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Hugo Guimarães Palhares

Bio: Hugo Guimarães Palhares is an academic researcher from Universidade Federal de Minas Gerais. The author has contributed to research in topics: Photocatalysis & Adsorption. The author has an hindex of 4, co-authored 6 publications receiving 30 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the effect of the RGO loading on both the structural properties and photocatalytic behavior of reduced graphene oxide (RGO)-TiO2 composites was deeply addressed.
Abstract: This work deals with the preparation of reduced graphene oxide (RGO)-TiO2 composites by a one-step hydrothermal treatment. The effect of the RGO loading on both the structural properties and photocatalytic behavior of RGO-TiO2 is deeply addressed herein. The hydrothermal treatment promoted the reduction of graphene oxide, crystallization of TiO2 into anatase, and anchoring of TiO2 nanoparticles on RGO sheets. It was observed that the prepared anatase particles showed sizes below 10 nm, whereas the RGO sheets displayed thicknesses smaller than 1 nm. The use of RGO at concentrations up to 15 wt% greatly increased the specific surface area of RGO-TiO2. It was demonstrated that the combination of RGO and TiO2 gives rise to materials with improved photocatalytic properties and tailored structural properties. The composite with the highest photoactivity was the one containing an RGO loading of 1 wt%; this composite displayed a photocatalytic rate constant about 9.5 times higher than that evaluated for pure TiO2. This behavior may be related to the stacking of RGO nanosheets when its concentration is above 1 wt%. Moreover, the addition of RGO in excess may prevent the activation of the TiO2 surface by UV light and also decrease the lifetime of the photogenerated electron-hole pairs. Therefore, it appears that 1 wt% is the optimal loading of RGO to obtain a close interfacial contact between RGO and TiO2, leading to both an effective activation of TiO2 by UV radiation and an enhanced charge transfer between RGO and TiO2.

23 citations

Journal ArticleDOI
TL;DR: In this paper, the mesoporosity and adsorption behavior of methylene blue (MB) were evaluated for the fabricated silica materials, and the results showed that large surface areas and pore sizes accelerate the MB kinetic and increase the amount of MB able to stay in equilibrium in the pore structure of silica.
Abstract: Silicon dioxide xerogels with controlled mesoporosity were produced by sol–gel technique. The mesoporosity and adsorption behavior of methylene blue (MB) were evaluated for the fabricated silica materials. This study is supported by several characterizations, including FTIR, TEM, SEM, and N2 sorption. The adsorption kinetics of MB on the prepared samples was evaluated at room temperature over time. It was demonstrated that the pore structure and adsorption performance of silica are closely dependent on the pH of the sol–gel solution, H2O:TEOS molar ratio, the addition of F127 template, and heat treatment performed. The present study shows that for the adsorption parameters used in this work, the control of sol–gel parameters can give rise to silica xerogels with higher adsorption capacities than SBA-16 silica molecular sieve used as the reference and already recognized as an efficient dye adsorbent. The highest adsorption capacities were measured for silica structures obtained without the use of acidic catalyst, heat treatment or F127 template. As the pore volume of the studied materials is much larger than the amount of MB captured in the adsorption tests, such results seem to be related to the specific surface area and pore size obtained in the sol–gel synthesis. Therefore, it appears that large surface areas and pore sizes accelerate the adsorption kinetic and increase the amount of MB able to stay in equilibrium in the pore structure of silica. As a matter of fact, the work developed here underlines the advantages regarding the simplicity, safety, environmental preservation and cost saving of the synthesis methodology developed herein when compared with the other methodologies commonly used to fabricate silica adsorbents.

18 citations

Journal ArticleDOI
TL;DR: In this paper, the functionality of different TiO2 coatings deposited on the exposed surface of Portland cement pastes was evaluated and the results suggest that the autoclave treatment did not favor the formation of crystalline TiO 2 phases.

13 citations

Journal ArticleDOI
TL;DR: In this paper, the adsorption capacity of the prepared materials was investigated using methylene blue (MB) and metamizole (sodium dipyrone) as reference pollutants.
Abstract: In this work, silica-based adsorbents were prepared by a facile and straightforward sol–gel route. The adsorption capacity of the prepared materials was investigated using methylene blue (MB) and metamizole (sodium dipyrone – DIP) as reference pollutants. We observed that the samples prepared here, regardless of the absence of catalyst, templating agent, or heat treatment step during their preparation, are promising materials for adsorption purposes. The adsorption kinetics was investigated based on the pseudo-first and pseudo-second-order kinetic laws of Lagergren. The most promising sample showed an adsorption capacity of 36.9 mg g−1 (removal capacity of 92.3%) for MB and 8.5 mg g−1 (20.5%) for DIP in aqueous media kept at a pH = 7.0. We observed that the adsorption of these species is strongly associated with the electrostatic interaction between the pollutant molecules and the silica surface. Such an interaction was increased when the pH of the solution increased from 3.0 to 4.5, 7.0, or 9.0. The incorporation of amino groups derived from (3-Aminopropyl)triethoxysilane (APTES) increased the affinity of silica for MB and DIP. These functional groups were incorporated into silica via post-grafting and co-condensation. Furthermore, it was shown that the silica matrices tested here can be easily regenerated by heat treatment in air at 450 °C for periods as short as 15 min, allowing its reuse in subsequent adsorption cycles.

6 citations


Cited by
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Journal ArticleDOI
29 Apr 2020
TL;DR: Halide perovskite CsPbBr3 has recently gained wide interest for its application in solar cells, optoelectronics, and artificial photosynthesis as discussed by the authors.
Abstract: Halide perovskite CsPbBr3 has recently gained wide interest for its application in solar cells, optoelectronics, and artificial photosynthesis, but further progress is needed to develop greener and...

60 citations

Journal ArticleDOI
TL;DR: Graphene, a two-dimensional single layered carbon atoms crystal lattice has grabbed much attention due to its unique electronic, surface, mechanical and optoelectronic characteristics.
Abstract: Graphene, a two-dimensional single layered carbon atoms crystal lattice has grabbed much attention due to its unique electronic, surface, mechanical and optoelectronic characteristics. Owing to its unique structure and properties, graphene has opened new opportunities for the future systems and devices, which has led to increase its demand in numerous applications. However, scaling up its production is still a challenging job. Although there is a huge body of literature on the graphene synthesis using various techniques but eco-friendly and cost–effective processes for mass scale production are still needed. In order to conceptualize and develop the processes fulfilling the growing concerns, it is important to overview the existing literature. The current review summarizes the production of graphene using several approaches as well as the potential of various waste materials as graphene precursors. The methods used for graphene synthesis have been categorized into top down techniques such as chemical exfoliation, mechanical exfoliation and chemical fabrication processes, and bottom up techniques including pyrolysis, plasma synthesis, epitaxial growth and chemical vapor deposition (CVD) processes. Conversely, several limitations are considerate for an individual procedure such as toxicity of chemicals, high-cost, time consumption or inadequate quality of the product. Furthermore, mass production of graphene derivatives under low-cost can also be considered by utilizing a variety of wastes precursors such as plastic and batteries waste, newspaper, biomass, chitosan, coal, insects waste etc. This review designates the current advances in wastes-derived graphene synthesis to relief synthetic difficulties as well as predicts the future development in this area.

58 citations

Journal ArticleDOI
TL;DR: In this paper, a Pb-free Cs2AgBiBr6 double perovskite nanoplates and their heterostructure with Cu-loaded reduced graphene oxide (Cu-RGO) for gas-phase photocatalytic CO2 reduction using water vapor as the proton source in the absence of a hole scavenger were reported.
Abstract: Pb-based halide perovskites have recently showed great potential in various applications such as solar cells, optoelectronics and photocatalysis. Despite their high performance, the Pb2+ toxicity along with poor stability hinders long term applications in photocatalysis. Herein, we report mechanochemically prepared Pb-free Cs2AgBiBr6 double perovskite nanoplates and their heterostructure with Cu-loaded reduced graphene oxide (Cu–RGO) for gas-phase photocatalytic CO2 reduction using water vapor as the proton source in the absence of a hole scavenger. The resulting Cs2AgBiBr6–Cu–RGO nanocomposite shows significant photocatalytic activity of 10.7 (±0.6) μmol CH4 g−1 h−1, 1.9 (±0.3) μmol CO g−1 h−1 and 1.0 (±0.2) μmol H2 g−1 h−1, with a CH4 selectivity of 93.0 (±0.5)% on an electron basis with 1 sun and a remarkable apparent quantum efficiency of 0.89 (±0.21)% at 590 nm. A further 32% enhancement in photocatalytic activity on an electron basis is achieved when the light intensity is doubled (2 suns). The high performance was attributed to their improved charge separation and suppressed electron–hole recombination, along with extended visible light absorption, better stability in a humid environment and improved CO2 adsorption. These findings support Cs2AgBiBr6 as a potential Pb-free alternative to conventional halide perovskites for photocatalytic solar-to-fuel conversion and CO2 utilization.

56 citations

Journal ArticleDOI
TL;DR: A survey of nanostructured TiO2 coatings obtained by means of different deposition techniques can be found in this article, where the authors discuss their characteristics and advantages, in the light of the experimental conditions and the supporting substrates.

36 citations

Posted ContentDOI
21 Apr 2021
TL;DR: A review of the literature on different nanocomposite coatings and surface finishing for textiles is presented in this article, focusing on smart materials, drug-delivery systems, industrial, antifouling and nano/ultrafiltration membrane coatings.
Abstract: This review presents current literature on different nanocomposite coatings and surface finishing for textiles, and in particular this study has focused on smart materials, drug-delivery systems, industrial, antifouling and nano/ultrafiltration membrane coatings. Each of these nanostructured coatings shows interesting properties for different fields of application. In this review, particular attention is paid to the synthesis and the consequent physico-chemical characteristics of each coating and, therefore, to the different parameters that influence the substrate deposition process. Several techniques used in the characterization of these surface finishing coatings were also described. In this review the sol–gel method for preparing stimuli-responsive coatings as smart sensor materials is described; polymers and nanoparticles sensitive to pH, temperature, phase, light and biomolecules are also treated; nanomaterials based on phosphorus, borates, hydroxy carbonates and silicones are used and described as flame-retardant coatings; organic/inorganic hybrid sol–gel coatings for industrial applications are illustrated; carbon nanotubes, metallic oxides and polymers are employed for nano/ultrafiltration membranes and antifouling coatings. Research institutes and industries have collaborated in the advancement of nanotechnology by optimizing conversion processes of conventional materials into coatings with new functionalities for intelligent applications.

22 citations