total of 112 VOCs were emitted during the six rounds of sampling in the two types of devices, with alkanes (61 %), aromatic hydrocarbons (24 %), and olefins (8 %) being the primary types of VOCs emitted. The results also revealed the unorganized emissions characteristic substances of VOCs in the two types of devices, with slight differences in the types of VOCs emitted. The study found significant differences in the detection concentrations of aromatic hydrocarbons and olefins, as well as the types of detected chlorinated organic compounds (CVOCs), between the two sets of aromatics extraction units in distinct regions. These differences were closely related to the processes and leakages in the devices and can be effectively controlled by enhancing leak detection and repair (LDAR) and other measures. This article offers guidance for compiling VOCs emission inventories and improving the management of VOCs emissions in petrochemical enterprises by refining the source spectrum at the device scale. The findings are significant for analyzing VOCs unorganized emission factors and promoting safe production in enterprises.

One-Pot and Unsymmetrical Bis-Allylation of Malononitrile with Conjugated Dienes and Allylic Alcohols.

A Pd/Ca catalytic system to promote the unsymmetrical bis-allylation of malononitrile was developed by selecting conjugated dienes and allylic alcohols as allylic reagents. This catalytic system suppressed the competitive symmetrical bis-allylation process and guaranteed the desired unsymmetrical bis-allylation with high chemoselectivity. A wide range of conjugated dienes and allylic alcohols were tolerated well in this transformation, and diverse 1,6-dienes were obtained with high efficiency.

A molecular beacon-like Ag nanocluster fluorescence probe for nucleic acid detection.

We have developed a type of low-cost, label-free silver nanocluster molecular beacon-like fluorescence sensor with a DNA template. To detect target DNA with this probe, we use a hairpin DNA sequence based on a "turn-on" strategy. The transformation of hairpin DNA would visibly influence the formation of Ag nanoclusters, such that the stronger fluorescence will be measured with the solution containing target nucleic acids than that without targets nucleic acids. There is a good liner relationship between the fluorescence and the target DNA concentrations, ranging from 1 to 750 nmol L-1. Importantly, the detection sensing platform allows down to 1 nmol L-1, which is much lower than other studies.

Coating layered double hydroxides with carbon dots for highly efficient removal of multiple dyes.

Layered double hydroxides (LDHs) and layered double oxides (LDOs) are desirable adsorption materials for printing and wastewater treatment owing to their outstanding anion exchange abilities, abundant active sites, and eco-friendly nature. In this study, a versatile LDO hybrid coated with carbon dots (CDs@MgAl-LDO) was constructed by modifying sodium dodecylbenzene sulfonate on the surface of MgAl-LDH as a carbon precursor, followed by ligand carbonization and hydrotalcite dehydration at 450 °C under N2 flow. CDs@MgAl-LDO displayed a hexagonal lamellar architecture with a plate lateral size of approximately 500 nm. It had a higher BET specific surface area (28.61 m2/g) than MgAl-LDO (11.48 m2/g). X-ray diffraction analysis revealed that CDs@MgAl-LDO maintained the "memory effect" of LDOs and could retrieve the original structure when dispersed in water. Moreover, the modified carbon dots change the intrinsically hydrophilic nature of LDOs and help to improve the affinity for organic contaminants, including both cationic and anionic dyes. The adsorption of dyes on CDs@MgAl-LDO followed a pseudo-second-order kinetic model with correlation coefficients (R2) ranging from 0.9901 to 0.9911 and exhibited Freundlich-type heterogeneous adsorption. It showed superior adsorption performance for three dyes, with the maximum adsorption capacity of 3628.9-5174.1 mg/g, thereby outperforming previously reported LDH-based adsorbents. This work developed a facile approach for preparing new carbon dots-LDH hybrids for the highly efficient removal of multiple dyes.

Giant Bulk Photostriction of Lead Halide Perovskite Single Crystals.

It is well known that the lattice structure for a crystal can be manipulated through mechanical strain, temperature, an electric field, a magnetic field, and light. In the past, the photostriction commonly occurs at the surface and the bulk photostriction is very small in most semiconductors. Here, the 532 nm laser can excite the excess electron-hole pairs in the surface layer and consequently these carriers diffuse in the millimeter-thick MAPbBr3-xIx crystal and introduce a giant bulk photostriction of 0.17, 0.28, and 0.35% for the 0.5 mm-thick MAPbBr3-xIx single crystals at x = 0, 1, and 2, respectively. Furthermore, the displacement of each crystal linearly increases from hundreds of picometers to several micrometers when the light intensity increases from about 0.2 to 536 mW/cm2. Since both the maximum strain and the displacement accuracy are as good as those of PZT ceramics used in piezoelectric actuators, these crystals can be used in light-driven actuators for precise positioning.

Design and Synthesis of Ag Nanocluster Molecular Beacon for Adenosine Triphosphate Detection.

This study presents a fluorescence method for detecting adenosine triphosphate (ATP) based on a label-free Ag nanocluster molecular beacon (MB) with high sensitivity. The sensor contains a hairpin-shaped MB, two short single-stranded DNA strands, and T4 DNA ligase. The MB consists of three parts, which are the template DNA sequence for synthesizing Ag nanoclusters at the 5' end, the middle DNA with a hairpin-shaped structure, and the guanine base-rich DNA sequence at the 3' end. The sensor exhibits high fluorescence intensity in the absence of ATP. However, when the probe is used for ATP detection, the two short DNA sequences in the sensor would form a long sequence by enzymatic ligation reaction; this long sequence opens the hairpin-shaped structure of the MB and decreases the fluorescence of the system. Under optimal analytical conditions, a clear linear relationship is observed between ATP concentration and fluorescence intensity in the range of 0.1-10 µM. The interference presented by other small molecules during ATP detection is evaluated, and results confirm the good selectivity of the proposed sensor. Compared with traditional methods, the sensor is label free, easy to operate, inexpensive, and highly sensitive.

Metabolic responses of Saccharomyces cerevisiae to ethanol stress using gas chromatography-mass spectrometry.

Ethanol, as one of the most important biological fuels, is mainly produced by Saccharomyces cerevisiae. But with the accumulation of ethanol, the viability and growth of Saccharomyces cerevisiae is often stressed during fermentation. At present, the reaction mechanism of Saccharomyces cerevisiae to ethanol stress has not been fully elucidated. In this paper, a metabolomics approach with gas chromatography-mass spectrometry was performed to investigate the metabolic changes of Saccharomyces cerevisiae cultured with 0%, 2% and 5% ethanol. The results of partial least-squares discriminant analysis (PLS-DA) clearly reflected the metabolic variations induced by ethanol stress. It was found that in total 36 metabolites changed significantly with univariate analysis, including amino acids, organic acids, and fatty acids. The citrate cycle and alanine, aspartate and glutamate metabolism were found as the markedly perturbed metabolic pathways. Significant alterations of metabolites in these pathways (succinic acid, citric acid, pyruvate, fumarate, glutamate, aspartate, alanine) indicated that ethanol stress impeded the citrate cycle at the node of citrate. This might cause insufficient energy supply of the cell and the synthesis reduction of some amino acids and other substrates. Furthermore, the growth of the cell was slowed down. These results demonstrated that metabolomics has potential to reveal the regulation mechanisms for ethanol stress in Saccharomyces cerevisiae.

Fe-doped H3PMo12O40 immobilized on covalent organic frameworks (Fe/PMA@COFs): a heterogeneous catalyst for the epoxidation of cyclooctene with H2O2.

Covalent organic frameworks (COFs) have arisen as one kind of devisable porous organic polymer that has attracted immense attention in catalytic applications. In this work, we prepared cost-effective imine-based COFs (COF-300, COF-LZU1 and CIN-1) via a reaction kettle operated in place of a traditional sealed Pyrex tube. Then, phosphomolybdic acid (PMA) and iron ions were immobilized on the COF supports by impregnation; the resulting frameworks were denoted as Fe/PMA@COFs (Fe/PMA@COF-LZU1, Fe/PMA@CIN-1 and Fe/PMA@COF-300). A series of characterization results demonstrated that the PMA and iron ions were uniformly dispersed on the surface/cavities of the COFs. The catalytic properties of the obtained Fe/PMA@COFs were investigated in the epoxidation of cyclooctene with H2O2 as the oxidant. The experimental results show that the Fe/PMA@CIN-1 composite can act as an efficient heterogeneous catalyst for the epoxidation of cyclooctene. The intramolecular charge transfer between the COFs and the dual sites (PMA and Fe ions), the spatial structure and the nitrogen content of the COFs played critical roles in dispersing and stabilizing the active species, which are closely connected with the activity and stability of the catalysts. A novel efficient heterogeneous catalyst for the epoxidation of olefins via a simple and cost-effective process is provided, and this experiment demonstrates the notable application prospects of the covalent organic skeleton as a catalyst support.

Ultrasensitive Biosensor for Detection of Mercury(II) Ions Based on DNA-Cu Nanoclusters and Exonuclease III-assisted Signal Amplification.

This paper describes a novel method for label-free mercury(II) ion detection based on exonuclease III-induced target signal recycling amplification using double-stranded DNA templated copper nanoclusters. The synthesized DNA-Cu nanoclusters were used with exonuclease III loop amplification technology for ultra-high sensitivity detection of mercury(II) ions, which were detected by significantly decreased fluorescence intensity. Under the optimal experimental conditions, there was a clear linear relationship between Hg2+ concentration in the range of 0.04 to 8 nM and fluorescence intensity. The detection limit for Hg2+ was 4 pM. In addition, the interference of other metal ions on the mercury(II) ion detection was also studied. To confirm the application of the fluorescent sensor, it was applied to determine the concentrations of mercury(II) ions in tap water, and the results showed that the method can be used to detect mercury(II) ions in water samples successfully.

Light-induced dilation in nanosheets of charge-transfer complexes.

We report the observation of a sizable photostrictive effect of 5.7% with fast, submillisecond response times, arising from a light-induced lattice dilation of a molecular nanosheet, composed of the molecular charge-transfer compound dibenzotetrathiafulvalene (DBTTF) and C60 An interfacial self-assembly approach is introduced for the thickness-controlled growth of the thin films. From photoabsorption measurements, molecular simulations, and electronic structure calculations, we suggest that photostriction within these films arises from a transformation in the molecular structure of constituent molecules upon photoinduced charge transfer, as well as the accommodation of free charge carriers within the material. Additionally, we find that the photostrictive properties of the nanosheets are thickness-dependent, a phenomenon that we suggest arises from surface-induced conformational disorder in the molecular components of the film. Moreover, because of the molecular structure in the films, which results largely from interactions between the constituent π-systems and the sulfur atoms of DBTTF, the optoelectronic properties are found to be anisotropic. This work enables the fabrication of 2D molecular charge-transfer nanosheets with tunable thicknesses and properties, suitable for a wide range of applications in flexible electronic technologies.

Building-Based Analysis of the Spatial Provision of Urban Parks in Shenzhen, China.

Urban parks provide important environmental, social, and economic benefits to people and urban areas. The literature demonstrates that proximity to urban parks is one of the key factors influencing people's willingness to use them. Therefore, the provision of urban parks near residential areas and workplaces is one of the key factors influencing quality of life. This study designed a solution based on the spatial association between urban parks and buildings where people live or work to identify whether people in different buildings have nearby urban parks available for their daily lives. A building density map based on building floor area (BFA) was used to illustrate the spatial distribution of urban parks and five indices were designed to measure the scales, service coverage and potential service loads of urban parks and reveal areas lacking urban park services in an acceptable walking distance. With such solution, we investigated the provision of urban parks in ten districts of Shenzhen in China, which has grown from several small villages to a megacity in only 30 years. The results indicate that the spatial provision of urban parks in Shenzhen is not sufficient since people in about 65% of the buildings cannot access urban parks by walking 10-min. The distribution and service coverage of the existing urban parks is not balanced at the district level. In some districts, the existing urban parks have good numbers of potential users and even have large service loads, while in some districts, the building densities surrounding the existing parks are quite low and at the same time there is no urban parks nearby some high-density areas.

Chiral Molecular Ferroelectrics with Polarized Optical Effect and Electroresistive Switching.

Multifunctional properties of chiral molecules arise from the coexistence of mirror-symmetry-induced stereoisomers and optical rotation characteristics in one material. One of these complex phenomena in these molecules is chiral ferroelectricity, providing the coupling between polarized light and the spatial asymmetry induced dipole moment. Herein we describe the chiral polarization and electroresistance in molecular ferroelectric (R)-(-)-3-hydroxyquinuclidinium chloride thin films with a Curie temperature of 340 K. The high transmittance of chiral ferroelectrics is coupled with polarized light for a linear electro-optic effect, which exhibits angle-dependent optical behaviors. The polarization-controlled conductance imposes a large on/off ratio (∼26.6) of electroresistive switching in molecular ferroelectrics with superior antifatigue endurance.

Observation of clinical effects of mineral trioxide aggregate as direct pulp capping in immature permanent an-terior teeth / 口腔疾病防治

Objective@# To evaluate the clinical effects of mineral trioxide aggregate (MTA) as apulp-dressing agent in immature permanent anterior teeth. @*Methods @#68 perma nent anterior teeth with deep caries or accidental pulp exposure were randomly divided into treatment group (MTA) and control group (calcium hydroxide). The exposed pulps were treated permanently with direct pulp capping. The effect of potential clinical variables on the treatment outcome was evaluated clinically and radiographically during a 24-month follow-up. In order to assess the cumulative successes, data were analyzed with chi-square test and log-rank test (α= 0.05). @*Results @#The successful rate of the treatment group (91.4%) was higher than that of the control group (60.6%) significantly (P < 0.05). None of the gender, occlusal site, type of pulp exposure, site and diameter of pulp exposure had a considerable influence on the outcome (P > 0.05).@*Conclusion@# MTA as a biocompatable, osteogenesis-inducing and inflammation-controlling material appears to be suitable for direct pulp capping.

Multifunctional Charge-Transfer Single Crystals through Supramolecular Assembly.

Centimeter-sized segregated stacking TTF-C60 single crystals are crystallized by a mass-transport approach combined with solvent-vapor evaporation for the first time. The intermolecular charge-transfer interaction in the long-range ordered superstructure enables the crystals to demonstrate external stimuli-controlled multifunctionalities and angle/electrical-potential-dependent luminescence.

All-polymeric control of nanoferronics.

In the search for light and flexible nanoferronics, significant research effort is geared toward discovering the coexisting magnetic and electric orders in crystalline charge-transfer complexes. We report the first example of multiferroicity in centimeter-sized crystalline polymeric charge-transfer superstructures that grow at the liquid-air interface and are controlled by the regioregularity of the polymeric chain. The charge order-driven ferroic mechanism reveals spontaneous and hysteretic polarization and magnetization at the donor-acceptor interface. The charge transfer and ordering in the ferroic assemblies depend critically on the self-organizing and molecular packing of electron donors and acceptors. The invention described here not only represents a new coupling mechanism of magnetic and electric ordering but also creates a new class of emerging all-organic nanoferronics.

A molecular ferroelectric thin film of imidazolium perchlorate that shows superior electromechanical coupling.

Molecular ferroelectric thin films are highly desirable for their easy and environmentally friendly processing, light weight, and mechanical flexibility. A thin film of imidazolium perchlorate processed from aqueous solution is an excellent molecular ferroelectric with high spontaneous polarization, high Curie temperature, low coercivity, and superior electromechanical coupling. These attributes make it a molecular alternative to perovskite ferroelectric films in sensing, actuation, data storage, electro-optics, and molecular/flexible electronics.