Sulfidization of ferrihydrite in the presence of organic ligands

In soils and sediments, short-range order (SRO) iron minerals constitute one of the most abundant and reactive mineral components. With high surface areas and points of zero charge near pH 7-8, SRO minerals like ferrihydrite (Fe10O14(OH)2+mH2O) are often linked to high adsorption of nutrients (C, N, P, S) and trace elements (e.g. As, Zn). However, under oxygen-limiting conditions, microbially derived sulfide (S(&#8722;II)) may cause the rapid reductive dissolution of ferrihydrite and the release of associated nutrients and trace elements, thus influencing the biogeochemical cycling of trace elements and nutrients, particularly in redox dynamic environments.Sulfidization of ferrihydrite occurs rapidly, whereby electron transfer between surface complexed sulfide and the ferrihydrite surface results in (partially) oxidized sulfur species and Fe(II). Depending on the S(-II):Fe molar ratios, secondary reactions then lead to mackinawite (FeS) or pyrite (FeS2) precipitation. In nature, however, ferrihydrite is often found associated with natural organic matter (NOM). Because coprecipitation of ferrihydrite with NOM decreases particle size, alters the surface charge, and may block surface sorption sites, we speculated that kinetics and pathways of sulfidization of organic-associated ferrihydrite may differ from those of the pure mineral. Therefore, in this study, we followed iron mineral transformations and sulfur speciation during sulfidization of a pure ferrihydrite over one year and compared this to ferrihydrite coprecipitated with model organic ligands (polygalacturonic acid, galacturonic acid, and citric acid). Using a combination of solid- and aqueous phase Fe and S speciation techniques, we show that the impact of OM on ferrihydrite sulfidization kinetics and pathways varies with the chemical structure of the organic ligand, and that secondary reactions continue well past the initial rapid consumption of S(-II).

Download Full-text

Ferrihydrite mineral transformations in the presence of Fe(II) and organic ligands

10.5194/egusphere-egu2020-21278 ◽

2020 ◽

Author(s):

Laurel K. ThomasArrigo ◽

Ruben Kretzschmar

Keyword(s):

Trace Elements ◽

High Surface ◽

Dynamic Environments ◽

Organic Ligands ◽

Mineral Transformation ◽

Iron Minerals ◽

Molar Ratios ◽

Reducing Conditions ◽

Soils And Sediments ◽

Mineral Transformations

In soils and sediments, poorly-crystalline, short-range order (SRO) iron minerals constitute one of the most abundant and reactive components. With high surface areas, SRO minerals like ferrihydrite (Fe10O14(OH)2+mH2O) influence the biogeochemical cycling of trace elements and nutrients, particularly in redox dynamic environments. While under oxic conditions SRO iron mineral adsorption capacity is high, in the absence of O2, FeIII acts as an electron acceptor during microbial respiration. Electron transfer induces transformations in pure iron minerals, impacting the release and re-distribution of SRO-associated trace elements and nutrients.In nature, however, pure SRO iron minerals rarely form. Rather, the ubiquitous presence of natural organic matter (OM) in soils and sediments promotes the formation mineral-organic associations. Coprecipitation of ferrihydrite with OM decreases particle size and alters the mineral susceptibility towards microbial reduction. Thus, under reducing conditions, an increased rate and extent of mineral transformation could be expected for OM-associated ferrihydrite. However, in the presence of abiotic reductants, mineral transformation rates and extents in OM-associated ferrihydrite are markedly inhibited when compared to that of a pure ferrihydrite. Using polygalacturonic acid (PGA) as a proxy for acid carbohydrate fraction found in exopolymeric substances, we reacted ferrihydrite-PGA coprecipitates of varying C:Fe molar ratios (0-2.5) with ferrous Fe (Fe(II), 0.5-5.0 mM) at neutral pH for up to 5 weeks. Through a combination of XRD and 57Fe M&#246;ssbauer spectroscopy, we showed that at all Fe(II) concentrations, the kinetics and extent of mineral transformation decreased with increasing C content of the coprecipitates. Similarly, ferrihydrite-OM coprecipitates comprising PGA, citric acid (CA), or galacturonic acid (GA) of similar C:Fe molar ratios (~0.6) also showed inhibited mineral transformations compared to a pure ferrihydrite, whereby the extent of inhibition of mineral transformations followed the order GA>>CA>PGA. In addition, electron microscopy imaging showed that the crystal morphology of the secondary mineral phases varied with the varying chemical structure of the coprecipitating organic ligands. Despite this, applications of stable Fe isotope tracers revealed that all OM-associated ferrihydrite actively partook in iron atom exchange, suggesting that the presence of OM inhibited crystal growth of more crystalline phases, therefore again leading to SRO phases during iron atom exchange. Collectively, the stabilization of high surface-area ferrihydrite under reducing conditions via recrystallization has implications for the release and re-distribution of ferrihydrite-associated trace elements and nutrients in redox-dynamic environments.

Download Full-text

Ultralow Surface Tension Solvents Enable Facile COF Activation with Reduced Pore Collapse

10.26434/chemrxiv.12374249.v1 ◽

2020 ◽

Author(s):

Dongyang Zhu ◽

Rafael Verduzco

Keyword(s):

Surface Tension ◽

Membrane Filtration ◽

High Surface ◽

Nitrogen Adsorption ◽

Activation Process ◽

Strong Impact ◽

Pore Collapse ◽

Surface Areas ◽

Accessible Surface ◽

The Impact

Covalent Organic Frameworks (COFs) are organic, crystalline, highly porous materials attractive for applications such as gas storage, gas separations, catalysis, contaminant adsorption and membrane filtration. Activation of COFs removes adsorbed solvents and impurities, but common methods for COF activation can result in collapse of porous structure and loss of accessible surface areas. Here, we present a study of the impact of solvent surface tension on the activation process and demonstrate that activation using the ultralow surface tension solvent perfluorohexane (PFH) is simple and effective for a range of COF materials. We synthesized six different imine-based COFs through imine condensation reactions between tris(4-aminophenyl) benzene (TAPB) or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and multi-functional di- and tri-benzaldehydes with different aromatic substituents. For each COF, we performed a solvent wash followed by vacuum drying using six solvents varying in surface tension from 11.9 – 72.8 mN m-1. Through powder X-ray diffraction (PXRD) measurements combined with nitrogen adsorption and desorption analysis, we found that some COF chemistries readily lost their porosity during activation with higher surface tension solvents while others were more robust. However, all COFs could be effectively activated using PFH to produce materials with excellent crystallinity and high surface areas, comparable to those for samples activated using supercritical CO2. This work demonstrates that the solvent surface tension used during activation has a strong impact on potential pore collapse, and activation using PFH provides a simple and effective activation method to produce COFs with excellent crystallinities and pore structures.

Download Full-text

Synergism at the Nanoscale

Research Perspectives on Functional Micro- and Nanoscale Coatings - Advances in Chemical and Materials Engineering ◽

10.4018/978-1-5225-0066-7.ch003 ◽

2016 ◽

pp. 42-77

Author(s):

Raquel Eugenia Galian ◽

Julia Pérez-Prieto

Keyword(s):

Optical Properties ◽

High Surface ◽

Organic Ligand ◽

Volume Ratio ◽

Colloidal Dispersions ◽

Organic Ligands ◽

Organic Media ◽

Intrinsic Properties ◽

Smart Systems ◽

Size Dependent

Photoactive nanoparticles are smart systems that exhibit unique optical properties. In general, their intrinsic properties are size dependent. The degree and type of response to size are both related to their composition. Nanoparticles usually require to be capped with organic ligands in order to be dispersible in an aqueous or organic media, thus leading to nanoparticle colloidal dispersions and enhancing the processability of the material. The organic ligand also plays a key role in their preparation. In addition, the high surface-to-volume ratio of the nanoparticles combined with the affinity of the ligands for the nanoparticle surface can be used to place a large number of functional molecules at their periphery. The purpose of this chapter is to understand the synergism between nanoparticles and organic ligands with regard to their preparation, performance, and applicability.

Download Full-text

Ultralow Surface Tension Solvents Enable Facile COF Activation with Reduced Pore Collapse

10.26434/chemrxiv.12374249 ◽

2020 ◽

Author(s):

Dongyang Zhu ◽

Rafael Verduzco

Keyword(s):

Surface Tension ◽

Membrane Filtration ◽

High Surface ◽

Nitrogen Adsorption ◽

Activation Process ◽

Strong Impact ◽

Pore Collapse ◽

Surface Areas ◽

Accessible Surface ◽

The Impact

Download Full-text

Recent Perspectives in Biochar Production, Characterization and Applications

10.5772/intechopen.99788 ◽

2021 ◽

Author(s):

Asfaw Gezae Daful ◽

Meegalla R. Chandraratne ◽

Marie Loridon

Keyword(s):

Physicochemical Properties ◽

Process Parameters ◽

Pyrolysis Temperature ◽

High Surface ◽

Molar Ratios ◽

High Affinity ◽

Surface Areas ◽

C And N ◽

Proximate And Ultimate Analysis

This chapter presents the most promising features and applications of biochar along with their optimal pyrolysis conditions. Biochars have a range of physicochemical properties depending on the feedstock and pyrolysis conditions, which greatly affect their wide applications. The biochar production and its characteristics, including the effect of feedstocks and different process-parameters on the properties and yield of biochar are thoroughly examined. The higher pyrolysis-temperature can give higher carbon-contents, pH, and surface-areas of biochars while volatiles and molar-ratios of O/C, H/C and N/C decrease with pyrolysis-temperature. Higher carbon-content and neutral-pH biochars have high affinity for organic pollutants due to high surface areas, making them attractive for adsorption and catalysis purposes. Biochars with higher-pH are preferred for soil application to correct soil-acidity. Thus, the pyrolysis temperature should be selected as per the final application of the biochar. Characterization of biochars of different feedstocks and pyrolysis conditions is reviewed and presented along with their proximate and ultimate analysis.

Download Full-text

Experimental and Theoretical Investigations of Complex Formation of Substituted Phenylazo-Derivatives of Methylphloroglucinol

JOURNAL OF ADVANCES IN CHEMISTRY ◽

10.24297/jac.v12i8.2837 ◽

2016 ◽

Vol 12 (8) ◽

pp. 295-300

Author(s):

Olga Kovalchukova ◽

Amangdam A.T. ◽

Strashnova S.B. ◽

Strashnov P.V. ◽

Romashkina E.P. ◽

...

Keyword(s):

Complex Formation ◽

Organic Ligand ◽

Spectrophotometric Titration ◽

Organic Ligands ◽

Oh Groups ◽

Tautomeric Forms ◽

Theoretical Investigations ◽

Derivatives Of ◽

Theoretical Results ◽

Titration Technique

Using spectrophotometric titration technique, the processes of complex formation of some phenylazo-derivatives of methylphloroglucinol (MPG) containing hydroxo-, nitro- and nitroso-substituents were studied. The spectral criteria of neutral and ionized forms of the organic ligands in their different tautomeric forms were determined.It was detected that the complex formation is accompanied by formation of one or two chelate cycles which involve azo- or nitroso-fragments and neighboring OH-groups of the organic ligands. Different types of coordination lead to different changes in the electronic absorption spectra.The DFT-B3LYP modeling of a Ni(II) complex of α-hydroxyphenylazo MPG established the most probable coordination mode of the organic ligand: tridentate chelating dianion, distorted square coordination of Ni-cations including one water molecule. The theoretical results are in a good accordance with the experimental data.

Download Full-text

A Highly Crystalline Anthracene-Based MOF-74 Series Featuring Electrical Conductivity and Luminescence

10.26434/chemrxiv.8222492 ◽

2019 ◽

Author(s):

Patricia Scheurle ◽

Andre Mähringer ◽

Andreas Jakowetz ◽

Pouya Hosseini ◽

Alexander Richter ◽

...

Keyword(s):

Electrical Conductivity ◽

Metal Ions ◽

Light Emission ◽

Block Design ◽

High Surface ◽

Visible Spectrum ◽

Building Blocks ◽

Divalent Metal Ions ◽

Conductivity Enhancement ◽

Surface Areas

Recently, a small group of metal-organic frameworks (MOFs) has been discovered featuring substantial charge transport properties and electrical conductivity, hence promising to broaden the scope of potential MOF applications in fields such as batteries, fuel cells and supercapacitors. In combination with light emission, electroactive MOFs are intriguing candidates for chemical sensing and optoelectronic applications. Here, we incorporated anthracene-based building blocks into the MOF-74 topology with five different divalent metal ions, that is, Zn2+, Mg2+, Ni2+, Co2+ and Mn2+, resulting in a series of highly crystalline MOFs, coined ANMOF-74(M). This series of MOFs features substantial photoluminescence, with ANMOF-74(Zn) emitting across the whole visible spectrum. The materials moreover combine this photoluminescence with high surface areas and electrical conductivity. Compared to the original MOF-74 materials constructed from 2,5-dihydroxy terephthalic acid and the same metal ions Zn2+, Mg2+, Ni2+, Co2+ and Mn2+, we observed a conductivity enhancement of up to six orders of magnitude. Our results point towards the importance of building block design and the careful choice of the embedded MOF topology for obtaining materials with desired properties such as photoluminescence and electrical conductivity.

Download Full-text

Mitigating the Agglomeration of Nanofiller in a Mixed Matrix Membrane by Incorporating an Interface Agent

Membranes ◽

10.3390/membranes11050328 ◽

2021 ◽

Vol 11 (5) ◽

pp. 328

Author(s):

Manh-Tuan Vu ◽

Gloria M. Monsalve-Bravo ◽

Rijia Lin ◽

Mengran Li ◽

Suresh K. Bhatia ◽

...

Keyword(s):

Gas Separation ◽

Polymer Matrix ◽

Ion Beam ◽

High Surface ◽

Mixed Matrix Membrane ◽

Mechanical And Thermal Properties ◽

Separation Membranes ◽

Surface Areas ◽

Separation Membrane ◽

Focus Ion Beam

Nanodiamonds (ND) have recently emerged as excellent candidates for various applications including membrane technology due to their nanoscale size, non-toxic nature, excellent mechanical and thermal properties, high surface areas and tuneable surface structures with functional groups. However, their non-porous structure and strong tendency to aggregate are hindering their potential in gas separation membrane applications. To overcome those issues, this study proposes an efficient approach by decorating the ND surface with polyethyleneimine (PEI) before embedding it into the polymer matrix to fabricate MMMs for CO2/N2 separation. Acting as both interfacial binder and gas carrier agent, the PEI layer enhances the polymer/filler interfacial interaction, minimising the agglomeration of ND in the polymer matrix, which is evidenced by the focus ion beam scanning electron microscopy (FIB-SEM). The incorporation of PEI into the membrane matrix effectively improves the CO2/N2 selectivity compared to the pristine polymer membranes. The improvement in CO2/N2 selectivity is also modelled by calculating the interfacial permeabilities with the Felske model using the gas permeabilities in the MMM. This study proposes a simple and effective modification method to address both the interface and gas selectivity in the application of nanoscale and non-porous fillers in gas separation membranes.

Download Full-text

The Impact of Gelatin on the Pharmaceutical Characteristics of Fucoidan Microspheres with Posaconazole

Materials ◽

10.3390/ma14154087 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4087

Author(s):

Marta Szekalska ◽

Aleksandra Citkowska ◽

Magdalena Wróblewska ◽

Katarzyna Winnicka

Keyword(s):

Antifungal Activity ◽

Drug Release ◽

Spray Drying ◽

Fungal Infections ◽

Drug Loading ◽

High Surface ◽

Vaginal Fluid ◽

Sustained Drug Release ◽

Candida Spp ◽

The Impact

Fungal infections and invasive mycoses, despite the continuous medicine progress, are an important globally therapeutic problem. Multicompartment dosage formulations (e.g., microparticles) ensure a short drug diffusion way and high surface area of drug release, which as a consequence can provide improvement of therapeutic efficiency compared to the traditional drug dosage forms. As fucoidan is promising component with wide biological activity per se, the aim of this study was to prepare fucospheres (fucoidan microparticles) and fucoidan/gelatin microparticles with posaconazole using the one-step spray-drying technique. Pharmaceutical properties of designed fucospheres and the impact of the gelatin addition on their characteristics were evaluated. An important stage of this research was in vitro evaluation of antifungal activity of developed microparticles using different Candida species. It was observed that gelatin presence in microparticles significantly improved swelling capacity and mucoadhesiveness, and provided a sustained POS release. Furthermore, it was shown that gelatin addition enhanced antifungal activity of microparticles against tested Candida spp. strains. Microparticles formulation GF6, prepared by the spray drying of 20% fucoidan, 5% gelatin and 10% Posaconazole, were characterized by optimal mucoadhesive properties, high drug loading and the most sustained drug release (after 8 h 65.34 ± 4.10% and 33.81 ± 5.58% of posaconazole was dissolved in simulated vaginal fluid pH 4.2 or 0.1 M HCl pH 1.2, respectively).

Download Full-text

A process-based method for predicting lateral erosion rates

Natural Hazards ◽

10.1007/s11069-021-04587-y ◽

2021 ◽

Author(s):

Myron van Damme

Keyword(s):

Soil Mechanics ◽

High Surface ◽

Shear Stresses ◽

Empirical Equations ◽

Predictive Capability ◽

Surface Shear ◽

Erosion Rates ◽

Material Texture ◽

Empirical Coefficients ◽

The Impact

AbstractAn accurate means of predicting erosion rates is essential to improve the predictive capability of breach models. During breach growth, erosion rates are often determined with empirical equations. The predictive capability of empirical equations is governed by the range for which they have been validated and the accuracy with which empirical coefficients can be established. Most empirical equations thereby do not account for the impact of material texture, moisture content, and compaction energy on the erosion rates. The method presented in this paper acknowledges the impact of these parameters by accounting for the process of dilation during erosion. The paper shows how, given high surface shear stresses, the erosion rate can be quantified by applying the principles of soil mechanics. Key is thereby to identify that stress balance situation for which the dilatency induced inflow gives a maximum averaged shear resistance. The effectiveness of the model in predicting erosion rates is indicated by means of three validation test cases. A sensitivity analysis of the method is also provided to show that the predictions lie within the range of inaccuracy of the input parameters.

Download Full-text