A comprehensive review of oxygen vacancy modified photocatalysts: synthesis, characterization, and applications.

Photocatalytic technology is a novel approach that harnesses solar energy for efficient energy conversion and effective pollution abatement, representing a rapidly advancing field in recent years. The development and synthesis of high-performance semiconductor photocatalysts constitute the pivotal focal point. Oxygen vacancies, being intrinsic defects commonly found in metal oxides, are extensively present within the lattice of semiconductor photocatalytic materials exhibiting non-stoichiometric ratios. Consequently, they have garnered significant attention in the field of photocatalysis as an exceptionally effective means for modulating the performance of photocatalysts. This paper provides a comprehensive review on the concept, preparation, and characterization methods of oxygen vacancies, along with their diverse applications in nitrogen fixation, solar water splitting, CO2 photoreduction, pollutant degradation, and biomedicine. Currently, remarkable progress has been made in the synthesis of high-performance oxygen vacancy photocatalysts and the regulation of their catalytic performance. In the future, it will be imperative to develop more advanced in situ characterization techniques, conduct further investigations into the regulation and stabilization of oxygen vacancies in photocatalysts, and comprehensively comprehend the mechanism underlying the influence of oxygen vacancies on photocatalysis. The engineering of oxygen vacancies will assume a pivotal role in the realm of semiconductor photocatalysis.

Double strengthening induced by grain boundary segregation of solute elements in gradient nano Ni-Co alloys.

Gradient induced unusual strain hardening achieves the equilibrium of the strength and plasticity of alloys, and is an important strategy for the optimization of the mechanical properties of metals and alloys. The segregation of solute elements can greatly improve the grain boundary stability, inhibit grain coarsening and promote the mechanical strength of the alloy. In our efforts, the segregation structure of the solute element Co was designed and added to the gradient nano Ni-Co alloy, and the two strengthening strategies were applied simultaneously in one structure. The mechanical strength of the alloy achieved a second increase based on the unique combination of gradient induced strain hardening and high plasticity, especially the yield strength of alloy increase amplitude reach to 42%. This provides a positive direction for the alloy strengthening strategy. In the process of secondary strengthening, the micro-mechanism is divided into two stages: in the first stage, the gradient strain provides the alloy with geometrically necessary dislocations and a multi-axial stress state, and the existence of large numbers of geometrically necessary dislocations creates good conditions for the second stage strengthening. In the second stage, the solute segregation induced stable grain boundaries produce a strong pinning effect on the geometrically necessary dislocation, which realizes the coupling of grain boundary strengthening and dislocation strengthening. This provides a new strengthening strategy and positive theoretical guidance for the experimental preparation of advanced alloys with excellent properties.

Insight into the Electronic Properties of Semiconductor Heterostructure Based on Machine Learning and First-Principles.

A first-principles approach is a powerful means of gaining insight into the intrinsic structure and properties of materials. However, with the implementation of material genetic engineering, it is still a challenging road to discover materials with high satisfaction. One alternative is to employ machine-learning techniques to mine data and predict performance. In this present contribution, the method is taken to predict the band gap opening value of graphene in a heterostructure. First, the data of 2076 binary compounds in the Materials Project library are used to achieve visual dimensionality reduction of the data set through a t-distributed stochastic neighbor embedding (t-SNE) algorithm in unsupervised learning. Then, a series of semiconductor components are screened out and form heterostructures with graphene. Second, by means of the ensemble learning EXtreme Gradient Boost (XGBoost) algorithm and support vector machine (SVM) technology, two prediction frameworks are built to predict the band gap opening value of the graphene in the system. Finally, density functional theory (DFT) is used to calculate the energy band and density of states for comparison. Analysis shows that the prediction model has an accuracy rate of 88.3%, and there is little difference between prediction results and calculation results. We anticipate that this framework model would have fascinating applications in predicting the electronic properties of various multiphase materials.

Efficient Warming Textile Enhanced by a High-Entropy Spectrally Selective Nanofilm with High Solar Absorption.

Solar and radiative warming are smart approaches to maintaining the human body at a metabolically comfortable temperature in both indoor and outdoor scenarios. Nevertheless, existing warming textiles are ineffective in frigid climates because the solar absorption of selective absorbing coating is significantly reduced when coated on rough textile surface. Herein, for the first time, high-entropy nitrides based spectrally selective film (SSF) is introduced on common cotton through a one-step magnetron sputtering method. The well-designed refractive index gradient enables destructive interference effects, offering a roughness-insensitive high solar absorptance (92.8%) and low thermal emittance (39.2%). Impressively, the solar absorptance is 9.1% higher than the reported best-performing selective nanofilm-based textile. As a result, such a textile achieves a record-high photothermal conversion efficiency (82.2% under 0.6 suns, at 0 °C). This textile yields a 3.5 °C drop in the set-point of indoor air-conditioner temperature. Besides, in a winter morning with an air temperature of 7.5 °C, it warms up the human skin by as large as 12 °C under weak sunlight (350 W m-2 ). More importantly, such a superior radiative warming performance is achieved by engineering the widely used cotton without compromising its breathability and durability, showing great potential for practical applications.

Molecular Dynamics as a Means to Investigate Grain Size and Strain Rate Effect on Plastic Deformation of 316 L Nanocrystalline Stainless-Steel.

In the present study, molecular dynamics simulations were employed to investigate the effect of strain rate on the plastic deformation mechanism of nanocrystalline 316 L stainless-steel, wherein there was an average grain of 2.5-11.5 nm at room temperature. The results showed that the critical grain size was 7.7 nm. Below critical grain size, grain boundary activation was dominant (i.e., grain boundary sliding and grain rotation). Above critical grain size, dislocation activities were dominant. There was a slight effect that occurred during the plastic deformation mechanism transition from dislocation-based plasticity to grain boundaries, as a result of the stress rate on larger grain sizes. There was also a greater sensitive on the strain rate for smaller grain sizes than the larger grain sizes. We chose samples of 316 L nanocrystalline stainless-steel with mean grain sizes of 2.5, 4.1, and 9.9 nm. The values of strain rate sensitivity were 0.19, 0.22, and 0.14, respectively. These values indicated that small grain sizes in the plastic deformation mechanism, such as grain boundary sliding and grain boundary rotation, were sensitive to strain rates bigger than those of the larger grain sizes. We found that the stacking fault was formed by partial dislocation in all samples. These stacking faults were obstacles to partial dislocation emission in more sensitive stress rates. Additionally, the results showed that mechanical properties such as yield stress and flow stress increased by increasing the strain rate.

Influence of Temperature on Mechanical Properties of Nanocrystalline 316L Stainless Steel Investigated via Molecular Dynamics Simulations.

Molecular dynamics simulations were conducted to study the mechanical properties of nanocrystalline 316L stainless steel under tensile load. The results revealed that the Young's modulus increased with increasing grain size below the critical average grain size. Two grain size regions were identified in the plot of yield stress. In the first region, corresponding to grain sizes above 7.7 nm, the yield stress decreased with increasing grain size and the dominant deformation mechanisms were deformation twinning and extended dislocation. In the second region, corresponding to grain sizes below 7.7 nm, the yield stress decreased rapidly with decreasing grain size and the dominant deformation mechanisms were grain boundary sliding and also grain rotation. The yield strength and Young's modulus were both found to decrease with increasing temperature, which increased the interatomic distance and thereby decreased the interatomic bonding force.

Synthesis of magnetic graphene oxide grafted polymaleicamide dendrimer nanohybrids for adsorption of Pb(II) in aqueous solution.

In this paper, using maleic anhydride and ethylenediamine as functional monomers, graphene oxide (GO) loaded magnetic Fe3O4 nanoparticles modified by (3-Aminopropyl) triethoxysilane as support, magnetic graphene oxide grafted polymaleicamide dendrimer (GO/Fe3O4-g-PMAAM) nanohybrids were fabricated by divergent method and magnetic separation technology. The obtained samples were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, elementary analyzer and vibrating sample magnetometer. The effects of PMAAM generations, solution pH, Pb(II) initial concentration, temperature and contact time on the adsorption property of the samples for Pb(II) in aqueous solution were studied. The results demonstrated that nitrogen content and adsorption capacity of the as-synthesized samples with amino terminal groups were all higher than their adjacent generations PMAAM with carboxyl terminal groups. Moreover, with increasing generations of PMAAM grafted on to the GO/Fe3O4, the nitrogen content and the adsorption capacity of the samples with the same terminal groups gradually increased. The maximum adsorption capacity of GO/Fe3O4-g-G3.0 for Pb(II) was 181.4mgg-1 at 298K. The rising of temperature was beneficial for the adsorption. The adsorption kinetics had a better agreement with pseudo-second-order equation, and equilibrium data followed the Langmuir model.

Preparation of polyamidoamine dendrimers functionalized magnetic graphene oxide for the adsorption of Hg(II) in aqueous solution.

In this study, using graphene oxide supported Fe3O4 nanoparticles as carriers, ethylenediamine and methyl acrylate as functional monomer, different generations of polyamidoamine dendrimers functionalized magnetic graphene oxide (MGO-PAMAM), up to generation 4.0, were successfully synthesized via step by step growth chemical grafting approach and magnetic separation technology. In the process of synthesizing dendrimers, the generation of dendrimers was increased with the increasing of reaction cycles. In other words, the dendrimers generation is determined from the number of branch iterations. The obtained MGO-PAMAM were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), elemental analysis, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), nitrogen adsorption/desorption isotherm and Zeta potential analysis. The adsorption properties of the synthesized products for Hg(II) in aqueous solution were investigated by batch experiments. The results showed that the MGO-PAMAM with generation 3.0 of dendrimers (MGO-PAMAM-G3.0) has the maximum adsorption capacity of 113.71mg·g-1. The adsorption process of MGO-PAMAM-G3.0 for Hg(II) was well described by the pseudo-second-order kinetics model and the Langmuir isotherm model. The Hg(II) adsorbed on the surface of MGO-PAMAM-G3.0 was reduced to Hg(I) in the adsorption process. In addition, the MGO-PAMAM possesse good magnetic separation performance.

Innovative nanoporous carbons with ultrahigh uptakes for capture and reversible storage of CO2 and volatile iodine.

Porous carbons as solid-state adsorbents have recently attracted considerable interest in the areas of storage and capture of CO2 as well as the adsorption of radioactive matters. In this work, cigarette butts, one kind of common wastes referring to the filters, were utilized to prepare highly porous carbons by KOH activation in argon atmosphere. The resulting porous carbon shows a high specific surface area of up to 2751m2g-1 with abundant micropores. The resulting porous carbon exhibits excellent iodine uptake of 262wt% and high CO2 adsorption capacity of 6.0mmolg-1 at ambient pressure and 273K, which both are among the highest values reported to date. Given these excellent iodine uptake, CO2 adsorption capacity, ease of preparation as well as good physiochemical stability, the porous carbons derived from cigarette butts show great potential in the reversible adsorption of radioactive iodine and CO2.

Molecular Dynamics Study of Superelastic Performance of a ß-Si3N4 Nanohelical Coil.

Superealsticity behavior has been discovered for the ß-Si3N4 nanohelical coil. By a series of cyclic loading and unloading simulation tests, the nanohelical coil could elastically recover its original shape after a relatively long axial tension far beyond the elastic limit, accompanying little residual plastic deformation. The spring constant is first a steady-state value of 0.72 N m-1 in the linear stage and then increases dramatically for up to 1.5 N m-1 in the nonlinear region. The fascinating performance of the nanocoil makes it stand out from its bulk counterparts in the development of future electronic devices such as nanoscale elastic energy storage.

Insight into the nanomechanical properties under indentation of ß-Si3N4 nano-thin layers in the basal plane using molecular dynamics simulation.

Molecular dynamics simulations were performed to clarify the nanomechanical responses of ß-Si3N4 nano-thin layers in the basal plane for indenters of various radii, different indentation velocities and at different temperatures. It was found that the maximum loading stress and indenter displacement both increase with increasing radius of the indenter. A large number of N(6h)-Si bond-breaking defects and one N(2c)-Si bond-breaking defects are responsible for the initiation of fracturing. With increasing loading velocity, the maximum loading stresses show almost no change; however, a high loading velocity can shorten the displacement of the indenter and contributes to the formation of new N(2c)-Si bond-breaking defects. Thermal fluctuations can decrease the mechanical properties of the thin layer. The maximum loading stresses and indenter displacements are sensitive to both the radius of the indenter and the loading temperature.

Three-dimensional superwetting mesh film based on graphene assembly for liquid transportation and selective absorption.

Superwetting membranes or porous absorbent materials have recently attracted considerable interest from both commercial and academic communities due to their excellent performance for separation or selective absorption of organic compounds and oils from water, which shows great potential for addressing environmental issues. Herein, the first example of engineering a commercially available stainless-steel grid based on the assembly of graphene for the fabrication of superwetting mesh films (SMFs) is reported. An excellent surface wettability of the SMFs, which exhibit a unique adhesion force to liquids, is observed; this makes it possible to transfer small quantities of liquid samples to perform microsample analysis. A three-dimensional SMF shows unprecedented performance in the separation, transportation, and selective absorption of organic compounds or oils from water. The performance is considerably improved in comparison to traditional separation/absorption technologies and may useful for a wide range of applications such as purification, water treatment, or oil-spill cleanup.

Superhydrophobic activated carbon-coated sponges for separation and absorption.

Highly porous activated carbon with a large surface area and pore volume was synthesized by KOH activation using commercially available activated carbon as a precursor. By modification with polydimethylsiloxane (PDMS), highly porous activated carbon showed superhydrophobicity with a water contact angle of 163.6°. The changes in wettability of PDMS- treated highly porous activated carbon were attributed to the deposition of a low-surface-energy silicon coating onto activated carbon (confirmed by X-ray photoelectron spectroscopy), which had microporous characteristics (confirmed by XRD, SEM, and TEM analyses). Using an easy dip-coating method, superhydrophobic activated carbon-coated sponges were also fabricated; those exhibited excellent absorption selectivity for the removal of a wide range of organics and oils from water, and also recyclability, thus showing great potential as efficient absorbents for the large-scale removal of organic contaminants or oil spills from water.

Superhydrophobic Mesoporous Graphene for Separation and Absorption.

Mesoporous graphene with a surface area of 306 m2 g-1 was synthesized by employing CaCO3 microspheres as hard templates. By surface modification with polydimethylsiloxane (PDMS) through chemical vapor deposition, the wettability of as-treated mesoporous graphene can be tailored to be superhydrophobic to water while superoleophilic to oils. The deposition of the low-surface-energy silicon-coating originated from PDMS pyrolysis on porous graphene was confirmed by X-ray photoelectron spectroscopy. As a result of its porous structures and excellent surface superhydrophobicity, the PDMS-treated mesoporous graphene exhibits good selectivity, excellent recyclability, and good absorption performance (up to 66 g g-1 ) for a wide range of oils and organic solvents. Thus, leading to potential use in a variety of applications such as water treatment and purification as well as cleanup of oil spills.

Investigation of Nanomechanical Properties of ß-Si3N4 Thin Layers in a Prismatic Plane under Tension: A Molecular Dynamics Study.

We report molecular dynamics simulations of the nanomechanical properties and fracture mechanisms of ß-Si3N4 thin layers in a prismatic plane under uniaxial tension. It is found that the thin layers in the y loading direction display a linear stress-strain relationship at ε < 0.021, and afterward, the stress increases nonlinearly with the strain until fracture occurs. However, for the z direction, the linear response is located at ε < 0.051. The calculated fracture stresses and strains of the thin layers increase with strain rates both in both directions. The thin layers exhibit the higher Young's modulus of 0.345 TPa in the z direction, higher than that in the y direction. The origins of crack derive from N(2c-1)-Si and N(6h-1)-Si bonds for the y and z loading directions, respectively.