Dispersions of Zirconia Nanoparticles Close to the Phase Boundary of Surfactant-Free Ternary Mixtures.

The achievement of a homogeneous dispersion of nanoparticles is of paramount importance in supporting their technological application. In wet processing, stable dispersions were largely obtained via surfactant or surface functionalization: although effective, the use of dispersant can alter, or even impair, the functional properties of the resulting nanostructured systems. Herein, we report a novel integrated modeling and experimental approach to obtain stable ZrO2 nanoparticle (NP) dispersions at native dimensions (about 5 nm) in homogeneous ternary mixtures of solvents (i.e., water, ethanol, and 1,2-dichlorobenzene) without any further surface functionalization. A miscibility ternary diagram was computed exploiting the universal quasi-chemical functional-group activity coefficient (UNIFAC) model, which was then experimentally validated. Dynamic light scattering (DLS) on these mixtures highlights that nanometric structures, resembling nanoemulsion droplets, form close to the mixture two-phase boundary, with a size that depends on the ternary mixture composition. ZrO2-NPs were then synthesized following a classic sol-gel approach and characterized by XRD and Raman spectroscopy. ZrO2-NPs were dispersed in HCl and mixed with different mixtures of ethanol and 1,2-dichlorobenzene (DCB), obtaining homogeneous and stable dispersions. These dispersions were then studied by means of DLS as a function of DCB concentration, observing that the nanoparticles can be dispersed at their native dimensions when the mass fraction of DCB was lower than 60%, whereas the increase of the hydrophobic solvent leads to the NPs' agglomeration and sedimentation. The proposed approach not only offers specific guidelines for the design of ZrO2-NPs dispersions in a ternary solvent mixture but can also be extended to other complex solvent mixtures in order to achieve stable dispersions of nanoparticles with no functionalization.

Dust emission and dispersion from mineral storage piles.

Dust pollution is a complex problem of growing interest because of its environmental, health, economic and political impact. Environmental impact assessment methods for dust pollution management are often based on the simulation of dust dispersion, which requires a precise characterization of the source term and of the source parameters. The source term model should be as simple and as accurate as possible and requires low time consumption in order to be easily connected to a more complex algorithm for the dispersion calculations. This work focuses on dust emissions from mineral storage piles, which are usually modelled as source terms by means of the algorithm proposed in the AP-42 US EPA standard. Unfortunately, this algorithm tends to overestimate emissions, and when coupled with a Gaussian dispersion model, it leads to inaccurate results in terms of estimation of both concentration and spatial distribution. This paper proposes a new methodology drawn from the original standard US EPA AP-42 https://www3.epa.gov/ttnchie1/ap42/ch13/ scheme with the purpose to account for the actual dynamics of erosion and to enhance the accuracy of the concentration and the pollutant spatial distribution assessment, thereby considering the effects of the wind interactions. The standard EPA methodology and the new one were compared by means of the AERMOD and CALPUFF dispersion models. Results are superimposable in terms of concentration values, leading to a quantification of the same order of magnitude, although with a different and more variable spatial distribution.

Emission of air pollutants from burning candles with different composition in indoor environments.

Candle composition is expected to influence the air pollutants emissions, possibly leading to important differences in the emissions of volatile organic compounds and polycyclic aromatic hydrocarbons. In this regard, the purity of the raw materials and additives used can play a key role. Consequently, in this work emission factors for some polycyclic aromatic hydrocarbons, aromatic species, short-chain aldehydes and particulate matter have been determined for container candles constituted by different paraffin waxes burning in a test chamber. It has been found that wax quality strongly influences the air pollutant emissions. These results could be used, at least at a first glance, to foresee the expected pollutant concentration in a given indoor environment with respect to health safety standards, while the test chamber used for performing the reported results could be useful to estimate the emission factors of any other candle in an easy-to-build standardised environment.

Definition of a short-cut methodology for assessing earthquake-related Na-Tech risk.

Na-Tech (Natural and Technological) refers to industrial accidents triggered by natural events such as storms, earthquakes, flooding, and lightning. Herein, a qualitative methodology for the initial assessment of earthquake Na-Tech risk has been developed as a screening tool to identify which situations require a much more expensive Quantitative Risk Analysis (QRA). The proposed methodology, through suitable Key Hazard Indicators (KHIs), identifies the Na-Tech risk level associated with a given situation (i.e., a process plant located in a given territory), using the Analytical Hierarchy Process as a multi-criteria decision tool for the evaluation of such KHIs. The developed methodology was validated by comparing its computational results with QRA results that involved Na-Tech events previously presented in literature.

Conversion of C5 into C6 cyclic species through the formation of C7 intermediates.

We have recently proposed that the addition of C2H2 to the cyclopentadienyl radical can lead to the rapid formation of the cycloheptatrienyl radical and, in succession, of the indenyl radical. These reactions represent an interesting and unexplored route for the enlargement of gas-phase cyclic species. In this work we report ab initio calculations we performed with the aim of investigating in detail the gas-phase reactivity of cycloheptatrienyl and indenyl radicals. We found that the reaction of the cycloheptatrienyl radical with atomic hydrogen can lead to its fast conversion into the more stable benzyl radical. This reaction pathway involves the intermediate formation of heptatriene, norcaradiene, and toluene. Successively we investigated whether this reaction mechanism can be extended to polycyclic aromatic hydrocarbons (PAHs). For this purpose we studied the reaction of C2H2 with the indenyl radical, which can be considered as a superior homologue of the cyclopentadienyl radical. This reaction proceeds through a pathway similar to that proposed for C5H5 but with a reaction rate about an order of magnitude smaller. The present calculations extend thus the previously proposed C5-C7-C9 mechanism to bicyclic PAH and suggest a fast route for the conversion of C5 into C6 cyclic radicals, mediated by the formation of C7 cyclic species.

The peculiar kinetics of the reaction between acetylene and the cyclopentadienyl radical.

The cyclopentadienyl radical (cC(5)H(5)) is a fascinating molecule characterized by several peculiar properties, such as its high internal symmetry and resonance enhanced stability. This makes cC(5)H(5) one of the most abundant radicals present in high temperature gaseous environments, such as flames. Therefore it is generally considered an interesting candidate as the starting point of reaction pathways leading to the formation of polycyclic aromatic hydrocarbons (PAH) and soot in combustion processes. However, known reaction pathways are not able to explain some recent experimental findings concerning the rapid conversion of cC(5)H(5) into C(7)H(7) and C(9)H(8) in the presence of acetylene. In this work, we used ab initio calculations and quantum Rice-Ramsperger-Kassel (QRRK) theory to investigate the cC(5)H(5) + C(2)H(2) reaction kinetics. We found that cC(5)H(5) can add acetylene to form, through a fast and not previously known reaction, the heptatrienyl radical (cC(7)H(7)), which, in many ways, can be considered the superior homologue of cC(5)H(5). The calculated reaction kinetic constant is (2.2 x 10(11))exp(-6440/T(K)) cm(3) mol(-1) s(-1) and is in good agreement with experimental data, while that of the inverse process is (4.2 x 10(16))T(-1) exp(-30 850/T(K)) s(-1). In a successive reaction, cC(7)H(7) can add a second acetylene molecule to form indene, cC(9)H(8), and H. The forward and backward kinetic constants are (6.6 x 10(11))exp(-10 080/T(K)) and (4.2 x 10(14))exp(-27 300/T(K)) cm(3) mol(-1) s(-1), respectively. These two successive reactions, leading from a single C5 cycle to a bicyclic C5-C6 species, represent a new PAH growth mechanism, characterized by a C5-C7 ring enlargement reaction.