Particle Chemistry Research Articles

Surface-Engineered Polydopamine Particles as an Efficient Support for Catalytic Applications.

Mussel-inspired polydopamine (PDA) particles with the size of ∼270 nm are used as a support of palladium (Pd) nanoparticles (NPs) for catalyst preparation. The surface morphology of the PDA particle has been modified via corrosion of CF3COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of a carboxylic acid-terminated alkanethiol monolayer. The obtained self-assembled monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H2PdCl4 solution to a suspension of SAM-PDA particles at room temperature. Transmission electron microscopy, energy-dispersive X-ray mapping, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis, and Fourier transform infrared are used to characterize the catalyst and to investigate the process. Uniform Pd NPs (2-3 nm) have been well-dispersed on the SAM-PDA particles via controllable surface engineering. Surface charges and interactions with a metal ion are regulated by the monolayer of carboxylic acids. The surface chemistry of PDA particles has been finely engineered for efficient loading of noble metal NPs. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H2. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir-Hinshelwood (L-H) model, and the calculated apparent activation energy of this process is 40.77 kJ mol-1.

Nanostructured Montmorillonite Clay for Controlling the Lipase-Mediated Digestion of Medium Chain Triglycerides.

Biocompatible lipid hybrid particles composed of montmorillonite and medium chain triglycerides were engineered for the first time by spray drying oil-in-water emulsions stabilized by montmorillonite platelets to form montmorillonite-lipid hybrid (MLH) microparticles containing up to 75% w/w lipid. In vitro lipolysis studies under simulated intestinal conditions indicated that the specific porous nanoarchitecture and surface chemistry of MLH particles significantly increased the rate (>10-fold) and extent of lipase-mediated digestion compared to that of coarse and homogenized submicrometer triglyceride emulsions. Proton nuclear magnetic resonance studies verified the rapid and enhanced production of fatty acids for MLH particles; these are electrostatically repelled by the negatively charged montmorillonite platelet faces and avoid the "interfacial poisoning" caused by incomplete digestion that retards lipid droplet digestion. MLH particles are a novel biomaterial and encapsulation system that optimize lipase enzyme efficiency and have excellent potential as a smart delivery system for lipophilic biomolecules owing to their exceptional physicochemical and biologically active properties. These particles can be readily fabricated with varying lipid loads and thus may be tailored to optimize the solubilization of specific bioactive molecules requiring reformulation.

Development of a Martian regolith simulant for in-situ resource utilization testing

Long-term human habitation of Mars will require in situ resources for construction and infrastructure development. In order to determine how to utilize in situ resources, such as Martian regolith, these materials need to be synthesized on Earth for testing and development. Here we address the process of synthesizing a targeted Martian simulant (i.e., Gusev Crater regolith near the Columbia Hills region on Mars) in sufficient quantities required for infrastructure development studies using volcanic material obtained from Banks Peninsula, New Zealand. Martian simulant produced via crushing, sieving, washing and blending of basalts and volcanic glass resulted in accurately reproducing material similar in particle size, chemistry and mineralogy to Gusev Crater regolith. Overall, our applied approach to synthesizing Martian regolith will aid in creating suitable quantities of material that can be used for a variety of research applications such as assessing aggregates for use in the production of construction materials.

Chemical characteristics and deposition fluxes of dust-carbon mixed coarse aerosols at three sites of Delhi, NCR

The present paper reports chemistry and fluxes of dust-carbon mixed coarse particles. For the purpose of this study, different carbonaceous fractions i.e. organic carbon ((OC), elemental carbon (EC) and carbonate carbon (CC) of atmospheric dust and their respective local soils were quantified at three sites of National Capital Region (NCR) of Delhi viz. Jawaharlal Nehru University campus (JNU), Connaught Place (CP) and Vishali area of Ghaziabad (GB). It has been observed that the OC and EC levels were approximately five to nine times higher in urban atmospheric dust than their corresponding soils, whereas CC levels were about three times higher than the corresponding soils. Average dustfall fluxes were significantly different at all the sites due to their different land-use patterns. At urban background site (JNU), the dust flux was lowest (172 mg/m2/day) followed by CP, a commercial site, (192 mg/m2/day) and GB, an industrial/residential area, (302 mg/m2/day). Similar to the dustfall pattern, the mean values of OC, EC and CC deposition fluxes were also observed to be lowest at JNU (9.2, 0.8 and 1.0 mg/m2/day, respectively) as compared to CP (12.2, 1.2 and 1.3 mg/m2/day, respectively) and GB sites (11.1, 1.1 and 1.4 mg/m2/day, respectively). Interestingly, unlike fine mode, different correlation pattern of OC and EC in coarse mode dust aerosols at three sites has suggested their independent deposition processes and source contribution. Fluxes of major water soluble inorganic ions (Na+, NH4+, K+, Ca2+, Mg2+, F−, Cl−, NO3− and SO42−) were also determined. Ca2+, Cl− and SO42− were found to be the major ionic species of water soluble fraction of the urban dust at all the sites. These interactions are corroborated by the morphology of the mixed aerosols. High levels of measured chemical species and their spatial distribution revealed close correspondence with the local emissions from transport, industries, biomass burning, road dust and construction activities etc.

Presentation of the EURODELTA III intercomparison exercise – evaluation of the chemistry transport models' performance on criteria pollutants and joint analysis with meteorology

Abstract. The EURODELTA III exercise has facilitated a comprehensive intercomparison and evaluation of chemistry transport model performances. Participating models performed calculations for four 1-month periods in different seasons in the years 2006 to 2009, allowing the influence of different meteorological conditions on model performances to be evaluated. The exercise was performed with strict requirements for the input data, with few exceptions. As a consequence, most of differences in the outputs will be attributed to the differences in model formulations of chemical and physical processes. The models were evaluated mainly for background rural stations in Europe. The performance was assessed in terms of bias, root mean square error and correlation with respect to the concentrations of air pollutants (NO2, O3, SO2, PM10 and PM2.5), as well as key meteorological variables. Though most of meteorological parameters were prescribed, some variables like the planetary boundary layer (PBL) height and the vertical diffusion coefficient were derived in the model preprocessors and can partly explain the spread in model results. In general, the daytime PBL height is underestimated by all models. The largest variability of predicted PBL is observed over the ocean and seas. For ozone, this study shows the importance of proper boundary conditions for accurate model calculations and then on the regime of the gas and particle chemistry. The models show similar and quite good performance for nitrogen dioxide, whereas they struggle to accurately reproduce measured sulfur dioxide concentrations (for which the agreement with observations is the poorest). In general, the models provide a close-to-observations map of particulate matter (PM2.5 and PM10) concentrations over Europe rather with correlations in the range 0.4–0.7 and a systematic underestimation reaching −10 µg m−3 for PM10. The highest concentrations are much more underestimated, particularly in wintertime. Further evaluation of the mean diurnal cycles of PM reveals a general model tendency to overestimate the effect of the PBL height rise on PM levels in the morning, while the intensity of afternoon chemistry leads formation of secondary species to be underestimated. This results in larger modelled PM diurnal variations than the observations for all seasons. The models tend to be too sensitive to the daily variation of the PBL. All in all, in most cases model performances are more influenced by the model setup than the season. The good representation of temporal evolution of wind speed is the most responsible for models' skillfulness in reproducing the daily variability of pollutant concentrations (e.g. the development of peak episodes), while the reconstruction of the PBL diurnal cycle seems to play a larger role in driving the corresponding pollutant diurnal cycle and hence determines the presence of systematic positive and negative biases detectable on daily basis.

Encasing Si particles within a versatile TiO2−xFx layer as an extremely reversible anode for high energy-density lithium-ion battery

The chemical phenomena occurring at the electrode-electrolyte interfaces profoundly determine the cycle behavior of a lithium ion battery. In this work, we report that silicon-based anodes can attain enhanced levels of capacity retention, rate performance and lifespan when a versatile protective layer of, F-doped anatase (TiO2−xFx), is applied towards taming the interfacial chemistry of the silicon particles. With careful choice of titanium fluoride as a precursor, internal voids can be generated upon in-situ fluoride etching of the native oxide layer and are used to alleviate the mechanical stress caused by volume expansion of silicon during cycling. In the course of F-doping, part of the Ti4+(d0) ions in anatase are reduced to Ti3+(d1), thereby increasing charge carriers in the crystal structure. Hence, the multifunctional F-doped TiO2−x coating, not only minimizes the direct exposure of the Si surface to the electrolyte, but also improves the electronic conductivity via inter-valence electron hopping. The best-performing composite electrode, Si@TiO2−xFx-3, delivered a satisfactory performance in both half-cell and full-cell configurations. Furthermore, we present a study of 1) the Si valence change at the buried interface using synchrotron based hard X-ray photoelectron spectroscopy, and 2) the phase transformation of the electrode monitored in operando using X-ray diffraction. Based on these characterizations, we observe that the Li+ conducting intermediate phase (LixTiO2−xFx) formed inside the surface coating enables deep lithiation and delithiation of the silicon during battery operation, and thus increase the capacity that can be accessed from the electrodes.

Clickable Janus Particles.

Janus particles are colloidal analogues of molecular amphiphiles that can self-assemble to form diverse suprastructures, exhibit motility under appropriate catalytic reactions, and strongly adsorb to fluid-fluid interfaces to stabilize multiphasic fluid mixtures. The chemistry of Janus particles is the fundamental parameter that controls their behavior and utility as colloid surfactants in bulk solution and at fluid interfaces. To enable their widespread utilization, scalable methods that allow for the synthesis of Janus particles with diverse chemical compositions and shapes are highly desirable. Here, we develop clickable Janus particles that can be modified through thiol-yne click reactions with commercially available thiols. Janus particles are modified to be amphiphilic by introducing either carboxyl, hydroxyl, or amine moieties. We also demonstrate that regulating the extent of the modification can be used to control the particle morphology, and thus the type of emulsion stabilized, as well as to fabricate composite Janus particles through sequential click reactions. Modifying Janus particles through thiol-yne click chemistry provides a fast-reacting, scalable synthesis method for the fabrication of diverse Janus particles.

Suspect screening of OH-PAHs and non-target screening of other organic compounds in wood smoke particles using HR-Orbitrap-MS

Wood combustion has been shown to contribute significantly to emissions of polycyclic aromatic hydrocarbons and hydroxylated polycyclic aromatic hydrocarbons, compounds with toxic and carcinogenic properties. However, only a small number of hydroxylated polycyclic aromatic hydrocarbons have been determined in particles from wood combustion, usually compounds with available reference standards. In this present study, suspect and non-target screening strategies were applied to characterize the wood smoke particles from four different wood types and two combustion conditions with respect to hydroxylated polycyclic aromatic hydrocarbons and other organic compounds. In the suspect screening, 32 peaks corresponding to 12 monohydroxylated masses were tentatively identified by elemental composition assignments and matching of isotopic pattern and fragments. More than one structure was suggested for most of the measured masses. Statistical analysis was performed on the non-target screening data in order to single out significant peaks having intensities that depend on the wood type and/or combustion condition. Significant peaks were found in both negative and positive ionization modes, with unique peaks for each wood type and combustion condition, as well as a combination of both factors. Furthermore, structural elucidation of some peaks was done by comparing the spectra in the samples with spectra found in the spectral databases. Six compounds were tentatively identified in positive ionization mode, and 19 in negative ionization mode. The results in this present study demonstrate that there are significant overall differences in the chemistry of wood smoke particles that depends on both the wood type and the combustion condition used.

Grain Refinement of Deoxidized Copper

Abstract This study reports the current status of grain refinement of copper accompanied in particular by a critical appraisal of grain refinement of phosphorus-deoxidized, high residual P (DHP) copper microalloyed with 150 ppm Ag. Some deviations exist in terms of the growth restriction factor (Q) framework, on the basis of empirical evidence reported in the literature for grain size measurements of copper with individual additions of 0.05, 0.1, and 0.5 wt pct of Mo, In, Sn, Bi, Sb, Pb, and Se, cast under a protective atmosphere of pure Ar and water quenching. The columnar-to-equiaxed transition (CET) has been observed in copper, with an individual addition of 0.4B and with combined additions of 0.4Zr-0.04P and 0.4Zr-0.04P-0.015Ag and, in a previous study, with combined additions of 0.1Ag-0.069P (in wt pct). CETs in these B- and Zr-treated casts have been ascribed to changes in the morphology and chemistry of particles, concurrently in association with free solute type and availability. No further grain-refining action was observed due to microalloying additions of B, Mg, Ca, Zr, Ti, Mn, In, Fe, and Zn (~0.1 wt pct) with respect to DHP-Cu microalloyed with Ag, and therefore are no longer relevant for the casting conditions studied. The critical microalloying element for grain size control in deoxidized copper and in particular DHP-Cu is Ag.

Comparison of rheological behaviors with fumed silica-based shear thickening fluids

Shear thickening fluids (STFs) of differing compositions were fabricated and characterised in order to observe the effect of varying chemical and material properties on the resultant rheological behavior. Steady shear tests showed that for a given carrier fluid and particle size exists an optimum weight fraction which exhibits optimal shear thickening performance. Testing also showed that increasing particle size resulted in increased shear thickening performance and its onset whilst altering the carrier fluid chemistry has a significant effect on the thickening performance. An explanation is provided connecting the effect of varying particle size, carrier fluid chemistry and weight fraction to the resultant rheological behavior of the STFs. Two STFs were chosen for further testing due to their improved but contrasting rheological behaviors. Both STFs displayed a relationship between steady and dynamic shear conditions via the Modified Cox-Merz rule at high strain amplitudes (γ≥500%). Understanding the effects of particle and liquid polymer chemistry on the shear thickening effect will assist in ‘tailoring’ STFs for certain potential or existing applications.

Cellular Internalization Mechanisms of Polyanhydride Particles: Implications for Rational Design of Drug Delivery Vehicles.

Polyanhydride nanoparticles have emerged as a versatile delivery platform, due to their ability to encapsulate diverse drugs, immunogens, antibodies, and proteins. However, mechanistic studies on the effects of particle chemistry interactions with immune cells have yet to be described. Understanding the mechanism by which these particles are internalized by immune cells will enable rational selection of delivery vehicles for specific applications. In the present study, the internalization, mechanism(s) of uptake by monocytes, and intracellular fate of polyanhydride nanoparticles were evaluated using copolymers based on 1,6-bis(p-carboxyphenoxy)hexane (CPH), sebacic acid (SA), and 1,8-bis(p-carboxyphenoxy)3,6-dioxaoctane (CPTEG). The results showed that 20:80 CPH:SA and 20:80 CPTEG:CPH nanoparticles were internalized to a greater extent by monocytes as compared to the 50:50 CPH:SA and 50:50 CPTEH:CPH nanoparticles. Further, cytochalasin-D treatment of cells inhibited uptake of all the particles, regardless of chemistry, indicating that actinmediated uptake is the primary mechanism of cellular entry for these particles. The insights gained from these studies were used to identify lead nanoparticle formulations to enhance treatment of intracellular bacterial infections. The use of doxycycline-loaded nanoparticles exhibited enhanced therapeutic efficacy compared to soluble drug in treating monocyte monolayers infected with the virulent intracellular pathogen Brucella abortus. Altogether, these studies demonstrate how rational design and selection of nanoscale delivery platforms can be used for a wide spectrum of biomedical applications.

Progress in the Analysis of Complex Atmospheric Particles

This article presents an overview of recent advances in field and laboratory studies of atmospheric particles formed in processes of environmental air-surface interactions. The overarching goal of these studies is to advance predictive understanding of atmospheric particle composition, particle chemistry during aging, and their environmental impacts. The diversity between chemical constituents and lateral heterogeneity within individual particles adds to the chemical complexity of particles and their surfaces. Once emitted, particles undergo transformation via atmospheric aging processes that further modify their complex composition. We highlight a range of modern analytical approaches that enable multimodal chemical characterization of particles with both molecular and lateral specificity. When combined, these approaches provide a comprehensive arsenal of tools for understanding the nature of particles at air-surface interactions and their reactivity and transformations with atmospheric aging. We discuss applications of these novel approaches in recent studies and highlight additional research areas to explore the environmental effects of air-surface interactions.

A Simple Maturation Process to Increase the Performance of Si-Based Anodes for Li-Ion Batteries

For several years, great attention has been paid to silicon as negative electrode material for Li-ion batteries, due to its very high gravimetric capacity (3579 mAh g-1) in comparison to that of graphite (372 mAh g-1). However, Si electrodes suffer from poor cyclability due to the large volumetric expansion (up to ~300%) of Si upon its lithiation, resulting in the electrode architecture disintegration, and in the instability of the solid electrolyte interphase (SEI). We have shown that low-cost and high-performance Si-based electrodes can be obtained by combining (i) the use of ball-milled (nanocrystalline) Si powder resulting in a smoother phase transition; (ii) the processing of the electrode at pH 3 with carboxymethylcellulose (CMC) binder favoring the covalent grafting of the CMC to the Si particles; (iii) the use of fluoroethylene and vinylene carbonates (FEC/VC) electrolyte additives resulting in a more stable SEI.1 More recently, we have shown that the storage conditions of the Si-based film before assembling in the electrochemical cell has also a major impact on the electrode performance.2 In this context, we have elaborated a film maturation process which simply consists of storing the electrode in humid air (85% RH) at room temperature for at least two days. This process has a significant positive impact on the electrode performance as is illustrated in Fig. 1a which compares the cycling performance of ball-milled Si-based electrodes cast on a copper foil with and without a film maturation step. Different mechanisms are proposed to explain why humid storage has such a beneficial impact on the electrode performance. Firstly, humid air may increase the film adherence on the copper current collector by increasing the amount of CuOH groups which can create bonds with the CMC binder. This tends to be supported by the fact that the film maturation step has no significant impact when a carbon layer is deposited on the copper current collector prior to the maturation step as shown on Fig. 1b. Secondly, water molecules from air can react with the film and modify the chemical links between the Si particles and the CMC binder. This tends to be confirmed by attenuated total reflectance Fourier transform infrared spectroscopy(ATR-FTIR) analysis of the composite electrodes. Indeed, as shown in Fig. 2a, a significant increase of the intensity of the peak centered at 1630 cm− 1 assigned to the stretching band of the carboxyl group of CMC is observed for the film stored in humid air, while the intensity of the peak centered at 1750 cm-1 assigned to ester bond between Si and CMC is decreased. This suggests that during the maturation step, some of the ester bonds between Si particles and CMC binder are converted into less rigid hydrogen bonds as schematized in Fig.2b. This may increase the deformability of the electrode, which can better accommodate volume variations with cycling. Thirdly, the humid air could modify the surface chemistry of silicon particles by increasing the amount of silicon oxide and/or silanols (SiOH). This would increase the amount of bonds between silicon particles and binder, and/or help to stabilise the SEI layer. Various experiments for supporting these different hypotheses will be presented. References M. Gauthier, D. Mazouzi, D. Reyter, B. Lestriez, P. Moreau, B. Lestriez, D. Guyomard, L. Roué. A low-cost and high-performance Si-based electrode for Li-ion batteries. Energy Environ. Sci. 6 (2013) 2145–2155.C. Real Hernandez, Z. Karkar, D. Guyomard, B. Lestriez, L. Roué. A film maturation process for improving the cycle life of Si-based anodes for Li-ion batteries. Electrochem. Comm. 61 (2015) 102-105. Figure 1

Liquid Water: Ubiquitous Contributor to Aerosol Mass

Aerosol liquid water (ALW) is a ubiquitous component of atmospheric aerosol and influences particle chemistry, visibility, human health, and regional climate. The global abundance and spatial patterns in ALW mass concentrations and its fractional contribution to total particle mass are not routinely documented. We estimate lower-bound ALW mass concentrations at locations and time periods of aerosol mass spectrometer (AMS) field campaigns using speciated ion measurements, meteorology from the Climate Forecast System Reanalysis, and thermodynamic predictions from ISORROPIA version 2.1. The contribution of water by organic compounds is estimated using κ-Kohler theory. Field campaign-specific patterns suggest that ALW mass is largest in urban and urban downwind areas, and that of growth factors is largest in rural areas. The highest average ALW mass concentration is estimated for the AMS study in Beijing and the highest mass fraction for rural Hyytiala. A more robust understanding of ALW is critical for devel...

Gold/silver core-shell 20 nm nanoparticles extracted from citrate solution examined by XPS

Silver nanoparticles of many types are widely used in consumer and medical products. The surface chemistry of particles and the coatings that form during synthesis or use in many types of media can significantly impact the behaviors of particles including dissolution, transformation and biological or environmental impact. Consequently it is useful to be able to extract information about the thickness of surface coatings and other attributes of nanoparticles produced in a variety of ways. It has been demonstrated that X-ray Photoelectron Spectroscopy (XPS) can be reliably used to determine the thickness of coatings and shells. However, care is required to produce reliable and consistent information. Here we report XPS spectra from gold/silver core-shell nanoparticles of nominal size 20 nm removed from a citrate saturated solution after one washing cycle. The Simulation of Electron Spectra for Surface Analysis (SESSA) program has been used to model peak amplitudes to obtain information on citrate coatings that remain after washing and demonstrate the presence of the gold core. This data is provided in digital form so that others can compare use of SESSA or other modeling approaches to quantify the nature of coatings to those already published and to explore the impacts particle non-uniformities on XPS signals from core-shell nanoparticles.

Contact angle and detachment energy of shape anisotropic particles at fluid-fluid interfaces

The three phase contact angle of particles, a measure of its wettability, is an important factor that greatly influences their behaviour at interfaces. It is one of the principal design parameters for potential applications of particles as emulsion/foam stabilizers, functional coatings and other novel materials. In the present work, the effect of size, shape and surface chemistry of particles on their contact angle is investigated using the gel trapping technique, which facilitates the direct visualization of the equilibrium position of particles at interfaces. The contact angle of hematite particles of spherocylindrical, peanut and cuboidal shapes, hematite-silica core-shell and silica shells is reported at a single particle level. The spherocylindrical and peanut shaped particles are always positioned with their major axis parallel to the interface. However, for cuboidal particles at air-water as well as decane-water interfaces, different orientations namely - face-up, edge-up and the vertex-up - are observed. The influence of gravity on the equilibrium position of the colloidal particles at the interface is studied using the hematite-silica core-shell particles and the silica shells. The measured contact angle values are utilized in the calculations of the detachment and surface energies of the hematite particles adsorbed at the interface.

Review of Particle Physics and Chemistry in Fluidized Beds for Development of Comprehensive Ash Agglomeration Prediction Models

This work elucidates the fundamental concepts that are essential to understand fluidized bed agglomeration and reviews the development of tools used to predict it. The process of agglomeration in fluidized bed combustion and gasification systems has been explained, along with the associated mechanisms. The ash chemistry and particle physics that influence the agglomeration process have been reviewed to help choose the type of fuel and reactor configurations that can minimize the problem. The parameters that affect agglomeration and their interdependence have been reviewed in detail in order to understand the demands placed on detection, modeling, and prediction tools. Further, the current status of various prediction methods, their challenges, and avenues for further development have been identified. Insights into the development of comprehensive mathematical models to predict agglomerate growth kinetics have also been provided.

Fundamental Studies of Adhesion of Dust to PV Module Surfaces: Chemical and Physical Relationships at the Microscale

Photovoltaic (PV) module soiling is a growing area of concern for performance and reliability. This paper provides evaluations of the fundamental interactions of dust/soiling particles with several PV module surfaces. The purpose is to investigate the basic mechanisms involving the chemistry, morphology, and resulting particle adhesion to the first photon-incident surface. The evaluation and mapping of the chemistry and composition of single dust particles collected from operating PV module surfaces are presented. The first correlated direct measurements of the adhesive force of individual grains from field-operating collectors on identical PV module glass are reported, including correlations with specific compositions. Special microscale atomic force microscopy techniques are adapted to determine the force between the particle and the module glass surface. Results are presented for samples under dry and moisture-exposed conditions, confirming the effects of cementation for surfaces having soluble mineral and/or organic concentrations. Additionally, the effects of hydrocarbon fuels on the enhanced bonding of soiling particles to surfaces are determined for samples from urban and highly trafficked regions. Comparisons between glass and dust-mitigating superhydrophobic and superhydrophilic coatings are presented. Potential limitations of this proximal probe technique are discussed in terms of results and initial proof-of-concept experiments.

Exploring on aqueous chemistry of micron-sized lignite particles in lignite–water slurry: Effects of pH on humics dissolution

The aqueous chemistry of lignite can change the properties of coal–water slurry. The aqueous chemistry of lignite–water slurry including dissolution kinetics of humics and properties of the residual lignite was studied using optical microscope imaging, SEM, FTIR, zeta potential and contact angle analysis. Also, the influence of humics dissolution on the interaction of micron-sized lignite particles was discussed by EDLVO theory. The dissolution kinetics demonstrates that humics concentration increases with increasing the slurry pH. The outer diffusion through the product layer is the rate controlling step according to shrinking unreacted core model. The value of D50 defined as the apparent particle size relevant to 50% of cumulative distribution is decreased when the lignite slurry pH is increased. The FTIR, zeta potential and contact angle results show that humics dissolution increases the surface hydrophilicity of the residual lignite. The total energy ET of the residual lignite particles at 10nm of separation distance is enhanced from −0.70×10−17 to 0.34×10−17J with the humics concentration is increased from 2.28 to 5.33mg/L. The EDLVO calculation indicates that the dispersion stability of micron-sized lignite particles is improved with humics dissolution.

Measuring Mass-Based Hygroscopicity of Atmospheric Particles through in Situ Imaging

Quantifying how atmospheric particles interact with water vapor is critical for understanding the effects of aerosols on climate. We present a novel method to measure the mass-based hygroscopicity of particles while characterizing their elemental and carbon functional group compositions. Since mass-based hygroscopicity is insensitive to particle geometry, it is advantageous for probing the hygroscopic behavior of atmospheric particles, which can have irregular morphologies. Combining scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDX), scanning transmission X-ray microscopy (STXM) analysis, and in situ STXM humidification experiments, this method was validated using laboratory-generated, atmospherically relevant particles. Then, the hygroscopicity and elemental composition of 15 complex atmospheric particles were analyzed by leveraging quantification of C, N, and O from STXM, and complementary elemental quantification from SEM/EDX. We found three types of hygroscopic responses, and correlated high hygroscopicity with Na and Cl content. The mixing state of 158 other particles from the sample broadly agreed with those of the humidified particles, indicating the potential to infer atmospheric hygroscopic behavior from a selected subset of particles. These methods offer unique quantitative capabilities to characterize and correlate the hygroscopicity and chemistry of individual submicrometer atmospheric particles.