RESUMO
In this study, we utilized a simple calcination method to prepare a Ni/TiO2/C composite, which was synchronously grown from magnetic, semiconductor, and conductive materials. XRD, SEM, Raman, and XPS characterization methods were used to analyze the crystal structure, graphitization degree, morphology size, and valence state of Ni/TiO2/C, and its electromagnetic wave absorption performance was tested. It was revealed that rod-like Ni/TiO2/C had good electromagnetic wave absorption performance at a thickness of 1-5.5 mm; in particular, its reflectance reached -40 dB at 3.5 mm and its absorption bandwidth (reflectivity < -10 dB) reached 4.4 GHz (6.0-10.4 GHz) at a thickness of 4.0 mm. It was thus revealed that its electromagnetic wave absorption rate and absorption bandwidth can be regulated by its thickness. Compared with Ni/TiO2, it was proven that the conductive materials (carbon), magnetic materials (Ni), and semiconductor materials (TiO2) in the rod-like Ni/TiO2/C composite can synergistically absorb electromagnetic wave energy through dielectric and magnetic losses.
RESUMO
Cu2ZnSnS4 (CZTS) and Cu2ZnSn(S,Se)4 (CZTSSe) as promising photovoltaic materials have drawn much attention because they are environmentally benign and earth-abundant elements. In this work, the monodispersed, low-cost Cu2ZnSnS4 nanocrystals with small size have been controllably synthesized via a wet chemical routine. And CZTSSe could be easily prepared after selenization of CZTS. When they are employed as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), the power conversion efficiency (PCE) has been improved from 3.54% to 7.13% as CZTS is converted to CZTSSe, which is also compared to that of Pt (7.62%). The exact reason for the enhanced catalytic activity of I3- is discussed with the work function and density functional theory (DFT) when CZTSSe converted from CZTS. The results of a Kelvin probe suggest that the work function of CZTSSe (5.61 eV) is closer to that of Pt (5.65 eV) and higher than that of CZTS, which matched the redox shuttle potential better. According to the theory calculation, all the atomic and bond populations changed significantly when Se replaced partly the S on the CZTS system, especially in the Zn site. During the catalytic process as CEs, the adsorption energy obviously increased compared to those at other sites when I3- adsorbed on the Zn site in CZTSSe. So, Zn plays an important role for the reduction of I3- after CZTS is converted to CZTSSe. Based on above analysis, the reason for enhanced performance of DSSCs when CZTS converted to CZTSSe is mainly due to the enhancement of Zn-site activity. This work is beneficial for understanding the catalytic reaction mechanism of CZTS(Se) as CEs of DSSCs.
RESUMO
Size controllable MnFe2O4 superparamagnetic nanoparticles (NPs) were prepared by a solvothermal method using low-cost metal oleate as the source. The particle size, chemical composition and magnetic properties were investigated. The MnFe2O4 nanomaterials exhibit high colloidal stabilities and superparamagnetic properties, with an average particle size in the range of 2 to 10 nm by modifying the reaction condition, such as surfactant, reaction temperature and reaction time. By changing Mn(2+) to different cations, CoFe2O4, NiFe2O4, and ZnFe2O4 with different magnetic properties could be obtained. The hydrophobic MnFe2O4 NPs could also be modified with many surfactants, such as cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecylsulfate (SDS), with the aim of achieving high zeta-potential hydrophilic bilayer-coated MnFe2O4 NPs. In addition, the water soluble MnFe2O4 magnetic NPs can be applied to the removal of Pb(ii) from waste water with good recovery under external magnetic field.
