Electrospun Nickel Manganite (NiMn2O4) Nanocrystalline Fibers for Humidity and Temperature Sensing.

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 °C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m2/g and (BJH) mesopore volume as 21.5 m2/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20-50 °C temperature range and a temperature sensitivity of -4.95%/K at room temperature (25 °C). The change of impedance with relative humidity was monitored at 25 and 50 °C for a relative humidity (RH) change of 40 to 90% in the 42 Hzπ1 MHz frequency range. At 100 Hz and 25 °C, the sensitivity of 327.36 ± 80.12 kΩ/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing.

Removal of methyl orange using combined ZnO/Fe2O3/ZnO-Zn composite coated to the aluminium foil in the presence of simulated solar radiation.

In this paper, the optimal preparative conditions (current density, deposition temperature, calcination temperature) for the original electrochemical synthesis of ZnO-Zn coating on aluminum foil support (ZnAF) were examined and determined the application for the removal of methyl orange (MO). Optimal application conditions for removing MO (volume and concentration of a treated solution) were also determined. In the following, four immobilized ZnO/Fe2O3 photocatalysts with different molar ratios of Zn to Fe (0.42, 0.84, 1.68, and 3.36) were synthesized via the chemical precipitation method on optimized electrochemically synthesized ZnAF support. Characterization studies of synthesized materials included SEM-EDS and Raman scattering analyses. The efficiency of these catalysts for MO removal in the presence/absence of simulated solar radiation (SSR) was investigated. The adsorption isotherms were investigated, and the results show that the adsorption data were best fitted with the Freundlich adsorption isotherm model. Assessment of the thermodynamic parameters showed that although the adsorption process was weakly endothermic over the range of temperatures studied, the relatively high entropy change gave an overall negative change in Gibbs free energy making the processes spontaneous. In the presence of SSR, the optimal molar ratio of Zn to Fe was determined to be 1.68. The possibility of potential reusing the catalyst was examined six times in a row. The possibility for multiple uses of suspension, which is used for immobilization, was also examined. It was also determined that the application of the 1.68Zn/Fe/ZnAF/H2O2/SSR system after the dye removal generates hydrogen at a rate of 186.5 µmol g-1 after 6 h. Furthermore, in the presence of SSR and using a suspended form of catalyst, the removal efficiency was 1.6 times higher than the efficiency achieved with immobilized ZnO/Fe2O3 catalyst. Using the HPLC method for 1.68Zn/Fe/ZnAF/SSR system, five primary intermediates were found to be formed. The applicability of ZnO/Fe2O3/ZnAF for removal of other dyes was also examined.

Natural Cyanobacteria Removers Obtained from Bio-Waste Date-Palm Leaf Stalks and Black Alder Cone-Like Flowers.

The impact of urbanization and modern agricultural practice has led to accelerated eutrophication of aquatic ecosystems, which has resulted in the massive development of cyanobacteria. Very often, in response to various environmental influences, cyanobacteria produce potentially carcinogenic cyanotoxins. Long-term human exposure to cyanotoxins, through drinking water as well as recreational water (i.e., rivers or lakes), can cause serious health consequences. In order to overcome this problem, this paper presents the synthesis of completely new activated carbons and their potential application in contaminated water treatment. The synthesis and characterization of new active carbon materials obtained from waste biomass, date-palm leaf stalks (P_AC) and black alder cone-like flowers (A_AC) of reliable physical and chemical characteristics were presented in this article. The commercial activated carbon (C_AC) was also examined for the purpose of comparisons with the obtained materials. The detailed characterization of materials was carried out by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), low-temperature N2 physisorption, and Field emission scanning electron microscopy (FESEM). Preliminary analyzes of the adsorption capacities of all activated carbon materials were conducted on water samples from Aleksandrovac Lake (Southern part of Serbia), as a eutrophic lake, in order to remove Cyanobacteria from water. The results after 24 h showed removal efficiencies for P_AC, A_AC, and C_AC of 99.99%, 99.99% and 89.79%, respectively.

Synthesis and antibacterial activity of iron manganite (FeMnO3) particles against the environmental bacterium Bacillus subtilis.

Nanocrystalline iron manganite powder was synthesized using the sol-gel combustion process, with glycine as fuel. It was further calcined at 900 °C for 8 h, resulting in the formation of a loose cubic FeMnO3 powder with a small specific surface area, net-like structure and plate-like particles as confirmed by XRD, N2 physisorption, FESEM and TEM analyses. The metal ion release was studied by ICP-OES and showed that less than 10 ppb of Fe or Mn ions were released by leaching in water, but 0.36 ppm Fe and 3.69 ppm Mn was found in LB (Luria-Bertani) bacterial medium. The generation of reactive oxygen species (ROS) was monitored in distilled water and bacterial medium and showed that FeMnO3 particles do not generate O2˙- ions with or without UV irradiation, but synthesize H2O2 and show an antioxidative effect. Besides the higher stability of FeMnO3 particles in aqueous solution they showed an inhibitory effect on Bacillus subtilis growth in LB medium even at low concentrations (0.01 mg ml-1), but not in BHI medium even at 1 mg ml-1. This study points out that the mechanism of antibacterial action of engineered metal oxides needs continued investigation and specific experimental controls.

Study on fisetin-aluminium(III) interaction in aqueous buffered solutions by spectroscopy and molecular modeling.

Spectroscopic (UV/visible and IR) and theoretical studies were used to assess relevant interaction of fisetin, a tetrahydroxylated flavone molecule, and trivalent aluminium in a wide range of buffered aqueous solutions. The chelation sites, stoichiometry, stability and the dependence of the complexes structures on pH and aluminium/fisetin mole ratios were defined. Obtained results implicated successive formation of two complexes with aluminium(III)-fisetin stoichiometries of 1:1 and 2:1. Considering the fisetin molecular structure, results of vibrational analysis and theoretical calculations, it is possible to implicate 3-hydroxyl-4-carbonyl and 3'4'-dihydroxyl groups as those with the possible chelating power. The equilibrium geometries were optimized in vacuum at the B3LYP/6-31G(d) level of theory, which predict structural modifications between the ligand molecule in free state and in the complex structure. The theoretical model has been validated by both vibrational and electronic spectroscopies.