•New sub-2μm C18 fully porous particles with narrow particle size distribution (nPSD).•Kinetic performance of nPSD columns is studied from a theoretical viewpoint.•Excellent kinetic performance comes ...from very small eddy dispersion term.•B- and C-term of van Deemter equation similar to those of fully porous C18 columns.
Columns packed with new commercially available 1.9 fully porous particles of narrow particle size distribution (nPSD) are characterized by extremely high efficiency. Under typical reversed phase conditions, these columns are able to generate very high number of theoretical plates (in the order of 300,000plates/m and more). In this paper, we investigate the origin of the high performance of these nPSD columns by performing a series of measurements that include, in addition to the traditional determination of the van Deemter curve, peak parking, pore blocking and inverse size exclusion experiments. Two nPSD columns (both 100×3.0mm) have been considered in this study: the first one, packed with particles of 80Å pore size, is commercially available. The second one is a prototype column packed with 1.9 fully porous particles of 120Å pore size.
The main conclusion of our study is that these nPSD columns are characterized by extremely low eddy dispersion, while longitudinal diffusion and mass transfer kinetics are substantially equivalent to those of other fully porous particles of similar chemistry.
Accurate measurements of atmospheric reactive mercury (RM or HgII) including gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM) are crucial to improving understanding of mercury (Hg) ...behavior in the ambient air and evaluating the effectiveness of the Minamata Convention. As part of the Speciation and Transformation of Atmospheric Mercury in a Polluted region (STAMP) campaign in eastern China, comparison of Tekran, the reactive mercury active system (RMAS) and the micro-orifice uniform deposit impactors (MOUDI) system for RM measurements was conducted in this study. The ratio of GOMTekran/GOMRMAS was found to be positively correlated with the ratio of PBM/GOM and the proportion of -Br/Cl in RM based on deconvolution of the RMAS thermal desorption profiles. HgII reduction by the aqueous HO2 radicals was found to be the most likely cause of GOM underestimation by denuder-based methods. PBM acting as a substitute for GOM in HgII reduction could limit the underestimation. High particulate matter (PM) environment could cause PBM breakthrough in RMAS sampling, resulting in PBM underestimation and GOM overestimation. The chemical compound characteristics of RM and HgII distribution on particles by size provide evidences for the sources of the discrepancies in PBM measurements by different methods. Particle-size-resolved compound profiles are useful approaches for accurate RM quantification.
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•Intercomparison for RM measurements was performed in the STAMP campaign.•A theory of mechanism for GOM underestimation by KCl denuders was proposed.•High PM environment could cause PBM breakthrough in the RMAS method.•Particle-size-resolved compound profiles are useful tools for RM quantification.
The particle‐size distribution (PSD) of a soil expresses the mass fractions of various sizes of mineral particles which constitute the soil material. It is a fundamental soil property, closely ...related to most physical and chemical soil properties and it affects almost any soil function. The experimental determination of soil texture, i.e., the relative amounts of sand, silt, and clay‐sized particles, is done in the laboratory by a combination of sieving (sand) and gravitational sedimentation (silt and clay). In the latter, Stokes' law is applied to derive the particle size from the settling velocity in an aqueous suspension. Traditionally, there are two methodologies for particle‐size analysis from sedimentation experiments: the pipette method and the hydrometer method. Both techniques rely on measuring the temporal change of the particle concentration or density of the suspension at a certain depth within the suspension. In this paper, we propose a new method which is based on the pressure in the suspension at a selected depth, which is an integral measure of all particles in suspension above the measuring depth. We derive a mathematical model which predicts the pressure decrease due to settling of particles as function of the PSD. The PSD of the analyzed sample is identified by fitting the simulated time series of pressure to the observed one by inverse modeling using global optimization. The new method yields the PSD in very high resolution and its experimental realization completely avoids any disturbance by the measuring process. A sensitivity analysis of different soil textures demonstrates that the method yields unbiased estimates of the PSD with very small estimation variance and an absolute error in the clay and silt fraction of less than 0.5%.
Key Points
New methodology for automated particle‐size analysis from sedimentation experiments
Accurate and precise identification of particle‐size distribution in high resolution
Contrary to pipette and hydrometer method, no manual operation necessary, and no disturbance of measurement process occurs
The extensive utilization of antibiotics has resulted in their frequent detection, contributing to an increased abundance of antibiotic resistance genes in rivers and posing a significant threat to ...environmental health. Particulate matter plays a crucial role as the primary carrier of various pollutants in river ecosystem. Its physicochemical properties and processes of sedimentation and re-suspension can influence the migration and transformation of antibiotics, yet the mechanisms of this impact remain unclear. In this study, we investigated the distribution characteristics at the micro-scale of particles in the upstream plain river network of the Taihu basin and the adsorption behaviors of antibiotics in particulate matter. The results revealed that particles were predominantly in the size range of 30 to 150 μm in the river network and highest total antibiotic concentrations in 0 to 10 μm particle size fractions. Adsorption experiments also confirmed that the smaller the suspended particle size, the stronger the adsorption capacity for antibiotics. Spatially, both the average particle size and total antibiotic concentrations were lower downstream than upstream. The distribution mechanism of antibiotic in river network sediments was significantly influenced by frequent resuspension and settling of fine particles with a stronger capacity to adsorb antibiotics under hydrodynamic conditions. This ultimately facilitated the release of antibiotics from sediment into the water, resulting in lower antibiotic concentrations in downstream sediments relative to upstream These findings suggest that fine particles serve as the primary carriers of antibiotics, and their sorting and transport processes can significantly influence the distribution of antibiotics in water-sediment systems. This study enhances our understanding of the migration mechanisms of antibiotics in river networks and will prove beneficial for the development of management strategies aimed at controlling antibiotic dissemination.
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•Total antibiotics concentrations in upstream were higher than those in downstream.•Average particle size in upstream was larger than that in downstream.•Adsorption capacity for antibiotics increased with decrease of particle size.
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•Ag particle size distribution over Ag/α-Al2O3 follows a lognormal distribution.•A Gaussian rate function explains particle size effects in ethylene epoxidation.•Ag particle size ...distributions centered ∼ 140 nm facilitate high epoxidation rates.
The post-reaction Ag surface area distribution of 16 Ag/α-Al2O3 ethylene epoxidation catalysts with varying Ag weight loadings (6.9 – 35 wt%) containing different distributions of Ag particle sizes was correlated with measured ethylene oxide (EO) rates in presence of 3.5 ppm ethyl chloride via a particle size dependent Gaussian rate function. The Gaussian rate function model differs from a description based on average particle size as it accounts for the effects of the breadth of particle size distribution as well as the population of different particle sizes that constitute the Ag particle distribution on measured EO rates. This description of particle size effects in ethylene epoxidation catalysis facilitates accurate prediction of EO rates over a wide range of particle sizes (5–400 nm) and suggests that very small (5–50 nm) and very large Ag particles (>250 nm) have low EO rates (<3 μmol gAg-1 s−1). A narrow Ag particle size distribution centered around ∼130–150 nm would enable operation of ethylene epoxidation with high EO rates and EO selectivity.
A discrete multi-particle model of Ostwald ripening based on direct pairwise interactions between precipitates with incoherent interfaces is presented. Although based on the mean field concept, it is ...a valid alternative to the classical LSW theory. The main differences with respect to the classical approach can be summarized as follows: i) Particles interact the one another; ii) The first Fick’s law is considered to evaluate the fluxes of matter instead of the quasi stationary solution of the concentration field around particles; iii) The rate of matter exchange depends on the average surface-to-surface interparticle distance, a characteristic feature of the system which naturally incorporates the effect of volume fraction of second phase; iv) The multi-particle diffusion is described through the definition of an interaction volume containing all the particles involved in the exchange of solute. The model is in excellent agreement with the experimental data available in the literature. The shape of the quasi-stationary 3D particle size distribution of solid-solid and solid-liquid systems is well predicted from volume fractions of 0.07, 0.30, 0.52 and 0.74. Similarly, a very good prediction of the dependence of the kinetic constant of the coarsening process on the volume fraction of precipitates is obtained with reference to literature data on solid-liquid mixtures in the volume fraction range from 0.20 to about 0.75. For volume fractions below about 0.1 the model predicts broad and right-skewed stationary size distributions resembling a lognormal function. Above this value, a transition to sharper, more symmetrical but still right-skewed shapes occurs.
The DPF regeneration is crucial for reducing backpressure, minimizing negative impacts on engine power and fuel economy, but the changes in particulate emission characteristics it brings are worth ...studying. In this study, the influence of DPFs with different soot loadings on exhaust back pressure and particle emission characteristics, as well as the particle number emission, particle size distribution, and thermal field distribution characteristics during regeneration was investigated based on engine bench test. Results reveal that the exhaust back pressure increases linearly with the engine speed, as well as the soot loading. The increase of DPF soot loading leads to a considerable increase in the reduction efficiency of particle number (PN) and particulate matter emissions, especially for the accumulation mode particles. Moreover, the performance in reducing nucleation mode particles is markedly better than that of accumulation mode ones, and this effect is greatly influenced by the engine operating conditions. At the beginning of DPF regeneration, the PN concentration increases sharply, especially the nucleation mode particles. After regeneration, the PN emissions decrease by two orders of magnitude. During regeneration, the particle size distribution exhibits a unimodal distribution, with the peak value increasing considerably and shifting toward smaller particle sizes. After regeneration, the particle size of the PN peak value slightly decreases and markedly shifts toward larger sizes, the accumulation mode particle concentration increases by 7.2 times, and the nucleation mode particle concentration increases by 2.6 times. Before the DPF regeneration, the axial temperature gradually decreases along the direction of the airflow, and the radial temperature gradually decreases from the center to the edge. During regeneration, the highest temperature occurs in the center of the DPF cross-section, whereas the temperature peak at the outlet interface occurs at the middle position of the DPF. The findings of this paper can provide scientific references to formulation and optimization of DPF regeneration strategies.
Gangue, produced from coal mining and washing process, is a serious threat to the ground environment. Gangue backfilling mining method can solve this problem and reduce mining-induced hazards, e.g., ...controlling surface subsidence and preventing water inrush from seeping into goaf by cracks in overlying strata. In this paper, effects of the original particle size distribution (PSD) and water content on the particle crushing behavior and seepage properties of granular gangues were investigated. Experimental results show that the crushing behavior can promote the compaction of gangue particles; the variation of PSD after crushing reveals distinct fractal characteristics. With the increasing compression stress, the particle crushing ratio and fractal dimension increase, while the permeability decreases. Due to the rearrangement of particles and newly generated fine particles filled the gap among larger particles, it is difficult to reduce the permeability by increasing the compressive stress. In addition, the variation of fractal dimensions is similar to the crushing ratio, so the particle crushing can be illustrated by fractal dimensions. The relationship between porosity and permeability established by the Kozeny-Carman equation can model the effect of particle crushing in this research. The reliability of the equation is verified by the comparison of model result and experimental data. To increase the mitigation rate of mining-induced hazards and environmental pollution by GBM method, granular gangues can be crushed into smaller particles and dehydrated before backfilling.
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•Gangue backfilling mining method can mitigate the mining-induced hazards and environment pollution.•Particle crushing behavior and hydraulic properties of granular gangues were experimentally investigated.•The permeability and porosity relationship established by Kozeny-Carman equation can model the effect of particle crushing.•Granular gangues should be crushed into fine particles and dehydrated before backfilling.
Many industrial catalysts involve nanoscale metal particles (typically 1–100 nm), and understanding their behavior at the molecular level is a major goal in heterogeneous catalyst research. However, ...conventional nanocatalysts have a nonuniform particle size distribution, while catalytic activity of nanoparticles is size dependent. This makes it difficult to relate the observed catalytic performance, which represents the average of all particle sizes, to the structure and intrinsic properties of individual catalyst particles. To overcome this obstacle, catalysts with well-defined particle size are highly desirable. In recent years, researchers have made remarkable advances in solution-phase synthesis of atomically precise nanoclusters, notably thiolate-protected gold nanoclusters. Such nanoclusters are composed of a precise number of metal atoms (n) and of ligands (m), denoted as Au n (SR) m , with n ranging up to a few hundred atoms (equivalent size up to 2–3 nm). These protected nanoclusters are well-defined to the atomic level (i.e., to the point of molecular purity), rather than defined based on size as in conventional nanoparticle synthesis. The Aun (SR)m nanoclusters are particularly robust under ambient or thermal conditions (<200 °C). In this Account, we introduce Au n (SR) m nanoclusters as a new, promising class of model catalyst. Research on the catalytic application of Au n (SR) m nanoclusters is still in its infancy, but we use Au25(SR)18 as an example to illustrate the promising catalytic properties of Au n (SR) m nanoclusters. Compared with conventional metallic nanoparticle catalysts, Au n (SR) m nanoclusters possess several distinct features. First of all, while gold nanoparticles typically adopt a face-centered cubic (fcc) structure, Au n (SR) m nanoclusters (<2 nm) tend to adopt different atom-packing structures; for example, Au25(SR)18 (1 nm metal core, Au atomic center to center distance) has an icosahedral structure. Secondly, their ultrasmall size induces strong electron energy quantization, as opposed to the continuous conduction band in metallic gold nanoparticles or bulk gold. Thus, nanoclusters become semiconductors and possess a sizable bandgap (e.g., ∼1.3 eV for Au25(SR)18). In addition, Au n (SR) m can be doped with a single atom of other metals, which is of great interest for catalysis, because the catalytic properties of nanoclusters can be truly tuned on an atom-by-atom basis. Overall, atomically precise Au n (SR) m nanoclusters are expected to become a promising class of model catalysts. These well-defined nanoclusters will provide new opportunities for achieving fundamental understanding of metal nanocatalysis, such as insight into size dependence and deep understanding of molecular activation, active centers, and catalytic mechanisms through correlation of behavior with the structures of nanoclusters. Future research on atomically precise nanocluster catalysts will contribute to the fundamental understanding of catalysis and to the new design of highly selective catalysts for specific chemical processes.
Switching on high activity in a relatively dense system of active Janus colloids, we observe fast clustering, followed by cluster aggregation towards full phase separation. The phase separation ...process is however interrupted when large enough clusters start breaking apart. Following the cluster size distribution as a function of time, we identify three successive dynamical regimes. Tracking both the particle positions and orientations, we characterize the structural ordering and alignment in the growing clusters and thereby unveil the mechanisms at play in these regimes. In particular, we identify how alignment between the neighboring particles is responsible for the interruption of the full phase separation. Our large scale quantification of the phase separation kinetics in active colloids points towards the new physics observed when both alignment and short-range repulsions are present.
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