Self-Diffusion versus Intentional Doping: Beneficial and Damaging Impact on Hematite Photoanode Interfaces.

The comprehension of side effects caused by high-temperature thermal treatments in the design of (photo)electrodes is essential to achieve efficient and cost-effective devices for solar water splitting. This investigation explores the beneficial and damaging impacts of thermal treatments in the (photo)electrode design, unraveling the impact of self-diffusion and its consequences. The industrial-friendly polymeric precursor synthesis (PPS) method, which is known for its easy technological application, was chosen as the fabrication technique for hematite photoabsorbers. For substrate evaluation, two types of conductive glass substrates, aluminum borosilicate and quartz, both coated with fluorine-doped tin oxide (ABS/FTO and QTZ/FTO, respectively), were subjected to thermal treatments following the PPS protocol. Optical and structural analyses showed no significant alterations in substrate properties, whereas X-ray photoelectron spectroscopy (XPS) revealed the migration of silicon and calcium ions from the glass component to the FTO surface. This diffusion can be further mitigated by an oxide buffer layer. To track the potential ion diffusion on the photoabsorber surface and assess its effect on the photoelectrode performance, hematite was selected as the model material and deposited onto the glass substrates. From all the ions that could possibly migrate, only Si4+ and Ca2+ originating from the glass component, as well as Sn4+ from the fluorine-doped tin oxide (FTO), were detected on the surface of the hematite photoabsorber. Interestingly, the so-called "self-diffusion" of these ions did not result in any beneficial effect on the hematite photoelectrochemical response. Instead, intentional modifications showed more substantial impacts on the photoelectrochemical efficiency compared to unintentional self-diffusion. Therefore, "self-diffusion", which can unintentionally dope the hematite, is not sufficient to significantly impact the final photocurrent. These findings emphasize the importance of understanding the true effect of thermal treatments on the photoelectrode properties to unlock their full potential in photoelectrochemical applications.

Challenges and prospects about the graphene role in the design of photoelectrodes for sunlight-driven water splitting.

Graphene and its derivatives have emerged as potential materials for several technological applications including sunlight-driven water splitting reactions. This review critically addresses the latest achievements concerning the use of graphene as a player in the design of hybrid-photoelectrodes for photoelectrochemical cells. Insights about the charge carrier dynamics of graphene-based photocatalysts which include metal oxides and non-metal oxide semiconductors are also discussed. The concepts underpinning the continued progress in the field of graphene/photoelectrodes, including different graphene structures, architecture as well as the possible mechanisms for hydrogen and oxygen reactions are also presented. Despite several reports having demonstrated the potential of graphene-based photocatalysts, the achieved performance remains far from the targeted benchmark efficiency for commercial application. This review also highlights the challenges and opportunities related to graphene application in photoelectrochemical cells for future directions in the field.

Tailoring a Zinc Oxide Nanorod Surface by Adding an Earth-Abundant Cocatalyst for Induced Sunlight Water Oxidation.

Herein, a detailed investigation of the surface modification of a zinc oxide (ZnO) nanorod electrode with FeOOH nanoparticles dispersed in glycine was conducted to improve the water oxidation reaction assisted by sunlight. The results were systematically analysed in terms of the general parameters (light absorption, charge separation, and surface for catalysis) that govern the photocurrent density response of metal oxide as photoanode in a photoelectrochemical (PEC) cell. ZnO electrodes surface were modified with different concentration of FeOOH nanoparticles using the spin-coating deposition method, and it was found that 6-layer deposition of glycine-FeOOH nanoparticles is the optimum condition. The glycine plays an important role decreasing the agglomeration of FeOOH nanoparticles over the ZnO electrode surface and increasing the overall performance. Comparing bare ZnO electrodes with the ones modified with glycine-FeOOH nanoparticles an enhanced photocurrent density can be observed from 0.27 to 0.57 mA/cm2 at 1.23 VRHE under sunlight irradiation. The impedance spectroscopy data aid us to conclude that the higher photocurrent density is an effect associated with more efficient surface for chemical reaction instead of electronic improvement. Nevertheless, the charge separation efficiency remains low for this system. The present discovery shows that the combination of glycine-FeOOH nanoparticle is suitable and environmentally-friend cocatalyst to enhance the ZnO nanorod electrode activity for the oxygen evolution reaction assisted by sunlight irradiation.

Controlling the Activation Energy for Single-Ion Diffusion through a Hybrid Polyelectrolyte Matrix by Manipulating the Central Coordinate Semimetal Atom.

The diffusion of lithium ions decoupled from a solid polymer electrolyte matrix is the key for high-energy electrochemical devices with the safety needed for commercial use. This Letter reports how the ion mobility in a single-phase hybrid polyelectrolyte (SPHP) matrix can be tuned by changing an inorganic coordinating atom from silicon (Si) to germanium (Ge). Nuclear Magnetic Resonance (NMR) results show that the lithium ion activation barrier in the polyelectrolyte with Si can be modulated from 0.26 eV to the unprecedented value of 0.12 eV in the polyelectrolyte with Ge. Density functional theory is used to show that the electronic structures of both polymers are very different, although their chemical structures are very similar, except for the coordinating atom. This simple chemical substitution route will certainly increase the interest in these polymers for applications in electrochemical devices.

Sunlight-driven water splitting using hematite nanorod photoelectrodes.

The efficiency of nanostructures for photoelectrochemical water-splitting is fundamentally governed by the capability of the surface to sustain the reaction without electron trapping or recombination by photogenerated holes. This brief review will summarize the latest progress on hematite, designed with columnar morphology via chemical synthesis, for photoelectrochemical cell application. The columnar morphology efficiently minimizes the number of defects, grain boundaries, and surface traps normally present on the planar morphology. The major drawback related to hole diffusion through the solid/liquid interface was addressed by using high annealing temperature combined with dopant addition. A critical view and depth of understanding of these two parameters were discussed focusing on the molecular oxygen evolution mechanism from the sunlight-driven water oxidation reaction.

Sunlight-driven water splitting using hematite nanorod photoelectrodes

ABSTRACT The efficiency of nanostructures for photoelectrochemical water-splitting is fundamentally governed by the capability of the surface to sustain the reaction without electron trapping or recombination by photogenerated holes. This brief review will summarize the latest progress on hematite, designed with columnar morphology via chemical synthesis, for photoelectrochemical cell application. The columnar morphology efficiently minimizes the number of defects, grain boundaries, and surface traps normally present on the planar morphology. The major drawback related to hole diffusion through the solid/liquid interface was addressed by using high annealing temperature combined with dopant addition. A critical view and depth of understanding of these two parameters were discussed focusing on the molecular oxygen evolution mechanism from the sunlight-driven water oxidation reaction.

Synergetic effect of Sn addition and oxygen-deficient atmosphere to fabricate active hematite photoelectrodes for light-induced water splitting.

This work describes the design of a microwave-assisted method using hydrothermal conditions to fabricate pure and Sn-doped hematite photoelectrodes with varied synthesis time and additional thermal treatment under air and N2 atmosphere. The hematite photoelectrode formed under N2 atmosphere, with Sn deposited on its surface-which is represented by material synthesized at 4 h -exhibits the highest performance. Hence, Sn addition followed by high temperature annealing conducted in an oxygen-deficient atmosphere seems to create oxygen vacancies, and to prevent the segregation of dopant to form the SnO2 phase at the hematite crystal surface, reducing its energy and suppressing the grain growth. The increased donor number density provided by the oxygen vacancies (confirmed by x-ray photoelectron data), and a possible reduction in the grain boundary energy or hematite crystal interface might favor charge separation, and increase the electron transfer through the hematite into the back contact (FTO substrate). In consequence, the light-induced water oxidation reaction efficiency of Sn-hematite photoelectrodes was significantly increased in comparison with pure ones, even though the vertical rod morphology was not preserved. This finding provides a novel insight into intentional Sn addition, revealing that dopant segregation at the hematite crystal surface (or at the grain boundaries) could-by increasing the electron mobility-be the more relevant factor in developing active hematite photoelectrodes than the control of columnar morphology.

Zinc Oxide Flower-Like Nanostructures That Exhibit Enhanced Toxicology Effects in Cancer Cells.

Nanostructured zinc oxide (ZnO) materials have been intensively studied because of their potential applications in cancer therapies. However, a better comprehension of the toxicity of the flower-like ZnO nanostructures toward cancer cells is still needed. In this study, we investigate the cytotoxicity of a ZnO flower-like nanostructure produced at low temperature via aqueous solution in human cervical carcinoma (HeLa) cells and noncancerous cell-line murine fibroblast (L929) cells. Nanotoxicology effects were analyzed to study apoptosis and necrosis processes, reactive oxygen species production, and cellular uptake. Cells remained incubated for 24 h in concentrations of 0.1, 1.0, and 10.0 µg mL-1 ZnO nanoparticles (NPs), with the estimated rods length varying from 1.7 ± 0.4 to 2.3 ± 0.4 µm, synthesized at different times (4, 2, and 0.5 h) by an aqueous solution method. The cytotoxic response observed in noncancerous and cancer cells showed that all of the ZnO NPs synthesized by an aqueous solution exhibited enhanced toxicology effects in cancer cells. ZnO flower-nanostructures exhibited a higher cytotoxic against cancer HeLa cells, in comparison to the noncancerous cell line L929. The cytotoxic response of ZnO NPs at 0.5, 2, and 4 h in L929 cells was not statistically significant. This ability may be of clinical interest because of the effectiveness of ZnO NPs to distinguish between normal and cancer cells in cancer therapy.

Hematite Surface Activation by Chemical Addition of Tin Oxide Layer.

In this study, the effect of tin (Sn(4+) ) modification on the surface of hematite electrodes synthesized by an aqueous solution route at different times (2, 5, 10, 18, and 24 h) is investigated. As confirmed from X-ray diffraction results, the as-synthesized electrode exhibits an oxyhydroxide phase, which is converted into a pure hematite phase after being subjected to additional thermal treatment at 750 °C for 30 min. The tin-modified hematite electrode is prepared by depositing a solution of Sn(4+) precursor on the as-synthesized electrode, followed by thermal treatment under the same abovementioned conditions. This modification results in an enhancement of the photocurrent response for all hematite electrodes investigated and attains the highest values of around 1.62 and 2.3 mA cm(-2) at 1.23 and 1.4 V versus RHE, respectively, for electrodes obtained in short synthesis times (2 h). Contact angle measurements suggest that the deposition of Sn(4+) on the hematite electrode provides a more hydrophilic surface, which favors a chemical reaction at the interface between the electrode and electrolyte. This result generates new perspectives for understanding the deposition of Sn(4+) on the hematite electrode surface, which is in contrast with several studies previously reported; these studies state that the enhancement in photocurrent density is related to either the induction of an increased donor charge density or shift in the flat-band potential, which favors charge separation.

Enhancing Hematite Photoanode Activity for Water Oxidation by Incorporation of Reduced Graphene Oxide.

Two effective methods to prepare reduced graphene oxide (rGO)/hematite nanostructured photoanodes and their photoelectrochemical characterization towards water splitting reactions are presented. First, graphene oxide (GO) is reduced to rGO using hydrazine in a basic solution containing tetrabutylammonium hydroxide (TBAOH), and then deposited over the nanostructured hematite photoanodes previously treated at 750 °C for 30 min. The second method follows the deposition of a paste containing a mixture of hematite nanoparticles and rGO sheets by the doctor-blade method, varying the rGO concentration. Since hematite suffers from low electron mobility, a low absorption coefficient, high recombination rates and slow reaction kinetics, the incorporation of rGO in the hematite can overcome such limitations due to graphene's exceptional properties. Using the first method, the rGO incorporation results in a photocurrent density increase from 0.56 to 0.82 mA cm(-2) at 1.23 VRHE. Our results indicate that the rGO incorporation in the hematite photoanodes shows a positive effect in the reduction of the electron-hole recombination rate.

Validating Internal Control Genes for the Accurate Normalization of qPCR Expression Analysis of the Novel Model Plant Setaria viridis.

Employing reference genes to normalize the data generated with quantitative PCR (qPCR) can increase the accuracy and reliability of this method. Previous results have shown that no single housekeeping gene can be universally applied to all experiments. Thus, the identification of a suitable reference gene represents a critical step of any qPCR analysis. Setaria viridis has recently been proposed as a model system for the study of Panicoid grasses, a crop family of major agronomic importance. Therefore, this paper aims to identify suitable S. viridis reference genes that can enhance the analysis of gene expression in this novel model plant. The first aim of this study was the identification of a suitable RNA extraction method that could retrieve a high quality and yield of RNA. After this, two distinct algorithms were used to assess the gene expression of fifteen different candidate genes in eighteen different samples, which were divided into two major datasets, the developmental and the leaf gradient. The best-ranked pair of reference genes from the developmental dataset included genes that encoded a phosphoglucomutase and a folylpolyglutamate synthase; genes that encoded a cullin and the same phosphoglucomutase as above were the most stable genes in the leaf gradient dataset. Additionally, the expression pattern of two target genes, a SvAP3/PI MADS-box transcription factor and the carbon-fixation enzyme PEPC, were assessed to illustrate the reliability of the chosen reference genes. This study has shown that novel reference genes may perform better than traditional housekeeping genes, a phenomenon which has been previously reported. These results illustrate the importance of carefully validating reference gene candidates for each experimental set before employing them as universal standards. Additionally, the robustness of the expression of the target genes may increase the utility of S. viridis as a model for Panicoid grasses.

UV-light effects on cytochrome c modulated by the aggregation state of phenothiazines.

The present study shows the factors that modulate the photodamage promoted by phenothiazines. Cytochrome c was irradiated with UV light for 120 min, over a pH range from 4.0 to 8.0, in the absence and in the presence of different concentrations of thioridazine (TR) and fluphenazine (FP). In the absence of phenothiazines, the maximal rate of a Soret band blue shift (nm/min) from 409 to 406 nm was obtained at pH 4.0 (0.028 nm/min). The presence of phenothiazines at the concentration range 10-25 µmol/L amplified and accelerated a cytochrome c blue shift (409 to 405 nm, at a rate = 0.041 nm/min). Above 25 µmol/L, crescent concentrations of phenothiazines contributed to cytochrome c protection with (maximal at 2500 µmol/L). Scanning electronic microscopy revealed the formation of nanostructures. The pH also influenced the effect of low phenothiazine concentrations on cytochrome c. Thus, the predominance of phenothiazine-promoted cytochrome c damage or protection depends on a balance of the following factors: the yield of photo-generated drug cation radicals, which is favored by acidic pH; the stability of the cation radicals, which is favored by the drug aggregation; and the cytochrome c structure, modulated by the pH.

Large-area plasmonic substrate of silver-coated iron oxide nanorod arrays for plasmon-enhanced spectroscopy.

One-dimensional iron oxide materials fabricated on conducting glass substrates and their unique properties make these nanostructures promising candidates for a wide range of applications. Herein, vertically oriented α-Fe2O3 nanorod arrays synthesized under hydrothermal conditions over a large area are described, as an active platform for surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF). From scanning electron microscopy images the formation of a homogeneous distribution of vertically oriented rods in a large area is confirmed. For activating the localized surface plasmon resonances, which are responsible for SERRS and SEF, a 6 nm layer of Ag is deposited onto the α-Fe2O3 nanorod arrays by physical vapor deposition to form Ag islands.

Vertically oriented iron oxide films produced by hydrothermal process: effect of thermal treatment on the physical chemical properties.

Our study describes the influence of the thermal treatment on the fundamental properties of the vertical oriented iron oxide nanorods synthesized under hydrothermal condition onto a conductor substrate. X-ray diffraction and X-ray absorption near edge structure spectra were used to investigate the phase evolution from iron oxyhydroxide (ß-FeOOH) to pure hematite phase. The formation of nanorods distributed along of substrate was observed by top-view SEM images and the rod growth preferentially oriented at the highly conductive (001) basal plane of hematite, perpendicular to the substrate. Light absorption capacity increases with the temperature of treatment and the electronic transitions (direct and indirect electronic transition) were estimated from this result. From the electrochemical measurement, the hematite/electrolyte interface was evaluated. These findings demonstrated that the temperature plays an important role on the hematite (structural, morphological, and catalytic) properties and that many influences must work in great harmony in order to produce a promising hematite photoanode.