A plasma/liquid microreactor for radical reaction chemistry: An experimental and numerical investigation by EPR spin trapping

Abstract

In this paper, a novel plasma/liquid microreactor has been developed to generate and inject radical species with the aim to perform chemical synthesis reactions in liquid phase. Plasma has always been considered as a source of reactive species, such as radicals, atoms, electrons, etc., with applications mostly dedicated to surface modifications of materials. By injecting reactive species created by the plasma to the liquid phase, it is possible to initiate liquid phase synthesis reactions. In addition, gas/liquid interactions can be enhanced with a high surface‐area‐to‐volume ratio by confining the plasma and the liquid in diphasic micro‐structured systems. Herein is reported a novel plasma/liquid microreactor for liquid phase radical reactions. Radicals are generated in the gas phase in a steady flow microreactor and then transported to the liquid phase. The spin trapping reaction and the electron paramagnetic resonance (EPR) spectroscopy have been used to identify and quantify the radical species generated in the microreactor. Hydroxyl radicals and hydrogen atoms have been detected and measured in the liquid phase, indicating the huge potential of the microreactor as a handful tool for chemical synthesis.

Cellulose defibrillation and functionalization by plasma in liquid treatment

“…Similarly, the broadening of the peak at 1700 – 1600 cm −1 after Ar/O 2 and Ar-ACN treatments indicates the presence of carbonyl and carboxyl groups overlapped with the OH bending of the absorbed water 42 , 43 . These chemical modifications of the cellulose surface are possible due to the reactive species (•OH, OH − , O 2 − , •NH 2 ) which may appear in water after plasma immersion 44 . No important changes were noticed in the position of the bands characteristic to C-O-C asymmetric stretching and C-O stretching vibrations at 1160 and 1057 cm −1 41 , 45 , showing that the cellulose backbone was not significantly disturbed, in agreement with the small changes observed in the thermal behavior of MCC after the 30 min plasma treatments.…”

A Microfluidic Atmospheric-Pressure Plasma Reactor for Water Treatment

“…Recently, by exploiting the advantages of miniaturisation, effective dielectric barrier discharge (DBD) systems within microfluidic platforms operated at atmospheric pressure have been presented and utilised for plasma characterisation and synthesis reactions [18][19][20][21][22], but these systems have yet to be applied to PWT. Plasma microfluidic devices have also been employed recently for plasma synthesis in dual phase plasma-liquid systems, in particular for gold nanoparticle synthesis [23], for synthesis reactions [24], and for controlled oxidative processes [25], with all three studies indicating the potential of dual phase plasma-liquid microfluidic systems for studies in plasma water treatment.…”

Special issue: Plasma and Liquids

“…Measurement of ·OH and other oxidative species is a significant challenge, and typically the major approaches, following the AOP, and environmental and radiation chemistry literature, include utilization of radical chemical probes, use of spin traps for electron paramagnetic resonance, EPR, and other methods (e.g., laser induced fluorescence). M. Zhang et al utilized EPR, with the spin trap DMPO, coupled with a COMSOL Multiphysics based model using the plasma module for Ar/H 2 O case in their micro reactor . The model includes both gas and liquid phase reactions.…”

“…Many different types of electrode configurations, plasma power sources, and reactor geometries have been developed and studied for contacting plasma with liquids, typically liquid water, but also including liquid organics . The work published here by M. Zhang et al demonstrates a miniaturization of the gas‐liquid water plasma reactor whereby the plasma is formed in a small gas cavity (3 mm deep) contacting a microchannel (500 μm wide) with flowing liquid water . In another case, Wandell et al utilize a small flowing water stream contacting a central gas core (4 mm gap with thin liquid film) with the electrical discharge propagating along the interface .…”

“…Other papers in this issue include analysis of direct underwater discharges (Yang et al and Kozakova et al), study of pollutant treatment (Magureanu et al, Kozakova et al, Tampieri et al), determination of the fundamental species formation for plasma formed in contacting with a liquid water stream (X. Zhang et al, Tarabova et al, and Wandell et al), and analysis of plasma with organic liquids (Rezaei et al and Franclemont et al) . Of particular importance for chemical oxidation is the determination of hydroxyl radical, ·OH, concentrations and production using chemical probes (M. Zhang et al and X. Zhang et al), and in the case of an air plasma contacting the liquid the determination of nitrogen containing species and their interactions with species such as hydrogen peroxide (Tarabova et al) is necessary.…”