On the impact of Cu dispersion on CO2 photoreduction over Cu/TiO2

A family of Cu/TiO2 catalysts was prepared using a refined sol–gel method, and tested in the photocatalytic reduction of CO2 by H2O to CH4 using a stirred batch, annular reactor. The resulting photoactivity was benchmarked against pure TiO2 nanoparticles (synthesised by an identical sol–gel route). CO2 photoreduction exhibited a strong volcano dependence on Cu loading, reflecting the transition from 2-dimensional CuOx nanostructures to 3-dimensional crystallites, with optimum CH4 production observed for 0.03 wt.% Cu/TiO2.

Evaluation on a 60 GHz radio over fiber system employing photonic up conversion and optically beam formed linear array antenna for broadband indoor access

In this study, two linear coplanar array antennas based on Indium Phosphide (InP) substrate are designed, presented and compared in terms of bandwidth and gain. Slot introduction in combination with coplanar structure is investigated, providing enhanced antenna gain and bandwidth at the 60 GHz frequency band. In addition the proposed array antennas are evaluated in terms of integration with a high-speed photodiode and investigated in terms of matching, providing a bandwidth that reaches 2 GHz. Moreover a potential beam forming scenario combined with photonic up-conversion scheme has been proposed. © 2013 IEEE.

Cost-efficient OFDM generation at 60-GHz by heterodyne technique with direct modulation and envelope detector

A cost-effective radio over fiber system to up-convert and transmit multigigabit signals at 60 GHz is presented. A low intermediate frequency OFDM signal is used to directly modulate a laser, which is combined with an independent unmodulated laser. The generated millimeter wave frequency can be adjusted by tuning the frequency separation between the lasers. Since no external modulator is required, this technique is low-cost and it is easily integrable in a single chip. In this paper, we present numerical results showing the feasibility of generating an IEEE 802.15.3c compliant 3.5-Gbps 60-GHz OFDM. We show that received signal quality is not limited by the lasers' linewidth but by the relative intensity noise. © 2013 IEEE.

Permanent matching of coupled optical bottle resonators with better than 0.16 GHz precision

The fabrication precision is one of the most critical challenges to the creation of practical photonic circuits composed of coupled high Q-factor microresonators. While very accurate transient tuning of microresonators based on local heating has been reported, the record precision of permanent resonance positioning achieved by post-processing is still within 1 and 5 GHz. Here we demonstrate two coupled bottle microresonators fabricated at the fiber surface with resonances that are matched with a better than 0.16 GHz precision. This corresponds to a better than 0.17 Å precision in the effective fiber radius variation. The achieved fabrication precision is only limited by the resolution of our optical spectrum analyzer and can be potentially improved by an order of magnitude.

Studio di stati fotoeccitati in nanoparticelle di V-TiO2 mediante scattering inelastico risonante di raggi X

La TiO2 è uno dei materiali più studiati degli ultimi decenni. I motivi sono da ricercarsi nelle sue numerose applicazioni, possibili in molti campi come dispositivi fotovoltaici, depurazione da agenti inquinanti o filtraggio di raggi UV. Per le celle elettrochimiche in particolare, il biossido di titanio offre molti vantaggi, ma non è privo di ostacoli. Il limite principale è lo scarso assorbimento dello spettro visibile, dovuto all’energy gap elevato (circa 3.2 eV). La ricerca da diversi anni si concentra sul tentativo di aumentare l’assorbimento di luce solare: promettenti sono i risultati raggiunti grazie alla forma nanoparticellare della TiO2, che presenta proprietà diverse dal materiale bulk. Una delle strategie più studiate riguarda il drogaggio tramite impurità, che dovrebbero aumentare le prestazioni di assorbimento del materiale. Gli elementi ritenuti migliori a questo scopo sono il vanadio e l’azoto, che possono essere usati sia singolarmente che in co-doping. In questo lavoro abbiamo realizzato la crescita di nanoparticelle di V-TiO2, tramite Inert Gas Condensation. La morfologia e la struttura atomica sono state analizzate attraverso microscopia a trasmissione, analizzandone la mappe tramite image processing. Successivamente abbiamo studiato le proprietà di assorbimento ottico dei campioni, nello spettro visibile e nel vicino ultravioletto, attraverso il metodo della riflettanza diffusa, determinando poi il bandgap tramite Tauc Plot. L’esperimento centrale di questo lavoro di tesi è stato condotto sulla beamline ID26 dell’European Synchrotron Radiation Facility, a Grenoble. Lì, abbiamo effettuato misure XANES, allo scopo di studiare gli stati fotoeccitati del materiale. L’eccitazione avveniva mediante laser con lunghezza d’onda di 532 nm. Tramite gli spettri, abbiamo analizzato la struttura locale e lo stato di ossidazione del vanadio. Le variazioni indotta dal laser hanno permesso di capire il trasferimento di carica e determinare la vita media.

Toxicity evaluation of TiO2 Nanoparticles embedded in consumer products

Lo studio è orientato alla determinazione dei rischi tossici posti dalle nanoparticelle di diossido di titanio rilasciate in ambiente marino. L’organismo modello utilizzato per questo studio è la diatomea Thalassiosira pseudonana, la quale è stata scelta per la sua semplicità biologica unita alla fondamentale rilevanza nella catena alimentare e nell’ecosistema marino. Oltre alle nanoparticelle prodotte industrialmente, questo studio ha lo scopo di determinare e confrontare la tossicità delle nanoparticelle utilizzate in alcuni prodotti di cura personale (in particolare crema solare e dentifricio), estraendole direttamente da essi. I nostri risultati mostrano una notevole ridondanza nel legame tra la natura (il tipo) delle nanoparticelle e l’inibizione della normale crescita delle diatomee, che supera la correlazione con tutti gli altri parametri monitorati (concentrazione di nanoparticelle, tempo di esposizione, pH, carica superficiale e dimensione delle particelle stesse), sebbene gli altri parametri risultino direttamente legati agli effetti inibitori. Tali risultati suggeriscono un’intensificazione della ricerca nell’ambito delle nanotecnologie, orientata allo sviluppo di nanomateriali “sostenibili”, ovvero dei quali sono note le potenzialità di impiego, ma anche gli aspetti negativi, che possono di conseguenza essere monitorati con maggiore consapevolezza.

Caracterização e avaliação da atividade fotocatalítica de catalisadores baseados no TiO2, sintetizados mediante hidrólise em uma mistura de solventes

This study involved the synthesis of photocatalysts based on titanium dioxide (TiO2). The photocatalysts were synthesized by the sol-gel method using three different proportions of acetone (25%, 50% and 75% v/v) in water/acetone mixtures, in order to control the hydrolysis of the precursor of titanium (titanium tetraisopropoxide). Aiming to investigate the structural, morphological and electronic changes provoked by the use of the solvent mixtures, different methodologies were used to characterize the oxides, such as X-ray diffraction (XRD), RAMAN spectroscopy, UV-Vis diffuse reflectance spectroscopy, and measurements of specific surface area (BET). XRD combined to RAMAN analyses revealed that the products are two-phase highly crystalline oxides involving anatase as main phase and brookite. Besides, the refined XRD using the method of Rietveld demonstrated that the presence of acetone during the synthesis influenced in the composition of the crystalline phases, increasing the proportion of the brookite phase between 13 and 22%. The band gap energy of these oxides practically did not suffer changes as function of the synthesis conditions. As shown by the isotherm, these photocatalysts are mesoporous materials with mean diameter of pores of 7 nm and approximately 20% of porosity. The surface area of the oxides prepared by hydrolysis in presence of acetone was 12% higher compared to the bare oxide. After characterized, these oxides had their photocatalytic activities evaluated by photodegradation of the azo dyes Ponceau 4R (P4R), Tartrazine (TTZ) and Reactive Red 120 (RR120), and also by the ability to mediate the photocatalytic production of hydrogen. Using the most efficient photocatalyst, the mineralization achieved for the dyes P4R, RR120 and TTZ was of respectively 83%, 79% and 56% in 120 minutes of reaction, while the discoloration of P4R e RR120 reached 100% and 94% for TTZ. In addition, the same photocatalyst in the presence of 0.5% w/w of Platinum and suspended in a 5:1 v/v water/methanol mixture, produced 56 mmol of gaseous hydrogen in five hours of experiment, corresponding to a specific rate of hydrogen production of 139.5 mmol h-1 g-1.

Probing the Role of Thermally Reduced Graphene Oxide in Enhancing Performance of TiO2 in Photocatalytic Phenol Removal from Aqueous Environments

We thank the INSA-RSE bilateral exchange programme for financial assistance (PD) and the Petroleum Technology Development Fund (PTDF, Nigeria) for the award of PhD scholarship, as well as Abubakar Tafawa Balewa University, Bauchi-Nigeria for the granted fellowship (H.A).

Probing the Role of Thermally Reduced Graphene Oxide in Enhancing Performance of TiO2 in Photocatalytic Phenol Removal from Aqueous Environments

We thank the INSA-RSE bilateral exchange programme for financial assistance (PD) and the Petroleum Technology Development Fund (PTDF, Nigeria) for the award of PhD scholarship, as well as Abubakar Tafawa Balewa University, Bauchi-Nigeria for the granted fellowship (H.A).

Lead oxide-modified TiO2 photocatalyst: tuning light absorption and charge carrier separation by lead oxidation state

Modification of TiO2 with metal oxide nanoclusters such as FeOx, NiOx has been shown to be a promising approach to the design of new photocatalysts with visible light absorption and improved electron–hole separation. To study further the factors that determine the photocatalytic properties of structures of this type, we present in this paper a first principles density functional theory (DFT) investigation of TiO2 rutile(110) and anatase(001) modified with PbO and PbO2 nanoclusters, with Pb2+ and Pb4+ oxidation states. This allows us to unravel the effect of the Pb oxidation state on the photocatalytic properties of PbOx-modified TiO2. The nanoclusters adsorb strongly at all TiO2 surfaces, creating new Pb–O and Ti–O interfacial bonds. Modification with PbO and PbO2 nanoclusters introduces new states in the original band gap of rutile and anatase. However the oxidation state of Pb has a dramatic impact on the nature of the modifications of the band edges of TiO2 and on the electron–hole separation mechanism. PbO nanocluster modification leads to an upwards shift of the valence band which reduces the band gap and upon photoexcitation results in hole localisation on the PbO nanocluster and electron localisation on the surface. By contrast, for PbO2 nanocluster modification the hole will be localised on the TiO2 surface and the electron on the nanocluster, thus giving rise to two different band gap reduction and electron–hole separation mechanisms. We find no crystal structure sensitivity, with both rutile and anatase surfaces showing similar properties upon modification with PbOx. In summary the photocatalytic properties of heterostructures of TiO2 with oxide nanoclusters can be tuned by oxidation state of the modifying metal oxide, with the possibility of a reduced band gap causing visible light activation and a reduction in charge carrier recombination.

Continuous flow gas phase photoreforming of methanol at elevated reaction temperatures sensitised by Pt/TiO2

Gas phase photoreforming of methanol using a Pt/TiO2 photocatalyst has been performed under flow conditions at elevated temperatures. Comparing the activity of the reforming process as a function of temperature under dark and irradiated conditions shows a significant enhancement in the rate of H2 production using the photo-assisted conditions at temperatures between 100-140 °C. At higher temperatures, the effect of irradiation is small with the process dominated by the thermal process. Deactivation of the catalyst was observed under irradiation but the catalyst was easily regenerated using an oxygen treatment at 120 °C. Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) showed that the activity of the catalyst could be correlated with the presence of the photogenerated trapped electrons. In addition, lower amounts of CO adsorbed on Pt, compared to those observed in the dark reaction, were found for the UV-irradiated systems. It is proposed that CO and adsorbed intermediates, such as formate, can act as inhibitors in the photoreforming process and this is further supported by the observation that, before and after the regeneration process in O2, the CO and surface adsorbed organic intermediate products are removed and the activity is recovered.

Mechanochemical synthesis of TiO2/NiFe2O4 magnetic catalysts for operation under RF field

Composite NiFe2O4–TiO2 magnetic catalysts were prepared by mechanochemical synthesis from a mixture of titania supported nickel ferrite nanoparticles and P25 titania (Evonic). The former provides fast and efficient heating under radiofrequency field, while the latter serves as an active catalyst or catalyst support. The highest heating rate was observed over a catalyst prepared for a milling time of 30 min. The catalytic activity was measured over the sulfated composite catalysts in the condensation of aniline and 3-phenylbutyric acid in a stirred tank reactor and in a continuous RF heated flow reactor in the 140–170 °C range. The product yield of 47% was obtained over the sulfated P25 titania catalyst in the flow reactor.

Mechanochemical solvent-free synthesis of Sn-β Zeolite and Ag2O/TiO2 catalysts

Preparations of heterogeneous catalysts are usually complex processes that involve several procedures as precipitation, crystallization and hydrothermal treatments. This processes are really dependent by the operative conditions such as temperature, pH, concentration etc. Hence the resulting product is extremely affected by any possible variations in these parameters making this synthesis really fragile. With the aim to improve these operations has been decided to exploit a new possible strong environment-respectful process by mechanochemical treatment, which permits to carry out solvent free-solvent synthesis exploiting the Mixer Mill MM400 (Retsch) in order to have reproducible results. Two different systems have been studied in this kind of synthesis: a tin β -zeolite tested in a H-trasnfer reaction of cyclohexanone and a silver on titania catalyst used in the fluorination of 2,2 dimethyl glucaric acid. Each catalyst has been characterized by different techniques in order to understand the transformations involved in the mechanochemical treatment.

Effet du greffage de TiO2 à la surface de fibres de lin sur les propriétés mécaniques d'un composite PLA/fibre de lin longues unidirectionnelles

Les matériaux composites sont utilisés dans beaucoup de domaines pour leurs propriétés mécaniques spécifiques, leur mise en forme facile et leur bas coût. Cependant, lorsque les composites pétro-sourcées sont en fin de vie, le traitement des déchets a un fort impact environnemental. C’est pour cette raison que les industriels se tournent vers des matériaux bio-sourcés. Ils souhaitent ainsi abaisser le coût des matières premières mais aussi se donner une image plus « verte » grâce à l’utilisation de matériaux renouvelables et/ou compostables. Le projet présenté s’inscrit dans dans cette optique où il est question d’élaborer de nouveaux composites à renfort et matrices bio-sourcés et tout particulièrement des composites fibre de lin/acide polylactique (PLA). Ces derniers sont généralement appelés bio-composites. L’originalité de cette étude réside dans le traitement des fibres de lin afin de les compatibilité avec la matrice PLA. Le traitement consiste au greffage de dioxyde de titane sur la surface de fibres de lin fonctionnalisée par oxydation au TEMPO. Ces fibres longues sont ensuite utilisées comme renfort sous forme de tissu unidirectionnel dans la matrice PLA. Le comportement mécanique en traction, flexion et la résistance à l’impact de ces biocomposites sont étudiés afin d’analyser l’influence du traitement des fibres sur leur performances.

Implications of TiO2 surface functionalization on polycrystalline mixed halide perovskite films and photovoltaic devices

We exploit TiO2 surface functionalization as a tool to induce the crystallization process of CH3NH3PbI3xClx perovskite thin films resulting in a reduction of the degree of orientation of the (110) crystallographic planes. Notably, the variation of the film crystalline orientational order does not affect the photovoltaic performances of the perovskite-based devices, whose efficiency remains mostly unchanged. Our findings suggest that other factors are more significant in determining the device efficiency, such as the non-homogenous coverage of the TiO2 surface causing charge recombination at the organic/TiO2 interface, defect distribution on the perovskite bulk and at the interfaces, and transport in the organic or TiO2 layer. This observation represents a step towards the comprehension of the perovskite film peculiarities influencing the photovoltaic efficiency for high performance devices.