Qingyong Tian

Tube-Like Ternary α-Fe2O3@SnO2@Cu2O Sandwich Heterostructures: Synthesis and Enhanced Photocatalytic Properties

Heterogeneous photocatalysis is of great interest for environmental remediation applications. However, fast recombination of photogenerated electron-hole pair and a low utilization rate of sunlight hinder the commercialization of currently available semiconductor photocatalysts. In this regard, we developed a unique ternary single core-double shell heterostructure that consists of α-Fe2O3@SnO2@Cu2O. This heterostructure exhibits a tube-like morphology possessing broad spectral response for the sunlight due to the combination of narrow bandgap and wide bandgap semiconductors forming a p-n heterojunction. To fabricate such a short nanotube (SNT), we used an anion-assisted hydrothermal route for deposition of α-Fe2O3, a seed-mediated deposition strategy for SnO2, and finally an aging process to deposit a Cu2O layer to complete the tube-like ternary α-Fe2O3@SnO2@Cu2O single core-double shell heterostructures. The morphology, composition, and photocatalytic properties of those ternary core-shell-shell heterostructures were characterized by various analytical techniques. These ternary heterostructures exhibited enhanced photocatalytic properties on the photodegradation of the organic dye of Rhodamine B (RhB) under simulated sunlight irradiation. The origin of enhanced photocatalytic activity is due to the synergistic effect of broad spectral response by combining narrow bandgap and wide bandgap semiconductors and, hence, an efficient charge separation of photogenerated electron-hole pairs facilitated through the p-n heterojunction. Furthermore, our unique structure provides an insight on the fabrication and controlled preparation of multilayer heterostructural photocatalysts that have intriguing properties.

Large-scale synthesis and screen printing of upconversion hexagonal-phase NaYF4:Yb3+,Tm3+/Er3+/Eu3+ plates for security applications

Up-conversion materials can be applied in anti-counterfeit fields because of their high concealment and high up-conversion fluorescence efficiency. Herein, different lanthanide ions-doped β-NaYF4 up-conversion micro-particles (UCMPs) with uniform hexagonal morphology were synthesized on a large-scale (more than 0.5 g) via a facile hydrothermal method. It is very interesting to find out the fluorescence intensity and the eventual morphology of the UCMPs were highly dependent on the reaction conditions. Then, the optimal UCMPs with uniform morphology and strong fluorescence intensity were selected as promising candidates for preparing ink. Eventually, we successfully printed designable and multicolor fluorescent patterns on flexible substrates (common paper and polyethylene terephthalate, PET) using the as-prepared β-NaYF4:Yb3+,Tm3+/Er3+/Eu3+ UCMPs inks. Under ambient conditions, the printed patterns on conventional paper are invisible, while such printed patterns on PET are white. However, all the patterns could display blue, yellow-green and green fluorescence patterns under the irradiation of a 980 nm laser when using the β-NaYF4:Yb3+,Tm3+/Er3+/Eu3+ UCMPs inks. We envision that the UCMPs fluorescent inks-based flexible and rapid screen printing patterns have enormous potential for anti-counterfeit and security applications.

Shape-controlled iron oxide nanocrystals: synthesis, magnetic properties and energy conversion applications

Iron oxide nanocrystals (IONCs) with various geometric morphologies show excellent physical and chemical properties and have received extensive attention in recent years. The various shape-induced magnetic and electrochemical properties of the IONCs make them suitable for diverse applications. Understanding the correlation between the physicochemical properties and morphology of IONCs is a prerequisite for their widespread applications. Hence, this review focuses on current research progress regarding shape-controlled IONCs in different dimensions, and the corresponding shape-dependent magnetic, catalytic and gas-sensor properties are discussed. Furthermore, the general preparation methods, shape-guided growth mechanisms and energy conversion applications in photoelectrochemical water splitting, dye-sensitized solar cells (DSSCs) and lithium-ion batteries (LIBs) of these IONCs (α-Fe2O3, γ-Fe2O3, Fe3O4) are also discussed. Finally, the perspectives of IONCs in promising research directions are proposed.

Facile synthesis and screen printing of dual-mode luminescent NaYF4:Er,Yb (Tm)/carbon dots for anti-counterfeiting applications

Rare-earth ion (RE3+) doped up-conversion (UC) fluorescent materials and novel fluorescent carbon quantum dots (CDs) have been widely used as traditional anti-counterfeiting materials owing to their excellent optical properties. The drawbacks of these materials are being exposed gradually with the widespread occurrence of counterfeit products in the market because of their single fluorescence mode and easy replication. In this work, we propose a novel strategy to combine both luminescent materials with different modes via a facile solvothermal method. Interesting, the composite materials show unalterable down-conversion (DC) blue light under a 365 nm ultraviolet (UV) analyzer, except for adjustable UC luminescence properties. The UC and DC optical properties are measured and the probable mechanism is proposed, indicating that the dual-mode fluorescence processes are separate and do not interference with each other. Moreover, we use a mixture containing a small number of UCMPs/CDs and poly(acrylic acid) (PAA) aqueous solution as a colorless anti-counterfeiting ink, and successfully print a variety of dual-mode fluorescence patterns through the screen printing technique, including QR codes, the logo of Wuhan University, and clover patterns. The composite materials show good dispersion and outstanding dual-mode fluorescence properties, suggesting that they are promising luminescent materials in the anti-counterfeiting field.

Wetting properties and SERS applications of ZnO/Ag nanowire arrays patterned by a screen printing method

Three-dimensional (3D) ZnO/Ag nanowire arrays (NWA) SERS substrates are fabricated by a screen-printing technique. The preparation of patterned ZnO NWA involves a two-step growth process. The ZnO nanoparticles-based ink is prepared and printed as seed layers, which are used as templates to fabricate patterned ZnO NWA via a hydrothermal method. During the screen printing process, the patterns of ZnO NWA are controlled by printing plates. The as-obtained NWA with uniform morphology was fabricated at 90 °C and exhibits hydrophilic and lipophilic properties. Subsequently, the sensitive 3D SERS substrates are fabricated through deposition of Ag nanoparticles (NPs) onto the surface of patterned ZnO NWA by magnetron sputtering. The detection limit of Malachite green (MG) can achieve 10−12 M with an enhancement factor of about 2.5 × 1010. Combined with the sensitivity and uniformity, the ZnO/Ag NWA is applied for the quick detection of low concentrations of molecules related to food safety, such as amoxicillin.

Anion-mediated synthesis of monodisperse silver nanoparticles useful for screen printing of high-conductivity patterns on flexible substrates for printed electronics

Monodisperse silver nanoparticles (NPs) have been synthesized on a large scale by oxidation–reduction reactions in water by adding triethylamine to the aqueous solutions of AgNO3, glucose and poly(vinyl pyrrolidone). Different anions, including –SO42−, –PO43−, –CO32− and –Br−, are introduced to the abovementioned mixture to form slightly soluble silver compounds, which are used as the precursor to synthesize silver NPs. The effects of silver nitrate–glucose ratio and reaction temperature are investigated. The electrical performance of the as-obtained Ag NPs has been studied, and the results reveal that the –CO32− mediated-synthesized Ag NPs possess the lowest resistivity. Note that silver NPs can be well-dispersed in ethanol and generated as inks, which can be screen printed onto flexible polyester (PET) and paper substrates and form conductive patterns after a low-temperature sintering treatment. An optimal electrical resistivity can be reached at 5.72 μΩ cm, which is much closer to the value of bulk silver (1.6 μΩ cm). Evidently, the synthesized silver NPs could be considered as low-cost and effective materials that have a great potential application for flexible printed electronics.

Tube-like α-Fe2O3@Ag/AgCl heterostructure: controllable synthesis and enhanced plasmonic photocatalytic activity

Plasmonic photocatalysts coupled with semiconductors are one of the most popular combinations in environmental remediation applications. In this regard, a novel tube-like α-Fe2O3@Ag/AgCl hybrid structure is fabricated by anchoring Ag/AgCl hybrid nanoparticles on the surface of α-Fe2O3 short nanotubes (SNTs) by a step-by-step strategy. Firstly, the monodispersed α-Fe2O3 SNTs have been synthesized via an anion-assisted hydrothermal process followed by the loading of Ag nanoparticles on the surface of α-Fe2O3 SNTs through the classic silver mirror reaction mechanism. From in situ oxidation of Ag nanoparticles, the final product α-Fe2O3@Ag/AgCl heterostructures has been obtained. We study the morphology, composition, and photocatalytic properties of the as obtained tube-like α-Fe2O3@Ag/AgCl nano-heterostructures. The photocatalytic activities of as obtained photocatalysts have been tested by the degradation of organic dye Rhodamine B (RhB) under simulated sunlight (UV + visible light), visible light and UV light irradiation. The main reason for the enhanced photocatalytic performance is attributed to the broad spectral response from the combination of narrow/wide bandgap semiconductors with metallic Ag nanoparticles and efficient charge transfer from plasmon-excited Ag nanoparticles to α-Fe2O3 and AgCl. Finally, this hybrid structure provides a roadmap for the controlled synthesis of plasmonic photocatalysts with excellent properties, and can be used for practical application in environmental issues.

Zinc Oxide Coating Effect for the Dye Removal and Photocatalytic Mechanisms of Flower-Like MoS2 Nanoparticles

Flower-like MoS2 nanoparticles (NPs) consist of ultra-thin MoS2 nanosheets are synthesized via a facile one-pot hydrothermal method. The MoS2/ZnO p-n heterostructure is formed by coating n-type ZnO on the surface of flower-like MoS2 NPs through the seed-mediate route and post-annealing treatment. The effects for the dye removal and photocatalytic performances after ZnO coating are systematically investigated. The results demonstrated that the coating of ZnO nanoparticles has a positive promotion to the photodegrading properties while negative effect on the adsorption capacity of the MoS2/ZnO heterostructures. The related mechanisms on the relationship of adsorption capacity and photocatalysis are discussed in detail.

Full-spectrum-activated Z-scheme photocatalysts based on NaYF4:Yb3+/Er3+, TiO2 and Ag6Si2O7

The development of efficient full-spectrum-activated photocatalysts has become a research topic of intense interest in environmental remediation or solar energy conversion applications. Herein, newly Z-scheme UV-vis-NIR-activated photocatalysts consisting of β-NaYF4:18% Yb3+, 2% Er3+@TiO2–Ag6Si2O7 (denoted as NaYF4@T–ASO) were designed and used as full-spectrum response photocatalysts. For tailoring NaYF4@T–ASO, the size of in situ deposited ASO nanoparticles on the surface of NaYF4@T microplates was determined by the pumping rate of the AgNO3 precursor, which played indirect roles in the photocatalytic activity with different carrier migration distances. Especially, NaYF4@T–ASO (S10) with the smallest and well distributed ASO nanoparticles showed superior photocatalytic activity than the commercial P25 TiO2 by 15 fold under the stimulated solar light irradiation. The enhanced photocatalytic performance of NaYF4@T–ASO could be ascribed to the synergic effect of the upconversion material and the direct Z-scheme heterojunction formed between TiO2/ASO, where the Z-scheme heterojunction induced efficient separation of photogenerated carriers and highly oxidative species (h+ and ˙O2−). Alternative mechanisms of carriers and energy transfer under various light sources have been proposed and discussed in detail.

Dual upconversion nanophotoswitch for security encoding

Light-harvesting lanthanide ions (Ln3+) doped NaYF4 inks could provide polychromatic patterns for opposing counterfeiting commodity infestation because of their distinctive upconversion photoluminescence (UPL) properties. Herein, three kinds of core-triple-shell Ln3+ ions doped NaYF4 upconversion nanocrystals (UCNCs) are synthesized through modified high-temperature coprecipitation, which demonstrate excellent UPL properties of independent emitting colors under 808 or 980 nm laser excitation. Additive mixing three kinds of 808 nm emitted red-green-blue (RGB) UCNCs colloid solution can precisely regulate the emissions of the suspension for achieving full-color display. The as-obtained RGB three-primary colors induced by 808 nm laser accomplish broader color gamut than traditional standard RGB (sRGB) model and printing cyan-magenta-yellow (CMY) model. In addition, various China zodiac patterns and complex multicolor images are printed by the as-formulated UCNCs inks through screen printing technology. The printed patterns present colorful and polychromatic sequential toning visualization patterns under 808 nm excitation, while present another succession of gradually changed versatile patterns under 980 nm excitation. As a proof of concept, transparent polyvinyl chloride (PVC) self-adhesive anti-counterfeiting label is attached to the bottle of wine package for practical application. The demonstration of multiple model patterns of Chinese zodiac and poetry images based on these core-tripleshell UCNCs can be selected as a conceivable substitute of traditional single model patterns, underlining the full-color anti-counterfeiting level.摘要镧系离子掺杂的NaYF4油墨由于其独特的上转换光致发光特性可以被应用到防伪领域. 本文首先通过高温共沉淀法合成了三种核-壳结构的镧系离子掺杂的NaYF4上转换纳米材料, 它们在808和980 nm激光激发下均可以表现出差异性的上转换荧光性能. 其次, 通过物理混合808 nm激发的不同颜色的悬溶液红绿蓝, 可以调节混合液的发光颜色, 实现全彩色显示. 808 nm激发产生的颜色可以实现比sRGB和印刷CMY颜色空间模型更宽的色域. 最后, 我们使用传统丝网印刷技术印刷出中国十二生肖图案和其他大面积的复杂图像, 印刷图案在808 nm激发下可以呈现出一组多色连续的图案, 同时在980 nm激发下也可呈现出另一组逐渐改变的多色图案, 而且,印刷在透明聚氯乙烯PVC标签的图案可以附在酒瓶包装上, 实现酒瓶包装的防伪. 基于NaYF4的双模式荧光图案可以替代传统单模式荧光图案, 实现高水平的全色防伪及安全编码.