RESUMO
In this study, we synthesized Fe3O4 using the co-precipitation method and then prepared magnetic carrier LDHs@Fe3O4 by immobilizing layered double hydroxide on Fe3O4 by in situ growth method. Cellulase was immobilized on this magnetic carrier by using glutaraldehyde as a coupling agent, which can be used for degrading Methoxychlor (MXC). The results demonstrated the maximum MXC removal efficiency of 73.4% at 45 °C and pH = 6.0 with excellent reusability. Through kinetic analysis, it was found that the degradation reaction conforms to the Langmuir-Hinshelwood model and is a first-order reaction. Finally, according to the EPR analysis, the active radicals in the system were found to be OH· and the degradation mechanism was proposed in combination with LC-MS. This study provides a feasible method for degrading organochlorine pesticides, which can be used for groundwater purification.
Assuntos
Celulase , Hidróxidos , Nanocompostos , Metoxicloro , CinéticaRESUMO
The structural and thermoelectric properties of the filled skutterudite (Sm,Gd)y(FexNi1-x)4Sb12 were investigated and critically compared to the ones in the Sm-containing system with the aim of unravelling the effect of double filling on filling fraction and thermal conductivity. Several samples (x = 0.50-0.90 and y = 0.15-0.48) were prepared by melting-sintering, and two of them were densified by spark plasma sintering in order to study their thermoelectric features. The crystallographic study enables the recognition of the role of the filler size in ruling the filling fraction and the compositional location of the p/n crossover: It has been found that the former lowers and the latter moves toward lower x values with the reduction of the filler ionic size, as a consequence of the progressively weaker interaction of the filler with the Sb12 cavity. The analysis of thermoelectric properties indicates that, despite the Sm3+/Gd3+ small mass difference, the contemporary presence of these ions in the 2a site significantly affects the thermal conductivity of both p- and n-compositions. This occurs by reducing its value with respect to the Sm-filled compound at each temperature considered, and making the overall thermoelectric performance of the system comparable to several multi-filled (Fe, Ni)-based skutterudites described in the literature.
RESUMO
Samples belonging to the series Sm(y)(Fe(x)Ni(1−x)4Sb12 were heated in Ar atmosphere up to 400 °C and cooled down to room temperature several times, with the aim to evaluate the effect of thermal cycles on microhardness. The treatment temperature was chosen in correspondence of the maximum ZT value, in order to simulate the operating conditions of the material in a thermoelectric device. Vickers measurements allowed to detect the effect of both composition and thermal treatments on the microhardness properties of the material. A decrease in the microhardness value was observed prior to thermal treatments with increasing Fe amount, due to the substitution of Ni by the larger Fe atom. Moreover, almost all compositions show an increase in the hardness of the skutterudite phase as a consequence of thermal cycles, accounting for the Sb enrichment of skutterudite. This evidence suggests also a possible improvement of the preparation procedure in order to obtain a stoichiometric Sb amount within the skutterudite. Samples were prepared by direct reaction of pure elements at 950 °C followed by thermal treatment at 620 °C. The composition and microstructure of the obtained samples were investigated by X-ray powder diffraction, and by optical and electronic microscopy.
RESUMO
A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and µ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and µ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.
