Surface Termination (-O, -F or -OH) and Metal Doping on the HER Activity of Mo2CTx MXene.

Two-dimensional MXenes have recently garnered significant attention as electrocatalytic materials for hydrogen evolution reaction (HER). However, previous theoretical studies mainly focused on the effect of pure functional groups while neglecting hybrid functional groups that are commonly observed in experiments. Herein, we investigated the hybrid functionalized Mo2CTx MXene (T=-O, -F or -OH) to probe the HER properties. In binary O/F co-functionalization, the presence of F groups would attenuate the H adsorption and lead to the enhanced HER activity than the fully O-terminated Mo2CO2. However, the surface HER activity of ternary O/F/OH functionalized Mo2CTx is not satisfactory owing to the relatively weak H adsorption capacity. To further enhance the catalytic activity, modification was performed by introducing another metal element into its lattice structure. The doped metal (Fe, Co, Ni, Cu) exhibits reduced charge transfer to O compared to Mo atoms, leading to enhanced H adsorption and improved overall activity. The synergistic effect of hybrid functionalization and TM modification provides useful guidance for achieving feasible Mo2CTx candidates with high HER performance, which can be applied to the electrocatalytic applications of other MXenes.

Application of Metal-Organic Frameworks (MOFs) in Environmental Biosystems.

Metal-organic frameworks (MOFs) are crystalline materials that are formed by self-assembling organic linkers and metal ions with large specific areas and pore volumes. Their chemical tunability, structural diversity, and tailor-ability make them adaptive to decorate many substrate materials, such as biomass-derived carbon materials, and competitive in many environmental biosystems, such as biofuel cells, bioelectrocatalysts, microbial metal reduction, and fermentation systems. In this review, we surmised the recent progress of MOFs and MOF-derived materials and their applications in environmental biosystems. The behavior of MOFs and MOF-derived materials in different environmental biosystems and their influences on performance are described. The inherent mechanisms will guide the rational design of MOF-related materials and lead to a better understanding of their interaction with biocomponents.

Exploring the Aroma Fingerprint of Various Chinese Pear Cultivars through Qualitative and Quantitative Analysis of Volatile Compounds Using HS-SPME and GC×GC-TOFMS.

To comprehensively understand the volatile compounds and assess the aroma profiles of different types of Pyrus ussuriensis Maxim. Anli, Dongmili, Huagai, Jianbali, Jingbaili, Jinxiangshui, and Nanguoli were detected via headspace solid phase microextraction (HS-SPME) coupled with two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC-TOFMS). The aroma composition, total aroma content, proportion and number of different aroma types, and the relative quantities of each compound were analyzed and evaluated. The results showed that 174 volatile aroma compounds were detected in various cultivars, mainly including esters, alcohols, aldehydes, and alkenes: Jinxiangshui had the highest total aroma content at 2825.59 ng/g; and Nanguoli had the highest number of aroma species detected at 108. The aroma composition and content varied among pear varieties, and the pears could be divided into three groups based on principal component analysis. Twenty-four kinds of aroma scents were detected; among them, fruit and aliphatic were the main fragrance types. The proportions of aroma types also varied among different varieties, visually and quantitatively displaying changes of the whole aroma of the different varieties of pears brought by the changes in aroma composition. This study contributes to further research on volatile compound analysis, and provides useful data for the improvement of fruit sensory quality and breeding work.

Systemic LPS-induced microglial activation results in increased GABAergic tone: A mechanism of protection against neuroinflammation in the medial prefrontal cortex in mice.

Neuroinflammation with excess microglial activation and synaptic dysfunction are early symptoms of most neurological diseases. However, how microglia-associated neuroinflammation regulates synaptic activity remains obscure. We report here that acute neuroinflammation induced by intraperitoneal injection of lipopolysaccharide (LPS) results in cell-type-specific increases in inhibitory postsynaptic currents in the glutamatergic, but not the GABAergic, neurons of medial prefrontal cortex (mPFC), coinciding with excessive microglial activation. LPS causes upregulation in levels of GABAAR subunits, glutamine synthetase and vesicular GABA transporter, and downregulation in brain-derived neurotrophic factor (BDNF) and its receptor, pTrkB. Blockage of microglial activation by minocycline ameliorates LPS-induced abnormal expression of GABA signaling-related proteins and activity of synaptic and network. Moreover, minocycline prevents the mice from LPS-induced aberrant behavior, such as a reduction in total distance and time spent in the centre in the open field test; decreases in entries into the open arm of elevated-plus maze and in consumption of sucrose; increased immobility in the tail suspension test. Furthermore, upregulation of GABA signaling by tiagabine also prevents LPS-induced microglial activation and aberrant behavior. This study illustrates a mode of bidirectional constitutive signaling between the neural and immune compartments of the brain, and suggests that the mPFC is an important area for brain-immune system communication. Moreover, the present study highlights GABAergic signaling as a key therapeutic target for mitigating neuroinflammation-induced abnormal synaptic activity in the mPFC, together with the associated behavioral abnormalities.

Acceleration Effect of Bases on Mn Pincer Complex-Catalyzed CO2 Hydroboration.

Herein, we report a comprehensive study of CO2 hydroboration catalyzed by Mn pincer complexes. The traditional metal-ligand cooperation (MLC) mechanism based on the H-Mn-N-Bpin pincer complex is not viable due to the competing abstraction of the Bpin group from the H-Mn-N-Bpin complex by NaOtBu. Instead, we propose an ionic mechanism based on the H-Mn-N-Na species with a low energy span (22.5 kcal/mol) and unveil the acceleration effect of bases. The X groups in the H-Mn-N-X catalyst models are further modulated, and the steric hindrance and H→B donor-acceptor interactions of the X group increase the energy barrier of the hydride transfer. The hydrogen bond and electrostatic interactions of the X group can accelerate the hydride transfer to HCOOBpin and HCHO molecules except for the nonpolar CO2 molecule. Based on these discoveries, we designed a pyridine-based Mn pincer catalyst system, which could achieve CO2 hydroboration in low-temperature and base-free conditions through a metal-ligand cooperation mechanism.

Substituent, Solvent, and Dispersion Effects on the Zwitterionic Character and Dimerization Thermochemistry of the Group 6 Fulvene Metal Tricarbonyl Complexes.

Dimerizations of fulvene metal tricarbonyl complexes of the type (C5H4CRR')M(CO)3 (R, R' = MeO, Me, H; M = Cr, Mo, W) to form a metal-metal bond and a new carbon-carbon bond, thereby giving binuclear cyclopentadienyl metal carbonyl derivatives, are predicted to be thermochemically favored but to have significant activation energies ranging from ΔE = 19 to 42 kcal/mol. However, the introduction of dimethylamino but not methoxy substituents onto the exocyclic carbon atom changes the situation drastically so that the monomers [C5H4CH(NMe2)]M(CO)3 and [C5H4C(NMe2)2]M(CO)3 become strongly thermochemically favored, lying ΔE = 43 kcal/mol (M = W) to 63 kcal/mol (M = Cr) below their corresponding dimers. In such dimethylamino-substituted (fulvene)M(CO)3 derivatives, the M-C distance to the exocyclic fulvene carbon is lengthened beyond the bonding distance to give a zwitterionic structure with a pentahapto fulvene ligand. Such M-C distances in (fulvene)M(CO)3 complexes, which have preferred zwitterionic structures, increase with increasing solvent polarity (i.e., dielectric constant) until a saturation point is reached.

Dual-mode microstrip leaky-wave antenna for pattern diversity application.

We present a dual-mode microstrip leaky-wave antenna (LWA), which is characterized by radiating a single beam or dual symmetrical beam. Different from the conventional single-mode microstrip LWA, the designed antenna is based on the odd mode and the even mode of the employed shorted microstrip line. The working principle of these two modes is fully studied by analyzing the electric-field distributions and their dispersion curves. Additionally, it can be found that the odd mode and the even mode are capable of realizing different radiation patterns. Furthermore, a mode translator is particularly designed in order to efficiently excite the concerned two modes. Finally, the presented antenna is simulated, fabricated, and measured, and the simulated results agree well with the measurements. The tested far-field results show that the designed dual-mode LWA realized single-beam scanning from 39° to 64° when the frequency ranges from 4.5 to 5.0 GHz and dual symmetrical beam scanning from 44° to 60° as the frequency varies from 4.5 to 4.9 GHz, respectively.

A Novel Auto-Synthesis Dataset Approach for Fitting Recognition Using Prior Series Data.

To address power transmission line (PTL) traversing complex environments leading to data collection being difficult and costly, we propose a novel auto-synthesis dataset approach for fitting recognition using prior series data. The approach mainly includes three steps: (1) formulates synthesis rules by the prior series data; (2) renders 2D images based on the synthesis rules utilizing advanced virtual 3D techniques; (3) generates the synthetic dataset with images and annotations obtained by processing images using the OpenCV. The trained model using the synthetic dataset was tested by the real dataset (including images and annotations) with a mean average precision (mAP) of 0.98, verifying the feasibility and effectiveness of the proposed approach. The recognition accuracy by the test is comparable with training by real samples and the cost is greatly reduced to generate synthetic datasets. The proposed approach improves the efficiency of establishing a dataset, providing a training data basis for deep learning (DL) of fitting recognition.

A Frequency-Programmable Miniaturized Radio Frequency Transmitter for Animal Tracking.

In animal tracking applications, smaller transmitters can reduce the impact of the transmitter on the tagged animal and thus provide more accurate data about animal behavior. By combining a novel circuit design and a newly developed micro-battery, we developed frequency-programmable and more powerful radio frequency transmitters that are about 40% smaller and lighter in weight than the smallest commercial counterpart for animal monitoring at the time of development. The new radio frequency transmitter has a miniaturized form factor for studying small animals. Designs of two coding schemes were developed: one transmits unmodulated signals (weight: 152 mg; dimensions: Ø 2.95 mm × 11.22 mm), and the other transmits modulated signals (weight: 160 mg; dimensions: Ø 2.95 mm × 11.85 mm). To accommodate different transmitter life requirements, each design can be configured to transmit in high or low signal strength. Prototypes of these transmitters were evaluated in the laboratory and exhibited comparable or longer service life and higher signal strength compared to their smallest commercial counterparts.

Comparative Study of the Thermal Stabilities of the Experimentally Known High-Valent Fe(IV) Compounds Fe(1-norbornyl)4 and Fe(cyclohexyl)4.

The high stability of the experimentally known homoleptic 1-norbornyl derivative (nor)4Fe of iron in the unusual +4 oxidation state is a consequence of the high reaction barriers of the singlet or triplet potential surfaces constrained by the global dispersion attraction and the great steric demands of the norbornyl groups. The much more limited stability of the corresponding cyclohexyl derivative (cx)4Fe may result from the conical intersection between the singlet potential surface and the quintet spin potential surface arising from the weaker dispersion attraction and the reduced steric effect of the cyclohexyl groups relative to the 1-norbornyl groups. In contrast, the high stability of the likewise experimentally known (cx)4M (M = Ru or Os) structures results from the larger ligand field splitting (Δ) of the d-orbital energies for the second and third-row transition metals ruthenium and osmium relative to that of the first-row transition metal iron. The cyclohexyl derivative (cx)4Fe is predicted to be reactive toward carbon monoxide to insert CO into up to two Fe-C bonds. However, the dispersion effect as well as the much larger size of the 1-norbornyl substituents prevents similar reactivity of (nor)4Fe with carbon monoxide.

Dispersion Effects in Stabilizing Organometallic Compounds: Tetra-1-norbornyl Derivatives of the First-Row Transition Metals as Exceptional Examples.

In 1972 Bower and Tennett first synthesized a series of tetra-1-norbornyl derivatives, (nor)4M, of the first-row transition metals from titanium to cobalt. These were found to be exceptionally stable for homoleptic metal alkyls containing only metal-carbon σ-bonds. The theoretical energies for the dissociation of 1-norbornyl ligands from these unusually high oxidation state organometallics through the reactions (nor)4M → (nor)3M + nor• and (nor)4M → (nor)2M + nor-nor indicate that dispersion effects play an important role in determining their exceptional stability. Thus, all of the (nor)4M (M = Ti to Cu) derivatives are viable with respect to 1-norbornyl radical dissociation when the London dispersion effect is considered. However, (nor)4Cu becomes disfavored if the dispersion correction is ignored. Thus, the stability of the (nor)4M molecules is seen to arise from the favorable combination of steric and dispersion force effects of the four 1-norbornyl groups tetrahedrally disposed around the metal atom and maximizing the dispersion attraction between them in a spherical hydrocarbon structure with a central metal atom. The tri-1-norbornyl derivatives (nor)3M appear be disfavored with respect to disproportionation into (nor)4M + (nor)2M. This is consistent with the experimental syntheses of the (nor)4M (M = Cr to Co) derivatives with the metal in the +4 oxidation by reactions with 1-norbornyllithium with metal halides in the +2 or +3 metal oxidation states. Both the OPBE method and the BPW91 method predict high-spin states for the d2 and d3 complexes (nor)4Cr and (nor)4Mn but low-spin states for (nor)4Fe and (nor)4Co, consistent with experiment.

Tris(butadiene) Metal Complexes of the First-Row Transition Metals versus Coupling of Butadiene to Eight- and Twelve-Carbon Hydrocarbon Chains.

The role that zerovalent nickel plays in catalyzing the trimerization of butadiene to 1,5,9-cyclododecatriene conveys interest in the properties of the tris(butadiene)metal complexes (C4H6)3M. In this connection the complexes (C4H6)3M (M = Ti-Ni) of the first-row transition metals have been investigated by density functional theory. The intermediate C12H18Ni which has been isolated in the nickel-catalyzed trimerization of butadiene but is too unstable for X-ray crystallography is suggested here to have an open-chain hexahapto η3,3-C12H18 ligand rather than the octahapto such ligand suggested by some investigators. The lowest energy (C4H6)3M structures of the other first-row transition metals from vanadium to cobalt are found to have related structures with open-chain C12H18 ligands having hapticities ranging from four to eight with hexahapto structures being most common. The nickel and cobalt (C12H18)M derivatives favor low-spin singlet and doublet spin states, respectively, whereas the manganese derivative (C12H18)Mn favors the high-spin sextet state corresponding to the half-filled d5 shell of Mn(II). A (C4H6)3Cr structure with three separate tetrahapto butadiene ligands analogous to the very stable (η4-C4H6)3M (M = Mo, W) with the favored 18-electron metal configuration is found to be a very high energy structure relative to isomers containing an open-chain C12H18 ligand.

Analysis of Volatile Compounds in Pears by HS-SPME-GC×GC-TOFMS.

Aroma plays an important role in fruit quality and varies among different fruit cultivars. In this study, a sensitive and accurate method based on headspace solid-phase microextraction (HS-SPME) coupled with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) was developed to comprehensively compare aroma components of five pear cultivars. In total, 241 volatile compounds were identified and the predominant volatile compounds were esters (101 compounds), followed by alcohols (20 compounds) and aldehydes (28 compounds). The longyuanyangli has the highest relative concentration (838.12 ng/g), while the Packham has the lowest (208.45 ng/g). This study provides a practical method for pear aroma analysis using SPME and GC×GC-TOFMS.

Highly efficient enhancement of municipal sludge dewaterability using persulfate activation with nZVI/HA.

This study presents a sulfate radical-based oxidation method for improving municipal sludge dewaterability by combining persulfate and nanoscale zero-valent iron supported on humic acid (nZVI/HA-PS). Sludge dewaterability using persulfate activation with nZVI/HA was assessed for specific resistance to filterability (SRF), time to filter (TTF), settling volume percentage (SV30) and water content (Wc). The influencing factors, such as mass ratios of nZVI to HA, initial pH, PS dosage and nZVI/HA nanocomposite dosage, were investigated. Experimental results indicated that the SRF reduction efficiency of the sludge reached 86.47% using initial concentrations of 1.2 mmol/gVSS PS and 300 mg/L nZVI/HA. The soluble chemical oxygen demand (SCOD) of sludge supernatants increased from 79 mg/L to 710 mg/L under optimum conditioning, indicating that sludge flocs were effectively decomposed. Economic analysis demonstrated that the nZVI/HA-PS conditioning process is a potential method for improving sludge dewaterability.

Butadiene as a ligand in open sandwich compounds.

Theoretical methods show that the lowest energy bis(butadiene)metal structures (C4H6)2M (M = Ti to Ni) have a perpendicular relative orientation of the two butadiene ligands corresponding to a tetrahedral coordination of the central metal atom to the four C[double bond, length as m-dash]C double bonds of the butadiene ligands. Distribution of the metal d electrons in the resulting tetrahedral ligand field rationalizes the predicted spin states increasing monotonically from singlet to quartet from nickel to manganese and back from quartet to singlet from manganese to titanium.

Fabrication of three-dimensional zinc oxide nanoflowers for high-sensitivity fiber-optic ammonia gas sensors.

ZnO is identified as one of the promising coating materials in optical fiber for ammonia gas sensors. In this work, three-dimensional ZnO nanoflowers are fabricated via a facile hydrothermal method and used as sensitive coating materials for optical fiber ammonia gas sensors. Results show that the sensor with ZnO nanoflowers exhibits a high sensitivity of 5.75 pm/(µg·L-1) for ammonia concentration ranging from 0 to 5460 µg·L-1, which is more than 2.6 times higher than that of the sensor with a coating of ZnO microspheres [2.2 pm/(µg·L-1)].

The combination of novel airlift magnetic separation loop system and an efficient biosorbent for the removal of Pb(II) from aqueous solution.

An efficient biosorbent containing magnetic nanoparticles, walnut shell powder, foam, and alginate (AMWSF) was prepared and used in Pb(II) removal. The adsorption process was performed in an airlift magnetic separation loop system. Optimum adsorption conditions were tested at pH 3-7, biomass dose of 0.03-0.4 g, temperature of 15-35 °C, initial Pb(II) ion concentration of 50-400 mg·L-1, and contact time of 10-480 min. The equilibrium adsorption capacity reached up to 69.45 mg·g-1. The physicochemical properties of AMWSF were analyzed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The experimental data were in agreement with the pseudo-second-order kinetic and Langmuir isotherm models. The influences of Cu(II), Cd(II), and Zn(II) on Pb(II) adsorption showed antagonistic effect strength in the order of Cu(II) > Cd(II) > Zn(II). AMWSF was reused seven times and separated rapidly by magnetic field. The results demonstrated the potential of AMWSF in practical applications involving Pb(II).

Determination and risk assessment of sixteen polycyclic aromatic hydrocarbons in vegetables.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic environmental pollutants posing a potential risk to human health. This study was constructed to investigate the presence of 16 PAHs in six commonly consumed vegetables collected from the markets in Shandong, China by a quick, easy, cheap, effective, rugged, safe (QuEChERS)-based extraction method coupled with gas chromatography-mass spectrometry (GC-MS). Our results showed that the vegetables were polluted with PAHs at an alarming level, of which celery contained the highest total concentration of PAHs (Σ16 PAH), whereas cucumbers contained the lowest Σ16 PAH. Besides, the dietary exposure of PAHs was assessed in these vegetables based on the maximum Σ16 PAH. The results showed that the populations in Shandong were exposed to 23-213 ng/d of PAHs through these six vegetables, suggesting that vegetables are the major sources of PAHs in the diet. Hence, it is necessary to monitor the PAH levels in vegetables. Our study provides guidance for future legislative actions regarding PAH levels in vegetables in China.

The Recently Synthesized Dimagnesiabutadiene and the Analogous Dimetalla-Beryllium, -Calcium, -Strontium, and -Barium Compounds.

The 2014 synthesis of the remarkable dimagnesium compound Mg2 [C4 (CH3 )2 (Si(CH3 )3 )2 ](C3 H7 )2 (C4 H8 O)2 may point the way to a new chapter in alkaline earth organometallic chemistry. Accordingly, we have studied the known Mg compound and the analogous Be, Ca, Sr, and Ba structures. Although most of our theoretical predictions come from density functional methods, the latter have been benchmarked using coupled cluster theory including single, double, and perturbative triplet excitations, CCSD(T) using cc-pVTZ basis sets. Among our most important predictions are the energies for dissociation to the butadiene plus the RM-MR [R=(C3 H7 )2 (C4 H8 O)2 ; M=Be, Mg, Ca, Si, and Ba] entities. The most reliable predictions for the dissociation energies are 99-104 (Be), 85-93 (Mg), 90-99 (Ca), 83-92 (Sr), and 83-94 (Ba) kcal mol-1 . Thus, there is reason to anticipate that the four unknown compounds should be achievable synthetically. The predicted metal-metal distances (not single bonds) are 2.89 Š(Mg⋅⋅⋅Mg), 3.46 Š(Ca⋅⋅⋅Ca), 3.75 Š(Sr⋅⋅⋅Sr), and 4.04 Š(Ba⋅⋅⋅Ba). The separated RM-MR compounds have longer M-M distances but genuine metal-metal single bonds. This perhaps counter intuitive result is due to the presence of the bridging carbons in the alkaline earth butadiene compounds. All five compounds incorporate metal-carbon ionic interactions.

Residues and dissipation kinetics of carbendazim and diethofencarb in tomato (Lycopersicon esculentum Mill.) and intake risk assessment.

Dissipation behaviors and residues of carbendazim and diethofencarb in combination in tomato were investigated. The half-lives were 2.1-3.4 days for carbendazim, and 1.8-3.2 days for diethofencarb at a dose of 1.5 times of the recommended dosage. The residues of carbendazim and diethofencarb were below the maximum residue limits (MRLs) in China one day after application of the combination. The ultimate residues were significantly lower than the maximum permissible intake (MPI) in China at the recommended high dose for both child and adult. The values of the maximum dietary exposure for carbendazim and diethofencarb were 0.26 and 0.27 mg per person per day, respectively. The theoretical maximum daily intake (TMDI) values for carbendazim and diethofencarb were 1.5 and 0.5 mg/day, respectively. The dietary exposure was lower than the MPI, which indicates the harvested tomato samples under the experimental conditions (open field) are safe for human consumption at the recommended high dosage of the wettable powder.