John H. Xin

Self-cleaning cotton

Nanocrystalline titanium dioxide has been prepared under ambient pressure and at temperatures close to or approaching room temperature using hydrolysis of titanium tetraisopropoxide in an acidic aqueous solution. A transparent thin layer of nanocrystalline titania has been produced on cotton textiles by a dip-pad–dry-cure process. These TiO2 coated cotton textiles possess significant photocatalytic self-cleaning properties, such as bactericidal activity, colorant stain decomposition and degradation of red wine and coffee stains. The UV absorption and tearing strength of the TiO2 coated cotton has also been studied. Self-cleaning cotton may find potential commercialization in the textile industry.

A New Approach to UV-Blocking Treatment for Cotton Fabrics

In this study, a new approach to a uv-blocking treatment for cotton fabrics is developed using the sol-gel method. The treatment forms a thin layer of titania on the surface of cotton fibers, and the treated fabrics show much improved protection against UV radiation. with a UPF factor of 50+ or excellent protection according to the Australian/New Zealand standards. The treated fabrics are also tested for washfastness. The results show that the excellent uv protection rating of the treated fabrics can be maintained even after 55 home launderings, indicating a high level of adhesion between the titania layer and the cotton. A bursting strength test of the treated fabrics shows no adverse effect from the treatment.

Role of Hydrogen in Graphene Chemical Vapor Deposition Growth on a Copper Surface

Synthesizing bilayer graphene (BLG), which has a band gap, is an important step in graphene application in microelectronics. Experimentally, it was broadly observed that hydrogen plays a crucial role in graphene chemical vapor deposition (CVD) growth on a copper surface. Here, by using ab initio calculations, we have revealed a crucial role of hydrogen in graphene CVD growth, terminating the graphene edges. Our study demonstrates the following. (i) At a low hydrogen pressure, the graphene edges are not passivated by H and thus tend to tightly attach to the catalyst surface. As a consequence, the diffusion of active C species into the area beneath the graphene top layer (GTL) is prohibited, and therefore, single-layer graphene growth is favored. (ii) At a high hydrogen pressure, the graphene edges tend to be terminated by H, and therefore, its detachment from the catalyst surface favors the diffusion of active C species into the area beneath the GTL to form the adlayer graphene below the GTL; as a result, the growth of BLG or few-layer graphene (FLG) is preferred. This insightful understanding reveals a crucial role of H in graphene CVD growth and paves a way for the controllable synthesis of BLG or FLG. Besides, this study also provides a reasonable explanation for the hydrogen pressure-dependent graphene CVD growth behaviors on a Cu surface.

Synthesis and stabilization of metal nanocatalysts for reduction reactions – a review

Since the fast development of various chemical industries nowadays poses a serious threat to the environment in terms of leaving behind an increasing quantity of aromatic pollutants, to find an effective approach for handling aromatic pollutants is of growing scientific and technological importance. Numerous research studies have attempted to address the environmental problems caused by aromatic pollutants with much attention to water-soluble aromatic dye and nitro compounds. In particular, the catalytic reduction of dye and nitro compounds over metal-based catalysts has gained much interest in these years. However, review studies are rarely reported that summarize the contributions in this hot research area. Herein, we perform a review study to summarize these contributions, to discuss the existing problems, and to offer guidelines for future exploration; in the meanwhile, other methods for processing aromatic pollutants are also briefly introduced. It is well known that the reduction reaction is highly dependent on catalysts since the reaction between an aromatic compound and a reducing agent either cannot take place or proceeds very slowly if without the assistance of a catalyst. As a result, this review article pays special attention to the widely reported metal-based catalysts for the reduction reaction. These catalysts are categorized into different groups on the basis of the stabilizing systems utilized for synthesis of metal catalysts, mainly including surfactants/ligands, polymer supports, unmodified inorganic supports, functionalized inorganic supports, and organic combined with inorganic supports. As an important material in science and technology, especially in the field of catalysis due to its unique 2D structure and remarkable physicochemical properties, graphene used for supporting and stabilizing metal catalysts for the catalytic reduction reaction is specifically reviewed and summarized in the article. Finally, the remaining problems associated with the design and fabrication of cost-effective, efficient, and durable metal-based catalysts for aromatic pollutant reduction are outlined.

Facile preparation of anatase/SiO2 spherical nanocomposites and their application in self-cleaning textiles

Anatase TiO2/SiO2 nanocomposites were prepared by a sol–gel process at a low temperature. The structural properties of these as-prepared nanocomposites were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing that TiO2 nanoparticles were deposited on the surface of SiO2 spheres. The spherical TiO2/SiO2 nanocomposites were coated onto cotton fabrics by a simple dip-pad–dry-cure process. The treated cotton fabrics demonstrated higher photocatalytic activity in comparison to pure TiO2 treated cotton fabrics in a typical photocatalytic test using a model compound of Neolan Blue 2G dye. Our results demonstrate that this composite material is a step towards better self-cleaning performance of textile materials.

Super-hydrophobic surfaces from a simple coating method: a bionic nanoengineering approach

Inspired by the self-cleaning behaviour of lotus leaves in nature, we developed a simple coating method that can facilitate the bionic creation of super-hydrophobic surfaces on various substrates, thus providing a feasible way of fabricating super-hydrophobic surfaces for civil and industrial applications. Micro–nanoscale binary structured composite particles of silica/fluoropolymer were prepared using an emulsion-mediated sol–gel process, and then these composite particles were applied to various substrates to mimic the surface microstructures of lotus leaves. Super-hydrophobic surfaces with a water contact angle larger than 150° are obtained, and these super-hydrophobic surfaces are expected to have potential applications for rusting-resistant, anti-fog and self-cleaning treatments.

Temperature-Triggered Collection and Release of Water from Fogs by a Sponge-Like Cotton Fabric

A sponge-like cotton fabric autonomously collects and releases water from fogs triggered by typical day-and-night temperature variations. The reversible switching between absorbing-superhydrophilic/releasing-superhydrophobic states results from structural changes of a temperature-responsive polymer grafted on the very rough fabric-surface. This material and concept presents a breakthrough into simple and versatile solutions for collection, uni-directional flow, and purification of water captured from the atmosphere.

Hydrophobic duck feathers and their simulation on textile substrates for water repellent treatment.

Inspired by the non-wetting phenomena of duck feathers, the water repellent property of duck feathers was studied at the nanoscale. The microstructures of the duck feather were investigated by a scanning electron microscope (SEM) imaging method through a step-by-step magnifying procedure. The SEM results show that duck feathers have a multi-scale structure and that this multi-scale structure as well as the preening oil are responsible for their super hydrophobic behavior. The microstructures of the duck feather were simulated on textile substrates using the biopolymer chitosan as building blocks through a novel surface solution precipitation (SSP) method, and then the textile substrates were further modified with a silicone compound to achieve low surface energy. The resultant textiles exhibit super water repellent properties, thus providing a simple bionic way to create super hydrophobic surfaces on soft substrates using flexible material as building blocks.

Room temperature synthesis of rutile nanorods and their applications on cloth

In order to achieve better photocatalytic performance, rutile nanorods dispersed in anatase and brookite phases were synthesized from titanium isopropoxide (TIP) in a concentrated HNO3 solution at room temperature (23 °C). X-ray diffraction results indicated that the percentage of rutile increased with increasing peptization time. Scanning electron microscopy and and high-resolution transmission electron microscopy measurements revealed that the nanosized titania particles mainly consisted of granular anatase and brookite, and rod-like rutile. It was interesting that the stability of the colloid increased with increasing nanoparticle concentration, and the tricrystalline titania showed a photocatalytic activity higher than that of pure anatase. These nanocrystals were applied onto cotton fabrics, and achieved a promising bactericidal photocatalytic activity and excellent protection against UV radiation.

Reflectance reconstruction for multispectral imaging by adaptive Wiener estimation.

In multispectral imaging, Wiener estimation is widely adopted for the reconstruction of spectral reflectance. We propose an improved reflectance reconstruction method by adaptively selecting training samples for the autocorrelation matrix calculation in Wiener estimation, without a prior knowledge of the spectral information of the samples being imaged. The performance of the proposed adaptive Wiener estimation and the traditional method are compared in the cases of different channel numbers and noise levels. Experimental results show that the proposed method outperforms the traditional method in terms of both spectral and colorimetric prediction errors when the imaging channel number is 7 or less. When the imaging system consists of 11 or more channels, the color accuracy of the proposed method is slightly better than or becomes close to that of the traditional method.