Hollow yolk–shell nanoreactors are of great interest in heterogeneous catalysis owing to their improved mass transfer ability and stability. Here, we report a facile and straight route to synthesize ...a highly efficient and recyclable yolk–shell Co@C–N nanoreactor with controllable properties by the direct thermolysis of a hollow Zn/Co-ZIF precursor. Based on systematical optimization of the pyrolysis temperature and the shell-thickness of Zn/Co-ZIFs, we could completely anchor and stabilize uniform Co nanoparticles (NPs) in the hollow yolk, accommodated by the Co-ZIF derived N-doped carbon nanosheets. This nanosheet-assembled yolk was further confined by a permeable and robust N-doped carbon (C–N) shell to protect the Co NPs against leaching and also enabled the reaction to take place in the hollow void. Consequently, the optimal yolk–shell Co@C–N nanoreactor showed a significantly enhanced catalytic activity for the aqueous oxidation of alcohols, yielding >99% conversion under atmospheric air and base-free conditions, which was much higher than that of the solid counterparts derived from pure ZIF-67 and solid core–shell ZIF-67@ZIF-8 precursors (with 14% and 59% conversion under the same reaction condition, respectively). The enhanced catalytic activity should be attributed to the yolk–shell structure that could facilitate the transport of reactant/product and the strong interaction between the Co NPs and N-doped carbon nanosheet to afford positive synergistic effects. Moreover, this catalyst also showed good recyclability, magnetically reusability, and general applicability for a broad substrate scope, further highlighting the structure superiority of our yolk–shell nanoreactor. This strategy might open an avenue to synthesize various hollow yolk–shell nanoreactors with controllable structures and enhanced catalytic performances.
Emerging clean energy technologies such as regenerative fuel cells and rechargeable metal–air batteries have attracted increasing global interest because of their high efficiency and environmental ...benignity, but the lack of highly active bifunctional electrocatalysts at low cost for both oxygen reduction and evolution reactions (ORR and OER) greatly hinders their commercial applications. Here, we report the multilevel architecture optimization of Co-based nanoparticles (NPs) embedded in hollow N-doped carbon polyhedra for boosting the ORR and OER, which are fabricated by a two-step pyrolysis–oxidation strategy with a Co-based MOF (ZIF-67) as precursor. The key for this strategy lies in the precise and effective control of the oxidation processes of Co NPs, which enables the synthesis of a series of Co–Co3O4-based nanoarchitectures that are embedded in hollow nitrogen-doped carbon polyhedra (HNCP), including core–shell Co/Co3O4, yolk@shell Co@Co3O4, and hollow Co3O4 NPs. Benefiting from its abundant oxygen vacancies and tetrahedral Co2+ and the potential synergies of CoO x species and nitrogen-doped carbon as well as the efficient mass transfer of hollow and yolk–shell structures, the optimal yolk@shell Co3O4/HNCP-40 exhibits high activity for the OER with a low overpotential of 333 mV at 10 mA cm–2 and a small Tafel slope of 69 mV dec–1, which is better than those of commercial IrO2 (its overpotential and Tafel slope are 409 mV at 10 mA cm–2 and 104 mV dec–1, respectively). Meanwhile, the catalyst also exhibits comparable ORR catalytic activity with a half-wave potential of 0.834 V but better stability and methanol tolerance relative to commercial Pt/C (20 wt %), making it a potential bifunctional electrocatalyst for both the OER and ORR. This MOF-templated strategy for multilevel nanostructures provides insights into the development of highly efficient and low-cost bifunctional electrocatalysts for the OER/ORR.
We constructed highly oriented and ordered macropores within metal-organic framework (MOF) single crystals, opening up the area of three-dimensional-ordered macro-microporous materials (that is, ...materials containing both macro- and micropores) in single-crystalline form. Our methodology relies on the strong shaping effects of a polystyrene nanosphere monolith template and a double-solvent-induced heterogeneous nucleation approach. This process synergistically enabled the in situ growth of MOFs within ordered voids, rendering a single crystal with oriented and ordered macro-microporous structure. The improved mass diffusion properties of such hierarchical frameworks, together with their robust single-crystalline nature, endow them with superior catalytic activity and recyclability for bulky-molecule reactions, as compared with conventional, polycrystalline hollow, and disordered macroporous ZIF-8.
In the DNA microarray research field, the increasing sample size and feature dimension of the gene expression data prompt the development of an efficient and robust feature selection algorithm for ...gene expression data classification. In this study, we propose a hybrid feature selection algorithm that combines the mutual information maximization (MIM) and the adaptive genetic algorithm (AGA). Experimental results show that the proposing MIMAGA-Selection method significantly reduces the dimension of gene expression data and removes the redundancies for classification. The reduced gene expression dataset provides highest classification accuracy compared to conventional feature selection algorithms. We also apply four different classifiers to the reduced dataset to demonstrate the robustness of the proposed MIMAGA-Selection algorithm.
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•Hollow N/Co codoped carbon spheres are successfully prepared.•PS@bimetal-ZIFs are synthesized and used as the sacrifice templates.•The structure properties of Co-HNCS can be well ...regulated.•The optimal catalyst is a promising candidate for oxygen reduction reaction.
To explore efficient non-noble metal-based electrocatalysts for oxygen reduction reaction (ORR), herein we developed a facile bottom-up approach for the fabrication of a hollow porous carbon sphere codoped with ultra-small Co nanoparticles and uniform nitrogen distribution (Co-HNCS) via one-step pyrolysis of a core-shell type precursor composing of polystyrene (PS) core and bimetallic ZIF (zeolite imidazolate framework) shell. The bimetallic Co-Zn-ZIFs (BMZIFs) was selected as the sacrifice template due to not only its high nitrogen content and regular porosity but also the superiority that Zn species in BMZIFs can both spatially separate Co species to suppress the aggregation of ultra-small Co NPs and be evaporated to afford extra pores during high-temperature pyrolysis. As expected, by adjusting the starting molar ratio of Zn to Co, we were able to prepare Co-HNCS-x (x represent the molar ratio of Co to total starting metal feeding) that exhibited unique hollow structure with large surface areas, enhanced mass transport, high porosities, tunable particle sizes and graphitization degrees, abundant highly active CoNx sites, and thus significantly improved ORR performance. Particularly, the optimal Co-HNCS-0.2 exhibited the remarkable ORR activity (the onset and half-wave potentials were 0.94 and 0.82Vvs. RHE, respectively) via an efficient four-electron-dominant ORR process in alkaline medium, which outperformed that of commercial Pt/C (20wt%, the onset and half-wave potentials were 0.93 and 0.80Vvs. RHE, respectively) and most of previously reported Co-based catalysts. Moreover, it also displayed much superior stability and tolerance to methanol as compared to Pt/C, further highlighting the merit of this facile synthesis approach. Our findings might inspire new thoughts on the development of precious-metal-free, highly-efficient and cost-effective ORR electrocatalysts derived from MOF.
Zeolite imidazolate frameworks (ZIFs), as an important part of metal–organic frameworks (MOFs), have received great attention in many application fields, such as gas adsorption, separation, and ...catalysis. It was found that the performances of these applications largely depend on ZIFs’ properties, such as particle size distribution, pore size, and specific surface area, which are essentially controlled by different synthetic methods. Among all the disclosed ZIF-type structures, researches on ZIF-8 are growing since it has high chemical and thermal stability and a flexible structure. Therefore, ZIF-8 was chosen as an example in this review to illustrate how synthetic factors affect the final properties of ZIF materials. We summarize the evolution process of ZIF-8 which is divided into three stages: supersaturation, nucleation, and particles. Emphasis is placed on the discussion of the influences of various factors on the formation of ZIF-8. The factors are classified into several types such as various salt sources, concentration of reactants, solvents, temperature, and so on. The challenges, prospects, and outlook of ZIF-8 in the future are presented last. This perspective aims to provide necessary information for industrial synthesis of MOF and other porous materials in the future.
MicroRNAs (miRNAs) are small, non-coding RNAs that are critical regulators of various diseases. MicroRNA-20a (miR-20a) has previously significantly altered in a range of cancers. In this study, we ...detected the relationship between miR-20a and the development of cervical cancer by qRT-PCR, we found that the expression level of miR-20a was significantly higher in cervical cancer patients than in normal controls, the aberrant expression of miR-20a was correlated with lymph node metastasis, histological grade and tumor diameter. Then we successfully established the stable anti-miR-20a cervical cancer cell lines by lentivirus. Inhibited miR-20a prevented tumor progression by modulating cell cycle, apoptosis, and metastasis in vitro and in vivo. TIMP2 and ATG7 were proved to be direct targets of miR-20a, using luciferase assay and western blot. These results indicate that miR-20a suppresses the proliferation, migration and invasion of cervical cancer cell through targeting ATG7 and TIMP2. Our results support the involvement of miR-20a in cervical tumorigenesis, especially lymph node metastasis. We propose that miRNAs might be used as therapeutic agent for cervical cancer.
Irrigation water management and real-time monitoring of crop water stress status can enhance agricultural water use efficiency, crop yield, and crop quality. The aim of this study was to simplify the ...calculation of the crop water stress index (CWSI) and improve its diagnostic accuracy. Simplified CWSI (CWSIsi) was used to diagnose water stress for cotton that has received four different irrigation treatments (no stress, mild stress, moderate stress, and severe stress) at the flowering and boll stage. High resolution thermal infrared and multispectral images were taken using an Unmanned Aerial Vehicle remote sensing platform at midday (local time 13:00), and stomatal conductance (gs), transpiration rate (tr), and cotton root zone soil volumetric water content (θ) were concurrently measured. The soil background pixels of thermal images were eliminated using the Canny edge detection to obtain a unimodal histogram of pure canopy temperatures. Then the wet reference temperature (Twet), dry reference temperature (Tdry), and mean canopy temperature (Tl) were obtained from the canopy temperature histogram to calculate CWSIsi. The other two methods of CWSI evaluation were empirical CWSI (CWSIe), in which the temperature parameters were determined by measuring natural reference cotton leaves, and statistical CWSI (CWSIs), in which Twet was the mean of the lowest 5% of canopy temperatures and Tdry was the air temperature (Tair) + 5 °C. Compared with CWSIe, CWSIs and spectral indices (NDVI, TCARI, OSAVI, TCARI/OSAVI), CWSIsi has higher correlation with gs (R2 = 0.660) and tr (R2 = 0.592). The correlation coefficient (R) for θ (0–45 cm) and CWSIsi is also high (0.812). The plotted high-resolution map of CWSIsi shows the different distribution of cotton water stress in different irrigation treatments. These findings demonstrate that CWSIsi, which only requires parameters from a canopy temperature histogram, may potentially be applied to precision irrigation management.
Hemin-functionalized WS2 nanosheets (hemin/WS2-NSs) were first obtained by hemin assembled on the surface of few-layered WS2 nanosheets (WS2-NSs) via van der Waals interactions. Significantly, this ...new material possessed the advantages of both hemin and WS2 nanosheets and exhibited some unique properties. Firstly, hemin/WS2-NSs had intrinsic peroxidase-like activity, which could effectively catalyze oxidation of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce a typical blue colored reaction. Secondly, the activity of hemin/WS2-NSs was much higher than the activity of hemin or WS2-NSs alone. The catalytic activity followed the typical Michaelis-Menten kinetics and was dependent on the temperature, pH, H2O2 concentration, as well as reaction time. Based on this finding, a new highly sensitive and selective colorimetric method for H2O2 and glucose detection was developed. This method was simple and inexpensive for glucose detection using glucose oxidase (GOx) and hemin/WS2-NSs with a linear range of 0.5 × 10(-5) to 2.0 × 10(-4) mol L(-1) with a detection limit of 1.5 × 10(-6) mol L(-1). The good catalytic activity and low-cost make the hemin/WS2-NSs a useful biocatalyst for a wide range of potential applications in environmental chemistry, biotechnology and clinical diagnostics.
Tai Chi (TC) is a traditional Chinese martial art with demonstrated beneficial effects on physical and mental health. In this study, the authors performed a systematic review to assess the efficiency ...of TC in different populations' cognitive function improvement.
The present systematic review utilized the Chinese National Knowledge Infrastructure (1915-), Wanfang (1998-), VIP (1989-), Chinese Biomedicine databases (1978-), PubMed (1950-), Web of Science (1900-), Cochrane Library (1948-), Embase (1974-), EBSCOhost (1922-), and OVID (1996-) databases to search and identify relevant articles published in English and Chinese from the beginning of coverage through October 17, 2020. Randomized controlled trials (RCTs) published from the beginning of coverage through October 17, 2020 in English and Chinese were retrieved from many indexing databases. Selected studies were graded according to the Cochrane Handbook for Systematic Reviews of Intervention 5.1.0. The outcome measures of cognitive function due to traditional TC intervention were obtained. Meta-analysis was conducted by using RevMan 5.4 software. We follow the PRISMA 2020 guidelines.
Thirty-three RCTs, with a total of 1808 participants, were included. The study showed that TC could progress global cognition when assessed in middle-aged as well as elderly patients suffering from cognitive and executive function impairment. The findings are as follows: Montreal Cognitive Assessment Scale: mean difference (MD) = 3.23, 95% CI = 1.88-4.58,
< 0.00001, Mini-Mental State Exam: MD = 3.69, 95% CI = 0.31-7.08,
= 0.03, Trail Making Test-Part B: MD = -13.69, 95% CI = -21.64 to -5.74,
= 0.0007. The memory function of older adults assessed by the Wechsler Memory Scale was as follows: MD = 23.32, 95% CI = 17.93-28.71,
< 0.00001. The executive function of college students evaluated by E-prime software through the Flanker test was as follows: MD = -16.32, 95% CI = -22.71 to -9.94,
< 0.00001.
The TC might have a positive effect on the improvement of cognitive function in middle-aged and elderly people with cognitive impairment as well as older adults and college students.
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