RESUMO
Moxa floss is a type of biomass used as the main combustion material in moxibustion, a therapy that applies heat from moxa floss combustion to points or body areas for treatment. Safety concerns regarding moxa smoke have been raised in recent years. Since moxa floss is the source material in moxibustion, its thermal behavior and pyrolysis products would be related to the products formed in moxa smoke. This work aims to understand the thermal behavior of moxa floss and investigate the pyrolysis products generated from moxa floss combustion. Six commercial moxa floss samples of 3 storage years and 10 storage years, and of low, medium, and high ratios, were selected. The kinetic data from moxa floss combustion was carried out by a thermogravimetric analyzer. Pyrolysis-gas chromatography and mass spectroscopy using a gas chromatograph and mass spectrometer equipped with a pyroprobe were used to examine the pyrolysis products. Thermogravimetric profiles for all the samples were overall similar and showed a monotonic weight decrease. The range of intensive reaction temperature occurred between 150°C and 450°C, which was characterized by a major weight loss and accompanied by an exothermal degradation of the main components. The average ignition temperature for the samples of 3 and 10 storage years was 218.3°C and 222.6°C, respectively, which was lower than most herbaceous plants. The identified pyrolysis products include monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons, ketones, acids, and alkanes. All were of relatively low intensities of below 5% in relative abundance. No volatiles were detected in the samples of 10 storage years. The relatively low values of ignition temperature suggested that moxa floss is more combustible and can be ignited more easily than other herbaceous plants. This may explain why moxa floss has remained as the preferred material used for moxibustion over the years.
RESUMO
One of vital issues that inhibit photoactivity of metal-organic frameworks is the poor electrical conductivity. In this work, one-dimensional mixed-valence iron chains are used to improve this poor situation in MIL-53(Fe). A series of mixed-valence MIL-53(Fe) photocatalysts were obtained through heating at different temperatures in vacuum. The effect of FeII coordinatively unsaturated metal sites (CUS) and one-dimensional mixed-valence iron chains on their photocatalytic property was discussed. The experimental results indicated that mixed-valence MIL-53(Fe) with a reference FeII/FeIII ratio of 0.2725 displayed the best photocatalytic performance, which showed 96.28 and 95.01% removal efficiencies of RhB and TC-H in 100 min, respectively. Moreover, MIL-53(Fe) heated in vacuum displayed better catalytic activity than MIL-53(Fe) heated in air for RhB and TC-H degradation. Based on the analysis of various characterizations, the reinforced catalytic activity can be attributed to the charge mobilities in mixed-valence FeII/FeIII chains. It is worth mentioning that the method is also applicable to MIL-88(Fe) and MIL-101(Fe). Additionally, mixed-valence MIL-53(Fe) can also perform the catalysis reaction in the nighttime by activating persulfate (PS) to produce free radicals. Interestingly, it was found that the FeII CUS lost in activating PS can be supplemented by self-reduction of photogenerated electrons during illumination in the daytime, so as to achieve a more stable cycle. This work demonstrated that the photoactivity of MIL-53(Fe) can be improved by adjusting the ratio of FeII/FeIII and the feasibility of using as an all-day-active catalyst.