An easy effective method for the activation of commercial screen-printed carbon electrodes (SPCEs) using H 2 O 2 is presented to enhance sensing performances of carbon ink. Electrochemical activation consists of 25 repetitive voltammetric cycles at 10 mVs 1 using 10 mM H 2 O 2 in phosphate buffer (pH 7). This treatment allowed us to reach a sensitivity of 0.24±0.01 µA µM-1 cm-2 for the electroanalysis of H 2 O 2 , which is 140-fold higher than that of untreated SPCEs and 6-fold more than screen-printed platinum electrodes (SPPtEs). Electrode surface properties were characterized by SEM, EIS and XPS. The results revealed atomic level changes at the electrode surface, with the introduction of new carbon-oxygen groups being responsible for improved electrotransfer properties and sensitivity. Our method was compared with other previously described ones. The methodology is promising for the activation of commercial carbon inks-based electrodes for sensor applications.

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The purpose of this study is to produce and characterize biomass pyrolysis liquids obtained in an ablative bed reactor at laboratory scale. The feedstocks selected include eucalyptus (Eucalyptus tereticornis) chips, camelina (Camelina sativa) straw pellets, and wheat (Triticum aestivum) straw pellets. Pyrolysis experiments were carried out at 550 °C and atmospheric pressure with a nitrogen flow rate of 2.24 N L/min and an average solids feeding rate of 2.5 g/min, yielding 42.4, 48.8, and 41.0 wt % liquids for eucalyptus, camelina straw pellets, and wheat straw pellets, respectively. Such liquids, also known as bio-oils, were characterized using gas chromatography−mass spectrometry and complemented with water content, pH measurements, higher heating values, viscosity, and proximate, and ultimate analyses. The distribution of products and their properties were influenced by both the raw materials characteristics (chemical composition and structure) and the operating conditions used in the experimental setup. With regard to raw material characteristics, features such as fixed carbon content in raw biomass seemed to impact the amount of solid products obtained as in the case of eucalyptus chips, which was the sample with higher fixed carbon content and the one that yielded a greater amount of solids. On the other hand, the experimental setup conditioned the results in the sense of how devolatilization of the materials took place, which in turn influenced the yield to liquid products obtained from the process. Wheat straw yielded a bio-oil with a significant number of unknown molecules in the organic phase (∼32.8 wt %), most likely produced from the protein fraction of this biomass. On the other hand, eucalyptus resulted in a larger fraction of carbonaceous residues (∼37.1 wt %), while wheat and camelina straw produced around 28.1 and 25.5 wt %, respectively. Finally, camelina presented interesting characteristics as feedstock for pyrolysis due to its low nitrogen content (0.4−0.5 wt %) and lower char yields (∼25.5 wt %).

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Screen-printed carbon electrodes (SPCEs) are widely used for the electroanalysis of a plethora of organic and inorganic compounds. These devices offer unique properties to address electroanalytical chemistry challenges and can successfully compete in numerous aspects with conventional carbon-based electrodes. However, heterogeneous kinetics on SPCEs surfaces is comparatively sluggish, which is why the electrochemical activation of inks is sometimes required to improve electron transfer rates and to enhance sensing performance. In this work, SPCEs were subjected to different electrochemical activation methods and the response to H2O2 electroanalysis was used as a testing probe. Changes in topology, surface chemistry and electrochemical behavior to H2O2 oxidation were performed by SEM, XPS, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The combination of electrochemical activation methods using H2SO4 and H2O2 proved particularly effective. A reduction in charge transfer resistance, together with functionalization with some carbon-oxygen groups on carbon ink surfaces, were likely responsible for such electrochemical improvement. The use of a two-step protocol with 0.5 M H2SO4 and 10 mM H2O2 under potential cycling conditions was the most effective activation procedure investigated herein, and gave rise to 518-fold higher sensitivity than that obtained for the untreated SPCEs upon H2O2 electrooxidation. The electrochemical behavior of acetaminophen, hydroquinone and dopamine is also shown, as a proof of concept upon the optimum activated SPCEs.

The sensitive determination of hydrogen peroxide has broad analytical applications. In this work, a novel non-enzymatic hydrogen peroxide sensor based on Pt nanoparticles (PtNPs) electrochemically deposited on previously modified and activated screen-printed carbon electrodes (aSPCEs) was constructed. The pretreatment consisted of subjecting the electrodes to a surface activation treatment with hydrogen peroxide followed by the electrodeposition of poly(azure A) films (PAA) in a sodium dodecyl sulfate micellar aqueous solution. The PtNPs/PAA/aSPCEs were characterized by scanning electron microscope, X-Ray photoelectron spectrometry, linear scan voltammetry and electrochemical impedance spectroscopy. Linear sweep voltammograms showed that the oxidation peak potential of H2O2 shifts from ~1 V at SPCEs to ~0.1 V at PtNPs/PAA/aSPCEs. The fabricated electrodes showed excellent electrocatalytic activity towards H2O2 oxidation, making its detection possible at 0.1 V. The detection limit was 51.6 nM, which is significantly lower than other modified electrodes found in the literature, and the linear range ranging from 0 to 300 µM. The proposed electrode was successfully applied to the determination of H2O2 in real samples in different areas. Additional experiments against common interfering agents (ascorbic acid, dehydroascorbic acid, glucose, salicylic acid, among other compounds) showed no increase in the current signal and only in the case of ascorbic acid a small interference, not greater than 10% is observed, which indicates high specificity of the sensor. These electrodes open up alternative avenues for the development of highly sensitive, robust and low cost electrochemical H2O2 sensors for field tests.

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A laboratory experiment in which students recycle silver and platinum selectively from spent screenprinted platinum electrodes is described. The recovered silver in solution is used to show its spontaneous redox reaction with a copper sheet. The recovered platinum is electrodeposited onto a screen-printed carbon electrode to develop a sensor for hydrogen peroxide quantification in a commercially available hair lightener. The experiment is designed for a 3 h laboratory period and can be adapted for upper-division undergraduate education, graduate education, or even research students in electrochemistry, environmental chemistry, analytical chemistry, materials science, chemical engineering, or physical chemistry laboratories. It allows students to train in adequately handling strong acids, working in fume hoods, and neutralizing acid gases. It also allows one to teach the basics of metal recycling and enables students to learn the fundamentals of electrochemical sensing. The experiment also helps to raise student awareness of waste disposal problems and how recycling can help to reduce the amount of waste that we create.