Effects of Lanthanum Substitution and Annealing on Structural, Morphologic, and Photocatalytic Properties of Nickel Ferrite.

Nanoparticles of NiLaxFe2-xO4 ferrite spinel incorporated in a SiO2 matrix were synthesized via a sol-gel method, followed by annealing at 200, 500, and 800 °C. The resulting materials were characterized via XRD, AFM, and BET techniques and evaluated for photocatalytic activity. The XRD diffractograms validate the formation of a single-phase cubic spinel structure at all temperatures, without any evidence of secondary peaks. The size of crystallites exhibited a decrease from 37 to 26 nm with the substitution of Fe3+ with La3+ ions. The lattice parameters and crystallite sizes were found to increase with the rise in La3+ content and annealing temperature. Isotherms were employed to calculate the rate constants for the decomposition of malonate precursors to ferrites and the activation energy for each ferrite. All nanocomposites have pores within the mesoporous range, with a narrow dispersion of pore sizes. The impact of La content on sonophotocatalytic activity was evaluated by studying Rhodamine B degradation under visible light irradiation. The results indicate that the introduction of La enhances nanocomposite performance. The prepared Ni-La ferrites may have potential application for water decontamination.

Recent Advances in Photochargeable Integrated and All-in-One Supercapacitor Devices.

Photoassisted energy storage systems, which enable both the conversion and storage of solar energy, have attracted attention in recent years. These systems, which started about 20 years ago with the individual production of dye-sensitized solar cells and capacitors and their integration, today allow more compact and cost-effective designs using dual-acting electrodes. Solar-assisted batterylike or hybrid supercapacitors have also shown promise with their high energy densities. This review summarizes all of these device designs and conveys the cutting-edge studies in this field. Besides, this review aims to emphasize the effects of point, extrinsic, intrinsic, and 2D-planar defects on the performance of photoassisted energy storage systems since it is known that defect structures, as well as electrical, optical, and surface properties, affect the device performance. Here, it is also targeted to draw attention to how critical the design, material selection, and material properties are for these new-generation energy conversion and storage devices, which have a high potential to see commercial examples quickly and to be recognized by more readers.

Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures.

In this study, three different morphologies, nanoflower (NF), nano sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures were synthesized successfully via a mild hydrothermal method. After synthesis, the samples were annealed in the atmosphere at 300, 600, and 800 °C. Although annealing provides different degradation kinetics for different morphologies, ZnO NS performed significantly better than other morphologies for all annealing temperatures we used in the study. When the photoluminescence, electron paramagnetic resonance spectroscopy, BET surface, and X-ray diffraction analysis results are examined, it is revealed that the defect structure, pore diameter, and crystallinity cumulatively affect the photocatalytic activity of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity in rhodamine B (RhB) degradation, it is necessary to develop a ZnO catalyst with fewer core defects, more oxygen vacancies, near band emission, large crystallite size, and large pore diameter. The ZnO NS-800 °C nanocatalyst studied here had a 35.6 × 10-3 min-1 rate constant and excellent stability after a 5-cycle photocatalytic degradation of RhB.

Photoluminescence and Photocatalytic Properties of MWNTs Decorated with Fe-Doped ZnO Nanoparticles.

The present work reports the photoluminescence (PL) and photocatalytic properties of multi-walled carbon nanotubes (MWCNTs) decorated with Fe-doped ZnO nanoparticles. MWCNT:ZnO-Fe nanocomposite samples with weight ratios of 1:3, 1:5 and 1:10 were prepared using a facile synthesis method. The obtained crystalline phases were evidenced by X-ray diffraction (XRD). X-ray Photoelectron spectroscopy (XPS) revealed the presence of both 2+ and 3+ valence states of Fe ions in a ratio of approximately 0.5. The electron paramagnetic resonance EPR spectroscopy sustained the presence of Fe3+ ions in the ZnO lattice and evidenced oxygen vacancies. Transmission electron microscopy (TEM) images showed the attachment and distribution of Fe-doped ZnO nanoparticles along the nanotubes with a star-like shape. All of the samples exhibited absorption in the UV region, and the absorption edge was shifted toward a higher wavelength after the addition of MWCNT component. The photoluminescence emission spectra showed peaks in the UV and visible region. Visible emissions are a result of the presence of defects or impurity states in the material. All of the samples showed photocatalytic activity against the Rhodamine B (RhB) synthetic solution under UV irradiation. The best performance was obtained using the MWCNT:ZnO-Fe(1:5) nanocomposite samples, which exhibited a 96% degradation efficiency. The mechanism of photocatalytic activity was explained based on the reactive oxygen species generated by the nanocomposites under UV irradiation in correlation with the structural and optical information obtained in this study.

Facile Preparation of PVDF/CoFe2O4-ZnO Hybrid Membranes for Water Depollution.

In this investigation, CoFe2O4-PVDF and CoFe2O4-ZnO-PVDF hybrid membranes were prepared using a modified phase inversion method in which a magnetic field was applied during the casting process to ensure a uniform distribution of nanomaterials on the membrane surface. Thus, better absorption of light and increased participation of nanoparticles in the photodegradation process is ensured. The influence of nanomaterials on the crystalline structure, surface morphology, and hydrophilicity properties of the PVDF membrane was investigated. The obtained results indicated that the hybrid membrane exhibited significant differences in its intrinsic properties due to the nanomaterials addition. The hydrophilicity properties of the PVDF membrane were improved by the presence of nanoparticles. The photocatalytic decomposition of aqueous Rhodamine B solution in the presence of the prepared membrane and under visible light irradiation was tested. The hybrid membrane containing CoFe2O4-ZnO on its surface exhibited a high removal rate.

Impact of Ni Content on the Structure and Sonophotocatalytic Activity of Ni-Zn-Co Ferrite Nanoparticles.

The structure, morphology, and sonophotocatalytic activity of Ni-Zn-Co ferrite nanoparticles, embedded in a SiO2 matrix and produced by a modified sol-gel method, followed by thermal treatment, were investigated. The thermal analysis confirmed the formation of metal succinate precursors up to 200 °C, their decomposition to metal oxides and the formation of Ni-Zn-Co ferrites up to 500 °C. The crystalline phases, crystallite size and lattice parameter were determined based on X-ray diffraction patterns. Transmission electron microscopy revealed the shape, size, and distribution pattern of the ferrite nanoparticles. The particle sizes ranged between 34 and 40 nm. All the samples showed optical responses in the visible range. The best sonophotocatalytic activity against the rhodamine B solution under visible irradiation was obtained for Ni0.3Zn0.3Co0.4Fe2O4@SiO2.

Electrospun Nanosystems Based on PHBV and ZnO for Ecological Food Packaging.

The electrospun nanosystems containing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and 1 wt% Fe doped ZnO nanoparticles (NPs) (with the content of dopant in the range of 0-1 wt% Fe) deposited onto polylactic acid (PLA) film were prepared for food packaging application. They were investigated by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), antimicrobial analysis, and X-ray photoelectron spectrometry (XPS) techniques. Migration studies conducted in acetic acid 3% (wt/wt) and ethanol 10% (v/v) food simulants as well as by the use of treated ashes with 3% HNO3 solution reveal that the migration of Zn and Fe falls into the specific limits imposed by the legislation in force. Results indicated that the PLA/PHBV/ZnO:Fex electrospun nanosystems exhibit excellent antibacterial activity against the Pseudomonas aeruginosa (ATCC-27853) due to the generation of a larger amount of perhydroxyl (˙OOH) radicals as assessed using electron paramagnetic resonance (EPR) spectroscopy coupled with a spin trapping method.

Photocatalytic and Electrocatalytic Properties of NGr-ZnO Hybrid Materials.

N-doped graphene-ZnO hybrid materials with different N-doped graphene:ZnO wt% ratios (1:10; 1:20; 1:30) were prepared by a simple and inexpensive sol-gel method. The materials denoted NGr-ZnO-1 (1:10), NGr-ZnO-2 (1:20), and NGr-ZnO-3 (1:30) were investigated with advanced techniques and their morpho-structural, photocatalytic, and electrocatalytic properties were reported. Hence, pure N-doped graphene sample contains flakes with the size ranging from hundreds of nanometers to micrometers. In the case of all NGr-ZnO hybrid materials, the flakes appear heavily decorated with ZnO nanoparticles, having a cauliflower-like morphology. The X-ray powder diffraction (XRD) investigation of N-doped graphene sample revealed that it was formed by a mixture of graphene oxide, few-and multi-layer graphene. After the ZnO nanoparticles were attached to graphene, major diffraction peaks corresponding to crystalline planes of ZnO were seen. The qualitative and quantitative compositions of the samples were further evidenced by X-ray photoelectron spectroscopy (XPS). In addition, UV photoelectron spectroscopy (UPS) spectra allowed the determination of the ionization energy and valence band maxima. The energy band alignment of the hybrid materials was established by combining UV-Vis with UPS results. A high photocatalytic activity of NGr-ZnO samples against rhodamine B solution was observed. The associated reactive oxygen species (ROS) generation was monitored by electron paramagnetic resonance (EPR)-spin trapping technique. In accordance with bands alignment and identification of radical species, the photocatalytic mechanism was elucidated.

Photocatalytic activity of SnO2-TiO2 composite nanoparticles modified with PVP.

Interface modified SnO2-TiO2 composite nanoparticles were produced in two stages: first SnO2 nanoparticles were prepared by chemical precipitation in the presence of polyvinylpyrrolidone (PVP) and thermally treated at 500 °C then TiO2 was deposited on top of modified SnO2 and followed by a final annealing. As a consequence SnO2-TiO2 composite nanoparticles get crystallized while PVP is decomposed into monomer units and other attached smaller molecular fragments. TGA coupled with FT-IR spectroscopy confirmed the presence of monomers and other moieties as a result of PVP thermal fragmentation. The crystalline phases and composition of the two oxides were evidenced by X-ray diffraction, HRTEM and XPS. It was found that specific surface area of the composites increases with the increase in the initial amount of PVP. Also, the oxidation potential of the TiO2 shell, as determined by UV photoelectron spectroscopy (UPS), significantly decreases as the PVP quantity increase and further modifies the band alignment between SnO2 and TiO2 components. Additionally, both XPS and UPS spectra as well as EPR investigations indicate the presence of many localized states inside the band gap of TiO2. With a moderate PVP content the combined effects of band alignment, gap localized states and porosity make possible an increased number of reactive oxygen species (ROS) generation thus increasing photocatalytic activity against RhB dye solution under visible irradiation. The photocatalytic mechanism was elucidated based on the identification of radical species involved and in accordance with energy bands alignment, gap states, and porosity. Besides water purification by photocatalysis, SnO2-TiO2, as ROS generating heterostructures may be used in applications like antibacterial and antitumoral, deodorizing, air purifying, self-cleaning, gas sensing, as well as in hydrogen production.