In this work, the synthesis of silver and copper nanoparticles and bimetallic silver-platinum and copper-platinum nanoparticles, in previously functionalized multi-walled carbon nanotubes (MWCNT), was carried out using the intermatrix synthesis for the charge of the first metal, and a galvanic replacement for the deposition of a second metal to form the bimetallic NPs. Well-controlled small size NPs were obtained as demonstrated by TEM, with a homogeneous distribution and mean particle diameters of ca. 2.9 nm. The hybrid MNPs/MWCNTs catalysts were characterized by FTIR, TEM and XPS. The metal content was determined by TGA and validated via FAAS. Thereupon, the metal-MWCNTs hybrid catalysts were incorporated into a polymeric membrane (PM) and characterized by SEM. The effects of the hybrid catalyst-polymeric support interactions and the role of the MNPs/MWCNTs/PM materials as heterogeneous catalysts were evaluated from the catalytic performance on the reduction of 4-nitrophenol as a model reaction. An apparent rate constant normalized by the metal content of 1706.7 s −1 mol −1 was achieved for the best system (Ag-PtNPs/MWCNTs/PMR) along with a decrease in the percentage of conversion from 95% (first cycle) to 80% (third cycle). Results indicated that the catalytic activity depends mainly on the MNPs size and the metal content in the catalyst. The catalytic activity of the MNPs/MWCNTs was only 3 times higher than for the MNPs/MWCNTs/PMs catalysts, with the former presenting the advantage of being easily recovered from the reaction medium, thus, demonstrating the capability to perform an efficient and sustainable process.

We report the synthesis of supported noble metal nanoparticles on cellulose nanofibers cross-linked with borate as highly efficient sustainable catalysts.

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A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of Au salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for Au extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L 4-nitrophenol aqueous solution with 10 mmol L NaBH solution within 25 min.

Corrosion is a serious problem that affects several industries and causes significant economic losses. In recent years, the transportation industry has replaced several ferrous parts with aluminum or magnesium alloys to produce lighter vehicles. Due to this, galvanic corrosion has been more frequent in that industry. In this work, a colorimetric sensor for the detection of Al(III) species during galvanic corrosion is presented. The sensor was made of a chromophore immobilized on a gel electrolyte based on NaCl and agar. The sensor developed a red coloration proportional to the Al(III) concentration under the pH interval studied (3.2–4.5). A galvanic couple consisting of an aluminum alloy and carbon steel was used to test the capacity of the sensor to develop the production of Al(III) into the gel electrolyte and over the whole aluminum surface. Through image processing, it was possible to construct 2D Al(III) concentration maps over time using a commercial aluminum alloy (AA7075) and a castable aluminum alloy from a steering rack as a real sample. Graphical Abstract

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The present work focuses on studying the acidity generated in the electrolyte during the galvanic corrosion of an aluminum alloy (AA) in contact with carbon steel (CS). A bare galvanic system exposed to a thin NaCl electrolyte has been considered. In this work, a mathematical model solved by the finite element method (FEM) is presented. It considers both electrochemical and aluminum hydrolysis reactions in the electrolyte solution. The model allows predicting the propagation of acidic pH fronts along the AA surface. Subsequently, the results obtained were validated by employing an innovative experimental technique using agar films doped with a pH indicator. The experimentally measured acid fronts show a similar trend to the numerical predictions and have a reasonable correlation in the first few minutes of the corrosion process.