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Nanostructured covalent organic frameworks (COFs) have attracted great attentions over the past few decades due to their unique physical and chemical properties. Crystallization is sought in many application fields since it allows enhancing or even promoting properties of catalysis, energy storage and photoelectric properties. However, the crystallization process of nanostructured COFs remains to be challenging. Synthetic approaches to establish nucleation and elongation growth of COFs for controlling crystallization have drawn substantial amount of attentions. Nanostructured COFs have exhibited significant advantages when applied in (electro)photocatalysis and energy storage devices as well. In this review, recent progress in precisely design strategy of fabricating various nanostructured COFs and their applications as (electro)photocatalyzer and energy storage devices are summarized. After a brief introduction of the design principles, composition and interior architecture, the morphology of nanostructured COFs including porous and mesoporous stacked-layer structure, nanosheet structure, nanorod structure, ordered stripe arrays and various nanocomposites are thoroughly described. Reactions dedicated to crystallization process for two-dimensional (2D) COFs are discussed further. Then, the applications of nanostructured COFs as (electro)photocatalysis and energy storage devices are demonstrated. Finally, the potential advantages and challenges for the synthetic technology of nanostructured COFs materials are particularly discussed. Personal insights into the challenges and opportunities on pursuing topologies as hollow structures, dense spheres, yolk–shell structures were raised to broaden the applications.

The refrigeration technology of electronic devices has faced severe challenges with the increasing demand for miniaturization and high frequency, and the research on the electrocaloric effect (ECE)...

The severe pollution caused by antibiotics has prompted considerable concerns in recent decades. In this study, the Bi

Nontrivial topological structures offer a rich playground in condensed matters and promise alternative device configurations for post-Moore electronics. While recently a number of polar topologies have been discovered in confined ferroelectric PbTiO3 within artificially engineered PbTiO3/SrTiO3 superlattices, little attention was paid to possible topological polar structures in SrTiO3. Here we successfully create previously unrealized polar antivortices within the SrTiO3 of PbTiO3/SrTiO3 superlattices, accomplished by carefully engineering their thicknesses guided by phase-field simulation. Field- and thermal-induced Kosterlitz–Thouless-like topological phase transitions have also been demonstrated, and it was discovered that the driving force for antivortex formation is electrostatic instead of elastic. This work completes an important missing link in polar topologies, expands the reaches of topological structures, and offers insight into searching and manipulating polar textures. While the role of PbTiO3 in PbTiO3/SrTiO3 superlattices has been widely studied, little attention is paid to possible polar topologies in SrTiO3. Here, the authors create atomic-scale vortex–antivortex pairs in the superlattices, expanding the understanding of topological structures.

Efficient photocatalytic activity is always pressingly expected for photocatalytic technology on removing organic water contaminations. Modulating the intrinsic electronic properties is one of the most effective approaches to improve photocatalytic efficiency. Herein, we developed a promising photocatalyst through modulation electronic properties of iron-based metal organic framework by sulfur (S-MIL-53(Fe)), in which the sulfur particles were intramolecularly in-suite inserted into MIL-53(Fe) through annealing treatment process. The constructed S3-MIL-53(Fe) crystal with regular spindle-shaped polyhedron morphology exhibited superior higher apparent quantum efficiency (AQE) of 27.82% which was over 30 times than that of pure MIL-53(Fe) (0.903%) indicating the significantly enhanced photoactivity. A computational study was conducted to reveal the electronic structure changes and the resulted charge transfer induced by the sulfur modulation. The experimental and computational analyses suggest that intramolecular modulation MIL-53(Fe) with sulfur to engineer band structure for promoting charge transfer is a promising approach to improve the photocatalytic efficiency.

Large electromechanical response of ferroelectric materials is particularly appealing for applications in functional devices, such as sensors and actuators. For conventional ferroelectric materials, however, the mechanical strain under an external electric field, i.e. the electrostrain, is often limited by the intrinsic electromechanical property of the materials. Domain engineering has been suggested as a practical way to overcome this limitation and to enhance the electrostrain. Here, we show from phase-field simulations that reversible domain switching in ordered ferroelectric nanostructures with optimized geometric configurations can enhance the electrostrain significantly. In the presence of an external electric field, the domains in such nanostructures can switch from a multi-domain state confined by the geometric configurations to a mono-domain state. It is interesting that the domains can switch back to the multi-domain state due to strong internal depolarization fields once the electric field is removed. As a result, accompanying the reversible domain switching behavior, a large and reversible electrostrain can be obtained. Going further, it is found that the temperature dependence of the large electrostrain is similar to that of polarization in such nanostructures. The present work opens a perspective to obtaining large electrostrain in nanoscale ferroelectrics, which holds great promise for designing electromechanical functional devices with high performance.

Polymeric carbon nitride (CN) as a metal-free photocatalyst with suitable band gap has attracted increasing attention. However, pristine CN has a limited visible-light absorption range and also suffers a high recombination rate of photo-excited charge carriers, resulting in low photocatalytic activity. With the development of modern material characterization technology and electronic structure calculation technology, it is found that vacancy defects in CN play a more decisive role in determining the kinetics, energetics and mechanism of photocatalytic reactions. Therefore, much effort has been made in the past years to enhance the visible light activity of CN through defects control. This review provides the recent progresses and technologies on fabricating defective CN, in which the bottom-up and top-down preparation strategies are systematically summarized. In the meantime, the advancement of defective CN photocatalysts toward versatile applications such as water oxidation, hydrogen production, CO2 reduction, nitrogen fixation, H2O2 and organic synthesis, and pollutants removal are fully discussed. Finally, the existing opportunities and challenges of CN photocatalysts designed with vacancies defects are proposed to highlight the development direction of this field. This paper can lay a theoretical basis and guidance for the preparation of defective graphitic carbon nitride.

This work focuses on understanding elastic wave propagation in the periodic dielectric elastomer (DE) laminates with geometry and material properties that can be tuned by an external electric field. In particular, shear horizontal (SH) wave propagation at oblique incidence is investigated using the Dorfmann and Ogden's finite electroelasticity theory and the Dielectric Gent (DG) energy model. Numerical calculations of the dispersion relations and transmission properties are presented. The numerical results show that the SH wave band gaps and transmission coefficient depend on various parameters that can be controlled by the applied external electrostatic field and the incident angle of the SH wave, thus providing a novel strategy for designing flexible phononic structures with tunable properties.

Herein, Ti3C2 MXene nanosheets and perylene diimide supramolecular (PDIsm) were successfully combined via a facile self-assembly method. The apparent rate constant of photodegradation for tetracycline hydrochloride (TCH) and Rhodamine B (RhB) of 1%-Ti3C2/PDIsm (0.079 min−1 and 0.082 min−1) were 2.5 times and 7.2 times higher than that of pure PDIsm, respectively. The introduction of Ti3C2 MXene nanosheets is beneficial to the stacking degree of PDIsm and the adsorption capacity of PDIsm for organic pollutants. Moreover, the excellent electrical conductivity of Ti3C2 also promotes the charge separation, which contributes to more photoelectrons participated in the photodegradation reaction of pollutants and thereby the enhanced photocatalytic performance. Additionally, the density functional theory (DFT) calculation also provides strong evidence for the enhanced photocatalytic degradation activity of Ti3C2/PDIsm structure. Meanwhile, the mechanism exploration indicates that h+, ∙O2– and 1O2 play leading roles in the photocatalytic process. This work provides a new insight into using 2D MXenes as co-catalysts to enhance the activity of self-assembled organic materials for environmental remediation.

Photo-assisted peroxydisulfate (PDS) activation has exhibited a great potential for pollution control. In this study, metal-free nitrogen-doped carbon quantum dots (N-CQDs) modified g-C3N4 composite was fabricated and used to activate PDS under visible light to effectively remove tetracycline hydrochloride (HTC) in wastewater. Specifically, almost 90% of HTC (20 mg/L) was removed in 60 min under the conditions of an initial value of catalysis dose of 0.5 g/L and PDS dose of 0.6 g/L. Electron spin resonance analysis and trapping experiments confirmed that SO4−, O2− and h+ were found as the dominant contributors to the HTC degradation. PDS and N-CQDs acted as an electron acceptor to transfer the photogenerated charges, resulting in the successful activation of PDS. The promoting visible light absorption can be ascribed to up-conversion effect of N-CQDs. The combination strategy provides an innovative approach to synthesize binary metal-free carbonaceous photocatalysts for implementing PDS-based oxidative degradation of pollutants.

A facile microemulsion-assisted co-precipitation method was carried out to synthesize nano-sized Ag2CrO4 highly dispersed on the surface of porous g-C3N4 as high-efficiency visible-light-driven composite photocatalysts for the first time. The structure and morphology of the composites were systematically characterized by various techniques. Compared with Ag2CrO4 and g-C3N4, g-C3N4/Ag2CrO4 composites showed a dramatically increased photocatalytic activity in degradation of rhodamine B (RhB) and methylene blue (MB). The optimum mass ratio of the Ag2CrO4 to g-C3N4 was about 30 wt%, the degradation rate of which were 6.1 (7.9) and 9.7 (15.2) times higher than pure Ag2CrO4 and g-C3N4 in RhB (MB) degradation, respectively. The excellent photocatalytic activity and stability mainly benefited from the synergistic effect including smaller Ag2CrO4 particle size, high specific surface area of the composites and matched band potentials which not only promoted the separation of photon-generated charge carriers, but also inhibited the photocorrosion of Ag2CrO4. Further study revealed that the photocatalytic mechanism followed a Z-scheme which provided an efficient transfer pathway for charge carriers meanwhile endowed the composites with strong oxidation and reduction ability. Hence the porous g-C3N4/Ag2CrO4 composites are potential in environmental purification.

Bismuth oxybromide-based heterostructure has been constructed widely for various photocatalytic application. However, the function of the exposed facets in heterostructure still remains to be elucidated. Herein, we chemically implanted bismuth oxybromide nano-units with dominantly exposed (0 1 0) facets on indium vanadate particles to form composites. Results showed that the absorption range of visible light was extended due to the high photosensitivity of InVO4 and the charge transfer was also effectively expedited by the formation of internal electric field. Contrast experiments manifested that BiOBr with dominant (0 1 0) facets was more suitable than that with (0 0 1) facets to act as electron acceptor in InVO4/BiOBr heterojunction, because the open channels on (0 1 0) facets provided large accommodation space for organic pollutants. Thus, the generated superoxide radicals on BiOBr could annihilate the adsorbed pollutants rapidly. Moreover, the hierarchical core-shell structure provided large surface area to further intensify the affinity of InVO4/BiOBr composites to pollutants. Consequently, the hierarchical InVO4/BiOBr heterojunction exhibited excellent photocatalytic activity and could degrade 92.59% of ciprofloxacin (CIP) within 1 h under visible light. The reaction data were fitted with multiple models to investigate the whole reaction process. Furthermore, the impacts of various simulated actual factors on CIP adsorption and degradation were explored. The intermediates and possible degradation pathways were also illustrated through Liquid Chromatography-Mass/Mass Spectrometry (LC-MS). This work not only provide a facet engineering concept for heterojunction construction, but also help us to further understand the relationship between adsorption and photocatalytic degradation.

Complementary effect of components in a hybrid photocatalyst is an essential factor for improving solar energy-conversion efficiency, yet the underlying correlation between nitrogen-doped carbon quantum dots (N-CQDs) and oxygen vacancy (OV) is still ambiguous. Herein, using BiOBr nanosheets as model photocatalyst, we studied the specific roles of N-CQDs and OV in antibiotic photodegradation over full-spectrum. Electrons were overwhelmingly collected on N-CQDs rather than OV, achieving prominent separation of photo-excitons. However, OV could extend the congenitally optical absorption boundary of BiOBr to maximum utilizing the up-converted photons by N-CQDs. Moreover, active radical tests revealed that N-CQDs mainly regulated the single-electron reduction of dissolved oxygen to produce superoxide radicals ( O2−) and OV mainly drove the robust H2O2 generation via two-electron reduction of the chemisorbed oxygen molecules. Although partial O2− were consumed as the raw of H2O2, a Photo-Fenton like reaction could transform H2O2 into hydroxyl radicals ( OH) to provide more powerful oxidizing force. This work provides an in-depth understanding on the complementary roles of N-CQDs and OV and is helpful for designing highly efficient metallic oxide catalysts for photocatalytic pollutant removal.

The overuse of refractory antibiotics in animal husbandry has caused serious aqueous environment pollution. Polymeric carbon nitride (CN) based photocatalysis, a promising method to address antibiotic pollution issues, has encountered with restricted efficiency because of the sluggish charge transfer and unexploited water matrices influence. In this study, an efficient metal to ligand charge transfer (MLCT) was successfully implanted into the Cu(I) coordinately polymeric carbon nitride framework (Cu-CNF) via the bonds of coordinated Cu(I) with organic N and few inorganic O atoms. The Cu-CNF photocatalysts were endowed with high-efficient chlortetracycline hydrochloride (CTC-HCl) removal in deionized water. To insure the feasibility of the Cu-CNF in antibiotics removal from different water matrices, a systematical exploration covering the reaction kinetics, the physicochemical stability, and the influence of specific water matrices on CTC-HCl removal was carried out by various ways. Results showed that the photo-induced MLCT route with shorter transfer distance was able to broaden light absorption of CN in the whole visible region, contributing to more available excitons and accelerating separation of the photoexcited electron-hole pairs. The boosted active oxidative species (h+, O2− and ∙OH) in porous Cu-CNF were found to promote the dechlorination and benzene ring cleavage process to favor the final mineralization of CTC-HCl molecules. Under the synergistic influence of water constituents, the removal efficiency of CTC-HCl was highest in river water (68.2%), followed by tap water (45.7%), and swine wastewater (33.1%). It was found that the existence of the high concentration NOx-N and NH3-N in the swine wastewater were responsible for the collapsed removal efficiency of CTC-HCl. Natural organic matter in river water and tap water was the main factor for the decreased CTC-HCl removal efficiency. The authors gratefully acknowledge the financial support provided by the Projects of the National Nature Science Foundation of China (No. 51708195、21776066、51521006、51739004).

Due to the symmetry breaking on surfaces of a ferroelectric crystal, the polarizations on surfaces are different from those inside the crystal. To describe this surface polarization effect which depends on the surface atomic termination, the extrapolation length is incorporated in the phase-field method based on the time-dependent Ginzburg-Landau equation to investigate different surface polarizations and their influence on the electrocaloric properties in PbTiO3 nanocylinders. The simulation results show that the extrapolation length can alter the maximum value of the adiabatic temperature change and shift its temperature location.

Electrocaloric effect (ECE) of ferroelectric materials is highly dependent on the domain transition with temperature. The effect of domain transition on the ECE of PbTiO3 (PTO) ferroelectric thin films subjected to different mismatch strains is investigated by a phase field model based on the time-dependent Ginzburg-Landau equation. The simulation results demonstrate that there exists a multiple-to-single domain transition induced by temperature in the PTO thin film. The domain transition occurs at a temperature that is much lower than Curie temperature, resulting in a giant negative ECE in the strained ferroelectric thin film. Furthermore, the domain transition temperature and the corresponding negative ECE can be tuned by the magnitude of mismatch strain. The present study suggests an effective way to obtain a giant negative ECE by domain transitions in the strained ferroelectric thin film.

The integrity of inner segment/outer segment (IS/OS) has high correlation with lower visual acuity in patients suffering from blunt trauma. An automated 3D IS/OS defect detection method based on the SD-OCT images was proposed. First, 11 surfaces were automatically segmented using the multiscale 3D graph-search approach. Second, the sub-volumes between surface 7 and 8 containing IS/OS region around the fovea (diameter of mm) were extracted and flattened based on the segmented retinal pigment epithelium layer. Third, 5 kinds of texture based features were extracted for each voxel. A KNN classifier was trained and each voxel was classified as disrupted or nondisrupted and the responding defect volume was calculated. The proposed method was trained and tested on 9 eyes from 9 trauma subjects using the leave-one-out cross validation method. The preliminary results demonstrated the feasibility and efficiency of the proposed method.

Tin oxide nanowire arrays on titania (001) have been successfully fabricated by chemical vapor deposition of Sn(O t Bu)4 precursor. The morphologies and structures of ordered SnO2 nanowires (NWs) were analyzed by cross-sectional SEM, HR-TEM and AFM. An FIB-tomography technique was applied in order to reconstruct a 3D presentation of ordered SnO2 nanowires. The achieved 3D analysis showed the spatial orientation and angles of ordered SnO2 NWs can be obtained in a one-shot experiment, and the distribution of Au catalysts showed the competition between 1D and 2D growth. The SnO2 nanowire arrays can be potentially used as a diameter- and surface-dependent sensing unit for the detection of gas- and bio-molecules.