First insights into photocatalytic degradation of HDPE and LDPE microplastics by a mesoporous N-TiO2 coating: Effect of size and shape of microplastics

Microplastics (MPs), which are small plastic debris of ≤5 mm size, are polluting the oceans with negative consequences for their biota. In this work, visible-light photocatalysis of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) MPs in aqueous medium using a mesoporous N-TiO2 coating is proposed as an alternative for fighting MP pollution. Spherical primary HDPE MPs were extracted from commercially available facial scrubs, while film-shaped secondary LDPE MPs were obtained from a plastic bag. For each plastic, two different sizes were tested. Degradation was measured by mass-loss and carbonyl-index (CI) calculation. The results obtained reveal that the photocatalytic degradation of HDPE and LDPE MPs using an N-TiO2 coating was affected by the size and shape of the MPs. Smaller MPs led to higher degradation, while film-shaped MPs led to lower degradation that was related to a poorly illuminated and oxygenated reaction medium. These results set the basis for further investigation on the on the design of more effective photocatalytic-reaction systems for decreasing MP inputs to the environment

Incorporation of photoactive TiO2 in an aluminosilicate inorganic polymer by ion exchange

In the present paper, it is described a procedure to ion exchange in an aluminosilicate inorganic polymer (geopolymer) in order to incorporate photoactive TiO 2. Metakaolin base geopolymers synthesized at 40 and 90 °C were chosen to be ion-exchanged with a solutions of (NH 4) 2 TiO (C 2O 4) 2-H 2O with and without previous treatment with NH 4Cl. The final geopolymers were characterized by SEM, FT-IR, Raman, XRD, BET, UV/Vis spectroscopy and fluorescence. It was confirmed that ion-exchange method incorporated anatase TiO 2 particles inside the geopolymer, affecting the geopolymers bond vibration modes of the AlO 4-SiO 4 framework. The observed blue shift in the UV/Vis spectra, suggest that those TiO 2 nanoparticles grew inside the micropores of the geopolymer producing quantum size effects. The photoactivity of such particles was determined by means of photoluminescent spectra and bleaching of methylene blue (MB), which confirms the potential applications of ion-exchanged geopolymers (IEGs) for photocatalytic purposes. © 2011 Elsevier Inc. All rights reserved.J.R. Gasca-Tirado wants to thank CONACYT for scholarship and to A. Galindo-Sifuentes, M.A. Hernandez-Landaverde, J.E. Urbina-Alvarez, F. Rodriguez-Melgarejo, A. Mauricio-Sanchez, J.L. Ojeda-Elizarraras, M.S. Garcia-Guillen, C. Vazquez-Ramos and G. Fonseca-Hernandez for their kind technical assistance.Gasca-Tirado, JR.; Manzano Ramirez, A.; Villaseñor-Mora, C.; Muñiz-Villarreal, MS.; Zaldivar-Cadena, AA.; Rubio-Ávalos, JC.; Amigó Borrás, V.... (2012). Incorporation of photoactive TiO2 in an aluminosilicate inorganic polymer by ion exchange. Microporous and Mesoporous Materials. 153:282-287. doi:10.1016/j.micromeso.2011.11.026S28228715

The effect of temperature on the geopolymerization process of a metakaolin-based geopolymer

This paper describes the effect of different curing temperatures on the geopolymerization process, physical, mechanical and optical properties of a metakaolin-based geopolymer activated by alkali. The influence of different curing temperatures (within the range 30 to 90 °C) was studied systematically by means of differential scanning calorimetry (DSC), SEM, UV/Vis Spectrophotometry, Leaching analysis and Brunauer-Emmet-Teller method (BET). The results showed the existence of an optimum temperature at which the geopolymer presents the best physical and mechanical properties. The geopolymers cured at 30 and 90 °C presented high porosity, and were translucent to the Visible light, which makes possible to tailor this inorganic polymers for optical and photocatalytic applications. © 2011 Elsevier B.V. All rights reserved.Muniz-Villarreal M.S. wants to thank CONACYT for scholarship, and Maria-Carmen Delgado, Eleazar-Urbina and Martin-Adelaido Landaverde for their technical assistance.Muñiz-Villarreal, MS.; Manzano Ramirez, A.; Sampieri-Bulbarela, S.; Gasca-Tirado, JR.; Reyes-Araiza, JL.; Rubio-Ávalos, JC.; Pérez Bueno, JJ.... (2011). The effect of temperature on the geopolymerization process of a metakaolin-based geopolymer. Materials Letters. 65(5):995-998. doi:10.1016/j.matlet.2010.12.049S99599865

CTA – the World’s largest ground-based gamma-ray observatory

International audienc

Searching for very-high-energy electromagnetic counterparts to gravitational-wave events with the Cherenkov Telescope Array

The detection of electromagnetic (EM) emission following the gravitational wave (GW) event GW170817 opened the era of multi-messenger astronomy with GWs and provided the first direct evidence that at least a fraction of binary neutron star (BNS) mergers are progenitors of short Gamma-Ray Bursts (GRBs). GRBs are also expected to emit very-high energy (VHE, > 100 GeV) photons, as proven by the recent MAGIC and H.E.S.S. observations. One of the challenges for future multi-messenger observations will be the detection of such VHE emission from GRBs in association with GWs. In the next years, the Cherenkov Telescope Array (CTA) will be a key instrument for the EM follow-up of GW events in the VHE range, owing to its unprecedented sensitivity, rapid response, and capability to monitor a large sky area via scan-mode operation. We present the CTA GW follow-up program, with a focus on the searches for short GRBs possibly associated with BNS mergers. We investigate the possible observational strategies and we outline the prospects for the detection of VHE EM counterparts to transient GW events

The Cherenkov Telescope Array transient and multi-messenger program

The Cherenkov Telescope Array (CTA) is a next generation ground-based very-high-energy gamma-ray observatory that will allow for observations in the >10 GeV range with unprecedented photon statistics and sensitivity. This will enable the investigation of the yet-marginally explored physics of short-time-scale transient events. CTA will thus become an invaluable instrument for the study of the physics of the most extreme and violent objects and their interactions with the surrounding environment. The CTA Transient program includes follow-up observations of a wide range of multi-wavelength and multi-messenger alerts, ranging from compact galactic binary systems to extragalactic events such as gamma-ray bursts (GRBs), core-collapse supernovae and bright AGN flares. In recent years, the first firm detection of GRBs by current Cherenkov telescope collaborations, the proven connection between gravitational waves and short GRBs, as well as the possible neutrino-blazar association with TXS 0506+056 have shown the importance of coordinated follow-up observations triggered by these different cosmic signals in the framework of the birth of multi-messenger astrophysics. In the next years, CTA will play a major role in these types of observations by taking advantage of its fast slewing (especially for the CTA Large Size Telescopes), large effective area and good sensitivity, opening new opportunities for time-domain astrophysics in an energy range not affected by selective absorption processes typical of other wavelengths. In this contribution we highlight the common approach adopted by the CTA Transients physics working group to perform the study of transient sources in the very-high-energy regime

Monte Carlo Simulations and Validation of NectarCAM, a Medium Sized Telescope Camera for CTA

The upcoming Cherenkov Telescope Array (CTA) ground-based gamma-ray observatory will open up our view of the very high energy Universe, offering an improvement in sensitivity of 5-10 times that of previous experiments. NectarCAM is one of the proposed cameras for the Medium-Sized Telescopes (MST) which have been designed to cover the core energy range of CTA, from 100 GeV to 10 TeV. The final camera will be capable of GHz sampling and provide a field of view of 8 degrees with its 265 modules of 7 photomultiplier each (for a total of 1855 pixels). In order to validate the performance of NectarCAM, a partially-equipped prototype has been constructed consisting of only the inner 61-modules. It has so far undergone testing at the integration test-bench facility in CEA Paris-Saclay (France) and on a prototype of the MST structure in Adlershof (Germany). To characterize the performance of the prototype, Monte Carlo simulations were conducted using a detailed model of the 61 module camera in the CORSIKA/sim_telarray framework. This contribution provides an overview of this work including the comparison of trigger and readout performance on test-bench data and trigger and image parameterization performance during on-sky measurements

Sensitivity of CTA to gamma-ray emission from the Perseus galaxy cluster

In these proceedings we summarize the current status of the study of the sensitivity of the Cherenkov Telescope Array (CTA) to detect diffuse gamma-ray emission from the Perseus galaxy cluster. Gamma-ray emission is expected in galaxy clusters both from interactions of cosmic rays (CR) with the intra-cluster medium, or as a product of annihilation or decay of dark matter (DM) particles in case they are weakly interactive massive particles (WIMPs). The observation of Perseus constitutes one of the Key Science Projects to be carried out by the CTA Consortium. In this contribution, we focus on the DM-induced component of the flux. Our DM modelling includes the substructures we expect in the main halo which will boost the annihilation signal significantly. We adopt an ON/OFF observation strategy and simulate the expected gamma-ray signals. Finally we compute the expected CTA sensitivity using a likelihood maximization analysis including the most recent CTA instrument response functions. In absence of signal, we show that CTA will allow us to provide stringent and competitive constraints on TeV DM, especially for the case of DM decay

The Cherenkov Telescope Array: layout, design and performance

The Cherenkov Telescope Array (CTA) will be the next generation very-high-energy gamma-ray observatory. CTA is expected to provide substantial improvement in accuracy and sensitivity with respect to existing instruments thanks to a tenfold increase in the number of telescopes and their state-of-the-art design. Detailed Monte Carlo simulations are used to further optimise the number of telescopes and the array layout, and to estimate the observatory performance using updated models of the selected telescope designs. These studies are presented in this contribution for the two CTA stations located on the island of La Palma (Spain) and near Paranal (Chile) and for different operation and observation conditions

Sensitivity of the Cherenkov Telescope Array to emission from the gamma-ray counterparts of neutrino events

We investigate the possibility of detection of the VHE gamma-ray counterparts to the neutrino astrophysical sources within the Neutrino Target of Opportunity (NToO) program of CTA using the populations simulated by the FIRESONG software to resemble the diffuse astrophysical neutrino flux measured by IceCube. We derive the detection probability for different zenith angles and geomagnetic field configurations. The difference in detectability of sources between CTA-North and CTA-South for the average geomagnetic field is not substantial. We investigate the effect of a higher night-sky background and the preliminary CTA Alpha layout on the detection probability