Yiqun Fan

Fabrication of supported mesoporous TiO2 membranes: matching the assembled and interparticle pores for an improved ultrafiltration performance.

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol-gel process where a ethylene oxide and propylene oxide triblock polymer (PEO-PPO-PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m(2) x h x bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.

Fabrication of a visible-light response mesoporous TiO2 membrane with superior water permeability via a weak alkaline sol–gel process

A visible-light response TiO(2) ultrafiltration membrane was fabricated via a weakly alkaline sol-gel method for the first time, and exhibited a cut-off molecular weight of 7500 Da and high pure water flux of 170 L m(-1) h(-1) bar(-1).

Pore evolution model of ceramic membrane during constrained sintering

Pore size has been found to strongly depend on the sintering program in the preparation of porous ceramic membranes. In this paper, a model was developed to predict the variation in pore size and porosity of membranes during the sintering process. A comparison of shrinkage characteristics was made between the sintering processes of supported membranes and unsupported membranes. For supported membranes, the effect of restriction coming from a rigid substrate on the sintering behavior has been taken into account in the calculation. It is predicted that the pore size increases in supported membranes and decreases in unsupported membranes as the sintering temperature is increased. Calculations also showed that the loss of porosity in the supported membranes was less than that in the unsupported membranes. In order to verify reliability of this model, unsupported and supported membranes were prepared with α-Al2O3 powders at the sintering temperatures ranging from 1125xa0°C to 1325xa0°C. The pore size and porosity were measured by gas permeation technique and Archimedes’s method. The experimental results for the unsupported and supported α-Al2O3 membranes showed a good agreement with those calculated from the model. Therefore, this model provides an effective tool in predicting the porosity and the pore size of ceramic membranes at the different sintering temperatures.

Environment-benign preparation of Ag toughening TiO2/Ti tight ultrafiltration membrane via aqueous sol–gel route

AbstractA new aqueous sol was synthesized to prepare Ag-doped TiO2/Ti composite tight ultrafiltration (UF) membranes. This sol was prepared based on water (>95xa0wt%), for which the hydrodynamic size of 8xa0nm could be obtained by tuning the electrostatic and steric repulsive forces, breaking the limit of the polymeric sol–gel method to prepare tight UF membranes. For the preparation of the sol, high water content can significantly reduce the use of organic solvents and is more environment-benign. Moreover, Ag doping can considerably improve the toughness of the supported membranes to efficiently prevent the TiO2/Ti composite membranes from cracking and overcome the thermal expansion mismatch of ceramic membranes and their metallic supports. The prepared Ag-doped TiO2/Ti composite membranes presented a molecular weight cut-off of 3xa0kDa with a pure water flux of 24xa0Lxa0m−2xa0h−1xa0bar−1 and exhibited good dye removal capabilities. The proposed Ag doping method has considerable potential for the fabrication of integrated hybrid ceramic–metallic composite membranes.n

Self-cleaning Piezoelectric Membrane for Oil-in-water Separation

Ultrasound (US) treatment coupled with membrane filtration has been utilized for membrane fouling control in water treatment; however, large-scale implementation of ultrasonic cleaning equipment appeared to be cost-prohibitive. In this study, a porous lead zirconate titanate (PZT) membrane is presented that enables in situ ultrasound generation by the application of an alternating voltage (AV) to mitigate fouling during oil-in-water (O/W) emulsion separation. We expect that this method is much more cost-effective because it is more direct, avoiding buildup of fouling and the need to take the membrane offline. Because the PZT membrane is hydrophilic, its underwater surface is oleophobic so that the accumulated oil droplets will have little affinity and hence can be removed easily by in situ-generated US. The effect of the in situ US generation on membrane fouling was investigated through variation in the excitation AV and its frequency, O/W emulsion pH, emulsified oil concentration, crossflow velocity, and transmembrane pressure. The results indicated that the in situ US generation resulted in a substantial decrease of fouling during the filtration process of O/W emulsions, whereas the membrane flux was maintained closely at its initial value.

1.11 Ceramic Membranes

The article reviews the fabrication and application of ceramic membranes and provides a comprehensive overview of structure–property relationships of ceramic membranes in various important applications to establish an application-oriented material design method. Due to the high amount of flux, great separation efficiency, and long lifetime, with a continuous decrease in fabrication costs, research on ceramic membranes is fast increasing, and ceramic membranes have become more competitive. Here, some novel fabrication techniques, including a pore-forming agent method, a fiber construction method, and a modified sol–gel route, are discussed extensively. Further research has been reported to produce membranes with a wide range of unique microstructures and surface properties, which can be adapted for the application and increase of their market volumes. Finally, five industrial applications (ceramic membrane reactors, oily wastewater treatments, biological fermentation treatments, plant extracts, and brine refinements) are introduced.