Mesoporous TiO2 based membranes for water desalination and brine processing

This work shows the preparation, characterisation and testing of TiO2 membranes dip-coated on commercial ot-Al2O3 tubes for desalination. TiO2 thin films (similar to 400 nm) were synthesised from titanium propoxide and exposed to a gentle thermal treatment to control particle and pore sizes (dp similar to 4 nm). The TiO2 membranes were tested for brackish (0.3 wt%), sea water (3.5 wt%) and brine concentrations (7.5 and 10 wt%) up to 75 degrees C in a pervaporation setup. Water fluxes as high as 10.5 kg m(-2) h(-1) were achieved for brackish concentrations, whilst values of up to 4.0 and 6.0 kg m(-2) h(-1) were measured for the highest brine concentration (10 wt%). Concentration and temperature polarisation both affected the water fluxes, particularly for brine solutions, though the latter was more dominant. Salt rejection remained very high at similar to 99% for all tested conditions, thus demonstrating the feasibility of mesoporous inorganic TiO2 structures for desalination and brine processing. The TiO2 membranes proved to be stable for long term (>350 h) testing even under thermal cycling conditions. (C) 2015 Elsevier B.V. All rights reserved

Salt storage and induced crystallisation in porous asymmetric inorganic membranes

The authors acknowledge the financial support from the Australian Research Council ( DP1901002502 ) and ( DP190101734 ) grants. Publisher Copyright: © 2021Processing brines to recover strategic mineral salts using evaporation ponds requires large surface areas and are slow, even in arid climates. Here we show a novel membrane macropore storage mechanism that induces fast salt crystallisation in mesoporous top-layers in inorganic asymmetric membranes, stemming from 789 million nucleation points per metre square of surface area. During membrane pervaporation, dissolved salts are retained mainly in the macropores of the substrate which subsequently provide ideal conditions for crystal nucleation and growth on the membrane surface upon drying. This novel pore storage mechanism is attained owing to the solution flow modulation of the mesoporous titania and gamma-alumina layers that is counterbalanced by the flow of water during pervaporation. Therefore, pore size control is imperative to avoid flooding in the macroporous substrate. This work further shows the fundamental properties of the salt storage mechanism described by a single salt production coefficient, and a global salt production coefficient for metal chloride salts. This technology could potentially be considered for unlocking and process strategic global minerals from brines.publishersversionpublishe

Physico-chemical properties of zinc partially substituted magnetite nanoparticles

In this work, a series of zinc partially substituted magnetite nanoparticles (FeZnO, 0 ≤ x ≤ 0.4), were synthesised through a facile precipitation-oxidation method. The partial substitution of zinc into the magnetite (FeO) structure was confirmed by the collective findings of nitrogen sorption, XRD and TG-DTG analysis. It was found that the partial substitution of zinc slightly changed the textural properties of the resultant FeZnxO nanoparticles. From the XRD analysis, there was no visible formation of secondary phase or impurity peaks in the nanoparticles. These findings indicated the partial substitution of zinc into the FeO crystal structure with a good dispersion within the FeO matrix

Vacuum-assisted tailoring of pore structures of phenolic resin derived carbon membranes

This work shows the preparation and separation performance assessment of carbon membranes derived from phenolic resin by a vacuum-assisted method and carbonisation in an inert atmosphere. The vacuum time played an important role in tailoring the structure of the membranes. For instance, pore volumes and surface areas increased from 0.81 and 834 to 2.2 cmgand 1910 mg, respectively, as the vacuum time exposure increased from 0 to 1200 s. The significant structural changes correlated very well with water permeation, as fluxes increased by 91% as the vacuum time increased from 0 to 1200 s reaching up to 169 L mhat 5 bar. Molecular weight cut-off tests showed no rejection for the smaller glucose and sucrose molecules, though this increased to ~ 80% and full rejection for 36 kDa and 400 kDa polyvinyl pyrrolidine. Interestingly, FTIR spectra showed that the peaks of C–H stretching vibration (2800–3200 cm) and C–O stretching (1030 cm) became more pronounced as a function of increasing vacuum time, strongly suggesting that the use of vacuum further assisted in the polycondensation of phenolic oligomers. Based on these outcomes, a cluster to cluster model is proposed, whereby vacuum application promoted crosslinking reactions of the phenolic resin, creating microporous regions within the clusters, and mesoporous regions between the clusters

Novel inorganic membrane for the percrystallization of mineral, food and pharmaceutical compounds

This work demonstrates for the first time the phenomenon of continuous percrystallization using a carbon membrane derived from the pyrolysis of food grade sugar. In addition, it is also the first demonstration of membranes separating solute from solvent and delivering dry crystals in a single step. This is contrary to membrane crystallization, which requires two further processing steps to filter crystals from a solution followed by drying the wet crystal particles. The results indicate that carbonised sugar membranes can confer ideal conditions of super-saturation, leading to instantaneous and continuous percrystallization of compounds at the permeate side of the membrane. As a result, very high percrystallization production rates of up to 55,000 kg m per year are achieved. It is proposed that the percrystallization occurs in a wet thin-film modulated by solution permeation via the mesopores of the membrane, where vapour and crystals are separated at the membrane's solid-liquid-vapour interface. The potential deployment of this novel technology is further demonstrated for a wide range of crystallization applications in chemical, hydrometallurgy, food and pharmaceutical industries

Tailoring the oxidation state of cobalt through halide functionality in sol-gel silica

The functionality or oxidation state of cobalt within a silica matrix can be tailored through the use of cationic surfactants and their halide counter ions during the sol-gel synthesis. Simply by adding surfactant we could significantly increase the amount of cobalt existing as Co3O4 within the silica from 44% to 77%, without varying the cobalt precursor concentration. However, once the surfactant to cobalt ratio exceeded 1, further addition resulted in an inhibitory mechanism whereby the altered pyrolysis of the surfactant decreased Co3O4 production. These findings have significant implications for the production of cobalt/silica composites where maximizing the functional Co3O4 phase remains the goal for a broad range of catalytic, sensing and materials applications

Enhanced hydrogen production from thermochemical processes

To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil fuels is the development of a H2 economy. Not only can H2 be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H2 is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H2 yields owing to their reversible nature. Removing H2 with membranes and/or extracting CO2 with solid sorbents in situ can overcome these issues by shifting the component equilibrium towards enhanced H2 production via Le Chatelier's principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research

Metal Oxide Silica Membranes for Gas Separation

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Long term performance cobalt oxide silica membrane module for high temperature H-2 separation

Here we show the long term performance at high temperatures of a multi-tube module containing 8 membranes in 4 parallel lines with a total of 545 cm(2) area. The membranes were prepared via thin film dip coating of cobalt oxide silica (CoOxSi) sol-gel on tubular alumina supports. A preliminary study found that the sol-gel containing 20 mol% cobalt oxide formed the best microporous structure with the highest surface area and pore volume. All resulting membranes delivered permeances of similar to 1 x 10(-7) mol m(-2) s(-1) Pa-1 at 500 degrees C, indicating a high repeatability for the membrane fabrication process. The permselectivities of helium (He) and hydrogen (H-2) over carbon dioxide (CO2) and nitrogen (N-2) increased from 10-20 at 100 degrees C to values close to 1000 at 500 degrees C. Additionally, the apparent energies of activation (E-act) for the smaller kinetic diameter gases He and H-2 at 12.2 and 19.5 kJ mol(-1) were high and contrary to the negative values for larger gases N-2 and CO2 at -1.8 and -7.4 kJ mol(-1). These remarkable results were attributed to the molecular sieving mechanism of the microporous silica which was enhanced by the embedding of cobalt oxide into the matrix, delivering structural control with an average pore size of 3 angstrom. The E-act for H-2 permeance was higher than that of He, indicating that the cobalt oxide played an important role in H-2 transport. Two membrane lines performed exceptionally well for binary gas mixture processing with H-2 purity reaching values close to 100% in the permeate stream for argon (Ar) concentrations of up to 80% in the retentate stream. A major finding here is that the binary gas selectivity was independent of temperature, contrary to the permselectivity observed for single gas permeance. Further, the H-2 flow rate was greatly affected by the concentration of Ar in the mixture, while the temperature dependency played only a marginal role. In particular, competitive adsorption in the percolative pathways containing pore constrictions or bottlenecks of the anisotropic CoOxSi matrix allowed Ar to impede H-2 diffusion. Finally, the CoOxSi membranes proved thermally stable and robust for 2000 h of testing for various thermal cycles up to 500 degrees C