Plasma production of nanomaterials for energy storage: continuous gas-phase synthesis of metal oxide CNT materials via a microwave plasma.

In this work we show for the first time that a continuous plasma process can synthesize materials from bulk industrial powders to produce hierarchical structures for energy storage applications. The plasma production process's unique advantages are that it is fast, inexpensive, and scalable due to its high energy density that enables low-cost precursors. The synthesized hierarchical material is comprised of iron oxide and aluminum oxide aggregate particles and carbon nanotubes grown in situ from the iron particles. New aerosol-based methods were used for the first time on a battery material to characterize aggregate and primary particle morphologies, while showing good agreement with observations from TEM measurements. As an anode for lithium ion batteries, a reversible capacity of 870 mA h g-1 based on metal oxide mass was observed and the material showed good recovery from high rate cycling. The high rate of material synthesis (∼10 s residence time) enables this plasma hierarchical material synthesis platform to be optimized as a means for energetic material production for the global energy storage material supply chain

Optimization of α-Fe2O3 Nanopillars Diameters for Photoelectrochemical Enhancement of α-Fe2O3-TiO2 Heterojunction.

Global warming is pushing the world to seek to green energy sources and hydrogen is a good candidate to substitute fossil fuels in the short term. In future, it is expected that production of hydrogen will be carried out through photo-electrocatalysis. In this way, suitable electrodes that acts as photoanode absorbing the incident light are needed to catalyse water splitting reaction. Hematite (α-Fe2O3) is one of the most attractive semiconductors for this purpose since it is a low-cost material and it has a suitable band gap of 2.1 eV, which allows the absorption of the visible region. Although, hematite has drawbacks such as low carrier mobility and short holes diffusion lengths, that here it has been tried to overcome by nanoengineering the material, and by using a semiconductor as a scaffold that enhances charge carrier separation processes in the electrode. In this work, we fabricate ultrathin quasi transparent electrodes composed by highly ordered and self-standing hematite nanopillars of a few tens of nanometers length on FTO and TiO2 supports. Photoanodes were fabricated utilizing electron beam evaporation technique and anodized aluminum oxide templates with well-defined pores diameters. Thus, the activity of the compact layer hematite photoanode is compared with the photoanodes fabricated with nanopillars of controllable diameters (i.e., 90, 260 and 400 nm) to study their influence on charge separation processes. Results indicated that optimal α-Fe2O3 photoanodes performance are obtained when nanopillars reach hundreds of nanometers in diameter, achieving for photoanodes with 400 nm nanopillars onto TiO2 supports the highest photocurrent density values

Study of the Photothermal Catalytic Mechanism of CO2 Reduction to CH4 by Ruthenium Nanoparticles Supported on Titanate Nanotubes

The Sabatier reaction could be a key tool for the future of the renewable energy field due to the potential of this reaction to produce either fuels or to stabilize H2 in the form of stable chemicals. For this purpose, a new composite made of ruthenium oxide nanoparticles (NPs) deposited on titanate nanotubes (TiNTs) was tested. Titanate nanotubes are a robust semiconductor with a one-dimensional (1D) morphology that results in a high contact area making this material suitable for photocatalysis. Small ruthenium nanoparticles (1.5 nm) were deposited on TiNTs at different ratios by Na+-to-Ru3+ ion exchanges followed by calcination. These samples were tested varying light power and temperature conditions to study the reaction mechanism during catalysis. Methanation of CO2 catalyzed by Ru/TiNT composite exhibit photonic and thermic contributions, and their ratios vary with temperature and light intensity. The synthesized composite achieved a production rate of 12.4 mmol CH4·gcat−1·h−1 equivalent to 110.7 mmol of CH4·gRu−1·h−1 under 150 mW/cm2 simulated sunlight irradiation at 210 °C. It was found that photo-response derives either from Ru nanoparticle excitation in the visible (VIS) and near-infrared (NIR) region (photothermal and plasmon excitation mechanism) or from TiNT excitation in the ultraviolet (UV) region leading to electron–hole separation and photoinduced electron transfer

Photocatalytic Water Splitting Promoted by 2D and 3D Porphyrin Covalent Organic Polymers Synthesized by Suzuki-Miyaura Carbon-Carbon Coupling

This work deals with the synthesis of metal-free and porphyrin-based covalent organic polymers (COPs) by the Suzuki–Miyaura coupling carbon-carbon bond forming reaction to study the photocatalytic overall water splitting performance. Apart from using 5,10,15,20-Tetrakis-(4-bromophenyl)porphyrin, we have chosen different cross-linker monomers to induce 2-dimensional (2D) or 3-dimensional (3D) and different rigidity in their resulting polymeric molecular structure. The synthesised COPs were extensively characterised to reveal that the dimensionality and flexibility of the molecular structure play an intense role in the physical, photochemical, and electronic properties of the polymers. Photoinduced excited state of the COPs was evaluated by nanosecond time-resolved laser transient absorption spectroscopy (TAS) by analysing excited state kinetics and quenching experiments, photocurrent density measurements and photocatalytic deposition of Ru3+ to RuO2, and photocatalysis. In summary, TAS experiments demonstrated that the transient excited state of these polymers has two decay kinetics and exhibit strong interaction with water molecules. Moreover, photocurrent and photocatalytic deposition experiments proved that charges are photoinduced and are found across the COP molecular network, but more important charges can migrate from the surface of the COP to the medium. Among the various COPs tested, COP–3 that has a flexible and 3D molecular structure reached the best photocatalytic performances, achieving a photocatalytic yield of 0.4 mmol H2 × gCOP–3−1 after 3 h irradiation

Microsecond transient absorption spectra of suspended semiconducting metal oxide nanoparticles

The time-resolved absorption spectra of opaque semiconductor powders have been typically studied by diffuse reflectance techniques. Herein, we show that time-resolved transmission spectroscopy of suspended nanoparticles is a suitable way to detect electrons and holes generated photochemically in these solids. Ultrasound dispersion of nanoparticulate metal oxide semiconductors, including TiO2, ZnO, NiO, and alpha-Fe2O3, in acetonitrile or water leads to the formation of indefinitely persistent suspensions in which metal oxide nanoparticles are dispersed in the liquid phase. Dynamic laser scattering reveals the presence of these nanoparticles of dynamic dimensions ranging from about 30 to 200 nm. Time-resolved transmission absorption spectroscopy of these suspensions allows detecting transients decaying in the microsecond time scale that are characterized by a broad absorption spanning the whole visible range and almost coincident temporal profiles in every wavelength that have been assigned to the state of charge separation. This assignment was supported by quenching experiments and by steady-state irradiation of the suspensions containing methyl viologen (electron acceptor) and tetramethyl-p-phenylenediarnine (hole acceptor) as probe molecules that lead to the generation of the visually observable corresponding radical cations.Financial support by Spanish Ministry of Economy and Competitiveness (Severo Ochoa, CTQ2010-18671 and CTQ2012-32315) and Generalidad Valenciana (Prometeo 2012-019) is gratefully acknowledged.Baldovi, HG.; Ferrer Ribera, RB.; Alvaro Rodríguez, MM.; García Gómez, H. (2014). Microsecond transient absorption spectra of suspended semiconducting metal oxide nanoparticles. Journal of Physical Chemistry C. 118(17):9275-9282. https://doi.org/10.1021/jp5018345S927592821181

Understanding the Origin of the Photocatalytic CO2 Reduction by Au- and Cu-Loaded TiO2: A Microsecond Transient Absorption Spectroscopy Study

Recent photocatalytic data for CO2 reduction by H2O using simulated sunlight have shown that, while TiO2 Evonik P25 containing Au nanoparticles (NPs; Au/P25) generates considerably higher amounts of hydrogen than methane, when P25 contains Au-Cu alloy NPs the selectivity toward methane increases dramatically. To gain insight into this photocatalytic behavior, in the present work we have performed a transient absorption spectroscopy study in the microsecond time scale of three samples, namely, Au/P25, Cu/P25, and (Au, Cu)/P25 using 355 (UV) and SR nm (visible) lasers. The transient spectra exhibit as common features a narrower peak at about 320 nm and a broad band from 400 to 800 run. Using oxygen as electron quencher and methanol as hole quencher, the transient signals have been assigned to charge separation. Several cases were observed, including: (i) absence of quenching attributed to the lack of accessibility of the quencher to the site, (ii) quenching of the signal, or (iii) increase of the transient signal intensity attributed to less charge recombination by removal of one of the charge carriers. Of relevance to understand the origin of the photo catalytic CO2 reduction by H2O is the quenching of the charge separated state by these two reagents. In this way, it was observed that H2O exerts a remarkable influence to the transient signal, quenching its intensity in the three samples at the two irradiation wavelengths, except for (Au, Cu)/P25 upon 532 run excitation. Importantly, the distinctive behavior due to the presence of Cu has been attributed to the observed quenching by CO2 of the broad 400-800 nm band when excitation is performed with UV 355 nm light.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa Grant CTQ2012-32315), the Deanship of Scientific Research (DSR), King Abdulaziz University, under Grant No. 75-130-35-HiCi, and Marie Curie Project PIEF-GA-2011-298740 is gratefully acknowledged. The authors acknowledge technical and financial support of KAU. We also thank the Generalidad Valenciana for postgraduate research contract to H.G.B. (Prometeo 2012/2013).Baldovi, HG.; Neatu, S.; Khan, A.; Asiri, AM.; Kosa, SA.; García Gómez, H. (2015). Understanding the Origin of the Photocatalytic CO2 Reduction by Au- and Cu-Loaded TiO2: A Microsecond Transient Absorption Spectroscopy Study. Journal of Physical Chemistry C. 119(12):6819-6827. doi:10.1021/jp5106136S681968271191

Enhanced Visible Light-Driven Photocatalytic Water-Splitting Reaction of Titanate Nanotubes Sensitised with Ru(II) Bipyridyl Complex

The ion exchange of Na+ cations was used to photosensitise titanates nanotubes (Ti-NTs) with tris(2,2’-bipyridine)ruthenium(II) cations (Ru(bpy)32+); this yielded a light-sensitised Ti-NTs composite denoted as (Ru(bpy)3)Ti-NTs, exhibiting the characteristic absorption of Ru(bpy)32+ in visible light. Incident photon-to-current efficiency (IPCE) measurements and the photocatalytic reduction of methyl viologen reaction confirmed that in the photosensitisation of the (Ru(bpy)3)Ti-NTs composite, charge transfer and charge separation occur upon excitation by ultraviolet and visible light irradiation. The photocatalytic potential of titanate nanotubes was tested in the water-splitting reaction and the H2 evolution reaction using a sacrificial agent and showed photocatalytic activity under various light sources, including xenon–mercury lamp, simulated sunlight, and visible light. Notably, in the conditions of the H2 evolution reaction when (Ru(bpy)3)Ti-NTs were submitted to simulated sunlight, they exceeded the photocatalytic activity of pristine Ti-NTs and TiO2 by a factor of 3 and 3.5 times, respectively. Also, (Ru(bpy)3)Ti-NTs achieved the photocatalytic water-splitting reaction under simulated sunlight and visible light, producing, after 4 h, 199 and 282 μmol×H2×gcat−1. These results confirm the effective electron transfer of Ru(bpy)3 to titanate nanotubes. The stability of the photocatalyst was evaluated by a reuse test of four cycles of 24 h reactions without considerable loss of catalytic activity and crystallinity

Enhanced Visible Light-Driven Photocatalytic Water-Splitting Reaction of Titanate Nanotubes Sensitised with Ru(II) Bipyridyl Complex.

Peer reviewed: TruePublication status: PublishedThe ion exchange of Na+ cations was used to photosensitise titanates nanotubes (Ti-NTs) with tris(2,2'-bipyridine)ruthenium(II) cations (Ru(bpy)32+); this yielded a light-sensitised Ti-NTs composite denoted as (Ru(bpy)3)Ti-NTs, exhibiting the characteristic absorption of Ru(bpy)32+ in visible light. Incident photon-to-current efficiency (IPCE) measurements and the photocatalytic reduction of methyl viologen reaction confirmed that in the photosensitisation of the (Ru(bpy)3)Ti-NTs composite, charge transfer and charge separation occur upon excitation by ultraviolet and visible light irradiation. The photocatalytic potential of titanate nanotubes was tested in the water-splitting reaction and the H2 evolution reaction using a sacrificial agent and showed photocatalytic activity under various light sources, including xenon-mercury lamp, simulated sunlight, and visible light. Notably, in the conditions of the H2 evolution reaction when (Ru(bpy)3)Ti-NTs were submitted to simulated sunlight, they exceeded the photocatalytic activity of pristine Ti-NTs and TiO2 by a factor of 3 and 3.5 times, respectively. Also, (Ru(bpy)3)Ti-NTs achieved the photocatalytic water-splitting reaction under simulated sunlight and visible light, producing, after 4 h, 199 and 282 μmol×H2×gcat-1. These results confirm the effective electron transfer of Ru(bpy)3 to titanate nanotubes. The stability of the photocatalyst was evaluated by a reuse test of four cycles of 24 h reactions without considerable loss of catalytic activity and crystallinity

Transient absorption spectroscopy and photochemical reactivity of CAU-8

[EN] CAU-8 is a metal organic framework with the composition [Al(OH)(BPDC)] (BPDC: 4,4'-benzophenone dicarboxylate) whose structure is constituted by chains of corner-sharing AlO6 octahedra connected by BPDC linkers, giving rise to an array of non-intersecting channels. According to the well known photochemical behavior of benzophenone, in the present study we have been able to obtain spectroscopic evidence of the photochemical reactivity of CAU-8, including the generation of short-lived triplet excited states that react with either electron donors (triethylamine) or hydrogen donors (isopropanol) and lead to the corresponding radical anions or ketyl radicals, respectively. These two species have long half live times in CAU-8 and their decay is not complete hundreds of microseconds after the laser pulse. The photochemical activity of the BPDC linker in CAU-8 has been used to promote the radical-induced (co)polymerization of styrene and the coupling of BPDC and ethanol has been followed with IR spectroscopy.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ 2012/32315) is gratefully acknowledged. We also thank the Generalitat Valenciana for financial assistance (Prometeo 2012/2013). HGB also thanks the Generalitat Valenciana for a postgraduate scholarship.Baldovi, HG.; Krüger, M.; Reinsch, H.; Alvaro Rodríguez, MM.; Stock, N.; García Gómez, H. (2015). Transient absorption spectroscopy and photochemical reactivity of CAU-8. Journal of Materials Chemistry C. 3(15):3607-3613. doi:10.1039/C4TC02518KS3607361331

Toxicological properties of two fluorescent carbon quantum dots with onion ring morphology and their usefulness as bioimaging agents

In the present work, two carbon quantum dots with onion ring morphology, C-NOR and C-NOR(Eu) with an average size of 40 nm differing in the absence or presence of Eu3+ as Lewis acids during their preparation were synthesized and fully characterized by several techniques. These nanoparticles can be internalized into human HeLa and Hep3B carcinoma cells where they exhibit interesting photoluminescent properties, in the same manner as in solution, confirming their utility as bioimaging agents. To address this possibility, a complete in vitro toxicological study has been performed here. Viability, proliferation, apoptosis and oxidative stress assessments upon limited or continuous exposure were done. It was observed that both nanoparticles did not show toxicity in both situations at low concentration, although some toxicity has been determined at higher concentrations under continuous exposure. These results support the possible use of C-NOR and C-NOR(Eu) nanoparticles as bioimaging agents.The present work was supported by grants CP13/00252, PI13/1025 from Carlos III Health Institute, and by the European Regional Development Fund (ERDF). In addition, this study was financed by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ-2012-32315), Generalitat Valenciana (Prometeo 2013/19), and FISABIO (UGP-14-95). This work was supported by the Ministerio de Economia y Competitividad (JCI-2012-15124 grant to A. B.-G.), and the Conselleria d'Educacio, Formacio i Ocupacio, Generalitat Valenciana (ACIF/2013/136 grant to M. P). V. M. V. is recipient of a contract from the Ministry of Health of the Valencian Regional Government and Carlos III Health Institute (CES10/030).Blas García, A.; Baldovi, HG.; Polo, M.; Victor, VM.; García Gómez, H.; Herance Camacho, JR. (2016). Toxicological properties of two fluorescent carbon quantum dots with onion ring morphology and their usefulness as bioimaging agents. RSC Advances. 6(36):30611-30622. https://doi.org/10.1039/c5ra27662dS306113062263