Oxygen Isotope Tracing Study to Directly Reveal the Role of O2 and H2O in the Photocatalytic Oxidation Mechanism of Gaseous Monoaromatics.

O2 and H2O influence the photocatalytic oxidation mechanism of gaseous monoaromatics, but still in an unclear manner, due to the lack of direct evidence. Tracing an oxygen atom from 16O2 and H218O to intermediates can clarify their roles. The low H218O content suppressed the formation of benzenedicarboxaldehydes during the oxidation of xylenes and 16O2 greatly affected the yield of total intermediates, while neither of them altered the percentage order of the products. Methylbenzaldehydes, methylbenzyl alcohols, and benzenedicarboxaldehydes possessed greater 16O percentage (≥69.49%), while higher 18O distribution was observed in methylbenzoic acids and phthalide (≥59.51%). Together with the interconversion results of the products revealed, 16O2 determined the transformation of xylenes initially to methylbenzaldehydes and then to methylbenzyl alcohols or benzenedicarboxaldehydes, while H218O mainly contributed to conversion of methylbenzaldehydes to methylbenzoic acids or phthalide. Further interaction sites of xylene and its products with H2O and O2 were confirmed by molecular dynamics calculations. The same roles of 16O2 and H218O in the degradation of toluene, ethylbenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene were also verified. This is the first report that provides direct evidence for the roles of O2 and H2O in the photocatalytic oxidation mechanism of gaseous monoaromatics. These findings are helpful to achieve controllable product formation from the oxidation of monoaromatics and predict their migration process in the atmospheric environment.

Enhanced H-abstraction contribution for oxidation of xylenes via mineral particles: Implications for particulate matter formation and human health.

Xylenes are important aromatic hydrocarbons having broad industrial emissions and profound implication to air quality and human health. Generally, homogeneous atmospheric oxidation of xylenes is initiated by hydroxyl radical (OH) resulting in minor H-abstraction and major OH-addition pathways. However, the effect of mineral particles on the homogeneous atmospheric oxidation mechanism of xylenes is still not well understood. In the present study, the heterogeneous atmospheric oxidation of xylenes on mineral particles (TiO2) is examined in detail. Both the experimental data and theoretical calculations are combined to achieve the feast. The experimental results detected a major H-abstraction (≥87.18%) and minor OH-addition (≤12.82%) pathways for the OH-initiated heterogeneous oxidation of three xylenes on TiO2 under ultraviolet (UV) irradiation. Theoretical calculations demonstrated favorable H-abstraction on methyl group of xylenes by surface OH with large exothermic energies, because of the reason that their methyl group rather than the phenyl ring is more occupied by TiO2 via hydrogen bonding. Furthermore, the particle monitor and acute risk assessment results indicated that the H-abstraction products significantly enhance the formation of particulate matter and health risk to human beings. Taken together, these results indicate that the atmospheric oxidation mechanism of xylenes is altered in the presence of mineral particles, highlighting the necessity to re-evaluate its implication in the environment and human health.

Development and calibration of an air-floating six-axis force measurement platform using self-calibration.

This paper describes the design, working principle, as well as calibration of an air-floating six-axis force measurement platform, where the floating plate and nozzles were connected without contact, preventing inter-dimensional coupling and increasing precision significantly. The measurement repeatability error of the force size in the platform is less than 0.2% full scale (FS), which is significantly better than the precision of 1% FS in the six-axis force sensors on the current market. We overcame the difficulties of weight loading device in high-precision calibration by proposing a self-calibration method based on the floating plate gravity and met the calibration precision requirement of 0.02% FS. This study has general implications for the development and calibration of high-precision multi-axis force sensors. In particular, the air-floating six-axis force measurement platform could be applied to the calibration of some special sensors such as flexible tactile sensors and may be used as a micro-nano mechanical assembly platform for real-time assembly force testing.