We investigated the inhibition of thermal runaway of styrene polymerization by DNPB. DNBP is an inhibitor in styrene polymerization reaction. Polymerization is one of eighteen hazardous processes. Styrene polymerization reaction is characterized by high heat production and fast reaction rate. Firstly, differential scanning calorimetry (DSC) and adiabatic calorimetry (ARC) were chosen to study the effect of different mass of DNBP on thermal behavior in non-isothermal and adiabatic environments. Secondly, exploring the inhibitory effect of DNBP at different runaway temperatures using an oil bath reactor. The results showed that when DNBP was at 0.80%, effective inhibition was obtained at different runaway temperatures. Finally, GC/MS and Gauss16 were used to infer the mechanism of inhibition in terms of macroscopic products and microscopic instabilities. The results showed that the products of the oil bath reactor experiments were related to the mass of DNBP, and when DNBP was 0.80%, the products increased and the main reaction was inhibited. Finally, it was deduced that the nitro group undergoes a possible path of direct addition reaction with the styrene radical before bond breaking.
PAEs usually adsorb on indoor surfaces to form organic films, which could be more hazardous after enriching VOCs. Two typical PAEs, DnBP and DEHP, in the film phase, were chosen to explore the enrichment capacity of gaseous toluene, hexanol, and benzyl alcohol in this study. Exposed to gaseous VOCs less than 250 ppb, film-phase DnBP and DEHP could capture benzyl alcohol significantly and hexanol slightly from the air, respectively, while toluene was hardly absorbed in the films. Henry's law constants and partition coefficients ( K ) of VOCs in DnBP or DEHP films were derived, supposing films as dilute solution systems. The K value of VOC in DnBP or DEHP films was 1∼2 orders larger than the octanol-air partition coefficient ( K oa ), indicating that the surface film composition greatly influences VOC adsorption. Benzyl alcohol was the largest VOC component in surface films, agreeing well with the molecular dynamics simulation results. The hydroxyl and phenyl groups of benzyl alcohol molecules may be key factors in VOC enrichment. They form hydrogen bonds with the ester group and π-π stacking interaction with the phenyl group of DnBP or DEHP molecules, respectively. After enriching VOCs, film-phase PAEs could evoke combined exposure risks to human beings.
Organic films were widely found on indoor impermeable surfaces exposed to gaseous organic compounds, but few studies have addressed the film growth details on different indoor substrates. In this study, we observed the topography evolution of phthalic acid ester (PAE) organic films on three impermeable substrates: polished glass (G-P), mirror-polished stainless steel (SS-M) and drawn stainless steel (SS-D). PAE organic films were preferentially formed upon the flat surface with sparse inherent nano-peaks of substrate G-P and in valleys of substrate SS-M and SS-D. Surface uniformity of substrates and viscosity of PAE molecules were inferred as critical parameters determining the surface average adhesion forces. We obtained the partition coefficients of DEP , DnBP, BBP and DEHP on substrate G-P, SS-M and SS-D by fitting the initial monolayer adsorption process. Organic films continuously grew instead of reaching adsorption equilibrium after long-term PAE exposure, indicating that multilayer adsorption may occur. The organic film growth rates in saturated gas-phase PAE concentrations were quantified as about one-tenth of the results in previous studies where substrates were simultaneously exposed to multiple pollutants. To sum up, the results outline PAE adsorption details on impermeable materials and provide a reference for better estimation on PAE exposure assessment.
The mesoporous MCM-41@mTiO 2 core-shell composite microspheres were synthesized successfully by combining sol-gel and simple hydrothermal treatment. The morphology and microstructure characteristics of the synthesized materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N 2 adsorption-desorption measurements, X-ray powder diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis/DRS) and Fourier transform infrared spectroscopy (FT-IR). The results indicate that the composite material possesses obvious core/shell structure, a pure mesoporous and well-crystallized TiO 2 layer (mTiO 2 ), high specific surface area (316.8 m 2 /g), large pore volume (0.42 cm 3 /g) and two different pore sizes (2.6 nm and 11.0 nm). The photocatalytic activity of the novel MCM-41@mTiO 2 composite was evaluated by degrading 2- sec -butyl-4,6-dinitrophenol (DNBP) in aqueous suspension under UV and visible light irradiation. The results were compared with commercial anatase TiO 2 and Degussa P25 and the enhanced degradation were obtained with the synthesized MCM-41@mTiO 2 composite under the same conditions, which meant that this material can serve as an efficient photocatalyst for the degradation of hazardous organic pollutants in wastewaters.
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