Graphene oxide (GO), the functionalized graphene with oxygen-containing chemical groups, has recently attracted resurgent interests because of its superior properties such as large surface area, ...mechanical stability, tunable electrical and optical properties. Moreover, the surface functional groups of hydroxyl, epoxy and carboxyl make GO an excellent candidate in coordinating with other materials or molecules. Owing to the expanded structural diversity and improved overall properties, GO and its composites hold great promise for versatile applications of energy storage/conversion and environment protection, including hydrogen storage materials, photocatalyst for water splitting, removal of air pollutants and water purification, as well as electrode materials for various lithium batteries and supercapacitors. In this review, we present an overview on the current successes, as well as the challenges, of the GO-based materials for energy and environmental applications.
A schematic showing the GO/RGO-based hybrid materials for energy and environmental applications along with the SCI-indexed journal publications until now (January, 2015), searched from ISI by the keyword of graphene oxide combined with another one listed in the outer circle (left panel) or the X axis (right panel). Display omitted
•The progresses of GO application in hydrogen storage and photocatalytic water splitting have been elaborately summarized.•The progresses of GO application in lithium batteries and supercapacitors have been systematically discussed.•We summarized the versatile application of GO in air and water purification.
Using ab initio methods, we have investigated the structures and stabilities of Si(N) clusters (N ≤ 24) on Ag(111) surface as the initial stage of silicene growth. Unlike the dome-shaped graphene ...clusters, Si clusters prefer nearly flat structures with low buckling, more stable than directly deposition of the 3D freestanding Si clusters on Ag surface. The p-d hybridization between Ag and Si is revealed as well as sp(2) characteristics in Si(N)@Ag(111). Three types of silicene superstructures on Ag(111) surface have been considered and the simulated STM images are compared with experimental observations. Molecular dynamic simulations show high thermal stability of silicene on Ag(111) surfaces, contrast to that on Rh(111). The present theoretical results constitute a comprehensive picture about the interaction mechanism of silicene on Ag(111) surface and explain the superiority of Ag substrate for silicene growth, which would be helpful for improving the experimentally epitaxial growth of silicene.
Composites of transition metal and carbon-based materials are promising bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and are widely used in ...rechargeable metal–air batteries. However, the mechanism of their enhanced bicatalytic activities remains elusive. Herein, we construct N-doped graphene supported by Co(111) and Fe(110) substrates as bifunctional catalysts for ORR and OER in alkaline media. First-principles calculations show that these heterostructures possess a large number of active sites for ORR and OER with overpotentials comparable to those of noble metal benchmark catalysts. The catalytic activity is modulated by the coupling strength between graphene and the metal substrates, as well as the charge distribution in the graphitic sheet, which is delicately mediated by N dopants. These theoretical results uncover the key parameters that govern the bicatalytic properties of hybrid materials and help prescribe the principles for designing multifunctional electrocatalysts of high performance.
Since the graphene boom, great efforts have been devoted to two-dimensional (2D) monolayer materials with exciting possibilities for applications. Most known 2D materials are inorganic. Using the ...covalent triazine framework (CTF) as a representative, we explored 2D organic semiconductors using first-principles calculations. From a systematic study of the electronic band structures, work functions, CBM/VBM positions, and optical absorption spectra, we identified the CTF as a new class of 2D visible-light-driven organocatalyst for water splitting. Controllable construction of such CTFs from suitable organic subunits paves the way to correlate band alignment and chemical composites. In addition, multilayer CTFs have enhanced visible-light absorption compared to monolayer CTFs due to interlayer coupling. Our theoretical prediction not only has fulfilled the search for organic counterparts of inorganic photocatalysts for water splitting, but also would motivate scientists to further search for novel 2D organic materials with other technological applications.
We identify 2D covalent triazine framework (CTF) as a new family of visible-light-driven photocatalyst for water splitting using first-principles simulation, which fulfils the search for organic counterparts of inorganic photocatalysts.
Plasmodium falciparum cases are rising in China due to the imported malaria cases from African countries. The main goal of this study is to examine the impact of imported malaria cases in African ...countries on the rise of P. falciparum cases in China before and during the COVID-19 pandemic.
A generalized regression model was used to investigate the association of time trends between imported malaria cases from 45 African countries and P. falciparum cases in 31 provinces of China from 2012 to 2018 before the COVID-19 pandemic and during the COVID-19 pandemic from October 2020 to May 2021. Based on the analysis, we proposed a statistical and deep learning hybrid approach to model the resurgence of malaria in China using monthly data of P. falciparum from 2004 to 2016. This study builds a hybrid model known as the ARIMA-GRU approach for modeling the P. falciparum cases in all provinces of China and the number of malaria deaths in China before and during the COVID-19 pandemic.
The analysis showed an emerging link between the rise of imported malaria cases from Africa and P. falciparum cases in many provinces of China. Many imported malaria cases from Africa were P. falciparum cases. The proposed deep learning model achieved a high prediction accuracy score on the testing dataset of 96%.
The study provided an analysis of the reduction of P. falciparum cases and deaths caused by imported P. falciparum cases during the COVID-19 pandemic due to the control measures regarding the limitation of international travel in China. The Chinese government has to prepare the imported malaria control measures after the normalization of international travel, to prevent the resurgence of malaria disease in China.
Atomic investigation of point defects is the basis for exploring the mechanisms underlying the macro performance of materials under irradiation. Owing to the complex local disordered chemical ...environments and unique site-to-site lattice distortions, there have been few related studies on high-entropy alloys (HEAs). In this work, we applied ab initio calculations to systemically characterize the chemical environment and magnetic moment effects on point defect formations in three equimolar alloys, namely: CoCrNi, CoCrNiFe, and CoCrNiFeMn. These calculations were based on investigations of a large number of statistical atomic sites. An appropriate method applying similar atomic environments (SAEs) and an efficient approach using Widom-type substitution techniques were employed to achieve results that were reliable. It was found that the vacancy formation energies (VFEs) were conspicuously larger in the CoCrNiFeMn HEA than in the CoCrNi or CoCrNiFe alloys. The local chemical environment—in particular, the number of first-nearest neighbor (1nn) Ni and Cr atoms—is the key factor affecting the VFE, as vacancies prefered Ni-rich and Cr-poor environments. Interstitial defects were primarily dominated by Co and Mn. Finally, the point defect formation energies were found to be negatively correlated with the anti-magnetic moment changes in 1nn atoms. Our results indicate that the low vacancy generation in HEAs is important for their enhanced irradiation resistance and that the local anti-magnetic moments influences of the constituent elements on the VFEs provide guidance for the design of advanced radiation-resistant HEAs.
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Ridged, orthorhombic two-dimensional (2D) group-V elemental and group IV–VI compound analogues of phosphorene provide a versatile platform for nanoelectronics, optoelectronics, and clean energy. ...However, phosphorene is vulnerable to oxygen in ambient air, which is a major obstacle for its applications. Regarding this issue, here we explore the oxidation behavior of monolayer group-IV monochalcogenides (GeS, GeSe, SnS, and SnSe), in comparison to that of phosphorene and arsenene by first-principles calculations. We find superior oxidation resistance of the monolayer group-IV monochalcogenides, with activation energies for the chemisorption of O2 on the 2D sheets in the range of 1.26–1.60 eV, about twice of the values of phosphorene and arsenene. The distinct oxidation behaviors of monolayer group-IV monochalcogenides and group-V phosphorene analogues originate from their different bond natures. Moreover, the chemisorption of a moderate amount of oxygen atoms does not severely deteriorate the electronic band structures of the monolayer group-IV monochalcogenides. These results shine light on the utilization of the monolayer group-IV monochalcogenides for next-generation 2D electronics and optoelectronics with high performance and stability.
Silicene, a two-dimensional hexagonal lattice of silicon, has been synthesized recently and exhibits fascinating electronic properties that resemble graphene. The substrate effect on the electronic ...properties of silicene is important for the practical applications of silicene. First-principles calculations were performed for silicene on two kinds of representative inert substrates, that is, hexagonal boron nitride (h-BN) monolayer and SiC(0001) surface. The silicene–substrate interaction energies range in 0.067–0.089 eV per Si atom, belonging to typical van der Waals interaction. The characteristic Dirac cone is preserved for silicene on h-BN monolayer or hydrogenated Si-terminated SiC(0001) surface. On the other hand, the silicene becomes metallic when it is placed on a hydrogenated C-terminated SiC(0001) surface. This effect was explained by the work functions for silicene and the substrates. The present results provide some guidelines for selecting proper substrates for silicene in future microelectronic devices.
In spintronics, it is highly desirable to find new materials that can simultaneously possess complete spin-polarization, high-speed conduction electrons, large Curie temperature, and robust ...ferromagnetic ground states. Using first-principles calculations, we demonstrate that the stable YN2 monolayer with octahedral coordination is a novel p-state Dirac half metal （DHM）, which not only has a fully spin-polarized Dirac state, but also the highest Fermi velocity （3.74×10^5 m/s） of the DHMs reported to date. In addition, its half-metallic gap of 1.53 eV is large enough to prevent the spin-flip transition. Because of the strong nonlocal p orbitals of N atoms （N-p） direct exchange interaction, the Curie temperature reaches over 332 K. Moreover, its ferromagnetic ground state can be well preserved under carrier doping or external strain. Therefore, the YN2 monolayer is a promising DHM for high-speed spintronic devices and would lead to new opportunities in designing other p-state DHMs.
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