Strategies for liquid-liquid extraction of oxide particles for applications in supercapacitor electrodes and thin films

Fluorescent MnO2@DEHP Nanoprobe for Rapid and Selective Detection of Fe(III) ions

Particle extraction via the liquid-liquid interface (PELLI) method has been utilized to produce Di-(2-ethylhexyl) phosphate (DEHP) coated MnO2 fluorescent nanoprobe denoted as MnO2@DEHP for the selective detection of Fe3+ ions. The synthesized MnO2@DEHP nanoprobe was characterized by various instrumental techniques such as FT-IR, PXRD, TEM, EDAX, HRTEM, DLS, and XPS. Since the high concentration of Fe3+ in waste water leads to water pollution, which in turn affects the ecosystem, and causes severe health hazards. Therefore, accurate detection of Fe3+ ions in the aqueous systems is essential as they are involved in various chemical and biological processes in living things. Here, the synthesized MnO2@DEHP nanoprobe selectively detects Fe3+ ions in the presence of various metal ions in an aqueous media by fluorescence quenching (turn-off) mechanism. The limit of detection (LOD) of MnO2@DEHP nanoprobe for Fe3+ was found to be 0.49 µM. The test-strip method and real water sample analysis were also used to demonstrate the viability of MnO2@DEHP as a fluorescent nanoprobe to detect Fe3+ ions visually and in environment monitoring applications.

Molybdenum-based two-dimensional materials: Synthesis, dispersion, exfoliation and thin film deposition

We report a simple and effective route to synthesize, disperse, exfoliate and process different molybdenum-based 2-dimensional (2D) materials. Starting from a reaction between ammonium molybdate and ammonium sulfide solutions, a powder consisting of a mixture between amorphous molybdenum oxide and sulfide is obtained. By tuning the atmosphere and the temperature, different compositions can be prepared by thermal treatment of this sample: heat treatments in ambient atmosphere produce MoO₃ with different morphologies, controllable according to the chosen temperature. On the other hand, heat treatments in inert atmosphere produce mixtures between crystalline 2D MoS₂ and MoO₃. Further handling of these mixtures with acetonitrile separates the components due to the different solvent/solid affinities, with the layered MoS₂ becoming homogeneously dispersed, and the MoO₃ agglomerating as a solid easily removed by centrifugation. The resulting sulfide dispersions in acetonitrile present high stability, and they are constituted by exfoliated MoS₂, which means that acetonitrile is a tri-functional agent, separating the sulfide/oxide mixture, exfoliating the sulfide and stabilizing the dispersion. The MoS₂ dispersions were used to produce homogeneous, freestanding and transparent thin films through the liquid-liquid interfacial route, which were easily deposited over different substrates and characterized by different techniques.

New developments in liquid-liquid extraction, surface modification and agglomerate-free processing of inorganic particles

This review describes new methods for the particle extraction through liquid-liquid interface (PELLI). The discovery of new surface modification techniques, advanced extractors and new adsorption mechanisms enabled novel applications of PELLI in nanotechnology of metals, quantum dots, oxides and hydroxides. Colloidal and interface chemistry of PELLI is emerging as a new area of technological and scientific interest. The progress achieved in the understanding of particle behavior and interactions at the liquid-liquid interface, phase transfer and interface reactions allowed for the development of new extraction mechanisms. An important breakthrough was the development of surface modification techniques for extraction of functional oxides. Especially important is the possibility of particle transfer from the synthesis medium to the device processing medium, which facilitates agglomerate-free processing of functional nanoparticles. Multifunctional extractor molecules were discovered and used as capping and reducing agents for particle synthesis or dispersing and charging agents for colloidal processing. The progress achieved in the development of extractors and extraction mechanisms has driven the advances in the surface modification and functionalization of materials. New PELLI techniques were used for the development of advanced materials and devices for optical, photovoltaic, energy storage, electronic, biomedical, sensor and other applications.

Adsorption of Maleic Acid Monomer on the Surface of Hydroxyapatite and TiO2: A Pathway toward Biomaterial Composites

Poly(styrene- alt-maleic acid) adsorption on hydroxyapatite and TiO₂ (rutile) was studied using experimental techniques and complemented by ab initio simulations of adsorption of a maleic acid segment as a subunit of the copolymer. Ab initio calculations suggest that the maleic acid segment forms a strong covalent bonding to the TiO₂ and hydroxyapatite surfaces. If compared to vacuum, the presence of a solvent significantly reduces the adsorption strength as the polarity of the solvent increases. The results of first-principles calculations are confirmed by the experimental measurements. We found that the adsorbed poly(styrene- alt-maleic acid) allowed efficient dispersion of rutile and formation of films by the electrophoretic deposition. Moreover, rutile can be codispersed and codeposited with hydroxyapatite to form composite films. The coatings showed an enhanced corrosion protection of metallic implants in simulated body fluid solutions, which opens new avenues for the synthesis, dispersion, and colloidal processing of advanced composite materials for biomedical applications.

Application of octanohydroxamic acid for liquid-liquid extraction of manganese oxides and fabrication of supercapacitor electrodes

MnO₂ and Mn₃O₄ particles were prepared by wet chemical methods and efficiently dispersed and mixed with multiwalled carbon nanotubes (MWCNT) for the fabrication of composite MnO₂-MWCNT and Mn₃O₄-MWCNT electrodes for electrochemical supercapacitors (ES). The problem of particle agglomeration was addressed by particle extraction through a liquid-liquid interface (PELLI) using octanohydroxamic acid (OHA) as a new extractor. OHA exhibited remarkable adsorption on particles due to a bidentate bonding mechanism. The use of OHA broadened the application of PELLI technology, because it allowed good extraction of particles from an aqueous phase at high pH. Moreover, OHA allowed efficient extraction by strong adsorption on particles not only at the liquid-liquid interface, but also in the bulk of an aqueous phase. Building on the advantages offered by the PELLI method and OHA as an extractor we found that Mn₃O₄-MWCNT electrodes exhibited a remarkably high capacitance of 4.2F cm^-2. Another major finding was that capacitance of Mn₃O₄-MWCNT electrodes was higher than that of MnO₂-MWCNT electrodes at active mass of 33 mg cm^-2. This finding showed processing advantages of PELLI and paved the way for applications of novel colloidal and surface modification strategies for the development of advanced ES. A conceptually new approach has been proposed based on the use of hydroxamic acids as capping agents for synthesis and extractor molecules for PELLI.