Junhui Xiang

Surface Modification of Bacterial Cellulose Aerogels’ Web-like Skeleton for Oil/Water Separation

The cellulose nanofibers of bacterial cellulose aerogel (BCA) are modified only on their surfaces using a trimethylsilylation reaction with trimethyichlorosilane in liquid phase followed by freeze-drying. The obtained hydrophobic bacterial cellulose aerogels (HBCAs) exhibit low density (≤6.77 mg/cm(3)), high surface area (≥169.1 m(2)/g), and high porosity (≈ 99.6%), which are nearly the same as those of BCA owing to the low degrees of substitution (≤0.132). Because the surface energy of cellulose nanofibers decreased and the three-dimensional web-like microstructure, which was comprised of ultrathin (20-80 nm) cellulose nanofibers, is maintained during the trimethylsilylation process, the HBCAs have hydrophobic and oleophilic properties (water/air contact angle as high as 146.5°) that endow them with excellent selectivity for oil adsorption from water. The HBCAs are able to collect a wide range of organic solvents and oils with absorption capacities up to 185 g/g, which depends on the density of the liquids. Hence, the HBCAs are wonderful candidates for oil absorbents to clean oil spills in the marine environment. This work provides a different way to multifunctionalize cellulose aerogel blocks in addition to chemical vapor deposition method.

Flexible aerogels based on an interpenetrating network of bacterial cellulose and silica by a non-supercritical drying process

Flexible and crack-free bacterial cellulose (BC)–silica composite aerogels (CAs) are prepared through a sol–gel process followed by freeze drying, in which the BC matrix and silica gel skeleton form an interpenetrating network microstructure. The BC–silica CAs exhibit low density (0.02 g cm−3), high specific surface area (734.1 m2 g−1) and low thermal conductivity (0.031 W m−1 K−1), almost the same as pure silica aerogels. Due to the synergic effects of the BC matrix and silica gel skeleton, the obtained CAs show excellent robustness and flexibility which overcome the inherent fragility of traditional inorganic aerogels. Furthermore, the dried CAs can withstand a huge capillary force and keep their integrity and flexibility even upon being immersed in a liquid phase again. Hence, the CAs can be functionalized conveniently in a liquid phase to extend their applications. The hydrophobization modified CAs have potential to be used as adsorbents for water purification and show excellent oil absorption capability on the surface of water, and can be removed from water conveniently.

Preparation of hierarchical C@MoS2@C sandwiched hollow spheres for lithium ion batteries

Hierarchical C@MoS2@C hollow spheres with active MoS2 nanosheets being sandwiched by carbon layers have been produced using a modified template method. The process applies polydopamine (PDA) layers that inhibit morphological changes of the template, enforcing the hollow microsphere structure. In addition, PDA forms complexes with the Mo precursor, leading to the in situ growth of MoS2 on its surface and preventing the nanosheets from agglomeration. It also supplies the carbon that finally sandwiches the 100–150 nm thin MoS2 spheres. The resulting hierarchically structured material provides a stable microstructure, where carbon layers strongly linked to MoS2 offer efficient pathways for electron and ion transfer, and concomitantly buffer the volume changes inevitably appearing during the charge–discharge process. Carbon-sandwiched MoS2-based electrodes exhibit high specific capacity of approximately 900 mA h g−1 after 50 cycles at 0.1C, excellent cycling stability up to 200 cycles, and superior rate performance. The versatile synthesis method reported here offers a general route to design hollow sandwich structures with a variety of different active materials.

Flexible aerogels with interpenetrating network structure of bacterial cellulose–silica composite from sodium silicate precursor via freeze drying process

Bacterial cellulose (BC)–silica composite aerogels (CAs) with interpenetrating network (IPN) microstructure are prepared through a permeation sol–gel process followed by freeze drying. The IPN structure is constructed by diffusing the precursor into a three-dimensional (3D) BC matrix followed by permeating the catalyst into the BC network gradually to promote the in situ condensation of precursor to form a SiO2 gel skeleton from outside to inside. The precursor used here is Na2SiO3 instead of traditional tetraethoxysilane. This IPN structure could offer excellent mechanical properties to aerogels, and is essential to prepare flexible aerogels by freeze drying. The compression modulus of CAs could be adjusted in the range of 0.38 MPa to 16.17 MPa. The BC–silica CAs exhibit low density (as low as 0.011 g cm−3), high specific surface area (as high as 534.5 m2 g−1) and low thermal conductivity (less than 0.0369 W m−1 K−1). Furthermore, the contact angle of the hydrophobization modified CAs is as high as 145°. The outstanding hydrophobicity and the large specific surface area endow the hydrophobic CAs with excellent oil absorption capability on the water surface. Moreover, the hydrophobic CAs that had absorbed oil could be washed and recycled.

Photocontrollable J-Aggregation of a Diarylethene–Phthalocyanine Hybrid and Its Aggregation-Stabilized Photochromic Behavior

The photocontrollable J-aggregation of a diarylethene-phthalocyanine hybrid (T-ZnPc) and its aggregation-stabilized photochromic behavior were investigated by various techniques. T-ZnPc initially exhibited slight J-aggregation tendency in solvents such as chloroform and toluene through conformational planarization effect, but formed much stronger J-aggregates upon the illumination of 254 nm UV light. In darkness, the UV-irradiated solutions gradually returned to their initial state. These phenomena can be explained by the pronounced change in molecular planarity accompanying the reversible isomerization of the diarylethene units of T-ZnPc. Besides, we have found that the thermal stability of the closed-ring diarylethene isomers in molecularly dispersed T-ZnPc is much poorer than that in aggregates. As long as the aggregates were broken, they converted to corresponding open-ring form instantly. This study provided an example of fully photocontrollable aggregation of phthalocyanines and paved a new way for improving the stability of the photochromic systems.

A facile synthesis method and electrochemical studies of a hierarchical structured MoS2/C-nanocomposite

A uniformly coated MoS2/carbon-nanocomposite with a three-dimensional hierarchical architecture based on carbonized bacterial cellulose (CBC) nanofibers is synthesized by a facile one-step hydrothermal method followed by thermal annealing at 700 °C in an Ar atmosphere. Strong hydrogen bonds between the Mo precursor and the BC nanofibers are found to be crucial for the in situ growth of MoS2 nanosheets on the nanofibers during the hydrothermal process. The fibrous structure was maintained and the connection between MoS2 and the nanofibers were strengthened in the sintering process, leading to an improved stability of the resulting nanocomposite upon electrochemical cycling. The low-cost and environmentally friendly 3D web-like structure enables binder-free and carbon-free electrodes for lithium-ion batteries, which exhibit high specific discharge capacities up to 1140 mA h g−1 at the C-rate of 1C without significant capacity fading for over 50 cycles. The porous conductive hierarchical structure of the composite endows excellent rate performance by avoiding the aggregation of the MoS2 nanosheets and by accommodating mechanical stress which appears upon electrochemical cycling.

Morphology controlling of calcium carbonate by self-assembled surfactant micelles on PET substrate

Spherical and hexagonal CaCO3 with hierarchical structures were prepared on surfactant-modified PET substrate between the interfaces of saturated Ca(OH)2 solution and n-hexane. The results show that CaCO3 synthesis follows the same nanoparticle-mediated self-organization process but the morphology of the products strongly depends on the properties of surfactant modification. The synthetic procedure offers several important characteristics for CaCO3 superstructure fabrication. Surfactants in this experimental system act not only as templates, but also as regulators for the fabrication of superstructures. This biomimetic system will be promising in synthesizing other functional nanoparticles or nanodevices.

Cellulose-Silica Composite Aerogels Prepared with Sodium Silicate by Freeze Drying Method

The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na2SiO3 instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na2SiO3 to form a SiO2 gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO2 gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m2 g-1) and low density (less than 0.182 g cm-3).

Bacterial Cellulose Aerogels Skeleton Strengthened by Regenerated Cellulose

Soft skeleton of bacterial cellulose aerogels (BCAs) was strengthened effectively by conformal coverage of regenerated cellulose to make sure the BCAs sustain more compression. After freeze drying, compression modulus of the strengthened sample is significantly higher than that of the BCAs, which endows the former more extensive applications. The regenerated cellulose solution was prepared by gelation of cellulose from aqueous alkali hydroxide/urea solution. Then the bacterial cellulose wet gels bulks were immersed in the regenerated cellulose solution with different contents to discuss the enhanced effect of the BCAs skeleton. The morphology of the enhanced BCAs was observed by scanning electron micrograph (SEM).The porous structure of the enhanced BCAs was investigated by Brunauer-Emmett-Teller (BET) instrument. The stress−strain curves of the enhanced BCAs were measured. The XRD pattern of the strengthened sample was also carried out. The results indicated that regenerated cellulose forms thin layers which conformally covered bacterial cellulose skeleton fibers and that had little effect on microstructure and crystal form of the bulk cellulose aerogels.

Liquid Phase Deposited TiO2 Films on Stainless Steel Mesh for Corrosion Resistance Application

Liquid phase deposition (LPD) method was used to prepare corrosion protective titanium dioxide (TiO2) film coatings on the stainless steel mesh which is composed of steel wires at a relatively low temperature (80°C). The as-prepared TiO2 coated samples were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectra (EDX). It was observed that the TiO2 film coatings could conformally coat the stainless steel wires which play a significant role in the corrosion resistance. The corrosion resistance of the samples was evaluated using Tafel polarization curves in a three-electrode electrochemical examination system. The TiO2 deposited samples all showed a certain improvement of corrosion resistance. Compared with the sample prepared in the acid condition (PH=3.7), the low alkaline (PH=9.5) sample could provide better corrosion protection which could increase the corrosion potential (Ecorr) from-0.53 V to-0.17 V.