Development of Composite Nanostructured Electrodes for Water Desalination via Membrane Capacitive Deionization.

Novel two-layer nanostructured electrodes are successfully prepared for their application in membrane capacitive deionization (MCDI) processes. Nanostructured carbonaceous materials such as graphene oxide (GO) and carbon nanotubes (CNTs), as well as activated carbon (AC) are dispersed in a solution of poly(vinyl alcohol) (PVA), mixed with polyacrylic acid (PAA) or polydimethyldiallylammonium chloride (PDMDAAC), and subsequently cast on the top surface of an AC-based modified graphite electrode to form a thin composite layer that is cross-linked with glutaraldehyde (GA). Cyclic voltammetry (CV) is performed to investigate the electrochemical properties of the composite electrodes and desalination experiments are conducted in batch mode using a MCDI unit cell to investigate the effects of i) the nanostructured carbonaceous material, ii) its concentration in the polymer blend, and iii) the molecular weight of the polymers on the desalination efficiency of the system. Comparative studies with commercial membranes are performed proving that the composite nanostructured electrodes are more efficient in salt removal. The improved performance of the composite electrodes is attributed to the ion exchange properties of the selected polymers and the increased specific capacitance of the nanostructured carbonaceous materials. This research paves the way for wider application of MCDI in water desalination.

Dynamics of Electron Transfer in CdS Photocatalysts Decorated with Various Noble Metals.

To address charge recombination in photocatalysis, the prevalent approach involves the use of noble metal cocatalysts. However, the precise factors influencing this performance variability based on cocatalyst selection have remained elusive. In this study, CdS hollow spheres loaded with distinct noble metal nanoparticles (Pt, Au, and Ru) are investigated by femtosecond transient absorption (fs-TA) spectroscopy. A more pronounced internal electric field leads to the creation of a larger Schottky barrier, with the order Pt-CdS > Au-CdS > Ru-CdS. Owing to these varying Schottky barrier heights, the interface electron transfer rate (Ke ) and efficiency (ηe ) of metal-CdS in acetonitrile (ACN) exhibit the following trend: Ru-CdS > Au-CdS > Pt-CdS. However, the trends of Ke and ηe for metal-CdS in water are different (Ru-CdS > Pt-CdS > Au-CdS) due to the influence of water, leading to the consumption of photogenerated electrons and affecting the metal/CdS interface state. Although Ru-CdS displays the highest Ke and ηe , its overall photocatalytic performance, particularly in H2 production, lags behind that of Pt-CdS due to the electron backflow from Ru to CdS. This work offers a fresh perspective on the origin of performance differences and provides valuable insights for cocatalyst design and construction.

Direct versus reverse vertical two-dimensional Mo2C/graphene heterostructures for enhanced hydrogen evolution reaction electrocatalysis.

Mo2C/graphene heterostructures prepared by chemical vapor deposition have demonstrated excellent electrocatalytic activity in a hydrogen evolution reaction (HER). This is attributed to the high catalytic activity of Mo2C while the high electrical conductivity of graphene facilitates charge transfer. In the as-grown direct vertical order, graphene is placed above the Mo2C film. This reduces the catalytic activity of the heterostructure, since graphene in chemically inert. Here, a simple transfer method is proposed that results in the reverse order deposition of the heterostructure on the electrode. This method places graphene at the interface between Mo2C and the electrode, enhancing charge transfer between them, which results in an overpotential of 440 mV at 10 mA cm-2 and corresponds to ∼65 mV overpotential reduction as compared to the direct heterostructure. At the same time, when a direct Cu/Mo2C/graphene junction with a Cu catalyst substrate is used as a working electrode, the improvement of the heterostructure HER activity is observed which is manifested in an overpotential of 275 mV at 10 mA cm-2 with a correspondent ∼230 mV reduction. All above performances are accompanied with excellent endurance.

Mo2C/graphene heterostructures: low temperature chemical vapor deposition on liquid bimetallic Sn-Cu and hydrogen evolution reaction electrocatalytic properties.

Thin 2D Mo2C/graphene vertical heterostructures have attracted significant attention due to their potential application as electrodes in the hydrogen evolution reaction (HER) and energy storage. A common drawback in the chemical vapor deposition synthesis of these structures is the demand for high temperature growth, which should be higher than the melting temperature of the metal catalyst. The most common metallic catalyst is Cu, which has a melting temperature of 1084 °C. Here, we report the growth of thin, ∼200 nm in thickness, semitransparent micrometer-sized Mo2C domains and Mo2C/graphene heterostructures at lower temperatures using liquid Sn-Cu alloys. No Sn-associated defects are observed, making the alloy an appealing growth substrate. Raman spectroscopy reveals the vertical interaction between graphene and Mo2C, as shown by the variation in the strain of the graphene film. The results demonstrate the capability to grow continuous nanometer-thin Mo2C films at temperatures as low as 880 °C, without sacrificing the growth rate. Mo2C films are proven to be efficient electrocatalysts for the HER. Moreover, we demonstrate the beneficial role of graphene overgrown on Mo2C in reducing the HER overpotential values, which is attributed to more efficient charge transfer kinetics, compared to pure Mo2C films.

Physical Properties of Photo-Aged Graphene/Polypropylene Nanocomposites.

In the present research, graphene nanoplatelets/polypropylene (GNP/PP) nanocomposites were prepared by melt mixing and were subjected to accelerated ageing. The effect of graphene on the morphology and physical properties of aged GNP/PP nanocomposites was investigated. The incorporation of graphene to non-aged PP matrix led to changes in its crystal conformation, decreased the ultraviolet-visible (UV-Vis) transmittance and tensile strain and increased the elastic modulus. The ageing of non-reinforced PP increased the ß-phase of PP and caused the formation of cracks on its surface, while voids were observed in its cross-section. The aged PP was also characterized by significantly lower UV-Vis transmittance, thermal stability and tensile strain, but increased elastic modulus compared to non-aged PP. Graphene retarded the ageing of PP matrix, according to Fourier Transform Infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) results. In the aged GNP/PP nanocomposite, the morphology did not present any changes and the examined properties were maintained to similar values with that of non-aged GNP/PP nanocomposite.

Recycling of typical supercapacitor materials.

A simple, facile and low-cost method for recycling of supercapacitor materials is proposed. This process aims to recover some fundamental components of a used supercapacitor, namely the electrolyte salt tetraethyl ammonium tetrafluoroborate (TEABF4) dissolved in an aprotic organic solvent such as acetonitrile (ACN), the carbonaceous material (activated charcoal, carbon nanotubes) purified, the current collector (aluminium foil) and the separator (paper) for further utilization. The method includes mechanical shredding of the supercapacitor in order to reduce its size, and separation of aluminium foil and paper from the carbonaceous resources containing TEABF4 by sieving. The extraction of TEABF4 from the carbonaceous material was based on its solubility in water and subsequent separation through filtering and distillation. A cyclic voltammetry curve of the recycled carbonaceous material revealed supercapacitor behaviour allowing a potential reutilization. Furthermore, as BF4(-) stemming from TEABF4 can be slowly hydrolysed in an aqueous environment, thus releasing F(-) anions, which are hazardous, we went on to their gradual trapping with calcium acetate and conversion to non-hazardous CaF2.

Synthesis of 2D PtSe2 Nanolayers on Glass Substrates and Their Integration in Near-Infrared Light Shutters.

PtSe2 has asserted its key role among the emerging 2D transition metal dichalcogenides, however, its simplified growth process with controlled number of layers, high crystalline quality, and on inexpensive substrates is still challenging. Here, we report the synthesis details of PtSe2 layers on soda lime glass substrates by selenization of predeposited Pt layers using the thermally assisted conversion method at atmospheric pressure. PtSe2 syntheses are confirmed by X-ray photoelectron spectroscopy and Raman analysis. The layers were further investigated with transmission electron microscopy and optical ellipsometry, revealing the thickness and its dependence on the metal precursor sputtering time. Finally, the integration of PtSe2 as transparent conductive layers in polymer-dispersed liquid crystal structures operating as near-infrared light shutters is demonstrated and device performance is discussed. The proposed simple and inexpensive synthesis approach opens up new directions toward PtSe2 potential technological applications, including ITO-free optoelectronics.

Tuning the dispersibility of carbon nanostructures from organophilic to hydrophilic: towards the preparation of new multipurpose carbon-based hybrids.

The hydroxyphenyl derivatives of carbon nanostructures (graphene and carbon nanotubes) can be easily transformed into highly organophilic or hydrophilic derivatives by using the ionic interactions between the phenolic groups and oleylamine or tetramethylammonium hydroxide, respectively. The products were finely dispersed in homo-polymers or block co-polymers to create homogeneous carbon-based nanocomposites and were used as nanocarriers for the dispersion and protection of strongly hydrophobic compounds, such as large aromatic chromophores or anticancer drugs in aqueous solutions.

CO2-Derived Nanocarbons with Controlled Morphology and High Specific Capacitance.

The conversion of CO2 to nanocarbons addresses a dual goal of harmful CO2 elimination from the atmosphere along with the production of valuable nanocarbon materials. In the present study, a simple one-step metallothermic CO2 reduction to nanocarbons was performed at 675 °C with the usage of a Mg reductant. The latter was employed alone and in its mixture with ferrocene, which was found to control the morphology of the produced nanocarbons. Scanning electron microscopy (SEM) analysis reveals a gradual increase in the amount of nanoparticles with different shapes and a decrease in tubular nanostructures with the increase of ferrocene content in the mixture. A possible mechanism for such morphological alterations is discussed. Transmission electron microscopy (TEM) analysis elucidates that the nanotubes and nanoparticles gain mainly amorphous structures, while sheet- and cloud-like morphologies also present in the materials possess significantly improved crystallinity. As a result, the overall crystallinity was preserved constant for all of the samples, which was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Finally, electrochemical tests demonstrated that the prepared nanocarbons retained high specific capacitance values in the range of 200-310 F/g (at 0.1 V/s), which can be explained by the measured high specific surface area (650-810 m2/g), total pore volume (1.20-1.55 cm3/g), and the degree of crystallinity. The obtained results demonstrate the suitability of ferrocene for managing the nanocarbons' morphology and open perspectives for the preparation of efficient "green" nanocarbon materials for energy storage applications and beyond.

Photocatalytic degradation of organic micropollutants under UV-A and visible light irradiation by exfoliated g-C3N4 catalysts.

In the present study, the photocatalytic performance of exfoliated graphitic carbon nitride (g-C3N4) catalysts, with enhanced properties and response in UV and visible light irradiation, was evaluated for the removal of selected contaminants i.e., diuron, bisphenol A and ethyl paraben. Commercial TiO2 Degussa P25 was also used as a reference photocatalyst. The g-C3N4 catalysts demonstrated good photocatalytic activity which in some cases is comparable to TiO2 Degussa P25 leading to high removal percentages of the studied micropollutants under UV-A light irradiation. In contrast to TiO2 Degussa P25, g-C3N4 catalysts were also able to degrade the studied micropollutants under visible light irradiation. For all the studied g-C3N4 catalysts under both UV-A and visible light irradiation, the overall degradation rate decreases in the order of bisphenol A > diuron > ethyl paraben. Among the studied g-C3N4, the chemically exfoliated catalyst (g-C3N4-CHEM) showed superior photocatalytic activity under UV-A light irradiation due to its enhanced characteristics, such as pore volume and specific surface area and ~ 82.0 % in 6 min, ~75.7 % in 15 min and ~ 96.3 % in 40 min removals were achieved for BPA, DIU and EP, respectively. Under visible light irradiation, the thermally exfoliated catalyst (g-C3N4-THERM) demonstrated the best photocatalytic performance and the degradation ranged from ~29.5 to 59.4 % after 120 min. EPR data revealed that the three g-C3N4 semiconductors generate mainly O2•-, whereas TiO2 Degussa P25 generates both HO• and O2•-, the latter only under UV-A light irradiation. Nevertheless, the indirect formation of HO• in the case of g-C3N4 should also be considered. Hydroxylation, oxidation, dealkylation, dechlorination and ring opening were the main degradation pathways. The process proceeded without significant alterations in toxicity levels. Based on the results, heterogeneous photocatalysis using g-C3N4 catalysts is a promising method for the removal of organic micropollutants without the formation of harmful transformation products.

Graphene fluoride: a stable stoichiometric graphene derivative and its chemical conversion to graphene.

Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.

Photocatalytic degradation of mecoprop and clopyralid in aqueous suspensions of nanostructured N-doped TiO2.

The work describes a study of the oxidation power of N-doped and undoped anatase TiO(2), as well as TiO(2) Degussa P25 suspensions for photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop) and 3,6-dichloro-pyridine-2-carboxylic acid (clopyralid) using visible and UV light. Undoped nanostructured TiO(2) powder in the form of anatase was prepared by a sol-gel route. The synthesized TiO(2), as well as TiO(2) Degussa P25 powder, were modified with urea to introduce nitrogen into the structure. N-doped TiO(2) appeared to be somewhat more efficient than the starting TiO(2) (anatase) powder when visible light was used for mecoprop degradation. N-doped TiO(2) Degussa P25 was also slightly more efficient than TiO(2) Degussa P25. However, under the same experimental conditions, no degradation of clopyralid was observed in the presence of any of the mentioned catalysts. When the kinetics of mecoprop degradation was studied using UV light, more efficient were the undoped powders, while in the case of clopyralid, N-doped TiO(2) Degussa P25 powder was most efficient, which is probably a consequence of the difference in the molecular structure of the two herbicides.

Multipurpose organically modified carbon nanotubes: from functionalization to nanotube composites.

We show that covalent functionalization of carbon nanotubes (CNTs) via 1,3-dipolar cycloaddition is a powerful method for enhancing the ability to process CNTs and facilitating the preparation of hybrid composites, which is achieved solely by mixing. CNTs were functionalized with phenol groups, providing stable dispersions in a range of polar solvents, including water. Additionally, the functionalized CNTs could easily be combined with polymers and layered aluminosilicate clay minerals to give homogeneous, coherent, transparent CNT thin films and gels.

Preparation of hydroxyapatite via microemulsion route.

Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1).

Study of TiO2 anatase nano and microstructures with dominant {001} facets for NO oxidation.

INTRODUCTION: TiO(2) anatase nanoplates and hollow microspheres were fabricated by a solvothermal-hydrothermal method using titanium isopropoxide as a titanium precursor and hydrofluoric acid as a capping agent in order to enhance the formation of the {001} crystal facets of the anatase nanocrystals. METHODS: These different morphological structures of TiO(2) anatase can be achieved by only changing the solvent, keeping the amount of the precursor and of the capping agent identical during the solvothermal-hydrothermal process. RESULTS AND DISCUSSION: After calcination of the samples, the adsorbed fluoride atoms on the {001} crystal facets of the TiO(2) anatase nanocrystals were completely removed from their surface according to XPS analysis. The calcined TiO(2) anatase structures were higher crystallized and the specific surface area of the catalysts increased, enhancing their photocatalytic activity in comparison to the non-calcined TiO(2) anatase structures. All TiO(2) anatase samples with adsorbed as well as non-adsorbed fluoride atoms on their {001} crystal facets, exhibited a higher photonic efficiency than Degussa P25, which was used as a reference. CONCLUSION: The fluoride free TiO(2) anatase nanoplates exhibited the best photocatalytic activity in oxidizing the NO gas to NO(2) and NO(3) (-).

Organic functionalisation of graphenes.

Graphene sheets derived from dispersion of graphite in pyridine were functionalised by the 1,3 dipolar cycloaddition of azomethine ylide. The organically modified graphene sheets are easily dispersible in polar organic solvents and water, and they are extensively characterised using several spectroscopic and microscopy techniques.

Salivary metal levels of orthodontic patients: a novel methodological and analytical approach.

The purpose of this study was to qualitatively and quantitatively assess the nickel, chromium, and ferrous levels in a population of 17 orthodontic patients undergoing treatment, compared with seven untreated individuals, employing a novel methodological approach and a new analytical technique. Salivary samples obtained from patients before and after rinsing with double distilled water were processed for Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) for simultaneous estimation of the concentration of the metallic elements. No statistically significant difference was detected between control and patient groups with respect to salivary metal content, regardless of element. The range of salivary metal levels found did not exceed those of daily intake through food and air. The lack of a continuous monitoring scheme for salivary metal concentrations in real time may impose substantial obstacles to defining the release rate of metals in vivo. The results of this study emphasize the necessity of incorporating the dimension of time in assessing the release potential of orthodontic alloys.