p-n异质结NiO/TiO2纳米复合材料的构建及应用研究进展

TiO_2和NiO分别作为n型和p型半导体材料,通过复合构建p-n异质结NiO/TiO_2纳米复合材料可以促进光生电子-空穴对的分离,从而提高光电性能。综述了不同形貌的p-n异质结NiO/TiO_2纳米复合材料的构建,如纳米球、纳米棒和纳米带等,以及其在光催化、锂离子电池、染料敏化太阳能电池和传感器等领域中的最新研究进展。     

Enhanced Photocatalytic Performances of CeO2/TiO2 Nanobelt Heterostructures

CeO₂/TiO₂ nanobelt heterostructures are synthesized via a cost‐effective hydrothermal method. The as‐prepared nanocomposites consist of CeO₂ nanoparticles assembled on the rough surface of TiO₂ nanobelts. In comparison with P25 TiO₂ colloids, surface‐coarsened TiO₂ nanobelts, and CeO₂ nanoparticles, the CeO₂/TiO₂ nanobelt heterostructures exhibit a markedly enhanced photocatalytic activity in the degradation of organic pollutants such as methyl orange (MO) under either UV or visible light irradiation. The enhanced photocatalytic performance is attributed to a novel capture–photodegradation–release mechanism. During the photocatalytic process, MO molecules are captured by CeO₂ nanoparticles, degraded by photogenerated free radicals, and then released to the solution. With its high degradation efficiency, broad active light wavelength, and good stability, the CeO₂/TiO₂ nanobelt heterostructures represent a new effective photocatalyst that is low‐cost, recyclable, and will have wide application in photodegradation of various organic pollutants. The new capture–photodegradation–release mechanism for improved photocatalysis properties is of importance in the rational design and synthesis of new photocatalysts.     

Enhanced Photocatalytic Property of Reduced Graphene Oxide/TiO2 Nanobelt Surface Heterostructures Constructed by an In Situ Photochemical Reduction Method

A facile method is proposed to assemble graphene oxide (GO) on the surface of a TiO₂ nanobelt followed by an in situ photocatalytic reduction to form reduced graphene oxide (rGO)/TiO₂ nanobelt surface heterostructures. The special colloidal properties of GO and TiO₂ nanobelt are exploited as well as the photocatalytic properties of TiO₂. Using water–ethanol solvent mixtures, GO nanosheets are tightly wrapped around the surface of the TiO₂ nanobelts through an aggregation process and are then reduced in situ under UV‐light irradiation to form rGO/TiO₂ nanobelt surface heterostructures. The heterostructures enhance the separation of the photoinduced carriers, which results in a higher photocurrent due to the special electronic characteristics of rGO. Compared to TiO₂ nanobelts, the rGO/TiO₂ nanobelt surface heterostructures possess higher photocatalytic activity for the degradation of methyl orange and for the production of hydrogen from water, as well as excellent recyclability, with no loss of activity over five cycles.     

Enhancement of photocatalytic properties of TiO2 nanobelts through surface-coarsening and surface nanoheterostructure construction

In this work, heterostructures were obtained by uniformly assembling NiO nanoparticles on the surface-coarsened TiO₂ nanobelts through a precipitation process. The uniform assembling of NiO nanoparticles led to a large number of nano-p-n-junction heterostructures on the surface of the TiO₂ nanobelts, where NiO and TiO₂ are p- and n-type semiconductors, respectively. Compared with both pure NiO nanoparticles and TiO₂ nanobelts, NiO nanoparticles/TiO₂ surface-coarsened nanobelt heterostructured composite exhibited a greatly enhanced photocatalytic activity in the decomposition of a model dye compound methyl orange under ultraviolet light irradiation. It was argued that the nano-p-n-junctions effectively reduce the recombination of electrons and holes, thus resulting in enhanced photocatalytic property of the heterostructured composites. The better performance of the surface-coarsened nanobelts is due to the increased photo absorption and production of charge carriers, which renders the composites with further enhanced photocatalytic performance. The established approach allows the control of the nano-p-n junction heterostructure on the nanobelts, and hence, their photocatalytic effect.     

Fundamentals of TiO2 Photocatalysis: Concepts,Mechanisms, and Challenges

Photocatalysis has been widely applied in various areas, such as solar cells, water splitting, and pollutant degradation. Therefore, the photochemical mechanisms and basic principles of photocatalysis, especially TiO₂ photocatalysis, have been extensively investigated by various surface science methods in the last decade, aiming to provide important information for TiO₂ photocatalysis under real environmental conditions. Recent progress that provides fundamental insights into TiO₂ photocatalysis at a molecular level is highlighted. Insights into the structures of TiO₂ and the basic principles of TiO₂ photocatalysis are discussed first, which provides the basic concepts of TiO₂ photocatalysis. Following this, details of the photochemistry of three important molecules (oxygen, water, methanol) on the model TiO₂ surfaces are presented, in an attempt to unravel the relationship between charge/energy transfer and bond breaking/forming in TiO₂ photocatalysis. Lastly, challenges and opportunities of the mechanistic studies of TiO₂ photocatalysis at the molecular level are discussed briefly, as well as possible photocatalysis models.     

Graphene in Photocatalysis: A Review

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets‐supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis‐related properties of graphene and its derivatives, and design rules and synthesis methods of graphene‐based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi‐junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H₂ production, and CO₂ reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene‐based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.     

Extension of the Stöber Method to Construct Mesoporous SiO2 and TiO2 Shells for Uniform Multifunctional Core–Shell Structures

Core–shell nanoparticles (CSNs) have attracted considerable attention because of their promising applications in a wide range of fields. Recently, substantial efforts have been focused on the development of facile and versatile methods for preparing CSNs with mesoporous SiO₂ or TiO₂ shells because of their fascinating properties, such as high surface area, large pore channels and high pore volume. This Research News reviews the recent progress in facile, versatile and reproducible approaches which are simply extended from the well‐known Stöber method to construct mesoporous SiO₂ and TiO₂ shells for uniform multifunctional core–shell nanostructures. Several strategies, including the surfactant‐templating process, the long‐chain organosilane‐assisted approach, the phase transfer assisted surfactant‐templating process, and the kinetics‐controlled coating approach, are discussed. In addition, new trends in this field for the creation of multifunctional CSNs and novel nanostructures are highlighted.     

Synthesis of Few‐Layer MoS2 Nanosheet‐Coated TiO2 Nanobelt Heterostructures for Enhanced Photocatalytic Activities

MoS₂ nanosheet‐coated TiO₂ nanobelt heterostructures—referred to as TiO₂@MoS₂—with a 3D hierarchical configuration are prepared via a hydrothermal reaction. The TiO₂ nanobelts used as a synthetic template inhibit the growth of MoS₂ crystals along the c‐axis, resulting in a few‐layer MoS₂ nanosheet coating on the TiO₂ nanobelts. The as‐prepared TiO₂@MoS₂ heterostructure shows a high photocatalytic hydrogen production even without the Pt co‐catalyst. Importantly, the TiO₂@MoS₂ heterostructure with 50 wt% of MoS₂ exhibits the highest hydrogen production rate of 1.6 mmol h^?1g^?1. Moreover, such a heterostructure possesses a strong adsorption ability towards organic dyes and shows high performance in photocatalytic degradation of the dye molecules.     

Protonated Titanates and TiO2 Nanostructured Materials: Synthesis,Properties, and Applications

Tubular and fibrous nanostructures of titanates have recently been synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO₂ are reviewed. The crystal structures, morphologies, and mechanism of formation of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar‐cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.     

Enhanced nanocatalysts

Rapid development of nanofabrication techniques has created many different types of advanced nanosized semiconductors. Photocatalytic materials used to degrade organic and inorganic pollutants now include, in addition to TiO₂, ZnO, Fe₂O₃, WO₃, MoS₂, and CdS. Nanoparticles’ unique properties, e.g. surface to volume ratio and quantum effects, continue to improve and expand photocatalysis’ role in areas like environmental remediation, odor control, sterilization, and renewable energy. Controlling semiconductor size, shape, composition, and microstructure promises to benefit future research and applications in these fields. This review examines recent advances at the interface of nanoscience and photocatalysis, especially pertaining to nanocatalyst enhancements, for current and future environmental applications.     

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

Semiconductor‐based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g‐C₃N₄) for visible‐light photocatalytic water splitting, g‐C₃N₄‐based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g‐C₃N₄‐based photocatalysts, including the fabrication and nanostructure design of pristine g‐C₃N₄, bandgap engineering through atomic‐level doping and molecular‐level modification, and the preparation of g‐C₃N₄‐based semiconductor composites. Also, the photo­catalytic applications of g‐C₃N₄‐based photocatalysts in the fields of water splitting, CO₂ reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non‐noble‐metal cocatalysts, and Z‐scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g‐C₃N₄‐based photocatalysts are highlighted.     

Titanium glycolate-derived TiO2 nanomaterials: Synthesis and applications

Titanium oxide (TiO₂) is one of the most widely studied materials due to its fascinating properties and versatile applications in environmental and energy fields ranging from photocatalysis to solar cells and lithium ion batteries. The significance and variety of these applications have attracted great attention and spurred substantial progress in the synthesis and fundamental understanding of TiO₂-based nanomaterials, nanocomposites, and nanoderivatives. This review summarizes the recent advances in the design and preparation of TiO₂-based nanomaterials, nanocomposites, and nanoderivatives obtained from titanium glycolate precursor. Utilizing different fabrication strategies, titanium glycolate precursor with controllable morphology and size has been successfully produced, and it can be directly transformed into crystalline TiO₂ nanomaterials through diverse post-treatments, including calcination thermal-decomposition, and refluxing, hydrothermal, and microwave treatment-assisted hydrolysis. Furthermore, doped TiO₂, TiO₂-composites, and other derivatives could be simply achieved by adding additional chemicals during transformation. The favorable properties of the resulting TiO₂-based materials are also discussed, which are relevant to energy and environmental applications in the areas of dye-sensitized solar cells, lithium ion batteries, photocatalytic hydrogen evolution, photocatalytic CO₂ reduction, photocatalytic degradation, and adsorption removal of pollutants.     

Self-cleaning engineered cementitious composites

Engineered cementitious composite (ECC) is a strain hardening cementitious composite with extreme tensile ductility of several percent. Few emerging applications of ECC, including lightweight building façade and pavement, make self-cleaning a desirable functionality to be added into the material. This study aims to impart photocatalytic properties into ECC for engaging self-cleaning. Influence of TiO₂ content on mechanical properties, cleaning efficiency, surface wettability, and dirt pick-up resistance of white ECC was studied. It shows that the inclusion of TiO₂ in ECC engages photocatalysis, facilitates the decomposition of RhB, and enhances photo-induced hydrophilicity significantly. As a result, TiO₂-ECC possesses self-cleaning with higher dirt pick-up resistance than normal ECC. However, TiO₂ photocatalysis may adversely affect the flexural strength and ductility of ECC due to weakened fiber/matrix interface bond after UV/sunlight irradiation.     

TiO<Subscript>2</Subscript> nanosheets with exposed {001} facets for photocatalytic applications

TiO₂ nanosheets with highly reactive {001} facets ({001}-TiO₂) have attracted great attention in the fields of science and technology because of their unique properties. In recent years, many efforts have been made to synthesize {001}-TiO₂ and to explore their applications in photocatalysis. In this review, we summarize the recent progress in preparing {001}-TiO₂ using different techniques such as hydrothermal, solvothermal, alcohothermal, chemical vapor deposition (CVD), and sol gel-based techniques. Furthermore, the enhanced efficiency of {001}-TiO₂ by modification of carbon materials, surface deposition of transition metals, and non-metal doping is reviewed. Then, the applications of {001}-TiO₂-based photocatalysts in the degradation of organic dyes, hydrogen evolution, carbon dioxide (CO₂) reduction, bacterial disinfection, and dye-sensitized solar cells are summarized. We believe this entire review on TiO₂ nanosheets with {001} facets can further inspire researchers in associated fields.

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Photocatalytic activity of nanostructured TiO2‐modified white cement

In this study, the photocatalysis of Alphazurine FG as a model water pollutant, by white Portland cement samples modified with different TiO₂ nanomaterials (TiO₂ in the form of Degussa P25, Millennium PC500, Millennium PC105 and anatase-Merck), was investigated. The pseudo first-order rate constants of Alphazurine FG photocatalysis were compared with the degradation rate by unmodified cement sample. A significant enhancement of the photocatalytic activity due to the addition of TiO₂ nanomaterials in the form of Degussa P25 to Portland cement was observed. The crystalline phase, average crystalline size and surface area of the photocatalyst were found to have a significant influence on the photocatalytic activity of the nanostructured TiO₂-modified cement samples. The photocatalysis of Alphazurine FG in the presence of TiO₂–P25/cement was experimentally studied through changing the UV light intensity and initial dye concentration. The electrical energy consumption of Alphazurine FG photocatalysis was estimated at different initial dye concentrations. The results open important perspective applications in the field of eco-friendly construction applications.     

Mussel‐Inspired Immobilization of Catalysts for Microchemical Applications

Immobilization of photocatalytic TiO₂ nanoparticles inside PDMS‐based microreactors was successfully attempted by sequential mussel‐inspired surface engineering of microchannels by using CA‐PVP and commercially available TiO₂ nanoparticles, respectively. TiO₂‐immobilized microreactors accomplished continuous photocatalytic degradation of MB for up to 30 days without releasing TiO₂ nanoparticles from the surface of the microchannels, confirming the robustness of TiO₂‐immobilization in photocatalysis media. Regeneration of microreactors with diminished photocatalytic activities was also possible with simple strong acid treatment, enabling efficient cleaning of used microreactors.     

ZnO Coated Anodic 1D TiO2 Nanotube Layers: Efficient Photo‐Electrochemical and Gas Sensing Heterojunction

The authors demonstrate, in this work, a fascinating synergism of a high surface area heterojunction between TiO₂ in the form of ordered 1D anodic nanotube layers of a high aspect ratio and ZnO coatings of different thicknesses, produced by atomic layer deposition. The ZnO coatings effectively passivate the defects within the TiO₂ nanotube walls and significantly improve their charge carrier separation. Upon the ultraviolet and visible light irradiation, with an increase of the ZnO coating thickness from 0.19 to 19 nm and an increase of the external potential from 0.4–2 V, yields up to 8‐fold enhancement of the photocurrent density. This enhancement translates into extremely high incident photon to current conversion efficiency of ≈95%, which is among the highest values reported in the literature for TiO₂ based nanostructures. In addition, the photoactive region is expanded to a broader range close to the visible spectral region, compared to the uncoated nanotube layers. Synergistic effect arising from ZnO coated TiO₂ nanotube layers also yields an improved ethanol sensing response, almost 11‐fold compared to the uncoated nanotube layers. The design of the high‐area 1D heterojunction, presented here, opens pathways for the light‐ and gas‐assisted applications in photocatalysis, water splitting, sensors, and so on.

     

Synthesis and visible-light photocatalytic activity of Bi-doped TiO2 nanobelts

Bi-doped anatase TiO₂ nanobelts were synthesized from layer-structural titanate nanobelts using two-step hydrothermal treatment approach. X-ray diffraction (XRD) patterns and transmission electron microscopic (TEM) images show that the doping of Bi³⁺ cations does not change the crystal structure and morphology of TiO₂ nanobelts. The energy-dispersive X-ray (EDX) and inductively coupled plasma-mass spectrometry (ICP-MS) analytic results suggest that the doping cations mainly exist near the surface of the TiO₂ nanobelts. The ultraviolet-visible (UV-vis) absorption spectra show that the absorption edge for the samples with Bi³⁺ has red shift as compared with that of undoped TiO₂ nanobelts, and correspondingly, the photocatalytic degradation of methylene blue under visible-light illumination is enhanced with the increase of Bi-doping content.     

TiO2‐Decorated Graphite Nanoplatelet Nanocomposites for High‐Temperature Sensor Applications

Temperature and/or composition mapping inside high temperature energy conversion and storage devices are challenging, yet of critical importance to improve the material design for optimum performance. Here, the great potential of TiO₂ nanoparticle (NP)‐decorated graphite nanoplatelet (GNP) nanocomposites as high temperature thermal senors or gas sensors is reported. Effects of the GNP substrate on phonon confinement in Raman spectrum, grain growth, and phase stability of anatase TiO₂ NPs at high temperatures are systematically studied. Thermally sensitive Raman signatures, indicating the ultrafast grain growth of TiO₂ NPs in response to short thermal shock treatments (0.1–25 s) at high temperatures, are exploited for high temperature thermal sensing applications. A very high accuracy of nearly 98% in temperature measurements is demonstrated for a given short‐time thermal exposure. Thermal stability of anatase TiO₂ NPs against transformation into the rutile phase in TiO₂‐GNP nancomposites is substantially increased by controlling the surface area of the substrate, which would significantly improve the performance of TiO₂‐based high temperature gas sensors.     

水热法制备TiO2纳米棒阵列及应用研究进展

TiO_2纳米棒阵列由于具有电子传输率高和光散射效应强等优异的特性,从而在太阳能电池、光催化、光解水制氢等领域中具有广阔的应用前景。主要从水热法制备工艺及生长机理、形貌优化及改性和应用几个方面综述了TiO_2纳米棒阵列的研究进展,并对今后的研究趋势进行展望。