Molecular Characterization of the Gas-Particle Interface of Soot Sampled from a Diesel Engine Using a Titration Method

Natural and simulated weathering of polystyrene: A molecular view of the polymeric interface

This work presents the changing abundance of surface functional groups (SFGs) on polystyrene (PS) upon weathering within one or a few molecular monolayers from a molecular point of view. PS particles were aged by exposing it to a gas flow of typically (5 %) O3 in O2 (PSO3), UV radiation using a solar simulator under controlled conditions in the laboratory (PSSS) and to the water/air interface immerged in a freshwater lake for 2 months (PSL). The chemical composition of the interface of weathered, compared to pristine (virgin or PSV) material was established using a titration technique that probed the chemical composition of the molecular interface of the polymer. The main conclusions of this exploratory study are: (a) The interface of PS changes significantly compared to ATR-FTIR spectra that do not show additional absorptions in the mid-IR spectrum over a penetration depth of more than hundred monolayers at 10 μm; (b) The average surface functionalization of the gas-solid interface, corresponding to the sum of all examined types of SFG, increases from 20 % of a monolayer for PSV to 40, 50 and 84 % for PSL, PSO3 and PSSS, respectively; (c) in all cases the most important SFG was surface -OH ranging from 11.2 to 64 % for PSV and PSSS, respectively; (d) each PS sample shows a characteristic SFG pattern or fingerprint using several probe gases; (e) O3 interaction led to interface acidification; (f) UV treatment leads to the highest degree of surface -OH functionalization compared to PSO3 and PSL. The accumulation of SFG's renders the interface more reactive towards adsorption of probe gases.

Dephenolization pyrolysis fluid improved physicochemical properties and microbial community structure of saline-alkali soils

Saline-sodic soil is widely distributed around the world and has induced severe impacts on ecosystems and agriculture. Biomass pyrolysis fluid (BPF), as a substance rich in organic acids, has been proposed as a saline-alkali soil conditioner. One of the main problems with BPF applications is the potential contamination of the phenolic substances it contains. Therefore, the purpose of this study is to reduce the phenolic substances in BFP and study the improvement effect of BFP on saline-alkali soil. Firstly, we explored the physicochemical properties of BPF prepared at different temperatures (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Then BPF was separated into upper phases (UP) and lower phases (LP) by a simple one-step salting-out extraction method. We found that phenolic substances were mainly concentrated in the UP (average content was 193.27 mg/g), and the content of phenolic substances in the LP was effectively reduced (average content was 64.52 mg/g). Next, we added the LP diluted at different times (0, 50, 100, 200, 400) into saline-alkali soil for improvement experiments. The experimental results show that the lower phase diluted 400 times at the pyrolysis temperature of 500℃ was added into saline-alkali soil, which greatly increased the content of soil available nutrients. Under the action of organic acids, soil pH (the average was 7.43) and total salt content could be reduced effectively, and soil enzyme activities can be increased. Microbial community analysis showed that the addition of LP could increase the proportion of Actinomycetes, which played a beneficial role in improving soil fertility and then improved the growth of Chinese cabbage.

Highly flexible and active potassium-supported sepiolite paper catalysts for soot oxidation

Highly flexible and active potassium-supported sepiolite paper catalysts were fabricated via a facile wet paper-making method.

The mesenchymoangioblast, mesodermal precursor for mesenchymal and endothelial cells

Mesenchymoangioblast (MB) is the earliest precursor for endothelial and mesenchymal cells originating from APLNR+PDGFRα+KDR+ mesoderm in human pluripotent stem cell cultures. MBs are identified based on their capacity to form FGF2-dependent compact spheroid colonies in a serum-free semisolid medium. MBs colonies are composed of PDGFRβ+CD271+EMCN+DLK1+CD73- primitive mesenchymal cells which are generated through endothelial/angioblastic intermediates (cores) formed during first 3-4 days of clonogenic cultures. MB-derived primitive mesenchymal cells have potential to differentiate into mesenchymal stromal/stem cells (MSCs), pericytes, and smooth muscle cells. In this review, we summarize the specification and developmental potential of MBs, emphasize features that distinguish MBs from other mesenchymal progenitors described in the literature and discuss the value of these findings for identifying molecular pathways leading to MSC and vasculogenic cell specification, and developing cellular therapies using MB-derived progeny.

Plausibility of potassium ion-exchanged ZSM-5 as soot combustion catalysts

Potassium (K) ion-exchanged ZSM-5 zeolites were investigated for catalytic soot combustion. X-ray absorption fine-structure (XAFS), Raman, in situ IR and NH₃-temperature programmed desorption (NH₃-TPD) confirmed the location of K⁺ at the ion-exchanged sites. Temperature-programmed oxidation (TPO) reactions showed that K-ZSM-5 decreased ignition tempeatures of soot combustion and increased selectivity to CO₂. The improved activity for soot combustion by increasing K⁺-exchanged amounts via decreasing the Si/Al ratio reinforced the K⁺ ions participating in soot combustion. ¹⁸O₂ isotopic isothermal reactions suggested the activation of gaseous oxygen by the K⁺ ions. This demonstrated a new appliction of alkali metal exchanged zeolites and the strategy for enhancement of catalytic soot combustion activity.

Chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot after reactive gas probing using diffuse reflectance FTIR spectroscopy (DRIFTS)

A chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot has been developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) before and after the reaction with different probe gases. Samples were generated under combustion conditions corresponding to an urban operation mode of a diesel engine and were reacted with probe gas-phase molecules in a Knudsen flow reactor. Specifically, NH₂OH, O₃ and NO₂ were used as reactants (probes) and selected according to their reactivities towards specific functional groups on the sample surface. Samples of previously ground soot were diluted with KBr and were introduced in a DRIFTS accessory. A comparison between unreacted and reacted soot samples was made in order to establish chemical changes on the soot surface upon reaction. It was concluded that the interface of diesel and HVO soot before reaction mainly consists polycyclic aromatic hydrocarbons, nitro and carbonyl compounds, as well as ether functionalities. The main difference between both soot samples was observed in the band of the C=O groups that in diesel soot was observed at 1719 cm^-1 but not in HVO soot. After reaction with probe gases, it was found that nitro compounds remain on the soot surface, that the degree of unsaturation decreases for reacted samples, and that new spectral bands such as hydroxyl groups are observed.

Aggregation Kinetics of Diesel Soot Nanoparticles in Wet Environments

Soot produced during incomplete combustion consists mainly of carbonaceous nanoparticles (NPs) with severe adverse environmental and health effects, and its environmental fate and transport are largely controlled by aggregation. In this study, we examined the aggregation behavior for diesel soot NPs under aqueous condition in an effort to elucidate the fundamental processes that govern soot particle-particle interactions in wet environments such as rain droplets or surface aquatic systems. The influence of electrolytes and aqueous pH on colloidal stability of these NPs was investigated by measuring their aggregation kinetics in different aqueous solution chemistries. The results showed that the NPs had negatively charged surfaces and exhibited both reaction- and diffusion-limited aggregation regimes with rates depended upon solution chemistry. The aggregation kinetics data were in good agreement with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The critical coagulation concentrations (CCC) were quantified and the Hamaker constant was derived for the soot (1.4 × 10^-20 J) using the colloidal chemistry approach. The study indicated that, depending upon local aqueous chemistry, single soot NPs could remain stable against self-aggregation in typical freshwater environments and in neutral cloud droplets but are likely to aggregate under salty (e.g., estuaries) or acidic (e.g., acid rain droplets) aquatic conditions or both.