Boosted charge separation via Ce2S3 over dual Z-scheme ZnO-Ce2S3-MnO2 core double-shell nanocomposite for the degradation of diverse dye pollutants.

Herein, core double-shell direct dual Z-scheme ZnO-Ce2S3-MnO2 nanocomposite was synthesized via a hydrothermal route along with pure ZnO, Ce2S3, MnO2, and characterized by numerous characterization tools for application in synthetic dyes degradation. The XRD, Raman, and FTIR analyses have confirmed the nanocomposite formation. TEM images exhibited the core double-shell morphology with an average particle diameter of 81 nm and stacking of ZnO, Ce2S3, and MnO2. EDX confirmed the existence of desired elements in the grown composition. The varied oxidation states, presence of defects, and fast charge transfer were also revealed from XPS, PL, and EIS. The ZnO-Ce2S3-MnO2 nanocomposite has an optical energy bandgap of 2.84 eV, capable of decomposing harmful dyes with excellent efficiency, 99.81% MB, 97.62% MO, 88.5% MR, and 58.9% EY in 40 min sunlight exposure. The effect of several operating parameters is also observed and obtained results showed the optimal catalyst dose was 20 mg, pH of 8, and dye concentration of 10 ppm. The scavenger's experiment suggests that •O2- and •OH are the main active radicals in the photodegradation reaction which is also evident in the dual Z-scheme formation. The MnO2 and ZnO layers covered the Ce2S3 (core) and dual Z-scheme formation allows rapid kinetics of redox reaction and provides plenteous channels for transfer of photo-generated charge carriers during photocatalysis. Thus, core double-shell direct dual Z-scheme photocatalysts having inorganic components could be an excellent choice for photocatalysis at the industrial level, particularly for water purification.

Photocatalytic microbial disinfection under indoor conditions: Prospects and challenges of near IR-photoactive materials.

The accumulation of microbes especially in the air and in water bodies is causing the major disease outbreaks. Indoor environment remediation methods are necessary today to clean up these microbes. Among the remediation methods available, in situ generation of highly reactive and oxidizing radical species by advanced oxidation processes (AOPs) inactivate most of the microbes unselectively. Of these AOPs, photocatalytic microbial disinfection especially under indoor conditions is of great interest to maintain microbe-free indoor environment. For efficient microbes' inactivation under indoor conditions, the near IR and IR response of the photocatalysts must be improved. Though the photocatalytic disinfection of microbes using semiconductor-based photocatalysts has been extensively investigated, most of the photocatalysts that have been investigated are either weekly responsive or totally not irresponsive to IR photons due to inappropriate bandgap energies. Several strategies have been investigated to enhance the light harvesting properties of semiconductor based photocatalysts under indoor conditions and make them active to near IR and IR radiations. This review summarizes the recent progress in the field of materials for photocatalysts employed for microbial removal in indoor environments over the past decade as well as outlines key perspectives to enlighten future researches. The paper details the fundamentals of photocatalysis and basic properties of photocatalytic materials in the disinfection of common microbes under indoor conditions. The applications of photocatalytic materials in the disinfection of microbes in indoor environmental conditions are discussed and reviewed. Finally, the remaining challenges and future strategies/prospects in the design and synthesis of IR (and near IR) responsive photocatalysts are discussed.

Insight into the Evolution of Ordered Mesoporous sp2 Carbonaceous Material Derived from Self-Assembly of a Block Copolymer.

Block-copolymer-derived ordered mesoporous carbon (OMC) materials have great potential in many applications, such as adsorption, catalysis, and energy conversions; however, their formation process and the kinetic mechanism remain unclear. Herein, a N-doped OMC (N-OMC) with sp2-bonded C atoms is developed via self-assembly of the polystyrene-block-poly(4-vinyl pyridine) block copolymer. By correlating the external morphologies with the internal chemical states, the formation process can be concluded as follows: (1) pore evolution via polystyrene domain degradation and (2) regularization and graphitization of the residual carbon via the removal of sp3 C atoms. In addition, the thickness of the N-OMC shows a power function relationship with the spin-coating rate, and the N content can be incredibly increased up to 26.34 at. % in an NH3 carbonization atmosphere. With the as-prepared N-OMC as the support for loading of the pseudo-atomic-scale Pt (Pt/N-OMC), a high electrochemical active surface area value of 99.64 m2·g-1 and a half-wave potential (E1/2) of 0.850 VRHE are achieved, showing great potential in developing single-atom electrocatalysts.

Remaining Useful Life prediction of rolling bearings based on risk assessment and degradation state coefficient.

Prediction of Remaining Useful Life (RUL) of bearings is very important for the condition-based maintenance of the rotating machinery. In order to predict the RUL more accurately, an approach of RUL prediction based on risk assessment and degradation state coefficient is proposed. The Mahalanobis Distance (MD) is calculated depending on the characteristics of vibration signals in the time domain and time-frequency domain. The features in the time-frequency domain are extracted by using Variational Mode Decomposition-Singular Value Decomposition (VMD-SVD). The monotonously increasing Health Indicator (HI) is obtained by using MD1-CUMSUM. The risk assessment is proposed to adaptively determine the thresholds of initial fault and failure, which is a trade-off between the false alarm rate and sensitivity. The RUL prediction of the testing bearing is completed based on the Genetic Algorithm-Support Vector Regression (GA-SVR) and Modified Health Indicator (MHI) with the degradation state coefficient. The proposed approach is verified by using two experimental vibration signal datasets. The results show that the proposed method has good capability to predict the RUL of rolling bearings.

Effects of cross-sectional area and aspect ratio coupled with orientation on mechanical properties and deformation behavior of Cu nanowires.

Metal nanomaterials exhibit excellent mechanical properties compared with corresponding bulk materials and have potential applications in various areas. Despite a number of studies of the size effect on Cu nanowires mechanical properties with square cross-sectional, investigations of them in rectangular cross-sectional with various sizes at constant volume are rare, and lack of multifactor coupling effect on mechanical properties and quantitative investigation. In this work, the dependence of mechanical properties and deformation mechanisms of Cu nanowires/nanoplates under tension on cross-sessional area, aspect ratio of cross-sectional coupled with orientation were investigated using molecular dynamics simulations and the semi-empirical expressions related to mechanical properties were proposed. The simulation results show that the Young's modulus and the yield stress sharply increase with the aspect ratio except for the 〈110〉{110}{001} Cu nanowires/nanoplates at the same cross-sectional area. And the Young's modulus increases while the yield stress decreases with the cross-sectional area of Cu nanowires. However, both of them increase with the cross-sectional area of Cu nanoplates. Besides, the Young's modulus increases with the cross-sectional area at all the orientations. The yield stress shows a mildly downward trend except for the 〈111〉 Cu nanowires with increased cross-sectional area. For the Cu nanowires with a small cross-sectional area, the surface force increases with the aspect ratio. In contrast, it decreases with the aspect ratio increase at a large cross-sectional area. At the cross-sectional area of 13.068 nm2, the surface force decreases with the aspect ratio of the 〈110〉 Cu nanowires while it increases at other orientations. The surface force is a linearly decreasing function of the cross-sectional area at different orientations. Quantitative studies show that Young's modulus and yield stress to the aspect ratio of the Cu nanowires satisfy exponent relationship. In addition, the main deformation mechanism of Cu nanowires is the nucleation and propagation of partial dislocations while it is the twinning-dominated reorientation for Cu nanoplates.

Highly Ordered Pt-Based Nanoparticles Directed by the Self-Assembly of Block Copolymers for the Oxygen Reduction Reaction.

Designing Pt-based nanoparticle (NP) catalysts is of great interest for the lowering of Pt usage and the enhancement of catalytic activity on the proton-exchange membrane fuel cells (PEMFCs). However, it is still challenging to develop well-arrayed catalyst NPs on supports over multiple-length scales. Herein, we presented a facile strategy of producing well-ordered Pt-based NPs toward oxygen reduction reaction (ORR) catalysts assisted by the self-assembly of block copolymers. In contrast to the conventional Pt/C ORR catalysts with a random dispersion on carbon, the as-prepared Pt, PtCo, and PtCo@Pt NPs in our work were hexagonally arranged with a uniform quasi-spherical shape and ordered distribution. The systematic study related to their ORR activities revealed that the PtCo@Pt core-shell NP arrays were more active and more durable than PtCo, Pt, and the commercial Pt/C catalyst. In the rotating-disk electrode test, a half-wave potential (E1/2) of 0.86 V versus RHE and a 4-e ORR mechanism were found for PtCo@Pt. Single-cell performance showed that the current density and the peak power density of PtCo@Pt achieved 0.86 A/cm2@0.7 V and 1.05 W/cm2, respectively, with a Pt loading of ∼0.15 mg/cm2 on the cathode. Also, they held 81.4 and 82.9% retention, respectively, after the durability test in the single-cell test. Density functional theory calculation results revealed that PtCo@Pt NPs had a lower d-band center and a weaker oxygen binding energy compared to Pt and PtCo, which contributed to the enhancement of the ORR activity.

Synthesis of Ordered Pt Nanocube Arrays Directed by Block Copolymer Nanotemplate and Their Potential on Ethanol Oxidation Reaction.

In this work, well-ordered platinum (Pt) nanocubes (NCs), with precise control on the size and the spatial arrangement, are synthesized from a microemulsion overgrowth in a block copolymer (BC) nanotemplate. The nanovials on this self-assembled BC template serve as microreactors for the reduction of the HCl/H2PtCl6 precursor and direct the ordered periodic arrangement of the reduced Pt nanoparticles (NPs). As the content of HCl increases from 0% to 25%, the Pt NPs evolve from quasi-spheres to NCs, for which the density functional theory (DFT) computation reveals that the different adsorption energies of Cl and HCl dominate this morphology transition. For their potential application in fuel cells, the electrochemical catalysis of the Pt NCs demonstrates a 2.8-fold mass activity in contrast to the commercial JM 40% catalyst at the same Pt loading in ethanol oxidation reaction (EOR) and a good stability of 2.2% ECSA loss over 10 000 CV cycling.

Nanoindentation of γ-TiAl with Different Crystal Surfaces by Molecular Dynamics Simulations.

The periodicity and density of atomic arrangement vary with the crystal orientation, which results in different deformation mechanisms and mechanical properties of γ-TiAl. In this paper, the anisotropic characteristics for γ-TiAl with (100), ( 1 ¯ 10 ) and (111) surfaces during nanoindentation at 300 K have been investigated by molecular dynamics simulations. It is found that there is no obvious pop-in event in all load-depth curves when the initial plastic deformation of γ-TiAl samples occurs, because the dislocation nucleates before the first load-drop; while a peak appears in both the unloading curves of the ( 1 ¯ 10 ) and (111) samples due to the release of energy. Stacking faults, twin boundaries and vacancies are formed in all samples; however, interstitials are formed in the (100) sample, a stacking fault tetrahedron is formed in the (111) sample; and two prismatic dislocation loops with different activities are formed in the ( 1 ¯ 10 ) and (111) samples, respectively. It is also concluded that the values of the critical load, strain energy, hardness and elastic modulus for the (111) sample are the maximum, and for the (100) sample are the minimum. Furthermore, the orientation dependence of the elastic modulus is greater than the hardness and critical load.

Sono-photocatalytic production of hydrogen by interface modified metal oxide insulators.

Dielectric oxide materials are well-known insulators that have many applications in catalysis as well as in device manufacturing industries. However, these dielectric materials cannot be employed directly in photochemical reactions that are initiated by the absorption of UV-Vis photons. Despite their insensitivity to solar energy, dielectric materials can be made sono-photoactive even for low energy IR photons by modifications of the interfacial properties of dielectric materials by noble metals and metal oxides. In this investigation, by way of interface modification of dielectric MgO nanoparticles by Ag metal and Ag2O nanoparticles, IR photon initiated sono-photocatalytic activity of MgO is reported. The observed photocatalytic activity is found to be the synergic action of both IR light and sonication effect and sonication assisted a multi-step, sub-bandgap excitation of electrons in the MgO is proposed for the observed catalytic activity of Ag/Ag2O coated MgO nanoparticles. Our investigation reveals that other dielectric materials such as silver coated SiO2 and Al2O3 also exhibit IR active sono-photocatalytic activity.