Chuanfang Yang

Cellulose is a natural polymer that is widely used in daily life, but it is susceptible to microorganism growth. In this study, a simple sol–gel technique was utilized to incorporate the cellulose scaffold with Ag/TiO₂ nanoparticles. The morphology and crystal structure of the as-prepared Ag/TiO₂/cellulose composite film were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. Antibacterial tests involving the use of Escherichia coli (E. coli) were carried out under dark and UV-light conditions to evaluate the efficiency of the Ag/TiO₂/cellulose composite film in comparison with pristine cellulose paper and TiO₂/cellulose composite film. The results indicated that the antibacterial activity of the Ag/TiO₂/cellulose composite film outperformed all other samples, where the Ag content of 0.030 wt% could inhibit more than 99% of E. coli. This study suggests that finely dispersed nanocale Ag/TiO₂ particles in the cellulose scaffold were effective at slowing down bacterial growth, and the mechanisms of this are also discussed.

Coalescence separation is a widely applied technology for oil/water emulsion separation. In this paper, we first review the existing coalescence theories regarding droplet capture, attachment and release. Two case studies are considered, dealing with the separation of oil-in-water emulsions using our recently developed coalescing filters. The first case (Case I) is associated with the separation of surfactant-stabilized hexadecane/water emulsions. The second case (Case II) addresses the separation of sulfonated kerosene/water emulsions in a continuous bench operation. In Case I, known wetting and collision theories were applied to understand the complex coalescence process occurring on the surface of the fibers. For this, the detrimental effect of surfactants on coalescence separation was taken into account. It was found that the best oil wetting coalescing material under water was not the most desired for coalescence, contradicting the existing theory. In addition, once the materials were pre-saturated with surfactant-containing emulsions, the oil wetting was enhanced significantly. However, the separation efficiency was maintained at the same level, unless the material adsorbed surfactant, resulting in minor reductions in the wetting angle. In Case II, based on the fiber properties and operation conditions, the droplet capture efficiency and released droplet size were calculated using the existing models. Fiber diameter and medium face velocity were found to affect not only the capture, but also drop release. Based on model predictions, the dominant capture mechanism was identified as interception followed by van der Waals forces. Overall, this work offers insights about the influencing parameters on oil/water emulsion separation for better designing coalescence systems.

Four fluorocarbon polymers including PTFE and PVDF were coated respectively on a stainless steel felt to separate emulsified water droplets from ultralow sulfur diesel fuels (ULSD). The original fuel treated with clay to remove additives was additized again with four known surfactants including Pentaerythrityoleate, (octadecadienoic acid) dipolymer, (octadecadienoic acid) tripolymer and monoolein individually. The different surfactants adsorbed on the fuel-water interface reduce the interfacial intension with different intensity. The separation efficiency at various surfactant concentrations was used to evaluate the coalescence effect exerted by these coatings. It was found the separation was both surfactant and coating dependent. A fluoro-polyurethane coating (FC1) stood out to counteract the adverse effect of all the surfactants. Solid free energy was then measured using Acid-Base and Kaelble-Uy adhesion theories for all the coatings, but its correlation with coalescence was not found at all. Coating aging in surfactant additized fuel on the coating’s water wettability was also examined to better understand how historical wetting affects separation. A tumbled model for fluorocarbons was identified that well explained the continuous decline of water contact angle on the FC1 coating in fuel. Subject to the challenge of foreign environment, the fluoroalkyl chains of the polymer tilt to expose the carbonyl groups underneath, resulting in favored coalescence separation in the presence of surfactants.

Background: TiO₂‐cellulose composite fibers are a new type of bio‐sorbent combining natural polymers and nanoparticles. However, their batch adsorption capacity is limited. Here mesoporous TiO₂‐cellulose composite fibers were synthesized and a filter medium was subsequently made from them to remove lead continuously by dynamic adsorption.Results: TiO₂‐cellulose composite fibers with rough hierarchical surface structure were fabricated by in situ growing mesoporous TiO₂ on cellulose fibers via microwave‐facilitated hydrolysis. The composite fibers were then wet‐laid into a filter medium to remove low‐concentration Pb²⁺ in water through adsorptive filtration. The breakthrough curves were found to be better predicted by the dose–response model originally established for a fixed column bed. With a volume of merely 2.07 cm³, the medium can treat 150.0 L of water containing 50 ppb lead to the drinking water standard. The filter performance was improved by incorporation of small non‐functional glass fibers to minimize the pore size and its distribution. The medium was also Pb²⁺ selective over co‐existing cations, and could be easily regenerated and reused without reduction in performance.Conclusion: The filter medium fabricated by nano‐TiO₂ decorated cellulose fibers showed enhanced adsorption capacity for lead through adsorptive filtration. Such filter beds have high potential for toxic micro‐pollutant removal from drinking water. © 2017 Society of Chemical Industry