Hao-Bo Jiang

Moisture‐Responsive Graphene Paper Prepared by Self‐Controlled Photoreduction

A facile and cost-effective preparation of moisture-responsive graphene bilayer paper by focused sunlight irradiation is reported. The smart graphene paper shows moisture-responsive properties due to selective adsorption of water molecules, leading to controllable actuation under humid conditions. In this way, graphene-based moisture-responsive actuators including a smart claw, an orientable transporter, and a crawler paper robot are successfully developed.

Biomimetic Graphene Surfaces with Superhydrophobicity and Iridescence

Triggered by the fantastic functions and bright appearance of biological systems in nature, enormous efforts have been devoted to biomimetic fabrication. For instance, butterfly wings and red rose petals have attracted increasing attention due to their excellent water repellency and splendid structural color. Consequently, colorful superhydrophobic surfaces have become a hot topic with significance in both fundamental research and practical applications. Previous studies have shown that hierarchical micro-/nanostructures on biosurfaces play a critical role in the multifunctional acquisition. On the one hand, the highly rough textures trap a wealth of air bubbles at the interface preventing a water droplet from spreading; thus, the surfaces exhibit a high water contact angle (CA>1508). Along this line, a variety of water-repellent surfaces with multiscale structures have been achieved by classical “top-down” and “bottomup” approaches. On the other hand, as inspired by many natural species that use structural color as a warning or protection, the surface microstructures are not randomly distributed but rigidly arranged in periodic micro-patterns, and therefore triggered light diffraction and scattering contribute to the brilliant appearance. However, due to technical challenges in the fabrication of uniform and well-defined nanostructures in the long-range order, most of the superhydrophobic surfaces hardly show any structural color. To date, only a few attempts to such multifunctional surfaces have been realized. For instance, Gu et al. fabricated colloidal photonic crystal films with both structural color and superhydrophobicity at the cost of long time and high temperature. Jiang et al. reported multicolor superhydrophobic coatings that depend on metal ions for the appearance of color; in their study, individual samples exhibited a single color. Wu et al. fabricated superhydrophobic surfaces with iridescence by employing multiple procedures including interference, surface modification, and chemical plating. Consequently, a facile and convenient approach for surfaces with superhydrophobicity and iridescent structural color is in urgent need. Unlike the classical slippery superhydrophobic surface represented by the famous self-cleaning lotus leaf, rose petals possess a sticky superhydrophobicity, exhibiting both a high water contact angle (CA>1508) and strong adhesion. Because of the adhesive force, flowers are able to maintain a fresh appearance, as a water droplet cannot roll off effortlessly but stays stably on the surface without any movement. To date, by tailoring the chemical composition, the geometrical structure, or interfacial capillary and van der Waals forces, superhydrophobic surfaces with high adhesion were successfully prepared. Due to their representativeness in wetting behavior and their research value in various realms, such as liquid transportation in microfluidic systems and biomedical applications, high-adhesion surperhydrophobic surfaces become increasingly important. Recently, graphene has attracted much attention due to its unique single atom-layer structure, which contributes to its wide applications in nanoelectronics, sensing devices, energy storage, and even tissue engineering. For example, graphene has proven to be a promising biocompatible scaffold that could accelerate the specific differentiation of human mesenchymal stem cells (hMSCs) into bone cells. In this case, the cell adhesion on the graphene surface plays a critical role in the long-term differentiation; therefore, a precise control of the surface wettability of graphene becomes a significant issue. Generally, superhydrophobic graphene substrates could be fabricated by using an irregular stack of graphene oxides (GO) prepared by chemical oxidation of graphite. In this procedure, to reduce the surface energy, the hydrophilic oxygen-containing groups on the GO surface have to be removed beforehand. To the best of our knowledge, modulation of the wetting property of graphene by micro-/nanostructuring and simultaneous control of chemical composition have not been realized. Moreover, despite the pioneering biomimetic fabrications of periodic micro-/nanostructures based on a wide range of materials, a bioinspired graphene surface with properties comparable to natural surfaces has not been reported yet. [a] J.-N. Wang, R.-Q. Shao, Dr. Y.-L. Zhang, L. Guo, Prof. H.-B. Sun State Key Laboratory on Integrated Optoelectronics College of Electronic Science and Engineering Jilin University 2699 Qianjin Street, Changchun 130012 (P. R. China) Fax: (+86)431-85168281 E-mail : yonglaizhang@jlu.edu.cn hbsun@jlu.edu.cn [b] H.-B. Jiang, D.-X. Lu, Prof. H.-B. Sun College of Physics Jilin University 2699 Qianjin Street, Changchun 130012 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100882.

A SERS-active microfluidic device with tunable surface plasmon resonances†

A surface‐enhanced Raman scattering (SERS)‐active microfluidic device with tunable surface plasmon resonances is presented here. It is constructed by silver grating substrates prepared by two‐beam laser interference of photoresists and subsequent metal evaporation coating, as well as PDMS microchannel derived from soft lithography. By varying the period of gratings from 200 to 550 nm, surface plasmon resonances (SPRs) from the metal gratings could be tuned in a certain range. When the SPRs match with the Raman excitation line, the highest enhancement factor of 2×107 is achieved in the SERS detection. The SERS‐active microchannel with tunable SPRs exhibits both high enhancement factor and reproducibility of SERS signals, and thus holds great promise for applications of on‐chip SERS detection.

Surface and Interface Engineering of Graphene Oxide Films by Controllable Photoreduction.

We report herein the engineering of the surface/interface properties of graphene oxide (GO) films by controllable photoreduction treatment. In our recent works, typical photoreduction processes, including femtosecond laser direct writing (FsLDW), laser holographic lithography, and controllable UV irradiation, have been employed to make conductive reduced graphene oxide (RGO) microcircuits, hierarchical RGO micro-nanostructures with both superhydrophobicity and structural color, as well as moisture-responsive GO/RGO bilayer structures. Compared with other reduction protocols, for instance, chemical reduction and thermal annealing, the photoreduction strategy shows distinct advantages, such as mask-free patterning, chemical-free modification, controllable reduction degree, and environmentally friendly processing. These works indicate that the surface and interface engineering of GO through controllable photoreduction of GO holds great promise for the development of various graphene-based microdevices.

Flame treatment of graphene oxides: cost-effective production of nanoporous graphene electrode for Lithium-ion batteries.

A facile production of highly porous graphene foam by using flame treatment of graphene oxide (GO) is proposed. Highly porous architectures with randomly distributed micro-crack and micro-slit were produced due to the high temperature induced ruinous reduction and rapid expansion of GO. Synchronously, abundant oxygen-containing groups (OCGs) on GO sheets could be effectively removed after flame treatment, which renders significantly increased conductivity to the resultant flame reduced GO (FR-GO). The synergistic effect of micro/nanostructuring and the OCGs removal makes FR-GO a promising candidate for electrode materials. Compared with chemically reduced GO (CR-GO), FR-GO delivers much higher specific capacity. It gives us some hints that flame treatment of graphene-based material is a smart strategy for cost-effective production of anode materials for commercial application.

Femtosecond Laser Direct Writing of Flexible All-Reduced Graphene Oxide FET

Reported here is the facile fabrication of all-reduced graphene oxide (RGO) field-effect-transistor (FET) on flexible substrates using a solo femtosecond laser direct writing (FsLDW) technology. By simply tuning the intensity of a femtosecond laser pulse, GO could be reduced in a controlled manner. Metallic and semiconducting RGO micro-patterns could be achieved by FsLDW under high and moderate laser power, respectively, which enables direct writing of source/drain and gate electrodes, as well as semiconducting channel of a FET on flexible substrates in ambient condition. In this way, a metal-free all-RGO FET was successfully fabricated by FsLDW without the use of any masks or chemical reagents. FsLDW of all-RGO devices shows unique advantages in both facile fabrication and flexible integration of graphene-based micro-devices, revealing great potential for the development of future electronics.

Bioinspired Fabrication of one dimensional graphene fiber with collection of droplets application

We designed a kind of smart bioinspired fiber with multi-gradient and multi-scale spindle knots by combining polydimethylsiloxane (PDMS) and graphene oxide (GO). Multilayered graphene structures can produce obvious wettability change after laser etching due to increased roughness. We demonstrate that the cooperation between curvature and the controllable wettability play an important role in water gathering, which regulate effectively the motion of tiny water droplets. In addition, due to the effective cooperation of multi-gradient and multi-scale hydrophilic spindle knots, the length of the three-phase contact line (TCL) can be longer, which makes a great contribution to the improvement of collecting efficiency and water-hanging ability. This study offers a novel insight into the design of smart materials that may control the transport of tiny drops reversibly in directions, which could potentially be extended to the realms of in microfluidics, fog harvesting filtration and condensers designs, and further increase water collection efficiency and hanging ability.

Reed leaf-inspired graphene films with anisotropic superhydrophobicity

Controlling the wettability of graphene and its derivatives is critical for broader applications. However, the dynamic dewetting performance of graphene is usually overlooked. Currently, superhydrophobic graphene with an anisotropic wettability is rare. Inspired by natural reed leaves, we report an ingenious fabrication process combining photolithography and laser holography technologies to create biomimetic graphene surfaces that demonstrate anisotropic wettability along two directions of grooved hierarchical structures, which are similar to reed leaf veins. Microgrooved structures with a period of 200 μm were fabricated via photolithography to endow the substrate with an obvious anisotropic wettability. Two-beam laser interference treatments of the graphene oxide (GO) film on the grooved substrate removed most of the hydrophilic oxygen-containing groups on the GO sheets and increased the surface roughness by introducing additional hierarchical micro-nanostructures. The combined effects endowed the resultant graphene films with a unique anisotropic superhydrophobicity similar to that of reed leaves. Superhydrophobic graphene surfaces with anisotropic antiwetting behavior might allow further innovations based on graphene in the fields of bionics and electronics.

Facile fabrication of moisture responsive graphene actuators by moderate flash reduction of graphene oxides films

We reported here a facile, green, and simple method to fabricate moisture-responsive graphene actuators by moderate flash reduction of graphene oxides (GO) films. Due to the limited light transparency and thermal relaxation, the oxygen containing groups (OCGs) on the GO sheets could be selectively removed from the radiation side, forming a photoreduction gradient along the lateral direction of the GO film. In this manner, we obtained a reduced GO (RGO)/GO bilayer film. The RGO/GO film can bend to the RGO side when exposed to moisture because RGO and GO layers show different absorption capabilities of water molecules. Taking advantage of this controllable deformation, we fabricated moisture-responsive actuators including a crawler and claw robots.

Facile fabrication of flexible graphene FETs by sunlight reduction of graphene oxide

We reported here a facile fabrication of flexible graphene-based field effect transistors (FETs) by sunlight reduction of graphene oxide (GO) as channel material. As a mask-free and chemical-free method, sunlight photoreduction of GO without the use of any complex equipments is simple and green. The resultant FET demonstrated excellent electrical properties (e.g., an optimized Ion/Ioff ratio of 111, hole mobility of 0.17  cm2  V-1 s-1), revealing great potential for development of flexible microelectrics. Additionally, since the reduced GO channel could be fabricated by sunlight treatment between two pre-patterned electrodes, the process features post-fabrication capability, which makes it possible to integrate graphene-based devices with given device structures.