Pristine zinc-based layered double hydroxides (LDHs) possess remarkable antibacterial properties. The antibacterial activity of zinc-based LDHs could be explained by three possible mechanisms: (1) direct contact interactions between the LDH and bacterial surfaces, (2) release of antibacterial Zn2+ aq ions, and (3) generation of reactive oxygen species (ROS) by LDHs in response to irradiation by a suitable light source. In this work, the potential contribution of ROS generation in the antibacterial activity of ZnAl LDH nanoparticles (NPs) was determined by comparing their effect against Gram-positive Staphylococcus aureus bacteria in the presence and absence of UVA irradiation (λ = 365 nm, irradiation period = 4 h). The bactericidal efficacy of ZnAl LDH NPs was significantly enhanced in the presence of UVA light. The bactericidal activity was hindered in the presence of histidine acting as a ROS scavenger and giving indirect evidence of the role of ROS. Moreover, Fourier-transform infrared spectroscopy revealed denaturation and suppression of several structural components in S. aureus cells exposed to ZnAl LDH NPs under dark conditions and in the presence of UVA radiation, with more pronounced alterations for the latter. The impacts of such alterations on the topographical properties of S. aureus cells were determined by atomic force microscopy imaging. Treated cells with ZnAl LDH NPs were completely deformed and exhibited increased roughness, especially upon treatment in UVA conditions. All these results suggest the presence of a dual antibacterial effect between ZnAl LDH NPs and their generated ROS to provide amplified antibacterial activity.

The intercalation of sodium into green rust sulfate, a layered double hydroxide (LDH), has been proposed to explain its large interlayer spacing (∼11 Å). We compare structures with and without sodium using ab initio molecular dynamics (AIMD) simulations and conclude that its composition most likely contains sodium: FeII6FeIII3(OH)18Na(SO4)2·nH2O, with 14 ≤ n ≤ 16.

Alkaline hydrothermal vents are plausible environments for the emergence of life on Earth. By means of a simplified analogical reconstruction of the vent-ocean interface of these systems reproducing early Earth conditions, we show that iron (oxy-hydr)oxide minerals may have carried out proto-bioenergetic processes driven by pH and redox gradients. The initial pH gradient precipitates the iron (oxy-hydr)oxide mineral barriers (magnetite, green rust and amakinite) and yields reducing conditions, enabling the production of metallic iron at room temperature via the disproportionation of Fe2+ to Fe3+ and Fe0. The crystallographic association of Fe0 surrounded by magnetite suggests the coupling of Fe3+ / H2 co-production at ambient temperature by amakinite oxidation with the thermodynamically unfavorable reduction of Fe2+ to Fe0. This abiotic disproportionation process coupling exergonic and endergonic reactions may serve as a proto-bioenergetic mechanism increasing the non-equilibrium reduction state of the system and offers an interesting analog of the biological electronic bifurcation reaction, the free energy coupling being a fundamental thermodynamic trait of life-as-we-know-it.

The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions (birA) to complete dehydration, and the involved mechanisms were scrutinized. Density Functional Theory (DFT) simulations were employed to derive structural models for lamellar A0.33MnO2xH2O (A = Na+ or K+, x = 0 or 0.66), subsequently compared with the experimental results obtained for Na0.30MnO20.75H2O and K0.22MnO20.77H2O materials. Thermal analysis (TGA-DSC), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Near Ambient Pressure X-ray Photoemission Spectroscopy (NAP-XPS) measurements were conducted for both birnessites. Dehydration under vacuum, annealing, or controlled relative humidity were considered. Results indicated that complete birnessite dehydration was a two-stage process. In the first stage, water removal from the interlayer of fully hydrated birnessite (birA) down to a molar H2O/A ratio of similar to 2 (birB) led to the progressive shrinkage of the interlayer distance (3% for Na birnessite, 1% for K birnessite). In the second stage, water-free (birC) domains with a shorter interlayer distance (20% for Na birnessite, 10% for K birnessite) appeared and coexisted with birB domains. Then, birB was essentially transformed into birC when complete dehydration was achieved. The vibrational properties of birA were consistent with strong intermolecular interactions among water molecules, whereas partially dehydrated birnessite (birB) showed a distinct feature, with 3 (for Na-bir) and 2 (for K-bir) vibrations that were reproduced by DFT calculations for organized water into the interlayer (x = 0.66). The study also demonstrated that the electronic structure of Na birnessite depends on the interlayer water content. The external Na+ electronic level (Na 2p) was slightly destabilized (+0.3 eV binding energy) under near ambient conditions (birA) compared to drier conditions (birB and birC). The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions to complete dehydration, and the involved mechanisms were scrutinized.

Green rust (GR) is a chemically reactive mineral of interest for environmental remediation. However, the lack of stability of this compound is a major drawback for practical applications. In this study, the precipitation of hydroxychloride green rust type 1 (GR1Cl) from soluble FeII and FeIII species was studied by analyzing pH titration curves and employing XRD, Raman and Mossbauer spectroscopies to find optimal conditions for synthesizing GR1Cl. Using the stoichiometric condition for FeII-FeIII corresponding to the [FeII3FeIII(OH)8]Cl compound, FeIIIO(OH)2.9Cl0.1 was formed in a first step during the addition of NaOH and then transformed into a mixture of GR1Cl and Fe3O4. The addition of phosphate anions (PO4) at a molar ratio PO4: Fe = 1: 10 in the initial solution was shown to avoid the formation of undesired magnetite. Interestingly, GR1Cl was also the only product without adding PO4 using an excess of FeII species in solution, i.e. for an initial ferric molar fraction x = FeIII: Fetot of 0.2. First experimental evidences of a hydroxyphosphate green rust type 2 GR2PO4 were also provided by XRD and Raman spectroscopy. Therefore, this work may attract interest for a better understanding of the geochemical cycle of iron and phosphate in natural environments such as hydromorphic soils or hydro- thermal chimneys where fougerite, the mineral homologue of synthetic GR, is supposed to play a significant role.

Antifungal resistance has become a very serious concern, and Candida albicans is considered one of the most opportunistic fungal pathogens responsible for several human infections. In this context, the use of new antifungal agents such as zinc-based layered double hydroxides to fight such fungal pathogens is considered one possible means to help limit the problem of antifungal resistance. In this study, we show that ZnAl LDH nanoparticles exhibit remarkable antifungal properties against C. albicans and cause serious cell wall damage, as revealed by growth tests and atomic force microscopy (AFM) imaging. To further link the antifungal activity of ZnAl LDHs to their adhesive behaviors toward C. albicans cells, AFM-based single-cell spectroscopy and single-particle force spectroscopy were used to probe the nanoscale adhesive interactions. The force spectroscopy analysis revealed that antimicrobial ZnAl LDHs exhibit specific surface interactions with C. albicans cells, demonstrating remarkable force magnitudes and adhesion frequencies in comparison with non-antifungal negative controls, e.g., Al-coated substrates and MgAl LDHs, which showed limited interactions with C. albicans cells. Force signatures suggest that such adhesive interactions may be attributed to the presence of agglutinin-like sequence (Als) adhesive proteins at the cell wall surface of C. albicans cells. Our findings propose the presence of a strong correlation between the antifungal effect provided by ZnAl LDHs and their nanoscale adhesive interactions with C. albicans cells at both the single-cell and single-particle levels. Therefore, ZnAl LDHs could interact with C. albicans fungal pathogens by specific adhesive interactions through which they adhere to fungal cells, leading to their damage and subsequent growth inhibition.

A vertical-flow unit containing four filters filled with shale was used to study the removal of phosphorous, nitrogen and organic matter of an urban residual wastewater during a period of 90 days. The influence of both the shale granulometry and the plant density of Panicum Maximum were studied. The decrease of the shale granulometry led to a significant improvement of all the measured parameters, while the presence of plants did only influence the phosphate retention with a lower extent. By comparing the results to previous studies, we hypothesised that the effect of the root system of Panicum maximum would be different depending on the size and the depth of the reactors. For practical application, adjusting the material granulometry was proposed to be the most important parameter for improving the filtration efficiency. Concomitantly, adjusting the plant density helps to control the clogging percentage of the filters.

Synthesized Fe@FeOx nanoparticles (NPs) were fully characterized by spectroscopic techniques and (scanning) transmission electron microscopy to resolve the presence of a Fe(OH)2-like phase. The different phases detected in the core–shell nanostructure of these NPs were corroborated by Mössbauer and X-ray photoelectron spectroscopies. Metallic iron (Fe0), ferrous (FeII) hydroxide, magnetite (FeIII2FeIIO4), and a top layer of ferric (FeIII) oxide were identified. Interestingly, ferrous hydroxide reacted with Pd2+aq upon coating of the supporting core–shell material when Pd was added to produce Fe@FeOx/Pd NPs.

Synthesized palladium-coated iron-iron oxide (Fe@FeOx/Pd) nanoparticles (NPs) using the successive salt reduction method are tested for their activity and stability toward formate oxidation (FO) and electrochemical CO2 reduction to formate (eCO(2)RF). The experimental results for FO show a current density at 0.12 V vs. Ag/ AgCl of 1.65 mA/cm(2) over 1 h, which is 16 times higher than that for Pd NPs. Furthermore, the same catalyst displays a higher current density with a faradaic efficiency (FE) of 95.6 % toward the eCO(2)RF, and exhibits a lower degree of CO adsorption. The iron-iron oxide interaction with the overlayer palladium is characterized by TEM/EDX, XPS/UPS, Mossbauer spectroscopy, and electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). NMR is used to estimate the amount of formate produced by the eCO(2)RF. A positive binding energy shift of the Pd 3d peak and the upshift of the d-band center as measured by XPS compared to monometallic homemade Pd NPs confirm that the electronic perturbation of the catalyst surface plays a major role in enhancing the performance of Fe@FeOx/Pd for both FO and eCO(2)RF. Furthermore, the work function as measured by UPS for the Fe@FeOx/Pd material is lower than that for monometallic Pd confirming a change in chemical properties of the catalyst surface. Finally, Mossbauer spectroscopy is used to determine the composition, structure and nature of all sites of the Fe@FeOx substrate before use and the perturbation of their intrinsic properties by the Pd overlayer. This change in intrinsic properties of the Pd coated material provides additional explanations for the electrochemical improvement measured for this catalyst toward both FO and eCO(2)RF.

Resistance to antimicrobial agents is responsible for major social and economic losses. The World Health Organization estimated 700,000 global deaths a year due to antimicrobial resistance. The use of layered double hydroxides (LDHs) as antibacterial materials could present a way to reduce the risk of bacterial infections and antibacterial resistance, by partial release of metallic ions in aqueous dispersion. The partial dissolution of different synthetic LDHs M-II-Al-III (M = Zn, Cu, Ni, Co, Mg) was studied in Lysogeny Broth (LB) and Tryptic Soy Broth (TSB), growth media of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria, respectively. The influence of several parameters (crystallinity, M-II:Al-III ratio, type of intercalated anion {CO32-, Cl-, NO3-, ClO4-} and nature of M-II cations) was investigated. In the absence of any post-synthetic hydrothermal treatment, Zn-II-Al-III LDH showed a release of Zn-III ions 6 times enhanced. Upon increasing Zn-II:Al-III molar ratio to 3: 1 and exchanging carbonate anions with other anions having lower intercalating affinities, a similar effect was observed. The dissolution properties of M-II-Al-III LDHs were correlated with the thermodynamic stability of their M-II(OH)(2) hydroxide counterparts with the exception of Cu-II-based LDH, which showed an amplified release of Cu-II due to its irregular structure presenting defects. Finally, the antibacterial activity was only noted for Zn-II and Cu-II-based LDHs. The antimicrobial effect of the studied LDHs was linked in the first place to the nature of divalent metal itself, and to the amount of released M-II ions into the culture media in the second place. This effect was more easily identified in Zn-II-Al-III LDHs whose minimum inhibitory concentration was decreased significantly from 12 to 0.375 mg.mL(-1) when higher amounts of Zn-II ions were released.

This article reports for the first time the synthesis of an LDH using only manganese as the divalent and trivalent metallic ion. Analysis of the pH, redox potential, and chemical composition during the oxidation of a manganese basic salt using persulfate indicates the oxidation of 1/3 of the initial MnII ions, in agreement with the paramagnetic structure and XPS analysis. Infrared, Raman spectra and thermogravimetric analysis results were similar to the ones obtained with Fe-LDH also known as green rust. X-Ray diffractograms and Rietveld refinement were used to determine the structure of this solid. Thermodynamic considerations predict that this solid could reduce nitrate into gaseous nitrogen without further reduction to ammonium or ammonia unlike what is observed for Fe-LDH.

Infections by pathogenic bacteria have been threatening several fields as food industries, agriculture, textile industries and healthcare products. Layered double hydroxides materials (LDHs), also called anionic clays, could be utilized as efficient antibacterial materials due to their several interesting properties such as ease of synthesis, tunable chemical composition, biocompatibility and anion exchange capacity. Pristine LDHs as well as LDH-composites including antibacterial molecules and nanoparticles loaded-LDHs were proven to serve as efficient antibacterial agents against various Gram-positive and Gram-negative bacterial strains. The achieved antibacterial effect was explained by the following mechanisms: (1) Direct contact between the materials and bacterial cells driven by electrostatic interactions between positively charged layers and negatively charged cell membranes, (2) Dissolution and gradual release over time of metallic ions or antibacterial molecules, (3) Generation of reactive oxygen species.

Synthesized Fe@FeOx nanoparticles (NPs) were fully characterized by spectroscopic techniques and (scanning-)transmission electron microscopy to resolve the presence of iron hydroxide (Fe(OH) 2 ). The different phases detected in the core-shell nanostructure of those nanoparticles were corroborated by Mössbauer and X-rays photoelectron spectroscopies. Metallic Fe 0 , Fe(OH) 2 , magnetite (Fe III 2 Fe II O 4 ) and a top layer of ferric oxide were identified. Interestingly, Fe(OH) 2 reacted with Pd 2+ aq upon coating of the supporting core-shell material with palladium to produce Fe@FeOx/Pd NPs.

This study evaluates the performance of shale from Ivory Coast used as substrate in vertical-flow constructed wetlands in removal of phosphates and nitrogen. The pilot-scale artificial wetland has been duplicated: filter planted with Panicum maximun and unplanted. They were set up outdoors, and fed with a municipal wastewater. The wetlands have been fed with three batches per week (intermittent) over a period of 3 months. During the operation period, the hydraulic residence time (HRT) 52 h was used, while wastewater temperatures varied from about ~33°C. The removal performance of the constructed wetland units was very good, since it reached on an average 98%, 89.4%, 89.4%, 84%, 80%, 84.8% and 92% for TSS, DOC, BOD5, , TKN, TP and respectively. In addition, the vegetation did not demonstrate superior performance to unplanted controls. Therefore, this study focuses on the role of shale in the phosphorus and nitrogen removal from wastewater by constructed wetland.

Understanding the mechanisms of the interactions between zinc-based layered double hydroxides (LDHs) and bacterial surfaces is of great importance to improve the efficiency of these antibiotic-free antibacterial agents. In fact, the role of surface interactions in the antibacterial activity of zinc-based LDH nanoparticles compared to that of dissolution and generation of reactive oxygen species (ROS) is still not well documented. In this study, we show that ZnAl LDH nanoparticles exhibit a strong antibacterial effect against Staphylococcus aureus by inducing serious cell wall damages as revealed by the antibacterial activity tests and atomic force microscopy (AFM) imaging, respectively. The comparison of the antibacterial properties of ZnAl LDH nanoparticles and micron-sized ZnAl LDHs also demonstrated that the antibacterial activity of Zn-based LDHs goes beyond the simple dissolution into Zn2+ antibacterial ions. Furthermore, we developed an original approach to functionalize AFM tips with LDH films in order to probe their interactions with living S. aureus cells by means of AFM-based force spectroscopy (FS). The force spectroscopy analysis revealed that antibacterial ZnAl LDH nanoparticles show specific recognition of S. aureus cells with high adhesion frequency and remarkable force magnitudes. This finding provides a first insight into the antibacterial mechanism of Zn-based LDHs through direct surface interactions by which they are able to recognize and adhere to bacterial surfaces, thus damaging them and leading to subsequent growth inhibition.

Layered double hydroxides (LDHs) have been intensively studied for phosphate (P-i) removal but suffer from poor stability and low sorption affinity under ambient conditions. In this paper, well crystallized (MnFeFeIII)-Fe-II-Fe-II-Cl, (MnFeIII)-Fe-II-CO3 and novel (MnFeIII)-Fe-IV-CO3 LDHs were synthesized. The LDHs show fast P-i sorption with 90 % uptake within 20 min, and high P-i sorption capacity of 11 mg P/g at low solution P-i concenrations of 0.1 mg P/L, corresponding to a very high Pi sorption affinity (K-d 1.1 x 10(5) L/kg). Fast MnII dissolution from the (MnFeFeCl)-Fe-II-Fe-II-Cl-III_ LDHs and formation of MnFe2O4 at pH 7 were observed in aqueous suspensions of non-oxidized material where up to 70% of total Mn was released within 2 h. However, when interlayer Cl- was exchanged with CO32-, much lower Mn dissolution (5.4%) was observed. Furthermore, after oxidation of MnII to MnIV, the obtained (MnFeIII)-Fe-IV-CO3 LDH maintained the layered structure of LDH and the particles were surrounded by birnessite nanorods. The (MnFeIII)-Fe-IV-CO3 LDH showed excellent stability but lower P-i sorption capacity. However, a high sorption affinity was maintained which is attributed to more positively charged Fe-centered sorption sites. XPS and ATR-FTIR data together with DFT calculations demonstrated that P-i was mainly sorbed via the formation of mononuclear mono- and bidentate P-i surface complexes on planar LDH particle surfaces.

It is expected that during a titration using a basic NaOH solution, the pH can only increase. In this article the formation of two different solids during the precipitation of a MnSO4 solution is discussed. The formation of a new compound Mn-4(OH)(6)SO4 center dot nH(2)O instead of Mn(OH)(2) is evidenced by the quantification of the remaining ions in solution as well as by X-Ray Diffraction, Raman and infrared spectroscopies. The transformation of this solid into Mn(OH)(2) after a sursaturation of the solid in OH can explain a drop of the pH in the titration curve.

Iron and cobalt monometallic Layered Double Hydroxide (LDH), combining divalent and trivalent cations of the same chemical element, are commonly used respectively for nitrate reduction and oxygen evolution reaction. This article reports the first synthesis of a LDH using only manganeseas metallic ion. X-Ray diffractograms, infrared and Raman spectra show that the structure obtained through the oxidation of a basic MnII salt with persulfate is comparable to the structure of Fe-LDH also known as Green Rust. XPS shows that in this solid coexist MnII and MnIII states. Thermodynamic considerations predict that this solid can reduce nitrate into gaseous nitrogen without further reductioninto ammonium or ammonia unlike what is observed for Fe-LDH.

Iron and manganese are ubiquitous in the natural environment. FeII-FeIII layered double hydroxide, commonly called green rust (GR), and MnIII-MnIV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)2, FeIIaq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O2. In oxic conditions for an initial FeII/OH− ratio of 0.6, a single GR phase was obtained in a first step; the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and Mössbauer spectroscopy. Hence, oxidation of FeII species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.

Layered double hydroxides (LDH) and their magnetic composites have been intensively investigated as recyclable high-capacity phosphate sorbents but with little attention to their stability as function of pH and phosphate concentration. The stability of a Fe3O4@SiO2-Mg3Fe LDH P sorbent as function of pH (5-11) and orthophosphate (P-i) concentration (1-300 mg P/L) was investigated. The composite has high adsorption capacity (approx. 80 mg P/g) at pH 5 but with fast dissolution of the LDH component resulting in formation of ferrihydrite as evidenced by Mossbauer spectroscopy. At pH 7 more than 60% of the LDH dissolves within 60 min, while at alkaline pH, the LDH is more stable but with less than 40% adsorption capacity as compared to pH 5. The high P-i sorption at acid to neutral pH is attributed to P-i bonding to the residual ferrihydrite. Under alkaline conditions P-i is sorbed to LDH at low P-i concentration while magnesium phosphates form at higher P-i concentration evidenced by solid-state P-31 MAS NMR, powder X-ray diffraction and chemical analyses. Sorption as function of pH and P-i concentration has been fitted by a Rational 2D function allowing for estimation of P-i sorption and precipitation. In conclusion, the instability of the LDH component limits its application in wastewater treatment from acid to alkaline pH. Future use of magnetic LDH composites requires substantial stabilisation of the LDH component. (C) 2020 Elsevier Inc. All rights reserved.