Thermal Swing Reduction-Oxidation of Me(Ba, Ca, or Mg)SrCoCu Perovskites for Oxygen Separation from Air

Funding Information: This research was financially supported by the Visiting Fellowship (for João C. Diniz da Costa) by the Associate Laboratory for Green Chemistry—LAQV, financed by the Portuguese National Government funds from FCT/MCTES (UIDB/50006/2020) and the Fundamental Research Fund for the Central University (Buctrc202115) in China. Publisher Copyright: © 2022 by the authors.The climate change impact associated with greenhouse gas emissions is a major global concern. This work investigates perovskite compounds for oxygen separation from air to supply oxygen to oxyfuel energy systems to abate these significant environmental impacts. The perovskites studied were Me0.5Sr0.5Co0.8Cu0.2O3−δ (MeSCC) where the A-site substitution was carried out by four different cations (Me = Ca, Mg, Sr, or Ba). SEM analysis showed the formation of small particle (<1 µm) aggregates with varying morphological features. XRD analysis confirmed that all compounds were perovskites with a hexagonal phase. Under reduction and oxidation reactions (redox), Ba and Ca substitutions resulted in the highest and lowest oxygen release, respectively. In terms of real application for oxygen separation from air, Ba substitution as BaSCC proved to be preferable due to short temperature cycles for the uptake and release of oxygen of 134 °C, contrary to Ca substitution with long and undesirable temperature cycles of 237 °C. As a result, a small air separation unit of 0.66 m3, containing 1000 kg of BaSCC, can produce 18.5 ton y−1 of pure oxygen by using a conservative heating rate of 1 °C min−1. By increasing the heating rate by a further 1 °C min−1, the oxygen production almost doubled by 16.7 ton y−1. These results strongly suggest the major advantages of short thermal cycles as novel designs for air separation. BaSCC was stable under 22 thermal cycles, and coupled with oxygen production, demonstrates the potential of this technology for oxyfuel energy systems to reduce the emission of greenhouse gases.publishersversionpublishe

Rapid thermally processed hierarchical titania-based hollow fibres with tunable physicochemical and photocatalytic properties

A series of photocatalytic TiO2–carbon composite hollow fibres (HFs) was prepared in this study by a wet-dry phase inversion spinning method followed by a rapid thermal processing (RTP). The RTP method consists of two stages: (1) calcination at 800 °C for 15 min encased in a quartz tube followed by (2) a short open heating exposure at 800 °C for 0 to 7.5 min in air. The innovative two-stage RTP method led to a time saving of more than 90%. Results revealed that the pyrolysis conditions during the second stage of HF fabrication were essential to the final physical and chemical properties of resultant TiO2-carbon HFs, such as TiO2 crystallinity and carbon content, mechanical, textural and electronic properties, as well as photocatalytic reactivity. The best results show that HFs pyrolysed for a short duration (< 2 min) in the second stage produced a high microporous surface area of 217.8 m2·g−1, a good mechanical strength of 11 MPa and a TiO2 anatase-to-rutile (A/R) ratio of 1.534 on the HF surface. The HFs also achieved a 68% degradation of acid orange 7 dye with a kapp of 0.0147 min−1 based on a Langmuir-Hinshelwood model during the photocatalysis under UV light. Thus, this work provides a new synthesis protocol with significant time and cost savings to produce high-quality HFs for wastewater treatment

Nanoscale assembly of lanthanum silica with dense and porous interfacial structures

This work reports on the nanoscale assembly of hybrid lanthanum oxide and silica structures, which form patterns of interfacial dense and porous networks. It was found that increasing the molar ratio of lanthanum nitrate to tetraethyl orthosilicate (TEOS) in an acid catalysed sol-gel process alters the expected microporous metal oxide silica structure to a predominantly mesoporous structure above a critical lanthanum concentration. This change manifests itself by the formation of a lanthanum silicate phase, which results from the reaction of lanthanum oxide nanoparticles with the silica matrix. This process converts the microporous silica into the denser silicate phase. Above a lanthanum to silica ratio of 0.15, the combination of growth and microporous silica consumption results in the formation of nanoscale hybrid lanthanum oxides, with the inter-nano-domain spacing forming mesoporous volume. As the size of these nano-domains increases with concentration, so does the mesoporous volume. The absence of lanthanum hydroxide (La(OH)(3)) suggests the formation of La2O3 surrounded by lanthanum silicate

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

Photocatalytic, hollow fiber membranes based on nanocomposites of titania nanoparticles and carbonaceous char were simultaneously fabricated in a single calcination step, and then optimized for the photo-degradation of pollutants and water recovery in an integrated membrane operation in this study. The physicochemical, mechanical and photocatalytic properties along with separation performance of two series of membranes were finely-tuned by systematically changing the calcination temperature (series 1: 500–1000 °C for 8 h holding time) and calcination time (series 2: 2–8 h at 600 °C). The calcined membranes were extensively characterized for morphology, thermal stability, microstructure, modulus and chemical compositions. Both constituents of titania and char are essential in deriving the desirable hollow fiber properties and membrane performance for photocatalysis and water recovery. By controlling the calcination conditions, membranes prepared at 600 °C for the 3 and 6 h duration displayed an optimal balance between enhanced mechanical strength (34 MPa) and high photo-degradation of acid orange 7 (90.4%). Membrane performance demonstrated water fluxes of 6.9 (H2O/dark), 12.9 (H2O/UV) 4.8 (AO7/dark) and 7.9 L m–2 h–1 (AO7/UV) with excellent organic dye rejection. Both membranes exhibited photo-induced super-hydrophilicity and defouling potential under the influence of UV light due to the photo-activation of exposed TiO2 nanoparticles on the membrane surface. The detailed mechanism of property correlation and separation performance for the photocatalytic hollow fibers is proposed and elucidated. This work offers an innovative material for the research avenue of photocatalytic, hollow fiber membrane reactors for advanced membrane treatment applications

Early-stage photodegradation of aromatic poly(urethane-urea) elastomers

The photooxidative stability of an aromatic segmented poly(urethane-urea) (PUU) elastomer, stabilised with a range of carbon black fillers, was assessed after very low UVA doses as a means to identify components that are highly susceptible to UV degradation, and suggest better design of such materials. Fourier-transform infrared (FTIR) analysis indicated rapid degradation of the urea bonds in the hard segments, followed by chain scission and photo-Fries reaction of the urethane linkages. In the soft segments, the oxidation of the original ether groups resulted in the formation of large amounts of ester groups, while some crosslinking of the ether groups was also evident. Carbon black provided moderate protection against degradation, with the smallest-sized particles being the most effective. Protection was evidenced by reduced surface cracking as well as an increased resistance to chemical changes in both the soft segments and hard segments. Even so, significant degradation was still evident at low UV doses suggesting that further stabilisation is required to increase the UV durability of these elastomers and improve their long-term performance

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

Ceramic metal oxides with Ni2+ active phase for the fast degradation of Orange II dye under dark ambiance

Ceramic metal oxides based on calcium strontium nickel (CSN) were synthesized via a combined EDTA-citric acid complexation method and evaluated using Orange II (OII) as the model pollutant under dark conditions, without adding any external stimulants. The CSN catalyst was characterized by a very fast reaction reaching 97% OII degradation within 5 min. The surface of CSN metal oxides proved to be very active toward the breakdown of the -N˭N- azo bond of OII. A second electron generating pathway was found as Ni phase in the CSN catalyst oxidized to Ni for the spent catalyst. Both electron generating pathways resulted in the formation of hydroxyl radicals (OH·) as determined using radical quenchers. Hydroxyl radicals were responsible for the formation of several intermediate products. The Ni phase was very active contrary to the Ni phase which could not degrade OII. The fast degradation kinetics of OII using CSN in dark at room temperature was attributed to the double electron generation pathways

Binary iron cobalt oxide silica membrane for gas separation

This work investigates the preparation, characterisation and performance of binary iron/cobalt oxide silica membranes by sol-gel synthesis using tetraethyl orthosilicate as the silica precursor, and cobalt and iron nitrates. It was found that cobalt and iron oxides were generally dispersed homogeneously in the silica structure, with the exception of a few minor patches rich in cobalt oxide. The ml-gel synthesis affected the micro-structural formation of binary metal oxide silica matrices. Increasing the iron content favoured condensation reactions and the formation of siloxane bridges, and consequently larger average pore sizes which lead to low He/N-2 permselectivity values below 20. In the case of high cobalt content, a higher silanol to siloxane ratio was observed with tighter pore size tailoring, as evidenced by higher He/N-2 permselectivities reaching 170. The binary metal oxide and silica interfaces proved to follow a molecular sieving mechanism characterised by activated transport where the permeance of the smaller gas molecules (He and H-2) increased with temperature up to 500 degrees C, whilst the permeance of larger gas molecules (CO2 and N-2) decreased. (C) 2014 Elsevier B.V. All rights reserved

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

Novel membrane percrystallisation process for nickel sulphate production

This research reports on an investigation of the performance of inorganic membranes for use in the percrystallisation of nickel sulphate hydrate. In this novel process, the separation of the solvent (water) and the crystallised solute (nickel sulphate hydrate) occurs continuously in a single-step, avoiding further downstream processing (crystal filtering and drying). The inorganic membranes were synthesised with sucrose solution followed by a post vacuum-assisted impregnation of the coated film on a α-alumina substrate and carbonisation under nitrogen atmosphere. The highest fluxes measured were 22 L m h and 1 kg m h (40 g L ) for water and nickel respectively. Interestingly, the transport of solution through the membrane also affected the hydration state of the nickel sulphate, as well as the crystal type and shape. High water fluxes delivered pure nickel sulphate heptahydrate with elongated and laminar crystal particles (~200 μm). Lower water fluxes produced both heptahydrate and hexahydrate salts with approximately spherical particles (also ~200 μm). There a number of factors that influence the crystallisation reaction such as the rate of evaporation which affects water availability and the resultant temperature at the permeate side of the membrane. Finally, the activation energy for nickel sulphate crystallisation was estimated to be approximately 16 kJ mol based on feed solution temperatures