Xinxin Yu

Highly efficient dye adsorption and removal: a functional hybrid of reduced graphene oxide–Fe3O4 nanoparticles as an easily regenerative adsorbent

A functional hybrid of reduced graphene oxide (RGO)–Fe3O4 nanoparticles (NPs) has been chemically synthesized with exceptionally high yield and tunable RGO/Fe3O4 ratio. The adsorption behaviors of a series of dyes using this hybrid as the adsorbent are systematically investigated in aqueous solutions through real-time monitoring of the fingerprint spectral changes of the dyes. The results show that, benefiting both from the surface property of RGO and from the magnetic property of Fe3O4, the hybrid possesses quite a good (although unoptimized) and versatile adsorption capacity to the dyes under investigation, and can be easily and rapidly extracted from water by magnetic attraction. Most importantly, it is found that by simply annealing in moderate conditions, this hybrid adsorbent can be easily and efficiently regenerated for reuse with hardly any compromise of the adsorption capacity. Furthermore, the adsorbability of this hybrid shows satisfactory tolerance against the variations in both pH environment and dye concentration. Even when exposed to a multi dye cocktail, the hybrid can work well without suppressing the adsorption capacity for each of the dyes, as compared with that measured separately. The inherent advantages of this nanostructured adsorbent, such as non-compromised adsorption capacity, low cost, easy, rapid extraction and regeneration, good tolerance, multiplex adsorbability, and handy operation, may pave a new, efficient and sustainable way towards highly-efficient dye pollutant removal in Earths water environments.

Tuning Chemical Enhancement of SERS by Controlling the Chemical Reduction of Graphene Oxide Nanosheets

Chemical enhancement is an important mechanism in surface-enhanced Raman spectroscopy. It is found that mildly reduced graphene oxide (MR-GO) nanosheets can significantly increase the chemical enhancement of the main peaks by up to 1 order of magnitude for adsorbed Rhodamine B (RhB) molecules, in comparison with the mechanically exfoliated graphene. The observed enhancement factors can be as large as ∼10(3) and show clear dependence on the reduction time of graphene oxide, indicating that the chemical enhancement can be steadily controlled by specific chemical groups. With the help of X-ray photoelectron spectra, these chemical species are identified and the origin of the observed large chemical enhancement can thus be revealed. It is shown that the highly electronegative oxygen species, which can introduce a strong local electric field on the adsorbed molecules, are responsible for the large enhancement. In contrast, the local defects generated by the chemical reduction show no positive correlation with the enhancement. Most importantly, the dramatically enhanced Raman spectra of RhB molecules on MR-GO nanosheets reproduce all important spectral fingerprints of the molecule with a negligible frequency shift. Such a unique noninvasive feature, along with the other intrinsic advantages, such as low cost, light weight, easy availability, and flexibility, makes the MR-GO nanosheets very attractive to a variety of practical applications.

Direct writing of electronic devices on graphene oxide by catalytic scanning probe lithography

Reduction of graphene oxide at the nanoscale is an attractive approach to graphene-based electronics. Here we use a platinum-coated atomic force microscope tip to locally catalyse the reduction of insulating graphene oxide in the presence of hydrogen. Nanoribbons with widths ranging from 20 to 80u2009nm and conductivities of >104u2009Su2009m−1 are successfully generated, and a field effect transistor is produced. The method involves mild operating conditions, and uses arbitrary substrates, atmospheric pressure and low temperatures (≤115u2009°C).

High Performance Ultraviolet Photodetector Fabricated with ZnO Nanoparticles‐graphene Hybrid Structures

Ultraviolet (UV) photodetector constructed by ZnO material has attracted intense research and commercial interest. However, its photoresistivity and photoresonse are still unsatisfied. Herein, we report a novel method to assemble ZnO nanoparticles (NPs) onto the reduced graphite oxide (RGO) sheet by simple hydrothermal process without any surfactant. It is found that the high‐quality crystallized ZnO NPs with the average diameter of 5 nm are well dispersed on the RGO surface, and the density of ZnO NPs can be readily controlled by the concentration of the precursor. The photodetector fabricated with this ZnO NPs‐RGO hybrid structure demonstrates an excellent photoresponse for the UV irradiation. The results make this hybrid especially suitable as a novel material for the design and fabrication of high performance UV photodector.

Synthesis of Nitrogen-Doped Graphene via Thermal Annealing Graphene with Urea

Chemical doping is an effective method to intrinsically modify the chemical and electronic property of graphene. We propose a novel approach to synthesize the nitrogen-doped graphene via thermal annealing graphene with urea, in which the nitrogen source can be controllably released from the urea by varying the annealed temperature and time. The doped N content and the configuration N as well as the thermal stabilities are also evaluated with X-ray photoelectron spectroscopy and Raman spectra. Electrical measurements indicate that the conductivity of doped graphene can be well regulated with the N content. The method is expected to produce large scale and controllable N-doped graphene sheets for a variety of potential applications.

A Green and Mild Approach of Synthesis of Highly-Conductive Graphene Film by Zn Reduction of Exfoliated Graphite Oxide

We report a simple and green approach to synthesize reduced graphene oxide (RGO) nanosheets at room temperature based on Zn reduction of exfoliated GO. The evolution of GO to RGO has been characterized by X-ray diffraction, UV-Vis absorption spectroscopy and Raman spectroscopy. The results of X-ray photoelectron spectroscopy reveal that the atomic ratio of carbon to oxygen in the RGO can be tuned from 1.67 to 13.7 through controlling the reduction time. Moreover, the conductivity of the RGO is measured to be 26.9±2.2 kS/m, much larger than those previously obtained by chemical reduction through other reducing agents. More importantly, the resistance of the RGO film with 20 nm thickness can be as low as 2 kΩ/square, while a high transparency over 70% within a broad spectral range from 0.45 μm to 1.50 μm can be retained. The proposed method is low-cost, eco-friendly and highly-efficient, the as-prepared thinner RGO films are useful in a variety of potential application fields such as optoelectronics, photovoltaics and electrochemistry by serving as an ultralight, flexible and transparent electrode material.

Facile route to synthesis and morphology control of anionic waterborne polyurethane hollow microspheres via self-crosslinking reaction

Porous waterborne polyurethane (WPU) hollow microspheres were synthesized via a self-crosslinking reaction of WPU prepolymer terminated by 3-aminopropyltriethoxysilane (APTES). The microspheres with different morphologies were fabricated by changing the content of small molecules and hydrophilic groups.

Highly efficient and controllable method to fabricate ultrafine metallic nanostructures

We report a highly efficient, controllable and scalable method to fabricate various ultrafine metallic nanostructures in this paper. The method starts with the negative poly-methyl-methacrylate (PMMA) resist pattern with line-width superior to 20 nm, which is obtained from overexposing of the conventionally positive PMMA under a low energy electron beam. The pattern is further shrunk to sub-10 nm line-width through reactive ion etching. Using the patter as a mask, we can fabricate various ultrafine metallic nanostructures with the line-width even less than 10 nm. This ion tailored mask lithography (ITML) method enriches the top-down fabrication strategy and provides potential opportunity for studying quantum effects in a variety of materials.

Utilization of Resist Stencil Lithography for Multidimensional Fabrication on a Curved Surface

The limited ability to fabricate nanostructures on nonplanar rugged surfaces has severely hampered the applicability of many emerging technologies. Here we report a resist stencil lithography based approach for in situ fabrication of multidimensional nanostructures on both planar and uneven substrates. By using the resist film as a flexible stencil to form a suspending membrane with predesigned patterns, a variety of nanostructures have been fabricated on curved or uneven substrates of diverse morphologies on demand. The ability to realize 4 in. wafer scale fabrication of nanostructures as well as line width resolution of sub-20 nm is also demonstrated. Its extraordinary capacity is highlighted by the fabrication of three-dimensional wavy nanostructures with diversified cell morphologies on substrates of different curvatures. A robust general scheme is also developed to construct various complex 3D nanostructures. The use of conventional resists and processing ensures the versatility of the method. Such an in situ lithography technique has offered exciting possibilities to construct nanostructures with high dimensionalities that can otherwise not be achieved with existing nanofabrication methods.

Graphene/TiO2 hybrid layer for simultaneous detection and degradation by a one-step transfer and integration method

During the past decades, researchers have made great efforts towards an ideal surface enhanced Raman spectroscopy (SERS) substrate. Here a smart SERS-active flexible substrate was designed and its performance was studied. The substrate is constructed from graphene and TiO2, and could be divided into two functional layers. Graphene provides a flat hot surface for Raman enhancement, which could be ascribed to chemical enhancement. The TiO2 layer is an effective photocatalyst, which could induce photocatalytic decomposition of adsorbed molecules under UV irradiation. Notably, the substrate was realized by a one-step transfer method, followed by annealing. In the synthesis process, a flexible TiO2 layer was produced by spin-coating on the CVD graphene and was used as a support in the transfer process of graphene instead of PMMA, which could exclude contamination and avoid degradation of the Raman enhancement performance. Combining detection with degradation of trace amounts of analyte, the versatility of the SERS substrate is greatly enhanced and could be adapted to fit a wide range of sensing and photocatalytic applications.