Functional Materials Letters

Ordered mesoporous carbon film supporting vanadium oxide nanoparticles has been synthesized via ultrasound-assistant impregnation method with ordered mesoporous carbon C-FDU15 film as the host and V₂O₅ sol as the guest precursor. The hybrids exhibit type IV sorption isotherms with H2 hysteresis loop, indicating the well-retained characteristics of ordered mesoporous structure. The capacitance of the materials is enhanced with V₂O₅ loading. Particularly, the hybrids with 32.26 wt.% V₂O₅ loading yield an important capacitance of 128 F/g in 1 mol/L KNO₃ electrolyte under a potential range from -0.6 V to 0.6 V. The improved specific capacitance of the hybrids is proposed to be the combination of the double-layer capacitance of ordered porous structure and the pseudocapacitance derived from V₂O₅.

We report about the modulation of the electrical properties of thin film solar cells due to the incorporation of size-selected Au nanostructures (NSs) at a textured FTO/p–i–n interface. By increasing the Au NSs size, the analyses of current-voltage characteristics show lower Schottky barrier heights and the gradual reduction of the open-circuit voltages (V_OC). The optical measurements show higher parasitic absorption by larger Au NSs that reduces the amount of radiation transmitted by the transparent to absorber layer. This process decreases the number of photo-generated carriers and may explain the V_OC reduction related to the devices with larger Au NSs at the interface. So, the correlation between materials properties and device performances was established.

A series of porous metal oxides nanowires (Fe₂O₃, Co₃O₄, NiO and CuO) have been successfully synthesized, where commercial carbon nanofibers were used as the template. The obtained samples were systematically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis diffuse reflectance (UV–Vis DR) spectra and transmission electron microscope (TEM). According to the photodegradation data, the porous metal oxides nanowires exhibit significantly photocatalytic activity for degrading tetracycline (TC). Furthermore, the porous Fe₂O₃ nanowires show the best photocatalytic performance among all the samples.

Chemically reduced graphene oxide containing hydroxyl groups and a wide size distribution of nanopores was prepared by a facile one-pot hydrothermal method. The resulting material was characterized by transmission electron microscopy (TEM), Raman spectroscopy, surface area measurement and attenuated total reflection infrared spectroscopy (ATR-FTIR), respectively. It was found that this reduced graphene oxide exhibited more clear nanopores and hydroxyl groups in the basal plane. Then the morphologies of the nanocomposite membrane incorporated into the nanoporous graphene were investigated through scanning electron microscopy (SEM), and the permeation test also was performed. Notably, the results showed that the nanocomposite membrane had a homogenous morphology and a better performance (separation factor 11.09) than polymer membrane in the separation of propylene/propane. This work demonstrates that nanoporous graphene exhibits great potential in the field of olefin/paraffin separation.

Epitaxial growth of Bi₂Se₃ thin films is of great current interest due to the advantages in spintronics and thermoelectrical applications. In this paper, Bi₂Se₃ thin films on Si (111) substrate have been prepared via magnetron sputtering deposition with post-annealing treatment and their microstructures and electrical transport properties were studied. Good quality with highly c-axis oriented films could be obtained after post-annealing treatment. The annealing temperature (T_a) obviously affected the phase structures and electrical properties. The crystallinity and the lattice parameters c of the Bi₂Se₃ thin-films increased with increasing T_a. The relative atomic ratio of Se/Bi decreased with increasing T_a and large number of Se vacancies was discovered in films with T_a = 350°C. The resistivity of films decreased monotonously and showed weakly metallic resistivity with the increase of T_a. Non-saturated high-field linear magnetoresistance and weak antilocalization were found in films with higher T_a.

Well-defined flowerlike Bi₂O₂CO₃ nanostructures were fabricated by a simple one-pot solvothermal method with high yield. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, nitrogen sorption, photoluminescence spectra and UV–visible diffuse reflectance spectroscopy. The photocatalytic properties of the as-prepared samples were further investigated by photocatalytic decomposition of Rhodamine B (RhB) dye, and it was found that the Bi₂O₂CO₃ nanoflowers showed a good photocatalytic activity under UV light. The excellent photocatalytic performance of Bi₂O₂CO₃ flowerlike nanostructures is related to its special nanostructure and morphology, indicates its potential application in photocatalysis and nanosensors.

A novel white-light-emitting Sr₃B₂O₆:Dy³⁺ phosphor was prepared by solid-state reactions and its luminescence properties were investigated. The excitation spectrum of obtained phosphor monitored at 479 nm covers a very broad spectral region from 320 nm to 460 nm with peaks at 323, 349, 363, 386, 427 and 456 nm. Under excitation at 349 nm, the phosphor exhibits a blue emission centered at 479 nm and a yellow emission centered at 574 nm. The optimal doping concentration of Dy³⁺ is obtained to be 7 mol%, and the concentration quenching is observed when the concentration of Dy³⁺ exceeds 7 mol%. This concentration quenching is due to the enhanced energy exchange among Dy³⁺ ions. The CIE chromaticity coordinate (0.289, 0.302) of Sr_3-0.07B₂O₆:0.07 Dy³⁺ located in the white-light region can be achieved. Theoretical calculations of electronic properties for Sr₃B₂O₆:Dy³⁺ phosphor in the framework of the density functional theory (DFT) were carried out. Our results suggest that the Sr₃B₂O₆:Dy³⁺ phosphor is a promising single-component white-light-emitting material.

Well crystallized TiO₂ nanoparticles were prepared by hydrothermal and sol–gel routes, respectively. The morphologies, structures, crystallinity and optical properties of resulted TiO₂ nanoparticles-based thin films via the two methods were examined by field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and reflectance spectra. In addition, comparison of photovoltaic performance of TiO₂ nanoparticles-based thin films by the two methods was performed. It is found that the maximum energy conversion efficiency of 4.06% was achieved based on the obtained electrode via hydrothermal, which is much better than that of the sol–gels route. The uniform film structure with improved dye absorption capability, increased diffused reflectance property and relatively low charge recombination rates for injected electrons are believed to be responsible to the superior photoelectrochemical properties of dye-sensitized solar cells (DSSC) via hydrothermal route.

Owing to the unique microporous structure and high specific surface area, activated carbon (AC) can act as a good candidate for functional materials. In this paper, Ni@AC magnetic nanocomposites with excellent magnetic response are synthesized by the hydrothermal method. All Ni@AC nanocomposites present ferromagnetism and Ni nanoparticles exist in the pores of AC. The saturation magnetization (M_s) increases with the increasing content of Ni, while the specific surface area and pore volume decrease. The S-50 sample possesses the parameters of the specific surface area of 1156.8 m² ⋅ g^-1 and M_s of 3.5 emu/g. Furthermore, the methylene blue (MB) removal analysis indicates that 99% MB can be adsorbed in 50 min. The as-prepared Ni@AC nanocomposites present good adsorptive capacity of MB and can be separated easily from water by magnetic separation technique.

Red-emitting Mn²⁺-doped AlN(AlN:Mn²⁺) phosphors were successfully prepared by a highly effective combustion synthesis method. The phase purity, morphology, element-composition and luminescence properties of the synthesized phosphors were investigated. X-ray diffraction (XRD) results show that the Mn²⁺-doped into the AlN host did not induce a second phase and distort the structure significantly. Scanning electron microscopy (SEM) images display that the phosphors have an irregular shape with a particle size in the range of 1–5 μm. X-ray photoelectron spectroscopy (XPS) spectrum indicates that Mn ions are divalent state. The synthesized AlN:Mn²⁺ phosphors exhibit a strong red emission centered at ~ 600 nm, which is ascribe to the ⁴T₁(⁴G)–⁶A₁(⁶S) transition of Mn²⁺ under ultraviolet excitation. The emission intensity reaches its maximum when Mn²⁺-doped concentration is 3 mol%.

The efficient synthesis of reduced graphene oxide (RGO) nanosheets via chemical reduction process of exfoliated graphene oxide (GO) nanosheets was performed by introducing sodium oxalate (Na₂C₂O₄) as a reducing agent. To study the effects of the reduction time on the synthesized RGO, the GO was reduced within -1/2, 1 and 2 h for RGO-1, RGO-2 and RGO-3, respectively. The C/O atomic ratio of the synthesized RGO-3 has increased from 2.16 to 6.32 after reduction as determined by X-ray photoelectron spectroscopy (XPS). The morphology analysis of the RGO-3 was determined by high-resolution transmission electron microscopy (HRTEM) almost revealed the formation of single layer. The number of RGO layers decreases as the time of the reduction increases. Based on these analysis results, sodium oxalate plays an important role in the efficient removal of the oxygen containing groups in the GO to produce high quality of RGO.

Conventional sintering and direct ball milling of Bi₂O₃ + Fe₂O₃ mixture were used for the fabrication of BiFeO₃ powders. The fabricated powders were performed annealing or high energy ball milling to vary the grain size from bottom-up or top-down. It was found that the magnetization of the powders synthesized by both methods plotted with the reciprocal of the grain size could be linearly fitted, indicating that the magnetism is from the finite size effect. Exchange bias phenomenon was observed after field cooling (FC) of the powders, confirming the magnetization is due to the uncompensated or canted surface spins. No spin glass behavior was found in these powders.

We herein report a feasible approach to improve the thermoelectric performance of p-type ZnSb compound by Zn content regulation. It is found that Zn vacancies formed by Zn deficiency not only efficiently enhance the electrical conductivity due to the improved hole concentration but also markedly lower the lattice thermal conductivity on account of the reinforced point defect scattering of phonons. The ZnSb compound with a nominal 3 mol.% Zn deficiency shows a maximum thermoelectric figure of merit ZT of ~ 0.8 at 700 K which is a ~ 60% improvement over the pristine sample. The strategies of further enhancing the performance of ZnSb-based material have been discussed.

A novel non-centrosymmetric (NCS) orthorhombic complex Zr(dmpu)₂Cl₄ (1) has been solvothermally prepared in situ from starting materials of Zirconium(IV) acetylacetonate (Zr(acac)₄) and N,N-dimethylpropyleneurea (dmpu), in which dmpu can act not only as solvent but also as organic ligand of monodentate oxygen donor. The second-harmonic generation (SHG) measurements reveal that complex 1 has a strong response of 1.4 times that of potassium dihydrogen phosphate (KDP) at 532 nm based on the Kurtz–Perry method. Furthermore, optical transmission study indicates that complex 1 has a wide transparency range in the UV region (200–850 nm) with a cutoff at 291 nm. According to first-principles calculations, the enhanced macroscopic SHG response of 1 can be attributed to the organic ligand dmpu. Therefore, 1 could be a promising candidate for non-linear optical material.

Sodium potassium niobate nanoparticles [(K_0.5Na_0.5)NbO₃, KNN], KNN-NPs, were synthesized using a modified sol–gel method. Structural and optical properties of the prepared samples were investigated by thermogravometric analyzer (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and UV–Vis spectroscopy. The XRD patterns showed that the formation of the orthorhombic KNN-NPs starts at 500°C calcination temperature. Raman spectroscopy was used to investigate the crystalline symmetry and the structural deformation of the prepared KNN-NPs. TEM images showed that the morphology of the prepared particles is cubic, with the average size of about 50 nm. From diffused reflectance spectroscopy along with using Kubelka–Munk method, the energy bandgaps were determined to be indirect with the values of 3.13 eV and 3.19 eV for the samples calcined at 500°C and 600°C, respectively.