Assessment of Unfrozen Water Content in Copper Bentonites Using the 1H NMR Technique: Optimization, the Method's Limitation, and Comparative Analysis with DSC.

Studies on changes in unfrozen water content in copper bentonite from Slovakia were conducted using both differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) methods. The aims of this study were to 1. optimize the method for determining changes in unfrozen water content using the 1H NMR technique in model bentonites based on the DSC results; 2. analyze the relationship between unfrozen water content, as determined via DSC and the optimized NMR technique, and the physicochemical parameters of bentonites; and 3. identify the limitations in determining changes in unfrozen water content using the 1H NMR technique in relation to copper-contaminated bentonites. The results obtained using the optimized NMR method applied to the model bentonites correlated well with the DSC results. The unfrozen water content in the Cu-contaminated bentonites was 2-18% lower after NMR compared to the DSC results, likely due to the mobility of copper ions and their paramagnetic properties. Statistically significant differences in unfrozen water content between the DSC and NMR methods were observed, depending on molar concentration, copper ion concentration, and temperature, confirmed via Analysis of Variance (ANOVA). Calorimetric studies are recommended for investigating unfrozen water content changes in contaminated clays. Further NMR research could identify metals influencing free induction decay signals under varying physicochemical conditions.

The WC and CrC Coatings Deposited from Carbonyls Using PE CVD Method-Structure and Properties.

This article presents a comparative study of WC and CrC coatings deposited by the plasma-enhanced chemical vapor method using the hexacarbonyls of W and Cr as precursors. The measured thicknesses of the WC and CrC coatings are equal to ca. 1.5 µm. The WC coating consists of microcolumns with a conical end, with gaps between the microcolumns up to approximately 100 nm, and their structure is formed by nanoparticles in the shape of globules with a diameter of up to 10 nm. In the case of the CrC coating, a cauliflower structure with gaps ranging from 20 to 100 nm was achieved. The diameter of cauliflower grains is from 50 nm to 300 nm. The C content in the WC and CrC coating is 66.5 at.% and 75.5 at.%. The W content is 1.4 at.% and the Cr content in the CrC coating is 1.2 at.%. The hardness and Young's modulus of the WC coating are equal to 9.2 ± 1.2 GPa 440.2 ± 14.2 GPa, respectively. The coefficients of friction and wear volume of the WC coating are equal to 0.7 and -1.6 × 106/+3.3 × 106 µm3, respectively. The hardness and Young's modulus of the CrC coating are 7.5 ± 1.2 GPa and 280 ± 18.5 GPa, respectively. The coefficients of friction and wear volume of the CrC coating are 0.72 and -18.84 × 106/+0.35 × 106 µm3, respectively.

A Unique Mechanochemical Redox Reaction Yielding Nanostructured Double Perovskite Sr2FeMoO6 With an Extraordinarily High Degree of Anti-Site Disorder.

Strontium ferromolybdate, Sr2FeMoO6, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation via a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that Sr2FeMoO6 can be mechanosynthesized at ambient temperature in air directly from its precursors (SrO, α-Fe, MoO3) in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity. The mechanically induced evolution of the Sr2FeMoO6 phase and the far-from-equilibrium structural state of the reaction product are systematically monitored with XRD and a variety of spectroscopic techniques including Raman spectroscopy, 57Fe Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. The unique extensive oxidation of iron species (Fe0 → Fe3+) with simultaneous reduction of Mo cations (Mo6+ → Mo5+), occuring during the mechanosynthesis of Sr2FeMoO6, is attributed to the mechanically triggered formation of tiny metallic iron nanoparticles in superparamagnetic state with a large reaction surface and a high oxidation affinity, whose steady presence in the reaction mixture of the milled educts initiates/promotes the swift redox reaction. High-resolution transmission electron microscopy observations reveal that the mechanosynthesized Sr2FeMoO6, even after its moderate thermal treatment at 923 K for 30 min in air, exhibits the nanostructured nature with the average particle size of 21(4) nm. At the short-range scale, the nanostructure of the as-prepared Sr2FeMoO6 is characterized by both, the strongly distorted geometry of the constituent FeO6 octahedra and the extraordinarily high degree of anti-site disorder. The degree of anti-site disorder ASD = 0.5, derived independently from the present experimental XRD, Mössbauer, and SQUID magnetization data, corresponds to the completely random distribution of Fe3+ and Mo5+ cations over the sites of octahedral coordination provided by the double perovskite structure. Moreover, the fully anti-site disordered Sr2FeMoO6 nanoparticles exhibit superparamagnetism with the blocking temperature T B = 240 K and the deteriorated effective magnetic moment µ = 0.055 µ B per formula unit.

Biochar from Wood Chips and Corn Cobs for Adsorption of Thioflavin T and Erythrosine B.

Biochars from wood chips (WC) and corn cobs (CC) were prepared by slow pyrolysis and used for sorption separation of erythrosine B (EB) and thioflavin T (TT) in batch experiments. Biochar-based adsorbents were extensively characterized using FTIR, XRD, SEM-EDX, and XPS techniques. The kinetics studies revealed that adsorption on external surfaces was the rate-limiting step for the removal of TT on both WC and CC biochar, while intraparticle diffusion was the rate-limiting step for the adsorption of EB. Maximal experimental adsorption capacities Qmaxexp of TT reached 182 ± 5 (WC) and 45 ± 2 mg g-1 (CC), and EB 12.7 ± 0.9 (WC) and 1.5 ± 0.4 mg g-1 (CC), respectively, thereby indicating a higher affinity of biochars for TT. The adsorption mechanism was found to be associated with π-π interaction, hydrogen bonding, and pore filling. Application of the innovative dynamic approach based on fast-field-cycling NMR relaxometry indicates that variations in the retention of water-soluble dyes could be explained by distinct water dynamics in the porous structures of WC and CC. The obtained results suggest that studied biochars will be more effective in adsorbing of cationic than anionic dyes from contaminated effluents.

Electrophoretic Deposition of Graphene Oxide on Stainless Steel Substrate.

We demonstrated the deposition of the architecture of graphene oxide on stainless steel substrate and its potential environmental application. The synthesis and characterization of graphene oxide were described. The controlled formation of graphene oxide coatings in the form of the homogenous structure on stainless steel is demonstrated by scanning electron microscopy (SEM). The structure, morphology and properties of the material were assessed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The morphology and stability of these structures are shown to be particularly related to the pre-treatment of stainless steel substrate before the electrophoretic deposition. This approach opens up a new route to the facile fabrication of advanced electrode coatings with potential use in environmental applications.

The Effect of Annealing Temperatures on Selected Properties of WC/C Coatings, Deposited Using Hexacarbonyl Wolfram in an N2-SiH4 Atmosphere.

In this paper, we present the results of an experimental study on WC/C coatings, deposited by using plasma-enhanced chemical vapor deposition in an N2-SiH4 atmosphere, annealed at temperatures of 200, 500 and 800 °C, in which the hexacarbonyl of W was used as a precursor. During the experiments, the topography, chemical composition, morphology, as well as selected mechanical properties, such as hardness, Young's modulus, and coefficient of friction of the WC/C coatings were analyzed. Annealing without the protective atmosphere in the mentioned temperatures caused a decrease in hardness (up to 15 ± 2.7 GPa). In addition, the coefficient of friction value increased only to 0.37 ± 0.03.

Bismuth Doping in Nanostructured Tetrahedrite: Scalable Synthesis and Thermoelectric Performance.

In this study, we demonstrate the feasibility of Bi-doped tetrahedrite Cu12Sb4-xBixS13 (x = 0.02-0.20) synthesis in an industrial eccentric vibratory mill using Cu, Sb, Bi and S elemental precursors. High-energy milling was followed by spark plasma sintering. In all the samples, the prevailing content of tetrahedrite Cu12Sb4S13 (71-87%) and famatinite Cu3SbS4 (13-21%), together with small amounts of skinnerite Cu3SbS3, have been detected. The occurrence of the individual Cu-Sb-S phases and oxidation states of bismuth identified as Bi0 and Bi3+ are correlated. The most prominent effect of the simultaneous milling and doping on the thermoelectric properties is a decrease in the total thermal conductivity (κ) with increasing Bi content, in relation with the increasing amount of famatinite and skinnerite contents. The lowest value of κ was achieved for x = 0.2 (1.1 W m-1 K-1 at 675 K). However, this sample also manifests the lowest electrical conductivity σ, combined with relatively unchanged values for the Seebeck coefficient (S) compared with the un-doped sample. Overall, the lowered electrical performances outweigh the benefits from the decrease in thermal conductivity and the resulting figure-of-merit values illustrate a degradation effect of Bi doping on the thermoelectric properties of tetrahedrite in these synthesis conditions.

New perception of Zn(II) and Mn(II) removal mechanism on sustainable sunflower biochar from alkaline batteries contaminated water.

The combination of several methods (X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy) was applied to study the changes that have occurred during the adsorption of Zn(II) and Mn(II) ions on a carbonized sunflower sample for understanding a mechanism of heavy metals adsorption. Sunflower biochar was obtained from the stem and inflorescences sunflower wastes through pyrolysis at 600 °C for 30 min. According to the infrared spectroscopy and Boehm titration data, this carbonized material has acidic and basic functional groups on its surface, but they do not participate in the metal ions adsorption. However, the synthesized carbon proved to be a sustainable high-effective adsorbent for zinc(II) and manganese(II) ions removal with adsorption capacity 138.3 mg g-1 of Zn2+ and 45.4 mg g-1 for Mn2+. Surface analysis of the carbonized material by energy dispersive X-ray analysis, X-ray diffraction, and X-ray photoelectron spectroscopy indicated the presence of soluble and insoluble inorganic salts, such as KCl, NaCl, NaHCO3, KHCO3, CaCO3, MgCO3. It was established, that during the adsorption process, soluble salts are washed away, and new insoluble ones are formed assisting by Zn(II) and Mn(II) ions. It has been revealed that the adsorptive removal of Zn2+ and Mn2+ is caused by the precipitation mechanism. The efficiency of removing Zn(II) and Mn(II) ions from water contaminated with battery waste by the same mechanism is shown.

Characterization of Fe(III) Adsorption onto Zeolite and Bentonite.

In this study, the adsorption of Fe(III) from aqueous solution on zeolite and bentonite was investigated by combining batch adsorption technique, Atomic adsorption spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. Although iron is commonly found in water and is an essential bioelement, many industrial processes require efficient removal of iron from water. Two types of zeolite and two types of bentonite were used. The results showed that the maximum adsorption capacities for removal of Fe (III) by Zeolite Micro 20, Zeolite Micro 50, blue bentonite, and brown bentonite were 10.19, 9.73, 11.64, and 16.65 mg.g-1, respectively. Based on the X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) analyses of the raw samples and the solid residues after sorption at low and high initial Fe concentrations, the Fe content is different in the surface layer and in the bulk of the material. In the case of lower initial Fe concentration (200 mg.dm-3), more than 95% of Fe is adsorbed in the surface layer. In the case of higher initial Fe concentration (4000 mg.dm-3), only about 45% and 61% of Fe is adsorbent in the surface layer of zeolite and bentonite, respectively; the rest is adsorbed in deeper layers.

Diverse Pathway to Obtain Antibacterial and Antifungal Agents Based on Silica Particles Functionalized by Amino and Phenyl Groups with Cu(II) Ion Complexes.

Production of environmentally friendly multitasking materials is among the urgent challenges of chemistry and ecotechnology. The current research paper describes the synthesis of amino-/silica and amino-/phenyl-/silica particles using a one-pot sol-gel technique. CHNS analysis and titration demonstrated a high content of functional groups, while scanning electron microscopy revealed their spherical form and ∼200 nm in size. X-ray photoelectron spectroscopy data testified that hydrophobic groups reduced the number of water molecules and protonated amino groups on the surface, increasing the portion of free amino groups. The complexation with Cu(II) cations was used to analyze the sorption capacity and reactivity of the aminopropyl groups and to enhance the antimicrobial action of the samples. Antibacterial activities of suspensions of aminosilica particles and their derivative forms containing adsorbed copper(II) ions were assayed against Gram-positive (Staphylococcus aureus ATCC 25923) and Gram-negative bacteria (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853). Meanwhile, antifungal activity was tested against fungi (Candida albicans UCM Y-690). According to zeta potential measurements, its value could be depended on the suspension concentration, and it was demonstrated that the positively charged suspension had higher antibacterial efficiency. SiO2/-C6H5/-NH2 + Cu(II) sample's water suspension (1%) showed complete growth inhibition of the bacterial culture on the solid medium. The antimicrobial activity could be due to occurrence of multiple and nonspecific interactions between the particle surfaces and the surface layers of bacteria or fungi.

Mechanochemically Synthesised Coal-Based Magnetic Carbon Composites for Removing As(V) and Cd(II) from Aqueous Solutions.

The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char were prepared by high-energy ball co-milling from either raw Slovak lignite or coal-based char together with a ferrofluid. The products were characterised by X-ray diffraction, electron microscopy, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), volumetric magnetic susceptibility, and low-temperature nitrogen adsorption, and both magnetic carbons were comparatively tested as potential sorbents of As(V) oxyanions and Cd(II) cations in aqueous solutions. The magnetic char was an excellent sorbent of As(V) oxyanions (Qm = 19.9 mg/g at pH 3.9), whereas the magnetic lignite was less effective. The different sorption properties towards arsenic anions may have been due to different oxidation states of iron on the surfaces of the two magnetic composites (determined by XPS), although the overall state of iron monitored by Mössbauer spectroscopy was similar for both samples. Both magnetic composites were effective sorbents for removing Cd(II) cations (Qm (magnetic lignite) = 70.4 mg/g at pH 6.5; Qm (magnetic char) = 58.8 mg/g at pH 6.8).

Study on Cr(VI) Leaching from Cement and Cement Composites.

This paper reports an experimental study on hexavalent chromium leaching from cement samples and cement composites containing silica fume and zeolite additions that were subjected to various leaching agents. The water-soluble Cr(VI) concentrations in cements ranged from 0.2 to 3.2 mg/kg and represented only 1.8% of the total chromium content. The presence of chromium compounds with both chromium oxidation states of III and VI was detected in the cement samples by X-ray photoelectron spectroscopy (XPS). Leaching tests were performed in a Britton-Robinson buffer to simulate natural conditions and showed increased dissolution of Cr(VI) up to 6 mg/kg. The highest amount of leached hexavalent chromium was detected after leaching in HCl. The findings revealed that the leaching of chromium from cements was higher by 55⁻80% than that from the cement composites. A minimum concentration was observed for all cement samples when studying the relationship between the soluble Cr(VI) and the cement storage time.

Accumulation of counterions and coions evaluated by cryogenic XPS as a new tool for describing the structure of electric double layer at the silica/water interface.

We introduce a new method of evaluating the structure of electric double layer (EDL) at the native solid/liquid interface using cryogenic X-ray photoelectron spectroscopy technique. This method is based on evaluating the atomic concentration ratio of counterions and co-ions of supporting electrolyte at the close-to-in situ state surface of colloid particles by the cryo-XPS and comparing it with analogous ratio predicted by EDL models. For silica colloids in aqueous KCl solutions at pH 6 to 8 it has been found that the latter ratio is higher than unity, as expected for the negatively charged surface of silica, but does not correspond with the prediction of the basic Gouy-Chapman EDL model for the ideal interface. However, it agrees with that deduced from experiments on electrolytic coagulation kinetics of analogous silica colloids by applying a simple EDL model of swellable ion-permeable (Donnanian) polyelectrolyte gel layer. It turns out that the traditional Stern layer-based concept of EDL at solid/liquid interfaces is not justified for metal oxides at least in KCl solutions.

Cytochrome c conjugated to ZnO-MAA nanoparticles: the study of interaction and influence on protein structure.

Nanoparticle-protein conjugates have potential for numerous applications due to the combination of the properties of both components. In this paper we studied the conjugation of horse heart cytochrome c with ZnO nanoparticles modified by mercaptoacetic acid (MAA) which may be a material with great potential in anticancer therapy as a consequence of synergic effect of both components. Cyt c adsorption to the ZnO-MAA NPs surface was studied by UV-vis spectroscopy and by a dynamic light scattering in various pH. The results indicate that the optimal pH for the association of protein with modified nanoparticles is in range 5.8-8.5 where 90-96% of cytochrome c was assembled on ZnO-MAA nanoparticles. The interaction of proteins with nanoparticles often results in denaturation or loss of protein function. Our observations from UV-vis spectroscopy and circular dichroism performed preserved protein structure after the interaction with modified nanoparticles.