Zhiyu Ren

Morphology and wettability control of silicon cone arrays using colloidal lithography.

In this paper we present a simple method to fabricate ordered silicon cone arrays with controllable morphologies on a silicon substrate using reactive ion etching with two-dimensional silica colloidal crystals as masks. The etching process and the morphologies of the obtained structure are quantified. Unlike works reported previously, we show that the surface roughness of the obtained silicon cone arrays can be adjusted by controlling the etching duration, which is proved to be of importance in tailoring the behavior of water droplets when being used as antireflection coatings with superhydrophobicity. Moreover, this strategy is compatible with the methods we have established on controlling the arrangement of colloidal spheres, and thus silicon cone arrays with tunable periodicities, different lattice structures, and various patterns can be prepared. The obtained silicon cone arrays with strips can be used as hydrophobic substrates with anisotropic dewetting just like the leaves of rice. It is found that by adjusting the strip width with and without silicon cones, the water droplets can transform from isotropic dewetting to anisotropic dewetting.

Morphology-controlled two-dimensional elliptical hemisphere arrays fabricated by a colloidal crystal based micromolding method

In this paper, we demonstrate a facile modified micromolding method to fabricate morphology-controlled elliptical hemisphere arrays (EHAs) by using stretched poly(dimethylsiloxane) (PDMS) nanowell arrays as molds. The PDMS nanowell arrays were fabricated via casting PDMS prepolymer onto two-dimensional (2D) non-close-packed (ncp) colloidal sphere arrays. By varying the stretching direction, stretching force, size of the colloidal spheres used and other experimental conditions in the fabrication process, we can control the shape, aspect ratio and size of the resulting microstructures. Moreover, our method does not involve any costly micromanufacture technique and can be applied to a great many materials, such as oil soluble polymers (e.g. polystyrene (PS)), water soluble polymers (e.g. poly(vinyl pyrrolidone) (PVP)), cross-linked polymers (e.g. photopolymerizable resin) and a variety of composites (e.g. polymer/nanoparticle composite). The anisotropic wetting properties of these EHAs were demonstrated. Potential application of the EHAs is to provide a model for the fundamental research of anisotropic surfaces and a template or mask for the fabrication of anisotropic surface patterns for potential applications of shape-dependent optical and magnetic devices.

Building cavities in microspheres and nanospheres

This paper describes a simple method of sculpturing cavities in silica spheres by reactive ion etching using a polymer as the mask, and investigates the changing process in detail. The morphology of the cavity in the silica structure undergoes transformation in three steps: (1) increase of the diameters of the opening of the cavities; (2) increase of the depth of the cavities; and (3) change in geometry of the resulting structure. As a result, silica bowls or silica rings could be obtained by controlling the etching stage, and this approach can be extended to a wide range, from a micrometer to a nanometer, based on the silica spheres.

Stably dispersed carbon nanotubes covalently bonded to phthalocyanine cobalt(II) for ppb-level H2S sensing at room temperature

Cost-efficient, highly sensitive and stable sensing materials play a key role in developing H2S sensors. Herein, tetra-β-carboxyphenyloxyphthalocyanine cobalt(II) (cPcCo) has been successfully bonded on the surface of acidified multiwalled carbon nanotubes (aCNTs) by a facile two-step condensation reaction in the presence of N,N′-dicyclohexylcarbodiimide (DCC), using hydroquinone (HQ), p-aminophenol (PAP), and p-phenylenediamine (PPD) as linking molecules, respectively. The obtained cPcCo–B–aCNT (B= HQ, PAP, and PPD) hybrids display good dispersibility in ethanol, which is beneficial to construct uniform sensing devices. The cPcCo–B–aCNT sensors, with a loose network-like structure, present abundant exposed sensing sites, oriented transmission of charges, and unimpeded pathways for H2S diffusion, which endow the cPcCo–B–aCNT hybrids with excellent sensing performance, in terms of sensitivity, reliability, reproducibility, and detection limit. The detection limit of the sensors composed of cPcCo–B–aCNT hybrids towards H2S reaches the ppb-level at room temperature, which is about the same as the odor threshold level for humans. For the cPcCo–HQ–aCNT sensor, the response to H2S varies linearly with respect to its concentration from 20 to 160 ppb and from 320 to 2560 ppb, with the highest gas response of 2.5% to 80 ppb H2S and a low detection limit of 5 ppb. Furthermore, the linking molecules play a critical role in the sensitivity of H2S, as evidenced from the current–voltage characteristics. The systematic study developed here provides a valid way to fabricate other high-efficient H2S sensors.

Assembly of non-close-packed 3D colloidal crystals from 2D ones in a polymer matrix viain situ layer-by-layer photopolymerization

3D colloidal crystals of bi-directional modulation have been fabricated via two steps: (1) the modulation of the sphere interstice in each layer depends on the process of modified microcontact printing (μCP); (2) the layer spacing of the 3D colloidal crystal is determined by the in situ layer-by-layer photopolymerization technology (LBLP). The versatility of this method has been demonstrated by the integration of colloidal spheres with different diameters or patterns.

Phthalocyanine-mediated non-covalent coupling of carbon nanotubes with polyaniline for ultrafast NH3 gas sensors

The development of innovative methods for the integration of carbon nanotubes (CNTs) and polyaniline (PANI) that preserve their exceptional quality, while robustly enriching their gas-sensing features, is still rare and remains challenging for the realization of rapid and sensitive gas detection. Herein, due to the advantages in its structure, tetra-β-carboxyphthalocyanine cobalt(II) (TcPcCo) acts not only as a sensing promoter, but also as an efficient mediator to couple multi-walled CNTs (MCNTs) with PANI, resulting in MCNT@PANI hybrids with a uniform 3D network; the planar 18π-electrons in TcPcCo allow it to closely conjugate on the surface of MCNT by π–π interactions; moreover, the outer –COOH groups in TcPcCo prompt it to link with the aniline monomers based on acid–base interactions. During the subsequent polymerization process, TcPcCo also serves as a protonic acid doped into PANI, increasing the electronic conductivity of PANI. Due to the specific selectivity of TcPcCo, high sensitivity of PANI towards NH3, and good conductivity and stability of the MCNTs, the obtained core–shell MCNT@PANI hybrids demonstrate radically enhanced NH3-sensing performance, especially in terms of response/recovery duration (∼5.0 s/12.0 s to 100 ppm NH3) and selectivity, outperforming the single components and previously reported materials at room temperature. In addition, the MCNT@1.0PANI hybrid shows a superior sensing sensitivity (140.99% to 100 ppm NH3) as well as remarkable stability over 60 days. The proposed strategy, TcPcCo-mediated non-covalent coupling of MCNT with PANI, is of potential importance towards the design and construction of ideal materials for future sensing devices, as well as many other applications.

Generalized Synthesis of Ultrathin Cobalt-Based Nanosheets from Metallophthalocyanine-Modulated Self-Assemblies for Complementary Water Electrolysis

The development of effective approaches for preparing large-area, self-standing, ultrathin metal-based nanosheets, which have proved to be favorable for catalytic applications such as water electrolysis, is highly desirable but remains a great challenge. Reported herein is a simple and versatile strategy to synthesize ultrathin Co3 O4 and CoP NSs consisting of close-packed nanoparticles by pyrolyzing cobalt(II) phthalocyanine/graphene oxide (CoPc/GO) assemblies in air and subsequent topotactic phosphidation while preserving the graphene-like morphology. The strong π-π stacking interactions between CoPc and GO, and the inhibiting effect of the tetrapyrrole-derived macrocycle for grain growth during the catalytic carbon gasification contribute to the NSs forming. The resulting homologous Co3 O4 and CoP NSs display outstanding catalytic activity in alkaline media toward the oxygen evolution reaction and the hydrogen evolution reaction, respectively, ascribed to the richly exposed active sites, and the expedited electrolyte/ion transmission path. The integrated asymmetrical two-electrode configuration also presents a superior cell voltage of 1.63 V at 10 mA cm-2 for overall water splitting, accompanied with the excellent durability during long-term cycling. Further evidences validate that this strategy is appropriate to fabricate graphene-like ultrathin NSs of many other metal oxides, such as Fe2 O3 , NiO, MoO3 , and mixed-metal oxides, for various applications.