Charge carrier separation is considered as a key factor in enhancing the photocatalytic process and can be maximized by mitigating surface recombination. Following this idea, the surface of zinc ...oxide (ZnO) was modified by thermal treatment and nickel oxide (NiO) deposition. The influence of the ZnO thermal treatment and NiO deposition conditions on the ZnO surface chemistry and heterostructure interface properties were investigated by in situ X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) and correlated to the dye photodegradation efficiency. The XPS analysis confirmed a change of doping of ZnO after thermal treatment, which mainly influenced the developed band bending, and has led to an improved photocatalytic activity. For the same reason, the heterostructures based on the surface cleaned ZnO surface had higher photocatalytic efficiency than the ones based on non-cleaned ZnO. The temperature input during NiO deposition had negligible effect on the heterostructure interface properties. The photocatalytic efficiency did not follow the band bending evolution because of a dominant contribution of charge recombination across the NiO layer as indicated by PL analysis.
Graphical Abstract
The heterocoagulation of lignocellulose nanofibers (LCNFs) with functionalized TiO
2
nanoparticles (NPs) is presented as an innovative revalorization strategy for the exploitation of lignocellulose ...wastes. Their use as bio-templates could be considered a promising alternative in a current biorefinery scheme, since the massive production of porous materials in numerous nanotechnological applications, could offer new alternatives of exploitation. The surface modification of TiO
2
NPs by adsorption of polyetilenimine (PEI) favors its anchorage with LCNFs through a peptide bond during heterocoagulation in aqueous suspension. The functionalization of LCNFs with TiO
2
NPs results in organic–inorganic core–shell nanostructures, used to shape coatings by dipping, and sinter them at low temperature (450 °C). In this process, the LCNFs were used as endo-templates for shaping stable porous coatings, when they burn during the consolidation of the inorganic structure. In this work, the successful inclusion and homogeneous distribution of biomaterials (LCNF templates) in the semiconductor inorganic microstructure is discussed in terms of dye loading (by UV–Visible Spectroscopy), photovoltaic efficiency and charge transfer (by Electrochemical Impedance Spectroscopy, EIS) in a Dye Sensitized Solar Cell (DSSC). Results confirm that the TiO
2
/template network yielded better photoefficiency and electron transport properties than mesoporous films assembled only from TiO
2
NPs. The preparation of TiO
2
-based photoanodes with enhanced performance (with an efficiency value around 6%, for a thickness of 8.7 µm) allows validating the successful colloidal procedure herein employed.
The orientation distributions of α-Al2O3 textured ceramics are determined from neutron diffraction spectra. A curved position-sensitive detector coupled to a tilt angle (χ) scan allowed the whole ...diffraction pattern treatment in the combined Rietveld−WIMV−Popa algorithm. Four textured alumina ceramics were prepared by slip-casting under a high magnetic field and sintered at 800, 1300, 1400, and 1600 °C. The calculation of the distribution density, correlated to the representation of the normal and inverse pole figures, highlights the influence of the magnetic field and sintering temperature on the texture development. The principal pole figures show a pronounced (00l) texture: (001) pole parallel to the direction of slip-casting, and (110) pole with higher distribution density for the directions perpendicular to the expected fiber axis. The inverse pole figures calculated for the fiber direction show a major (001) component for all the samples. With the increasing sintering temperature, the texture strength is enhanced and the c-axis distribution is sharper. The effectiveness of the approach for determining the crystallite size is also evident. As a global trend, the calculated crystallite size and observed grain size are similar and increase with the increasing sintering temperature. The mechanism of the texture development in the sintered specimens is certainly initiated from the preferred orientation of the green body after slip-casting under a high magnetic field. The basal texture is enhanced during sintering by selective anisotropic grain growth. We evidenced here the powerfulness of the Rietveld texture analysis to provide a basis for the correlation of texture, microstructural parameters, and anisotropic properties.
A porous well-consolidated and crack-free TiO2 multilayer coatings have been manufactured from a colloidal approach based on the preparation of particulate suspensions for DSSC. The study of the ...suspension parameters to optimize dispersion and stabilization of the TiO2 nanoparticle in the liquid media as well as a thermal stabilization step between the layers have been defined as two key points in the processing method to obtain interconnected microstructures, free of defects and heterogeneities, that prevent the application of an additional scattering layer or any kind of specific or clean conditions during deposition. The sintering process at low temperature, 450⁰C, has allowed obtaining open microarchitectures avoiding the complete densification and favoring the dye adsorption. A thickness of 12.8 μm resulted in a successful dye loading of 4.52 × 10−10 mol·mm−2 and a photoefficiency of 5.7%, both in the range of the others particulate systems. EIS measurements were also made to study the transfer charge phenomena.
This article describes a cell architecture that achieves enhanced light harvesting with less dye quantity while simultaneously improving the performance of the polysiloxane-based solid-state ...dye-sensitized solar cells (DSSCs). We report the synthesis of bimodal mesoporous anatase TiO2 films by a dual templating approach, combining a block-copolymer template (Pluronic P123) and polystyrene nanospheres (PS) as soft and hard templates, respectively. The AFM and TEM analysis of TiO2 films revealed a mixture of mesoporous and macroporous morphology in which dual porosity is generated by combustion of soft and hard templates. The size of the macropores was varied by employing PS beads with different diameters (62, 130 and 250 nm). The influence of the macropore size on the dye loading and pore infiltration is the main purpose of this article. The bimodal porosity leads to increased light scattering due to enhanced optical path length, and better pore infiltration of the polysiloxane electrolyte is achieved. The amount of dye uptake by the dual films is lower than that of soft films because the large pore size reduces the total surface area. The optimum bimodal structure was obtained when combining P123 surfactant and the 130 nm PS beads leading to the lowest charge transfer resistance and a high efficiency for DSSCs is reported with both liquid and polymer electrolytes. Even if the dye uptake was lower, the photovoltaic performance has been maintained and improved in some devices. The open circuit voltage and fill factor were improved, owing to a successful joining of different effects i.e. increased light harvesting, facile electrolyte penetration and reduced charge recombination.
Among other applications, magnesium hydroxide is commonly used as a flame-retardant filler in composite materials, as well as a precursor for magnesium oxide refractory ceramic. The microstructure of ...the powder is of prime importance in both technical applications. The influence of synthesis parameters on the morphological characteristics of magnesium hydroxide nanoparticles precipitated in dilute aqueous medium was studied. Several parameters were envisaged such as chemical nature of the base precipitant, type of counter-ion, temperature and hydrothermal treatment. Special attention was given to the obtaining of platelet-shaped, nanometric and de-agglomerated powders. The powders were characterized in terms of particle size distribution, crystal habits, morphology and ability to be re-dispersed in water. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and laser diffusion analyses were used for this purpose.
•Surfactant-assisted USP: a novel and low cost process to obtain high quality nickel oxide films, with or without lithium dopant.•Increased uniformity and reduced light scattering thanks to the ...addition of a surfactant.•Improved electrochromic performance (coloration efficiency and contrast) for lithium-doped films by comparison with the undoped NiO film.
Lithium-doped nickel oxide and undoped nickel oxide thin films have been deposited on FTO/glass substrates by a surfactant-assisted ultrasonic spray pyrolysis. The addition of polyethylene glycol in the sprayed solution has led to improved uniformity and reduced light scattering compared to films made without surfactant. Furthermore, the presence of lithium ions in NiO films has resulted in improved electrochromic performances (coloration contrast and efficiency), but with a slight decrease of the electrochromic switching kinetics.
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•BaFe12O19 powders were synthesized via single and double microemulsion techniques.•The synthesis process effect on the structural and magnetic properties is presented.•The average ...particle size of powders prepared via single microemulsion is 110nm.•The saturation magnetization at 300K is 65.12emu/g.
Barium hexaferrite powders of nanometer particle size synthesized via two variants of the microemulsion technique, namely, single microemulsion and double microemulsion, were studied. The influence was explored of the type of microemulsion technique on the microstructure and on the magnetic properties of the barium hexaferrite powders. The average particle size of the barium hexaferrite powders was in the range from 110nm to 442nm depending on the method and conditions of synthesis. The particles with size below 150nm had irregular shapes between spherical and plate-hexagonal; the bigger ones had an almost perfect hexagonal shape. The powders obtained by single microemulsion had better magnetic characteristics (saturation magnetization of 65.12emu/g and coercivity field of 3.6×105A/m) than those obtained by double microemulsion.
Herein, a surface cleaning procedure involving vacuum annealing under oxygen was applied for cleaning the zinc oxide nanorod (ZNR) scaffold film's surface before nickel oxide (NiO) deposition for ...heterostructure formation. The scaffold properties (surface stoichiometry, defects fluctuation, Fermi level shift, carrier concentration) were studied as a function of the vacuum level and the NiO deposition time and correlated to the NiO/ZNR interface (charge transfer resistance, band bending) and photo‐response properties. The surface cleaning under a higher vacuum enabled the adsorbate and surface oxygen vacancy passivation but also influenced the surface doping. Our best performing NiO/ZNR interface in terms of photocatalytic efficiency was composed of a high‐vacuum‐cleaned (0.5 Pa) ZNR scaffold and 40 s sputter deposited NiO layer which was post‐annealed. The high photocatalytic efficiency could be correlated with a maximized near‐band edge emission, effective band bending, low charge transfer resistance (as proven by photoelectrochemical impedance measurements), and optimum light harvesting (maximized photocurrent density). The optimized NiO/ZNR showed about 1.5 times increase in photo‐response and improved photodegradation efficiency compared to the ZNR scaffold.
Improved interface bonding and charge separation was achieved in NiO/ZNR heterostructured films by controlling the ZnO nanorod (ZNR) scaffold surface charge through vacuum annealing and by optimizing the NiO thickness. These modifications led to a 1.5‐fold increase in photocurrent, photodegradation efficiency and corrosion protection compared to the ZNR scaffold.
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