NOx attenuation in flue gas by •OH/SO4•--based advanced oxidation processes

High-performance NiO@Fe3O4 magnetic core-shell nanocomposite for catalytic ozonation degradation of pharmaceutical pollution

Pharmaceuticals that are present in superficial waters and wastewater are becoming an ecological concern. Therefore, it is necessary to provide high-performance methods to limit the harmful ecological effects of these materials to achieve a sustainable environment. In this research, NiO@Fe3O4 nanocomposite was prepared by the co-precipitation method and utilized in the catalytic ozonation process for the degradation of 1-cyclopropyl-6-fluoro-4-oxo-7-piperazin-1-yl-quinoline-3-carboxylic acid (ciprofloxacin antibiotic), for the first time. The influencing parameters in the degradation process were analyzed and optimized via response surface methodology (RSM). The optimal ciprofloxacin removal efficiency (100%) was found at pH = 6.5, using 7.5 mg of the NiO@Fe3O4 nanocatalyst and 0.2 g L-1 h-1 ozone (O3) flow, applied over 20 min. Results showed a significant synergistic effect in the analyzed system, which makes the proposed catalytic ozonation process more efficient than using the catalyst and ozone separately. Also, based on the kinetic analysis data, the catalytic ozonation process followed the pseudo-first-order model. In addition, the nanocatalyst showed high recyclability and stability (88.37%) after five consecutive catalytic ozonation process cycles. In conclusion, the NiO@Fe3O4 nanocatalyst/O3 system can be effectively used for the treatment of pharmaceutical contaminants.

Insights into highly effective catalytic persulfate activation on oxygen-functionalized mesoporous carbon for ciprofloxacin degradation

Nanocarbons have been demonstrated as promising carbon catalysts for substituting metal-based catalysts for the green treatment of wastewater. In this study, oxygen-functionalized mesoporous carbon (OCMK-3) was prepared by wet oxidation and exhibited high catalytic performance against ciprofloxacin (CIP) by activation of persulfate. The effects of environmental parameters (pH, temperature, coexisting ions) and process parameters (temperature, sodium persulfate concentration, catalyst agent dosage, initial concentration) on the removal of CIP were investigated. Compared with the pristine ordered mesoporous carbon (CMK-3), the removal efficiency of CIP by OCMK-3 was increased by 32% under optimal conditions. This rise in activity was attributed to the increase in oxygen-containing functional groups, porosity, and specific surface area of OCMK-3 with improved structural defects and electron transfer efficiency. Furthermore, based on active species scavenging experiments, a dual-pathway mechanism of the radical and nonradical pathways was discovered. The rational degradation pathway of CIP was investigated based on liquid chromatography-mass spectrometry (LC-MS). In addition, the OCMK-3/PS system exhibited high decomposition efficiency in pharmaceutical wastewater treatment. This study provides an in-depth mechanism for the degradation of organic pollutants by carbon-based PS-AOPs and provides theoretical support for further studies.

Mechanism and Kinetic Study of Cyclodextrin Use to Facilitate NO2 Absorption in Sulfite Solutions

An innovative strategy to control nitrogen oxide emission from flue gas was developed using the wet flue gas denitrification technology. The use of cyclodextrin (CD) as an additive facilitated NO₂ absorption by the sulfite absorbent. Compared with absorption by a sulfite solution (59.12%), the instantaneous absorption efficiencies employing CD improved to 94.57%. Moreover, 48 h of continuous absorption indicated cyclic utilization of CD. The favorable role of CD was ascribed to facilitating the limiting step for the entire NO₂ absorption-dissolution process which included both water solubility and gas-liquid mass transfer. Furthermore, we propose a potential mechanism of CD/sulfite mixed solution absorbing NO₂, among which the favorable role of the additive is related to its amphiphilic behavior toward gas and liquid phases. Additionally, a kinetic model describing the rates of gas-liquid transfer and macro absorption was established based on various operating conditions. This model explains the absorption improvement in the kinetic aspect and provides theoretical guidance for practical applications.