Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Nano‐photocatalytic Materials: Possibilities and Challenges

Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor–semiconductor heterojunction, the semiconductor–metal heterojunction, the semiconductor–carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degradation of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.

Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

The morphologies of silver nanocrystals have been successfully tuned from wire to versatile rod, cube, and sphere by varying the molecular structure of polyols. Effects of crystal shape on the catalytic performance of silver for hydrogen generation from HCHO solution have also been investigated. It was found that silver nanocubes were more active than nanorods, nanowires, and nanospheres.

Morphology-controlled Preparation of Silver Nanocrystals and Their Application in Catalysis

Here, we demonstrate the controlled construction of FeVO4 nanobelts and nanosheets with selectively exposed {010} and {001} facets, respectively. More importantly, the FeVO4 nanobelts exhibit more efficient electrocatalytic activities than the nanosheets, with a low overpotential of 240 mV (10 mA cm−2) and durability (36 h) towards the oxygen evolution reaction (OER). Further studies clearly reveal that the improved activity of FeVO4 nanobelts is mainly attributed to the open surface structure and favorable atomic arrangements of {010} facets, which assure rapid charge transfer and Fe–V dual-active sites for the OER.

Engineering the surface atomic structure of FeVO4 nanocrystals for use as highly active and stable electrocatalysts for oxygen evolution

A facile hydrothermal reaction has been developed for the large-scale growth of Bi2MoO6 nanosheets on conductive substrates with robust adhesion as high performance electrodes for electrochemical capacitors. It was found that the nickel foam facilitates the formation of a uniform nanosheet array with fast electron and ion transportation, a large electroactive surface area and an excellent structural stability. As a result, it shows a specific capacitance of 37.3 F g−1 even at a current density of 2 A g−1 and a high cycling stability with 89% retention of its initial specific capacitance after 1000 cycles in 1 M KCl solution. These results provide a way of fabricating Bi2MoO6 nanosheet arrays as efficient electrodes for electrochemical capacitors.

Facile growth of Bi2MoO6 nanosheet arrays on Ni foam as an electrode for electrochemical applications

The nanoporous bismuth tungsten oxide (Bi2WO6) photoanodes are synthesized via a facile drop-casting strategy for one-step fabrication. The Bi2WO6 photoanode exhibits a significantly improved solar-light photoelectrochemical capability for water oxidation. The photocurrent density is nearly 10 times higher than the traditional particle photoanodes. In addition, a novel synchronous illumination X-ray photoelectron spectroscopy (SIXPS) was employed to directly identify the charge separation and electrons transfer in the nanoporous Bi2WO6 photoanodes, which clearly reveal that the electron transfer from the sites consisted of Bi and W atoms to the site composed of O atoms. These demonstrations provide further new insights into the origin of high efficiency in nanoporous photoanodes, which may be promising for rational construction of solar conversion and storage devices.

Facile Fabrication of Nanoporous Bi2WO6 Photoanodes for Efficient Solar Water Splitting

Herein, we demonstrated a one-step ammonia treatment for fabricating homostructural Ta3N5 nanotube/nanoparticle photoanodes with a top-open structure. Compared with the relatively low activities of traditional Ta3N5 nanotube photoanode, this homo-photoanode exhibited a remarkably enhanced photocurrent density (1.58 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE)). Moreover, after the decoration of Co(OH)x cocatalyst, the photocurrent density could be further increased up to 8.73 mA cm−2 at 1.23 VRHE, accompanying with the significantly improved water oxidation stability as well as an evident negative shift of onset-potential (200 mV). More detailed studies reveal that the significantly promoted PEC activities should be attributed to the matched bandgaps between Ta3N5 nanotube and nanoparticle as well as the ordered top-open nanoarchitecture, which could accelerate charge separation and provide more active sites for water oxidation. Thereby, the construction of homostructural semiconductor photoanodes should be highly promising for promoting the development of PEC water splitting for practical applications.

Yingpu Bi

Papers

Morphology-controlled Preparation of Silver Nanocrystals and Their Application in Catalysis

Engineering the surface atomic structure of FeVO4 nanocrystals for use as highly active and stable electrocatalysts for oxygen evolution

Facile growth of Bi2MoO6 nanosheet arrays on Ni foam as an electrode for electrochemical applications

Facile Fabrication of Nanoporous Bi2WO6 Photoanodes for Efficient Solar Water Splitting

Homostructural Ta3N5 nanotube/nanoparticle photoanodes for highly efficient solar-driven water splitting