Solid Surface Research Articles

Hexagonal Boron Nitride Quantum Dots Embedded on Layer-by-Layer Films for Peroxidase-Assisted Colorimetric Detection of β-Galactosidase Producing Pathogens.

Pathogen detection has become a major research area all over the world for water quality surveillance and microbial risk assessment. Therefore, designing simple and sensitive detection kits plays a key role in envisaging and evaluating the risk of disease outbreaks and providing quality healthcare settings. Herein, we have designed a facile and low-cost colorimetric sensing strategy for the selective and sensitive determination of β-galactosidase producing pathogens. The hexagonal boron nitride quantum dots (h-BN QDs) were established as a nanozyme that showed prominent peroxidase-like activity, which catalyzes 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by H2O2. The h-BN QDs were embedded on a layer-by-layer assembled agarose biopolymer. The β-galactosidase enzyme partially degrades β-1,4 glycosidic bonds of agarose polymer, resulting in accessibility of h-BN QDs on the solid surface. This assay can be conveniently conducted and analyzed by monitoring the blue color formation due to TMB oxidation within 30 min. The nanocomposite was stable for more than 90 days and was showing TMB oxidation after incubating it with Escherichia coli (E. coli). The limit of detection was calculated to be 1.8 × 106 and 1.5 × 106 CFU/mL for E. coli and Klebsiella pneumonia (K. pneumonia), respectively. Furthermore, this novel sensing approach is an attractive platform that was successfully applied to detect E. coli in spiked water samples and other food products with good accuracy, indicating its practical applicability for the detection of pathogens in real samples.

A master plot approach on rice husk decomposition through pyrolysis and kinetic elucidation using iso-conversional models

The present study aimed at predicting the intricate mechanism followed by the pyrolysis of locally available rice husk, uses noval modified master plots through continuous slope-based differential techniques. An average apparent activation energy was found in the range of 187.29 (KAS model) and 199.85 kJ mol−1 (OFW model), respectively. The rice husk revealed higher volatile matter; 54.51 wt-%, HHV; 18.42 MJ kg−1and a critical pyrolysis zone around 250 to 550 °C with two sharp peaks through differential thermogravimetric analysis. Using Karl–Pearson correlation, experimental curve showed highest correlation coefficient of 0.94 and 0.75 with respect to A2 and A3 models (Avrami–Erofeev) for g( α). However, for Z( α), the process is limited by first-order multi-diffusion processes (D1) coupled with solid phase surface reaction (F3) showing correlation coefficient of 0.8. The experimental data worked out the generalized model of f( α) as f( α) = 12.74 α3 – 24 α2 + 12.6 α - 0.92 with R2 value of 0.99, narrating the usage of master plots for better understanding of the process.

Autonomous Development of Compositional Diversity in Self‐spreading Flat Protocells

An experimental pathway to the spontaneous generation of compositionally diverse synthetic protocells is presented. The pathway is initiated by flat giant unilamellar vesicles (FGUVs) that originate from compositionally different multilamellar lipid reservoirs and undergo spontaneous spreading across solid surfaces. On contact, the spreading FGUVs merge to produce a concentration gradient in membrane lipids across the fusion interface. Subsequent reconstruction through a series of shape transformations produces a network of nanotube‐connected lipid vesicles that inherit different ratios of the membrane constituents derived from the bilayers of the parent FGUVs. The fusion process leads to the engulfment of small FGUVs by larger FGUVs, mimicking predator‐prey behavior in which the observable characteristics of the prey are lost but the constituents are carried by the predator FGUV to the next generation of lipid vesicles. We speculate that our results could provide a feasible pathway to autonomous protocell diversification in origin of life theories and highlight the possible role of solid surfaces in the development of diversity and rudimentary speciation of natural protocells on the early Earth.

Transport and deposition of nanoparticles in porous media at the pore scale using an Eulerian-Lagrangian method

BackgroundNanoparticle deposition in a subsurface environment decreases the amount of material in the bulk fluid, increases surface roughness, and affects nanofluid flow. Nanoparticle transport in porous media is a complex, multiscale phenomenon. Its macroscopic behavior is determined by phenomena at the pore-scale. Hence, it is necessary and of interest to study the transport and deposition of nanoparticles in porous media using a pore-scale approach. MethodsA computational solver is developed using an Eulerian-Lagrangian approach within the OpenFOAM library. A Berea sandstone and three open-cell metal foams with porosities of 0.8, 0.85, and 0.9, constructed by Laguerre-Voronoi tessellation, were analyzed to study nanoparticle behavior in water. Significant findingsNanoparticle deposition on solid surfaces is influenced by porosity, double layer thickness (NDL), surface potential magnitude (NE1), and nanoparticle diameter. Brownian motion that has a significant impact on nanoparticle transport and deposition is also examined. For nanoparticles with 20 nm diameter, the fraction of particles deposited in foam with 0.8 porosity is about 17 % more than the foam with 0.9 porosity. This difference decreases with nanoparticle diameter. For the particles with 100 nm diameter and more, the effects of Brownian motion on nanoparticle deposition becomes negligible.

Microscopic behavior of nano-water droplets on a silica glass surface

Recent advancements in computational science and interfacial measurements have sparked interest in microscopic water droplets and their diverse behaviors. A previous study using nonlinear spectroscopy revealed the heterogeneous wetting phenomenon of silica glass in response to humidity. Building on this premise, we employed high-resolution atomic force microscopy to investigate the wetting dynamics of silica glass surfaces at various humidity levels. Our observations revealed the spontaneous formation of nano-water droplets at a relative humidity of 50%. In contrast to the conventional model, which predicts the spreading of nanodroplets to form a uniform water film, our findings demonstrate the coexistence of nano-water droplets and the liquid film. Moreover, the mobility of the nano-water droplets suggests their potential in inducing the transport of adsorbates on solid surfaces. These results may contribute to the catalytic function of solid materials.

Crystal Growth of CO2–CH4 Hydrate on a Solid Surface with Varying Wettability in the Presence of PVCap

Crystal Growth of CO₂–CH₄ Hydrate on a Solid Surface with Varying Wettability in the Presence of PVCap

Unveiling the interaction regimes between atomic oxygen and amorphous carbon surface depending on incident energy

The chemical reactions between atomic oxygen (AO) and solid surface are particularly crucial for numerous fundamental fields. However, it is lack of clearly understanding the reaction mechanisms between AO and the solid surface because the complex interaction dynamics are extremely difficult to be measured experimentally and to be modelled theoretically. In this work, the reactive molecular dynamics simulations are conducted to fully reveal the interactive mechanisms of AO irradiation on the amorphous carbon surface. As the incident energy (E) increases, our simulations demonstrate three distinct interaction regimes: (I) surface oxidation without carbon removal, (II) surface oxidation accompanied by minor material removals, and (III) continuous material removal. The first critical energy (E1) of ∼3.5 eV as the boundary between regime I and II is related to the dissociative energy of C–C bonds. The second critical energy (E2) of ∼6.5 eV as the boundary between regime II and III corresponds to the largest repulsion energy that the oxidized surface could provide. We further establish a phenomenological model to quantitatively describe how the rebound ratio varies with incident energy and surfacial oxygen density, which not only fit all simulation data perfectly but also give a very precise prediction of E2 value.

Photochemical and Patternable Synthesis of 2D Covalent Organic Framework Thin Film Using Dynamic Liquid/Solid Interface.

2D covalent organic frameworks (COFs) are highly porous crystalline materials with promising applications in organic electronics. Current methods involve either on-surface synthesis (solid surface) or interfacial synthesis (liquid/liquid, liquid/gas interface) to create thin films for these applications, each with its drawbacks. On-surface synthesis can lead to contamination from COF powder or unreacted chemicals, while interfacial synthesis risks damaging the film during post-transfer processes. These challenges necessitate the development of alternative synthesis methods for high-quality 2D COF films. This study presents a novel approach for synthesizing homogeneous 2D COF thin films by combining photochemistry and a liquid-flowing system. Leveraging previous work on liquid flow systems to prevent contamination during solvothermal synthesis, this approach to the photochemical method, resulting in the synthesis of high-crystalline 2D COF films with tunable thickness is adopted. The photochemical approach offers spatially controllable energy sources, enabling patternable COF synthesis. Notably, it is successfully fabricated ultrasmooth patterned 2D COF films on hexagonal boron nitride, offering a streamlined process for optoelectronic device fabrication without additional pre, post-processing steps.

Control of spontaneous charging of sliding water drops by plasma-surface treatment

Slide electrification is the spontaneous separation of electric charges at the rear of water drops sliding over solid surfaces. This study delves into how surfaces treated with a low-pressure plasma impact water slide electrification. Ar, O2, and N2 plasma treatment reduced the drop charge and contact angles on glass, quartz, and SU-8 coated with 1H,1H,2H,2H-perfluoroctyltrichlorosilane (PFOTS), and polystyrene. Conversely, 64% higher drop charge was achieved using electrode-facing treatment in plasma chamber. Based on the zeta potential, Kelvin potential, and XPS measurements, the plasma effects were attributed to alterations of the topmost layer's chemistry, such as oxidation and etching, and superficially charge deposition. The surface top layer charges were less negative after electrode-facing and more negative after bulk plasma treatment. As a result, the zeta potential was less negative after electrode-facing and more negative after bulk plasma treatment. Although the fluorinated layer was applied after plasma activation, we observed a discernible impact of plasma-glass treatment on drop charging. Plasma surface modification offers a means to adjust drop charges: electrode-facing treatment of the fluorinated layer leads to an enhanced drop charge, while plasma treatment on the substrate prior to fluorination diminishes drop charges, all without affecting contact angles or surface roughness.

Propagation of nanosecond discharge in an air gap containing a water droplet: modelling and comparison with time-resolved images

The plasma-water interface is a complex medium characterized by interesting physical and chemical phenomena useful for many applications such as water processing or material synthesis. In this context, optimizing the transport of reactive species from plasma to water is crucial, and it may be achieved by increasing the surface-to-volume ratio of the processed object. Herein, we study the characteristics of a streamer produced by nanosecond discharge in air gap with a droplet of deionized water. The discharge is characterized experimentally by electrical measurements as well as by 1 ns-intergated ICCD images. To report plasma properties that are not accessible through experiment, such as the spatio-temporal evolution of electron density, electric field, and space charge density, a 2D fluid model is developed and adapted to the experimental geometry. Due to the fast propagation of the ionization front, the droplet is considered as a solid dielectric. The model solves Poisson’s equation as well as the drift-diffusion equation for electrons, positive ions, and negative ions. The utilized transport coefficients are tabulated as a function of the reduced electric field. Helmholtz equations are also included in the model to account for photoionization. The electron impact ionization source obtained from the model is compared to experimental 1 ns-integrated ICCD images, and a good agreement is observed. Finally, the model is used to investigate the influence of droplet dielectric permittivity and wetting angle (the angle between a liquid surface and a solid surface) on the properties of the discharge. Overall, the data reported herein demonstrate that the model can be used to investigate plasma properties under different conditions.

Molecular dynamics study of confined liquid film viscosity in Constant-Pressure and Constant-Distance systems

Viscosity changes in confined liquids have been explored using experimental techniques including surface force apparatus (SFA) and fiber wobbling method (FWM), revealing different magnitudes of viscosity increment as the gap between confining solid surfaces decreases. To address this disparity, we performed molecular dynamics simulations to gain insights into the mechanisms of viscosity changes in confined liquid UV-curable resin films used in nanoimprint lithography. Solid surfaces were fixed to maintain a constant pressure or distance, resembling SFA and FWM, respectively. Consistent with experimental results, our simulations confirmed that the viscosity increases with decreasing solid–solid gaps, notably, more pronounced in the constant-distance system than in the constant-pressure one. However, the two systems exhibited no distinct difference in the liquid molecular distribution. By introducing a new concept of free volume change rate, we conducted an in-depth analysis of liquid molecular motion, revealing more active motion in the constant-pressure system, particularly in the central region between the solid surfaces. This motion correlated positively with atomic vibrations of the confining surfaces. Our findings emphasize that different confinement conditions (constant pressure or constant distance) distinctly alter the liquid molecular motion and thus the magnitude of viscosity, underscoring the necessity for precise characterization of the rheological properties of confined UV-curable resins.

Equation-of-state-based lattice Boltzmann model of multicomponent adsorption onto fluid–fluid interfaces

In diffuse interface models, such as the lattice Boltzmann method (LBM), interfacial physics plays an important role. An example of an important interfacial phenomenon is adsorption onto a fluid–fluid interface. In the context of LBM, adsorption studies have traditionally only focused on adsorption onto a solid surface. The studies on adsorption onto fluid–fluid interfaces have been qualitative in nature, suffer from restrictions on the number of components, or are based on simple thermodynamic models designed for fully immiscible phases. Our recently published fugacity-based LBM model introduces a platform for the accurate modeling of multiphase fluids unrestricted by the number of components, and governed through accurate equations of state (Soomro and Ayala, 2023). In this study, we utilize the fugacity-based LBM to capture interfacial adsorption. This paper begins by simulating adsorption in a binary system with a flat interface, and shows that the amount of adsorption, quantified by relative adsorption measures, is in exact agreement with Gibbs theory. Next, the analysis is continued for a ternary system with two species adsorbing onto the interface. The binary and ternary simulations are then repeated for the case of a droplet and finally a five component case is presented. The study shows that the fugacity-based LBM can capture adsorption in full agreement with Gibbs adsorption theory. This provides a path for a generalized LBM model for adsorption, based on robust thermodynamic models for the fluids and unrestricted by the number of components, marking a significant contribution to the LBM literature.

Effects on structure by spectroscopic investigations, valence state and morphology properties of FeCo-containing SnO2 catalysts for glycerol valorization to cyclic acetals

The effects on the structure, valence state and morphological properties of FeCo-containing SnO2 nanostructured solids were investigated. The physicochemical features were tuned by distinct synthesis routes e.g., sol–gel, coprecipitation and nanocasting, to apply them as catalysts in the glycerol valorization to cyclic acetals. Based on Mössbauer and XPS spectroscopy results, all nanosized FeCoSn solids have Fe-based phases, which contain Co and Sn included in the structure, and well-dispersed Fe3+ and Fe2+ surface active sites. Raman, FTIR and EPR spectroscopies measurements of the spent solids demonstrated structural stability for the sol–gel based solid, which is indeed responsible for the highest catalytic performance, among the nanocasted and coprecipitated counterparts. Morphological and elemental analyses illustrated distinct morphologies and composition on solid surface, depending on the synthesis route. The Fe/Co and Fe/Sn surface ratios are closely related to the catalytic performance. The improved glycerol conversion and selectivities of the solid obtained by sol–gel method was ascribed to the leaching resistance and the Sn action as a structural promoter.

The architectural application of shells whose boundaries subtend a constant solid angle

Surface geometry plays a central role in the design of bridges, vaults and shells, using various techniques for generating a geometry which aims to balance structural, spatial, aesthetic and construction requirements.In this paper we propose the use of surfaces defined such that given closed curves subtend a constant solid angle at all points on the surface and form its boundary. Constant solid angle surfaces enable one to control the boundary slope and hence achieve an approximately constant span-to-height ratio as the span varies, making them structurally viable for shell structures. In addition, when the entire surface boundary is in the same plane, the slope of the surface around the boundary is constant and thus follows a principal curvature direction. Such surfaces are suitable for surface grids where planar quadrilaterals meet the surface boundaries. They can also be used as the Airy stress function in the form finding of shells having forces concentrated at the corners.Our technique employs the Gauss-Bonnet theorem to calculate the solid angle of a point in space and Newton's method to move the point onto the constant solid angle surface. We use the Biot-Savart law to find the gradient of the solid angle. The technique can be applied in parallel to each surface point without an initial mesh, opening up for future studies and other applications when boundary curves are known but the initial topology is unknown.We show the geometrical properties, possibilities and limitations of surfaces of constant solid angle using examples in three dimensions.

Recent advancements in harnessing biodiesel from microalgae through attached growth systems

Conventional microalgal cultivation method relied on suspended growth or attached growth that uses inert solid surfaces, requiring the addition of external carbon sources to promote microalgal growth. The inert solid substrates for attached microalgae pose constraints on the maximal capabilities of these microorganisms as it does not possess the ability to provide the necessary nutritional support required for optimal microalgal growth. As a result, microalgae are obliged to only rely on the solid substrate as a means of attachment, without any further nutritional provisions. Slower growth rates, larger resource requirements, and exorbitant operating expenses had prompted the exploration of an alternative strategy, i.e; the innovative use of solid organic waste as nutritional source cum attachment platform. The findings of this review unveil key insights into microalgae cultivation system, offering a solution to economic challenges in the production phase. This innovation not only promotes economic feasibility and sustainability, but also contributes to economically viable and environmentally sustainable biofuel production.

Repetitively pulsed streamer discharge with laser-induced surface trapped electron desorption to exploit residual charges in situ

Abstract Positive streamer behaviors under repetitive pulses are predominantly dependent on the availability of free electrons. If surface residual electrons stored from previous discharges could be intentionally released and involved into the next discharge, an alternative control freedom is provided apart from voltage waveform tailoring methods that mainly attract or repel gaseous residual charges. Evolutions of repetitively pulsed surface streamers in compressed (0.2 MPa) air were investigated after low-photon-energy pulsed visible (532 nm) and infrared (1064 nm) laser irradiations. Pulse-sequence and temporally resolved diagnostics were implemented to investigate effects of laser parameters (irradiation moment, wavelength, energy) and gas composition. A 2D surface streamer fluid simulation was performed to qualitatively unveil impacts of localized plasma patches. The surface streamer morphology and emission light are significantly and repeatably affected by the laser irradiation before the streamer inception, while, variations totally disappear without the solid surface. The secondary streamer is prolonged accompanied by a higher flashover probability after the pulsed laser irradiation in compressed air. Intriguingly, influences of the infrared laser persist for tens of microseconds before the next voltage pulse. Residual charge dynamics under the laser irradiation are analyzed, where the additional increase of O- 2 of low electron bound energy is emphasized. The laser induced surface trapped electron desorption is achieved through the direct or the step-wise process, dependent on the laser energy and the surface trap state distribution.

On the conditions for self-catapulting of freezing water droplets

Despite the remarkable progress of anti-icing and deicing technologies in the past decades, it remains a grand challenge to dislodge freezing water from a solid surface without consuming external energy. Herein, we propose a strategy to dislodge freezing water from solid surfaces just by leveraging its volume expansion resulting from the phase change from water to ice. The implementation of this energy-saving strategy relies on a simple micropillar-based gadget on the surface, termed freezing-empowered droplet catapult (FEDC), whereby the work done by the volume expansion of a freezing droplet accreted on it can be harvested and stored as elastic energy, and subsequently released in due course to catapult the freezing droplet away from the surface. Mechanics-based modelling is carried out to reveal the necessary conditions of occurrence for the self-catapulting of freezing water droplets on an FEDC, yielding a phase map that manifests the necessary synergy among the characteristic dimensions and stiffness of the FEDC as well as the volume of the droplet in triggering its self-catapulting. Our study not only demonstrates the feasibility of an energy-saving strategy for shedding off freezing droplets from solid surfaces but also provides a quantitive guideline for the design of the gadget for implementation, paving the way to a new technology for controlling ice accretion on solid surfaces with zero consumption of external energy.

Self-Assembly of Single-Virus SERS Hotspots for Highly Sensitive In Situ Detection of SARS-CoV-2 on Solid Surfaces.

Microbial surface transmission has aroused great attention since the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Developing a simple in situ detection method for viruses on solid surfaces is of great significance for timely public health surveillance. Taking advantage of the natural structure of SARS-CoV-2, we reported the assembly of Au@AgNPs on the surface of a single virus by the specific aptamer-spike protein interaction. Multiple hotspots can be created between the neighboring Au@AgNPs for the highly sensitive surface-enhanced Raman scattering (SERS) detection of SARS-CoV-2. Using two different aptamers labeled with Cy3 and Au@AgNPs, in situ SERS detection of pseudotyped SARS-CoV-2 (PSV) on packaging surfaces was achieved within 20 min, with a detection limit of 5.26 TCID50/mL. For the blind testing of 20 PSV-contaminated packaging samples, this SERS aptasensor had a sensitivity of 100% and an accuracy of 100%. This assay has been successfully applied to in situ detection of PSV on the surfaces of different packaging materials, suggesting its potential applicability.

Wetting and interfacial behavior of aqueous Deep eutectic solvents on Graphite, silica and calcite surfaces: Molecular dynamics study

Understanding the wetting behavior of liquids/fluids on solid surfaces at the nanoscale can help develop more effective and efficient technologies in various applications, including microfluidics, biomedical, enhanced oil recovery, and many others. Deep eutectic solvents (DESs) have recently gained attention due to their physical and chemical properties and tunability, making them useful in many applications. This article reports the investigation of the wetting behavior of aqueous deep eutectic solvent (DES) on graphite, silicon dioxide (SiO2), and calcite (CaCO3) using molecular dynamics (MD) simulation. The study's main objective is to understand the interfacial behavior of aqueous DES on these surfaces. In the current study, two different DESs, choline-chloride (ChCl) as hydrogen bond acceptor (HBA) and two different hydrogen bond donors (HBD), urea (U) and ethylene glycol (EG) with molar ratio 1:2are used. Aqueous DES has been studied for three different concentrations of10, 20, and 30 wt% of DES molecules to explore the effect of concentration.AqueousDES system on the graphite makes a finite contact angle for all concentrations of DES.In contrast, for SiO2 and CaCO3, droplets spread and attain a contact angle below ∼ 10° due to high hydrophilicity. We confirmed that our simulation had attained equilibrium by computing the interaction energy with the substrate and system molecules. The wetting behavior of aqueous DES thin film on the surfaceis characterizedby a density profile along the z-axis (normal to the surface). Furthermore, hydrogen bond (HB) analysisis performedto elucidate the structural relationship of these aqueous-DES systems. Overall, this study provides insights into the wetting behavior of nanodroplets/film of aqueous DES on different surfaces and illustrates the structural characteristics of these systems through various properties such as contact angle, density profiles, and hydrogen bonds.

Influence of continuous phase evolution of non-aqueous phase liquid on the retention and transport of coexistence perfluorooctanoic acid in saturated porous media

Non-aqueous phase liquid (NAPL) undergoing continuous evolution presents challenges in predicting the migration of co-contaminants within saturated porous media. This study explores the impact of the ongoing evolution of dimethyl phthalate (DMP-NAPL) on retention and transport of coexisting perfluorooctanoic acid (PFOA). The presence of PFOA facilitates the dispersion of free-phase DMP by mobilization and enhances the migration flux of solution phase through dissolution of both free and residual phase. The retardation of PFOA migration initially increases and then decrease as the evolution process continues. The retardation factor (R) demonstrates a negatively correlation with free-phase saturation (r = −0.987, p < 0.05), but a positively with residual-phase saturation (r = 0.948, p < 0.05). The primary factors controlling PFOA migration are its adsorption on the NAPL-water interface (fKi = 0 ∼ 58.51 %) and on solid surface (fKd = 41.18 ∼ 100 %). The contribution of partitioning to overall retention (fKn) remains consistently below 2 %, indicating limited partitioning into bulk DMP-NAPL. Dissolved DMP exhibits a slight retardation effect on low-concentration PFOA migration due to competitive adsorption. This study elucidates the migration characteristics of PFOA throughout the complete dynamic evolution of NAPL, providing valuable insights into contaminant transport in a multi-phase contaminated groundwater environment.