Spin-Injection in Graphene: An EPR and Raman Study.

In this article, the enrichment of graphene and graphene oxide with free radicals through their functionalization with tyrosine is studied. In contrast with what is commonly observed in the functionalization of graphene with organic species the addition of tyrosine radicals on to the graphene substrate led to a remarkable increase of the aromatic character as indicated by the spectroscopic data. Similar behaviour was observed for the functionalization of graphene oxide. In addition, a brief analysis of the tyrosine functionalized graphene with EPR spectroscopy showed a remarkable enhancement of the spin density that could be useful in spintronics.

Correlation of magnetic resonance (EPR, ssNMR) parameters and crystal-microstrain in marbles as a tool to probe their provenance.

Marbles constitute a significant family of materials, for antiquities, as well as modern constructions. Herein, we have studied Greek marbles, using electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopies, focusing on their structural microenvironment. Spin-Hamiltonian parameters derived from EPR spectra of naturally occurring 55Mn2+ (S = 5/2, I = 5/2) atoms in marbles, were studied as structural-probes. EPR data at 300 K provide a library of 55Mn2+ zero-field-splitting parameters (E, D). The effect of temperature (300 up to 700 K) on 55Mn2+-ZFS (E, D) and the strain of the D-tensor (Dstrain) was studied by high-temperature EPR spectroscopy. The EPR data, combined with 13C-ssNMR, provide detailed physicochemical information of the calcite and dolomite crystal phases in the marbles. In parallel, we have analyzed the lattice-microstrain (ε0) of the marbles' crystallites using high-resolution XRD data. Analysis of the correlation between the D-values of Mn2+ centers and (ε0)-XRD, reveals trends that reflect the provenance of the marbles. In this context, we discuss the correlation between the D-values of Mn2+ centers and (ε0)-microstrain as a novel tool to elucidate the provenance of marbles.

Antioxidant Hydrogen-Atom-Transfer to DPPH Radicals by Hybrids of {Hyaluronic-Acid Components}@SiO2.

Hydrogen-atom-transfer (HAT) is among the key mechanisms of antioxidant and antiradical activity in natural systems. Hyaluronic acid (HyA) is currently used extensively in health and cosmetics applications. Herein it is shown that {HyA@SiO2} hybrids based on hyaluronic acid (HyA) components grafted on SiO2 nanoparticles enable significant HAT activity versus DPPH radicals, while the homogeneous HyA counterparts are practically inactive. The {HyA@SiO2} hybrids consist of the two building blocks of HyA [d-glucuronic acid (GLA) and N-acetyl-d-glucosamine (GLAM)] covalently grafted on SiO2 nanoparticles. Based on the kinetic-thermodynamic Arrhenius study, we show that the {SiO2@GLA} hybrids operate spontaneously via hydrogen-atom-transfer (HAT) with a low activation energy barrier, i.e., by ΔΕα ∼ 20 kJ/mol vs the nongrafted counterparts. Moreover, a doubly grafted {GLA@SiO2@GLAM} nanohybrid, i.e. that contains both components of HyA, shows the most significant antioxidant activity. FTIR and Raman analysis reveal that local H-bonding between the SiO2 matrix, GLA, and GLAM in {GLA@SiO2@GLAM} decreases the activation barrier of the HAT mechanism. Thus, {GLA@SiO2@GLAM} nanohybrids exemplify a novel family of materials that are not the mere sum of their components. The present case is the first example of non-phenolic molecules being able to perform antiradical HAT, opening new perspectives not foreseen until today.

Control of Tyrosyl Radical Stabilization by {SiO2@Oligopeptide} Hybrid Biomimetic Materials.

Tyrosine radicals are notoriously short-lived/unstable in solution, while they present an impressive degree of stability and versatility in bioenzymes. Herein, we have developed a library of hybrid biomimetic materials (HBMs), which consists of tyrosine-containing oligopeptides covalently grafted on SiO2 nanoparticles, and studied the formation, lifetime, and redox properties of tyrosyl radicals. Using electron paramagnetic resonance spectroscopy, we have studied the radical-spin distribution as a probe of the local microenvironment of the tyrosyl radicals in the HBMs. We find that the lifetime of the tyrosyl radical can be enhanced by up to 6 times, by adjusting three factors, namely, a proximal histidine, the length of the oligopeptide, and the interface with the SiO2 nanomatrix. This is shown to be correlated to a significant lowering of E1/2 from +736 mV, in free tyrosine, to +548 mV in the {12-peptide}@SiO2 material. Moreover, we show that grafting on SiO2 lowers the E1/2 of tyrosine radicals by ∼50 mV in all oligopeptides. Analysis of the spin-distribution by EPR reveals that the positioning of a histidine at a H-bonding distance from the tyrosine further favors tyrosine radical stabilization.

Detection and Sorption of Heavy Metal Ions in Aqueous Media by a Fluorescent Zr(IV) Metal-Organic Framework Functionalized with 2-Picolylamine Receptor Groups.

Increasing global environmental pollution due to heavy metal ions raises the importance of research on new multifunctional materials for simultaneous detection and removal of these contaminants from water resources. In this study, we report a microporous 8-connected Zr4+ metal-organic framework (MOF) based on a terephthalate ligand decorated with a chelating 2-picolylamine side group (dMOR-2), which shows highly efficient fluorescence sensing and sorption of heavy metal cations. We demonstrate by detailed fluorescence studies the ability of a water-dispersible composite of dMOR-2 with polyvinylpyrrolidone for real-time detection of Cu2+, Pb2+, and Hg2+ in aqueous media. The limits of detection were found to be below 2 ppb for these species, while the system's performance is not affected by the presence of other potentially competitive ions. In addition, sorption studies showed that a composite of dMOR-2 with calcium alginate (dMOR-2@CaA) is an excellent sorbent for Pb2+ and Cu2+ ions with capacities of 376 ± 15 and 117 ± 4 mg per gram of dMOR-2@CaA, respectively, while displaying the capability for simultaneous removal of various heavy metal ions in low initial concentrations and in the presence of large excesses of other cationic species. Structural and spectroscopic studies with model ligands analogous to our material's receptor unit showed chelation to the 2-picolylamine moiety to be the main binding mode of metal ions to dMOR-2. Overall, dMOR-2 is shown to represent a rare example of a MOF, which combines sensitive fluorescence detection and high sorption capacity for heavy metal ions.

Model-Based Nanoengineered Pharmacokinetics of Iron-Doped Copper Oxide for Nanomedical Applications.

The progress in nanomedicine (NM) using nanoparticles (NPs) is mainly based on drug carriers for the delivery of classical chemotherapeutics. As low NM delivery rates limit therapeutic efficacy, an entirely different approach was investigated. A homologous series of engineered CuO NPs was designed for dual purposes (carrier and drug) with a direct chemical composition-biological functionality relationship. Model-based dissolution kinetics of CuO NPs in the cellular interior at post-exposure conditions were controlled through Fe-doping for intra/extra cellular Cu2+ and biological outcome. Through controlled ion release and reactions taking place in the cellular interior, tumors could be treated selectively, in vitro and in vivo. Locally administered NPs enabled tumor cells apoptosis and stimulated systemic anti-cancer immune responses. We clearly show therapeutic effects without tumor cells relapse post-treatment with 6 % Fe-doped CuO NPs combined with myeloid-derived suppressor cell silencing.

Molybdena deposited on titania by equilibrium deposition filtration: structural evolution of oxo-molybdenum(vi) sites with temperature.

The equilibrium deposition filtration (EDF) method, an advanced catalyst synthesis route that is based on a molecular level approach, can be used for tailoring the oxometallic phase deposited on a porous oxide support. Here, the EDF method is used for synthesizing (MoOx)n/TiO2 catalysts. In situ Raman spectroscopy in the temperature range of 25-450 °C, low temperature (77 K) EPR spectroscopy and DR-UV spectroscopy are used for studying the evolution of the structural configuration of oxo-Mo(VI) species on TiO2 with increasing temperature as well as the influence of the supported (MoOx)n species on the photo-generation of electrons and holes of TiO2. This study concerns (MoOx)n/TiO2 samples in which the surface densities after calcination are 0.3, 2.6 and 3.9 Mo per nm(2), thereby covering a very wide range of submonolayer coverage. The gradual heat treatment of the catalysts results in a transformation of the initially (prior to drying) deposited species and the pertinent species evolution at the nano-level is discussed by means of a number of mechanisms including anchoring, association, cleavage and surface diffusion.

Stabilization of Phenolic Radicals on Graphene Oxide: An XPS and EPR Study.

A graphene oxide-gallic acid hybrid material was synthesized by the immobilization of gallic acid (3,4,5-trihydroxobenzoic acid) on graphene oxide. The grafting was achieved via the formation of amide bonds between the amine groups on the organofunctionalized graphite oxide surface and the carboxyl groups of the gallic acid molecules. The EPR signal of the gallic acid radicals in this hybrid material remained almost unaltered over at least 500 days, with less than 3% signal decay over that period, pointing to the truly remarkable stability of these radicals. The produced material was characterized by Fourier transform infrared, X-ray photoelectron, and electron paramagnetic resonance spectroscopies as well as by thermogravimetric analysis and the Kaiser test. The stability of the radicals in the material was studied in powder form and in aqueous solution vs pH. We demonstrate that in the graphene oxide-gallic acid hybrid material a radical is favorably stabilized on the ring-O while the oxidation of the second OH is precluded, and this results in long-term stabilization of the gallic acid radicals in solid hybrid material. Thus, in applications where it will be used under O2-free and humidity-free conditions, the graphene oxide-gallic acid hybrid material is a reliable spintronics scaffold.

Flame Spray Pyrolysis Synthesis of Vo-Rich Nano-SrTiO3-x.

Engineering of oxygen vacancies (Vo) in nanomaterials allows diligent control of their physicochemical properties. SrTiO3 possesses the typical ABO3 structure and has attracted considerable attention among the titanates due to its chemical stability and its high conduction band energy. This has resulted in its extensive use in photocatalytic energy-related processes, among others. Herein, we introduce the use of Flame Spray Pyrolysis (FSP); an industrial and scalable process to produce Vo-rich SrTiO3 perovskites. We present two types of Anoxic Flame Spray Pyrolysis (A-FSP) technologies using CH4 gas as a reducing source: Radial A-FSP (RA-FSP); and Axial A-FSP (AA-FSP). These are used for the control engineering of oxygen vacancies in the SrTiO3-x nanolattice. Based on X-ray photoelectron spectroscopy, Raman and thermogravimetry-differential thermal analysis, we discuss the role and the amount of the Vos in the so-produced nano-SrTiO3-x, correlating the properties of the nanolattice and energy-band structure of the SrTiO3-x. The present work further corroborates the versatility of FSP as a synthetic process and the potential future application of this process to engineer photocatalysts with oxygen vacancies in quantities that can be measured in kilograms.

Just Soaping Them: The Simplest Method for Converting Metal Organic Frameworks into Superhydrophobic Materials.

The incorporation of superhydrophobic properties into metal organic framework (MOF) materials is highly desirable to enhance their hydrolytic stability, gas capture selectivity in the presence of humidity and efficiency in oil-water separations, among others. The existing strategies for inducing superhydrophobicity into MOFs have several weaknesses, such as increased cost, utilization of toxic reagents and solvents, applicability for limited MOFs, etc. Here, we report the simplest, most eco-friendly, and cost-effective process to impart superhydrophobicity to MOFs, involving a rapid (90 min) treatment of MOF materials with solutions of sodium oleate, a main component of soap. The method can be applied to both hydrolytically stable and unstable MOFs, with the porosity of modified MOFs approaching, in most cases, that of the pristine materials. Interestingly, this approach was used to isolate superhydrophobic magnetic MOF composites, and one of these materials formed stable liquid marbles, whose motion could be easily guided using an external magnetic field. We also successfully fabricated superhydrophobic MOF-coated cotton fabric and fiber composites. These composites exhibited exceptional oil sorption properties achieving rapid removal of floating crude oil from water, as well as efficient purification of oil-in-water emulsions. They are also regenerable and reusable for multiple sorption processes. Overall, the results described here pave the way for an unprecedented expansion of the family of MOF-based superhydrophobic materials, as virtually any MOF could be converted into a superhydrophobic compound by applying the new synthetic approach.

Quantitative In Situ Monitoring of Cu-Atom Release by Cu2O Nanocatalysts under Photocatalytic CO2 Reduction Conditions: New Insights into the Photocorrosion Mechanism.

Cu2O is among the most promising photocatalysts for CO2 reduction, however its photocorrosion remains a standalone challenge. Herein, we present an in situ study of the release of Cu ions from Cu2O nanocatalysts under photocatalytic conditions in the presence of HCO3 as a catalytic substrate in H2O. The Cu-oxide nanomaterials were produced by Flame Spray Pyrolysis (FSP) technology. Using Electron Paramagnetic Resonance (EPR) spectroscopy in tandem with analytical Anodic Stripping Voltammetry (ASV), we monitored in situ the Cu2+ atom release from the Cu2O nanoparticles in comparison with CuO nanoparticles under photocatalytic conditions. Our quantitative, kinetic data show that light has detrimental effect on the photocorrosion of Cu2O and ensuing Cu2+ ion release in the H2O solution, up to 15.7% of its mass. EPR reveals that HCO3 acts as a ligand of the Cu2+ ions, promoting the liberation of {HCO3-Cu} complexes in solution from Cu2O, up to 27% of its mass. HCO3 alone exerted a marginal effect. XRD data show that under prolonged irradiation, part of Cu2+ ions can reprecipitate on the Cu2O surface, creating a passivating CuO layer that stabilizes the Cu2O from further photocorrosion. Including isopropanol as a hole scavenger has a drastic effect on the photocorrosion of Cu2O nanoparticles and suppresses the release of Cu2+ ions to the solution. Methodwise, the present data exemplify that EPR and ASV can be useful tools to help quantitatively understand the solid-solution interface photocorrosion phenomena for Cu2O.

Nanoantioxidant Materials: Nanoengineering Inspired by Nature.

Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.

Advanced Flame Spray Pyrolysis (FSP) Technologies for Engineering Multifunctional Nanostructures and Nanodevices.

Flame spray pyrolysis (FSP) is an industrially scalable technology that enables the engineering of a wide range of metal-based nanomaterials with tailored properties nanoparticles. In the present review, we discuss the recent state-of-the-art advances in FSP technology with regard to nanostructure engineering as well as the FSP reactor setup designs. The challenges of in situ incorporation of nanoparticles into complex functional arrays are reviewed, underscoring FSP's transformative potential in next-generation nanodevice fabrication. Key areas of focus include the integration of FSP into the technology readiness level (TRL) for nanomaterials production, the FSP process design, and recent advancements in nanodevice development. With a comprehensive overview of engineering methodologies such as the oxygen-deficient process, double-nozzle configuration, and in situ coatings deposition, this review charts the trajectory of FSP from its foundational roots to its contemporary applications in intricate nanostructure and nanodevice synthesis.

In Tandem Control of La-Doping and CuO-Heterojunction on SrTiO3 Perovskite by Double-Nozzle Flame Spray Pyrolysis: Selective H2 vs. CH4 Photocatalytic Production from H2O/CH3OH.

ABO3 perovskites offer versatile photoactive nano-templates that can be optimized towards specific technologies, either by means of doping or via heterojunction engineering. SrTiO3 is a well-studied perovskite photocatalyst, with a highly reducing conduction-band edge. Herein we present a Double-Nozzle Flame Spray Pyrolysis (DN-FSP) technology for the synthesis of high crystallinity SrTiO3 nanoparticles with controlled La-doping in tandem with SrTiO3/CuO-heterojunction formation. So-produced La:SrTiO3/CuO nanocatalysts were optimized for photocatalysis of H2O/CH3OH mixtures by varying the La-doping level in the range from 0.25 to 0.9%. We find that, in absence of CuO, the 0.9La:SrTiO3 material achieved maximal efficient photocatalytic H2 production, i.e., 12 mmol g-1 h-1. Introduction of CuO on La:SrTiO3 enhanced selective production of methane CH4. The optimized 0.25La:SrTiO3/0.5%CuO catalyst achieved photocatalytic CH4 production of 1.5 mmol g-1 h-1. Based on XRD, XRF, XPS, BET, and UV-Vis/DRS data, we discuss the photophysical basis of these trends and attribute them to the effect of La atoms in the SrTiO3 lattice regarding the H2-production, plus the effect of interfacial CuO on the promotion of CH4 production. Technology-wise this work is among the first to exemplify the potential of DN-FSP for scalable production of complex nanomaterials such as La:SrTiO3/CuO with a diligent control of doping and heterojunction in a single-step synthesis.

Non-graphitized carbon/Cu2O/Cu0 nanohybrids with improved stability and enhanced photocatalytic H2 production.

Cu2O is a highly potent photocatalyst, however photocorrosion stands as a key obstacle for its stability in photocatalytic technologies. Herein, we show that nanohybrids of Cu2O/Cu0 nanoparticles interfaced with non-graphitized carbon (nGC) constitute a novel synthesis route towards stable Cu-photocatalysts with minimized photocorrosion. Using a Flame Spray Pyrolysis (FSP) process that allows synthesis of anoxic-Cu phases, we have developed in one-step a library of Cu2O/Cu0 nanocatalysts interfaced with nGC, optimized for enhanced photocatalytic H2 production from H2O. Co-optimization of the nGC and the Cu2O/Cu0 ratio is shown to be a key strategy for high H2 production, > 4700 µmoles g-1 h-1 plus enhanced stability against photocorrosion, and onset potential of 0.234 V vs. RHE. After 4 repetitive reuses the catalyst is shown to lose less than 5% of its photocatalytic efficiency, while photocorrosion was < 6%. In contrast, interfacing of Cu2O/Cu0 with graphitized-C is not as efficient. Raman, FT-IR and TGA data are analyzed to explain the undelaying structural functional mechanisms where the tight interfacing of nGC with the Cu2O/Cu0 nanophases is the preferred configuration. The present findings can be useful for wider technological goals that demand low-cost engineering, high stability Cu-nanodevices, prepared with industrially scalable process.

MOF-Derived Defective Co3O4 Nanosheets in Carbon Nitride Nanocomposites for CO2 Photoreduction and H2 Production.

In photocatalysis, especially in CO2 reduction and H2 production, the development of multicomponent nanomaterials provides great opportunities to tune many critical parameters toward increased activity. This work reports the development of tunable organic/inorganic heterojunctions comprised of cobalt oxides (Co3O4) of varying morphology and modified carbon nitride (CN), targeting on optimizing their response under UV-visible irradiation. MOF structures were used as precursors for the synthesis of Co3O4. A facile solvothermal approach allowed the development of ultrathin two-dimensional (2D) Co3O4 nanosheets (Co3O4-NS). The optimized CN and Co3O4 structures were coupled forming heterojunctions, and the content of each part was optimized. Activity was significantly improved in the nanocomposites bearing Co3O4-NS compared with the corresponding bulk Co3O4/CN composites. Transient absorption spectroscopy revealed a 100-fold increase in charge carrier lifetime on Co3O4-NS sites in the composite compared with the bare Co3O4-NS. The improved photocatalytic activity in H2 production and CO2 reduction is linked with (a) the larger interface imposed from the matching 2D structure of Co3O4-NS and the planar surface of CN, (b) improvements in charge carrier lifetime, and (c) the enhanced CO2 adsorption. The study highlights the importance of MOF structures used as precursors in forming advanced materials and the stepwise functionalization of the individual parts in nanocomposites for the development of materials with superior activity.

Coordination properties of Cu(II) ions towards a phosphorylated fragment from the R1 domain of the tau protein and the effect of Ser phosphorylation on Cu(II) binding affinity.

Tau hyperphosphorylation plays a key role in Alzheimer's disease, mediating tau protein aggregation and deposition as neurofibrillary tangles in the intracellular space of neurons. The potential implications of Cu(II) ions on the disease have been studied intensively, focusing both on Cu(II)-amyloid and on Cu(II)-tau fragment interactions. Nevertheless, there is still a lack of information concerning the metal binding properties and the affinity of phosphorylated fragments of tau. In this work, the coordination properties of Cu(II) ions toward the peptides Ac-GSTENLKH-NH2 (R1) and Ac-GS(P)TENLKH-NH2 (R1P) (Ser phosphorylated analogue) were studied using potentiometric and spectroscopic (vis-EPR) methods. The above sequence belongs to the 261-268 segment of the R1 pseudorepeat of the microtubule-binding domain of the longest tau isoform. It includes both the required metal anchor site (His268) and the residue Ser262, a well-known tau phosphorylation site. There was no surprise in the coordination process of both peptides, which form 1 : 1 metal : ligand complexes and follow the already well-known binding trend (i.e., His imidazole as an anchor site followed by the deprotonation and subsequent coordination of 1-3 amide donors). The additional participation of the Glu-γ-COOH in the equatorial plane was evident for the species detected in acidic solutions, while in the pH range of 7-10, the same group occupies an axial position. The comparison of the Cu(II) binding affinities, revealed that the phosphorylated peptide (R1P) is a more effective ligand than R1 in acidic media. Above pH ∼ 7.9, the order is reversed, highlighting the role of the phosphate inter- or intra-molecular interactions in Cu(II) binding.

Control of monomeric Vo's versus Vo clusters in ZrO2-x for solar-light H2 production from H2O at high-yield (millimoles gr-1 h-1).

Pristine zirconia, ZrO2, possesses high premise as photocatalyst due to its conduction band energy edge. However, its high energy-gap is prohibitive for photoactivation by solar-light. Currently, it is unclear how solar-active zirconia can be designed to meet the requirements for high photocatalytic performance. Moreover, transferring this design to an industrial-scale process is a forward-looking route. Herein, we have developed a novel Flame Spray Pyrolysis process for generating solar-light active nano-ZrO2-x via engineering of lattice vacancies, Vo. Using solar photons, our optimal nano-ZrO2-x can achieve milestone H2-production yield, > 2400 µmolg-1 h-1 (closest thus, so far, to high photocatalytic water splitting performance benchmarks). Visible light can be also exploited by nano-ZrO2-x at a high yield via a two-photon process. Control of monomeric Vo versus clusters of Vo's is the key parameter toward Highly-Performing-Photocatalytic ZrO2-x. Thus, the reusable and sustainable ZrO2-x catalyst achieves so far unattainable solar activated photocatalysis, under large scale production.

Flame Spray Pyrolysis Co3O4/CoO as Highly-Efficient Nanocatalyst for Oxygen Reduction Reaction.

The oxygen reduction reaction (ORR) is the rate-limiting reaction in the cathode side of fuel cells. In the quest for alternatives to Pt-electrodes as cathodes in ORR, appropriate transition metal oxide-based electrocatalysts are needed. In the present work, we have synthesized Co3O4 and CoO/Co3O4 nanostructures using flame spray pyrolysis (FSP), as electrocatalysts for ORR in acidic and alkaline media. A detailed study of the effect of (Co-oxide)/Pt ratio on ORR efficiency shows that the present FSP-made Co-oxides are able to perform ORR at very low-Pt loading, 0.4% of total metal content. In acid medium, an electrode with (5.2% Pt + 4.8% Co3O4), achieved the highest ORR performance (Jmax = 8.31 mA/cm2, E1/2 = 0.66 V). In alkaline medium, superior performance and stability have been achieved by an electrode with (0.4%Pt + 9.6% (CoO/Co3O4)) with ORR activity (Jmax = 3.5 mA/cm2, E1/2 = 0.08 V). Using XRD, XPS, Raman and TEM data, we discuss the structural and electronic aspects of the FSP-made Co-oxide catalysts in relation to the ORR performance. Cyclic voltammetry data indicate that the ORR process involves active sites associated with Co3+ cations at the cobalt oxide surface. Technology-wise, the present work demonstrates that the developed FSP-protocols, constitutes a novel scalable process for production of co-oxides appropriate for oxygen reduction reaction electrodes.

Lattice Defects Engineering in W-, Zr-doped BiVO4 by Flame Spray Pyrolysis: Enhancing Photocatalytic O2 Evolution.

A flame spray pyrolysis (FSP) method has been developed, for controlled doping of BiVO4 nanoparticles with W and Zr in tandem with the oxygen vacancies (Vo) of the BiVO4 lattice. Based on XPS and Raman data, we show that the nanolattice of W-BiVO4 and Zr-BiO4 can be controlled to achieve optimal O2 evolution from H2O photocatalysis. A synergistic effect is found between the W- and Zr-doping level in correlation with the Vo-concentration. FSP- made W-BiVO4 show optimal photocatalytic O2-production from H2O, up to 1020 µmol/(g × h) for 5%W-BiVO4, while the best performing Zr-doped achieved 970 µmol/(g × h) for 5%Zr-BiVO4. Higher W-or Zr-doping resulted in deterioration in photocatalytic O2-production from H2O. Thus, engineering of FSP-made BiVO4 nanoparticles by precise control of the lattice and doping-level, allows significant enhancement of the photocatalytic O2-evolution efficiency. Technology-wise, the present work demonstrates that flame spray pyrolysis as an inherently scalable technology, allows precise control of the BiVO4 nanolattice, to achieve significant improvement of its photocatalytic efficiency.