Guizhen Wang

Microwave Absorption Properties of Carbon Nanocoils Coated with Highly Controlled Magnetic Materials by Atomic Layer Deposition

In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

High densities of magnetic nanoparticles supported on graphene fabricated by atomic layer deposition and their use as efficient synergistic microwave absorbers

An atomic layer deposition (ALD) method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe3O4 or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic (EM) absorption properties compared to the pristine graphene. The optimal reflection loss (RL) reaches −46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe3O4/graphene composites obtained by applying 100 cycles of Fe2O3 deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.

Enhanced microwave absorption of ZnO coated with Ni nanoparticles produced by atomic layer deposition

In this work, flower-like ZnO coated by Ni nanoparticles has been synthesized by the reduction of NiO-coated ZnO produced by an atomic layer deposition (ALD) method. The structure and electromagnetic (EM) absorption properties of the as-prepared samples are investigated. By applying 800 ALD cycles of NiO deposition followed by a reduction process, the surfaces of ZnO are densely covered by Ni nanoparticles with a narrow particle size distribution and an average size of 13.1 nm. ZnO@Ni exhibits remarkably improved EM absorption properties compared to ZnO. The optimal RL calculated from the measured complex permittivity and permeability is −48.0 dB at 10.4 GHz. Moreover, the EM wave absorption less than −10 dB is found to reach 5.3 GHz for an absorber thickness of 1.5 mm. The enhanced absorption ability arises from the effective combination of multiple dielectric–magnetic loss mechanisms.

Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions

To design highly efficient catalysts, new concepts for optimizing the metal-support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni-based nanocatalyst. The Ni nanoparticles are not only confined in Al2 O3 nanotubes, but also embedded in the cavities of Al2 O3 interior wall. The cavities create more Ni-Al2 O3 interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni-based catalyst supported on the outer surface of Al2 O3 nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD-assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.

NiO/SiC Nanocomposite Prepared by Atomic Layer Deposition Used as a Novel Electrocatalyst for Nonenzymatic Glucose Sensing

NiO nanoparticles are deposited onto SiC particles by atomic layer deposition (ALD). The structure of the NiO/SiC hybrid material is investigated by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The size of the NiO nanoparticles is flexible and can be adjusted by altering the cycle number of the NiO ALD. Electrochemical measurements illustrate that NiO/SiC prepared with 600 cycles for NiO ALD exhibits the highest glucose sensing ability in alkaline electrolytes with a low detection limit of 0.32 μM (S/N = 3), high sensitivity of 2.037 mA mM(-1) cm(-2), a linear detection range from approximately 4 μM to 7.5 mM, and good stability. Its sensitivity is about 6 times of that for commercial NiO nanoparticles and NiO/SiC nanocomposites prepared by a traditional incipient wetness impregnation method. It is revealed that the superior electrochemical ability of ALD NiO/SiC is ascribed to the strong interaction between NiO and the SiC substrate and the high dispersity of NiO nanoparticles on the SiC surface. These results suggest that ALD is an effective way to deposit NiO on SiC for nonenzymatic glucose sensing.

Nanoporous Nitrogen‐Doped Titanium Dioxide with Excellent Photocatalytic Activity under Visible Light Irradiation Produced by Molecular Layer Deposition

cone, [13, 14] have been grown through MLD and those were mainly based on reactions between metal alkyl/chloride and glycol/glycerol. Given the great promise of MLD, it is highly demanded to develop new processing strategies for MLD. One important aspect for producing a larger range of organic–inorganic mixtures is the variability of compositions of the constituting organic and inorganic fractions of the resulting films. A limitation to rather short organic spacers, such as glycol, between the metal ions is a bottleneck for the synthesis of films with a broader range of organic–inorganic

Efficient adsorptive removal of dibenzothiophene by graphene oxide-based surface molecularly imprinted polymer

Molecularly imprinted polymers on GO nanosheets (MIPs/GO) for desulfurization are synthesized using dibenzothiophene (DBT) as template, methacrylic acid (MAA) as monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker. The formation of this hybrid material is verified by Fourier transform infrared spectroscopy, thermal gravimetric and atomic force microscopy analysis. The adsorption results show that the prepared MIPs/GO exhibit excellent adsorption capacity (up to 181.9 mg g−1 at 298 K) and fast mass transfer and binding kinetics for DBT. The kinetics and isotherm data can be well described by the pseudo-first-order kinetic model and the Freundlich isotherm, respectively. Competitive adsorption experiments demonstrate that MIPs/GO show higher affinity toward target molecule DBT than toward structural analogue benzothiophene.

Defective Ti2Nb10O27.1: an advanced anode material for lithium-ion batteries.

To explore anode materials with large capacities and high rate performances for the lithium-ion batteries of electric vehicles, defective Ti2Nb10O27.1 has been prepared through a facile solid-state reaction in argon. X-ray diffractions combined with Rietveld refinements indicate that Ti2Nb10O27.1 has the same crystal structure with stoichiometric Ti2Nb10O29 (Wadsley-Roth shear structure with A2/m space group) but larger lattice parameters and 6.6% O2– vacancies (vs. all O2– ions). The electronic conductivity and Li+ion diffusion coefficient of Ti2Nb10O27.1 are at least six orders of magnitude and ~2.5 times larger than those of Ti2Nb10O29, respectively. First-principles calculations reveal that the significantly enhanced electronic conductivity is attributed to the formation of impurity bands in Ti2Nb10O29–x and its conductor characteristic. As a result of the improvements in the electronic and ionic conductivities, Ti2Nb10O27.1 exhibits not only a large initial discharge capacity of 329 mAh g–1 and charge capacity of 286 mAh g–1 at 0.1 C but also an outstanding rate performance and cyclability. At 5 C, its charge capacity remains 180 mAh g–1 with large capacity retention of 91.0% after 100 cycles, whereas those of Ti2Nb10O29 are only 90 mAh g–1 and 74.7%.

Preparation and microwave absorption properties of uniform TiO2@C core–shell nanocrystals

In this work, carbon-coated TiO2 (TiO2@C) core–shell nanocrystals have been synthesized by a simple acetylene decomposition method and further explored for the microwave absorbing application. Results demonstrate that a well-graphitized carbon layer with a thickness of about 3.5 nm can be uniformly coated on the surface of TiO2. It is found that the microwave absorption properties of TiO2@C are remarkably enhanced compared to the bare TiO2. The optimal RL calculated from the measured complex permittivity and permeability is −58.2 dB at 7.6 GHz for TiO2@C with a loading of 40 wt%. Whereas for TiO2@C with a loading of 60 wt%, the effective bandwidth of less than −10 dB is found to reach 5.0 GHz with the coating thickness of 2.2 mm. The enhanced performance can be attributed to the increased dielectric properties and the multiple relaxation processes caused by the core–shell composite materials.

Uniform and Conformal Carbon Nanofilms Produced Based on Molecular Layer Deposition

Continuous and uniform carbon nanofilms (CNFs) are prepared by pyrolysis of polyimide films which are produced by molecular layer deposition (MLD). The film thickness can be easily controlled at nanometer scale by altering the cycle numbers. During the annealing process at 600 °C, the polyimide film is subject to shrinkage of 70% in thickness. The obtained CNFs do not exhibit a well-graphitized structure due to the low calcination temperature. No clear pore structures are observed in the produced films. CNFs grown on a glass substrate with a thickness of about 1.4 nm shows almost 98% optical transmittance in the visible spectrum range. Au nanoparticles coated with CNFs are produced by this method. Carbon nanotubes with uniform wall thickness are obtained using anodic aluminum oxide as a template by depositing polyimide films into its pores. Our results demonstrate that this method is very effective to coat conformal and uniform CNFs on various substrates, such as nanoparticles and porous templates, to produce functional composite nanomaterials.