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This paper deals with the kinetic and isotherm studies of manganese ion removal by zeolite X and its hierarchically porous composites as ion-exchange materials. A hydrothermal treatment was applied to grow a layer of zeolite X over diatomite and carbon surfaces. The hierarchically porous composites used for Mn 2+ ion removal showed higher ion-exchange capacity when compared to pure zeolite X under same conditions. A thermodynamic study of the rate of ion-exchange revealed that the intra-particle diffusion rate constant of zeolite X/carbon and zeolite X/diatomite was higher than that of pure zeolite X indicating that the intra-particle diffusion was enhanced when zeolite was prepared in form of hierarchically porous composites. The study showed that the thickness of boundary film of zeolite X/carbon and zeolite X/diatomite was less than that of pure zeolite X indicating ion diffusion resistance to the active sites was reduced when the composites were utilised. The experimental data showed good agreement with Freundlich model. The calculated thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicated the ion-exchange process of Mn 2+ ion by zeolite X and its composites was spontaneous, endothermic and the randomness increased at the liquid/solid interface under the conditions studied. The results of kinetic study showed that the ion-exchange of Mn 2+ ion by zeolite X and its composites followed a pseudo second order kinetic model indicating Mn 2+ ion removal is a chemical reaction related to valence forces. The encapsulation of Mn 2+ ion was successfully achieved by vitrification and geopolymerization processes demonstrating the efficacy of both processes for environmental management. [ABSTRACT FROM AUTHOR]

Background: Biogeochemical processing of metals including the fabrication of novel nanomaterials from metal contaminated waste streams by microbial cells is an area of intense interest in the environmental sciences. Results: Here we focus on the fate of Ce during the microbial reduction of a suite of Ce-bearing ferrihydrites with between 0.2 and 4.2 mol% Ce. Cerium K-edge X-ray absorption near edge structure (XANES) analyses showed that trivalent and tetravalent cerium co-existed, with a higher proportion of tetravalent cerium observed with increasing Ce-bearing of the ferrihydrite. The subsurface metal-reducing bacterium Geobacter sulfurreducens was used to bioreduce Ce-bearing ferrihydrite, and with 0.2 mol% and 0.5 mol% Ce, an Fe(II)-bearing mineral, magnetite (Fe(II)(III)2O4), formed alongside a small amount of goethite (FeOOH). At higher Ce-doping (1.4 mol% and 4.2 mol%) Fe(III) bioreduction was inhibited and goethite dominated the final products. During microbial Fe(III) reduction Ce was not released to solution, suggesting Ce remained associated with the Fe minerals during redox cycling, even at high Ce loadings. In addition, Fe L2,3 X-ray magnetic circular dichroism (XMCD) analyses suggested that Ce partially incorporated into the Fe(III) crystallographic sites in the magnetite. The use of Ce-bearing biomagnetite prepared in this study was tested for hydrogen fuel cell catalyst applications. Platinum/carbon black electrodes were fabricated, containing 10% biomagnetite with 0.2 mol% Ce in the catalyst. The addition of bioreduced Ce-magnetite improved the electrode durability when compared to a normal Pt/CB catalyst. Conclusion: Different concentrations of Ce can inhibit the bioreduction of Fe(III) minerals, resulting in the formation of different bioreduction products. Bioprocessing of Fe-minerals to form Ce-containing magnetite (potentially from waste sources) offers a sustainable route to the production of fuel cell catalysts with improved performance. [ABSTRACT FROM AUTHOR]

• Operando synchrotron X-ray study on Phosphorus and Platinum migration. • Graphene-related-material applied as interventional materials for comparison. • X-ray Absorption Near Edge Structure applied to study chemical structural change. • Conducting mechanistic studies via the three-phase interface. • Performance and durability of high-temperature proton exchange membrane fuel cells. The application of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) addresses challenges in water management, fuel purity, and overheating under high current density. However, phosphoric acid (PA) migration hinders their development. This study uses synchrotron-based X-ray fluorescence spectroscopy to investigate PA and catalyst migration. Interventions with single-layer graphene and electrochemically exfoliated graphene oxide improve performance and durability. X-ray absorption spectroscopy provides insights into relevant mechanisms, advancing understanding of membrane electrode assembly preparation and the intricate influences of PA and catalyst migration on performance and durability in HT-PEMFCs. [ABSTRACT FROM AUTHOR]

Abstract Thin film nanocomposite (TFN) membranes of polymer of intrinsic microporosity PIM-1 incorporating graphene oxide (GO) nanosheets of different sizes and chemistries are presented. These membranes show an improved separation performance for the recovery of n -butanol from aqueous solutions through pervaporation; an improvement of ca. a third of the value achieved for pristine PIM-1 thin films is obtained for TFN membranes filled with nanometer-sized reduced octyl-functionalized GO. In addition, these nanometer-sized fillers lead to a maximum increase in total flux of approximately 40%. The thickness of the supported films is in the range 1–1.5 µm, and fillers used are micrometer- and nanometer-sized alkyl-functionalized GO nanosheets and their chemically reduced counterparts. As evidenced by a superior overall membrane performance, the interfacial interaction between the filler and the polymer matrix is enhanced for those whose lateral size is in the nanometer range. Moreover, an enhancement in the separation performance and productivity of such membranes is observed for higher operating temperatures and higher contents of n -butanol in the feed. Graphical abstract fx1 Highlights • PIM-1/alkyl-functionalized graphene thin film nanocomposite (TFN) membranes were prepared. • TFN membranes were tested for n-butanol recovery from aqueous solutions via pervaporation. • The addition of nano-sized fillers improved the separation performance of PIM-1 thin film membranes. • Nano-sized fillers enhanced the total flux up to approximately 40%. [ABSTRACT FROM AUTHOR]

Air gap membrane distillation (AGMD) is an emerging desalination technology with the potential to meet the challenge of global water scarcity due to its low cost and high thermal efficiency compared to other processes. However, despite the potential of AGMD, a lack of appropriate membranes limits its commercial application. Therefore, this study was focussed on the fabrication of high flux, robust membranes for the purification of artificial sea water by incorporating graphene oxide functionalized with 3-(aminopropyl)triethoxysilane (APTS) into PVDF polymer solutions. Successful functionalisation of GO with APTS was confirmed with XPS and FTIR. It was shown that the addition of GO and GO-APTS enhanced the permeate flux by 52% and 86%, respectively, compared to pure PVDF. The best performing membrane contained 0.3 wt% GO-APTS (with respect to PVDF) and had a flux of 6.2 LMH (L m −2 h −1 ) whilst maintaining perfect salt rejection (>99.9%). These improvements were attributed to increased surface and bulk porosity, larger mean pore size and hydrophilic interactions owing to the functional groups of GO and GO-APTS. These membranes are evidence of the potential that GO and related materials have as nanocomposite fillers in high performance desalination membranes. [ABSTRACT FROM AUTHOR]

In this work, graphene oxide (GO) was combined with polyethersulfone (PES) to form mixed matrix membranes (MMMs) for ultrafiltration of aqueous solutions. Also, the effect of adding various pore formers (poly(vinylpyrrolidinone (PVP), reverse triblock Pluronic (P31R1), and poloxamine Tetronic (T904)) to the dope solution was investigated. The prepared MMMs were characterised using various techniques, including Fourier-transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the incorporation of 0.5 wt% of GO increased the flux from 2 to 13 L m −2 h −1 (LMH) and the rejection of bovine serum albumin (BSA) from 89.2 to 97% compared to benchmark PES membranes. SEM analysis revealed the increased pore size and porosity of the GO modified membranes, which contributed to the increased flux. The addition of pore formers further increased the flux compared to pure PES and also displayed synergistic effects with GO. The combination of T904 with 0.3 wt% GO increased the water flux significantly from 2 to 245 LMH and increased the rejection of acridine orange (from 40.5 to 48.4%) and BSA (from 89.6 to 93.3%), respectively. Also, fouling properties of the membranes were investigated with the parameters: flux recovery ratio ( FRR ), total flux decline ratio ( R t ), reversible flux decline ratio ( R r ), and irreversible flux decline ratio ( R ir ), and improved anti-fouling properties were obtained with the addition of GO. This work shows the promise of GO as a performance-enhancing additive in MMMs for wastewater treatment. [ABSTRACT FROM AUTHOR]

Hierarchical ZSM-5 coatings supported on macrocellular β-SiC foams were prepared by a microwave-accelerated secondary growth method. Under microwave irradiation, differential heating was enabled due to the high microwave-adsorbing ability of SiC leading to the fast assembly of ZSM-5 zeolites on the SiC foams. The effects of crystallisation temperature, time and agitation on the growth of ZSM-5 zeolites on SiC foams were also investigated under microwave heating. A specific surface area of ca. 52 m 2 g −1 was obtained under the optimum condition of 150 °C and 4 h. Comparative studies of conventional hydrothermal and microwave-accelerated synthesis were conducted and the resulting materials were characterised extensively using XRD, SEM and N 2 adsorption. The combination of microwave heating, high microwave absorption of SiC substrates and agitation allowed a much more focused heating across the surface of SiC foams than conventional heating, which suppressed the formation of ZSM-5 crystals in the liquid phase and the consequent sedimentation. Additionally, for the first time, mesoscopic features of ZSM-5 coatings on SiC foam composites (>10 μm) were studied in 3D by X-ray micro computed tomography (μ-CT), providing quantitative information on the quality of the ZSM-5 coating such as the global thickness and distribution of ZSM-5 across the SiC foam supports. It was concluded that microwave-accelerated secondary growth synthesis offered an efficient route to give high quality coatings on structured foams with the good crystal quality and uniform thickness as well as lower energy consumption, especially for the substrate with a high loss tangent. [ABSTRACT FROM AUTHOR]

Energy production from direct alcohol fuel cells depends strongly on the operating conditions. In this paper, the aim was to find the best conditions of direct methanol fuel cells (DMFC) and direct ethanol fuel cells (DEFC) to obtain the maximum power density with the response surface method using Program Design Expert 7.0.0. Three related independent variables, including operating temperature in the range of 30–70 °C, alcohol flow rate in the range of 5–50 ml/min, and alcohol concentration in the range of 0.5–3 M, were covered. Nafion117 was used as an electrolyte and Pt-Ru and Pt were used as catalysts in anode and cathode, respectively. The effect of those variables on the maximum power density was illustrated in the form of quadratic models which predicted the appropriate operating conditions. The Nafion membrane was modified by adding mordenite (MOR) to improve its alcohol permeability. The result from response revealed that the higher operating temperatures and higher alcohol concentrations led to an increase in maximum power density, in both the DMFC and DEFC. The DMFC had a higher maximum power density and greater current than the DEFC had. This was because methanol was easier to oxidize than ethanol In addition, it was found that the MOR content of 1.47 wt% in the Nafion composite membrane reduced the alcohol permeability and resulted in a higher power density. Therefore, the model suggested the optimum conditions to produce greener energy (less resource use with high energy produced). [ABSTRACT FROM AUTHOR]

PIM-1-based freestanding mixed matrix membranes (MMMs) and thin film nanocomposites (TFNs) were prepared by incorporating porous silica nanosheets (SN) and exfoliated SN (E-SN) derived from natural vermiculite (Verm) in the PIM-1 polymer matrix. In addition, SN were functionalized by sulfonic acid and amine groups (S-SN and N-SN, respectively) and were also used as fillers for the preparation of MMMs. The gas separation performance was evaluated using CO 2 /CH 4 and CO 2 /N 2 (1:1, v:v) binary gas mixtures. Among freestanding membranes, fresh ones (i.e. tested right after preparation) containing 0.05 wt% functionalized SN and E-SN outperformed the neat PIM-1, surpassing the 2008 Robeson upper bound. At the same filler concentration, fresh MMMs with sulfonic acid-functionalized SN (S-SN) exhibited 40% higher CO 2 permeability, 20% higher CO 2 /N 2 selectivity and almost the same CO 2 /CH 4 selectivity as neat PIM-1 membranes. Moreover, after 150 days of aging, these membranes were capable of maintaining up to 68% of their initial CO 2 permeability (compared to 37% for neat PIM-1). When prepared as TFN membranes, the incorporation of 0.05 wt% of S-SN led to 35% higher initial CO 2 permeance and five times higher CO 2 permeance after 28 days. [Display omitted] • Freestanding and thin PIM-1-based films were fabricated using silica nanosheets (SNs). • The prepared MMMs and TFNs were tested for CO 2 /N 2 and CO 2 /CH 4 separation. • PIM-1/sulfonated SNs (0.05 wt%) showed the best initial performance. • The incorporation of SNs partially prevented aging in both TFNs and MMMs. [ABSTRACT FROM AUTHOR]

To improve the performance and durability of phosphoric acid (PA) doped polybenzimidazole (PBI) membranes in high–temperature proton exchange membrane fuel cells (HT–PEMFCs), in this work, as–received natural muscovite (Mus), a clay material, was successfully incorporated into PBI matrix as an inorganic filler through the doctor blade method. The amount of Mus was varied (0.5–2 wt%) to explore its impact on the proton conductivity, mechanical and dimensional stability, power density, durability, and acid retention ability of the composite membranes. As the incorporation of Mus into membranes can introduce interactions with polymer chains and PA molecules to afford additional proton transport pathways at the interfaces in Mus–PBI and Mus–PA crosslinks, the membrane with 1 wt% Mus showed highest power density of 586 mW cm−2 at 150 °C without humidification, 24% higher than the pure PBI membrane (474 mW cm−2). Meanwhile, the PA doped composite membrane with 1 wt% Mus also displayed the highest mechanical strength (7.5 MPa) and lowest dimensional swelling (70.99% in area swelling and 202% in volume swelling). Compared with the pristine PBI membrane, the composite membranes had significantly improved durability under accelerated stress test (AST). The decreased ohmic resistance and increased polarization resistance after AST are related to the membrane thinning and the loss of catalyst active area, respectively. Most importantly, it was found that the strong interactions between Mus and PA molecules lead to improved acid retention ability of the composite membranes, thus less leached acid from the composite membrane reduces the negative effects on the catalyst degradation to alleviate degradation on cell performance and durability. [Display omitted] • Natural muscovite was successfully incorporated into PBI membranes using the doctor blade method. • The prepared composite membranes show better power density and durability than the pure PBI membrane. • The interactions between Mus and PA explored by EDS, TGA and XPS benefit improved acid retention ability. [ABSTRACT FROM AUTHOR]

Abstract: Composite polymer proton exchange membranes (PEM) were prepared by solution recasting. The composite membranes formed are based on Nafion incorporating a silane functionalized zeolite, mordenite, as an additive. The composite membranes were placed within a single cell DMFC and compared to an MEA featuring a standard Nafion 125μm membrane. The impact of mordenite particle size, the choice of the silane functionalizing agent and the membrane preparation procedure are investigated. A composite ion exchange membrane which featured Nafion and a ground mordenite which was functionalized using glycidoxypropyltrimethoxysilane achieved a power density that outperformed a standard Nafion MEA under all conditions. [Copyright &y& Elsevier]

A machine-learning approach is used to segment 14 X-ray computed-tomography datasets acquired by lab-based scanning of laser-milled, high-temperature polymer electrolyte fuel cell samples mounted in a 3D-printed sample holder. Two modes of operation, one with constant current load and the other with current cycling, are explored and their impact on microstructural change is correlated with electrochemical performance degradation. Constant-current testing shows the overall quantity of phosphoric acid in the gas diffusion layers is effectively unchanged between 50 and 100 h of operation but that inter-electrode distribution becomes less uniform. Current-cycling tests reveal similar quantities of phosphoric acid but a different intra-electrode distribution. Membrane swelling appears more pronounced after current-cycling tests and in both cases, significant catalyst layer migration is observed. The present analysis provides a lab-based approach to monitoring microstructural degradation in high-temperature polymer electrolyte fuel cells and provides a more accessible and more statistically robust platform for assessing the impact of phosphoric acid mitigation strategies. • Lab-based X-ray micro-computed tomography to investigate phosphoric acid leaching. • Machine learning segmentation yields quantification of microstructural changes. • Electrochemical performance loss linked to microstructure evolution. • Redistribution of phosphoric acid depends on fuel cell operation mode. • Accelerated stress tests give more membrane swelling and less uniform Pt migration. [ABSTRACT FROM AUTHOR]

• Plasma-assisted dry reforming of methane (DRM) over UiO-67 MOF-based catalyst. • UiO-67 material in the discharge zone improved the plasma generation and gas-phase reactions. • Pt nanoparticles supported on UiO-67 promoted surface reactions, improving DRM. • PtNP@UiO-67 catalysts were robust and stable in the plasma-assisted catalytic DRM. Plasma-assisted dry reforming of methane (DRM) was performed in a dielectric barrier discharge (DBD) reactor. The effect of different packing materials including ZrO 2 , UiO-67 MOF and PtNP@UiO-67 on plasma discharge was investigated, showing that ZrO 2 suppressed the plasma generation while UiO-67 improves it due to its porous nature which favours the formation of filamentary microdischarges and surface discharges. The improved plasma discharge increased the conversion of CH 4 and CO 2 by about 18% and 10%, respectively, compared to the plasma-alone mode. In addition, the distribution of hydrocarbon products changed from dominant C 2 H 6 in the plasma-alone mode to C 2 H 2 and C 2 H 4 in the UiO-67 promoted plasma-assisted DRM. The UiO-67 MOF was stable in plasma, showing no significant changes in its properties under different treatment times, discharge powers and gases. Pt nanoparticles (NPs) on UiO-67 improved plasma-assisted DRM, especially the selectivity due to the presence of surface reactions. Due to the dehydrogenation of hydrocarbons over Pt NPs, the selectivity to hydrocarbons decreased by 30%, compared to the UiO-67 packing. In situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) was carried out to probe the surface reactions on PtNP@UiO-67 catalyst, showing the decomposition of surface formats to CO and C 2 H 4 dehydrogenation over the metallic Pt. The PtNP@UiO-67 catalyst showed good reusability in the plasma-assisted DRM, and H 2 production was improved by high CH 4 /CO 2 molar ratio and low feed flow rate. [ABSTRACT FROM AUTHOR]