Vermiculite Surface Research Articles

Quantifying resistance to very-long-chain fatty acid-inhibiting herbicides in Amaranthus tuberculatus using a soilless assay.

Resistance to preemergence (PRE) soil-applied herbicides, such as inhibitors of very-long-chain fatty acid (VLCFA) elongases, was documented in two waterhemp [Amaranthus tuberculatus (Moq.) J.D. Sauer] populations (SIR and CHR) from Illinois, USA. To limit the spread of resistant weed populations, rapid detection measures are necessary. Soil-based resistance assays are limited by edaphic factors, application timing, variable seeding depth and rainfall amount. Therefore, cost-effective techniques mitigating effects of edaphic factors that are appropriate for small- to large-scale assays are needed. Our research goal was to identify and quantify resistance to the VLCFA-inhibiting herbicides, S-metolachlor and pyroxasulfone, using a soilless greenhouse assay. Dose-response experiments were conducted under greenhouse conditions with pre-germinated waterhemp seeds planted on the vermiculite surface, which had been saturated with S-metolachlor (0.015-15 μM), pyroxasulfone (0.0005-1.5 μM), or S-metolachlor plus the cytochrome P450 (P450) inhibitor, malathion. Lethal dose estimates of 50% (LD50) and growth reduction of 50% (GR50) were calculated for S-metolachlor and pyroxasulfone PRE and used to determine resistance indices (RI) for resistant populations (CHR and SIR) relative to sensitive populations, SEN and ACR. RI values for S-metolachlor using LD50 values calculated relative to SEN and ACR were 17.2 and 15.2 (CHR) or 11.5 and 10.1 (SIR), while RI values for pyroxasulfone using LD50 values calculated relative to SEN and ACR were 3.8 and 3.1 (CHR) or 4.8 and 3.8 (SIR). Malathion decreased the GR50 of S-metolachlor to a greater degree in CHR compared to ACR, consistent with P450 involvement in S-metolachlor resistance in CHR. Results from these soilless assays are in accord with previous findings in soil-based systems that demonstrate CHR and SIR are resistant to S-metolachlor and pyroxasulfone. This method provides an effective, reproducible alternative to soil-based systems for studying suspected PRE herbicide-resistant populations and will potentially assist in identifying non-target-site resistance mechanisms.

Experimental and theoretical study to control the heavy metals in solid waste and sludge during pyrolysis using modified expanded vermiculite

Na+/K+/Mg2+/Ca2+ expansion–modified vermiculite and calcination expansion (700 °C, 800 °C and 900 °C)–modified vermiculite (700-Mg-V, 800-Mg-V and 900-Mg-V) were prepared as additives to control the emission of five heavy metals (Zn, Cr, Cu, Pb, and Cd) during the pyrolysis of municipal sewage sludge, paper mill sludge, municipal domestic waste, and aged refuse. Mg2+-Modified vermiculite obtained via thermally activated calcination at 800 °C retained 65% of heavy metals from all raw materials at 450 °C. Zn, Cr, and Cu retained nearly 90%. Although modified vermiculite could reduce the ecological risk, Cd had an ecological risk level higher than Zn, Cr, Cu, and Pb. The fine textural properties, laminated morphology, and expansion capacity of modified vermiculite were positively correlated with its retention of heavy metals. Heavy metals interacted with the (002) surface of vermiculite, and the reactions were mainly concentrated near the 17-O and surrounding atoms. The heavy-metal monomers were less capable of binding to the (002) surface of vermiculite than the oxides and chlorides of heavy metals. The effect of heavy-metal oxides and chlorides binding to the (002) surface of vermiculite was related to heavy metals.

Adsorption of uranium(VI) by natural vermiculite: Isotherms, kinetic, thermodynamic and mechanism studies

Human activities such as mining uranium resources, hydrometallurgy, and nuclear fuel preparation inevitably produce wastewater sludge containing radionuclides, posing a severe threat to the environment around the production site. Natural clay minerals have been widely used in groundwater pollution remediation because of their high cation exchange capacity. Through static batch experiments, the optimal pH range of vermiculite for U(VI) adsorption was 6–8,the maximum adsorption capacity was 1.62 × 10−5 mol g−1. The kinetic adsorption results indicated that the adsorption mode was mainly multilayer non-homogeneous chemisorption. In addition, the adsorption of vermiculite on U(VI) was found to be a heat absorption process according to the thermodynamic model fitting, and the spontaneous reactivity of U(VI) adsorption on vermiculite surface was positively correlated with temperature and negatively correlated with the initial concentration of U(VI). Combined with SEM-EDS and FT-IR results, the adsorption process of vermiculite on U(VI) is mainly an ion exchange and complexation reaction, and U(VI) is removed in the form of ≡ SUOU22+ or ≡ SOUO2OH, etc., by XPS means. The results of this study not only investigated the adsorption behavior and mechanism of natural vermiculite in groundwater contaminated with simulated uranium but also provided theoretical support for its feasibility in remediating uranium-polluted groundwater.

Vermiculite-derived cationic molecular-intercalated fluorescent MgAl-LDHs for assembling ultrathin solid-state light-emitting films

Solid-state light-emitting devices are of special interest in optoelectronic applications, owing to inherent advantages in terms of low cost, high efficiency and desirable durability. However, the accumulation of solid fluorescent chromophores causes serious energy transfer, resulting in fluorescence quenching. Herein, exfoliated vermiculite (VMT) was structurally disassembled into Mg-O octahedral and Si-O tetrahedral layers to produce hydrotalcite (LDHs) and SiO2, respectively, realizing efficient utilization of each component and VMT surface. The fluorescent intercalated LDHs was intercalated with organic fluorescent dyes, including rhodamine 6G (R6G), pyronine G (PG) and sodium fluorescein (Fl-Na), to prepare high-performance fluorescent LDHs, which was further assembled with VMT nanosheets to form ultrathin solid-state light-emitting films. Based on the electrostatic self-assembly strategy, the localization of chromophores and light-emitting intensity of solid films can be precisely controlled by adjusting ordered multilayers. In fact, the exfoliated VMT could cause the quenching of organic fluorescent dyes in liquid, therefore VMT can be used as fluorescent quencher, which could be regenerated by heating. The designed assembly strategy avoids the fluorescence quenching of VMT. Without the addition of any surfactant, both anionic and cationic organic fluorescent dye can be intercalated into hydrotalcite, overcoming the disadvantage of LDHs that can only intercalate anionic molecules. In particular, the VMT encapsulation overcomes the quenching problem of fluorescent dye and improves the stability of the light-emitting films. This work provides a potential strategy for assembling solid-state light-emitting films and opens new applications in various optoelectronics, such as surface-emitting light source and full-color flat-panel displays.

In Ukrainian

The purpose of the work is synthesis of new organomineral composites by in situ immobilization and adsorption of poly[8-methacroyloxy-quinoline] on the surface of vermiculite and study of sorption properties of cations Cu(II), Pb(II) and Fe(III). In situ immobilization of poly [8-oxyquinolinemethacrylate] on the surface of vermiculite was carried out by initiated radical polymerization of 8 oxyquinoline methacrylate using 2,2′-azobisisobutyronitrile (AIBN) as a dinitrile initiator in the presence of vermiculite. To obtain the composite by adsorption of poly[8-oxyquinolinemethacrylate] on the surface of vermiculite, the polymer was synthesized in advance, then dissolved in tetrahydrofuran and adsorbed on vermiculite. The fact of immobilization of poly[8-oxyquinolinemethacrylate] on the surface of vermiculite was confirmed by comparative analysis of the IR spectra of the source mineral and relative composites. The regularities of thermal decomposition of immobilized polymer were studied by thermogravimetric analysis combined with mass spectrometry. Using the results of low-temperature adsorption-desorption of nitrogen and scanning electron microscopy, changes in the morphology of the vermiculite surface after immobilization of poly[8-oxyquinolinemethacrylate] by the selected methods are shown. The sorption characteristics of the synthesized composites with respect to Cu(II), Pb(II) and Fe(III) ions were examined in static mode. The polymer with oxyquinoline groups immobilized on the surface of vermiculite showed sorption activity against those metal ions with which 8-oxyquinoline forms stable complexes, the sorption capacity relative to cations Cu(II) is doubled after in situ immobilization of poly [8-oxyquinoline methacrylate] on the surface of vermiculite and increases almost 3 times after adsorption of this polymer. For Pb(ІІ) ions this effect is lower: after in situ immobilization of [8-methacroyloxy-quinoline] sorption capacity increases by one-third and as the result, the increasing of adsorption of this polymer is insignificant and is within the experimental accuracy.

Chitosan coated - porous low expansion vermiculite for efficient removal of cesium from radioactive wastewater

Radioactive elements have very important applications in practical life and work. The long-lived 137 Cs has a half-life of 30.2 years, it is easily absorbed by the human body. At present, the treatment methods of 137 Cs are mainly adsorption, ion exchange, co-precipitation and membrane separation technology. Among them, the adsorption method is widely used because of its low cost and easy availability, and with the continuous upgrading and improvement of the removal methods, the removal cost is also rising, so it is important to develop inexpensive and high removal rate adsorbent materials. Based on this, porous adsorbents made of pre‑sodiumed low expansion vermiculite modified by urea porogenesis and polyglutamic acid covalent grafting followed by chitosan coating had been used to remove Cs + . The proposed adsorbent was successfully applied for radioactive Cs removal to be used as the potential candidate in Fukushima nuclear wastewater treatment. It showed that the porous expanded vermiculite modified with low swelling, with urea as porogen and polyglutamic acid added to increase the negative charge vacancies on the expanded vermiculite surface, could greatly improve the chemisorption capacity of Cs + after chitosan coating. The maximum removal rate for radioactive 137 Cs + was 97.91%, and 89.89% of 137 Cs + could be effectively removed in 0.5 h. Even in the presence of competing ions such as K + , the adsorbent material still has a good adsorption effect. The maximum desorption rate of 98.43% was achieved after elution by CaCl 2 . • Pre-treated vermiculite was covalently grafted and chitosan coated to prepare new adsorbents. • Adsorption equilibrium process consistent with Langmuir adsorption isotherm and pseudo-second-order kinetics • Removal of Cs + and 137 Cs + by synergistic action of ion exchange, ligand complexation and electrostatic adsorption • The adsorbent can be reused 5 times after CaCl 2 elution.

Recycling spent iron-based disposable-chemical-warmer as adsorbent for as(v) removal from aqueous solution

The use of iron-based disposable-chemical-warmer (DCW) produces huge amount of solid wastes every year (e.g. at least 2 million tons of solid waste every year for China and Japan only), which are directly abandoned as trash now. In this work, spent DCW was recycled as adsorbent for As(V) removal from water. For the first time, we elucidated that the spent DCW was a magnetic nanocomposite consisted mainly of Fe3O4 nanoparticles and vermiculite with large surface area (56.6 m2/g). The detailed morphology characterization revealed the formation of Fe3O4 nanoparticles on vermiculite's surface, with the average crystallites’ size estimated to be ~10 nm. The adsorbent exhibited superparamagnetism with a strong saturation magnetization value 40 emu /g, which can be utilized to recollect the adsorbent after water treatment. The As(V) adsorption isotherm conformed to Langmuir isotherm model with the maximum adsorption capacity of 130 mg/g under neutral pH and room temperature. The adsorption capacity for As(V) outperformed most of the reported adsorbents, which was attributed to the hybrid structure of the adsorbent. The adsorption kinetic curve was well described by the pseudo-second order model. The favorable pH for As(V) was below 8.0, and the adsorbent had good As(V) selectivity over common co-existing anions (SO42−, H2PO4−, and SiO32−). Moreover, the adsorbent could be readily regenerated using 0.1 M NaOH aqueous solution as eluting solution. The adsorption capacity towards As(V) was still over 85% after 10 consecutive adsorption-desorption cycles. This work provided an efficient way for recycling spent DCW with minimal efforts.

Individual and simultaneous adsorption of tetracycline and cadmium by dodecyl dimethyl betaine modified vermiculite

Tetracycline-cadmium combined contaminants have drawn increasing attentions due to their high environmental risk. In this study, vermiculite was modified by dodecyl dimethyl betaine (BS-12) to obtain a kind of organo-vermiculite (BS-VER). After modification, BS-12 was grafted on the surface of vermiculite successfully. Due to the negatively charged head group of BS-12 and improved hydrophobicity of BS-VER, the affinities of BS-VER towards cadmium (Cd2+) and tetracycline (TC) were enhanced. In the single system, the maximum adsorption capacities of Cd2+ and TC on BS-VER increased from 14.98 to 19.72 mg g−1 and from 16.03–20.95 mg g−1, respectively. In the binary system, Cd-TC complex was formed and considered to be new adsorption site for Cd2+ adsorption, resulting in slight enhanced adsorption capacity of BS-VER towards Cd2+ and TC. Ion exchange, electrostatic attraction, hydrophobic interaction and chelation reaction were the main mechanisms. BS-VER exhibited good advantages in the simultaneous removal of heavy metals and organic contaminants.

Preparation of Fe2O3-coated vermiculite composite by hydrophobic agglomeration and its application in As/Cd co-contaminated soil

ABSTRACT Exploring an economic and efficient method for simultaneous passivation of As and Cd in soils is of great current significance. In this study, a low-cost composite material, Fe2O3-vermiculite (Fe-V), for effectively passivating As/Cd was synthesized successfully based on hydrophobic aggregation method. The reaction products were characterized by XRD, SEM, EDS and FTIR, results showed that Fe2O3 was successfully loaded onto the surface of vermiculite by the connection with sodium stearate and employed this composite material to passivate the co-contaminated soil with As/Cd. All the percentage of toxicity reduction (Pd value) was higher than the control group, which indicated the passivation was effective. In soil A (As 45 mg/kg and Cd 6 mg/kg), the Pd of As were higher than 90%, the Pd of Cd were 80–100%. And in soil B (As 80 mg/kg and Cd 10 mg/kg), the Pd of As were more than 84.68%, the Pds of Cd were about 99%. In the meantime, the application of Fe-V could apparently increase the residual fraction of As and Cd in soil A and soil B. Moreover, the passivation of As and Cd in soils by Fe-V composite materials was a combined physical and chemical action system. This research shows that Fe-V could play a good role in the passivation of As/Cd in different pollution levels of soils.

Vermiculites from Brazil and Palabora: Structural changes upon heat treatment and influence on the depolymerization of polystyrene

Although clay minerals have been widely used as catalysts and catalyst supports, the reports of natural clay minerals studied in their role as a catalyst are still rare. This work, therefore, for the first time reports the possible catalytic effects of the two raw vermiculites from Brazil (VerS) and Palabora (VerP) on the depolymerization of polystyrene (PS). The main experimental methods used to obtain a detailed structural characterization of vermiculites before and after the depolymerization experiment were X-ray powder diffraction (XRD), thermogravimetric DTA/TG analysis, infrared (FT-IR) and Raman spectroscopy. The detailed assignment of the vibration bands of vermiculites occurring in the near-IR and the analysis of carbon coatings on the surface of vermiculite using Raman spectra are performed for the first time. The thermal products of PS are styrene monomer (SM) about 54.5 mass% and pyrolytic volatile oligomers (dimers and trimers) about 32.1 mass%. The presence of VerS and VerP changes the relation between SM (about 50.7 and 53.6 mass%, respectively) and oligomers (about 37 and 33.3 mass%) due to the pyrolytic carbons deposited on the VerS as coke and on the VerP as glassy carbon. The variable yields of the products can be attributed to the natural vermiculite properties such as are different negative layer charge emerging from the cation substitution in tetrahedra, number of water molecules released during thermal treatment, and textural properties (SBET and pores).

Cation-controlled wetting properties of vermiculite membranes and its promise for fouling resistant oil\u2013water separation

Manipulating the surface energy, and thereby the wetting properties of solids, has promise for various physical, chemical, biological and industrial processes. Typically, this is achieved by either chemical modification or by controlling the hierarchical structures of surfaces. Here we report a phenomenon whereby the wetting properties of vermiculite laminates are controlled by the hydrated cations on the surface and in the interlamellar space. We find that vermiculite laminates can be tuned from superhydrophilic to hydrophobic simply by exchanging the cations; hydrophilicity decreases with increasing cation hydration free energy, except for lithium. The lithium-exchanged vermiculite laminate is found to provide a superhydrophilic surface due to its anomalous hydrated structure at the vermiculite surface. Building on these findings, we demonstrate the potential application of superhydrophilic lithium exchanged vermiculite as a thin coating layer on microfiltration membranes to resist fouling, and thus, we address a major challenge for oil–water separation technology.

A molecular level insight into adsorption of β-lactam antibiotics on vermiculite surface

The adsorption processes of β-lactam antibiotics including ampicillin (AP), amoxicillin (AX) and benzylpenicillin (BP) on the vermiculite surface were investigated using density functional theory computations. The C09-vdW density functional was used to include van der Waals interactions for determination of the most stable configurations governing the interactions between AP, AX and BP molecules and the vermiculite surface. Each molecule prefers to arrange horizontally on the surface to form both Mg∙∙∙S and Mg∙∙∙π contacts, or two Mg∙∙∙O electrostatic interactions between S atom in CS, π-electrons of benzene ring or O atoms of -COOH, OH groups in molecules and Mg2+ sites on surface. Remarkably, an important role of Mg∙∙∙π interaction in the complex stabilization has been observed for the first time. These are strong chemisorption processes with adsorption energies ranging from −72 to −78 kcal.mol−1. AIM calculations show a significant contribution of Mg∙∙∙O/S/π interactions and OH∙∙∙O hydrogen bonds to the complex stabilization. Formation and role of different interactions on the stability of complexes were thoroughly examined by MOs and EDTs analysis based on NBO approach. Overall, vermiculite, a clay mineral, emerges to offer an efficient adsorption surface and can be used as a material to remove antibiotic molecules from waste water sources.

α-Fe2O3 nanoparticles/vermiculite composites prepared for catalytic decomposition of polystyrene

The chemical recycling waste of polystyrene (PS) is expected to be recycled into styrene monomer. Among the most commonly used catalysts in the catalytic degradation of PS are base-promoted α-Fe2O3 (hematite) catalysts. In industrial catalysis, nanoparticles/clay mineral composites as catalysts could not only offer active species thanks to larger pores and surface area but make the separation of the used catalysts easier. The expandable layers of clay minerals provide useful two-dimensional hosts, which facilitate introduction and docking of catalytically active metal oxide nanoparticles. Acid/base catalysts to provide styrene monomers. The aim of this work is to investigate and compare pure nanoparticles α-Fe2O3 and those nanoparticles anchored on/in α-Fe2O3/vermiculite composites, prepared from the precursor solution of ferric chloride and precipitates NaOH and NH4OH on different vermiculites. The functionality difference of α-Fe2O3 nanoparticles and α-Fe2O3 nanoparticles/Ver composites as catalysts for degradation of polystyrene is assumed based on the findings that the precipitating agents and vermiculite surface have a significant effect on the crystal growth and structure symmetry of α-Fe2O3 nanoparticles.

Efficient Adsorption and Photocatalytic Degradation of Dyes by AgI‐Bi2MoO6/Vermiculite Composite under Visible Light

AbstractA novel efficient AgI‐Bi2MoO6/vermiculite adsorption‐photocatalyst is successfully synthesized by sol‐gel method and precipitation method. The structure and properties of AgI‐Bi2MoO6/vermiculite were analyzed by XRD, FT‐IR, XPS, SEM, TEM, BET, and DRS. All the AgI‐Bi2MoO6/vermiculite composites with different AgI content show enhanced photocatalytic performance for malachite green (MG) dye degradation compared to pure Bi2MoO6 and Bi2MoO6/vermiculite composites. The highest degradation efficiency for MG (30 mg/L) via 5 wt%‐AgI‐Bi2MoO6/vermiculite composite (AgI content 5 wt%) photocatalyst (1 g/L) reaches 98.89% in 60 min at pH 9 without salt. The enhanced performance can be attributed to the uniform dispersion of Bi2MoO6 and AgI on the surface of vermiculite, the stable structure, the enhanced adsorption and the widened visible‐light absorption range as well as the faster separation of electron‐hole pairs. Besides, the photocatalyst still shows relatively high adsorption and photocatalytic performance after three times recycling. In addition, the possible photocatalytic mechanism is proposed at the end.

Effects of Ultrasound on Zinc Oxide/Vermiculite/Chlorhexidine Nanocomposite Preparation and Their Antibacterial Activity.

Microbial infection and biofilm formation are both problems associated with medical implants and devices. In recent years, hybrid organic-inorganic nanocomposites based on clay minerals have attracted significant attention due to their application potential in the field of antimicrobial materials. Organic drug/metal oxide hybrids exhibit improved antimicrobial activity, and intercalating the above materials into the interlayer of clay endows a long-term and controlled-release behavior. Since antimicrobial activity is strongly related to the structure of the material, ultrasonic treatment appears to be a suitable method for the synthesis of these materials as it can well control particle size distribution and morphology. This study aims to prepare novel, structurally stable, and highly antimicrobial nanocomposites based on zinc oxide/vermiculite/chlorhexidine. The influence of ultrasonic treatment at different time intervals and under different intercalation conditions (ultrasonic action in a breaker or in a Roset’s vessel) on the structure, morphology, and particle size of prepared hybrid nanocomposite materials was evaluated by the following methods: scanning electron microscopy, X-ray diffraction, energy dispersive X-ray fluorescence spectroscopy, carbon phase analysis, Fourier transforms infrared spectroscopy, specific surface area measurement, particle size analysis, and Zeta potential analysis. Particle size analyses confirmed that the ultrasonic method contributes to the reduction of particle size, and to their homogenization/arrangement. Further, X-ray diffraction analysis confirmed that ultrasound intercalation in a beaker helps to more efficiently intercalate chlorhexidine dihydrochloride (CH) into the vermiculite interlayer space, while a Roset’s vessel contributed to the attachment of the CH molecules to the vermiculite surface. The antibacterial activity of hybrid nanocomposite materials was investigated on Gram negative (Escherichia coli, Pseudomonas aeruginosa) and Gram positive (Staphylococcus aureus, Enterococcus faecalis) bacterial strains by finding the minimum inhibitory concentration. All hybrid nanocomposite materials prepared by ultrasound methods showed high antimicrobial activity after 30 min, with a long-lasting effect and without being affected by the concentration of the antibacterial components zinc oxide (ZnO) and CH. The benefits of the samples prepared by ultrasonic methods are the rapid onset of an antimicrobial effect and its long-term duration.

Theoretical study on the adsorption of benzylpenicillin molecule onto vermiculite surface

AbstractTwo stable configurationss (P1 and P2) formed by interaction of benzylpenicillin molecule with vermiculite surface are obtained on the potential energy surface. The adsorption energies of P1 and P2 complexes are significantly negative at ca. ‐58 and ‐47 kcal.mol‐1, respectively. The adhesion of benzylpenicillin on vermiculite surface is favorable via > C=O···Mg interactions and O‐H···O hydrogen bonds between ‐COOH group of the molecule with Mg2+ and O2‐ ions on the surface. Notably, the benzylpenicilline molecule is adsorbed favorably onto vermiculite surface at Mg2+ site binding to O2‐ ions in ‐SiO3 group as compared to that in ‐AlO3 group. It is found that stability of P1 and P2 is contributed by both >C=O···Mg and O‐H···O interactions. Remarkably, the electron density transfer from the surface to the molecule is slightly stronger than that from molecule to surface. Calculated results indicate that the adsorption of benzylpenicillin on vermiculite surface is regarded as a strong chemisorption process.

β-Cyclodextrin-loaded minerals as novel sorbents for enhanced adsorption of Cd2+ and Pb2+ from aqueous solutions

The use of minerals to capture heavy metal pollution is limited by their capacity. Here, β-cyclodextrin (β-CD) with a good ability to capture heavy metals is loaded onto the surface of zeolite and vermiculite to adsorb lead and cadmium ions. Using epichlorohydrin (EPI) as a crosslinking agent, β-CD is loaded onto zeolite and vermiculite, as confirmed by a characterization analysis. Isothermal adsorption of Cd2+ and Pb2+ by the loaded minerals is tested at different concentrations, while contact time, pH, and kinetic and thermodynamic characteristics of the adsorption processes are analyzed. The amount of β-CD and crosslinker loaded onto a unit mass of zeolite is higher than that of vermiculite due to the unique porous structure of the zeolite surface. After β-CD loading, the adsorption saturation of zeolite for Cd2+ and Pb2+ are 93.06 and 175.25 mg/g, respectively. The adsorption saturation of Cd2+ and Pd2+ by β-CD-loaded vermiculite is 68.65 and 126.35 mg/g, respectively. The mechanism study revealed that the adsorption process of lead and cadmium ions by β-CD-loaded minerals was combined by diffusional movement with a chemical exchange of ionizable protons or cations, as well as by chemical bonding among heavy metal ions and functional groups (-OH, -COOH and CO).

α-Fe2O3 Nanoparticles/Vermiculite Clay Material: Structural, Optical and Photocatalytic Properties.

Photocatalysis is increasingly becoming a center of interest due to its wide use in environmental remediation. Hematite (α-Fe2O3) is one promising candidate for photocatalytic applications. Clay materials as vermiculite (Ver) can be used as a carrier to accommodate and stabilize photocatalysts. Two different temperatures (500 °C and 700 °C) were used for preparation of α-Fe2O3 nanoparticles/vermiculite clay materials. The experimental methods used for determination of structural, optical and photocatalytic properties were X-ray fluorescence (ED-XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), N2 adsorption method (BET), diffuse reflectance UV-Vis spectroscopy (DRS), photoluminescence spectroscopy (PL) and photocatalytic reduction of CO2, respectively. The data from XRD were confronted with molecular modeling of the material arrangement in the interlayer space of vermiculite structure and the possibility of anchoring the α-Fe2O3 nanoparticles to the surface and edge of vermiculite. Correlations between structural, textural, optical and electrical properties and photocatalytic activity have been studied in detail. The α-Fe2O3 and α-Fe2O3/Ver materials with higher specific surface areas, a smaller crystallite size and structural defects (oxygen vacancies) that a play crucial role in photocatalytic activity, were prepared at a lower calcination temperature of 500 °C.

Polyethylene/Organo-Inorgano Vermiculites and Their Antimicrobial Properties.

Clay mineral vermiculite was treated with silver and copper nitrate solutions and samples were subsequently modified with organic compound (dodecylamine) via solid-solid melt intercalation. Prepared organo-inorgano vermiculites were used as nanofillers to the polyethylene matrix. Mixtures of polyethylene with vermiculite nanofillers, prepared by melt compounding technique, were pressed into thin plates. Structure changes of prepared powder vermiculite nanofillers and polyethylene/vermiculite composites were studied by X-ray diffraction analysis. The X-ray diffraction patterns of vermiculite nanofillers confirm intercalation of dodecylamine into the vermiculite interlayer. Antimicrobial properties of powder vermiculite nanofillers were evaluated by the minimum inhibitory concentration of samples which is needed to completely stop the bacterial growth and polyethylene/vermiculite composites were evaluated by the number of colony forming units survived on surfaces of composite plates. Different bacterial strains were studied: (1) Gram-positive, represented by bacteria Staphylococcus aureus and Enterococcus faecalis, (2) Gram-negative, represented by bacteria Escherichia coli and Pseudomonas aeruginosa, and (3) yeast, Candida albicans. Powder vermiculite nanofillers and surfaces of polyethylene/vermiculite composites showed good antimicrobial effect against tested bacteria and yeast. Powder vermiculite nanofillers show antimicrobial effect already after 30 minutes of tested time. Composite plates exhibited decrease of colony forming units number about 5-7 logarithmic orders depending on bacteria after 24 hours of tested time.

Methylene Blue removal using polyamide-vermiculite nanocomposites: Kinetics, equilibrium and thermodynamic study

A novel low-cost adsorbent was produced from clay mineral of vermiculite using chemical modification. The vermiculite was modified with polyamide through in-situ interfacial polymerization. Adsorption performance of the modified adsorbent was investigated for methylene blue removal from aqueous solution. The influence of various operational parameters of the adsorption process was studied through kinetics, thermodynamics, and equilibrium. Noticeable enhancement in methylene blue removal was achieved for modified vermiculite compared to that of un-modified samples. The obtained equilibrium results were fitted to Langmuir, Freundlich, Temkin, Dubinin – Radushkevich, and Sips, where Langmuir model was best followed. Maximum removal uptake was found to be 76.42 mg/g, whereas maximum removal efficiency of 99% was achieved. Pseudo-second order kinetic model was best followed for the experimental kinetics. The modified vermiculite was characterized by scanning electron microscope coupled with energy dispersive spectrometer (SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauer–Emmett–Teller (BET). The characterization outcome revealed that polymer chain was successfully attached to the vermiculite surface. The thermodynamic investigations showed that negative values of the free energy ΔG were reported, and the negativity was found to increase with increasing the temperature, which implies that the adsorption is spontaneous, energetic and favorable. Moreover, a positive value of enthalpy ΔH (10.98 KJ/mole) was reported, which indicated that the nature of adsorption is endothermic.