Search

Highlights • Pure CeO 2 can achieve both photocatalysis and catalytic ozonation in VUV-PCO system. • High toluene removal, mineralization and ozone removal can be achieved by pure CeO 2. • Amount of Ce3+ plays a critical role in toluene removal. • Differences in photocatalytic activity were explained by electrochemical behaviors. Abstract Volatile organic compounds (VOCs) are one of the biggest concerns in the ambient environment that have attracted a great number of studies related to its remediation. Vacuum ultraviolet (VUV)-based photocatalytic oxidation (PCO) is a promising technology in controlling VOCs. CeO 2 is found to be a promising catalyst for the VUV-PCO technology possessing catalytic capacities in both the photocatalysis and ozonation processes. In this study, three typical kinds of pure CeO 2 with various nanostructures were synthesized and creatively applied for VUV-photocatalytic oxidation of toluene. Material characterizations, including BET, SEM, TEM, XRD, Raman, XPS, H 2 -TPR and DRS, were conducted to characterize different CeO 2 samples. Results indicated that synthetic CeO 2 samples have a much more remarkable enhancement in degrading toluene compared to commercial ones. Higher COx generation and mineralization rates were obtained with the use of all the synthetic CeO 2 samples. Compared to commercial CeO 2 , the synthetic samples have much better capacity towards removing ozone and the best activity in ozone decomposition was observed in CeO 2 Nanorods catalysts. Both the effects of photocatalysis and catalytic ozonation exist in all the CeO 2 catalysts. The amount of Ce3+ plays a critical role in both the catalytic activity of photocatalysis and ozonation that higher ratio of Ce3+ leads to better performance in toluene removal. The differences in photocatalytic activity were further explained by the results of electrochemical behaviors of different CeO 2 samples which showed varying responses to UV irradiation. [ABSTRACT FROM AUTHOR]

• Toluene was efficiently removed over F-TiO 2 nanosheets under VUV-PCO process. • The role of F ion on photocatalytic toluene degradation was systematically explored. • α-MnO 2 nanowire was excellent for residual ozone removal. • Different substrates were studied for potential industrial application. The particular role of fluorine (F) doping in the photocatalytic activity of nanocrystalline titanium dioxide (TiO 2) towards toluene degradation was systematically studied. TiO 2 nanosheet catalysts doped with different amounts of F− (denoted by F-TiO 2) were synthesized by hydrothermal method. For comparison, calcination was performed on the catalyst to remove F-. The photocatalytic oxidation (PCO) of toluene over F-TiO 2 was found to be much higher than those of TiO 2 and commercial P25 under the irradiation of vacuum ultraviolet (VUV) light, with a high toluene degradation efficiency of about 90 %. Moreover, the toluene degradation efficiency increased to 96 % with the addition of only 1 wt.% α-MnO 2 nanowires, and the residual ozone (O 3) in the system can be completely eliminated. In addition, four different substrates were explored for catalyst coating to facilitate the operation and minimize catalyst loading, which can provide a promising strategy for practical volatile organic compounds (VOCs) abatement in industrial applications. [ABSTRACT FROM AUTHOR]

TiO 2 /MnO 2 heterojunction catalysts are fabricated by in situ method, which exhibit excellent performance in degrading toluene through VUV-PCO process as well as O 3 elimination. • TiO 2 /MnO 2 shows superior toluene removal efficiency in VUV-PCO process. • Heterojunction structure benefits the separation of photogenerated charge carrier. • O 3 can be utilized to enhance toluene oxidation and completely eliminated in the process. A series of TiO 2 /MnO 2 heterojunction catalysts were fabricated through an in-situ hydrothermal method, and for the first time, catalysts with this heterojunction structure were used for VUV-PCO toluene degradation. After the MnO 2 coating, the TiO 2 /MnO 2 catalysts performed excellently for both VOCs degradation and residual ozone decomposition with removal efficiency reaching 96.0% and 99.9%, respectively. The enhanced photocatalytic activity towards toluene degradation could be attributed to the heterojunction structure of TiO 2 /MnO 2 , which provides excellent contact between MnO 2 and TiO 2 , and suppresses the recombination of photogenerated electron-hole pairs. Moreover, benefiting from the MnO 2 , the ozone generated in the system could be efficiently utilized and eliminated during the VUV-PCO process. The photocatalytic mechanism of TiO 2 /MnO 2 for the toluene degradation and ozone decomposition was proposed. [ABSTRACT FROM AUTHOR]

• MnO 2 -rGO composite sample exhibits excellent toluene removal performance in VUV-OZCO process. • With the use of catalysts, more complete reactions occur that by-products with shorter chains can be detected. • Two reaction pathways of toluene degradation are proposed under the action of •O 2 – and OH•. Advanced oxidation processes (AOPs) are regarded as one of the most promising technologies for VOC degradation. In this study, MnO 2 -rGO composite samples were prepared and applied in a system consisting of VUV photolysis and ozone catalytic oxidation for the degradation of toluene. Extensive characterizations, including BET, SEM, TEM, HRTEM, Raman, XRD, FTIR and XPS, were conducted to analyze the features of the composite MnO 2 -rGO samples. Results of toluene removal, mineralization and ozone decomposition showed that the MnO 2 -rGO composite sample with Mn loading of 25 wt% exhibited the best performance in this study due to its superior adsorption activity and moderated MnO 2 loading. The intermediates of the degradation process were analyzed showing more by-products with shorter chains in the presence of the MnO 2 -rGO catalysts compared to VUV photolysis alone, indicating more complete reactions occurred. Generation of hydroxyl radicals (•OH) and superoxide radicals (•O 2 –) were confirmed to contribute in the toluene degradation. Two reaction pathways (i.e. •O 2 – and OH• based) and mechanism of toluene degradation were proposed. [ABSTRACT FROM AUTHOR]