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.

There is little evidence of sphalerite oxidation accounting for interfacial behavior, evolution of its oxidation capacity and kinetics processes under simulated weathering conditions. Accordingly, the present study combines surface analyses of pristine and leached low Fe-bearing and Pb-bearing sphalerite samples (PbS-ZnS) including Xray Photoelectron Spectroscopy (XPS), Glow Discharge Optical Emission Spectroscopy (GDOES), Raman spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), along with the chemical evolution of leachates obtained after 24 h of mineral contact with 0.1 M NaOH, 0.1 M NaNO3, 0.1 M H2SO4 or 0.1 M HClO4 solution. An electrochemical study using Cyclic voltammetry (CV), Chronopotentiometry (CP), Chronoamperometry (CA), Linear sweep voltammetry (LSV) and Tafel plots (TP) of PbS-ZnS and marmatite-like sphalerite ((Fe, Zn)S) samples were also conducted to evaluate the oxidation capacity of the mineral interfaces in the solutions. Results reveal slow sphalerite oxidation linked to formation and heterogeneous polysulfides distribution, thus defining bare modifications of surface as indicated by SEM, AFM, GDOES, XPS and Raman studies. The highest oxidation was obtained in NaOH solution (NaOH > NaNO3 > HClO4 > H2SO4). While the corresponding K-f.C-R(b) parameters were 1.07 x 10(-7) and 3.14 x 10(-8) mol.s(-1) for PbS-ZnS and (Fe, Zn)S samples, respectively. A clear oxidation trend involving the progressive passivation of (Fe, Zn)S sample was revealed during evolution of sphalerite oxidation, whereas an alternative passive to transpassive oxidation was observed for the PbS-ZnS sample. We suggest weathering mechanisms for sphalerite, and their environmental implications are discussed.

In the framework of pollutant sequestration by magnetic nano materials, this work focuses on the synthesis and the physico-chemical properties of starch functionalized nano magnetites. Nanoparticles were prepared by the Fe2+/Fe3+ coprecipitation method with increasing amount of starch in the synthesis medium (starch to iron mass ratio (R) in the range 0–10). Obtained materials were characterized by Transmission Electron Microscopy (TEM), Powder X-Ray Diffraction (PXRD), Raman, Fourier Transform Infrared (FTIR) and 57Fe Mössbauer spectroscopies, as well as by vibrating sample magnetometry. The presence of starch into the synthesis medium lowers magnetite crystallinity and increases the dispersion of the oxide particles. Both effects lead to fast relaxing superparamagnetic particles at RT for high R. The role of starch on nano-magnetite growth and stabilization is evidenced.

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.

Abstract The present study combines surface analyses of pristine and leached low Fe-bearing and Pb-bearing sphalerite (PbS-ZnS) samples including XPS, GDOES, Raman spectroscopy, SEM and AFM, along with chemical evolution of leachates after 24 h of contact with 0.1 M NaOH, 0.1 M NaNO3, 0.1 M H2SO4 or 0.1 M HClO4 solution. A comprehensive electrochemical analysis using Cyclic voltammetry, Chronopotentiometry, Chronoamperometry, Linear sweep voltammetry and Tafel plots of PbS-ZnS and marmatite-like sphalerite (FeZnS) are conducted to compare its oxidation activities. Mineral characterizations reveal sluggish weathering linked to inhomogeneous and minor secondary polysulfides (Sn2−) surface compounds distribution, thus defining bare modifications of surface-activity relationships. The occurrence of secondary Zn-bearing compounds was not identified on altered samples, which suggests that this heavy metal diffuses into the bulk-solution. Electrochemical assessments confirm sluggish sphalerite oxidation mainly composed by two subsequent stages, where the highest mineral activity was obtained in NaOH conditions. It was found that the sphalerite oxidation is more active in the presence of Pb, while the activity of sphalerite gradually decreases when it is a mineral rich in Fe probably associated with progressive accumulation of Sn2−/S0 compounds. We suggest general oxidation mechanisms for sphalerite, and their environmental implications are discussed.

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.

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.

Antimony (Sb) is a naturally occurring element; it is enriched in the environment by anthropogenic activities. Like other metalloid species, Sb partitions to mineral phases such as oxyhydroxides. In reducing environments, Fe(III) may serve as a terminal electron acceptor during dissimilatory iron reduction leading to its transformation. Relatively little is known concerning the effect of Sb(V) on the precipitation of biogenic minerals in relation to microbiologically mediated redox reactions. To further our understanding, Sb-bearing ferrihydrites (0.5 g) with variable Sb/(Fe + Sb) molar ratios of 0.04, 0.06 and 0.1, were incubated in the presence of Shewanella oneindensis MR-1 (1 x 10(8) cell mL(-1)) under N-2 atmosphere. Additionally, we synthesized abiotic GR1(CO32-) in the presence of Sb(V) to examine the effect of Sb(V) on this mineral formation and stabilization. A combination of wet chemistry and solid analysis techniques (XRD, Mossbauer and Raman spectroscopies) was used to characterize the reactions. The Sb loading affected the rate and the extent of bio-reduction compared with pure ferrihydrite. Only a minor fraction of the total Sb, less than 0.5%, was released into the solution by the end of the incubation period, suggesting that the metalloid partitioned mainly in a newly formed phase. Furthermore, XPS analyses showed the presence of Sb(V) and Sb(III) species on the biogenic minerals. Magnetite was the main biogenic precipitate (91%) in the absence of Sb(V). Increasing of the molar ratios [Sb/(Fe + Sb)] to 0.1 resulted mainly in the precipitation of carbonated green (47%) rust and goethite (37%). Abiotic green rust synthesis carried out in the presence of Sb(V) indicated the latter's stabilizing effect on the green rust structure, as for phosphate species. Thus, it is likely that Sb(V) preserve biogenic green rust, hindering its transformation to more thermodynamically stable phases. (C) 2021 Published by Elsevier Ltd.

Here, mixed nanostructured ceria/zirconia oxides have been prepared either by wet impregnation on nanostructured ZrO2 or by co-condensation through an evaporation-induced self-assembly (EISA)-deriv...

We report the effect of the synthesis route of starch-functionalized magnetite nanoparticles (NPs) on their adsorption properties of As(V) and As(III) from aqueous solutions. NP synthesis was achieved by two different routes implying the alkaline precipitation of either a mixed Fe2+/Fe3+ salt solution (MC samples) or a Fe2+ salt solution in oxidative conditions (MOP samples). Syntheses were carried out with starch to Fe mass ratio (R) ranging from 0 to 10. The crystallites of starch-free MC NPs (14 nm) are smaller than the corresponding MOP (67 nm), which leads to higher As(V) sorption capacity of 0.3 mmol gFe−1 to compare with respect to 0.1 mmol gFe−1 for MOP at pH = 6. MC and MOP starch-functionalized NPs exhibit higher sorption capacities than a pristine one and the difference in sorption capacities between MOP and MC samples decreases with increasing R values. Functionalization tends to reduce the size of the magnetite crystallites and to prevent their agglomeration. Size reduction is more pronounced for MOP samples (67 nm (R0) to 12 nm (R10)) than for MC samples (14 nm (R0) to 9 nm (R10)). Therefore, due to close crystallite size, both MC and MOP samples, when prepared at R = 10, display similar As(V) (respectively, As(III)) sorption capacities close to 1.3 mmol gFe−1 (respectively, 1.0 mmol gFe−1). Additionally, according to the effect of pH on arsenic trapping, the electrostatic interactions appear as a major factor controlling As(V) adsorption while surface complexation may control As(III) adsorption.

The adsorption of carboxylate collectors is largely assumed to be affected by the monazite surface speciation. In order to provide key information for the understanding of this phenomenon, we propose in this study a thermodynamic model for the equilibrium of monazite-(La) crystal in an H2O-CO2 system. This model allows access to the speciation information of the dissolved lattice species. Based on this model, we identify potential chemical reactions that may affect, under certain conditions, lanthanide ions on monazite surface. Since these surface ions have vacant coordination sites, they may react with water molecules and media species to restore their coordination shells. Therefore, it has been suggested that surface lanthanide ions undergo hydroxylation and carbonation reactions under alkaline conditions. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to analyse synthetic monazite-(La) samples treated in deionised water or sodium carbonate solutions. The spectroscopy results suggest that surface lanthanide ions do tend to hydroxylate under alkaline conditions. Furthermore, under the tested conditions, no significant monazite surface carbonation was observed. These results indicate that surface lanthanide ions have limited affinity for dissolved carbonate species, contrary to what is suggested by the thermodynamic model for free lanthanide ions in the bulk.

In this study we report the preparation of starch-functionalized magnetic nanoparticles (Starch@MNPs) by the oxidation-precipitation method of iron (II). Special attention was devoted to the characterization of the modification of structural and magnetic properties depending on the starch to iron mass ratio R. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), Raman, Mossbauer, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopies (XPS) and thermogravimetric analysis (TGA) were used to carefully characterize and compare the as-synthesized products. TEM and PXRD revealed the reduction of the crystallite size as R increases. The size varies from 67 +/- 5 to 12 +/- 4 nm by changing R from 0 to 10. The formation of a cubic inverse spinel iron oxide phase was demonstrated by PXRD and the discrimination between magnetite Fe3O4 and maghemite Fe2O3 was realized by Raman and Mossbauer spectroscopy. Mossbauer spectroscopy allowed to monitor the evolution of the magnetic properties with respect to R. The superparamagnetic behaviour was evidenced by the appearance of a doublet in the Mossbauer spectra that strongly increased in intensity with R ratio. The relative abundance (RA) of the doublet at room temperature was observed to increase from 10 to 36% for R equal 1 to 10. Lastly, the iron environment was highly perturbed by the presence of starch.

Dolomite is a cheap and robust catalyst used for biomass gasification, but its deactivation under relevant conditions of pilot-scale gasifiers has still been poorly understood. For this reason, the catalytic activity of fresh and used dolomites produced from an industrial air-blow fluidized bed was investigated. Fresh and used dolomites were characterized by BET, SEM-EDX, XPS, ICP-MS, XRD, TPD and TPO. Benzene steam reforming was selected as a surrogate reaction of tar conversion in order to probe the reactivity of the two dolomites. The activity of used dolomite was 25% lower than that of fresh dolomite. This difference could be explained by: (1) the deposition of a Si-based layer from biomass ashes at the surface of used dolomite, and (2) the production of coke during gasification. The reaction mechanism of benzene steam reforming over fresh and used dolomites was discussed. For used dolomite, the Si and coke depositions reduced the availability of the active sites (CaO, MgO) thus lowering the conversion of benzene. These deposits could also inhibit the interactions between CaO and MgO and enhance the formation of a stable coke.

Single phase Ca-Fe layered double hydroxide (LDH) minerals containing Cl- species in the interlayer was synthesized by coprecipitation with a Ca-II: Fe-III ratio of 2: 1. In both phosphate (PO4) free water and at low aqueous PO4 concentration, the LDH was fully transformed into a mixture of a "ferrihydrite-like" material, calcite and soluble calcium species. Mossbauer spectroscopy and transmission electron microscopy showed that phosphate was removed by the "ferrihydrite like" phase that contained a significant quantity of Ca. At high phosphate concentration the Ca species released from the LDH precipitated to form hydroxyapatite leading to a maximal removal capacity of similar to 130 mg P-PO4 g(-1). The Ca-Fe LDH was deposited onto a pozzolana volcanic rock in order to perform a column experiment under hydrodynamic conditions for 70 days. A high removal capacity was observed, a q(B) of similar to 4 mg P-PO4 g(-1) was measured at the breakthrough of the column, however the pH in the outflow was measured to be higher than 11. Such an increase was due to the very high solubility of the Ca-Fe LDH.

Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L− showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

Mesostructured titania as support for the CoMoS active phase in deep HDS of 4,6-dimethydibenzothiophene leads to a modification of the main desulfurization way in contrast with the conventional CoMoS/alumina catalyst. Indeed, the dispersion of MoS2 active phase onto mesostructured titania supports leads to catalysts, which favor the direct desulfurization of 4,6-dimethydibenzothiophene. We demonstrate that this unexpected behavior is related to the intrinsic acid properties of the supports, arising from the coexistence of amorphous phase with semi-crystalline anatase. Indeed, these solids present both Lewis and Bronsted acidities, which are conserved after the impregnation of cobalt and molybdenum. The characteristic and the efficiency of the mesoporous titania catalysts have been compared either with conventional Al2O3, used for hydrotreatment, or P25, a commercial TiO2 support used as titania reference.

Aqueous phosphate removal by three geomaterials from Ivory Coast was evaluated to determine their potential application as low-cost phosphate adsorbents in wastewater treatment. Batch experiments showed that phosphate uptake strongly depended on pH. Laterite and sandstone dissolution was less pronounced compared to shale. A correlation between concentrations of aqueous cation species released from shale and phosphate uptake was observed. The kinetics were well described using the pseudo-second-order model. Isotherms displayed a saturation level on shale, while phosphate uptake continuously increased for laterite and sandstone. The removal efficiency decreased in the following ranking order: laterite>sandstone>shale. Laterite was also the most efficient adsorbent in column experiments. The high phosphate removal efficiency of laterite (8.3mgPO4g−1) was attributed to the presence of superparamagnetic low grain sizes of goethite. Laterite is a particularly promising material for further investigation in wastewater treatment technology such as constructed wetlands.