Preparation, Characterization and Performance of Templated Silica Membranes in Non-Osmotic Desalination

Abstract

In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined in a vacuum to carbonize the template and trap it within the silica matrix. The resultant xerogels were analyzed with FTIR, Thermogravimetric analysis (TGA) and N2 sorption techniques, wherein it was determined that template loadings of 10 and 20% produced silica networks with enhanced pore volumes and appropriately sized pores for desalination. Membranes were created via two different routes and tested with feed concentrations of 3, 10 and 35 ppk of NaCl at room temperature employing a transmembrane pressure drop of <1 atm. All membranes demonstrated a salt rejection capacity of >85% (in most cases >95%) and fluxes higher than 1.6 kg m−2 h−1. Furthermore, the carbonized templated membranes displayed equal or improved performance compared to similarly prepared non-templated silica membranes, with the best results of a flux of 3.7 kg m−2 h−1 with 98.5% salt rejection capacity, exceeding previous literature reports. In addition, the templated silica membranes exhibited superior hydrostability demonstrating their potential for long-term operation.

Interlayer-free P123 carbonised template silica membranes for desalination with reduced salt concentration polarisation

“…With increasing the carbon template (P123-20 and 35) concentration, the xerogels tended to form mesoporous materials with a higher adsorption saturation capacity above 0.35 p/p1 and a small degree of hysteresis. This results in an estimate of 25% increase in the surface area and pore volume with increasing P123 copolymer incorporation which is in good agreement with Ladewig et al [7] for similar sols, but prepared by the acid catalysed sol-gel method. Furthermore, when P123 concentration reached 50 wt%, it is clearly observed that the isotherm profiles are truly type IV isotherms and mesoporous as evidenced by their large extent of hysteresis near 0.5 p/p1 indicating the occurrence of capillary condensation.…”

“…The high water fluxes coupled with consistent excellent salt rejections ( 499.5%) clearly indicate that the performance of the base catalysed silica membrane containing carbon moieties derived from P123 triblock copolymers is beyond the state of art. For instance, the water flux of 2.5 kg m À 2 h À 1 and salt rejections 4 99.8% of base catalysed P123-50 silica membranes at room temperature for a sea water with NaCl concentration of 3.5 wt% are comparable or even better than those reported in the literature for acid catalysed silica membranes prepared with hexadecyl trimethyl ammonium bromide surfactant (1.9 kg m À 2 h À 1 and 94%) [10], methyl tri-ethoxy silane and TEOS (1.7 kg m À 2 h À 1 and 95%) [8], triblock copolymer templated silica membranes (3.0 kg m À 2 h À 1 ; 97%) [7]. When compared to the performance of the cobalt oxide silica membranes [33], the water fluxes produced by the membranes in this work are at least 300% (P123-5) to 800% (P123-50) higher yet with similar salt rejections, irrespective of the feed salt concentration and temperature.…”

“…In this process, the integrity of the silica membrane remained generally unaffected under water exposure, in particular inhibiting micropore collapse. Several groups modified carbon templated silica using Pluronics s triblock copolymers [7] and surfactants [8][9][10][11] as molecular sieving membranes in desalination. The organic templates were retained in the silica matrices as the membranes were calcined in inert nitrogen gas atmosphere.…”

Rational design and synthesis of molecular-sieving, photocatalytic, hollow fiber membranes for advanced water treatment applications

“…Therefore, as shown in this study that the carbon matrix offers the fine-tuning of porosity and pore volume, which are extremely important for determining water flux of the hollow fibers for water production as membranes. This is exemplified by numerous studies of microporous ceramic membranes for desalination [59][60][61] and alcohol pervaporation [62][63][64]. On the other hand, highly mesoporous membranes, although lead to a high water production, will fail to separate the solute from water due to pore-wetting effect [39,65].…”

Synthesis of mesoporous carbon–silica nanocomposite water-treatment membranes using a triconstituent co-assembly method

“…The experimental set-up included a feed vessel, peristaltic pump, membrane module, condenser unit, vacuum pump and data logging system connected to computer. 35 Despite the appearance of several smaller peaks and shoulders, the main exothermic peak at ~350 °C is sharp and narrow. The feed was introduced into membrane module at a flow rate of 5 L h -1 and circulated back into the feed vessel.…”