Search Results (5)

Single-crystalline magnetite (Fe₃O₄) particles having a size beyond the nanometric range (1 µm to 50 µm) and showing high (close to the bulk value) saturation-specific magnetization (σ_s = 92 emu/g), were obtained by the hydrothermal decomposition of the Fe-EDTA complex. The very low values of the magnetic remanence (σ_r = 0.82 emu/g) and coercitivity (μ_oH_c = 1.53 mT) observed at room temperature (RT) suggest a superparamagnetic-like behavior, which is quite remarkable for such micrometric magnetite particles. As confirmed by vibrating sample magnetometer (VSM)-based measurements, minor changes in their magnetic properties occur between RT and 5K. Scanning electron microscopy (SEM) has revealed a morphology consisting of a combination of non-porous octahedral- and dodecahedral-shaped particles, energy dispersive X-ray analysis (EDX) has indicated high elemental (Fe and O) purity, whereas X-ray diffraction (XRD) has confirmed a single crystal structure. The nitrogen adsorbtion–desorption isotherm and pore size distribution are presented for the magnetite sample. Thermomagnetic records under zero field-cooled (ZFC) and field-cooled (FC) conditions have revealed a thermal hysteresis of the Verwey transition.The Verwey point (T_V) at which the major step of the phase transformation takes place is located around 132 K for heating and around 122 K for cooling. These microcrystals do not remain agglomerated when the polarizing field is removed, an essential requirement in biomedical applications is met. Full article

The goal of this study is to assess Ziziphus lotus’s potential for producing carboxymethylcellulose adsorption membranes with the ability to adsorb methyl green from wastewaters by the revalorization of its cellulosic fraction. The cellulose from this feedstock was extracted by an alkaline process and TAPPI standard technique T 203 cm-99 and afterwards they were carboxymethylated. The obtained carboxymethylcelluloses were deeply characterized, being observed that the carboxymethylcellulose produced from the alkaline cellulose presented the higher solubility due to its lower crystallinity degree (53.31 vs. 59.4%) and its higher substitution degree (0.85 vs. 0.74). This carboxymethylcellulose was cross-linked with citric acid in an aqueous treatment in order to form an adsorption membrane. The citric acid provided rigidity to the membrane and although it was hydrophilic it was not soluble in water. By evaluating the potential of the produced membrane for the removal of pollutant dyes from wastewater, it was observed that the adsorption membrane prepared from the carboxymethylcellulose’s produced from the Ziziphus lotus was able to remove 99% of the dye, methyl green, present in the wastewater. Thus, this work demonstrates the potential of the Ziziphus lotus for the production of a novel and cost-effective carboxymethylcellulose adsorption membrane with high capacity to treat wastewaters. Full article

In this work, the possibility of using carbon nanotubes for the treatment of olive vegetation waters (OVWs) was investigated. In general, the disposal of OVWs represents an important environmental problem. The possibility of considering these waters no longer just as a problem but as a source of noble substances, thanks to the recovery of biophenols from them, was tested. In particular, predetermined quantities of olive vegetation waters were treated with carbon nanotubes. The quantities of adsorbed biophenols were studied as a function of the quantities of carbon nanotubes used and the contact time. The experimental conditions for obtaining both the highest possible quantities of biophenol and a purer adsorbate with the highest percentage of biophenols were studied. After the adsorption tests, the vegetation waters were analyzed by UV spectrophotometry to determine, in particular, the variation in the concentration of biophenols. The carbon nanotubes were weighed before and after each adsorption test. In addition, kinetic studies of the adsorption processes were considered. Carbon nanotubes proved their effectiveness in recovering biophenols. Full article

A full scale lab prototype of an adsorptive heat transformer (AHT), consisting of two adsorbers, an evaporator, and a condenser, was designed and tested in subsequent cycles of heat upgrading. The composite LiCl/SiO₂ was used as an adsorbent with methanol as an adsorbtive substance under boundary temperatures of T_L/T_M/T_H = −30/20/30 °C. Preliminary experiments demonstrated the feasibility of the tested AHT in continuous heat generation, with specific power output of 520 W/kg over 1–1.5 h steady-state cycling. The formal and experimental thermal efficiency of the tested rig were found to be 0.5 and 0.44, respectively. Although the low potential heat to be upgraded was available for free from a natural source, the electric efficiency of the prototype was found to be as high as 4.4, which demonstrates the promising potential of the “heat from cold” concept. Recommendations for further improvements are also outlined and discussed in this paper. Full article

The adsorption properties of water molecules on TiO₂ nanotubes (TiO₂NT) and the interaction mechanisms between water molecules are studied by first principles calculations. The adsorption preferences of water molecules in molecular or dissociated states on clean and H-terminated TiO₂NT are evaluated. Adsorption of OH clusters on (0, 6) and (9, 0) TiO₂ nanotubes are first studied. The smallest adsorption energies are −1.163 eV and −1.383 eV, respectively, by examining five different adsorption sites on each type of tube. Eight and six adsorption sites were considered for OH adsorbtion on the H terminated (0, 6) and (9, 0) nanotubes. Water molecules are reformed with the smallest adsorption energy of −4.796 eV on the former and of −5.013 eV on the latter nanotube, respectively. For the adsorption of a single water molecule on TiO₂NT, the molecular state shows the strongest adsorption preference with an adsorption energy of −0.660 eV. The adsorption of multiple (two and three) water molecules on TiO₂NT is also studied. The calculated results show that the interactions between water molecules greatly affect their adsorption properties. Competition occurs between the molecular and dissociated states. The electronic structures are calculated to clarify the interaction mechanisms between water molecules and TiO₂NT. The bonding interactions between H from water and oxygen from TiO₂NT may be the reason for the dissociation of water on TiO₂NT. Full article