Monitoring Reaction Intermediates in Plasma-Driven SO₂, NO, and NO₂ Remediation Chemistry Using In Situ SERS Spectroscopy

Abstract

In situ surface-enhanced Raman scattering (SERS) spectroscopy is used to identify the key reaction intermediates during the plasma-based removal of NO and SO 2 under dry and wet conditions on Ag nanoparticles. Density functional theory (DFT) calculations are used to confirm the experimental observations by calculating the vibrational modes of the surface-bound intermediate species. Here, we provide spectroscopic evidence that the wet plasma increases the SO 2 and the NO x removal through the formation of highly reactive OH radicals, driving the reactions to H 2 SO 4 and HNO 3 , respectively. We observed the formation of SO 3 and SO 4 species in the SO 2 wet-plasma-driven remediation, while in the dry plasma, we only identified SO 3 adsorbed on the Ag surface. During the removal of NO in the dry and wet plasma, both NO 2 and NO 3 species were observed on the Ag surface; however, the concentration of NO 3 species was enhanced under wet-plasma conditions. By closing the loop between the experimental and DFT-calculated spectra, we identified not only the adsorbed species associated with each peak in the SERS spectra but also their orientation and adsorption site, providing a detailed atomistic picture of the chemical reaction pathway and surface interaction chemistry.

Recent Advances in Plasma Catalysis

“…Li et al used surface-enhanced Raman scattering on Ag nanoparticles to identify surface intermediates, their orientations, and adsorption sites during plasma-driven removal of NO and SO 2 . 5 Inelastic neutron scattering performed by Barboun et al revealed the presence of NH x and Ni−hydrides after sequential N 2 and H 2 plasma exposure, providing evidence of plasma-facilitated surface reactions in ammonia synthesis. 6 Xu et al utilized in situ DRIFTS and mass spectrometry to show that the plasma mitigates CO surface poisoning, enhancing water− gas shift reaction, and regenerating the catalyst in situ.…”

“…Along with plasma phase characterization, an effort has been made to identify surface species and discover surface reaction mechanisms via in situ/operando spectroscopy. Li et al used surface-enhanced Raman scattering on Ag nanoparticles to identify surface intermediates, their orientations, and adsorption sites during plasma-driven removal of NO and SO 2 . Inelastic neutron scattering performed by Barboun et al revealed the presence of NH x and Ni–hydrides after sequential N 2 and H 2 plasma exposure, providing evidence of plasma-facilitated surface reactions in ammonia synthesis .…”

Ag/ZnO Nanocomposite-Decorated Capillary for Rapid Trace Gas Identification Based on Surface-Enhanced Raman Scattering under Ambient Conditions

“…At high concentrations, SO 2 reacts with reactive oxygen species on the surface of nanocomposites to generate SO 3 , which dissolves in water and forms SO 4 2– . SO 3 2– has two characteristic peaks at 615 and 925 cm –1 , adjacent to the peaks of SO 4 2– at 650 and 960 cm –1 , − respectively. Therefore, the superposition of the peaks results in two broad peaks located around 620 and 940 cm –1 , which gradually red-shifted with the increment of SO 2 concentration.…”

Nanomaterial-based surface-enhanced Raman scattering spectroscopy for sensing and diagnostics of gas molecules in environment and healthcare

“…In another work, Kim et al 93 demonstrated that similar SERS-active plasmonic chips with a 3D nanoporous architecture composed of Ag NWs deposited with Au hemispheres on their surfaces were extremely sensitive with fast NO 2 gas sensitivity at room temperature. Recently, Li et al 94 frequency (RF) magnetron sputtering on PSCCs creating a hot spot with large electromagnetic enhancement provides excellent SERS sensitivity and reliability. It occurred due to the self-assembled flexible hexagonally close-packed PSCCs producing 75 and 25 nm voids in the 500 and 200 nm PSCCs monolayers acting as an effective plasmonic propagator for SERS sensors signal.…”

“…In another work, Kim et al 93 demonstrated that similar SERS-active plasmonic chips with a 3D nanoporous architecture composed of Ag NWs deposited with Au hemispheres on their surfaces were extremely sensitive with fast NO 2 gas sensitivity at room temperature. Recently, Li et al 94 studied the interaction of oxides of S and N ( i.e. , NO 2 , NO 3 , SO 3 , and SO 4 ) on plasmonic metal Ag surfaces.…”