Influence of the Structure on Magnetic Properties of Calcium-Phosphate Systems Doped with Iron and Vanadium Ions

The aim of this study was to prepare and characterize the glasses made of x(Fe₂O₃∙V₂O₅)∙(100 - x)[P₂O₅∙CaO] with x ranging of 0-50%. The contribution of Fe₂O₃ and V₂O₅ amount on the structure of P₂O₅·CaO matrix was investigated. The vitreous materials were characterized by XRD (X-ray diffraction analysis), EPR (Electron Paramagnetic Resonance) spectroscopy, and magnetic susceptibility measurements. A hyperfine structure typical for isolated V⁴⁺ ions was noticed to all spectra containing low amount of V₂O_5. The XRD spectra show the amorphous nature of samples, apart x = 50%. An overlap of the EPR spectrum of a broad line without the hyperfine structure characteristic of clustered ions was observed with increasing V₂O₅ content. The results of magnetic susceptibility measurements explain the antiferromagnetic or ferromagnetic interactions expressed between the iron and vanadium ions in the investigated glass.

Ti2C MXene Modified with Ceramic Oxide and Noble Metal Nanoparticles: Synthesis, Morphostructural Properties, and High Photocatalytic Activity

Among two-dimensional (2D) materials, such as graphene, a new family of 2D anisotropic carbides and nitrides of early transition metals (MXenes) is very interesting because of the potential applications in electronics, medicine, and photocatalysis. In this paper, preparation, morphostructural characterization, band gaps determination, and salicylic acid photodegradation ability of Ti₂C MXene and six nanocomposites consisting of the MXene modified by TiO₂, Ag₂O, Ag, PdO, Pd, and Au are reported. It was confirmed using electron diffraction studies, energy dispersive X-ray spectroscopy, and high-resolution transmission microscopy that metals and metal oxides occur on the MXene flakes as nanoparticles in a shape of spots. The band gaps determined experimentally using Tauc's method are placed in the region of 0.90-1.31 eV. In recent years, the method of photocatalytic decomposition of pollutants using semiconductor photocatalysts and UV-vis energy has become increasingly important. The MXene based nanocomposites revealed high activity in the salicylic acid (SA) photodegradation reaction (86.1-97.1% of degraded SA after 3 h, concentration of SA initial solution 100 μM, the circulation rate of the SA solution 0.875 cm³/min). The interfacial charge transfer mechanism and the role of the metallic and metal oxide nanoparticles in the photocatalytic activity of the MXene based nanocomposites are presented and discussed.

Assessment of TiO2 photoactivity on the lead removal: kinetic and mechanistic processing

Removal of lead ions from aqueous solutions, in the presence and in absence of commercial TiO₂, under UV-light was studied. The influence of catalyst mass, concentration of Pb(II) ions and of citric acid in the starting solution as well as the impact of illumination conditions on the removal rate were also investigated. The results were fitted on the pseudo-first order, pseudo-second order and Elovich kinetic models, Weber-Morris intraparticle and liquid film diffusion models, in order to establish the photoreduction mechanism. The Pb removal rate increased in time by a combined linear-exponential mechanism. The catalyst had a positive influence on the removal rate at the start of the photoreduction. At a low concentration of Pb(II) ions (20 mg/L), the amount of photoreduced Pb(II) ions was proportional to the concentration of the citric acid solution, but at high concentrations (240 mg/L), the correlation was inversely proportional. The rate limiting steps in the removal of lead were both the photoreduction on the TiO₂ surface and the diffusion through the film surrounding the catalyst particle. The lead removal was significantly influenced by the mobility and by the concentration of the species in solution.

Morphology, structure, and photoactivity of two types of graphene oxide–TiO2 composites

Two types of graphene oxide-TiO

Adsorption of heavy metal cations by Na-clinoptilolite: equilibrium and selectivity studies

This paper summarizes the conclusions of experiments conducted on the adsorption of Cd(2+), Co(2+), Cu(2+), Mn(2+), Ni(2+), Pb(2+) and Zn(2+) onto zeolite. The focus of the experiments was to establish the influence of the initial pH of the contact solution as well as the selectivity of zeolite on the efficiency of the adsorption process. To this end, experimental adsorption isotherms were established for the pH values ranging from 1 to 4 by using the Na-form of clinoptilolite (particle size range 0.5-1 mm) as an adsorbent. Langmuir, Freundlich and Dubinin-Raduschkevich isotherm models were used to validate the experimental data and the Gibbs free energy was calculated based on the distribution coefficient. From the Langmuir model, correlations between the maximum adsorption capacity and selected physical-chemical parameters of the cations studied were established. The results of the experiments suggest that the selectivity of zeolite is strongly influenced by the pH of the contact solution, dehydration energy of cations, diffusion coefficient and the pH at which the precipitation of hydroxides occurs.

Removal of toxic elements from aqueous solution using bentonite modified with L-histidine

This study proposes the use of bentonite modified with L-histidine for the removal of Cu, Co, Cr, Fe, Hg, Ni, U and Zn from aqueous solutions such as those impacted by acidic drainage. The surface areas of natural bentonite and bentonite-histidine were 73.8 and 61.2 m(2) g(-1), respectively. Elemental analysis showed an increase in the amount of carbon (0.258%) and nitrogen (0.066%) for the bentonite-histidine. At a fixed solid/solution ratio, the operating variables affecting the adsorption of metal ions from aqueous solution such as pH, initial concentration, contact time and temperature were studied in batch mode. The Freundlich isotherm model yielded a better fit than the Langmuir for the adsorption of Cu, Co, Ni and Zn, implying adsorption on a heterogeneous surface. Adsorption kinetics followed a pseudo-second-order model, suggesting chemisorption as the rate-limiting step. The apparent activation energy was greater than 40 kJ mol(-1) for Cu, Zn, Ni, Co and U, which is characteristic of a chemically controlled reaction. Thermodynamic constants ΔG and ΔH showed that the adsorption of metals was endothermic and spontaneous. Adsorption of heavy metals onto bentonite-histidine was efficient at low pH values, meaning that the adsorbent could be useful for remediating acid mine water.