Nonthermal plasma catalysis enhances simultaneous removal of toluene and ozone over TiO2@ZIF-8

Ultrasmall TiO 2 nanoparticles (average diameter of 6.6 nm) were encapsulated inside zeolitic imidazolate framework-8 (ZIF-8) via a self-assembly method, and the synthesized TiO 2 @ZIF-8 catalyst was applied for the removal of toluene using nonthermal plasma (NTP). Physicochemical characterization was performed to investigate the structure and morphology of TiO 2 @ZIF-8. The results revealed the high dispersion of TiO 2 nanoparticles in ZIF-8 and the formation of a Z-type heterojunction between TiO 2 and ZIF-8, which efficiently utilized the UV light generated during plasma discharge to produce •OH and •O 2 ‾ . Upon treating toluene exhaust gas of 100 mg·(m 3 ) −1  at 92.5% relative humidity, the toluene conversion efficiency was significantly improved to 91.17% with a CO X selectivity of 76.45% by TiO 2 @ZIF-8 in NTP-catalysis at a specific energy density (SED) of 507 J L −1 , which was improved by 45.96% and 52.27%, respectively. This was mainly due to the good hydrophobicity of ZIF-8, which helped maintain efficient catalytic performance under high humidity. The maximum ozone decomposition efficiency of 99.22% was achieved for the accelerated charge transfer efficiency and nearly formed NTP discharge behavior in the porous structures of the catalyst. In the 36-h stability test, high efficiency of toluene conversion, CO X selectivity, and ozone decomposition were maintained with no significant decay observed. Discharge characteristic analysis and electron paramagnetic resonance (EPR) characterization revealed the mechanism of toluene degradation in which electrons, ·OH, ·O 2 ⁻, and O 3 participated in toluene degradation. The possible pathways of toluene degradation were proposed based on the intermediates detected by chromatography–mass spectrometry. This work provides a new approach for anchoring and dispersing nanoparticles by ZIF-8 to avoid the reunion of nanoparticles and a new direction for synthesizing high-performance catalysts for volatile organic compound (VOC) degradation in NTP-catalysis.