In this work, silver nanoparticles (AgNPs) obtained from photographic waste were synthesized and electrodeposited via cyclic voltammetry using epoxy-graphite composite as an electrochemical substrate. Both electrodes, unmodified (Epoxy/C) and modified (Epoxy/C/AgNPs), were characterized electrochemically by electrochemical impedance spectroscopy (EIS), charge transfer constant (K0), and electroactive area. The modified electrode provided lower charge transfer resistance (275 Ω), more kinetically favored electron transfer (K0 = 1.15 × 10-3 cm s-1), and a 1.7-fold increase in the active area compared to the unmodified electrode. Additional characterizations by scanning electron microscopy (SEM) and Raman spectroscopy confirmed the presence of AgNPs structures on the carbonaceous surface. As a proof of concept, Pb2+ was used as a model analyte, and a square wave anodic stripping voltammetry (SWASV) method was developed to evaluate the analytical performance of both electrodes. A wider linear range (4.0 to 40.0 µg L-1), the appropriate limit of detection (1.2 µg L-1), and a 6-fold increase in sensitivity were found using the modified electrode, suggesting that the AgNPs significantly contributed to the performance of the electrode. The proposed method was applied to three real water samples, where the Pb2+ levels varied from 11.3 to 19.5 µg L-1. The proposed protocol (reuse of silver waste) has proven to be a powerful tool for improving the detection of Pb2+, which can be helpful for other electrochemical sensing applications in locations with minimal infrastructure.

Reduced graphene oxide/ruthenium oxide hexacyanoferrate (rGO/RuOHCF) modified electrode showed synergic activity between the materials attested by the increase of electrochemical current and stability. The preparation of the nanocomposite was made by a simple two-step electrochemical approach. The material structure was characterized by spectroscopic techniques (Raman, infrared and energy-dispersive X-ray) as well as its morphology by scanning electron microscopy and compared to the analogously prepared reduced graphene oxide (rGO) and ruthenium oxide hexacyanoferrate (RuOHCF) thin films spectra and images. The results suggest that the improvement of the nanocomposite electrochemical activity is generated by the well-distributed RuOHCF nanometric particles over high-surfaced graphene sheets. Ethanol electrochemical oxidation in the rGO/RuOHCF modified electrode was performed in 0.1 mol L-1 NaCl (pH = 1.5) solution and it showed an anodic current peak starting at 0.9 V. Scan rate tests exhibited a diffusion-controlled process not followed by any coupled chemical reaction. The determination of ethanol by amperometry coupled with batch injection analysis (BIA) system resulted in a wide linear range (20-400 mmol L-1) and good sensitivity (0.150 µA L mmol-1). The nanocomposite also showed application as an electrochemical sensor of ethanol in commercial samples mainly because of its easy preparation comparing to biosensors.

Zinc hexacyanoferrate (ZnHCF) is a Prussian Blue analog and can be intercalated by both monovalent and divalent ions. ZnHCF/multi-walled carbon nanotube (MWCNT) film could be used as a cathode for zinc ions battery. Carbon nanotubes improved significantly the electrochemical performance of the electrode. It is described the preparation of ZnHCF/MWCNT films by the interfacial method with cyclohexane/water mixture as solvent. The crystal structure, morphology, and microstructure of the as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, Mossbaüer, Raman spectroscopy, and infrared spectroscopy. Results revealed that the MWCNTs extend the electrochemical properties of the ZnHCF and influence the structure and morphology of the hexacyanoferrate particles. If tested as cathode material for zinc ion batteries, the nanocomposite film exhibits a capacity of 25.81 mA h g-1, which is much higher than those obtained for a ZnHCF single-component film (3.28 mA h g-1). The physical characteristics and properties that allow good reversibility to a high potential difference, achieved with the ZnHCF/MWCNT film, suggest new developments in the manufacture of translucent, flexible and light energy storage devices, which can be used as a lower-cost, safer and environmentally friendly alternative to the currently existing technologies.

This work presents the development and characterization of a new chemically modified electrode exploiting recordable Au-rewritable compact discs (AuCDs) as substrate for drop casting of a chemically-reduced graphene-oxide slurry focusing on simple and low-cost electrochemical sensors. Increase in electrochemical responses in cyclic voltammetric and amperometric measurements were achieved using the proposed sensor. Both scanning electron microscopy and atomic force microscopy data showed increase in rugosity (about 46% higher) for the chemically reduced graphene oxide (CRGO) AuCD surface while Raman spectroscopy confirmed the presence of structural defects of graphene. The calculated charge transfer resistances (Rct) and heterogeneous electron transfer rate constants (k0) were 1638 Ω and 0.0022 cm s-1 for the bare substrate, and 91 Ω and 0.0027 cm s-1 for the modified electrode, evidencing the facilitated electron transfer of the CRGO-AuCD surface. The dopamine (DP) amperometric detection using CRGO-AuCD provided low detection limit (0.12 µg L-1) compared with other modified electrodes already reported, high precision (relative standard deviation (RSD) < 5%) and analytical frequency (370 h-1). As a proof-of-concept, DP determination in synthetic saliva samples was performed and a satisfactory recovery value (98.6 ± 0.9%) was obtained.

Many studies have reported significant improvements in the photocatalytic degradation capacity of TiO2 immobilized in carbonaceous materials, mainly due to a well-characterized synergistic effect. The photocatalytic degradation of the estrogens 17β-estradiol and 17α-ethynylestradiol was evaluated using 1 mg L-1 aqueous solutions, employing a nanocomposite containing TiO2 and activated carbon (TiO2-AC) prepared by sol-gel technique. The synthesized materials were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). These techniques allowed to estimate the carbon proportion (11.4 wt.%), the phase composition (anatase: 80.2%, brookite: 14.0%, and rutile: 5.8%) and the superficial morphology. Using UV-A radiation provided by a high pressure mercury vapor lamp (125 W) and the synthesized photocatalysts, it was observed the almost complete removal of both estrogens in times shorter than 10 minutes. Considering the similarity between the degradation percentage of nanocomposites (TiO2 and TiO2-AC), no synergistic effects between AC and TiO2 could be assumed.

In this work the sol-gel method was used to synthesize a nanocomposite containing TiO2 and graphene oxide (GO). The photocatalytic activity of the TiO2/GO nanocomposite was evaluated regarding the degradation of a reactive dye (reactive black 5) in aqueous solution using processes assisted by UV-A radiation. Under these conditions the nanocomposite showed higher degradation efficiency than the reference photocatalyst (Degussa P25 TiO2), mainly due to the high degradation capacity of the synthesized TiO2 nanoparticles. Although contradictory to several reports in the specialized literature, no synergistic effect was observed between the nanocomposite components.