Molecular Weight Cut-Off and Structural Analysis of Vacuum-Assisted Titania Membranes for Water Processing

Abstract

This work investigates the structural formation and analyses of titania membranes (TM) prepared using different vacuum exposure times for molecular weight (MW) cut-off performance and oil/water separation. Titania membranes were synthesized via a sol-gel method and coated on macroporous alumina tubes followed by exposure to a vacuum between 30 and 1200 s and then calcined at 400 °C. X-ray diffraction and nitrogen adsorption analyses showed that the crystallite size and particle size of titania increased as a function of vacuum time. All the TM membranes were mesoporous with an average pore diameter of ~3.6 nm with an anatase crystal morphology. Water, glucose, sucrose, and polyvinylpyrrolidone with 40 and 360 kDa (PVP-40 kDa and PVP-360 kDa) were used as feed solutions for MW cut-off and hexadecane solution for oil filtration investigation. The TM membranes were not able to separate glucose and sucrose, thus indicating the membrane pore sizes are larger than the kinetic diameter of sucrose of 0.9 nm, irrespective of vacuum exposure time. They also showed only moderate rejection (20%) of the smaller PVP-40 kDa, however, all the membranes were able to obtain an excellent rejection of near 100% for the larger PVP-360 kDa molecule. Furthermore, the TM membranes were tested for the separation of oil emulsions with a high concentration of oil (3000 ppm), reaching high oil rejections of more than 90% of oil. In general, the water fluxes increased with the vacuum exposure time indicating a pore structural tailoring effect. It is therefore proposed that a mechanism of pore size tailoring was formed by an interconnected network of Ti–O–Ti nanoparticles with inter-particle voids, which increased as TiO2 nanoparticle size increased as a function of vacuum exposure time, and thus reduced the water transport resistance through the TM membranes.

Biocompatible Wax-Based Microcapsules with Hermetic Sealing for Thermally Triggered Release of Actives

“…Here, eicosane was selected as the control wax material as it exhibits a melting point of 38 °C, which is similar to palm oil with the melting point in the range of 30−40 °C. Sucrose with a molecular weight (M w ) of 342 g mol −1 and a hydrodynamic diameter of 0.9 nm 25 was chosen as the representative model small molecule. To verify the smallmolecule permeability of these two wax layers, we prepared 40% sucrose solution and dispensed 500 μL each in two centrifuge tubes.…”

Hydrogel Microcapsules with a Thin Oil Layer: Smart Triggered Release via Diverse Stimuli

“…[ 25 ] Moreover, hydrogel shell is permeable to sucrose as the hydrodynamic diameter of sucrose is 0.9 nm and thus smaller than the mesh size of the hydrogel shell. [ 26 ] The influx of water causes the aqueous core to expand in volume and the oil layer destabilizes over time resulting in the cargo release through the hydrogel shell as shown in schematics of Figure 2C. One of the major advantages of utilizing osmotic pressure as a cue for cargo release lies in the fact that the osmotic pressure can be tuned precisely by either altering the osmolyte concentration in the aqueous core or the continuous phase to which the microcapsules are exposed.…”

Substrate Effect on Carbon/Ceramic Mixed Matrix Membrane Prepared by a Vacuum-Assisted Method for Desalination

“…The vacuum-assisted method conferred controlled pore sizes for desalination using pervaporation, in addition to molecular weight cut-off pore tailoring [45,46]. Carbon precursors are excellent materials for pore size tailoring under controlled pyrolysis (i.e., polymer carbonization) [47][48][49], including the preparation of mixed matrix membranes containing carbonised polymer and an inorganic phase [50,51].…”