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The ionic silsesquioxanes are hybrid polymers formed from the polycondensation of organoalkoxysilane precursors that contain charged groups, such as ammonium quaternary salts, where the silica network is combined with the charged organic moiety in a molecular level. These charged polymers present very peculiar characteristics such as self-organization, ionic exchange, water solubility, capacity to form strong adhered films over metal oxide surfaces and ability to stabilize metal nanoparticles. These characteristics open the possibility to synthesize or modify materials producing several multifunctional nanostructures and our research group has been devoted great attention to these systems in the last years. Here, we give an overview of the research activities of the Laboratory of Solids and Surfaces using the ionic silsesquioxanes in the development of nanostructures and nanodevices.

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N,N-Dimethyltryptamine (DMT) is a serotonergic psychedelic that, when combined with monoamine oxidase enzyme inhibitors in the hallucinogenic beverage commonly known as ayahuasca, surpasses most common orally administered psychoactive drugs. There is a growing interest in the therapeutic potential of DMT due to recent clinical data showing the improvement of cognitive deficits associated with depression and Alzheimer’s disease. The development of analytical methodology for the monitoring of concentrations of DMT molecules to control the appropriate dosage for their use is essential for the treatment of patients. For this, we propose a novel flexible inkjet-printed paper substrate based on Au nanostars as proof of concept for DMT detection by surface-enhanced Raman scattering (SERS). The substrate was applied to detect DMT in water as a first approach to more complex matrices like ayahuasca beverages or blood samples. The optimization and performance of SERS substrates with different print cycles indicate that one print is enough to achieve the great performance of the flexible paper substrates. The SERS analyses for DMT in different concentrations, 10-3 to 10-10 mol L-1, reveal a high sensitivity of the sensors with a silhouette coefficient of 0.84 obtained by principal component analysis (PCA) statistical projections.

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Metallic nanoparticles remain the focus of diverse studies across various fields due to their exceptional properties and applications in biology, sensing, energy, and (electro)catalysis. Typical syntheses of metallic nanoparticles are solution-based and require the use of stabilizing agents. Although these surface agents prevent agglomeration, they also hinder access to active sites on the nanoparticle surface. A promising alternative is mechanochemical synthesis, offering a solvent and surfactant-free approach, which yields uniform nanoparticles with clean surfaces. Here, we employ ball milling as a mechanochemical method to prepare metallic bismuth nanoparticles in a single step, using BiVO4 semiconductor both as a bismuth source and a support. Our results demonstrate that, in addition to the formation of nanoparticles by the partial reduction of BiVO4, there is an increase in charge carriers in the semiconductor structure as probed by electrochemical experiments. The final properties of Bi@BiVO4 material make it a relevant candidate for (electro)catalysis.

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Surface tension (SFT) can shape the behavior of liquids in industrial chemical processes, influencing variables such as flow rate and separation efficiency. This property is commonly measured with experimental approaches such as Du Noüy ring and Wilhelmy plate methods. Here, we present machine learning (ML) methodologies that can predict the SFT of hydrocarbons. A comparative analysis encompassing k-nearest neighbors, random forest, and XGBoost (extreme gradient boosting) methods was done. Results from our study reveal that XGBoost is the most accurate in predicting hydrocarbon SFT, with a mean squared error (MSE) of 4.65 mN2 m-2 and a coefficient of determination (R2) score of 0.89. The feature importance was evaluated with the permutation feature importance method and Shapley analysis. Enthalpy of vaporization, density, molecular weight and hydrogen content are key factors in accurately predicting SFT. The successful integration of these methodologies holds the potential to impact efficiency in different industry processes.

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Developing new non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is an essential challenge in electrochemical device research. Among these, we highlight the metal Schiff-base complexes, which can be used as modified carbon paste electrodes (CPE). Herein, we present a facile one-pot method for preparing a new family of cobalt(II) complexes with Schiffbase ligands obtained from glycine and para-substituted aldehydes. Complexes were characterized by different techniques, and the effects of para-substituents on the electronic properties of the complexes were confirmed by ultraviolet-visible spectroscopy and cyclic voltammetry (CV). The CV was also used to evaluate the ORR behavior of metal complex-modified CPE in an alkaline medium. The three complex-modified CPE were found to be highly effective for ORR, and the electron-withdrawing character of para-substituent affects the electrochemical reactivity. Density functional theory (DFT) calculations were used to complement the study and correlate the electrochemical activity, the redox potentials, and the Hammett parameter (σp) with the singly occupied molecular orbital (SOMO) energy of the complexes. DFT data were also able to shed light on the likely ORR mechanism. In summary, electronic tuning of the ligand affects the electronic properties of the metal center and allows for systematic oxygen reduction-catalytic control.

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Silver nanowires thin films have gained attention due to their excellent optical and electrical properties, being a potential material to be applied in optoelectronic devices as transparent conductive films, deposited on a substrate in a such way that forms a percolated network. We report the synthesis of silver nanowires with average length of 9.5 ± 0.4 µm and diameter of 75 ± 3 nm by a modified polyol method and fabrication of transparent and conductive thin films using a simple and low-cost technique as drop-casting. Additionally, we examined the influence of the drop-casting method in function of number of deposition cycles on the optical and electrical properties of the films through optical absorption and electrical resistance measurements using the two-point methodology. Increasing the number of silver nanowire deposition layers, the optical transmittance decreased from 97 (for one layer) to 60% (for five layers), and electrical resistance decreased from 940 ± 0.35 Ω for the 2-layer film to 32 ± 0.02 Ω, for the 5-layer film. Due to the electrical conductivity range of the produced silver nanowires films, we suggested their application in low-voltage circuits.

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Intercalation of deprotonated folic acid (FA; vitamin B9) is of great interest for nutraceutical and cosmeceutical purposes. Although some studies have already reported the intercalation of divalent (HFol2−) or trivalent (Fol3−) folate anions into layered double hydroxides (LDH), the structure, spectroscopic, and thermal behavior of such hybrid materials still need to be better understood. This work revisited the synthesis of LDH constituted by M2+/Al3+ (M2+ = Mg or Zn) intercalated with HFol2− or Fol3−. Insights concerning how the physicochemical properties of the materials are tuneable according to the synthetic approach (slow or fast coprecipitation) and pH value (7.5 or 9.0/9.5) of synthesis were pointed out. Materials synthesized at pH above 9.0 (Fol3−) presented larger particles and lower loading capacity than the ones synthesized at pH 7.5 (HFol2−). The fast coprecipitation approach led to the formation of materials with smaller particles. This work could address the following research concerning LDH-FA applications.

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Cadmium silicates are materials of interest due to their stability and possible application as phosphors. There are three stable forms: cadmium metasilicate, CdSiO3, cadmium orthosilicate, Cd2SiO4 and cadmium oxyorthosilicate, Cd3SiO5. Of these, oxyorthosilicate is particularly challenging to obtain, leading to fewer studies. We have successfully prepared Cd3SiO5 using a sol-gel approach, employing cadmium acetate and tetraethylorthosilicate as precursors in a stoichiometric proportion of 2:1. Additionally, cetyltrimethylammonium bromide served as a template for creating a mesoporous structure. Adjusting the pH to 3 and subjecting the material to calcination at 800 °C for 6 h, we achieved the formation of cadmium oxyorthosilicate compound, identified by X-ray diffraction. Electron diffractometry and energy dispersive X-ray spectrometry confirm the phase purity. Characterization via nitrogen adsorption analysis and transmission microscopy shows aggregates of nanoparticles with a surface area of 6 m2 g 1 and a narrow pore diameter distribution centered at 5 nm.

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The catalytic performance of γ-Fe2O3 nanopowder was investigated in the acetone hydrodeoxygenation (HDO) reaction, an essential catalytic reaction in biomass valorization. Sequential reduction/oxidation thermal pre-treatments of the γ-Fe2O3 nanopowder induced significant structural and electronic modifications that directly impacted its catalytic performance. The co-existence of Fe3+/Fe2+/Fe0 sites led to different reaction pathways (C-C coupling, hydrogenolysis, hydrogenation, and (hydro)deoxygenation) that formed a wide range of products. The correlation of the catalytic and structural data provided a better understanding of C-O, C-C, and C-H bond activation under the HDO reactional stream in the presence of metallic and oxidized phases of iron. This study demonstrates the tunability of FeOx catalysts in the acetone HDO reaction to favor different reaction pathways and the formation of products. It highlights that tailoring active sites is crucial for developing selective and optimized catalysts for the HDO reaction.

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Phthalates are organic molecules found in various everyday materials, such as plastics, but they do not bond chemically to the product. Consequently, they are released and contaminate the environment. In humans, ingesting phthalates can stimulate a functionality similar to estrogen hormones, acting as endocrine disruptors, thus requiring selective adsorption. This paper demonstrates the use of cyclodextrins (CDs), which are useful due to their capacity for selective adsorption by the inclusion of organic molecules in their internal cavities to remove pollutants from water. Graphene (Gr) is also evaluated due to its interesting electronic properties and a large surface, making this nanomaterial ideal for molecule adsorption. Through ab initio simulations, three phthalate molecules, benzyl butyl phthalate (BBP), dicyclohexyl-phthalate (DCHP), and dipropyl phthalate (DPP) interacting with β-CD and Gr, were evaluated. The results indicate that a weak interaction occurs, through physical adsorption. β-CD interacting with phthalates tends to form a host-guest complex. In the case of Gr, weak adsorption is favored by π-π interactions and H-bonds. Therefore, this study shows that these nanosystems are promising for removing phthalate molecules from wastewater.

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Metal-organic framework (MOF) derivatives, such as porous metal oxides with controlled morphology have received great attention for applications in various fields. In this paper, the experimental results show that porous CeO2 with high specific surface area (90.5 m2 g-1) and nanorod morphology can be obtained by calcining a Ce-MOF template at optimized temperature (300-500 °C). The formation mechanism of this porous structure as well as the influence of the calcination temperature are well explained by taking into account thermal behavior and intrinsic structural features of the Ce-MOF precursor. We employed the oxides formed as heterogeneous catalysts to reduce the soot originating from the incomplete combustion of diesel or diesel/biodiesel blends. The CeO2 materials exhibit outstanding catalytic activity, lowering the temperature of soot combustion from 610 to 370 °C. Compared with similar work, our catalyst exhibits enhanced soot oxidation activity, making it highly promising for diesel particulate filter applications. Such outstanding catalytic performance of the porous CeO2 nanorods benefits from their large specific surface area, and morphological and structural characteristics.

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Azo dyes are widely used in various industries. However, many of these dyes are carcinogenic and reduce light penetration into aqueous systems, posing a threat to human health and hampering photosynthesis in aquatic environments. In this study, guava seeds were used to produce activated carbon by chemical activation with ZnCl2. The carbon was characterized and used as an adsorbent to remove tartrazine dye in aqueous medium. X-ray diffraction showed the formation of a material with disordered graphitic planes, typical of activated carbons. The equilibrium time for the dye-activated carbon system was found to be 80 min by the Southwell plot method. The adsorbent removed 97.6% of the dye, representing an adsorbed concentration of 1.62 mg g-1 for an adsorbent dosage of 12 g L-1. The pseudo-second-order and Elovich kinetic models provided the best fit to experimental data, suggesting that chemisorption is the predominant mechanism, combined with the effect of surface heterogeneity. From an environmental point of view, the results suggest that the activated carbon produced is an efficient material for the treatment of industrial wastewater containing azo dyes.

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Complex oxides can present interesting semiconductor properties since the simultaneous presence of different metallic cations can modulate the conduction and valence band edges, affecting the bandgap energy, the onset potential for reactions and also the photocatalyst long-term stability. Here, we demonstrated that the synthesis of multinary oxides, very challenging using “traditional” methodologies, can be fast achieved by melting the precursor binary oxides in an arc furnace. As a proof of concept, arc-melting a mixture of Bi2O3 and V2O5 (Bi:V molar ratio of 1:1.05) resulted in almost pristine BiVO4 (97.3% from Rietveld refinement of X-ray diffraction (XRD) data); photoelectrochemical (PEC) measurements indicated a promising application as a photoanode for O2 evolution reaction. Conversely, the arc-melting of Bi2O3 and WO3 mixture (Bi:W molar ratio of 2:1.15) resulted in the biphasic Bi2WO6/Bi2W2O9; preliminary PEC analysis revealed characteristics of n-type semiconductor electrode with photoactivity under UV irradiation. Finally, the hierarchical Ag@α-AgVO3/Fe2O3 consisted of micrometric Fe2O3 particles decorated by AgVO3 nanoribbons and Ag nanoparticles, was obtained from melting Ag2O, Fe2O3 and V2O5 as precursors (Ag:Fe:V molar ratio of 3:1:2); PEC measurements also revealed possible application as a photoanode. The results for these three materials demonstrated the arc-synthesis as a fast, effective and scalable methodology for synthesizing complex oxides.

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Molecular and periodic allotropes based on cyclo[18]carbon, known as archicarbons, were investigated using density functional theory (DFT) in both molecular and periodic models. This study explores the physicochemical characteristics of these exquisite carbon allotropes, including various molecular archicarbons (spiro[18]carbon, bicyclo[8]carbon, 0-tricyclo[8] carbon, 0-bi(cyclo[19]carbon), l-bi(cyclo[19]carbon), and 0-fused[18]carbon) and periodic archicarbons (poly-spiro[8]carbon, poly-0-bi(cyclo[8]carbon), poly-l-bi(cyclo[8]carbon)). Most proposed molecular archicarbons showed higher cohesive energy than cyclo[18]carbon, except for bicyclo[8]carbon, which suggests that those may be experimentally observable. Proposed synthetic routes for both molecular and periodic archicarbons are suggested, highlighting their potential, particularly in semiconductor applications, and paving the way for further exploration of their distinct electronic properties.

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The graphene oxide (GO)-silver nanoparticles (AgNPs) hybrid material (GO-AgNPs) has garnered significant interest due to its ability to combine the unique properties of GO and AgNPs, showing promise applications in biomedicine, nanocomposites, biosensors, and antimicrobial materials. However, further investigation is needed to understand the nanobio-interactions and toxicity of GO-AgNPs nanohybrid. Assessing the toxicity of GO-AgNPs on red blood cells (hemolysis) and its interactions with blood biomolecules (biocorona formation) is mandatory for biomedical applications and safety evaluation of this material. In this work, we investigate the biocorona formation associated with GO-AgNPs after interaction with human plasma and hemolysate biomolecules linked to its hemolytic effects. Both GO and GO-AgNPs exhibited a dose-dependent hemolytic effect, with GO-AgNPs showing three times greater hemolysis than GO. Nonetheless, biocorona formation fully mitigated the hemolytic effect of both materials, however, morphological damages in red blood cells may occur yet. Our findings show that biocorona formation dramatically changes the surface chemistry, colloidal behavior and toxicity of this hybrid material. Finally, this work contributes to understanding how graphene-silver nanoparticles interact with blood components to design strategies to minimize toxicity risks and enhance their applications in biomedicine and nanobiotechnology.

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This study demonstrated the utility of real-time electrical impedance, utilizing the xCELLigence system to assess the cytotoxic effects of silver nanoparticles (AgNPs) and hydroxyapatite nanoparticles (HANPs) on A549 cells. Method validation confirmed the accuracy and reliability of cell index (CI) measurements. The NPs were thoroughly characterized to confirm their elemental composition, size, and morphology through energy dispersive spectroscopy, transmission electron microscopy, and dynamic light scattering. Cytotoxicity assays revealed a concentration-dependent response. Exposure to AgNPs resulted in a significant change in CI, with a pronounced increase followed by a sharp decrease in the first few hours after treatment at the highest concentration of 50 μg mL-1. This pattern suggested an initial cell response to AgNPs exposure, possibly indicating mechanisms such as apoptosis or necrosis, followed by a decrease in cell adhesion. Conversely, HANPs demonstrated a tendency to restore CI at higher concentrations (1-100 μg mL-1) before 48 h, suggesting a potential recovery in cell proliferation capacity. This underscores the diverse cell responses to NPs, emphasizing the sensitivity of the method in detecting subtle cytotoxic effects. These findings highlight the efficacy of real-time electrical impedance in dynamic nanoparticle cytotoxicity assessments, surpassing traditional assays. Adapting to high-throughput screening enhances nanomaterial safety evaluations.

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The Stern-Volmer equation is commonly used to describe the fluorescence quenching process, but its application faces challenges for quenchers with heterogeneous physicochemical characteristics (size and surface composition), such as graphene oxide. This study proposes a mathematical approach to calculate the association constant and the change in the Gibbs free energy in graphene oxide-fluorophore systems, considering the influence of quencher concentration (0.12 to 250 µg mL-1) and the net charge of the fluorophore on the formation of the non-fluorescent complex. It was identified that increasing the concentration of graphene oxide favors the formation of the non-fluorescent complex in the interaction with charged fluorophores, starting from 0.48 µg mL-1 for methylene blue and from 31.25 µg mL-1 for fluorescein sodium, predominantly leading to static fluorescence quenching. The interaction between graphene oxide and naphthalene lead to dynamic fluorescence quenching. This evaluation could be explored, for example, in nanotechnologies for environmental and biomedical applications.

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Brazil has abundant agro-industrial residues, such as cassava peel, opening the opportunity to produce high-added value chemicals by catalytic fast pyrolysis, in which the desirable products can be tailored. Aiming to provide an application of cassava peel residues, as well as to produce high-value BTEX (benzene, toluene, ethylbenzene and xylenes), beta zeolite-supported nickel (3 and 5 wt.%) catalysts were evaluated in fast pyrolysis. Without any catalyst, large amounts of high-value oxygenated compounds (ketones, carboxylic acid and phenolics) were produced while no BTEX was formed. This was related to the higher amount of cellulose and hemicellulose, as compared to lignin in cassava peel. However, over beta zeolite, these oxygenated compounds go on oligomerization, decarboxylation and decarbonylation producing aromatics (BTEX and polyaromatics), indicating a new reaction route provided by the catalyst. The amount of BTEX and other aromatics increased even more over zeolite-supported nickel, suppressing polyaromatics formation. This is related to the increased strength and amount of acidity of Lewis sites. The most selective catalyst (3% Ni) produces 67% of BTEX and no polyaromatics. Cassava peel and beta zeolite-supported nickel thus proved to be a promising combination to produce BTEX generating a new application of cassava peel residues.