Quantification and description of photothermal heating effects in plasmon-assisted electrochemistry.

A growing number of reports have demonstrated plasmon-assisted electrochemical reactions, though debate exists around the mechanisms underlying the enhanced activity. Here we address the impact of plasmonic photothermal heating with cyclic voltammetry measurements and finite-element simulations. We find that plasmonic photothermal heating causes a reduction in the hysteresis of the anodic and cathodic waves of the voltammograms along with an increase in mass-transport limiting current density due to convection induced by a temperature gradient. At slow scan rates, a temperature difference as low as 1 K between the electrode surface and bulk electrolytic solution enhances the current density greater than 100%. Direct interband excitation of Au exclusively enhances current density by photothermal heating, while plasmon excitation leads to photothermal and nonthermal enhancements. Our study reveals the role of temperature gradients in plasmon-assisted electrochemistry and details a simple control experiment to account for photothermal heating.

Tracking Electrochemistry on Single Nanoparticles with Surface-Enhanced Raman Scattering Spectroscopy and Microscopy.

Studying electrochemical reactions on single nanoparticles is important to understand the heterogeneous performance of individual nanoparticles. This nanoscale heterogeneity remains hidden during the ensemble-averaged characterization of nanoparticles. Electrochemical techniques have been developed to measure currents from single nanoparticles but do not provide information about the structure and identity of the molecules that undergo reactions at the electrode surface. Optical techniques such as surface-enhanced Raman scattering (SERS) microscopy and spectroscopy can detect electrochemical events on individual nanoparticles while simultaneously providing information on the vibrational modes of electrode surface species. In this paper, a protocol to track the electrochemical oxidation-reduction of Nile Blue (NB) on single Ag nanoparticles using SERS microscopy and spectroscopy is demonstrated. First, a detailed protocol for fabricating Ag nanoparticles on a smooth and semi-transparent Ag film is described. A dipolar plasmon mode aligned along the optical axis is formed between a single Ag nanoparticle and Ag film. The SERS emission from NB fixed between the nanoparticle and the film is coupled into the plasmon mode, and the high-angle emission is collected by a microscope objective to form a donut-shaped emission pattern. These donut-shaped SERS emission patterns allow for the unambiguous identification of single nanoparticles on the substrate, from which the SERS spectra can be collected. In this work, a method for employing the SERS substrate as a working electrode in an electrochemical cell compatible with an inverted optical microscope is provided. Finally, tracking the electrochemical oxidation-reduction of NB molecules on an individual Ag nanoparticle is shown. The setup and the protocol described here can be modified to study various electrochemical reactions on individual nanoparticles.

Use of brewing industry waste to produce carbon-based adsorbents: Paracetamol adsorption study.

This work aimed to produce activated carbon (AC) from brewing industry waste (the malt bagasse) to adsorb Paracetamol. Malt bagasse was characterized by moisture and ash contents and thermogravimetric analysis. Three types of AC were prepared: C400 (400 °C) and C500 (500 °C) under oxidizing atmosphere, and CN550 (550 °C) under nitrogen atmosphere. Some of these ACs were characterized by pH, point of zero charge (pHPZC), infrared spectroscopy, N2 adsorption-desorption isotherms, scanning electron microscopy, and temperature-programed desorption of CO2 and NH3. A pHPZC value < 7.0 and high density of acid sites were identified for CN550. Specific surface areas were between 192.5 and 364.0 m2.g-1. Adsorption kinetic studies were performed in a batch system with 50 mL of Paracetamol solution (100 mg.L-1) under pH 4 and 0.75 g of adsorbent (optimized conditions). The time to reach adsorption equilibrium was 20 min with 98.3% Paracetamol removal for CN550 AC. The pseudo-second order model and the Langmuir isotherm best fitted experimental data. Brewing industry waste can be used as a source of organic matter for AC production, since the percentage of Paracetamol removal in this study showed that CN550 AC presentes high adsorption efficiency and economically viable production.