Microwave Synthesis of Silver Sulfide and Silver Nanoparticles: Light and Time Influence

UIDB/50025/2020 UIDP/50025/2020 UID/CTM/50025/2019 .Silver sulfide (Ag2S) is a low band gap material, which absorbs near-infrared light and is of great importance in areas such as nanotechnology and biomedicine. We report the influence of the starting reagents, synthesis time, and light radiation on the geometry and size of silver sulfide nanoparticles and on the fraction of metallic Ag obtained in a microwave reactor. The X-ray diffraction diffractograms confirmed that Ag2S is the main product if the reaction's precursor contains silver in the oxidation state of +1 and mostly metallic silver (Ag°) when it is +2. Small nanoparticles (∼6 nm) of spherical geometry are present in the transmission electron microscopy images for the synthesis performed with the lamp light ON, while with the light switched OFF, wider and hundreds of nanometers longer particles are observed. This discriminative effect occurs with shorter synthesis time duration (<10 min) but when the time of reaction is extended, the particles coalesce for both light and dark conditions. Overall, it was observed by photoluminescence that crystalline Ag and Ag2S 4-8 nm nanoparticles obtained in 15 min and light irradiation during synthesis have a clear relative increase of the radiative recombination channels of the charged carriers, which are typical of materials characterized by the involvement of low density of states inside the band gap.publishersversionpublishe

Síntese de aerogéis e xerogéis de sílica com troca de solvente e secagem a pressão ambiente

O presente trabalho estuda as características estruturais de géis de sílica preparados a partir da sonohidrólise do Tetraetilortosilicato (TEOS) em função de diferentes quantidades de álcool isopropílico (IPA), denominado conjunto de amostras A, e em função de diferentes quantidades de dimetilformamida (DMF), denominado conjunto de amostras B. Os géis são estudados desde o estágio saturado (gel úmido) até o estágio do gel seco (aerogel e xerogel) resultante da secagem a pressão ambiente. As caracterizações estruturais das amostras são realizadas através das técnicas de Termogravimetria (TG), densidade aparente, análise de distribuição de tamanho de poros e área superficial por adsorção de nitrogênio, e espalhamento de raios X a baixo ângulo (SAXS). A sonohidrólise foi realizada a partir de volumes constantes das misturas reagentes, mantendo-se a mesma razão molar água/TEOS para as diferentes adições de IPA do conjunto A e também a mesma razão molar água/TEOS para as diferentes adições de DMF do conjunto B. Géis úmidos produzidos a partir da estimulação ultrassônica do TEOS com aumento da quantidade de IPA (conjunto A) exibem uma estrutura de fractal de massa com dimensão fractal D em torno de 2,0 e com tamanho característico  do fractal de massa crescendo de 4,1 nm para 5,1 nm, quando a razão molar [IPA]/[TEOS] cresce de 0 para 10,8. Os géis do conjunto B exibem uma estrutura fractal de massa com dimensão fractal D em torno de 2,2 e com  decrescendo de 9,2 nm para 7,8 nm quando a razão molar R = [DMF]/[TEOS] cresce de 0 para 4. Aerogéis foram obtidos após lavagem dos géis úmidos de ambos os conjuntos com IPA, para remoção de resíduos provenientes da sonohidrólise, e depois imersos em solução de trimetilclorosilano (TMCS) em álcool isopropílico, para modificação...The present work studies the structural characteristics of silica gels prepared from the sonohydrolysis of tetraetoxisilane (TEOS) as a function of different amounts of isopropyl alcohol (IPA), which will be called the set of samples A, and for different amounts of dimethylformamide (DMF) , which will be called set of samples B. The gels are studied from the saturated stage (wet gel) until the stage of dry gel (xerogel and aerogel) that results from a drying process at ambient pressure. The samples are characterized by Termogravimetry (TG), apparent density, surface area and pores size distribution by nitrogen adsorption, and small-angle X-ray scattering (SAXS). The sonohydrolysis was carried out from reagent mixtures with constant volumes, keeping the same water/TEOS molar ratio for different additions of IPA in the set A and also the same water/TEOS molar ratio for different additions of DMF in the set B. Wet gels produced from the ultrasonic stimulation of TEOS with increasing the quantity of IPA (set A) exhibit a structure of fractal mass with fractal dimension D around 2.0 and with characteristic size  growing from 4.1 nm to 5.1 nm, when the [IPA]/[TEOS] molar ratio increases from 0 to 10,8. The gels of the set B exhibit a structure of fractal mass with fractal dimension D around 2.2 and with  decreasing from 9.2 nm to 7.8 nm when increasing the molar ratio R =[DMF]/[TEOS] from 0 to 4. Aerogels were obtained after washing the wet gels from both sets with IPA, to remove wastes from the sonohydrolysis, and then immersing them in a solution of trimethylchlorosilane (TMCS) in isopropyl alcohol, for the silica surface modification (silylation), and finally in pure isopropyl alcohol. The drying process narrows the range of characteristic lengths  of the original structure of fractal mass of the wet gels, however, it does not change... (Complete abstract click electronic access below)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Structure of Hydrophobic Ambient-Pressure-Dried Aerogels Prepared by Sonohydrolysis of Tetraethoxysilane with Additions of N,N-Dimethylformamide

Silica wet gels with the same silica content were prepared by the sonohydrolysis of tetraethoxysilane (TEOS) with additions of dimethylformamide (DMF). DMF plays a role in the overall hydrolysis/gelification/aging step of the sol gel process, providing more consolidated wet gels with larger syneresis degrees and densities. The structure of the as-obtained wet gels can be interpreted as being built up of mass-fractal domains with fractal dimension D = 2.2 and radius of gyration decreasing from about 14 to 12 nm with increasing quantity of DMF. Monolithic hydrophobic aerogels were prepared after washing of the wet gels with isopropyl alcohol (IPA), silylation with trimethylchrorosilane (TMCS), and ambient-pressure drying (APD). The specific surface area of the APD aerogels was found to be about 900 m(2)/g, and the mean silica particle size was about 2.0 nm, approximately independent of the DMF quantity, whereas the porosity decreased slightly with increasing amount of DMF, fairly accompanying the behavior of the radius of gyration of the precursor wet gels. The mass-fractal characteristics were preserved in the APD aerogels, but the radius of gyration of the mass-fractal domains was reduced to values between 2.8 to 4.0 nm, with the values decreasing slightly with the DMF quantity, and the fractal domains developed a surface-mass-fractal structure with the overall washing/silylation/APD treatment. The structural characteristics of the APD aerogels as determined by SAXS were found to be in notable agreement with those inferred from nitrogen adsorption.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Dynamic Scaling and Growth Kinetics of 3-Glycidoxypropyltrimethoxysilane-Derived Organic/Silica Hybrids

Structural evolution and dynamic scaling properties have been probed by small-angle X-ray scattering (SAXS) in the growth kinetics of 3-glycidoxypropyltrimethoxysilane (GPTS)-derived organic/silica hybrids in basic solution. The SAXS intensity curves were found to be well described by a particle form factor valid for polydisperse coils of linear chains and for particular cases of random and nonrandom polycondensates in solution together with an interference factor accounting for very weak correlations of particles. The SAXS data are consistent with formation and growth of GPTS-derived organic/silica hybrids in solution with polydispersity increasing with time. The following properties have been found: (i) The SAXS intensities I(q,t) corresponding to different times t are given by a time-independent function F(qR(g)) = I(q,t)R(g)(-D), R(g) being the average radius of gyration of the hybrid particles; (ii) the average radius of gyration grows in a power-law with time t as R(g) proportional to t(alpha), with alpha = 0.307 +/- 0.009, suggesting growth of domains by a diffusion-controlled mechanism; (iii) the SAXS intensity I(0) extrapolated to q = 0 increases in a power-law with time t as I(0) proportional to t(beta), with beta = 0.547 +/- 0.020, so beta/alpha = 1.78 +/- 0.12; (iv) the extrapolated intensity I(0) scales with R(g) as I(0) proportional to R(g)(D), with D = 1.69 +/- 0.01, which is in good agreement with the value beta/alpha and suggests that the macromolecules grow in a dimensionality approximate to 1.7, typical of macromolecules in good-solvent conditions in diluted or semidiluted solution. This set of findings is in notable agreement with the dynamic scaling properties. Dynamic scaling properties are important to confront phase-separation theories through the remarkable characteristics of the structure function associated. New insights on the development of the structural heterogeneities in hybrid materials are apprehended from the present dynamics of the sol-gel process probed by SAXS.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Structure and aggregation kinetics of vinyltriethoxysilane-derived organic/silica hybrids

The aggregation kinetics of solutions of vinyltriethoxysilane-derived organic/silica hybrid species were studied by small-angle X-ray scattering (SAXS) in a strongly basic medium. The SAXS intensity was analysed by a modified Sharp-Bloomfield (SB) global function and its evolution was found to be compatible with the growth, coiling and branching of the polymeric macromolecules in solution. A form factor valid for randomly and nonrandomly branched polycondensates and for polydisperse coils of linear chains was used in the modified SB model, instead of the Debye function valid for monodisperse coils of linear chains. The aggregation kinetics are accelerated with increasing base concentration in the studied range, but all the kinetics curves can be matched to a unique curve using an appropriate time scaling factor. The aggregation kinetics suggest that physical forces (hydrothermal forces) associated with phase coarsening could be active in the aggregation process, together with diffusion mechanisms.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A historical overview of the research on TiO2 thin films deposited by atomic layer deposition – Part I: Early Studies

<p>Molecular Layering (ML) or Atomic Layer Epitaxy (ALE) or Atomic Layer Deposition (ALD) technique is a gas-phase layer by layer deposition method which belongs to the general class of Chemical Vapor Deposition (CVD) techniques, and which has become of worldwide importance due to success in down-scaling of microelectronic devices. Among the materials obtained by the technique, titanium dioxide (TiO₂) stands out due to its crystallographic importance and numerous applications ranging from the photovoltaics to self-cleaning surfaces. Here we present an overview of the history of TiO₂ thin films grown by ALD technique organized into three periods: early studies (1960s-1990s), consolidation period (2000s) and current stage (2010-present). First, we report the early material synthesis and characterization studies on ALD TiO₂ thin films during the 4 decades between 1960s to 1990s. Then we address the evolution of the research field from the 2000s until the present day. The purpose of this historical survey is to synthetize the evolution of ALD TiO₂ thin films technology for different applications, which could be useful for students and researchers working in this field. In this manuscript, Part I is presented reporting the first published studies on TiO₂ thin films deposited by ALD. </p

Physicochemical Studies on the Surface of Polyamide 6.6 Fabrics Functionalized by DBD Plasmas Operated at Atmospheric and Sub-Atmospheric Pressures

This work proposes the use of a dielectric barrier discharge (DBD) reactor operating at atmospheric pressure (AP) using air and sub-atmospheric pressure (SAP) using air or argon to treat polyamide 6.6 (PA6.6) fabrics. Here, plasma dosages corresponding to 37.5 kW&middot;min&middot;m&minus;2 for AP and 7.5 kW&middot;min&middot;m&minus;2 for SAP in air or argon were used. The hydrophilicity aging effect property of untreated and DBD-treated PA6.6 samples was evaluated from the apparent contact angle. The surface changes in physical microstructure were studied by field emission scanning electron microscopy (FE-SEM). To prove the changes in chemical functional groups in the fibers, Fourier transform infrared spectroscopy (FTIR) was used, and the change in surface bonds was evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the whiteness effect was investigated by the color spectrophotometry (Datacolor) technique. The results showed that the increase in surface roughness by the SAP DBD treatment contributed to a decrease in and maintenance of the hydrophilicity of PA6.6 fabrics for longer. The SAP DBD in air treatment promoted an enhancement of the aging effect with a low plasma dosage (5-fold reduction compared with AP DBD treatment). Finally, the SAP DBD treatment using argon functionalizes the fabric surface more efficiently than DBD treatments in air

MOS Capacitance Measurements for PEALD TiO2 Dielectric Films Grown under Different Conditions and the Impact of Al2O3 Partial-Monolayer Insertion

In this paper, we report the plasma-enhanced atomic layer deposition (PEALD) of TiO2 and TiO2/Al2O3 nanolaminate films on p-Si(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. In the PEALD process, we used titanium tetraisopropoxide (TTIP) as a titanium precursor, trimethyl aluminum (TMA) as an aluminum precursor and O2 plasma as an oxidant, keeping the process temperature at 250 &deg;C. The effects of PEALD process parameters, such as RF power, substrate exposure mode (direct or remote plasma exposure) and Al2O3 partial-monolayer insertion (generating a nanolaminate structure) on the physical and chemical properties of the TiO2 films were investigated by Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM) techniques. The MOS capacitor structures were fabricated by evaporation of Al gates through mechanical mask on PEALD TiO2 thin film, followed by evaporation of an Al layer on the back side of the Si substrate. The capacitors were characterized by current density-voltage (J-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Our results indicate that RF power and exposure mode promoted significant modifications on the characteristics of the PEALD TiO2 films, while the insertion of Al2O3 partial monolayers allows the synthesis of TiO2/Al2O3 nanolaminate with well-spaced crystalline TiO2 grains in an amorphous structure. The electrical characterization of the MOS structures evidenced a significant leakage current in the accumulation region in the PEALD TiO2 films, which could be reduced by the addition of partial-monolayers of Al2O3 in the bulk of TiO2 films or by reducing RF power

Applications of Plasma-Activated Water in Dentistry: A Review

The activation of water by non-thermal plasma creates a liquid with active constituents referred to as plasma-activated water (PAW). Due to its active constituents, PAW may play an important role in different fields, such as agriculture, the food industry and healthcare. Plasma liquid technology has received attention in recent years due to its versatility and good potential, mainly focused on different health care purposes. This interest has extended to dentistry, since the use of a plasma&ndash;liquid technology could bring clinical advantages, compared to direct application of non-thermal atmospheric pressure plasmas (NTAPPs). The aim of this paper is to discuss the applicability of PAW in different areas of dentistry, according to the published literature about NTAPPs and plasma&ndash;liquid technology. The direct and indirect application of NTAPPs are presented in the introduction. Posteriorly, the main reactors for generating PAW and its active constituents with a role in biomedical applications are specified, followed by a section that discusses, in detail, the use of PAW as a tool for different oral diseases