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•Rational design of catalyst by means of a CO reduction treatment.•Very high Ce(III) fraction values obtained by CO reduction treatment.•Surface hydrophobicity plays an important role ...in the CeO2-x nanoparticles reduction.•Low reduction temperatures values found for CeO2-x nanoparticles.
Oxygen vacancies are one of the most active defects existing at the surface of metal oxides. Engineering of defect chemistry, especially oxygen vacancies, represents the possibility of controlling the catalytic properties of nanoparticles. This work was dedicated to study the reduction properties of CeO2-x nanoparticles prepared using different synthesis parameters when exposed to a CO reducing atmosphere. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) and in situ time-resolved X-Ray Absorption Near Edge Spectroscopy (XANES) techniques were used to probe in situ the electronic properties of these nanoparticles exposed to the CO atmosphere. Compared to typical results found for CeO2-x nanoparticles, an improved reduction tendency is observed for these synthesized nanoparticles. It was possible to tune the oxygen vacancy population and the reduction temperature (TR) by means of the combination of synthesis and CO reducing atmosphere. The TR and Ce(III) fraction values reached can be as low as 108°C and as high as 0.92, respectively. The influence of structural and electronic properties of the nanoparticles on the reduction kinetics of the CeO2-x reduction is elucidated. The results provide a valuable route for the rational design of CeO2-x nanoparticles with the desired oxygen vacancy population, and then preparing them in the best conditions for applications.
This work describes the preparation, characterization and application of a hybrid material composed of disordered mesoporous silica (SiO2) modified with multiwalled carbon nanotubes (MWCNTs), ...obtained by the sol–gel process using HF as the catalyst. This hybrid material was characterized by N2 adsorption–desorption isotherms, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HR-TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This new hybrid material was used for the construction of a thin film on a glassy carbon electrode. The modified electrode using this material was designated SiO2/MWCNT/GCE. The electrocatalytic properties of the electrode toward dopamine, uric acid and paracetamol oxidation were studied by differential pulse voltammetry. Well-defined and separated oxidation peaks were observed in phosphate buffer solution at pH 7.0, in contrast with the ill-defined peaks observed with unmodified glassy carbon electrodes. The electrode had high sensitivity for the determination of dopamine, uric acid and paracetamol, with the limits of detection obtained using statistical methods, at 0.014, 0.068 and 0.098µmolL−1, respectively. The electrode presented some important advantages, including enhanced physical rigidity, surface renewability by polishing and high sensitivity, allowing the simultaneous determination of these three analytes in a human urine sample.
•A new silica-based hybrid material containing carbon nanotubes physically incorporated in the mesoporous silica matrix, SiO2/MWCNT, was obtained by the sol–gel process using HF as catalyst.•Good separation peaks between dopamine, uric acid and acetaminophen allowed the simultaneous determination of species.•Good electrocatalytic response regarding individual and simultaneous determination of species with a low detection limit.•Determination of these species in urine without any interference between them.
•Quinoa starch was used for development of biofilms.•Gold nanoparticles (AuNPs) were added to biofilms.•Effects of the addition of AuNPs about characteristics of biofilms quinoa starch.
Active ...biofilms of quinoa (Chenopodium quinoa, W.) starch were prepared by incorporating gold nanoparticles stabilised by an ionic silsesquioxane that contains the 1,4-diazoniabicyclo2.2.2octane chloride group. The biofilms were characterised and their antimicrobial activity was evaluated against Escherichiacoli and Staphylococcusaureus. The presence of gold nanoparticles produces an improvement in the mechanical, optical and morphological properties, maintaining the thermal and barrier properties unchanged when compared to the standard biofilm. The active biofilms exhibited strong antibacterial activity against food-borne pathogens with inhibition percentages of 99% against E. coli and 98% against S. aureus. These quinoa starch biofilms containing gold nanoparticles are very promising to be used as active food packaging for the maintenance of food safety and extension of the shelf life of packaged foods.
Because of its high surface area and combination of various functional groups, graphene oxide (GO) is currently one of the most actively studied materials for electroanalytical applications. It is ...not practical to utilize self-supported GO on its own and thus it is commonly integrated with different supporting carriers. Having a large lateral size, GO can only wrap the particles of the support and thus can significantly reduce the surface area of porous materials. To achieve synergy from the high surface area and polyfunctional nature of GO, and the rigid structure of a porous support, the lateral size of GO must essentially be decreased. Recently reported graphene oxide quantum dots (GOQDs) can fulfil this task. Here we report the successful preparation of an SiO
2
-GOQDs hybrid, where GOQDs have been incorporated into the mesoporous network of silica. The SiO
2
-GOQDs emit a strong luminescence with a band maximum at 404 nm. The Raman spectrum of SiO
2
-GOQDs shows two distinct peaks at 1585 cm
−1
(G-peak) and 1372 cm
−1
(D-peak), indicating the presence of a graphene ordered basal plane with aromatic sp
2
-domains and a disordered oxygen-containing structure. Covalent immobilization of GOQDs onto aminosilica
via
such randomly structured oxygen fragments was proven with the help of Fourier transform infrared spectroscopy, solid-state cross-polarization magic angle spinning
13
C nuclear magnetic resonance, and X-ray photoelectron spectroscopy. SiO
2
-GOQDs were used as a modifier of a carbon paste electrode for differential pulse voltammetry determination of two antibiotics (sulfamethoxazole and trimethoprim) and two endocrine disruptors (diethylstilbestrol (DES) and estriol (EST)). The modified electrodes demonstrated a significant signal enhancement for EST (370%) and DES (760%), which was explained by a π-π stacking interaction between GOQDs and the aromatic system of the analytes.
Graphene oxide quantum dots incorporated into a mesoporous silica network have been used as a modifier of a carbon paste electrode for the determination of antibiotics and hormones.
A new electrochemical sensor based on a carbon nanotube paste electrode modified with a Santa Barbara Amorphous material (SBA‐15) decorated with silver nanoparticles, namely CNT/SBA/Ag‐PE, was ...developed. It was successfully applied for individual and simultaneous determination of both paracetamol (PC) and sulfamethoxazole (SMZ) medicines. The electrode exhibited a linear dynamic range of 0.12–110 μmol L−1 for paracetamol and 0.06–70 μmol L−1 for sulfamethoxazole, and detection limits of 38 and 19 nmol L−1, respectively. The proposed sensor offered high sensitivity, fast response time and the potential for detecting both drugs simultaneously. The CNT/SBA/Ag‐PE enabled the simultaneous determination of PC and SMZ in urine samples with high recovery rates.
Organofunctionalized SBA-15 was obtained using two organic precursors, mercaptopropyltrimethoxysilane and/or an ionic silsesquioxane that contains the 1,4-diazoniabicyclo2.2.2octane group. These ...materials were used as support for gold nanoparticles loading, aiming to study their ability as gold nanoparticle stabilizers and also as adhesion agents on SBA-15 pore surface. Different gold amounts were employed to synthesize gold nanoparticles inside of pores. The materials were studied by using elemental and thermogravimetric analyses, adsorption-desorption isotherms, X-ray diffraction, UV–Vis spectroscopy and transmission electron microscopy. From these techniques, it was possible to compare the behaviour of both organic groups and their performance aiming to obtain gold nanocatalyst supported on SBA-15. The use of ionic silsesquioxane leads to smaller and spherical gold nanoparticles with narrower size distribution, and as consequence, the material presents better performance as catalyst.
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•Influence of stabilizer and adhesion agent on size and shape of AuNPs nanocatalyst.•Small size AuNPs dispersed inside of SBA-15 pores.•Narrow size distribution of AuNPs adhered on surface of ordered silica pores.•Ionic silsesquioxane as efficient stabilizer and adhesion agent for AuNPs.
In the present work, an experimental procedure was developed in order to obtain different amounts of titanium oxide highly dispersed on the surface of mesoporous ordered silica material, SBA-15 type. ...The procedure is based on successive grafting reactions using small quantities of titanium alkoxide precursor that allow obtaining high amounts of highly dispersed titanium oxide, even after calcination at 500 °C, and at the same time, preserves the mesopore structure of the silica. The proposed procedure avoids the aggregation of titanium oxide that forms crystallites, which can be detected by XRD, and consequently closes the mesopores. This behavior produces the artifact known as Tensile Strength Effect (TSE) which is detected by textural analysis. Mesoporous silica containing highly dispersed titanium oxide was applied as modifier MWCNT paste electrode for evaluation of sulfamethoxazole (SMZ) and trimethoprim (TMP). The electrode presents excellent response for simultaneous determination of both antibiotics in a wide linear concentration range. It presents high sensitivity, 10.5 and 25.1 nA μmol−1·L and low detection limit 60 and 70 nmol L−1, for SMZ and TMP respectively.
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•Reveling route to obtain titania highly dispersed inside of SBA-15 mesopores.•Identifying TSE effect in SBA-15 grafted with large amount of titania.•Simultaneous determination of SMZ and TMP antibiotics.
Structural, chemical, morphological, and hydrophilic surface characteristics of SBA-15 silica synthesized by hydrothermal method in an autoclave and in a microwave-heated reactor were analyzed in ...this work. The influence of time and temperature on these characteristics was investigated. Materials were characterized by textural analysis (BET), FTIR, TGA, XRD, goniometer contact angle, SEM, and TEM. It was possible to obtain SBA-15 silicas assisted by microwave heating irradiation with short-time synthesis (0.5–8 h) compared with the hydrothermal classic method (24 h). Materials presented surface area between 650 and 850 m
2
g
−1
. Through the XRD and TEM results, it was observed that mesostructured materials with two-dimensional, long-range, and hexagonal ordered channels are characteristic of SBA-15. This study showed that heating by microwave irradiation during silica synthesis generates materials with a greater amount of silanol groups. It is possible to control the surface properties of SBA-15 during the microwave-assisted synthesis through temperature tuning. Higher temperature provided SBA-15 with higher hydrophilicity.
Highlights
SBA-15 synthesis by MW reduces significant reaction time.
SBA-15 synthesized in MW at 80 °C showed 805 m
2
g
−1
of specific surface area.
Heating by MW in the silica synthesis generates materials with higher hydrophilicity.
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•Active, isolated gold ion sites on silica surface.•Gold catalyst efficiently applied in diyne cross coupling reactions.•Designing high-performance recyclable heterogeneous catalyst.
...A new strategy is presented to obtain an efficient heterogeneous gold catalyst constituted by isolated ionic gold sites, which is known to be effective in alkyne coupling reaction. The procedure is based on a significant difference between offered gold amount and available adsorbent sites on the support, ensuring the formation of very active isolated gold ion sites. In order to achieve this purpose, mesoporous silica xerogel was grafted with an ionic silsesquioxane containing charged ammonium quaternary group. The modified silica showed 0.25 mmol of cationic sites per gram of material and presented thermal stability up to 200 °C. This material was applied as support for immobilization of Au(III) ions as square planar AuCl4− complex. The gold amount offered was just 12 % of the exchangeable capacity. The catalyst was efficiently applied in the cross coupling reactions, in which only 0.22 mol% was applied to obtain symmetric and non-symmetric 1,3-diynes.
Mesoporous SBA-15-type silica, with cylindrical pores hexagonally ordered, was obtained and modified with niobium oxide in a highly dispersed way. Subsequently, a further modification with cobalt ...hematoporphyrin was performed. The ordered pore structure of the SBA-15 was preserved after successive modifications, maintaining its textural properties. The material was used to modify a carbon paste electrode that was successfully applied to the individual and simultaneous detection of both oxalic acid and uric acid, by using cyclic voltammetry and differential pulse voltammetry. For individual evaluation, the obtained detection limits for oxalic acid and uric acid were 9.94 and 0.17 μmol∙L
−1
, respectively. However, for the simultaneous evaluation of both analytes, the detection limits were 2.83 and 0.14 μmol∙L
−1
, for oxalic acid and uric acid, respectively.
Highlights
Well-ordered silica grafted with niobia and cobalt hematoporphyrin.
SBA-15 texture preserved after successive modifications with niobium oxide and hematoporphyrin macromolecule.
Simultaneous electrochemical evaluation of oxalic acid and uric acid.
Modified carbon paste electrode for sensitive evaluation of uric and oxalic acids.
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