Synthesis, structural studies, electrical conductivity and optical properties of new Sb₂₋<i>_x</i>Ln<i>_x</i>Te₃ (Ln: Lu³⁺, Er³⁺ and Ho³⁺) nanomaterials

<div><p>Ln-doped Sb₂Te₃ (Ln: Lu³⁺, Er³⁺, Ho³⁺) nanomaterials were synthesised by a co-reduction method in hydrothermal condition. Powder X-ray diffraction (XRD) patterns indicate that the Ln<i>_x</i>Sb₂₋<i>_x</i>Te₃ crystals (Ln = Lu³⁺, <i>x</i> = 0.00–0.06; Er³⁺ and Ho³⁺<i>x</i> = 0.00–0.04) are isostructural with Sb₂Te₃. The cell parameter <i>a</i> decreases for Ln<i>_x</i>Sb₂₋<i>_x</i>Te₃ compounds upon increasing the dopant content (<i>x</i>), while <i>c</i> increases. Scanning electron microscopy and transmission electron microscopy images show that doping of Lu³⁺ and Ho³⁺ ions in the lattice of Sb₂Te₃ results in spherical nanoparticles while that in Er³⁺ leads to hexagonal nanoplates, respectively. The electrical conductivity of Ln-doped Sb₂Te₃ is higher than that of pure Sb₂Te₃ and increases with temperature. By increasing the concentration of Ln³⁺ ions, the absorption spectrum of Sb₂Te₃ shows red shifts and some intensity changes. In addition to the characteristic red emission peaks of Sb₂Te₃, emission spectra of doped materials show other emission bands originating from <i>f</i>–<i>f</i> transitions of the Ho³⁺ ions.</p></div

Performance of chitosan based nanocomposite hollow fibers in the removal of selenium(IV) from water

Fe3O4-chitosan nanocomposite hollow fibers were prepared via impregnation of Fe3O4 nanoparticles on dry-wet spun chitosan hollow fibers (CS-HFs) and its performance in the removal of selenium(IV) from water was investigated. The prepared nanocomposite was characterized using XRD, SEM and TEM analyses confirming the formation of Fe3O4 nanoparticles throughout the heterogeneous surface of CS-HFs. Response surface methodology (RSM) was utilized to optimize Se(IV) adsorption and investigate operational parameters including nanocomposite amount, Se(IV) concentration, pH and contact time. The polynomial second order regression, which is conventionally developed in RSM for describing the process, did not accurately fit the experimental data owing to significant lack of fit. However, in modified polynomial third order regression, all model evaluation criteria had been confirmed the accuracy of the developed model. The adsorption of Se(IV) on prepared Fe3O4-CS HFs followed from pseudo-second-order kinetics with participating both intraparticle and boundary layer diffusion in the rate-controlling step