A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO2 nanowires and amorphous Fe2O3 nanotubes grown on flexible carbon fabric is first designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm3 and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows.

Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO2 Nanowires and Fe2O3 Nanotubes

One-dimensional TiO2 nanostructured surface heterostructures (1D TiO2NSHs) have been comprehensively studied during the past two decades because of the possible practical applications in various fields, including photocatalysis, dye-sensitized solar cells, sensors, lithium batteries, biomedicine, catalysis, and supercapacitors. Combining extensive advancements in materials science and nanotechnology, a 1D TiO2NSH material with well-controlled size, morphology, and composition has been designed and synthesized. More importantly, its superior properties, including a high aspect ratio structure, chemical stability, large specific surface area, excellent electronic or ionic charge transfer, and a specific interface effect, have attracted a great deal of interest in improving current performance and exploring new applications. In this tutorial review, we introduce the characteristics of 1D TiO2 nanostructures, the design principles for the fabrication of 1D TiO2NSHs, and we also summarize the recent progress in developing synthesis methods and applications of 1D TiO2NSHs in different fields. The relationship between the secondary phase and the 1D TiO2 nanostructure and between the performance in applications and the excellent physical properties of 1D TiO2NSHs are also discussed.

Recent progress in design, synthesis, and applications of one-dimensional TiO2 nanostructured surface heterostructures: a review

Semiconductor photocatalysts have received much attention in recent years due to their great potentials for the development of renewable energy technologies, as well as for environmental protection and remediation. The effective harvesting of solar energy and suppression of charge carrier recombination are two key aspects in photocatalysis. The formation of heterostructured photocatalysts is a promising strategy to improve photocatalytic activity, which is superior to that of their single component photocatalysts. This Feature Article concisely summarizes and highlights the state-of-the-art progress of semiconductor/semiconductor heterostructured photocatalysts with diverse models, including type-I and type-II heterojunctions, Z-scheme system, p–n heterojunctions, and homojunction band alignments, which were explored for effective improvement of photocatalytic activity through increase of the visible-light absorption, promotion of separation, and transportation of the photoinduced charge carries, and enhancement of the photocatalytic stability.

State‐of‐the‐Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance

We herein demonstrate self-doping of the CO32– anionic group into a wide bandgap semiconductor Bi2O2CO3 realized by a one-pot hydrothermal technique. The photoresponsive range of the self-doped Bi2O2CO3 can be extended from UV to visible light and the band gap can be continuously tuned. Density functional theory (DFT) calculation results demonstrate that the foreign CO32– ions are doped in the caves constructed by the four adjacent CO32– ions and the CO32– self-doping can effectively narrow the band gap of Bi2O2CO3 by lowering the conduction band position and meanwhile generating impurity level. The photocatalytic performance is evaluated by monitoring NO removal from the gas phase, photodegradation of a colorless contaminant (bisphenol A, BPA) in an aqueous solution, and photocurrent generation. In comparison with the pristine Bi2O2CO3 which is not sensitive to visible light, the self-doped Bi2O2CO3 exhibits drastically enhanced visible-light photoreactivity, which is also superior to that of many other ...

Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-Functional Applications of High-Performance CO32–-Doped Bi2O2CO3

Defect engineering in photocatalytic materials

Near-infrared active photocatalytic properties of Bi2 WO6 nanosheets owing to the oxygen vacancies of the Bi2 WO6 nanosheets are reported. The broad spectrum photocatalyst, Bi2 WO6 -TiO2 nanobelt heterostructures, are obtained by assembling Bi2 WO6 nanocrystals on TiO2 nanobelts. The active light band of the novel hybrid photocatalyst with high photocatalytic activity covers full-spectrum solar light including the UV, visible, and near-infrared ranges.

A Bi2WO6‐Based Hybrid Photocatalyst with Broad Spectrum Photocatalytic Properties under UV, Visible, and Near‐Infrared Irradiation

Renewable, cost-effective and eco-friendly electrode materials have attracted much attention in the energy conversion and storage fields. Bagasse, the waste product from sugarcane that mainly contains cellulose derivatives, can be a promising candidate to manufacture supercapacitor electrode materials. This study demonstrates the fabrication and characterization of highly porous carbon aerogels by using bagasse as a raw material. Macro and mesoporous carbon was first prepared by carbonizing the freeze-dried bagasse aerogel; consequently, microporous structure was created on the walls of the mesoporous carbon by chemical activation. Interestingly, it was observed that the specific surface area, the pore size and distribution of the hierarchical porous carbon were affected by the activation temperature. In order to evaluate the ability of the hierarchical porous carbon towards the supercapacitor electrode performance, solid state symmetric supercapacitors were assembled, and a comparable high specific capacitance of 142.1 F g−1 at a discharge current density of 0.5 A g−1 was demonstrated. The fabricated solid state supercapacitor displayed excellent capacitance retention of 93.9% over 5000 cycles. The high energy storage ability of the hierarchical porous carbon was attributed to the specially designed pore structures, i.e., co-existence of the micropores and mesopores. This research has demonstrated that utilization of sustainable biopolymers as the raw materials for high performance supercapacitor electrode materials is an effective way to fabricate low-cost energy storage devices.

Hierarchical porous carbon aerogel derived from bagasse for high performance supercapacitor electrode

A novel scaly Sn3O4/TiO2 nanobelt heterostructured photocatalyst was fabricated via a facile hydrothermal route. The scaly Sn3O4 nanoflakes can be synthesized in situ and assembled on surface coarsened TiO2 nanobelts through a hydrothermal process. The morphology and distribution of Sn3O4 nanoflakes can be well-controlled by simply tuning the Sn/Ti molar ratio of the reactants. Compared with single phase nanostructures of Sn3O4 and TiO2, the scaly hybrid nanobelts exhibited markedly enhanced photoelectrochemical (PEC) response, which caused higher photocatalytic hydrogen evolution even without the assistance of Pt as a co-catalyst, and enhanced the degradation ability of organic pollutants under both UV and visible light irradiation. In addition to the increased exposure of active facets and broad light absorption, the outstanding performance is ascribed to the matching energy band structure between Sn3O4 and TiO2 at the two sides of the heterostructure, which efficiently reduces the recombination of photo-excited electron–hole pairs and prolongs the lifetime of charge carriers. Both photocatalytic assessment and PEC tests revealed that Sn3O4/TiO2 heterostructures with a molar ratio of Sn/Ti of 2/1 exhibited the highest photocatalytic activity. This study provides a facile and low-cost method for the large scale production of Sn3O4 based materials in various applications.

Synthesis of scaly Sn3O4/TiO2 nanobelt heterostructures for enhanced UV-visible light photocatalytic activity

A SnO2 gas sensor was prepared by a two-step oxidation process whereby a Sn(II) precursor was partially oxidized by a hydrothermal process and the resulting Sn3O4 nanoplates were thermally oxidized to yield SnO2 nanoplates. The SnO2 sensor was selective and responsive toward ethanol at a temperature as low as 43 °C. This low sensing temperature stems from the rapid charge transport within SnO2 and from the presence of high-energy (001) facets available for oxygen chemisorption. SnO2/TiO2 nanobelt heterostructures were fabricated by a similar two-step process in which TiO2 nanobelts acted as support for the epitaxial growth of intermediate Sn3O4. At temperatures ranging from 43 to 276 °C, the response of these branched nanobelts is more than double the response of SnO2 for ethanol detection. Our observations demonstrate the potential of low-cost SnO2-based sensors with controlled morphology and reactive facets for detecting gases around room temperature.

High-Energy Faceted SnO2-Coated TiO2 Nanobelt Heterostructure for Near-Ambient Temperature-Responsive Ethanol Sensor

NaNbO3 cubes and nanowires have been synthesized by a hydrothermal-based method utilizing thin Nb foil and low-concentration NaOH solution with the presence of H2O2. The Na2Nb2O6·H2O precursor can be obtained under hydrothermal conditions at 200 °C for only 4 h. Both long-time hydrothermal treatment and calcination on the precursor nanowires can realize the transition from Na2Nb2O6·H2O nanowires to NaNbO3 crystalline particles. However, the crystalline phases of the two products are different. NaNbO3 microcubes obtained by long-time hydrothermal treatment are in the antiferroelectric phase with space group Pbma, while NaNbO3 nanowires obtained by annealing Na2Nb2O6·H2O at 500 °C for 3 h are in the ferroelectric phase with space group P21ma. The experimental results from X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution electron microscopy (HRTEM) and Raman spectroscopy proved the difference between the crystalline phases of NaNbO3 microcubes and nanowires. Piezoelectric force microscopy (PFM) analysis proved that NaNbO3 nanowires exhibit piezoelectricity, while no piezoelectric response can be detected for NaNbO3 microcubes synthesized by direct hydrothermal treatment.

Guangwei Yu

Papers

A Bi2WO6‐Based Hybrid Photocatalyst with Broad Spectrum Photocatalytic Properties under UV, Visible, and Near‐Infrared Irradiation

Hierarchical porous carbon aerogel derived from bagasse for high performance supercapacitor electrode

Synthesis of scaly Sn3O4/TiO2 nanobelt heterostructures for enhanced UV-visible light photocatalytic activity

High-Energy Faceted SnO2-Coated TiO2 Nanobelt Heterostructure for Near-Ambient Temperature-Responsive Ethanol Sensor

Synthesis, structure, and piezoelectric properties of ferroelectric and antiferroelectric NaNbO3 nanostructures