Anion Exchange Process Research Articles

Hybrid polymer inclusion membrane as anion exchange membrane for recovering Pd2+ ions in electrogenerative process

A novel non-plasticized nano-porous hybrid inorganic-organic polymer inclusion membrane (PIM) was synthesized, characterized, and evaluated as an anion exchange membrane for application in electrogenerative processes to recover Pd2+ ions. Ionic liquids 1-ethyl-3-me­thyl­imidazolium chloride (EMIM-Cl) and 1-butyl-3-methylimidazolium chloride (BMIM-Cl) were used as the carrier molecules in the polymeric network of PIM to enhance anion exchange process. This hybrid anion exchange membrane also consists of a polymeric matrix of non-plasticized cellulose triacetate modified by incorporating an inorganic material (silane) prepared by the sol-gel route. Different parameters affecting the ion transport performance efficiency, i.e., the composition of the membrane, type of ionic liquid (carrier molecule) and ion–exchange capacity, were investigated and optimized. In the electrogenerative process, the results revealed that the prepared PIM yields better recovery results for recovering Pd2+ ions from its chloride solution compared to the commercial anion exchange membrane Neosepta® AM-01, with a full recovery of 100 mg/L Pd2+ ions in 30 min. This preliminary study shows that the prepared low-cost hybrid anion exchange membrane PIM can act as an inexpensive material suitable for the rapid and efficient recovery of Pd2+ ions from an aqueous solution.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles.

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT-.

On-chip electromembrane extraction of some polar acidic drugs from plasma samples by the development of an active and efficient polymeric support for liquid membrane based on electrospinning process

Electromembrane extraction (EME), despite its high performance in the extraction of highly polar basic analytes, has challenges in extracting polar acidic compounds. This is the result of a lack of access to the suitable supported liquid membrane (SLM) for this group of analytes. Therefore, it would be valuable to provide a suitable solution for this problem. Accordingly, in the present study, a new method based on on-chip EME followed by HPLC with UV detection was developed for the extraction and determination of some polar acidic drugs in order to provide high extraction efficiency. Here, a new polymeric sheet was introduced as a support for SLM immobilization, which is not only used to impregnate 1-octanol as SLM but also enhances extraction recovery by exerting effective interactions with target acidic analytes. The polymeric sheet was composed of nanofibers prepared by electrospinning polycaprolactone blended with a composite of graphene oxide and aluminum polycations. Encapsulation of the composite in polycaprolactone nanofibers improved the extraction efficiency of polar acidic compounds by creating additional interactions with the target analytes, including hydrogen bonding, dipole-dipole, π-π stacking, and anion exchange process. The electrospun nanofiber-based sheet was characterized by FE-SEM, EDX, elemental mapping, TEM, and AFM. The extraction parameters were further optimized with an orthogonal-rotatable central composite design (CCD). Applying CCD determined optimal conditions by minimum experiments, and interactions between the parameters were clarified. Under optimized conditions, the proposed method provided extraction recoveries from 36.5 to 64.1%, relative standard deviations less than 5.7% (n = 4), and detection limits of 0.3–0.5 μg L−1. Furthermore, the proposed method was successfully used for the determination of target analytes in plasma samples, providing good accuracy (87–110%) and precision (3.2–8.8%).

Energy conversion performance of porous ZrTe hybrid derived from chemical transformation of Zr(OH)4

• Hydrothermal treatment was employed for the synthesis of ZrTe. • ZrTe deposited on carbon cloth (CC) perform well for OER. • ZrTe/CC exhibits lower overpotential of 294 mV and smaller Tafel slope of 71 mV dec -1 . • The high performance of ZrTe/CC was also confirmed via the density functional theory (DFT). Next-generation fuels are produced via electrochemical water splitting technology, and energy conversion processes can be improved by fabricating high-performance oxygen evolution (OER) electrocatalysts. Among all types of electrocatalysts, alternative, cheap, and high-performance OER catalysts are the metal tellurides. Here in the present report, the novel ZrTe has directly grown on carbon cloth (CC) and outperforms OER due to its 3D shell-like structure, high conductivity, and porous nature. Hydrothermal conditions are employed to promote an anion-exchange process that leads to zirconium tellurium nanostructure from synthesized tellurium ions and hydroxide of the zirconium hexagonal nanosheets. The electrochemical measurements are performed using modified electrodes, and are tested in the alkaline environment using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and a constant potential chronoamperometry (CA). The ZrTe/CC resulted in a lower overpotential of 294 mV with a smaller Tafel slope of 71 mV dec −1 and high stability of 45 h towards OER because of its unique shape resulting in large electrochemical active zones and more active sites without any binding agent. Additionally, the present study also validates that ZrTe/CC hybrid is more active towards OER via the density functional theory (DFT) and theoretical calculations, as our findings show that it is possible to produce multi-metal telluride-based materials that can be exceptionally efficient and stable electrocatalyst for OER, and also in future applications.

Iron‑sulfur geochemistry and acidity retention in hydrologically active macropores of boreal acid sulfate soils: Effects of mitigation suspensions of fine-grained calcite and peat

Acid sulfate soils discharge large amounts of sulfuric acid along with toxic metals, deteriorating water quality and ecosystem health of recipient waterbodies. There is thus an urgent need to develop cost-effective and sustainable measures to mitigate the negative effects of these soils. In this study, we flushed aseptically-prepared MQ water (reference) or mitigation suspensions containing calcite, peat or a combination of both through 15-cm-thick soil cores from an acid sulfate soil field in western Finland, and investigated the geochemistry of Fe and S on the surfaces of macropores and in the solid columnar blocks (interiors) of the soil columns. The macropore surfaces of all soil columns were strongly enriched in total and HCl-extractable Fe and S relative to the interiors, owing to the existence of abundant Fe oxyhydroxysulfates (schwertmannite and partly jarosite) as yellow-to-brownish surface-coatings. The dissolution/hydrolysis of Fe oxyhydroxysulfates (predominantly jarosite) on the macropore surfaces of the reference columns, although being constantly flushed, effectively buffered the permeates at pH close to 4. These results suggest that Fe oxyhydroxysulfates accumulated on the macropore surfaces of boreal acid sulfate soils can act as long-lasting acidification sources. The treatments with mitigation suspensions led to a (near-)complete conversion of jarosite to Fe hydroxides, causing a substantial loss of S. In contrast, we did not observe any recognizable evidence indicating transformation of schwertmannite. However, sulfate sorbed by this mineral might be partially lost through anion-exchange processes during the treatments with calcite. No Fe sulfides were found in the peat-treated columns. Since Fe sulfides can support renewed acidification events, the moderate mineralogical changes induced by peat are desirable. In addition, peat materials can act as toxic-metal scavengers. Thus, the peat materials used here, which is relatively cheap in the boreal zone, is ideal for remediating boreal acid sulfate soils and other similar jarosite-bearing soils.

Copper-Cobalt-Based Sulfides: Strategy To Boost Energy Storage Performance Utilizing the Synergistic Effect of a Double Metal Ion

The copper cobaltite chalcogenides were designed and developed via a simple and economically effective electrochemical route followed by the hydrothermal anion-exchange process without altering the morphological features. The systematic synthetic approach provided spinel crystalline-structured copper cobalt sulfide (CuCo2S4) through in situ co-deposition and copper sulfide/cobalt sulfide composite (CuS/CoS) via layer-by-layer deposition. Obtained high-resolution scanning electron microscopy explains the unique dendrite morphology of copper cobalt sulfide (CuCo2S4) with a primary midrib followed by secondary and tertiary trunks, whereas CuS/CoS governs a distinct CuS dendrite covered with thin CoS sheets homogeneously. Furthermore, the CuCo2S4 electrode material governed a superior charge storage property in supercapacitor application with a capacitive value of 966–676.8 C g–1 at a current density ranging from 10 to 40 A g–1 with a 70.15% retention value, whereas CuS/CoS delivered only 455.3–278.8 C g–1 at current densities with 61.23% retention. The promising faradaic behavior of the as-prepared material was attributed by the stable charge-discharge profile at different applied current densities as 10, 20, 30, 40, and 10 A g–1 for 5000 cycles for CuCo2S4 and CuS/CoS electrodes, respectively. To evaluate real-time charge storage behavior, an asymmetric device was assembled by coupling the CuCo2S4 electrode with activated carbon electrode using a 3 M KOH aqueous electrolyte. The fabricated device delivered 126.8 and 81.45 C g–1 at 10 and 50 A g–1, respectively. Moreover, the device demonstrated excellent cycling stability up to 5000 cycles at 50 A g–1 with 96.70% capacitive retention. Thus, the present work demonstrates the most effective strategy to exploit the synergistic effect of bimetal ions to boost the charge storage properties of a ternary chalcogenide electrode.

Photocatalytic performance for palm-fiber-like SnS2 nanoflakes with full solar spectrum light response

A palm-fiber-like SnS2 with multilayer structure has been hydrothermally synthesized by anion exchange process from vertically-aligned Sn3O4 nanoflake arrays precursors. Compared to monolayer SnS2, the multilayer SnS2 exhibits obvious photothermal effect and displays excellent photocatalytic activity for RhB degradation and CO2 reduction under full solar spectrum. The multilayer SnS2 is found to have a larger electrochemically active surface area, and increased absorption for full solar spectrum with the merits of micron- and nanometer-scale structure favors to absorb the full spectrum of sunlight. The combined effect for the UV–vis absorption by the nanoscale primary structure and NIR absorption by the secondary micron-structure likely play an important role for its superior absorption capability and photocatalytic activity. This work is expected to provide a foundation to develop photocatalysts, photodetectors, solar cells and other solar energy conversion devices with full solar spectrum light response.

Enriched-Bromine Surface State for Stable Sky-Blue Spectrum Perovskite QLEDs With an EQE of 14.6.

Halogen vacancies are of great concern in blue-emitting perovskite quantum-dot light-emitting diodes because they affect their efficiency and spectral shift. Here, an enriched-bromine surface state is realized using a facile strategy that employs a PbBr2 stock solution for anion exchange based on Cd-doped perovskite quantum dots. It is found that the doped Cd ions are expected to reduce the formation energy of halogen vacancies filled by the external bromine ions, and the excess free bromine ions in solution are enriched in the surface by anchoring with halogen vacancies as sites, accompanied with the shedding of surface long-chain ligands during the anion exchange process, resulting in a Br-rich and "neat" surface. Moreover, the surface state exhibits good passivation of the surface defects of the controlled perovskite QDs and simultaneously increases the exciton binding energy, leading to excellent optical properties and stability. Finally, the sky-blue emitting perovskite quantum-dot light-emitting diodes (QLEDs) (490nm) are conducted with a record external quantum efficiency of 14.6% and current efficiency of 19.9cd A-1 . Meanwhile, the electroluminescence spectra exhibit great stability with negligible shifts under a constant operating voltage from 3 to 7V. This strategy paves the way for improving the efficiency and stability of perovskite QLEDs.

Replacement of interlayer anion via memory effect of layered double hydroxide: A promising strategy for fabricating nanostructures with better flame-retardant performance

According to the memory effect of layered double hydroxide (LDH), the LDH nanostructure containing polyoxometalates anion (LDH-MoP) was prepared by an anion exchange process. Compared with the original LDH contained carbonate ion (LDH-C), the LDH-MoP exhibited a hydrotalcite laminated structure with larger interlayer spacing than that of LDH-C, implying that the carbonate ions between LDH-C layers were replaced by polyoxometalates anions. The LDH-MoP obtained via replacement of anions by polyoxometalates anion could lead to a more homogeneous dispersion and better synergistic effect of flame-retardant components than those in the physically mixed sample of LDH-C and Na3[PMo12O40] ·xH2O. After adding 3 wt% LDH-MoP in epoxy resin (EP), EP/LDH-MoP shows the most significant decrease in peak heat release rate (PHRR), total heat release (THR), peak smoke rate (PSPR), and total smoke release (TSR). The Limited Oxygen Index (LOI) value of EP/LDH-MoP has been significantly improved, and a UL-94 V-0 rating (LOI = 32.1%) can be achieved. In addition, compared with that of the physical mixture, the EP/LDH-MoP generates a denser and more compact char residue after the cone calorimeter test, suggesting that the oxygen exchange, smoke diffusion, and heat transfer could be more effectively hindered during the combustion process of the latter. This study could provide a novel strategy for designing high-performance flame retardants and some valuable clues for the enhancement of homogeneous dispersion and the synergistic effect of inorganic flame retardants.

Scalable synthesis of efficiently luminescent and color-tunable CsPbX3 (X=Cl, Br, I) nanocrystals by regulating the reaction parameters

All-inorganic CsPbX3 (X=Cl, Br, I) perovskite nanocrystals (NCs) exhibit attractive optoelectronic properties for lighting and displays application but suffer from the lack of profound insights into their reaction kinetics. Herein, a modified ligand-assisted reprecipitation (LARP) method was developed to synthesize high-quality CsPbBr3 NCs by utilizing oleic acid (OA) and n-octylamine (OTAm) as surface ligands, and the effect of Cs/Pb ratio, precursors and ligands concentration on the structure, morphology and fluorescence properties was systematically investigated. The monodisperse CsPbBr3 NCs with cubic shape and average particle size of 13.7 nm are obtained by optimizing the reaction parameters. Appropriately increasing the Cs/Pb ratio and precursors concentration to 0.5 and 1.0 mM are favorable for forming a more complete crystal structure with lower defect states density, which can significantly enhance the PL intensity. Notably, the surface defect states of CsPbBr3 NCs are effectively passivated by the coordinated OA and OTAm ligands, and the maximum photoluminescence quantum yield (PLQY) can reach to 85.2%. Importantly, the effective synthesis of high-quality CsPbBr3 NCs can be amplified up to 50 times of reaction volume after finely optimizing the reaction parameters. Based on a facile anion exchange process, the CsPbX3 NCs with variable halogen composition exhibit tunable emission of 443.3∼649.1 nm and a wide color gamut of 117% NTSC standard. This work provides profound sights on the reaction kinetics of perovskite NCs, and further promotes its practical application in optoelectronic field.

Precisely decorating CdS on Zr-MOFs through pore functionalization strategy: A highly efficient photocatalyst for H2 production

Different materials, such as metal sulphides, are often combined with metal-organic frameworks (MOFs) to develop multi-functional composites and improve their photocatalytic properties. However, the high interfacial energy barrier limits the formation and nano-assembly of the heterogeneous junctions between MOFs and metal sulphides. Herein, the heterostructured Zr-MOF-S@CdS are successfully constructed through a sequential synthesis method, in which the mesoporous Zr-MOF are firstly decorated with thioglycolic acid through pore functionalization, and followed by the S2- anion exchange process resulting in the surface close attached growth of CdS onto Zr-MOF-S materials. Due to the presence of molecules linkers, the CdS can be precisely decorated onto Zr-MOF-S without aggregation, which can provide more active sites. Moreover, the intimate connections and the suitable band structures between two materials can also facilitate the photogenerated electron-hole pairs separation. Therefore, the resulting Zr-MOF-S@CdS with appropriate ratio exhibits high photocatalytic activity for water reduction, in which the H2 evolution rate can reach up to 1861.7 μmol·g−1·h−1, 4.5 times higher than pure CdS and 2.3 times higher than of Zr-MOF/CdS, respectively. Considering the promising future of MOF-based photocatalysts, this work may provide an avenue for the further design and synthesis MOF-based composite photocatalysts for efficient H2 evolution.

A water-soluble luminescent cesium-lead perovskite nanocrystal probe for sensitive detection of penicillamine

In this paper, a water-soluble CsPbBr3 perovskite nanocrystals (PNCs) probe with high photoluminescence was prepared and its analytical application for penicillamine detection was studied after an anion exchange process. The result indicated that the CsPbBr3 PNCs probe after iodide anion exchange (CsPbX3, X = Br/I) had a sensitive optical property that can be changed by penicillamine. The fluorescence intensity of the CsPbX3 PNCs increased and the maximum emission peak of the CsPbX3 blue-shifted in the presence of a lower concentration of penicillamine. By optimizing the degree of anion exchange and the experimental condition, penicillamine in the concentration from 5.0 to 35.0 nM can be linearly detected by the luminescence changes of the CsPbX3 PNCs probe. The color change of the PNCs probe was just right in the red and green bands that can be easily recognized by the naked eyes under 365 nm UV lamps. The mechanism of the phenomenon was further studied and the results indicated the interaction of the sulfhydryl group in the penicillamine with the iodide exchanged in the perovskite is the cause of spectral changes. The CsPbX3 PNCs probe prepared here also had a similar response to other sulfur compounds. Thus, the method proposed here has the potential to establish a universal analytical method for the visualization of sulfur-containing substances in water environments.

Bimetallic sulfide nanoneedle arrays for lithium ion storage: monocrystalline versus polycrystalline

Growing mixed metal sulfides onto conductive substrates is promising in constructing self-supported flexible electrodes. However, most mixed metal sulfides grown on conductive substrates exhibit polycrystalline properties, while single crystallites are rarely reported due to the Kirkendall effect during the anion exchange process. In this work, single-crystalline CoNi2S4 directly grown on carbon cloth is obtained via tuning the diffusion of involved species with the help of fluorine ions during the anion exchange process. The received single-crystalline CoNi2S4 exhibits better electrochemical properties than the polycrystalline counterpart, establishing its significance as an electroactive material for lithium-ion batteries. Ex-situ data indicate that the single-crystalline CoNi2S4 particles exhibit local homogeneity and higher active material utilization upon lithiation/delithiation process, accounting for the enhanced electrochemical performance. These results highlight the importance of single-crystal active materials in constructing self-supported electrodes and reveal a promising opportunity for obtaining high-performance flexible electrodes.

NOx uptake capacities and sequestration pathways by hydrated cementitious phases

This study seeks to quantify NOx sequestration by individual hydrated cementitious phases (C-S-H, AFm-SO4, and Ca (OH)2), establish a fundamental understanding of the reaction pathways, and reveal the effects of carbonation (CaCO3 and AFm-CO3). For uncarbonated phases, the highest NOx uptake was measured in C-S-H, with the produced nitrite/nitrate physically bound on solid surface. For AFm-SO4, an anion exchange process was observed, where nitrite/nitrate substitute for sulfate and form new AFm-NO2/NO3. Ca(OH)2 showed undetectable NOx uptake, which may be due to the relative low temperature and relative humidity. For carbonated phases, CaCO3 exhibited an improved NOx uptake compared to uncarbonated phases, with uptake capacity three times higher than that of C-S-H. The result of AFm-CO3 indicates that carbonation could potentially inhibit the anion exchange process that was observed in AFm-SO4. These findings provide guidelines for the rational design and optimization of cement-based materials for enhanced NOx sequestration.

Ligands Mediate Anion Exchange between Colloidal Lead-Halide Perovskite Nanocrystals.

The soft lattice of lead-halide perovskite nanocrystals (NCs) allows tuning their optoelectronic characteristics via anion exchange by introducing halide salts to a solution of perovskite NCs. Similarly, cross-anion exchange can occur upon mixing NCs of different perovskite halides. This process, though, is detrimental for applications requiring perovskite NCs with different halides in close proximity. We study the effects of various stabilizing surface ligands on the kinetics of the cross-anion exchange reaction, comparing zwitterionic and ionic ligands. The kinetic analysis, inspired by the “cage effect” for solution reactions, showcases a mechanism where the surface capping ligands act as anion carriers that diffuse to the NC surface, forming an encounter pair enclosed by the surrounding ligands that initiates the anion exchange process. The zwitterionic ligands considerably slow down the cross-anion exchange process, and while they do not fully inhibit it, they confer improved stability alongside enhanced solubility relevant for various applications.

Operando Converting BiOCl into Bi2O2(CO3)xCly for Efficient Electrocatalytic Reduction of Carbon Dioxide to Formate

HighlightsAn operando synthetic approach was exemplified to enhance catalyst stability for efficient reduction of CO2 to formate.A highly stable Bi2O2(CO3)xCly electrocatalyst was synthesized by direct electrochemical conversion of BiOCl via a cathodic potential-promoted anion-exchange process under operando CO2RR conditions.The surface Cl− in Bi2O2(CO3)xCly changes the p-orbital electron states to enhance the stability and alters the CO2RR pathway to markedly reduce the energy barrier.

In-situ anion exchange based Bi2S3/OV-Bi2MoO6 heterostructure for efficient ammonia production: A synchronized approach to strengthen NRR and OER reactions

• The Bi 2 S 3 /OV-Bi 2 MoO 6 S-scheme heterojunction is constructed using a simple in-situ anion exchange process enabling oxygen vacancy (OV) abundant Bi 2 MoO 6 microspheres with surface deposited Bi 2 S 3 . • The as-fabricated Bi 2 S 3 /OV-Bi 2 MoO 6 functioned as an effective photocatalyst to convert N 2 -to-NH 3 under mild conditions without any sacrificial agent. • The photocatalytic NH 3 production rate reached 126 μmol g cat −1 under visible light for 2.5 h with 2% Bi 2 S 3 /OV-Bi 2 MoO 6 photocatalyst, which was 8 fold higher than Bi 2 MoO 6 . • The S-scheme heterojunction accelerated the e − / h + pairs spatial separation and accumulation on the Bi 2 S 3 and Bi 2 MoO 6 side, respectively, thus simultaneously strengthening both OER and NRR half-reactions. Photocatalytic ammonia generation via nitrogen reduction reaction (NRR) is a green and prospective nitrogen fixation technique. However, NRR is often hampered by the high N 2 adsorption/activation energies and is accompanied by a slow kinetics oxygen evolution reaction (OER). Herein, a robust Bi 2 S 3 /OV-Bi 2 MoO 6 S-scheme heterojunction is constructed using a simple in-situ anion exchange process, which enables oxygen vacancy (OVs) abundant Bi 2 MoO 6 microspheres with surface deposited Bi 2 S 3 . The as-fabricated Bi 2 S 3 /OV-Bi 2 MoO 6 functioned as an effective photocatalyst to convert N 2 -to-NH 3 under mild conditions. The photocatalytic NH 3 /NH 4 + production rate reached 126 μmol g cat −1 under visible light for 2.5 h with 2% of Bi 2 S 3 /OV-Bi 2 MoO 6 photocatalyst, which was 8-fold higher than pristine Bi 2 MoO 6 . Furthermore, the as-fabricated Bi 2 S 3 /Bi 2 MoO 6 heterojunction exhibited good selectivity, high stability and reproducibility. The excellent photocatalytic NRR performance was ascribed to the Bi 2 S 3 /Bi 2 MoO 6 heterojunction formed subsequent to the strong interaction between Bi 2 S 3 and Bi 2 MoO 6 . The OVs facilitated the chemical adsorption process allowing activation of N 2 molecule on the Bi 2 S 3 /Bi 2 MoO 6 . Simultaneously, the S-scheme heterojunction prolonged the lifetime of photogenerated carriers, accelerated the electrons/holes spatial separation and accumulation on the Bi 2 S 3 (reduction) and Bi 2 MoO 6 side (oxidation), respectively, thus strengthening both OER and NRR half-reactions. This simple in-situ anion exchange method offers a novel technique for strengthening OER and NRR half-reactions in Bi-based photocatalysts for effective photocatalytic ammonia generation.

The influence of using wet cellulose poultice on nanolime consolidation treatments applied on a limestone

Consolidation treatment with nanolime is a common conservation intervention which needs more research to enhance penetration and mechanical properties while also minimizing the undesired white veil on the surface which significantly alters the surface appearance. In this light, the application of a cellulose poultice soaked in distilled water over the treated surface with nanolime tries to prevent the formation of white hazes and to favour nanolime carbonation and penetration in the pore structure. However, the real influence of this practice on the consolidation effectiveness has never been studied yet and is not yet well understood. In order to provide more insights about its most suitable application method, in this study, we investigated the effectiveness of a wet cellulose poultice for two different nanolime consolidation treatments on a weathered limestone. Nanolime has been synthetized by anion exchange processes and dispersed in two mediums: i) water and ii) 50% v/v of water and alcohol. The influence of the poultice on the penetration and aesthetic properties has been studied by drilling resistance measurement, ultrasounds test, stereomicroscopy, measurements of roughness and static contact angle, spectrophotometry and scanning electron microscopy (superficial and cross sectioned samples). Additionally, consolidation effectiveness has been evaluated through the changes in apparent density, open porosity, porosity network in the outer 5 mm of the surface by mercury intrusion porosimetry and surface cohesion by the peeling test. Results show that, contrary to what is usually assumed, samples where a wet cellulose poultice was applied after the consolidant reached the lowest penetration levels and retained lower dry matter in comparison to their counterparts without poultice. A consolidation treatment with nanolime is more complex that it is generally considered, and the application of poultices is not always enhancing consolidation level; the most suitable application procedure must be chosen with regards to the nanolime and substrate specific characteristics.

A silicate-loaded MgAl LDH self-healing coating on biomedical Mg alloys for corrosion retardation and cytocompatibility enhancement

Clinical application of magnesium (Mg) alloys such as bone fracture fixation is hindered by the fast degradation rate under physiological conditions. In this work, a magnesium‑aluminum layered double hydroxide coating intercalated with silicate (LDH-SiO3) is fabricated on the anodized AZ31B Mg alloy by a hydrothermal technique and anion exchange process to tailor the corrosion rate and cytocompatibility. The LDH-SiO3 coating comprising a porous outer layer and compact inner layer adheres strongly to the anodized Mg alloy substrate. Electrochemical tests reveal that the LDH-SiO3 coating reduces the corrosion current density by 266 times to 0.8 ± 0.1 μA cm−2 in addition to yielding a large charge transfer resistance of 4.98 × 104 Ω cm2 in the simulated body fluid (SBF), revealing decreased corrosion because of inhibition of diffusion of aggressive ions through the compact and adherent inner LDH layer on the Mg alloy substrate. Immersion tests in SBF for 360 h reveal that the LDH-SiO3 coating mitigates corrosion propagation, Mg release, hydrogen evolution, and pH variation, indicating the notable long-term protection ability resulting from the self-healing LDH-SiO3 coating after localized corrosion occurs on the Mg alloy substrate. The self-healing mechanism mainly stems from SiO32− released from the LDH coating in conjunction with Mg leaching during natural degradation, resulting in the formation of Mg silicate precipitate that covers the corroded areas. Biologically, the LDH-SiO3 coating enhances attachment and proliferation of MC3T3-E1 pre-osteoblasts suggesting good cytocompatibility stemming from the favorable outcome including inhibited Mg leaching and alkalization as a result of the LDH-SiO3 coating. The self-healing LDH-SiO3 coating is very promising in expanding the clinical application of Mg-based implants by offering a viable approach to control corrosion and improve cytocompatibility.

Engineering Sulfur Vacancies in Spinel-Phase Co3S4 for Effective Electrocatalysis of the Oxygen Evolution Reaction

Restricted by the sluggish kinetics of the oxygen evolution reaction (OER), efficient OER catalysis remains a challenge. Here, a facile strategy was proposed to prepare a hollow dodecahedron constructed by vacancy-rich spinel Co3S4 nanoparticles in a self-generated H2S atmosphere of thiourea. The morphology, composition, and electronic structure, especially the sulfur vacancy, of the cobalt sulfides can be regulated by the dose of thiourea. Benefitting from the H2S atmosphere, the anion exchange process and vacancy introduction can be accomplished simultaneously. The resulting catalyst exhibits excellent catalytic activity for the OER with a low overpotential of 270 mV to reach a current density of 10 mA cm–2 and a small Tafel slope of 59 mV dec–1. Combined with various characterizations and electrochemical tests, the as-proposed defect engineering method could delocalize cobalt neighboring electrons and expose more Co2+ sites in spinel Co3S4, which lowers the charge transfer resistance and facilitates the formation of Co3+ active sites during the preactivation process. This work paves a new way for the rational design of vacancy-enriched transition metal-based catalysts toward an efficient OER.