Zhaoyong Lin

Electronic Reconstruction of α-Ag2WO4 Nanorods for Visible-Light Photocatalysis

α-Ag2WO4 (AWO) has been studied extensively due to its H2 evolution and organic pollution degradation ability under the irradiation of UV light. However, the band gap of AWO is theoretically calculated to be 3.55 eV, resulting in its sluggish reaction to visible light. Herein, we demonstrated that, by using the electronic reconstruction of AWO nanorods upon a unique process of laser irradiation in liquid, these nanorods performed good visible-light photocatalytic organics degradation and H2 evolution. Using commercial AWO powders as the starting materials, we achieved the electronic reconstruction of AWO by a recrystallization of the starting powders upon laser irradiation in liquid and synthesized AWO nanorods. Due to the weak bond energy of AWO and the far from thermodynamic equilibrium process created by laser irradiation in liquid, abundant cluster distortions, especially [WO6] cluster distortions, are introduced into the crystal lattice, the defect density increases by a factor of 2.75, and uneven intermediate energy levels are inset into the band gap, resulting in a 0.44 eV decrease of the band gap, which modified the AWO itself by electronic reconstruction to be sensitive to visible light without the addition of others. Further, the first-principles calculation was carried out to clarify the electronic reconstruction of AWO, and the theoretical results confirmed the deduction based on the experimental measurements.

Ag/AgCl plasmonic cubes with ultrahigh activity as advanced visible-light photocatalysts for photodegrading dyes

Among numerous visible-light photocatalysts, plasmonic structure is a promising photocatalyst for photodegradation and energy generation. Ag/AgCl composite as an alternative visible-light photocatalyst has attracted extensive interests; however, its syntheses has many visible flaws, e.g. high temperature environment, requirement of various templates or additives, complicated synthetic procedures and impurities in the final products. For these issues, herein, we report, for the first time, a simple, facile, rapid and green technique to synthesize Ag/AgCl heterostructured cubes using a one-step process of laser irradiation in liquids. The fabricated Ag/AgCl cubes possess some active {111} facets and a high visible-light utilization efficiency induced by the localized surface plasmon resonance (SPR) from the Ag/AgCl heterostructure. As plasmonic photocatalysts, these Ag/AgCl cubes exhibited excellent photodegrading performance for dye molecules of methyl orange, Rhodamine B and methylene blue, and the photodegradation rates were about 0.268, 0.057, and 0.094 min−1, which are considerably higher than that of commercial Ag3PO4 by a factor of 29.8, 3.8 and 6.7, respectively. The high photo-stability of the Ag/AgCl cubes was also demonstrated. The SPR-mediated photocatalytic mechanism was proposed to address the ultrahigh activity of the Ag/AgCl heterostructure as an advanced visible-light photocatalyst. These results showed the broad applicability of the developed technique for accessing a new plasmonic photocatalyst with high-performance.

Reduced TiO2-Graphene Oxide Heterostructure As Broad Spectrum-Driven Efficient Water-Splitting Photocatalysts

The reduced TiO2-graphene oxide heterostructure as an alternative broad spectrum-driven efficient water splitting photocatalyst has become a really interesting topic, however, its syntheses has many flaws, e.g., tedious experimental steps, time-consuming, small scale production, and requirement of various additives, for example, hydrazine hydrate is widely used as reductant to the reduction of graphene oxide, which is high toxicity and easy to cause the second pollution. For these issues, herein, we reported the synthesis of the reduced TiO2-graphene oxide heterostructure by a facile chemical reduction agent-free one-step laser ablation in liquid (LAL) method, which achieves extended optical response range from ultraviolet to visible and composites TiO(2-x) (reduced TiO2) nanoparticle and graphene oxide for promoting charge conducting. 30.64% Ti(3+) content in the reduced TiO2 nanoparticles induces the electronic reconstruction of TiO2, which results in 0.87 eV decrease of the band gap for the visible light absorption. TiO(2-x)-graphene oxide heterostructure achieved drastically increased photocatalytic H2 production rate, up to 23 times with respect to the blank experiment. Furthermore, a maximum H2 production rate was measured to be 16 mmol/h/g using Pt as a cocatalyst under the simulated sunlight irradiation (AM 1.5G, 135 mW/cm(2)), the quantum efficiencies were measured to be 5.15% for wavelength λ = 365 ± 10 nm and 1.84% for λ = 405 ± 10 nm, and overall solar energy conversion efficiency was measured to be 14.3%. These findings provided new insights into the broad applicability of this methodology for accessing fascinate photocatalysts.

Matching energy levels between TiO2 and α-Fe2O3 in a core–shell nanoparticle for visible-light photocatalysis

Coupling TiO2 with other semiconductors is a route to extend the optical response range of TiO2 and to improve the efficiency of its photon quantum. α-Fe2O3 seems compatible with TiO2 and possesses a high solar-light-harvesting capability that is fifteen times as large as that of TiO2. However, there is an energy level mismatch between TiO2 and α-Fe2O3. The photocatalytic performance of TiO2 would be inhibited when compositing with α-Fe2O3 due to the α-Fe2O3-induced photo-generated carriers trapping and dissipation. The composite acts like a one-way valve, in which photo-generated carriers flow from a thick pipe to a thin one and then jam up. Herein, we achieved the goal of matching the energy levels between TiO2 and α-Fe2O3 in a core–shell nanoparticle for enhancing visible-light photocatalysis. Heterostructured TiO2@α-Fe2O3 core–shell nanoparticles were fabricated by the long-pulsed laser ablation of a titanium target in water followed by a hydrothermal reaction. A well-matched interface between TiO2 and α-Fe2O3 was observed, which promoted photo-generated electrons and holes migration and separation. The energy band of the TiO2 nanoparticle was demonstrated to be matched with that of α-Fe2O3, resulting from the upward shift of its valence band due to the abundant oxygen vacancies and bridging hydroxyls on its surface. In this situation, the “blocked pipe” seems to be dredged effectively and the visible-light photocatalytic methyl orange dyes degradation performance of the TiO2@α-Fe2O3 nanoparticles is improved by a factor of two over that of the as-synthesized TiO2 nanoparticles. These findings provide new insights into TiO2 nanostructure photocatalysts and energy band engineering for visible-light photocatalysis.

Manipulating the hydrogen evolution pathway on composition-tunable CuNi nanoalloys

The supply of clean hydrogen energy through photocatalysis in the future requires the finding of low-cost, efficient and durable cocatalysts to replace noble metal Pt. Cu and Ni are believed to be two promising materials. However, their cocatalytic performance is still limited. The theory of the hydrogen evolution pathway on Cu and Ni surfaces reveals that Cu can release H2 molecules easily but capture H atoms and photoelectrons with difficulty, while Ni performs inversely. To overcome this issue, we consider that improved cocatalytic performance could be achieved by the substitution of Ni atoms into a Cu crystal lattice to form a CuNi alloy. Here, we reported that CuNi alloy nanoparticles were prepared by a process of laser ablation in liquid (LAL). Their compositions could be tuned by varying the concentration of the isopropanol aqueous solution, which is novel in LAL. We demonstrated that the photocatalytic H2 evolution performance of TiO2 nanorods can be greatly improved by loading these CuNi nanoalloys on them to act as cocatalysts. Furthermore, these cocatalysts present favorable stability. The best cocatalytic performance was achieved by Cu63Ni37 alloy nanoparticles, even better than Pt. First-principles calculations demonstrated that the Cu63Ni37 alloy nanoparticles possess a high H atom adsorption energy, a large work function and a small H2 molecule adsorption energy, resulting in the rational manipulation of the hydrogen evolution pathway and the optimal cocatalytic performance. This work provided a strategy to design cheap, robust and durable cocatalysts for photocatalytic H2 evolution.

Midrefractive Dielectric Modulator for Broadband Unidirectional Scattering and Effective Radiative Tailoring in the Visible Region

Nanoantennas have found many applications in ultrasmall sensors, single-molecule detection, and all-optical communication. Conventional nanoantennas are based on noble-metal plasmonic structures, but suffer from large ohmic loss and only possess dipolar plasmon modes. This has driven an intense search for all-dielectric materials beyond noble metals. Here, we propose midrefractive nanospheres as a novel all-dielectric material to realize broadband unidirectional radiation and effective radiative tailoring in the visible region. Midrefractive all-dielectric materials such as boron nanospheres possess broad and overlapping electric and magnetic dipole modes. The internal interaction between these two modes can route the radiation almost on the one side covering the whole visible range. Unlike the elaborate design in plasmonic nanostructures to obtain strong coupled broad and narrow modes, the bright mode in boron nanospheres is intrinsic, independent, and easily coupled with adjacent narrow modes. So the strong interaction in boron-based heterodimer is able to realize an independent and precise tailoring of the radiant and subradiant states by simply changing the particle sizes, respectively. Our findings imply midrefractivity materials like boron are excellent building blocks to support electromagnetic coupling operation in nanoscale devices, which will lead to a variety of emerging applications such as nanoantennas with directing exciton emission, ultrasensitive nanosensors, or even potential new construction of photonic metamaterials.

Modifying photocatalysts for solar hydrogen evolution based on the electron behavior

Converting abundant solar energy into precious and clean hydrogen energy through photocatalytic water splitting is a highly promising way to address energy shortages. Solar H2 evolution is a practical technology in the environmental and energy fields. The electron is the protagonist in solar H2 evolution and the electron behavior determines performance. Three pivotal steps, electron generation, electron survival and electron utilization, are involved in this photocatalytic process. This review discusses some typical cases from the last two years of improving the performance of solar H2 evolution through elaborately manipulating the electron behavior. The manipulation can be accomplished by modifying the photocatalyst itself (self-modification) and with the assistance of foreign materials (extra-modification). It is expected that the main ideas behind these strategies can be extracted and used when designing efficient and robust photocatalytic systems in the future.

A design of Si-based nanoplasmonic structure as an antenna and reception amplifier for visible light communication

Visible light communication has been widely investigated due to its larger bandwidth and higher bit rate, and it can combine with the indoor illumination system that makes it more convenient to carry out. Receiving and processing the visible light signal on chip request for nanophotonics devices performing well. However, conventional optical device cannot be used for light-on-chip integration at subwavelength dimensions due to the diffraction limit. Herein, we propose a design of Si-based nanoplasmonic structure as an antenna and reception amplifier for visible light communication based on the interaction between Si nanoparticle and Au nanorod. This device integrates the unique scattering property of high-refractive index dielectric Si nanoparticles, whose scattering spectrum is dependent on the particle size, with the localized surface plasmon resonance of Au nanorod. We calculated the spectra collected by plane detector and near field distribution of nanostructure, and theoretically demonstrate that the...

Gold nanoarray deposited using alternating current for emission rate-manipulating nanoantenna

We have proposed an easy and controllable method to prepare highly ordered Au nanoarray by pulse alternating current deposition in anodic aluminum oxide template. Using the ultraviolet–visible-near-infrared region spectrophotometer, finite difference time domain, and Green function method, we experimentally and theoretically investigated the surface plasmon resonance, electric field distribution, and local density of states enhancement of the uniform Au nanoarray system. The time-resolved photoluminescence spectra of quantum dots show that the emission rate increased from 0.0429 to 0.5 ns−1 (10.7 times larger) by the existence of the Au nanoarray. Our findings not only suggest a convenient method for ordered nanoarray growth but also prove the utilization of the Au nanoarray for light emission-manipulating antennas, which can help build various functional plasmonic nanodevices.PACS82.45.Yz, 78.47.jd, 62.23.Pq

Self-assembling solid-state hydrogen source for drylands photocatalytic hydrogen production

Water finding, collection and retention are important issues in drylands because of the rareness and high evaporation of water. Efficiently and fully utilizing water for photocatalytic hydrogen production is thus a challenge in desert areas. Inspired by the decent water absorption and retention properties of super absorbent polymers (SAPs), it is a bracing idea to use SAPs for water storage and hydrogen production reactors to enable full use of precious water for light-driven water splitting. Herein, for the first time, we have prepared a self-assembling solid-state hydrogen source (SHS) for photocatalytic hydrogen evolution. In the SHS, Pt/TiO2 and NiB/CdS nanocomposites were used as solar-driven and visible-light driven hydrogen production model catalysts, respectively, integrated with commercial agricultural acrylamide-acrylate copolymerized crosslinked SAP (AAC). It exhibits hydrogen production comparable to that of a typical suspension system, is reusable, and can be more readily recycled than conventional powdery catalysts, because of its monolithic structure. All water molecules in the SHS can be used to produce hydrogen. Accordingly, the SHS developed in this work offers a strategy for integrating SAPs with catalysts that would be practical in water-efficient photocatalytic hydrogen evolution in drought regions.