ambient air

Determination of NO densities in a surface dielectric barrier discharge using optical emission spectroscopy

A new computationally assisted diagnostic to measure NO densities in atmospheric-pressure microplasmas by Optical Emission Spectroscopy (OES) is developed and validated against absorption spectroscopy in a volume Dielectric Barrier Discharge (DBD). The OES method is then applied to a twin surface DBD operated in N2 to measure the NO density as a function of the O2 admixture (0:1%–1%). The underlying rate equation model reveals that NO(A2Σ+) is primarily excited by reactions of the ground state NO(X2Π) with metastables N2(A3Σ+u).

Publisher: 
AEPT
Project: 
SFB 1316
Authors: 
B. Offerhaus
F. Kogelheide
D. Jalat
N. Bibinov
J. Schulze
K. Stapelmann
P. Awakowicz

Characterisation of volume and surface dielectric barrier discharges in N2–O2 mixtures using optical emission spectroscopy

A volume and a twin surface dielectric barrier discharge (VDBD and SDBD) are generated in different nitrogen–oxygen mixtures at atmospheric pressure by applying damped sinusoidal voltage waveforms with oscillation periods in the microsecond time scale. Both electrode configurations are located inside vacuum vessels and operated in a controlled atmosphere to exclude the influence of surrounding air. The discharges are characterised with different spatial and temporal resolution by applying absolutely calibrated optical emission spectroscopy in conjunction with numerical simulations and current–voltage measurements. Plasma parameters, namely the electron density and the reduced electric field, and the dissipated power are found to depend strongly on the oxygen content in the working gas mixture. Different spatial and temporal distributions of plasma parameters and dissipated power are explained by surface and residual volume charges for different O2 admixtures due to their effects on the electron recombination rate. Thus, the oxygen admixture is found to strongly influence the breakdown process and plasma conditions of a VDBD and a SDBD.

Publisher: 
AEPT
Project: 
SFB 1316
Authors: 
F. Kogelheide
B. Offerhaus
N. Bibinov
P. Krajinski
L. Schücke
J. Schulze
K. Stapelmann
P. Awakowicz

Plasma‐driven in situ production of hydrogen peroxide for biocatalysis

Peroxidases and peroxygenases are promising classes of enzymes for biocatalysis because of their ability to carry out one‐electron oxidation reactions and stereoselective oxyfunctionalizations. However, industrial application is limited, as the major drawback is the sensitivity toward the required peroxide substrates. Herein, we report a novel biocatalysis approach to circumvent this shortcoming: in situ production of H2O2 by dielectric barrier discharge plasma. The discharge plasma can be controlled to produce hydrogen peroxide at desired rates, yielding desired concentrations. Using horseradish peroxidase, it is demonstrated that hydrogen peroxide produced by plasma treatment can drive the enzymatic oxidation of model substrates. Fungal peroxygenase is then employed to convert ethylbenzene to (R)‐1‐phenylethanol with an ee of >96 % using plasma‐generated hydrogen peroxide. As direct treatment of the reaction solution with plasma results in reduced enzyme activity, the use of plasma‐treated liquid and protection strategies are investigated to increase total turnover. Technical plasmas present a noninvasive means to drive peroxide‐based biotransformations.

Publisher: 
Applied Microbiology
Project: 
SFB 1316
Authors: 
A. Yayci
A. Gomez Baraibar
M. Krewig
E. Fernandez Fueyo
F. Hollmann
M. Alcaide
R. Kourist
J. Bandow