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1.
Nat Chem ; 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32541950

RESUMO

Single-atom catalysts not only maximize metal atom efficiency, they also display properties that are considerably different to their more conventional nanoparticle equivalents, making them a promising family of materials to investigate. Herein we developed a general host-guest strategy to fabricate various metal single-atom catalysts on nitrogen-doped carbon (M1/CN, M = Pt, Ir, Pd, Ru, Mo, Ga, Cu, Ni, Mn). The iridium variant Ir1/CN electrocatalyses the formic acid oxidation reaction with a mass activity of 12.9 [Formula: see text] whereas an Ir/C nanoparticle catalyst is almost inert (~4.8 × 10-3 [Formula: see text]). The activity of Ir1/CN is also 16 and 19 times greater than those of Pd/C and Pt/C, respectively. Furthermore, Ir1/CN displays high tolerance to CO poisoning. First-principle density functional theory reveals that the properties of Ir1/CN stem from the spatial isolation of iridium sites and from the modified electronic structure of iridium with respect to a conventional nanoparticle catalyst.

2.
Chem Rev ; 2020 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-32242408

RESUMO

Manipulating metal atoms in a controllable way for the synthesis of materials with the desired structure and properties is the holy grail of chemical synthesis. The recent emergence of single atomic site catalysts (SASC) demonstrates that we are moving toward this goal. Owing to the maximum efficiency of atom-utilization and unique structures and properties, SASC have attracted extensive research attention and interest. The prerequisite for the scientific research and practical applications of SASC is to fabricate highly reactive and stable metal single atoms on appropriate supports. In this review, various synthetic strategies for the synthesis of SASC are summarized with concrete examples highlighting the key issues of the synthesis methods to stabilize single metal atoms on supports and to suppress their migration and agglomeration. Next, we discuss how synthesis conditions affect the structure and catalytic properties of SASC before ending this review by highlighting the prospects and challenges for the synthesis as well as further scientific researches and practical applications of SASC.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32189435

RESUMO

The solar-driven photocatalytic reduction of CO2 (CO2 RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO2 emissions. However, low catalytic efficiency and poor selectivity, especially in a pure-water system, hinder the development of photocatalytic CO2 RR owing to the lack of effective catalysts. Herein, we report a novel atom-confinement and coordination (ACC) strategy to achieve the synthesis of rare-earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er1 /CN-NT) with a tunable dispersion density of single atoms. Er1 /CN-NT is a highly efficient and robust photocatalyst that exhibits outstanding CO2 RR performance in a pure-water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO2 RR.

4.
Angew Chem Int Ed Engl ; 59(3): 1295-1301, 2020 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-31654544

RESUMO

It is highly desirable but challenging to optimize the structure of photocatalysts at the atomic scale to facilitate the separation of electron-hole pairs for enhanced performance. Now, a highly efficient photocatalyst is formed by assembling single Pt atoms on a defective TiO2 support (Pt1 /def-TiO2 ). Apart from being proton reduction sites, single Pt atoms promote the neighboring TiO2 units to generate surface oxygen vacancies and form a Pt-O-Ti3+ atomic interface. Experimental results and density functional theory calculations demonstrate that the Pt-O-Ti3+ atomic interface effectively facilitates photogenerated electrons to transfer from Ti3+ defective sites to single Pt atoms, thereby enhancing the separation of electron-hole pairs. This unique structure makes Pt1 /def-TiO2 exhibit a record-level photocatalytic hydrogen production performance with an unexpectedly high turnover frequency of 51423 h-1 , exceeding the Pt nanoparticle supported TiO2 catalyst by a factor of 591.

5.
Chem Rev ; 120(2): 623-682, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31868347

RESUMO

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

6.
Sci Rep ; 9(1): 3374, 2019 03 04.
Artigo em Inglês | MEDLINE | ID: mdl-30833648

RESUMO

Synchronous liver metastasis (SLM) remains a major challenge for rectal cancer. Early detection of SLM is a key factor to improve the survival rate of rectal cancer. In this radiomics study, we predicted the SLM based on the radiomics of primary rectal cancer. A total of 328 radiomics features were extracted from the T2WI images of 194 patients. The least absolute shrinkage and selection operator (LASSO) regression was used to reduce the feature dimension and to construct the radiomics signature. after LASSO, principal component analysis (PCA) was used to sort the features of the surplus characteristics, and selected the features of the total contribution of 85%. Then the prediction model was built by linear regression, and the decision curve analysis was used to judge the net benefit of LASSO and PCA. In addition, we used two independent cohorts for training (n = 135) and validation (n = 159). We found that the model based on LASSO dimensionality construction had the maximum net benefit (in the training set (AUC [95% confidence interval], 0.857 [0.787-0.912]) and in the validation set (0.834 [0.714-0.918]). The radiomics nomogram combined with clinical risk factors and LASSO features showed a good predictive performance in the training set (0.921 [0.862-0.961]) and validation set (0.912 [0.809-0.97]). Our study indicated that radiomics based on primary rectal cancer could provide a non-invasive way to predict the risk of SLM in clinical practice.

7.
Angew Chem Int Ed Engl ; 58(13): 4271-4275, 2019 Mar 22.
Artigo em Inglês | MEDLINE | ID: mdl-30730605

RESUMO

Incorporating atomically dispersed metal species into functionalized metal-organic frameworks (MOFs) can integrate their respective merits for catalysis. A cage-controlled encapsulation and reduction strategy is used to fabricate single Ru atoms and triatomic Ru3 clusters anchored on ZIF-8 (Ru1 @ZIF-8, Ru3 @ZIF-8). The highly efficient and selective catalysis for semi-hydrogenation of alkyne is observed. The excellent activity derives from high atom-efficiency of atomically dispersed Ru active sites and hydrogen enrichment by the ZIF-8 shell. Meanwhile, ZIF-8 shell serves as a novel molecular sieve for olefins to achieve absolute regioselectivity of catalyzing terminal alkynes but not internal alkynes. Moreover, the size-dependent performance between Ru3 @ZIF-8 and Ru1 @ZIF-8 is detected in experiment and understood by quantum-chemical calculations, demonstrating a new and promising approach to optimize catalysts by controlling the number of atoms.

8.
Nat Commun ; 9(1): 5422, 2018 12 21.
Artigo em Inglês | MEDLINE | ID: mdl-30575726

RESUMO

Efficient, durable and inexpensive electrocatalysts that accelerate sluggish oxygen reduction reaction kinetics and achieve high-performance are highly desirable. Here we develop a strategy to fabricate a catalyst comprised of single iron atomic sites supported on a nitrogen, phosphorus and sulfur co-doped hollow carbon polyhedron from a metal-organic framework@polymer composite. The polymer-based coating facilitates the construction of a hollow structure via the Kirkendall effect and electronic modulation of an active metal center by long-range interaction with sulfur and phosphorus. Benefiting from structure functionalities and electronic control of a single-atom iron active center, the catalyst shows a remarkable performance with enhanced kinetics and activity for oxygen reduction in both alkaline and acid media. Moreover, the catalyst shows promise for substitution of expensive platinum to drive the cathodic oxygen reduction reaction in zinc-air batteries and hydrogen-air fuel cells.

9.
Front Neurol ; 9: 618, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30093881

RESUMO

Background: Alzheimer's disease (AD) is a progressive neurodegenerative disease that causes the decline of some cognitive impairments. The present study aimed to identify the corpus callosum (CC) radiomic features related to the diagnosis of AD and build and evaluate a classification model. Methods: Radiomics analysis was applied to the three-dimensional T1-weighted magnetization-prepared rapid gradient echo (MPRAGE) images of 78 patients with AD and 44 healthy controls (HC). The CC, in each subject, was segmented manually and 385 features were obtained after calculation. Then, the feature selection were carried out. The logistic regression model was constructed and evaluated according to identified features. Thus, the model can be used for distinguishing the AD from HC subjects. Results: Eleven features were selected from the three-dimensional T1-weighted MPRAGE images using the LASSO model, following which, the logistic regression model was constructed. The area under the receiver operating characteristic curve values (AUC), sensitivity, specificity, accuracy, precision, and positive and negative predictive values were 0.720, 0.792, 0.500, 0.684, 0.731, 0.731, and 0.583, respectively. Conclusion: The results demonstrated the potential of CC texture features as a biomarker for the diagnosis of AD. This is the first study showing that the radiomics model based on machine learning was a valuable method for the diagnosis of AD.

10.
J Am Chem Soc ; 140(24): 7407-7410, 2018 06 20.
Artigo em Inglês | MEDLINE | ID: mdl-29863867

RESUMO

The hydrosilylation reaction is one of the largest-scale application of homogeneous catalysis and is widely used to enable the commercial manufacture of silicon products. However, considerable issues including disposable platinum consumption, undesired side reactions and unacceptable catalyst residues still remain. Here, we synthesize a heterogeneous partially charged single-atom platinum supported on anatase TiO2 (Pt1δ+/TiO2) catalyst via an electrostatic-induction ion exchange and two-dimensional confinement strategy, which can catalyze hydrosilylation reaction with almost complete conversion and produce exclusive adduct. Density functional theory calculations reveal that unexpected property of Pt1δ+/TiO2 originates from atomic dispersion of active species and unique partially positive charge Ptδ+ electronic structure that conventional nanocatalysts do not possess. The fabrication of single-atom Pt1δ+/TiO2 catalyst accomplishes a reasonable use of Pt through recycling and maximum atom-utilized efficiency, indicating the potential to achieve a green hydrosilylation industry.

11.
Chem Commun (Camb) ; 54(34): 4274-4277, 2018 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-29630077

RESUMO

We successfully prepared Fe and Co isolated single atoms on metal-organic framework derived nitrogen-doped carbon (FeCo-ISAs/CN) by an adsorption-calcination strategy. The obtained FeCo-ISAs/CN exhibited top-level catalytic reactivity for the alkaline oxygen reduction reaction (ORR) with a half-wave potential of 0.920 V, which was 70 mV more positive than that of commercial Pt/C. Moreover, the catalyst was durable and showed negligible activity decay in the alkaline ORR during 5000 voltage cycles.

12.
Chem Commun (Camb) ; 54(38): 4882, 2018 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-29697117

RESUMO

Correction for 'Isolated Fe and Co dual active sites on nitrogen-doped carbon for a highly efficient oxygen reduction reaction' by Diyang Zhang et al., Chem. Commun., 2018, DOI: 10.1039/c8cc00988k.

13.
J Am Chem Soc ; 139(29): 9795-9798, 2017 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-28696113

RESUMO

Here we report a novel approach to synthesize atomically dispersed uniform clusters via a cage-separated precursor preselection and pyrolysis strategy. To illustrate this strategy, well-defined Ru3(CO)12 was separated as a precursor by suitable molecular-scale cages of zeolitic imidazolate frameworks (ZIFs). After thermal treatment under confinement in the cages, uniform Ru3 clusters stabilized by nitrogen species (Ru3/CN) were obtained. Importantly, we found that Ru3/CN exhibits excellent catalytic activity (100% conversion), high chemoselectivity (100% for 2-aminobenzaldehyde), and significantly high turnover frequency (TOF) for oxidation of 2-aminobenzyl alcohol. The TOF of Ru3/CN (4320 h-1) is about 23 times higher than that of small-sized (ca. 2.5 nm) Ru particles (TOF = 184 h-1). This striking difference is attributed to a disparity in the interaction between Ru species and adsorbed reactants.

14.
Angew Chem Int Ed Engl ; 56(24): 6937-6941, 2017 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-28402604

RESUMO

The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential (E1/2 ) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density (Jk ) of 37.83 mV cm-2 at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species.

15.
Chem Commun (Camb) ; 52(35): 5985-8, 2016 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-27063415

RESUMO

Herein, we exploit two typical crystal growth modes, namely, "stacking" and "carving" routes, to synthesize Pt-based bimetallic nanomaterials with defect-rich surface structures, which exhibit enhanced electrocatalytic properties toward both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) compared with commercial Pt/C.

16.
Adv Mater ; 28(13): 2540-6, 2016 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-26836038

RESUMO

Kinetic control of surface defects is achieved, and cubic, concave cubic, and defect-rich cubic intermetallic Pt3 Sn nanocrystals are prepared for the electro-oxidation of formic acid. The generality of this kinetic approach is demonstrated by the fabrication of Pt-Mn nanocrystals with different surface defects. The defect-rich nanocrystals exhibit high catalytic activity and stability concurrently, indicating their potential application in fuel cells.

17.
Zhonghua Yi Xue Za Zhi ; 95(23): 1837-41, 2015 Jun 16.
Artigo em Chinês | MEDLINE | ID: mdl-26712402

RESUMO

OBJECTIVE: To evaluate the diagnostic value of quantitative Dynamic Contrast Enhanced MRI analysis on pituitary adenoma. METHODS: With the standard of pathology and follow-up results, 67 cases of microadenoma, 20 cases of macroadenoma and 15 cases of normal pituitary were selected and taken routine scanning, meanwhile the dynamic contrast-enhanced scanning was performed, then the characteristics of lesions on conventional images were analyzed, and the mean permeability parameters were measured, including transfer rate (K(trans)), back flux rate (Kep), fractional EES volume (Ve) using Tofts model, which were compared with each other among those three groups and between prolactinoma and somatotroph adenoma; finally, the areas under the ROC curve of permeability parameters were compared. RESULTS: 61 cases of 67 cases of pituitary adenoma could be diagnosed by conventional methods, therefore the diagnostic accuracy was 91.1%. The K(trans), Kep and Ve values were(0.90 ± 0.23)/min, (1.14 ± 0.58)/min, 1.02 ± 0.51 respectively in normal pituitary, and (0.46 ± 0.23)/min, (0.80 ± 0.27)/min, 0.73 ± 0.32 in microadenoma and (0.41 ± 0.25)/min, (0.71 ± 0.48)/min, 0.66 ± 0.40 in macroadenoma. The K(trans) and Kep in normal adenoma were respectively higher than in microadenoma and macroadenoma, and the difference had statistical significance (P < 0.05), while the Ve value among these three groups had no statistical significance; the K(trans) in prolactinoma was higher than in somatotroph adenoma, and the difference had statistical significance(P < 0.05), while the difference of Kep and Ve between prolactinoma and somatotroph adenoma had no statistical significance. The area under the ROC curve in finding the microadenoma, K(trans), Kep were 0.915 and 0.738, and the sensitivity of K(trans) and Kep were 92.3% and 53.8%, and the specificity of K(trans) and Kep were 85% and 100%. CONCLUSION: Dynamic contrast-enhanced quantitative parameters, K(trans) and Kep are help to the diagnosis of pituitary adenoma, and K(trans) exhibits a relatively high diagnostic efficacy, and the value of diagnosis in K(trans) is higher than which in MRI conventional method; while K(trans) can differentiate certain secreting type of pituitary microadenoma.


Assuntos
Adenoma , Neoplasias Hipofisárias , Meios de Contraste , Humanos , Imagem por Ressonância Magnética , Prolactinoma , Curva ROC
18.
Chem Commun (Camb) ; 51(84): 15406-9, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26344362

RESUMO

In this work, we present a facile etching-reduction-selective epitaxial growth synergistic strategy to synthesize trimetallic nanocrystals. The methodology demonstrated here provides some general guidelines for the design and fabrication of multimetallic heteronanostructures, which would open up new opportunities for practical fuel cell applications or other chemical reactions.


Assuntos
Cobre/química , Técnicas Eletroquímicas , Nanopartículas Metálicas/química , Paládio/química , Platina/química , Catálise , Tamanho da Partícula , Propriedades de Superfície
19.
Molecules ; 15(11): 8469-77, 2010 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-21088661

RESUMO

Four phenolics, salviaplebeiaside (1), γ-tocopherol (2), chrysosplenol-D (4), and isovitexin (5), along with α-tocoquinone (3) and ß-sitosterol (6) were isolated from the aerial parts of Vitex negundo var. cannabifolia. The isolation was performed using bio-assay tracking experiments. The structures of compounds 1-5 were established by spectroscopic means. The antibacterial activities of the compounds were assessed against Escherichia coli, Bacillus subtilis, Micrococcus tetragenus and Pseudomonas fluorescens. Chrysosplenol-D (4) exhibited activities against all the four spoilage microorganisms.


Assuntos
Antibacterianos/química , Antibacterianos/farmacologia , Fenóis/química , Fenóis/farmacologia , Componentes Aéreos da Planta/química , Extratos Vegetais/química , Extratos Vegetais/farmacologia , Vitex/química , Apigenina/química , Apigenina/farmacologia , Bacillus subtilis/efeitos dos fármacos , Escherichia coli/efeitos dos fármacos , Flavonoides/química , Flavonoides/farmacologia , Micrococcus/efeitos dos fármacos , Pseudomonas fluorescens/efeitos dos fármacos , Sitosteroides/química , Sitosteroides/farmacologia , Vitamina E/análogos & derivados , Vitamina E/química , Vitamina E/farmacologia , gama-Tocoferol/química , gama-Tocoferol/farmacologia
20.
AJR Am J Roentgenol ; 191(2): 582-8, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18647936

RESUMO

OBJECTIVE: The purpose of our study was to describe the characteristic MRI appearance of cerebral infection with Schistosoma japonicum. CONCLUSION: Cerebral infection with S. japonicum can cause a characteristic MRI pattern of a large mass comprising multiple intensely enhancing nodules, sometimes with areas of linear enhancement. The typical appearance may be useful for diagnosis in endemic regions and may potentially be useful in cases imported into countries in which the disease is not endemic.


Assuntos
Imagem por Ressonância Magnética/métodos , Neuroesquistossomose/diagnóstico , Adolescente , Adulto , Idoso , Animais , Criança , Meios de Contraste , Diagnóstico Diferencial , Feminino , Gadolínio DTPA , Humanos , Masculino , Pessoa de Meia-Idade , Neuroesquistossomose/parasitologia , Schistosoma japonicum
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