Semiconductor Solid-Solution Nanostructures: Synthesis, Property Tailoring, and Applications

An Overview of Modeling Approaches for Compositional Control in III-V Ternary Nanowires

Modeling of the growth process is required for the synthesis of III-V ternary nanowires with controllable composition. Consequently, new theoretical approaches for the description of epitaxial growth and the related chemical composition of III-V ternary nanowires based on group III or group V intermix were recently developed. In this review, we present and discuss existing modeling strategies for the stationary compositions of III-V ternary nanowires and try to systematize and link them in a general perspective. In particular, we divide the existing approaches into models that focus on the liquid-solid incorporation mechanisms in vapor-liquid-solid nanowires (equilibrium, nucleation-limited, and kinetic models treating the growth of solid from liquid) and models that provide the vapor-solid distributions (empirical, transport-limited, reaction-limited, and kinetic models treating the growth of solid from vapor). We describe the basic ideas underlying the existing models and analyze the similarities and differences between them, as well as the limitations and key factors influencing the stationary compositions of III-V nanowires versus the growth method. Overall, this review provides a basis for choosing a modeling approach that is most appropriate for a particular material system and epitaxy technique and that underlines the achieved level of the compositional modeling of III-V ternary nanowires and the remaining gaps that require further studies.

Formation Mechanism and Bandgap Reduction of GaN-ZnO Solid-Solution Thin Films Fabricated by Nanolamination of Atomic Layer Deposition

Nanolamination of GaN and ZnO layers by atomic layer deposition (ALD) is employed to fabricate GaN-ZnO homogenous solid-solution thin films because it offers more precise control of the stoichiometry. By varying the ALD cycle ratios of GaN:ZnO from 5:10 to 10:5, the (GaN)_{1- x} (ZnO)_x films with 0.39 ≦ x ≦ 0.79 are obtained. The formation of solid solution is explained based on the atomic stacking and preferred orientation of the layers of GaN and ZnO. However, the growth rates of GaN and ZnO during the lamination process are different from those of pure GaN and ZnO films. It is found that GaN grows faster on ZnO, whereas ZnO grows slower on GaN. The density functional theory (DFT) calculations are performed using a superlattice model for GaN and ZnO laminated layers fabricated by ALD to understand the difference of density of states (DOS) and evaluate the bandgaps for various atomic configurations in the solid-solution films. The band positions are experimentally defined by ultraviolet photoelectron spectroscopy. Significant bandgap reduction of the solid solutions is observed, which can be explained by the DOS from the DFT calculations. Visible-light-driven photocatalytic hydrogen evolution is conducted to confirm the applicability of the solid-solution films.

Kinetic modeling of interfacial abruptness in axial nanowire heterostructures

Kinetic modeling of the formation of axial III-V nanowire heterostructures grown by the Au-catalyzed vapor-liquid-solid method is presented. The method is based on a combination of kinetic growth theory for different binaries at the liquid-solid interface and thermodynamics of ternary liquid and solid alloys. Non-stationary treatment of the compositional change obtained by swapping material fluxes allows us to compute the interfacial abruptness across nanowire heterostructures and leads to the following results. At high enough supersaturation in liquid, there is no segregation of dissimilar binaries in solid even for materials with strong interactions between III and V pairs, such as InGaAs. This leads to the suppression of the miscibility gaps by kinetic factors. Increasing the Au concentration widens the heterointerface at low Au content and narrows it at high Au content in a catalyst droplet. The model fits quite well the data on the compositional profiles across nanowire heterostructures based on both group III and group V interchange. Very sharp heterointerfaces in double of InAs/InP/InAs nanowire heterostructures is explained by a reduced reservoir effect due to low solubility of group V elements in liquid.

A Chemical-Pressure-Induced Phase Transition Controlled by Lone Electron Pair Activity

The chemical pressure approach offers a new paradigm for property control in functional materials. In this work, we disclose a correlation between the β → α pressure-induced phase transition in SnMoO₄ and the substitution process of Mo⁶⁺ by W⁶⁺ in SnMo_1-xW_xO₄ solid solutions (x = 0-1). Special attention is paid to discriminating the role of the lone pair Sn²⁺ cation from the structural distortive effect along the Mo/W substitution process, which is crucial to disentangle the driven force of the transition phase. Furthermore, the reverse α → β transition observed at high temperature in SnWO₄ is rationalized on the same basis as a negative pressure effect associated with a decreasing of W⁶⁺ percentage in the solid solution. This work opens a versatile chemical approach in which the types of interactions along the formation of solid solutions are clearly differentiated and can also be used to tune their properties, providing opportunities for the development of new materials.

Highly Efficient and Selective Visible-Light Driven Photoreduction of CO2 to CO by Metal-Organic Frameworks-Derived NiCoO Porous Microrods

Photocatalytic CO₂ reduction by solar energy into carbonaceous feedstock chemicals is recognized as one of the effective ways to mitigate both the energy crisis and greenhouse effect, which fundamentally relies on the development of advanced photocatalysts. Here, the exploration of porous microrod photocatalysts based on novel NiCoO solid solutions derived from bimetallic metal-organic frameworks (MOFs) is reported. They exhibit overall enhanced photocatalytic performance with both high activity and remarkable selectivity for reducing CO₂ into CO under visible-light irradiation, which are superior to most related photocatalysts reported. Accordingly, the Ni_0.2 -Co_0.8 -O microrod (MR-N_0.2 C_0.8 O) photocatalyst delivers high efficiency for photocatalytic CO₂ reduction into CO at a rate up to ≈277 µmol g^-1 h^-1 , which is ≈35 times to that of its NiO counterpart. Furthermore, they display a high selectivity of ≈85.12%, which is not only better than that of synthesized Co₃ O₄ (61.25%) but also superior to that of reported Co₃ O₄ -based photocatalysts. It is confirmed that the Co and Ni species are responsible for CO₂ CO conversion activity and selectivity, respectively. In addition, it is verified, by adjusting the Ni contents, that the band structure of NiCoO microrods can be tailored with favorable reduction band potentials, which thus enhance the selectivity toward CO₂ photoreduction.

Dispersible CdS1-xSex solid-solution nanocrystal photocatalysts: Photoinduced self-transformation synthesis and enhanced hydrogen-evolution activity

Modulating the electronic structure of Cadmium sulfide (CdS) by non-metallic elements to produce solid-solution photocatalysts serves as a potential route to improve its performance of photocatalytic hydrogen (H₂) evolution. However, exploring an effective synthetic route of CdS-based solid solution is still a great challenge. Herein, the CdS_1-xSe_x solid-solution nanocrystals were successfully synthesized by an accessible photoinduced self-transformation route, including the direct formation of dispersible CdS_1-x(SeS)_x and the in situ self-transformation of selenosulfide ((SeS)^2-) to Se^2- by photoexcited electrons. The prepared CdS_1-xSe_x solid-solution photocatalysts possess a small crystallite size of ca. 5 nm and their bandgaps can be easily tuned in a wide range of 1.84-2.28 eV by tailoring the mole ratio of Se/S. The resultant CdS_0.90Se_0.10 solid-solution photocatalyst realizes the highest H₂-production tempo of 94.6 μmol·h^-1, which is 1.6 folds higher than that of CdS. The experimental and theoretical studies supported that the incorporation of Se atoms could not only narrow the bandgap value to reinforce visible-light absorption, but also tune its electronic structure to optimize interfacial H₂-evolution dynamics, thus achieving an efficient photocatalytic H₂-production rate of the dispersible CdS_1-xSe_x solid solution. This study may deliver advanced inspirations for optimizing the electronic structure of photocatalysts towards sustainable H₂ production.

Photocatalytic Reduction of CO2 on a Bi2MoxW1-xO6 Solid Solution with Enhanced Activity

This paper reports on a Bi₂Mo_xW_1-xO₆ solid solution with excellent photocatalytic activity in CO₂ reduction. Under simulated sunlight, the Bi₂Mo_0.25W_0.75O₆ solid solution achieved a CO generation yield of ≤298.2 μmol g^-1 over 3 h, which was 2.1 and 1.5 times larger than those of pristine Bi₂WO₆ and Bi₂MoO₆, respectively. Via an in-depth study of the mechanism, this excellent photocatalytic activity was determinied to be probably due to two major contributions: (1) the formation of oxygen vacancies on the Bi₂Mo_0.25W_0.75O₆ solid solution, which provided more reactive sites for adsorption and activation of CO₂, and (2) modulation of the electronic band structure, which facilitated charge separation. Mechanistic and reaction pathways have been deeply explored and proposed.

Tuning composition of CuCo2S4-NiCo2S4 solid solutions via solvent-less pyrolysis of molecular precursors for efficient supercapacitance and water splitting

Mixed metal sulfides are increasingly being investigated because of their prospective applications for electrochemical energy storage and conversion. Their high electronic conductivity and high density of redox sites result in significant improvement of their electrochemical properties. Herein, the composition-dependent supercapacitive and water splitting performance of a series of Ni_(1−x)Cu_xCo₂S₄ (0.2 ≤ x ≤ 0.8) solid solutions prepared via solvent-less pyrolysis of a mixture of respective metal ethyl xanthate precursors is reported. The use of xanthate precursors resulted in the formation of surface clean nanomaterials at low-temperature. Their structural, compositional, and morphological features were examined by p-XRD, SEM, and EDX analyses. Both supercapacitive and electrocatalytic (HER, OER) properties of the synthesized materials significantly vary with composition (Ni/Cu molar content). However, the optimal composition depends on the application. The highest specific capacitance of 770 F g⁻¹ at a current density of 1 A g⁻¹ was achieved for Ni_0.6Cu_0.4Co₂S₄ (NCCS-2). This electrode exhibits capacitance retention (C_R) of 67% at 30 A g⁻¹, which is higher than that observed for pristine NiCo₂S₄ (838 F g⁻¹ at 1 A g⁻¹, 47% C_R at 30 A g⁻¹). On the contrary, Ni_0.4Cu_0.6Co₂S₄ (NCCS-3) exhibits the lowest overpotential of 124 mV to deliver a current density of 10 mA cm⁻². Finally, the best OER activity with an overpotential of 268 mV at 10 mA cm⁻² was displayed by Ni_0.8Cu_0.2Co₂S₄ (NCCS-1). The prepared electrodes exhibit high stability, as well as durability.

A multi-component CuCo₂S₄ and NiCo₂S₄ thiospinel solid solution is prepared over an entire range by a low-temperature solvent-less route. The synergistic effect from both thiospinels on water splitting and capacitance is studied.

Anchoring bismuth oxybromo-iodide solid solutions on flexible electrospun polyacrylonitrile nanofiber mats for floating photocatalysis

Constructing floating photocatalysts with highly efficient visible-light utilization is a promising approach for practical photocatalytic wastewater treatment. In this study, we anchored bismuth oxybromo-iodide (BiOBr_xI_1-x (0 ≤ x ≤ 1)) on flexible electrospun polyacrylonitrile (PAN) nanofiber mats to create BiOBr_xI_1-x@PAN nanofibers with tunable light absorption properties as floating photocatalysts at room temperature. As x increased, the photocatalytic activity of the BiOBr_xI_1-x@PAN nanofibers with similar loading content initially increased, and then decreased, for the degradation of bisphenol A (BPA) and methyl orange (MO) under visible-light irradiation (λ > 420 nm) conditions. The BiOBr_xI_1-x@PAN (0 < x < 1) nanofibers exhibited better photocatalytic performance compared to the BiOBr@PAN and BiOI@PAN nanofibers. Under visible-light irradiation, the BPA degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 1.9 times higher than that of the BiOI@PAN nanofibers, while the BiOBr@PAN nanofibers had no noticeable degradation performance. The MO degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 2.5 and 3.2 times higher than that of the BiOBr@PAN and BiOI@PAN nanofibers, respectively. The enhanced performance possibly originated from a balance between the light absorption and redox capabilities, along with efficient separation of electron-hole pairs in the BiOBr_0.5I_0.5@PAN nanofibers, as determined by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectra analysis of the valence bands, and photocurrent response characterization. Compared to the powder structures, the BiOBr_xI_1-x@PAN nanofibers showed enhanced performance due to the excellent dispersion and immobilization of the BiOBr_xI_1-x solid solution, which provided more active sites during photocatalytic degradation. In addition, their flexible self-supporting structures allowed for floating photocatalysis near the water surface. They could be reused directly without separation and maximized the absorption of visible light during the photocatalytic reaction. Therefore, these solid-solution-based floatable nanofiber photocatalysts are good potential candidates for wastewater treatment applications.

Interfacial profile of axial nanowire heterostructures in the nucleation limited regime

We report thermodynamic modeling of the formation of axial III–V nanowire heterostructures grown by the self-catalyzed and Au-catalyzed vapor–liquid–solid methods.

Structural Variations of Metal Oxide-Based Electrocatalysts for Oxygen Evolution Reaction

Electrocatalytic oxygen evolution reaction (OER), an important electrode reaction in electrocatalytic and photoelectrochemical cells for a carbon-free energy cycle, has attracted considerable attention in the last few years. Metal oxides have been considered as good candidates for electrocatalytic OER because they can be easily synthesized and are relatively stable during the OER process. However, inevitable structural variations still occur to them due to the complex reaction steps and harsh working conditions of OER, thus impending the further insight into the catalytic mechanism and rational design of highly efficient electrocatalysts. The aim of this review is to disclose the current research progress toward the structural variations of metal oxide-based OER electrocatalysts. The origin of structural variations of metal oxides is discussed. Based on some typical oxides performing OER activity, the external and internal factors that influence the structural stability are summarized and then some general approaches to regulate the structural variation process are provided. Some operando methods are also concluded to monitor the structural variation processes and to identify the final active structure. Additionally, the unresolved problems and challenges are presented in an attempt to get further insight into the mechanism of structural variations and establish a rational structure-catalysis relationship.

Solid Solution Metal Chalcogenides for Sodium-Ion Batteries: The Recent Advances as Anodes

The sodium-ion battery (SIB) has attracted ever growing attention as a promising alternative of the lithium-ion battery (LIB). Constructing appropriate anode materials is critical for speeding up the application of SIB. This review aims at guiding anode design from the material's perspective, and specifically focusing on solid solution metal chalcogenide anode. The sodium ion storage mechanisms of a solid solution metal chalcogenide anode is overviewed on basis of the elements it is composed of, and discusses how the solid solution character alters the electrochemical performances through diffusion and surface-controlled processes. In addition, by classifying solid solution metal chalcogenide as cation and anion, their recent applications are updated, and understanding the roles of guest elements in improving the electrochemical behaviors of a solid solution metal chalcogenide is carried out. After that, discussion of possible strategies to further optimize these anode materials in the future, flowing from crystal structure design to morphology control and finally to the intimacy improvement between conductive matrix and solid solution metal chalcogenide are also provided.

Assembling your nanowire: an overview of composition tuning in ternary III-V nanowires

The ability to grow defect-free nanowires in lattice-mismatched material systems and to design their properties has made them ideal candidates for applications in fields as diverse as nanophotonics, nanoelectronics and medicine. After studying nanostructures consisting of elemental and binary compound semiconductors, scientists turned their attention to more complex systems-ternary nanowires. Composition control is key in these nanostructures since it enables bandgap engineering. The use of different combinations of compounds and different growth methods has resulted in numerous investigations. The aim of this review is to present a survey of the material systems studied to date, and to give a brief overview of the issues tackled and the progress achieved in nanowire composition tuning. We focus on ternary III _x III_1-x V nanowires (AlGaAs, AlGaP, AlInP, InGaAs, GaInP and InGaSb) and IIIV _x V_1-x nanowires (InAsP, InAsSb, InPSb, GaAsP, GaAsSb and GaSbP).

Solventless synthesis of nanospinel Ni1−xCoxFe2O4 (0 ≤ x ≤ 1) solid solutions for efficient electrochemical water splitting and supercapacitance

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites. However, solid solutions have been predominantly prepared via wet chemical routes, which involve the use of harmful and/or expensive chemicals. In the present study, a facile, inexpensive and environmentally benign solventless route is employed for the composition-controlled synthesis of nanoscopic Ni_1−xCo_xFe₂O₄ (0 ≤ x ≤ 1) solid solutions. The physicochemical characterization of the samples was performed by p-XRD, SEM, EDX, XPS, TEM, HRTEM and UV-Vis techniques. A systematic investigation was also carried out to elucidate the electrochemical performance of the prepared nanospinels towards energy generation and storage. Based on the results of CV, GCD, and stability tests, the Ni_0.4Co_0.6Fe₂O₄ electrode showed the highest performance for the supercapacitor electrode exhibiting a specific capacitance of 237 F g⁻¹, superior energy density of 10.3 W h kg⁻¹ and a high power density with a peak value of 4208 W kg⁻¹, and 100% of its charge storage capacity was retained after 4000 cycles with 97% coulombic efficiency. For HER, the Ni_0.6Co_0.4Fe₂O₄ and CoFe₂O₄ electrodes showed low overpotentials of 168 and 169 mV, respectively, indicating better catalytic activity. For OER, the Ni_0.8Co_0.2Fe₂O₄ electrode exhibited a lower overpotential of 320 mV at a current density of 10 mA cm⁻², with a Tafel slope of 79 mV dec⁻¹, demonstrating a fast and efficient process. These results indicated that nanospinel ferrite solid solutions could be employed as promising electrode materials for supercapacitor and water splitting applications.

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites.

Surface energy driven miscibility gap suppression during nucleation of III–V ternary alloys

We have explained how the surface energy influences the miscibility gap during nucleation from a liquid melt.

Zn-rich (GaN)1−x(ZnO)x: a biomedical friend?

The synthesis of (GaN)_1−x(ZnO)_x with the assistance of high-gravity using a green approach for the first time, with the application of delivering pCRISPR.

Role of Thermodynamics and Kinetics in the Composition of Ternary III-V Nanowires

We explain the composition of ternary nanowires nucleating from a quaternary liquid melt. The model we derive describes the evolution of the solid composition from the nucleated-limited composition to the kinetic one. The effect of the growth temperature, group V concentration and Au/III concentration ratio on the solid-liquid dependence is studied. It has been shown that the solid composition increases with increasing temperature and Au concentration in the droplet at the fixed In/Ga concentration ratio. The model does not depend on the site of nucleation and the geometry of monolayer growth and is applicable for nucleation and growth on a facet with finite radius. The case of a steady-state (or final) solid composition is considered and discussed separately. While the nucleation-limited liquid-solid composition dependence contains the miscibility gap at relevant temperatures for growth of In_xGa_1−xAs NWs, the miscibility gap may be suppressed completely in the steady-state growth regime at high supersaturation. The theoretical results are compared with available experimental data via the combination of the here described solid-liquid and a simple kinetic liquid-vapor model.

Photocatalytic H2 Production from Water by Metal-free Dye-sensitized TiO2 Semiconductors: The Role and Development Process of Organic Sensitizers

The utilization of solar energy to produce hydrogen from water is showing increased importance and desirability in the field of artificial photosynthesis to produce clean and sustainable fuels. In a typical three-component dye-sensitized semiconductor system for photocatalysis, the dye sensitizer plays an essential role of energy antenna for harvesting visible light and promoting the reduction reaction to generate hydrogen. In recent decades, a lot of attention has focused on metal-free organic sensitizers, which have the advantages of low cost, high molar extinction coefficient, good modifiability and, most importantly, ability to avoid the use of noble metal ions. This Review enumerates the design strategies, specific properties and photocatalytic performances of metal-free sensitizers in the past 30 years and concludes their evolution process. The advantages of different types of metal-free sensitizers are highlighted and the instructively enlightening experiences are systematic summarized.

Photocatalysts for H2 Generation from Starburst Triphenylamine/Carbazole Donor-Based Metal-Free Dyes and Porous Anatase TiO2 Cube

A series of novel triphenylamine/carbazole-based D-D-π-π-A dyes DH1-4 and a mesoporous anatase cubic "microcage" TiO₂ material (denoted as MC-TiO₂ ) were synthesized and combined to obtain dye-sensitized photocatalysts (denoted as DHn/Pt/MC-TiO₂ , n=1-4). These catalysts showed better performances in visible-light-driven H₂ evolution from water than DHn/Pt/P25-TiO₂ catalysts based on commercial P25-TiO₂ bulk semiconductor under similar conditions. Compared with P25-TiO₂ particles, the porous MC-TiO₂ had a large Brunauer-Emmett-Teller surface area, porosity, and exposed {0 0 1} crystal plane, which greatly contributed to the photocatalytic activity. The optimized DH2/Pt/MC-TiO₂ photocatalyst exhibited an attractive H₂ production rate (16.28 mmol g^-1  h^-1 based on catalyst mass), and the optimized DH4/Pt/MC-TiO₂ photocatalyst showed good stability [turnover number (TON) of 16 699 in 105 h based on dye number], which represents one of the best performances among all reported visible-light-driven heterogeneous catalytic systems. Compared with the other dyes in this series, the high H₂ production rate of DH2 on Pt/MC-TiO₂ can be attributed to its size-matching effect and thus high dye loading amount, whereas the high TON and durability of DH4/Pt/MC-TiO₂ are probably related to the rapid regeneration kinetics of DH4.

Carbon Sphere Template Derived Hollow Nanostructure for Photocatalysis and Gas Sensing

As a green and preferred technology for energy crisis and environmental issues, continuous research on photocatalysis and gas sensing has come forth at an explosive rate. Thus far, promising synthetic methods have enabled various designs and preparations of semiconductor-based nanostructure which have shown superior activity. This review summarized various synthetic routines toward carbon sphere template derived hollow nanostructures and their successful attempts in synthesize doping, solid solution, heterostructure, and surface modified nanostructures for heterogeneous photocatalysis and gas sensing. Moreover, the challenges and future prospects are briefly discussed. It is eagerly anticipated that this review may broaden the view and in-depth understanding of carbon sphere template derived hollow nanostructures while expected to have further progresses in heterogeneous photocatalysis, gas sensing and other related fields which will make great contributions to their application.

Band-Gap Tunable 2D Hexagonal (GaN)1-x(ZnO)x Solid-Solution Nanosheets for Photocatalytic Water Splitting

A (GaN)_1-x(ZnO)_x solid solution as a promising visible-light-driven photocatalyst for overall water splitting has attracted extensive attention. In this work, we proposed a template reactive strategy toward the synthesis of band-gap tunable 2D (GaN)_1-x(ZnO)_x nanosheets as thin as 14 nm to reduce the carrier transportation path and thus efficiently decrease the recombination of electrons and holes. It is demonstrated that the template strategy enables an ideal morphology and structure transformation from hexagonal 2D ZnGa₂O₄ nanosheets to 2D (GaN)_1-x(ZnO)_x nanosheets in the nitridation process. After the modification of 1 wt % of Rh cocatalyst, the flowerlike (GaN)_0.89(ZnO)_0.11 nanosheets show an enhanced hydrogen evolution in pure water (pH 4.5).

Redistribution of native defects and photoconductivity in ZnO under pressure

Control and design of native defects in semiconductors are extremely important for industrial applications. Here, we investigated the effect of external hydrostatic pressure on the redistribution of native defects and their impact on structural phase transitions and photoconductivity in ZnO. We investigated morphologically distinct rod- (ZnO-R) and flower-like (ZnO-F) ZnO microstructures where the latter contains several native defects namely, oxygen vacancies, zinc interstitials and oxygen interstitials. Synchrotron X-ray diffraction reveals pressure-induced irreversible phase transformation of ZnO-F with the emergence of a hexagonal metallic Zn phase due to enhanced diffusion of interstitial Zn during decompression. In contrast, ZnO-R undergoes a reversible structural phase transition displaying a large hysteresis during decompression. We evidenced that the pressure-induced strain and inhomogeneous distribution of defects play crucial roles at structural phase transition. Raman spectroscopy and emission studies further confirm that the recovered ZnO-R appears less defective than ZnO-F. It resulted in lower photocurrent gain and slower photoresponse during time-dependent transient photoresponse with the synergistic application of pressure and illumination (ultra-violet). While successive pressure treatments improved the photoconductivity in ZnO-R, ZnO-F failed to recover even its ambient photoresponse. Pressure-induced redistribution of native defects and the optoelectronic response in ZnO might provide new opportunities in promising semiconductors.

Creation of Centimeter-Sized 2 D Crystalline Film by Crystallization of Homopolymer in Solution

The 2 D assembly of polymers to form free-standing and large crystalline films is quite appealing but very challenging. Although there have been some works using interface templates, reports of in situ assembly in solution are still rare. Herein, a simple strategy is developed for the creation of a free-standing and centimeter-sized 2 D crystalline polymer film through crystallization of an amphiphilic brush polydiacetylene (PDA) in solution. The film exhibits good shape memory, a low dielectric constant, and good carrier mobility. This strategy may be applied extensively to produce a variety of other macroscopic 2 D crystalline polymer films for applications in electronics, catalysis, and so on.

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Composition and Band Gap Tailoring of Crystalline (GaN)1- x(ZnO) x Solid Solution Nanowires for Enhanced Photoelectrochemical Performance

Photoelectrochemical water splitting has emerged as an effective artificial photosynthesis technology to generate clean energy of H₂ from sunlight. The core issue in this reaction system is to develop a highly efficient photoanode with a large fraction of solar light absorption and greater active surface area. In this work, we take advantage of energy band engineering to synthesize (GaN)_{1- x}(ZnO) _x solid solution nanowires with ZnO contents ranging from 10.3% to 47.6% and corresponding band gap tailoring from 3.08 to 2.77 eV on the basis of the Au-assisted VLS mechanism. The morphology of nanowires directly grown on the conductive substrate facilitates the charge transfer and simultaneously improves the surface reaction sites. As a result, a photocurrent approximately 10 times larger than that for a conventional powder-based photoanode is obtained, which indicates the potential of (GaN)_{1- x}(ZnO) _x nanowires in the preparation of superior photoanodes for enhanced water splitting. It is anticipated that the water-splitting capability of (GaN)_{1- x}(ZnO) _x nanowire can be further increased through alignment control for enhanced visible light absorption and reduction of charge transfer resistance.