Mechanisms of Active Substances in a Dielectric Barrier Discharge Reactor: Species Determination, Interaction Analysis, and Contribution to Chlorobenzene Removal

Mechanism of chlorobenzene removal in biotrickling filter enhanced by non-thermal plasma: Insights from biodiversity and functional gene perspectives

Biotrickling filter (BTF) technology is inefficient in the treatment of Cl-containing volatile organic compounds (VOCs) such as chlorobenzene (CB). This study adopted non-thermal plasma (NTP) as a pretreatment and conducted in-depth analyses, especially in microorganisms, to investigate strengthening mechanism of a NTP to a BTF in the process. The introduction of NTP enhance efficiency of CB removal from 65 % to 90 %, and CO2 generation from 60 % to 85 %. It is found that the protein content of the extracellular polymeric substances increases from 212 × 10-3 mg·g-1 filler to 299 × 10-3 mg·g-1 filler, thus CB capturing and utilization enhanced. Metagenomic analysis showed that bacteria with CB-degrading properties were enriched in BTF, and CB was involved in cellular metabolism as a carbon source. The presence of active substances from NTP is found to stimulate the ability of BTF treatment. The findings of this study will provide theoretical support for the application of NTP-BTF technology.

Enhanced Removal Performance and Economical Efficiency of Volatile Organic Sulfur Compounds by Silver-Modified ZSM-5 Zeolites under a High-Humidity Environment: A Mechanistic Study of the Adsorption-Plasma Catalytic Process

Dimethyl sulfide (DMS) is a harmful volatile organic sulfur compound (VOSC), which must be effectively controlled. The adsorption-plasma catalytic (APC) process is an efficient and economical route for the elimination of low-concentration VOSCs; however, there are still many challenges in humid environment. In this study, a series of zeolites with different Si/Al ratios and Ag loadings were designed, and were performed for DMS removal by APC process. At 80% relative humidity, the DMS adsorption capacity of Ag5-ZSM25 reached 33.9 mg/g, which was 7.9 times that of ZSM25 and nearly 2 times that of Ag5-ZSM200. Analyses via UV-vis, X-ray photoelectron spectroscopy (XPS), and CO-FTIR confirmed that Ag+ was the predominant species for DMS adsorption and degradation in Ag5-ZSM25. DMS-temperature-programmed desorption (TPD) and density functional theory (DFT) calculations indicated that Ag+ significantly enhanced the binding energy with DMS and weakened the competitive adsorption impact of H2O. In the plasma regeneration stage, Ag5-ZSM25 demonstrated an 89% mineralization, with Ag+ being crucial for DMS mineralization. Based on the in situ plasma DRIFT spectra, a possible degradation pathway for DMS was proposed. The APC process achieved an energy efficiency of 1.66 g/kWh, tripling that of the continuous plasma catalytic process and providing guidance for low-concentration DMS elimination.

Cotton stalk decomposition with DBD low-temperature plasma: Characteristics and kinetics

DBD low-temperature plasma (DLTP) is recognized as one of the most efficient technologies for treating cotton stalks. This study investigates the impact of various conditions on the gas production characteristics of cotton stalks (CS) and delves into the DLTP decomposition kinetics of CS and CSC in oxygen-enriched (30 % O2/Ar) and CO2 atmospheres. The decomposition rates of CS followed the order CO2 > N2 > Ar. The decomposition behavior of CSC in oxygen-enriched DLTP (30 % O2/Ar) aligned well with the chemical reaction model. The activation energies for CSC decomposition at 900 °C and 1000 °C were determined to be 23.8 kJ/mol and 33.8 kJ/mol, respectively. Moreover, the reaction rate decreased at higher carbonization temperatures, which proved to be detrimental to the decomposition of CSC. The DLTP decomposition of CSC in CO2 exhibited consistency with the fitting results of the unreacted shrinking core model, revealing an observed activation energy of 19.4 kJ/mol.

Impact of the geometric structure parameter on the performance of dielectric barrier reactor for toluene removal

The reasonable geometry design of non-thermal plasma (NTP) reactor is significant for its performance. However, optimizing the reactor structure has received insufficient attention in the studies on removing volatile organic compounds by NTP. Several dielectric barrier discharge (DBD) reactors with various barrier thicknesses and discharge gaps were designed, and their discharge characteristics and toluene degradation performance were explored comprehensively. The number and intensity of current pulses, discharge power, emission spectrum intensity and gas temperature of the DBD reactors increased as barrier thickness decreased. The toluene removal efficiency and mineralization rate increased from 23.2-87.1% and 5.3-27.9% to 81.7-100% and 15.9-51.3%, respectively, when the barrier thickness reduced from 3 to 1 mm. With the increase of discharge gap, the breakdown voltage, discharge power, gas temperature and residence time increased, while the discharge intensity decreased. The reactor with the smallest discharge gap (3.5 mm) exhibited the highest toluene removal efficiency (78.4-100%), mineralization rate (15.6-40.9%) and energy yield (8.4-18.7 g/kWh). Finally, the toluene degradation pathways were proposed based on the detected organic intermediates. The findings can provide critical guidance for designing and optimizing of DBD reactor structures.

Effect of gas components on the degradation mechanism of o-dichlorobenzene by non-thermal plasma technology with single dielectric barrier discharge

In this paper, the degradation of o-DCB under different gas-phase parameter conditions was investigated using the SDBD-NTP system. The results showed that the increase in initial and oxygen concentrations had opposite effects on the degradation of o-DCB. Among them, the increase of oxygen concentration promoted the degradation of o-DCB. Relative humidity promoted and then inhibited the degradation of o-DCB. The highest degradation efficiency of o-DCB was achieved at RH = 15%, reaching 91% at 29W. In the study of by-products, it was found that O3 and NOx were the main inorganic by-products, and that different oxygen levels and relative humidity conditions had a large effect on the production of O3 and NOx. In all of them, the concentration of O3 decreased with the increase of input power. NOx increased with increasing oxygen concentration, but the increase in relative humidity inhibited the production of NO and N2O and promoted the conversion of NO2. A study of organic by-products revealed this. In the absence of oxygen, a higher number of benzene products appeared. Whereas, with the addition of oxygen, only in the by-products under conditions where no relative humidity was introduced, benzene ring products were predominantly present in the by-products. However, when RH was added, n-hexane was found to be present in the by-products. This may be because the introduction of OH• favors the destruction of the benzene ring. Finally, the possible reaction pathways and reaction mechanisms of o-DCB under different gas-phase parameters are given. It provides a reference for future related scientific research as well as scientific problems in practical applications.

Volatile organic compound removal by post plasma-catalysis over porous TiO2 with enriched oxygen vacancies in a dielectric barrier discharge reactor

Non-thermal plasma (NTP) degradation of volatile organic compounds (VOCs) into CO₂ and H₂O is a promising strategy for addressing ever-growing environment pollution. However, its practical implementation is hindered by low conversion efficiency and emissions of noxious by-products. Herein, an advanced low-oxygen-pressure calcination process is developed to fine-tune the oxygen vacancy concentration of MOF-derived TiO₂ nanocrystals. Vo-poor and Vo-rich TiO₂ catalysts were placed in the back of an NTP reactor to convert harmful ozone molecules into ROS that decompose VOCs via heterogeneous catalytic ozonation processes. The results indicate that Vo-TiO₂-5/NTP with the highest Vo concentration exhibited superior catalytic activity in the degradation of toluene compared to NTP-only and TiO₂/NTP, achieving a maximum 96% elimination efficiency and 76% CO_x selectivity at an SIE of 540 J L^-1. Mechanistic analysis reveals that the ¹O₂, ˙O₂^- and ˙OH species derived from the activation of O₃ molecules on Vo sites contribute to the decomposition of toluene over the Vo-rich TiO₂ surface. With the aid of advanced characterization and density functional theory calculations, the roles of oxygen vacancies in manipulating the synergistic capability of post-NTP systems were explored, and were attributed to increased O₃ adsorption ability and enhanced charge transfer dynamics. This work presents novel insights into the design of high-efficiency NTP catalysts structured with active Vo sites.

Gaseous ethylbenzene removal by photocatalytic TiO2 nanoparticles immobilized on glass fiber tissue under real conditions: evaluation of reactive oxygen species contribution to the photocatalytic process

Photocatalytic oxidation (PCO) using a TiO₂ catalyst is an effective technique to remove gaseous volatile organic compounds (VOCs). Herein, a lab-scale continuous reactor is used to investigate the photocatalytic performance toward ethylbenzene (EB) vapor removal over TiO₂ nanoparticles immobilized on glass fiber tissue. The role of the reactive species in the removal of EB and the degradation pathway were studied. Firstly, the effect of key operating parameters such as EB concentration (13, 26, 60 mg/m³), relative humidity levels (From 5 to 80%), gas carrier composition (dry air + EB, O₂ + EB and N₂ + EB) and ultraviolet (UV) radiation wavelength (UV-A _365 nm, UV-C _254 nm) were explored. Then, using superoxide dismutase and tert-butanol as trapping agents, the real contribution of superoxide radical anion (O₂^.-) and hydroxyl radicals (OH^.) to EB removal was quantified. The results show that (i) small water vapor content enhances the EB degradation; (ii) the reaction atmosphere plays an important role in the photocatalytic process; and (iii) oxygen atmosphere/UV-C radiation shows the highest EB degradation percentage. The use of radical scavengers confirms the major contribution of the hydroxyl radical to the photocatalytic mechanism with 75% versus 25% for superoxide radical anion.

Recent advances in the abatement of volatile organic compounds (VOCs) and chlorinated-VOCs by non-thermal plasma technology: A review

Most of the volatile organic compounds (VOCs) and especially the chlorinated volatile organic compounds (Cl-VOCs), are regarded as major pollutants due to their properties of volatility, diffusivity and toxicity which pose a significant threat to human health and the eco-environment. Catalytic degradation of VOCs and Cl-VOCs to harmless products is a promising approach to mitigate the issues caused by VOCs and Cl-VOCs. Non-thermal plasma (NTP) assisted catalysis is a promising technology for the efficient degradation of VOCs and Cl-VOCs with higher selectivity under relatively mild conditions compared with conventional thermal catalysis. This review summarises state-of-the-art research of the in plasma catalysis (IPC) of VOCs degradation from three major aspects including: (i) the design of catalysts, (ii) the strategies of deep catalytic degradation and by-products inhibition, and (iii) the fundamental research into mechanisms of NTP activated catalytic VOCs degradation. Particular attention is also given to Cl-VOCs due to their characteristic properties of higher stability and toxicity. The catalysts used for the degradation Cl-VOCs, chlorinated by-products formation and the degradation mechanism of Cl-VOCs are systematically reviewed in each chapter. Finally, a perspective on future challenges and opportunities in the development of NTP assisted VOCs catalytic degradation were discussed.

Adsorption and catalytic degradation of organic contaminants by biochar: Overlooked role of biochar's particle size

Biochar (BC) is considered as a promising adsorbent and/or catalyst for the removal of organic contaminants. However, the relationship between the particle size of BC and its adsorption/catalysis performance is largely unclear. We therefore investigated the influence of particle size on the performance of BC pyrolyzed at 300-900 °C in trichloroethylene (TCE) adsorption and persulfate (PS) activation for sulfamethazine (SMT) degradation. The results showed that high-temperature pyrolyzed BC (BC900) presented superior adsorption capacity for TCE and excellent catalytic activity for PS activation to degrade SMT. Compared to 150-250 µm, 75-150 µm and pristine BC900, 0-75 µm BC900 showed the highest TCE adsorption efficiency, which increased by 19.5-62.3%. Similarly, SMT removal by BC900/PS systems also increased from 24.2% to 98.3% with decreasing BC particle size. However, the catalytic activity of BC after grinding was not significantly improved as expected, indicating the properties of biochar was not only controlled by size effect. Characterization measurements proved that small-sized BC tended to have larger specific surface area, more micropores, higher conductivity, rich graphitic domains and surface redox-active functional groups, thus resulting in an enhanced adsorption and catalytic ability of BC.