Zhenhuan Zhao

From UV to Near‐Infrared, WS2 Nanosheet: A Novel Photocatalyst for Full Solar Light Spectrum Photodegradation

Narrow-bandgap semiconductor WS2 nanosheets are active photocatalysts, either under visible or under NIR irradiation. The photocatalyst functions are confirmed via photogeneration of an electron-hole pair, with a low rate of recombination.

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.

Structure, Synthesis, and Applications of TiO2 Nanobelts

TiO2 semiconductor nanobelts have unique structural and functional properties, which lead to great potential in many fields, including photovoltaics, photocatalysis, energy storage, gas sensors, biosensors, and even biomaterials. A review of synthetic methods, properties, surface modification, and applications of TiO2 nanobelts is presented here. The structural features and basic properties of TiO2 nanobelts are systematically discussed, with the many applications of TiO2 nanobelts in the fields of photocatalysis, solar cells, gas sensors, biosensors, and lithium-ion batteries then introduced. Research efforts that aim to overcome the intrinsic drawbacks of TiO2 nanobelts are also highlighted. These efforts are focused on the rational design and modification of TiO2 nanobelts by doping with heteroatoms and/or forming surface heterostructures, to improve their desirable properties. Subsequently, the various types of surface heterostructures obtained by coupling TiO2 nanobelts with metal and metal oxide nanoparticles, chalcogenides, and conducting polymers are described. Further, the charge separation and electron transfer at the interfaces of these heterostructures are also discussed. These properties are related to improved sensitivity and selectivity for specific gases and biomolecules, as well as enhanced UV and visible light photocatalytic properties. The progress in developments of near-infrared-active photocatalysts based on TiO2 nanobelts is also highlighted. Finally, an outline of important directions of future research into the synthesis, modification, and applications of this unique material is given.

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.

Enhanced performance of layered titanate nanowire-based supercapacitor electrodes by nickel ion exchange.

Titania nanostructured materials have been used extensively for the fabrication of electrochemical capacitors. However, the devices typically exhibit relatively low capacitance and poor cycling stability. Herein, we report the synthesis of a core-shell heterostructure based on layered titanate nanowires coated with nickel hydroxide nanosheets on a titanium mesh, referred to as K2Ti4O9@Ni(OH)2/Ti, by a simple nickel ion exchange reaction. The incorporation of nickel into the titanate nanowires is confirmed by X-ray photoelectron spectroscopic measurements and elemental mapping. Scanning electron microscopic and transmission electron microscopic measurements show the formation of a highly porous network of the hybrid nanowires. Electrochemical studies show that the K2Ti4O9@Ni(OH)2/Ti electrodes possess a high specific capacitance of 340 mF/cm(2) at 50 mV/s in an aqueous electrolyte of 3 M KOH and 3 mF/cm(2) at 0.04 mA/cm(2) in the KOH/PVA solid-state electrolyte, with an excellent retention rate of 92.5% after 2000 cycles and 92.7% after 10 000 cycles, respectively. Such a performance is a few tens of times better than that of the unmodified K2Ti4O9/Ti electrode. The enhanced capability of the chemically modified titanate electrodes may open up new opportunities in the development of low-cost, high-performance, and flexible supercapacitors.

UV-visible-light-activated photocatalysts based on Bi2O3/Bi4Ti3O12/TiO2 double-heterostructured TiO2 nanobelts

Surface engineering of TiO2 nanobelts by the controlled assembly of functional heterostructures represents an effective approach for the synthesis of high-performance photocatalysts. In this study, we prepared a novel Bi2O3/Bi4Ti3O12/TiO2 double-heterostructured nanobelt by depositing bismuth hydroxide onto the TiO2 nanobelt surface. A thermal annealing treatment led to the formation of a Bi4Ti3O12 interlayer that functioned as a bridge to link Bi2O3 and TiO2. The double-heterostructured TiO2 nanobelts exhibited better UV light photocatalytic performance than commercial P25. Importantly, the photocatalytic activity in the visible range was markedly better than that of Bi2O3 and Bi2O3/TiO2 heterostructured TiO2 nanobelts. The enhanced performance was accounted for by the material band structures where the matching was improved by the unique interlayer.

Cr(VI), Pb(II), Cd(II) adsorption properties of nanostructured BiOBr microspheres and their application in a continuous filtering removal device for heavy metal ions

Uniform well-defined nanostructured BiOBr microspheres have been fabricated via a simple hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG). The heavy metal ion adsorption on the as-synthesized nanostructured BiOBr microspheres was systematically assessed by measuring the residual concentration during the adsorption process using a colorimetric method for Cr(VI) concentration, and an extraction-colorimetric method for Cd(II) and Pb(II) concentrations. The nanostructured BiOBr microspheres showed good removal capacity for heavy metal ions (Cr, Cd, Pb), and excellent adsorption properties for low concentration heavy metal ions, indicating potential applications in water purification. Based on the quick and efficient heavy metal ion removal ability of nanostructured BiOBr microspheres, a continuous filtering-type water purification device was designed and constructed. In using this continuous filtering type water purification device, 1 g of adsorbent can purify about 4900 g of Pb(II) contaminated water, 5900 g of Cd(II) contaminated water, or 21 500 g of Cr(VI) contaminated water having initial concentrations of 200 μg L−1 to successfully attain the World Health Organization standard for drinking water. The good removal capacity can be attributed to the hierarchical nanostructure, which displays a large specific surface area and strong adsorption of heavy metal ions.

Hierarchical hybrid nanostructures of Sn3O4 on N doped TiO2 nanotubes with enhanced photocatalytic performance

Semiconductor nanostructures with photocatalytic activity have many potential applications including remediation of environmental pollutants and photocatalytic hydrogen evolution. An effective way of promoting photocatalytic activity is by creating heterogeneous photocatalysts. In this paper, a hybrid nanostructured photocatalyst with desired three-dimensional (3D) nanoarchitecture by assembling Sn3O4 nanosheets on N-doped TiO2 nanotubes has been constructed with enhanced broad spectrum photocatalytic properties, which can harness UV and visible light to decompose organic contaminants in aqueous solutions and split water to hydrogen. Photocatalytic tests showed that the Sn3O4/N-TiO2 hierarchical hybrid nanostructures possessed a much higher degradation rate of methyl orange and hydrogen evolution rate than that of the unmodified TiO2 nanotubes, N-TiO2 nanotubes, Sn3O4 nanosheets and Sn3O4/TiO2 hybrid nanostructures. The mechanism related to the enhancement of the photocatalytic activity was discussed. Deposition of Sn3O4 nanosheets onto N-TiO2 nanotubes resulted in a dramatic increase in light-induced generation of hydroxyl radicals, superoxides and singlet oxygen, and the production of holes and electrons. This work is the first instance of combining Sn3O4 with N-TiO2, the Sn3O4/N-TiO2 hierarchical hybrid nanostructures show good photocatalytic performance. This study is potentially applicable to a range of 3D hybrid nanostructures with promising applications in photocatalysis and relevant areas.

Lignosulphonate-cellulose derived porous activated carbon for supercapacitor electrode

The notion of environmental protection and renewable sources for energy conversion and storage has become particularly important nowadays. In this research, a meso-microporous carbon was prepared by the combination of a template method and chemical activation with earth abundant cellulose and lignosulphonate as the sources. The as-synthesized meso-microporous carbon contained mesopores generated by regeneration of cellulose with the assistance of a silica template, and micropores created by chemical activation of carbon. Such a unique porous structure makes the as-synthesized meso-microporous carbon the ideal electrode active material for energy storage. The two-electrode symmetric supercapacitors built using the meso-microporous carbon electrodes show a specific capacitance of 286 F g−1 at a current density of 0.25 A g−1 in aqueous electrolyte. More importantly, the symmetric supercapacitor achieves a high energy density of 13 W h kg−1 while at a high power density of 27 kW kg−1. It is demonstrated that using renewable natural sources for the manufacturing of porous carbon with high performance for energy storage can be an effective way to lower the cost of a supercapacitor.

A TiO2/FeMnP Core/Shell Nanorod Array Photoanode for Efficient Photoelectrochemical Oxygen Evolution

A variety of catalysts have recently been developed for electrocatalytic oxygen evolution, but very few of them can be readily integrated with semiconducting light absorbers for photoelectrochemical or photocatalytic water splitting. Here, we demonstrate an efficient core/shell photoanode with a highly active oxygen evolution electrocatalyst shell (FeMnP) and semiconductor core (rutile TiO2) for photoelectrochemical oxygen evolution reaction. Metal-organic chemical vapor deposition from a single-source precursor was used to ensure good contact between the FeMnP and the TiO2. The TiO2/FeMnP core/shell photoanode reaches the theoretical photocurrent density for rutile TiO2 of 1.8 mA cm-2 at 1.23 V vs reversible hydrogen electrode under simulated 100 mW cm-2 (1 sun) irradiation. The dramatic enhancement is a result of the synergistic effects of the high oxygen evolution reaction activity of FeMnP (delivering an overpotential of 300 mV with a Tafel slope of 65 mV dec-1 in 1 M KOH) and the conductive interlayer between the surface active sites and semiconductor core which boosts the interfacial charge transfer and photocarrier collection. The facile fabrication of the TiO2/FeMnP core/shell nanorod array photoanode offers a compelling strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.