An improvement of photocatalytic activity of TiO2 Degussa P25 powder

The photocatalytic activities of Degussa P25 powders annealed at various temperatures in vacuum and air were studied together with investigations of their compositions by XPS, of their crystal structures by XRD and of their specific surface areas by BET. It is shown that the photocatalytic activity of P25 powders was remarkably enhanced after vacuum annealing; the kinetic coefficient can be raised by 75% during annealing at 400 degrees C. It is obvious that this enhancement is not related to the adhesion ability of the P25 powders. (C) 2015 Elsevier B.V. All rights reserved.Fundacao para a Ciencia e Tecnologia (FCT) Portugal; FCT [Pest-OE/CTM/LA0024/2013]info:eu-repo/semantics/publishedVersio

Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[ 6] arene and calix[ 8] arene, with this feature much more evident for calix[ 6] arene. For calix[ 4] arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[ 4] arene and from the constrained dimers inside the cavities of calix[ 6] arene and calix[ 8] arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[ 6] arene and calix[ 8] arene. This feature is particularly relevant for calix[ 6] arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[ 6] arene and calix[ 8] arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene

Electrochemical properties of oxygen-enriched carbon-based nanomaterials

The introduction of oxygen moieties on a carbon-based material to enhance the electrode material activity for the oxygen reduction reaction (ORR) is a most unexplored experimental approach due to the risk of reducing the electron-transport ability of the electrode material. Herein, it is shown that carbon nanomaterials generated electrochemically from graphite can simultaneously show an anomalous high content of oxygen functionalities and a high heterogeneous electron transfer rate. This study was demonstrated with a set of four samples, prepared at different galvanostatic conditions. All the samples display a non-ordered carbon network dominated by aromatic rings, an O/C ratio greater than 0.4, but different amounts of various oxygen-containing functionalities. The electron-transport properties of the obtained films were appraised by cyclic voltammetry and electrochemical impedance spectroscopy. The application of these metal-free electrode materials to the ORR in the alkaline medium has shown a direct correlation between the materials catalytic activity (potential onset, kinetic current and number of electrons transferred) and the Cdouble bondO amount, whereas a negative correlation was found for Csingle bondO. Their excellent ability for the H2O2 reduction was also demonstrated. This work opens a new perspective on the use of highly oxidized carbon nanomaterials in electrocatalysis.publishe

A Comparative Study

This research was funded by EU funds through the FEDER European Regional Development Fund (project LISBOA-02-0145-FEDER-031311) project LA/P/0056/2020 of Institute of Molecular Sciences, and LA/P/0140/2020 of i4HB, project UID/EEA/00066/2020 from the Center of Technology and Systems, and from the Instituto Politécnico de Lisboa with IPL/2018/STREAM_ISEL and IPL/2020/AGE-SPReS_ISEL projects. APCR and AMF thank the Instituto Superior Técnico for the scientific employment contracts IST-ID/119/2018 and IST-ID/131/2018, respectively. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Aiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobi-lization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV–Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.publishersversionpublishe

TiO 2

Nanocomposites TiO2-CdS with different relative contents of CdS (molar ratios Cd/Ti = 0.02, 0.03, 0.05, 0.1, 0.2, and 0.5) were studied. The structural, photophysical, and chemical properties were investigated using XRD, Raman spectroscopy, XPS, GSDR, and LIL. XRD and Raman results confirmed the presence of TiO2 and CdS with intensities dependent on the ratio Cd/Ti. The presence of CdSO4 was detected by XPS at the surface of all TiO2-CdS composites. The relative amount of sulphate was dependent on the CdS loading. Luminescence time-resolved spectra clearly proved the existence of an excitation transfer process from CdS to TiO2 through the luminescence emission from TiO2 after excitation of CdS at λexc=410 nm, where no direct excitation of TiO2 occurs. Photodegradation of a series of aromatic carboxylic acids—benzoic, salicylic, 4-bromobenzoic, 3-phenylpropionic, and veratric acids—showed a great enhancement in the photocatalytic efficiency of the TiO2-CdS composites, which is due, mainly, to the effect of the charge carriers’ increased lifetime. In addition, it was shown that the oxidation of CdS to CdSO4 did not result in the deactivation of the photocatalytic properties and even contributed to enhance the degradation efficiency

Electrostatic interactions between graphene layers and their environment

We analyze the electrostatic interactions between a single graphene layer and a SiO$_2$ susbtrate, and other materials which may exist in its environment. We obtain that the leading effects arise from the polar modes at the SiO$_2$ surface, and water molecules, which may form layers between the graphene sheet and the substrate. The strength of the interactions implies that graphene is pinned to the substrate at distances greater than a few lattice spacings. The implications for graphene nanoelectromechanical systems, and for the interaction between graphene and a STM tip are also considered.Comment: improved introduction, section on suspended graphene correcte

A new and easy method for anchoring manganese salen on MCM-41

This work reports a new method to covalently attach manganese salophen complex onto MCM-41, using a diisocyanate as a binder. The prepared catalyst was tested on the liquid phase limonene oxidation reaction. Diluted t-Butyl hydroperoxide was used as oxygen supplier. Limonene oxide, carveol and carvone are formed, but the main product obtained was a polymer. The preservation of the MCM-41 channel system was checked by X-ray diffraction and nitrogen adsorption analysis. The use of the same catalyst sample in four consecutive experiments, without loss of activity, is a confirmation of the success of the anchoring process

Poly(dimethylsiloxane) as a pre-coating in layer-by-layer films containing phosphotungstate nanoclusters electrochemically sensitive toward s-triazines

One of the major advantages of the Layer-by-Layer (LbL) deposition technique is the possible control of molecular architecture, not only to achieve optimized properties but also to seek synergy among different materials. In this study, LbL films containing nanoclusters of a Keggin type polyoxometalate, phosphotungstic acid (HPW), alternated with the polycation poly(allylamine hydrochloride) (PAH) were deposited on indium-tin oxide (ITO) substrates. The electrochemical properties of the hybrid LbL film investigated in acidic conditions indicated no significant desorption of HPW, when a layer of poly(dimethylsiloxane) terminated with 3-aminopropyl groups (PDMS) was previously deposited on the ITO substrate. Such effect occurred because PDMS prevents desorption of HPW from the hybrid film, as shown by X-ray Photoelectron Spectroscopy (XPS) analyses. The porous structures of the films were revealed by Fourier transform infrared reflection absorption spectroscopy, scanning electron microscopy and XPS. PDMS/PAH as a pre-coating allowed the HPW/PAH films to be sensitive to the electrochemical detection of the triazines atrazine and melamine. In conclusion, the precise control of the LbL films architecture is important to develop opportunities for new applications. © 2014 The Royal Society of Chemistry.One of the major advantages of the Layer-by-Layer (LbL) deposition technique is the possible control of molecular architecture, not only to achieve optimized properties but also to seek synergy among different materials. In this study, LbL films containin4562961229621FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORsem informaçãosem informaçãosem informaçãoDecher, G., (1997) Science, 277, p. 1232Stockton, W.B., Rubner, M.F., (1997) Macromolecules, 30, p. 2717Shimazaki, Y., Mitsuishi, M., Ito, S., Yamamoto, M., (1997) Langmuir, 13, p. 1385Kohli, P., Blanchard, G.J., (2000) Langmuir, 16, p. 8518Anzai, J., Kobayashi, Y., (2000) Langmuir, 16, pp. 2851-2856Shi, X., Shen, M., Mohwald, H., (2004) Prog. Polym. Sci., 29, p. 987Zucolotto, V., Ferreira, M., Cordeiro, M.R., Constantino, C.J.L., Moreira, W.C., Oliveira Jr., O.N., (2006) Sens. Actuators, B, 113, p. 809Alexeyeva, N., Tammeveski, K., (2008) Anal. Chim. Acta, 618, p. 140Liu, S., Volkmer, D., Kurth, D.G., (2003) J. Cluster Sci., 14, p. 405Kuhn, A., Mano, N., Vidal, C., (1999) J. Electroanal. Chem., 462, p. 187Cherstiouk, O.V., Simonov, A.N., Tsirlina, G.A., (2012) Electrocatalysis, 3, p. 230Lu, M., Lee, D., Xue, W., Cui, T., (2009) Sens. Actuators, A, 150, p. 280Han, B.H., Manners, I., Winnik, M.A., (2005) Chem. Mater., 17, p. 3160Perinotto, A.C., Caseli, L., Hayasaka, C.O., Riul Jr., A., Oliveira Jr., O.N., Zucolotto, V., (2008) Thin Solid Films, 516, p. 9002Moraes, M.L., De Souza, N.C., Hayasaka, C.O., Ferreira, M., Rodrigues-Filho, U.P., Riul Jr., A., Zucolotto, V., Oliveira Jr., O.N., (2009) Mater. Sci. Eng., C, 29, p. 442Liu, S., Mohwald, H., Volkmer, D., Kurth, D.G., (2006) Langmuir, 22, p. 1949Katsoulis, D.E., (1998) Chem. Rev., 98, p. 359Papaconstantinuou, E., (1989) Chem. Soc. Rev., 18, p. 1Timofeeva, M.N., (2003) Appl. Catal., A, 256, p. 19Sadakane, M., Steckhan, E., (1998) Chem. Rev., 98, p. 219Yamase, T., (1998) Chem. Rev., 98, p. 307De Oliveira Jr., M., Lopes De Souza, A., Schneider, J., Pereira Rodrigues-Filho, U., (2011) Chem. Mater., 23, p. 953Ferreira-Neto, E.P., De Carvalho, F.L.S., Ullah, S., Zoldan, V.C., Pasa, A.A., De Souza, A.L., Battirola, L.C., Rodrigues Filho, U.P., (2013) J. Sol-Gel Sci. Technol., 66, p. 363Souza, A.L., Marques, L.A., Eberlin, M.N., Nascente, P.A.P., Herrmann Jr., P.S.P., Leite, F.L., Rodrigues-Filho, U.P., (2012) Thin Solid Films, 520, p. 3574Liu, S., Tang, Z., (2010) Nano Today, 5, p. 267Dong, T., Ma, H., Zhang, W., Gong, L., Wang, F., Li, C., (2007) J. Colloid Interface Sci., 311, p. 523Ma, H., Dong, T., Wang, F., Zhang, W., Zhou, B., (2006) Electrochim. Acta, 51, p. 4965Cheng, L., Cox, J.A., (2002) Chem. Mater., 14, p. 6Gu, Y., Ma, H., O'Halloran, K.P., Shi, S., Zhang, Z., Wang, X., (2009) Electrochim. Acta, 54, p. 7194Kulesza, P.J., Chojak, M., Karnicka, K., Miecznikowski, K., Palys, B., Lewera, A., Wieckowski, A., (2004) Chem. Mater., 16, p. 4128Ernst, A.Z., Zoladek, S., Wiaderek, K., Cox, J.A., Kolary-Zurowska, A., Miecznikowski, K., Kulesza, P.J., (2008) Electrochim. Acta, 53, p. 3924Sun, L., Ca, D.V., Cox, J.A., (2005) J. Solid State Electrochem., 9, p. 816Liu, S., Kurth, D.G., Bredenkotter, B., Volkmer, D., (2002) J. Am. Chem. Soc., 124, p. 12279Cheng, L., Cox, J.A., (2001) Electrochem. Commun., 3, p. 285Feng, Y., Han, Z., Peng, J., Lu, J., Xue, B., Li, L., Ma, H., Wang, E., (2006) Mater. Lett., 60, p. 1588Xu, B., Xu, L., Gao, G., Jin, Y., (2007) Appl. Surf. Sci., 253, p. 3190Cheng, L., Dong, S., (2000) J. Electrochem. Soc., 147, p. 606Fernandes, D.M., Carapuça, H.M., Brett, C.M.A., Cavaleiro, A.M.V., (2010) Thin Solid Films, 518, p. 5881Cheng, L., Dong, S., (2000) J. Electroanal. Chem., 481, p. 168Liu, S., Volkmer, D., Kurth, D.G., (2004) Anal. Chem., 76, p. 4579Sosnowska, M., Goral-Kurbiel, M., Skunik-Nuckowska, M., Jurczakowski, R., Kulesza, P.J., (2013) J. Solid State Electrochem., 17, p. 1631Layla Mehdi, B., Rutkowska, I.A., Kulesza, P.J., Cox, J.A., (2013) J. Solid State Electrochem., 17, p. 1581Shiu, K.-K., Anson, F.C., (1991) J. Electroanal. Chem., 309, p. 115Martel, D., Kuhn, A., (2000) Electrochim. Acta, 45, p. 1829Chan, Z.C.Y., Lai, W.-F., (2009) Trends Food Sci. Technol., 20, p. 366Gammon, D.W., Aldous, C.N., Carr Jr., W.C., Sanborn, J.R., Pfeifer, K.F., (2005) Pest Manage. Sci., 61, p. 331Yu, J., Zhang, C., Dai, P., Ge, S., (2009) Anal. Chim. Acta, 651, p. 209Shoji, R., Takeuchi, T., Kubo, I., (2003) Anal. Chem., 75, p. 4882Donley, C., Dunphy, D., Paine, D., Carter, C., Nebesny, K., Lee, P., Alloway, D., Armstrong, N.R., (2002) Langmuir, 18, p. 450Sawyer, D.T., Sobkowiak, A., Roberts Jr., J.L., (1995) Electrochemistry for Chemists, pp. 68-78. , John Wiley & Sons, New York, 2nd edn, ch. 3Beamson, G., Briggs, D., (1992) High Resolution of XPS of Organic Polymers: The Scienta ESCA 300 Database, , John Wiley & Sons, ChichesterPope, M.T., Varga Jr., G.M., (1966) Inorg. Chem., 5, p. 1249Keita, B., Nadjo, L., (1987) J. Electroanal. Chem., 227, p. 77Stotter, J., Show, Y., Wang, S., Swain, G., (2005) Chem. Mater., 17, p. 4880Senthilkumar, M., Mathiyarasu, J., Joseph, J., Phani, K.L.N., Yegnaraman, V., (2008) Mater. Chem. Phys., 108, p. 403Vanleugenhague, C., Pourbaix, M., (1966) Atlas of Electrochemical Equilibra in Aqueous Solution, pp. 436-442. , ed. M. Pourbaix, Pergamon Press, OxfordDeltombe, E., De Zoubov, N., Vanleugenhague, C., Pourbaix, M., (1966) Atlas of Electrochemical Equilibra in Aqueous Solution, pp. 475-484. , ed. M. Pourbaix, Pergamon Press, OxfordPope, M.T., (1987) Comprehensive Coordination Chemistry, 3, p. 1039. , ed. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Plenum Press, New YorkAkhtar, M.S., Cheralathan, K.K., Chun, J.M., Yang, O.B., (2008) Electrochim. Acta, 53, p. 6623Oliveira, F.C., Schneider, J., Siervo, A., Landers, R., Plepis, A.M.G., Pireaux, J.J., Rodrigues-Filho, U.P., (2002) Surf. Interface Anal., 34, p. 580Zhang, L., Jin, Q., Huang, J., Liu, Y., Shan, L., Wang, X., (2010) Appl. Surf. Sci., 256, p. 5911(2011) X-Ray Photoelectron Spectroscopy Database, Standard Database 20, Version 3.5, , http://srdata.nist.gov/xps/Version_his.aspxNunes De Carvalho, C., Botelho Do Rego, A.M., Amaral, A., Brogueira, P., Lavareda, G., (2000) Surf. Coat. Technol., 124, p. 70Lourenço, J.M.C., Ribeiro, P.A., Botelho Do Rego, A.M., Braz Fernandes, F.M., Moutinho, A.M.C., Raposo, M., (2004) Langmuir, 20, p. 8103Liu, Y.T., Deng, J., Xiao, X.L., Ding, L., Yuan, Y.L., Li, H., Li, X.T., Wang, L.L., (2011) Electrochim. Acta, 56, p. 4595Liao, C.W., Chen, Y.-R., Chang, J.-L., Zen, J.-M., (2011) J. Agric. Food Chem., 59, p. 9782Akter, H., Shaikh, A.A., Chowdhury, T.R., Rahmam, M.S., Bakshi, P.K., Saleh Ahammad, A.J., (2013) ECS Electrochem. Lett., 2 (8), p. 13Tran, H.V., Yougnia, R., Reisberg, S., Piro, B., Serradji, N., Nguyen, T.D., Tran, L.D., Pham, M.C., (2012) Biosens. Bioelectron., 31, p. 62Norouzi, P., Larijani, B., Ganjali, M.R., Faridbod, F., (2012) Int. J. Electrochem. Sci., 7, p. 10414Xu, G., Zhang, H., Zhong, M., Zhang, T., Lu, X., Kan, X., (2014) J. Electroanal. Chem., 713, p. 112Pesavento, M., D'Agostino, G., Biesuz, R., Alberti, G., (2009) Electroanalysis, 21, p. 604Svorc, L., Rievaj, M., Bustin, D., (2013) Sens. Actuators, B, 181, p. 294This work was supported by FAPESP, CNPq, CAPES and Brazilian Network nBioNe

Prospects for microwave plasma synthesized N-graphene in secondary electron emission mitigation applications

PTDC/NAN-MAT/30565/2017 D01-284/2019 (INFRAMAT) IBB BASE 2020-2023 UID/FIS/00068/2019.The ability to change the secondary electron emission properties of nitrogen-doped graphene (N-graphene) has been demonstrated. To this end, a novel microwave plasma-enabled scalable route for continuous and controllable fabrication of free-standing N-graphene sheets was developed. High-quality N-graphene with prescribed structural qualities was produced at a rate of 0.5 mg/min by tailoring the high energy density plasma environment. Up to 8% of nitrogen doping levels were achieved while keeping the oxygen content at residual amounts ( 1%). The synthesis is accomplished via a single step, at atmospheric conditions, using ethanol/methane and ammonia/methylamine as carbon and nitrogen precursors. The type and level of doping is affected by the position where the N-precursor is injected in the plasma environment and by the type of precursors used. Importantly, N atoms incorporated predominantly in pyridinic/pyrrolic functional groups alter the performance of the collective electronic oscillations, i.e. plasmons, of graphene. For the first time it has been demonstrated that the synergistic effect between the electronic structure changes and the reduction of graphene $-plasmons caused by N doping, along with the peculiar “crumpled” morphology, leads to sub-unitary (textless 1) secondary electron yields. N-graphene can be considered as a prospective low secondary electron emission and plasmonic material.publishersversionpublishe

Novel organotin-PTA complexes supported on mesoporous carbon materials as recyclable catalysts for solvent-free cyanosilylation of aldehydes

The work was also funded by national funds through FCT, under the Scientific Employment Stimulus-Institutional Call (CEEC-INST/00102/2018). AGM is grateful to Associação do Instituto Superior Técnico para a Investigação e Desenvolvimento ( IST-ID ) for his post-doctoral fellowship through grant no. BL133/2021-IST-ID . AP and AMF are grateful to FCT and Instituto Superior Técnico (IST), Portugal through DL/57/2017 (Contract no. IST-ID/197/2019 and IST-ID/131/2018). This publication is also supported by the RUDN University Strategic Academic Leadership Program (recipient AJLP, preparation). The authors also acknowledge the Portuguese NMR Network (IST-UL Centre) for access to the NMR facility. Publisher Copyright: © 2023 Elsevier B.V.New organotin compounds with general formula [(PTA-CH2-C6H4-p-COO)SnR3]Br (where R is Me for 3 and Ph for 4; PTA = 1,3,5-triaza-7-phosphaadamantane), bearing the methylene benzoate PTA derivative, were synthesized through a mild two-step process. The compounds were characterized by Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry, elemental analysis and nuclear magnetic resonance spectroscopy (NMR). They were heterogenized on commercially available activated carbon (AC) and multi-walled carbon nanotubes (CNT), as well as on their chemically modified analogues. The obtained materials were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Complex 3 supported on activated carbon (3-AC) was found to be an active and recyclable catalyst for the cyanosilylation of several aromatic and aliphatic aldehydes. Using 3-AC with a low loading of 0.1 mol% several substrates were quantitatively converted, within just 5 min at 50 °C and under microwave irradiation in solvent-free conditions. Multinuclear NMR analysis suggested a mechanism that potentially involves a double activation process, where the nucleophilic phosphorus at the PTA derivative acts as a Lewis base and the Sn(IV) metal centre as a Lewis acid.publishersversionpublishe