Effect of temperature on the physical, optical and photocatalytic properties of TiO2 nanoparticles

In this paper we describe the effect of calcination temperature on the structural, morphological, optical and photocatalytic properties of TiO2 nanoparticles. The titanium dioxide powders were produced by the sol–gel method starting from titanium tetraisopropoxide (TTIP) in neutral aqueous medium (pH 5.5). After that, the TiO2 nanoparticles were treated at three different calcination temperatures for 4 h: 100, 450 and 800 °C. Then, the powders were characterized by XRD, Raman and photoluminescence techniques. We observed the anatase phase for the powders treated at 100 and 450 °C and rutile for that treated at 800 °C. The photocatalytic activity of the TiO2 powders was investigated using Methylene Blue test and showed a strong correlation with the temperature (i.e. TiO2 phase). The better photocatalysis exhibited by the nanoparticles treated at 100 and 450 °C compared to the powder at 800 °C was due to the higher recombination of photo-generated electrons and holes of rutile with respect to anatase

Emittance Characterization of Ion Beams Provided by Laser Plasma

Laser ion sources offer the possibility to obtain ion beams useful for particle accelerators. Nanosecond pulsed lasers at intensities of the order of 108 W/cm2, interacting with solid matter in a vacuum, produce plasma of high temperature and high density. To increase the ion energy, an external post-acceleration system can be employed by means of high voltage power supplies of some tens of kV. In this work, we characterize the ion beams provided by an LIS source and post-accelerated. We calculated the produced charge and the emittance. Applying 60 kV of accelerating voltage and laser irradiance of 0.1 GW/cm2 on the Cu target, we obtain 5.5 mA of output current and normalized beam emittance of 0.2 mm mrad. The brightness of the beams was 137 mA (mm mrad)−2

A Proton Source via Laser Ablation of Hydrogenated Targets

In this work we present results on the extraction of proton beams from a plasma generated by pulsed laser ablation of solid hydrogenated targets. The laser used was an excimer KrF operating at low irradiances (108–109 W/cm2) and nanosecond pulse duration. The ablated targets were disks obtained by compression of TiH2 powder. The ion emission was analyzed by the time-of-flight technique using a Faraday cup as ion collector. In order to improve the ion yield, an electrostatic extraction system was applied. Studies on the produced plasma for different laser irradiances and accelerating voltages have been performed. The results obtained show that this setup is suitable for a high yield proton source

Electron beams produced by innovative photocathodes based on nanodiamond layers

The investigation of two different photocathodes (PCs) based on nanodiamond (ND) layers, irradiated by a KrF nanosecond excimer laser (wavelength, \ensuremath{\lambda}=248\text{ }\text{ }\mathrm{nm}; photon energy, ${E}_{\mathrm{Ph}}=5\text{ }\text{ }\mathrm{eV}$) is reported. The ND layers were deposited by means of a pulsed spray technique. Specifically, the active layer of each PC consisted of untreated (as-received) and hydrogenated ND particles, 250 nm in size, sprayed on a $p$-doped silicon substrate. The ND-based photocathodes were tested in a vacuum chamber at {10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{mbar} and compared to a Cu-based one, used as reference. All the photocathodes were irradiated at normal incidence. The quantum efficiency (QE) of the photocathodes was assessed. QE values of the ND-based photocathodes were higher than that of the reference one. In particular, the hydrogenated ND-based PC exhibited the highest QE due to the negative electron affinity that results from the surface terminated by hydrogen. Additionally, the photocathode surface/local temperature and the multiphoton process contribution to the electron emission were studied

Enhanced adsorption capacity of porous titanium dioxide nanoparticles synthetized in alkaline sol

Abstract In recent years, the exploitation of natural resources and industrial development have led to the production of harmful pollutants. Much of these contaminants end up in water resources, reducing the availability of drinking water. Therefore, it is necessary to find remedies to this situation. Solutions could be the adsorption or the degradation through photocatalysis of these compounds. A good candidate for this task is titanium dioxide (TiO2), due to its non-toxicity, stability and low cost. In this work, we propose a novel synthesis of TiO2 nanoparticles (NPs), with high adsorption capacity, produced at low temperature in alkaline environment. Adsorption tests were conducted using methylene blue and diclofenac as model pollutants. Moreover, the obtained NPs have been characterized through Raman spectroscopy, Scanning and Transmission electron microscopies and with thermogravimetric analysis. The results showed a porous structure with a high surface area, able to efficiently adsorb large amounts of dye from the aqueous solution. These properties make the obtained TiO2 powders suitable for applications devoted to the adsorption and recovery of harmful compounds. Graphic abstrac

Quasi-monoenergetic proton beams by laser-plasma X-rays

We report the details of a technique for the production of proton beams with very low energy spread exploiting the short soft X-rays obtained by laser ablation. These beams have been generated by the dissociation and ionization of an hydrogen buffer gas induced by the laser-plasma X-rays and then accelerated by means of an electrostatic accelerator. Their properties have been analyzed through the time-of-flight method applying different accelerating voltages. The resulting energetic spread ranges between 6 and 11%, as a function of the applied voltage. Such a system could be extremely useful for producing quasi-monoenergetic proton beams

UV photocathodes based on nanodiamond particles: Effect of carbon hybridization on the efficiency

Photocathodes working in reflection-mode are made of rich-diamond (R-D) and rich-graphite (R-G) nanodiamond (ND) layers, deposited on different conductive substrates by means of the pulsed spray technique at low deposition temperatures (120 and 150 °C) and starting from two types of ND particles. The two powders with an average grain size of 250 nm have variable sp2(graphite phase) and sp3(diamond phase) hybridized carbon contents, as assessed by Raman spectroscopy and transmission electron microscopy. The ND particles are employed as-received or treated in H2microwave plasmas. The principal aim of the paper is the comparative study of R-D and R-G photocathodes in the vacuum ultraviolet spectral range from 140 to 210 nm, where they exhibit a high quantum efficiency and a good stability over time upon exposure to air. Specifically, the quantum efficiency values at 140 nm of photocathodes based on hydrogenated R-D and R-G layers are 26.8 and 47%, respectively, proving that the more defective ND particles are, the more efficiently they emit. Moreover, these QE values are higher than those derived by photocathodes based on microwave plasma enhanced chemical vapor deposition diamond films (14% at 140 nm) and the highest recorded in the state of international art

Proton extraction from transition metals using PLATONE

In thisworkwepresentastudyonprotonbeamsextractionfromaplasmageneratedbypulsedlaser ablation oftitaniumandtantalumdisks.ThedeviceusedwasthePLATONElaserionsourceoperatingat the LEASLaboratoryinLecce,Italy.ItisbasedonaKrFlaseroperatingatlowirradiance(109–1010 W/cm2) and nspulseduration.Theprotonandionsemissionwasanalyzedbythetime-of-flight techniqueusing a Faradaycupasioncollectorandanelectrostaticbarriertoidentifytheparticles.Studiesonthe produced protonsandionsatdifferentlaserirradiancevalueswereperformed.Theextractedbeams showedhighproton flux upto1010 protons/cm2

Comparison between photoemitting and colloidal properties of nanodiamond particles

In this paper, we present an investigation on two types of nanodiamond (ND) powders with average size of particles around 250nm and having different sp2 (graphite phase) and sp3 (diamond phase) carbon contents. The ND surface modification is carried out by physical methods i.e. treatments in H2 microwave plasma. The quantum efficiency (QE) of photocathodes and the stability of aqueous dispersions are assessed by photoemission and zeta potential (ZP) measurements, respectively.The resultant hydrogenated surface affects in the solid state the QE of ND-based photocathodes and in solution the particle ZP. The effect of the hydrogen treatment is beneficial inducing an enhancement of photocathode QE and a corresponding increase of the ZP. A schematized energy diagram is proposed to illustrate and explain the strong correlation between QE and ZP parameters