DLVO Research Articles

Comparative study of polystyrene microplastic transport behavior in three different filter media: Quartz sand, zeolite, and anthracite

Microplastics (MPs) are emerging contaminants that are attracting increasing interest from researchers, and the safety of drinking water is greatly affected by their transportation during filtration. Polystyrene (PS) was selected as a representative MPs, and three filter media (quartz sand, zeolite, and anthracite) commonly found in water plants were used. The retention patterns of PS-MPs by various filter media under various background water quality conditions were methodically investigated with the aid of DLVO theory and colloidal filtration theory. The results show that the different structures and elemental compositions of the three filter media cause them to exhibit different surface roughnesses and surface potentials. A greater surface roughness of the filter media can provide more deposition sites for PS-MPs, and the greater surface roughness of zeolite and anthracite significantly enhances their ability to inhibit the migration of PS-MPs compared with that of quartz sand. However, surface roughness is not the only factor affecting the migration of MPs. The lower absolute value of the surface potential of anthracite causes the DLVO energy between it and PS-MPs to be significantly lower than that between zeolite and PS-MPs, which results in stronger retention of PS-MPs by anthracite, which has a lower surface roughness, than zeolite, which has a higher surface roughness. The transport of PS-MPs in the medium is affected by the combination of the surface roughness of the filter media and the DLVO energy. Under the same operating conditions, the retention efficiencies of the three filter materials for PS-MPs followed the order of quartz sand < zeolite < anthracite. Additionally, the conditions of the solution markedly influenced the transport ability of PS-MPs within the simulated filter column. The transport PS-MPs in the simulated filter column decreased with increasing solution ionic strength and cation valence. Naturally, dissolved organic matter promoted the transfer of PS-MPs in the filter layer, and humic acid had a much stronger facilitating impact than fulvic acid. The study findings might offer helpful insight for improving the ability of filter units ability to retain MPs.

Joint use of sodium silicate and polysaccharides in the flotation of talcose copper-nickel ores

The paper considers the combined effect of polysaccharides (carboxymethyl cellulose and carboxymethyl starch) with sodium silicate in the f lotation of talcose copper-nickel ore. The analysis of the f lotation results and the assessment of hydrophobicity and surface charge of minerals showed that the composition of carboxymethylated polysaccharides and sodium silicate hydrophilizes the talc surface more effectively than each of the reagents separately. Moreover, sodium silicate alone hardly depresses the talc surface at all. The depression of f lotation-active silicates is effective when polysaccharide and sodium silicate are sequentially supplied. Under these conditions, sodium silicate makes a significant contribution to increasing the negative charge on the talc particles surface. The effect is more pronounced for compositions with starch, characterized by a lower degree of substitution compared to cellulose. It results in a significantly reduced recovery of f lotation-active magnesium-containing silicates and a slight decrease in sulfide recovery. To determine the features of the mechanism of talc and sulfide minerals depression in f lotation, we performed calculations using the extended DLVO theory based on the obtained values of the zeta potential and force of detachment. We established that sulfide minerals have no potential barrier preventing their interaction with an air bubble, regardless of the compositions of the studied depressants used. We propose the following interaction mechanism: when sodium silicate is supplied first, the talc basal surface is very insignificantly hydrophilized as SiO(OH)– ions are not easy to fix. On the contrary, when the carboxymethylated polysaccharide is supplied first, significant hydrophilization of the talc surface with carboxyl groups occurs due to the hydrophobic interaction between the corresponding regions of the macromolecule and the talc basal surface.

Migration Rules and Mechanisms of Nano-Biochar in Soil Columns under Various Transport Conditions.

Compared to traditional biochar (BC), nano-biochar (NBC) boasts superior physicochemical properties, promising extensive applications in agriculture, ecological environments, and beyond. Due to its strong adsorption and migration properties, NBC may carry nutrients or pollutants to deeper soil layers or even groundwater, causing serious environmental risks. Nevertheless, the migration rules and mechanisms of NBC in soil are still unclear. Therefore, this study employed soil column migration experiments to systematically explore the migration rules and mechanisms of NBC under various flow rates, initial soil water contents, soil depths, and soil textures. The results showed that regulated by smaller particle size differences and greater surface charges, NBC exhibited a stronger migration ability compared with traditional BC. As the soil texture transitioned from fine to coarse, the migration capability of NBC significantly improved, driven by both pore structure and interaction forces as described by the DLVO theory. The migration ability of NBC was also greatly boosted as the soil transitioned from saturated to unsaturated conditions, primarily because of preferential flow. When the flow rate increased from 70% KS to 100% KS and 130% KS, the migration ability of NBC also increased accordingly, as changes in injection flow rates altered the velocity distribution of pore water. NBC in 25 cm soil columns was more prone to shallow retention compared with 10 cm soil columns, resulting in weaker overall migration ability. In addition, through fitting of the two-site kinetic model and related parameters, the penetration curves of NBC under various variable conditions were effectively characterized. These findings could offer valuable insights for NBC's future efficient, rational, and sustainable utilization, facilitating the evaluation and mitigation of its potential environmental risks.

P‐239: Late‐News Poster: Modeling Particle Deposition in Evaporating Colloidal Droplets

Inkjet printing is a cost‐effective method of particle deposition applicable, for example, in the manufacture of Quantum Dot (QD) color filters. However, it is a challenge to achieve uniform deposition of particles because evaporating colloidal dispersions are prone to the coffee‐ring effect.When the particle size is small, it is difficult to gauge directly by experiment how particles migrate during the evaporation process. Consequently, it is a challenge to optimize the process conditions to improve uniformity by experiment alone. To aid in this task, we have developed a simulator for colloidal droplet evaporation. Rather than use an effective particle concentration field as in previous works, motion of each individual particle is calculated by Stokesian Dynamics, with particle interactions governed by the DLVO theory. In order to facilitate the simulation of large collections of particles, GPU computing is applied to reduce the simulation time.A phase‐field approach is taken to capture the interface physics at the solvent‐air interface. Within a colloidal droplet we find that, by controlling the temperature, it is possible to promote Marangoni flow and, in turn, improve deposition uniformity. In future, we aim to use simulation to further optimize the process conditions, such as the chamber pressure and temperature, in order maximize uniformity.

Enhanced performance and mechanism of adsorption pretreatment for alleviating membrane fouling in AGMBR: Impact of structural variations in carbon adsorbents

The structural variances of adsorbents play a crucial role in determining the number of effective adsorption sites and pretreatment performance. However, there is still a gap in comprehending the impact of different carbon structural adsorbents on membrane fouling. Therefore, this study aimed to compare the efficacy of granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) in mitigating membrane fouling during municipal sewage reclamation using an aerobic granular sludge membrane bioreactor (AGMBR). The results demonstrated that the utilization of PAC significantly enhanced the normalized flux and reduced fouling resistance in comparison to GAC and ACF systems. PAC effectively adsorbed low and medium-molecular-weight pollutants present in raw sewage, resulting in an increase in average particle size and a decrease in foulant content on the membrane surface. The Hermia model indicated that adsorption pretreatment minimized standard blocking while promoting the formation of a sparse and porous cake layer. Moreover, according to the extended Derjaguin–Landau–Verwey–Overbeek theory, PAC has been demonstrated as the optimal antifouling system owing to its enhanced repulsion between membrane-foulant and foulant-foulant interactions. Correlation analysis revealed that the exceptional antifouling performance of the PAC system was due to its high removal rates of chemical oxygen demand (~78 %) and suspended solids (~97 %). This research offers valuable insights into the mitigation of membrane fouling through the utilization of adsorbents featuring diverse carbon structures.

Single-Digit Nanobubble Sensing via Nanopore Technology.

Nanobubbles play an important role in diverse fields, including engineering, medicine, and agriculture. Understanding the characteristics of individual nanobubbles is essential for comprehending fluid dynamics behaviors and advancing nanoscale science across various fields. Here, we report a strategy based on nanopore sensors for characterizing single-digit nanobubbles. We investigated the sizes and diffusion coefficients of nanobubbles at different voltages. Additionally, the finite element simulation and molecular dynamics simulation were introduced to account for counterion concentration variation around nanobubbles in the nanopore. In particular, the differences in stability and surface charge density of nanobubbles under various solution environments have been studied by the ion-stabilized model and the DLVO theory. Additionally, a straightforward method to mitigate nanobubble generation in the bulk for reducing current noise in nanopore sensing was suggested. The results hold significant implications for enhancing the understanding of individual nanobubble characterizations, especially in the nanofluid field.

Order–disorder–order mesophase transitions in self-assembled mesoporous alumina for enhanced CO2 adsorption

The addition of a hydrophobic micelle pore expander to self-assembling mesostructured hybrid materials enables access to new combinations with differently ordered mesophases and enhanced structural properties. Here we detail our investigations into the influence of 1,3,5-trimethylbenzene (TMB) on the self-assembly behaviors of an F127 Pluronic triblock copolymer with an aluminum oxide sol additive. By varying the chemical mixing sequence, the TMB-to-F127 mass ratio and the acid-to-metal molar ratio, we observe that TMB exhibits dual roles, functioning both as a hydrophobic swelling agent and as a low dielectric co-solvent. This induces a mesophase transition from an ordered p6mm lattice to a disordered state and subsequently back to the ordered p6mm phase. We propose a structure formation mechanism based on the DLVO theory to describe the thermodynamics and kinetic mobility of the hybrid micelles during the order-disorder and ensuing disorder-order mesophase transitions. The resulting ordered mesoporous alumina structures, with considerable pore sizes (up to 12 nm), high surface areas (up to 314 m2/g) and pore volumes (up to 0.74 cm3/g), organized pore geometry and variable inorganic wall thicknesses, have shown excellent CO2 adsorption capacities and are appealing for various applications, including stable high temperature catalyst supports, separation and sensing.

Quantifying Contributions of Different Repulsion to Film Drainage Time during the Bubble-Solid Surface Attachment and Implications for the Flotation of Fine Particles.

The flotation recovery of fine particles faces serious challenges due to the lack of kinetic energy required for supporting their radial displacement and attachment with bubbles. Generally, the hydrodynamic resistance and repulsive disjoining pressure successively inhibit the liquid outflow intervening between the bubble and solid surfaces. To quantitatively characterize the influence of the main repulsion on film thinning time, experiments have been designed in three different aqueous systems. Bubble surface mobility closely associated with hydrodynamic resistance was determined by the rising bubble technique, and the DLVO theory was employed to confirm the evolution of electrostatic repulsion. The film drainage process was then measured based on the high-speed microscopic interferometry. Furthermore, the influence of the main repulsion on bubble-solid surface interactions was examined by flotation recovery. Results show that the earlier buildup of hydrodynamic force ran through the whole film thinning process, and under immobile conditions, the central region gradually became dominant in film thinning due to the very limited fluid flow at the thinnest rim position. Therefore, to achieve the identical film thickness (∼100 nm), the large hydrodynamic resistance could prolong the film thinning time by about 1 order of magnitude, compared with that induced by electrostatic repulsion, which accounts for the increased flotation recovery by 10% using mobile bubbles. This study not only enhances the understanding of how typical repulsive forces work in film drainage dynamics but also opens up an avenue for enhancing flotation and avoiding wasting resources by modulating bubble surface mobility and thus micro/nanoscale fluid flow.

Heteroaggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles with polystyrene nanoplastics in water

Iron oxide nanomaterials play important roles in biogeochemical processes. This study investigates the effects of representative natural carbonaceous materials (humic acid [HA] and extracellular polymeric substances [EPS]) and cations on the heteroaggregation and sedimentation of engineered and natural iron oxide nanomaterials with montmorillonite and sulfate- and amine-modified polystyrene (PS) nanoparticles (NPs) (S- and N-PS NPs, respectively) in water, assessing their environmental behavior and differences in colloidal stability parameters. In addition, a novel extended Derjaguin–Landau–Verwey–Overbeek theory (XDLVO) was developed to describe the mechanism of colloidal behavior that concurrently considers gravitational and magnetic attraction forces. In CaCl2 solution and most natural water samples, negatively charged S-PS NPs promoted heteroaggregation with goethite and iron oxide (Fe3O4) NPs more than positively charged N-PS NPs with increased nanoplastic particle concentration. In seawater, the introduction of S- and N-PS NPs increased the maximum net energy (barrier) (ΦMAX) of heteroaggregation and sedimentation with goethite and Fe3O4 NPs, facilitating dispersal and suspension of the system. The X-ray photoelectron spectroscopy (XPS) and molecular dynamics simulation results suggested that Ca2+ forms bridging interactions between Fe3O4 and S-PS NPs to promote aggregation, while competitive adsorption occurs between the N atoms of N-PS NPs and Ca2+ on the surface of Fe3O4 NPs. The study findings will help to improve the understanding of interfacial processes affecting ions at nanomaterial/water interfaces and assessments of the geochemical behavior and ecological risks of nanoplastics.

Transport of nanoscale zero-valent iron in the presence of rhamnolipid

Nanoscale zero-valent iron (nZVI) particles have gained widespread use for in-situ treatment of various chlorinated hydrocarbons. Their non-toxic nature, affordability, and minimal maintenance requirements have made them a favored material for nanoremediation. The treatment typically involves the injection of nZVI particles into contaminated sites using direct-push well injection systems. However, their small size leads to high surface energy, causing aggregation that alters their physiochemical properties, reactivity, and transport behavior. To counteract aggregation, nZVI suspension can be stabilized with different surfactants, reducing the surface energy during subsurface soil transport. This study investigates the impact of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa during the late growth phase, on the aggregation and mobility of nZVI particles. The retardation factor of nZVI in the model media of zeolite, ZK406H, decreased from 1.66 in the absence of rhamnolipid to 1.03, 0.98, 0.93, and 0.87, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The deposition coefficient also decreased from 2.39 in the absence of rhamnolipid to 0.459, 0.279, 0.217, and 0.0966, corresponding to the presence of rhamnolipid at concentrations of 20, 50, 80, and 100 mg/L. The transport parameters of nZVI in ZK406H were linked to the interactions of nZVI particles with ZK406H by the DLVO theory.

Purification of graphite from spent carbon cathodes through the reduction of the mechanical entrainment of cryolite using polyaluminium chloride as a flocculant

Spent carbon cathodes (SCCs) generated during electrolytic aluminum production pose significant environmental hazards. To optimize resource utilization, flotation is used as an early process for the clean recovery of valuable graphite from waste cathodes. However, the mechanical entrainment in flotation restricts the further improvement of product purity, resulting in an increase in waste gas and wastewater discharge in the subsequent purification process. In this study, to increase the fixed carbon content of flotation products, flocculant was first applied to the flotation separation of SCCs, and polyaluminum chloride (PAC) was used to flocculate cryolite with high impurity content to reduce mechanical entrainment in the flotation process. Zeta potential measurements, particle size analysis, optical microscopy, and scanning electron microscopy confirmed the agglomeration of cryolite under the action of PAC. Additionally, the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory was used to estimate the interaction energy to further explain the mechanism underlying cryolite agglomeration. Interaction energy calculation revealed that the attraction energy between particles was dominant at the PAC concentration of 2000 mg/L. Flotation experiments indicated that under a constant pulp pH of 7.8, the absence of sodium silicate, and a stirring speed of 1200 rpm, mechanical entrainment decreased from 91.53 ± 1.53 g/L to 69.80 ± 1.90 g/L, and the carbon grade of the product increased from 83.07 ± 0.28% to 88.94 ± 0.30%. Overall, the proposed purification method provides a new approach for the efficient recovery of graphite in waste cathodes, which is of great significance for the sustainable development of graphite resources.

Effect of bulk nanobubbles on flocculation of kaolin in the presence of cationic polyacrylamide

The study explores the impact of nanobubble flotation technology on fine mineral processes, focusing on its interaction with cationic polyacrylamide (CPAM) in kaolin flocculation. Nanobubbles influence particle size and promote aggregation. Experimental procedures involve bulk nanobubble preparation, kaolin suspension, and CPAM solutions, with analysis of sedimentation rates, turbidity, and zeta potential. Results show accelerated sedimentation and reduced turbidity with nanobubbles compared to traditional methods. Zeta potential measurements and DLVO theory support nanobubbles' role in reducing electrostatic interaction, facilitating flocculation. This research advances understanding in nanobubble-mediated mineral processing, highlighting eco-friendly flocculants and practical implications for optimization.

Recovery of biochar particles laden with lead in saturated porous media by DC electric field

The co-transport behavior of environmental pollutants with biochar particles has aroused great interests from researchers due to the concerns about pollutant diffusion and environmental exposure after biochar is applied to soil. In this work, the recovery and co-transport behavior of biochar micron-/nano-particles (BCMP and BCNP) and lead (Pb2+) in saturated porous media were investigated under different ionic strength conditions (IS = 1, 5 and 10 mM) under a direct current electric field. The results showed that the electric field could significantly enhance the mobility of Pb adsorbed biochar particles, particularly BCNP. The recovery of Pb laden biochar particles was improved by 1.8 folds, reaching 78.8% at maximum under favorable condition at +0.5 V cm−1. According to the CDE (Convection-Dispersion-Equation) model and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory analysis, the electric field facilitated the transport of Pb carried biochar mainly by increasing the negative charges on biochar surface and improving the repulsive force between biochar and porous media. High IS was favorable for biochar transport under the electric field, but inhibited desorbing Pb2+ from biochar (18% by maximum at IS = 10 mM). By switching the electric field power, a two-stage strategy was established to maximize the recovery of both biochar particles and Pb, where BCNP and Pb recovery were higher than electric field free case by 90% and 35%, respectively. The findings of this study can help build a biochar recovery approach to prevent potential risks from biochar application in heavy metal contaminated soil remediation.

Evaluation and improvement of Gay-Berne interaction potential to simulate 3D DLVO interaction of clay particles

This paper first presents a set of DLVO-based energy-separation functions for a pair of finite uniformly charged square platelets of infinitesimal thickness in three elementary configurations: face-to-face, edge-to-edge, and edge-to-face. The novel dataset was generated by summing the electrostatic interaction energy computed numerically by solving the non-linear 3D Poisson-Boltzmann equation and the van der Waals interaction energy calculated analytically. The dataset aims to inform qualitatively and quantitatively the energy/force separation functions used in the Discrete Element Method (DEM) and Coarse-Grained Molecular Dynamics (CGMD) modelling of clays. The same dataset was then used to calibrate and evaluate two Gay-Berne (GB)-type potentials: i) a DLVO-adapted Gay-Berne potential, where the Born-van der Waals branches of the underlying Lennard-Jones (LJ) potential are replaced with van der Waals-Columbic branches to represent DLVO interactions; ii) the Mie potential, where the exponents of the two energy terms are ‘unlocked’ instead of being set equal to 12 and 6 as per the original LJ potential. It is shown that the orientation parameter, µ, and the anisotropy parameter, ν, need to be different from µ = 2 and ν = 1 as adopted in CGMD clay modelling to capture the progression of the shape of the pair energy-separation function from face-to-face to edge-to-face and edge-to-edge configuration. It is also shown that the MIE potential (with exponents m = 3 and n = 1.5) better captures the slow decay of the electrostatic repulsive energy component of the DLVO potential energy Coulombic branch of the interaction potential compared to the DLVO-adapted GB potential, which embeds the Lennard-Jones (LJ) exponents m = 12 and n = 6.

A Meta-Analysis to Revisit the Property-Aggregation Relationships of Carbon Nanomaterials: Experimental Observations versus Predictions of the DLVO Theory.

Contradicting relationships between physicochemical properties of nanomaterials (e.g., size and ζ-potential) and their aggregation behavior have been constantly reported in previous literature, and such contradictions deviate from the predictions of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. To resolve such controversies, in this work, we employed a meta-analytic approach to synthesize the data from 46 individual studies reporting the critical coagulation concentration (CCC) of two carbon nanomaterials, namely, graphene oxide (GO) and carbon nanotube (CNT). The correlations between CCC and material physicochemical properties (i.e., size, ζ-potential, and surface functionalities) were examined and compared to the theoretical predictions. Results showed that the CCC of electrostatically stabilized carbon nanomaterials increased with decreasing nanomaterial size when their hydrodynamic sizes were smaller than ca. 200 nm. This is qualitatively consistent with the prediction of the DLVO theory but with a smaller threshold size than the predicted 2 μm. Above the threshold size, the material ζ-potential can be correlated to CCC for nanomaterials with moderate/low surface charge, in agreement with the DLVO theory. The correlation was not observed for highly charged nanomaterials because of their underestimated surface potential by the ζ-potential. Furthermore, a correlation between the C/O ratio and CCC was observed, where a lower C/O ratio resulted in a higher CCC. Overall, our findings rationalized the inconsistency between experimental observation and theoretical prediction and provided essential insights into the aggregation behavior of nanomaterials in water, which could facilitate their rational design.

Experimental and theoretical studies on water adsorption and capillary condensation in nanopores of calcium carbonate

Understanding the water vapor sorption in nanopores has significant implications for hydrocarbon extraction and waste storage. This study presents gravimetric water sorption isotherms of nanoporous calcium carbonates. A methodology for quantifying equilibrium water sorption through matrix potential, even as the matrix potential approaches zero is introduced. This method facilitated the determination of adsorption via the Derjaguin‒Landau‒Verwey‒Overbeek (DLVO) theory and of capillary condensation, including the conjugate state, based on Young's Laplace equation. The relative errors between the experimental and calculated values ranged from 0.24% to 10.42%. Quantitative parameters characterizing the water distribution were calculated, and their dependences on water sorption were analyzed. The increase in water sorption over time exhibited a gradual decline, which was better described by a second-order exponential decay function. The stable decline point of the sorption rates ranged from 13.24% to 22.47% of the total time. In most cases, water vapor sorption in the pores is dominated by adsorption, with nanopores showing enhanced adsorption due to weaker inhibition of sidewall effects compared to an increase in adsorption sites. Notably, a substantial increase in equilibrium water sorption occurs when the matrix potential exceeds −106 MPa, corresponding to a relative humidity exceeding 96.6%, indicating strong capillary condensation. Additionally, nanoscale pores exhibit a pronounced propensity for capillary condensation when the pore throat diameter is less than 3.5 nm. These findings enhance our understanding of water sorption in tight rock formations when direct measurements are unavailable, with implications for estimating multiphase fluid transport in unconventional reservoirs.

Effect of sodium carboxymethyl cellulose on the interaction between hematite particles and bubbles

Sodium carboxymethyl cellulose (CMC) is a potential depressant which is an indispensable reagent for the treatment of complex refractory iron ores during reverse flotation. In this study, the interaction force between hematite particles adsorbed with CMC and bubbles was calculated, thereby revealing the inhibitory mechanism of CMC on hematite particles. When dodecylamine (DDA) was 15 mg/L and CMC was 3 mg/L, pH=10, the content and recovery rate of hematite reached 83.25% and 87.41%, respectively. Zeta potential tests showed that adsorption of CMC hindered the adsorption of DDA on hematite. AFM images visualized the adsorption status and adsorption layer thickness of CMC on the surfaces of hematite and quartz. FTIR results indicated that the adsorption of CMC on the surface of hematite was strong chemical adsorption, but the adsorption on quartz was physical adsorption. Based on the extended DLVO theory, the total potential of interaction between hematite particles adsorbed with CMC and bubbles was measured. The calculation results demonstrated that the hydration repulsion interaction potential owing to the adsorption of CMC dominated the total potential energy, preventing the adhesion of hematite and bubbles.

Colloidal Engineering of Microplastic Capture with Biodegradable Soft Dendritic "Microcleaners".

The introduction of colloidal principles that enable efficient microplastic collection from aquatic environments is a goal of great environmental importance. Here, we present a novel method of microplastic (MP) collection using biodegradable hydrogel soft dendritic colloids (hSDCs). These dendritic colloids have abundant nanofibrils and a large surface area, which provide an abundance of interfacial interactions and excellent networking capabilities, allowing for the capture of plastic particles and other contaminants. Here, we show how the polymer composition and morphology of the hSDCs can impact the capture of microplastics modeled by latex microbeads. Additionally, we use colloidal DLVO theory to interpret the capture efficiencies of microbeads of different sizes and surface functional groups. The results demonstrate the microplastic remediation efficiency of hydrogel dendricolloids and highlight the primary factors involved in the microbead interactions and adsorption. On a practical level, the results show that the development of environmentally benign microcleaners based on naturally sourced materials could present a sustainable solution for microplastic cleanup.

Particle deposition and clogging as an Obstacle and Opportunity for sustainable energy

Fine particle motions have significant implications in porous media, manifesting in various natural phenomena and industrial applications. The movement of particles can lead to channel blockage, resulting in clogging. Depending on the context, clogging can be either advantageous or detrimental. At the scale of fine particles, physiochemical interactions play a crucial role in the clogging process. To examine the influence of these interactions, we have coupled the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory into the Computational Fluid Dynamic-Discrete Element (CFD-DEM) approach. Aside from the physical properties of the fracture systems and the characteristics of fine particles, the injection rate also plays a pivotal role in clogging occurrence. Consequently, we investigated 10 different injection rates and modeled 20 simulation setups with identical particle insertion rates to concurrently analyze the effects of the DLVO theory and injection rate. Our study focused on examining the impact of these parameters on particle behavior in various regions of the domain, including particle-particle force, fluid-particle force, transitional velocity, rotational velocity, fluid velocity, and fluid-particle momentum exchange. Our findings reveal that the DLVO force significantly influences fluid and particle characteristics within the throat blockage. Our results indicated that DLVO consideration increased the particle concentrations by more than 40% before the throat. Moreover, our results demonstrate a transition between different injection rates, where a slight change in injection rate (i.e., 0.06μm/s) can change the system's behavior. We identified a critical fluid injection rate, whereby injecting fluid into the system at a rate surpassing the critical velocity can prevent clogging, while lower rates result in clogging occurrence.

Electrocatalytic Reduction of Benzyl Bromide during Single Ag Nanoparticle Collisions.

Previous reports of the electrocatalytic activity of Ag nanoparticles (AgNPs) toward the reduction of organic halides have been limited to measurements of immobilized nanoparticle ensembles. Here, we have investigated the electrochemical reduction of benzyl bromide (PhCH2Br) occurring at single AgNPs (4.2 to 37 nm radius) in methanol, where the effects of nanoparticle size on catalytic behavior can be more thoroughly examined and rigorously quantified. AgNP collisions at a 6.3 μm radius Au ultramicroelectrode (UME) result in measurable electrocatalytic amplification currents from the reduction of PhCH2Br, where collision events are indicated by a sudden step increase in the reduction current recorded in the current-time trace. The dependence of the height of these steps on the applied potential allowed for an analysis of reaction kinetics based on the Butler-Volmer model, resulting in an estimation of the standard rate constant (k0) as a function of AgNP size. Measured values of k0 range from 4.0 × 10-4 to 8.0 × 10-4 cm/s on AgNPs with radii of 14, 29, and 37 nm, whereas k0 was found to be 6.2 × 10-4 cm/s at a 12.3 μm radius Ag disk UME. The results indicate that the kinetics of PhCH2Br reduction are independent of AgNP size and are similar to the reaction kinetics observed at a Ag UME. The frequency of observed particle collisions was found to be dependent on particle size, where 14 nm radius AgNPs resulted in the highest-frequency collisions. The potential- and size-dependent interactions of AgNPs with the Au UME are discussed in terms of the DLVO theory.