Monolayer Surface Coverage Research Articles

Factors influencing surface coverage and structural organization of phosphonic acid self-assembled monolayers on zinc oxide

Factors influencing surface coverage and structural organization of phosphonic acid self-assembled monolayers on zinc oxide

Artificial neural network modelling and experimental investigations of malachite green adsorption on novel carboxymethyl cellulose/β-cyclodextrin/nickel cobaltite composite

This study presents a novel polymer nanocomposite based on carboxymethyl cellulose and β-cyclodextrin crosslinked with succinic acid (CMC-SA-β-CD) containing nickel cobaltite (NCO) nano-reinforcement. Various analytical techniques have been employed to investigate the structural, thermal, and morphological features of the resulting nanocomposite. The CMC-SA-β-CD/NCO nanocomposite has been utilized as an adsorbent for the removal of bisphenol-A (BPA, R% <40 %), malachite green (MG, R% > 75 %)), and Congo red (CR, no adsorption) from the synthetic wastewater. The study systematically explored the impact of various parameters on the adsorption process, and the interactions between MG and CMC-SA-β-CD/NCO were discussed. The adsorption data were fitted to different models to elucidate the kinetics and thermodynamics of the adsorption process. An artificial neural network (ANN) analysis was employed to train the experimental dataset for predicting adsorption outcomes. Despite a low BET surface area (0.798 m2 g−1), CMC-SA-β-CD/NCO was found to exhibit high MG adsorption capacity. CMC-SA-β-CD/NCO exhibited better MG adsorption performance at pH 5.5, 40 mg L−1 MG dye concentration, 170 min equilibrium time, 20 mg CMC-SA-β-CD/NCO dose with more than 90 % removal efficiency. Moreover, the thermodynamic studies suggest that the adsorption of MG was exothermic with ΔH° value −9.93 ± 0.76 kJ mol−1. The isotherm studies revealed that the Langmuir model was the best model to describe the adsorption of MG on CMC-SA-β-CD/NCO indicating monolayer surface coverage with Langmuir adsorption capacity of 182 ± 4 mg g−1. The energy of adsorption (11.4 ± 0.8 kJ mol−1) indicated chemisorption of MG on the composite surface. The kinetics studies revealed that the pseudo-first-order model best described the adsorption kinetics with qe = 86.7 ± 2.9 mg g−1. A good removal efficiency (>70 %) was retained after five regeneration reuse cycles. The ANN-trained data showed good linearity between predicted and actual data for the adsorption capacity (R-value>0.99), indicating the reliability of the prediction model. The developed nanocomposite, composed predominantly of biodegradable material, is facile to synthesize and exhibited excellent monolayer adsorption of MG providing a new sustainable adsorbent for selective MG removal.

Mixing and transport of CO2 across a monolayer-covered surface in an open cylinder driven by a rotating knife edge

The dissolution of CO2 into water has attracted much attention for the modeling of air-sea gas exchange, CO2 sequestration into porous aquifers, and gas transport in bioreactors. In nearly all circumstances, the surface of water is covered by surfactants that make the gas-liquid interface behave elastically and exhibit surface (excess) shear viscosity. Here, transport and mixing of CO2 across the interface is studied in an axisymmetric system with inertia. A rotating knife edge at the interface with negligible contact surface area takes advantage of surface shear viscosity to drive a strong overturning flow in the bulk via viscous coupling. When CO2 is dissolved into water, this system has a forced convection nature that enhances the transport of CO2 into water. This transport leads to intense radial gradients in the dissolved CO2 resulting in baroclinic production of azimuthal vorticity which alters the underlying meridional flow and further enhances mixing by breaking down transport barriers. Flow visualization experiments reveal baroclinic instability and numerical simulations detail the hydrodynamics, including the effects of varying the CO2 partial pressure above the water.

Structural, electronic, and thermoelectric properties of hydroxyl groups adsorption on SnO2 (110) surface: A first‐principles study

Structural, electronic, and thermoelectric properties of bridging OHb and terminal OHt groups adsorbed on stoichiometric SnO2 (110) surfaces have been investigated using density functional theory and semiclassical Boltzmann transport theory with effective core pseudopotential implemented in CRYSTAL17 program. Our results indicate that H and OH yield significant structural relaxation around the adsorption sites O2c and Sn5c. The results have shown that the absolute value of adsorption energy increases with decreasing the coverage from 1 to 1/4 monolayer. Mulliken charge analysis, band structures, and density of states were calculated and discussed. We found that H and OH adsorption increases the band gap energy from 2.81 eV for clean surfaces to 3.04, 2.95, and 2.89 eV with, respectively, 1, 1/2 and 1/4 monolayer surface coverages. Thermoelectric properties revealed that the presence of hydroxyl groups on the SnO2 (110) surfaces may enhance the Seebeck coefficient, electrical conductivity, and electronic thermal conductivity.

Tailored hybrid Ce-Zr-La hydrous oxide material: Preparation, characterization and application towards removal of fluoride and copper(II) from their contaminated water

We report herein the tailored preparation and characterization insight of hybrid CeIV-ZrIV-LaIII hydrous oxide (CZL) and application as a solid-phase extractor towards F− and Cu(II) to reduce water contamination levels. Obviously, characterization of the as-prepared sample was done using electron microscopy (TEM, SEM), energy-dispersive X-ray spectroscopy (EDS), Föurier transform infrared (FT-IR) spectroscopy, BET surface analyzer, powder X-ray diffraction (p-XRD), and Zeta meter and reported. The BET analysis indicates very high surface area 219.971 m2 g−1 and pore volume 0.1374 cm3 g−1 of CZL, the value get decreased after adsorbing the Cu(II) and F−, this indicates interior surface involved on the adsorption process. Transfer of F− and/Cu(II) from aqueous phases over the CZL surfaces was investigated at optimized pH adopting batch procedure. The parameters investigated are the effects of concentration, reaction time and co-existing ions. Kinetically seen distribution of both F− and Cu(II) agree best with the pseudo-second-order model. Fitness of the equilibrium data with isotherm models has confirmed almost monolayer surface coverage; and computed ΔH0, ΔS0, and ΔG0 have suggested the spontaneous nature of the reactions. The order of percentage of F− transfer declines in presence of ions occurring in water as HCO3− > PO43− > SO42− > NO3− > Cl−. The exhausted CZL material is regenerated using NaOH (pH 12) solution. At optimal circumstances, the CZL shows Langmuir monolayer capacity of 213.99 mg g−1 and 61.52 mg g−1 respectively, for F− and Cu(II), which are greater than previously reported some materials. Overall, the CZL is an efficient material for extracting F− and Cu(II) from their aqueous phases.

Restoring Piezoelectric Properties in 2D Zinc Oxide Nanosheets by Surface Modifications: Implications for Piezoelectric Nanogenerators

Nanoelectronic devices that are self-powered through the conversion of mechanical energy into electronic energy are of great interest for the fields of wearables and medical implants. The ability to find nanomaterials that have piezoelectric properties suitable for nanogenerators can be a challenge. Zinc oxide (ZnO) is a well-known material that has one of the highest piezoelectric tensors among tetrahedrally bonded semiconductors, due to its buckled noncentrosymmetric structure on the (0001) and (0001̅)] surfaces. However, this piezoelectric response is diminished in few-layered two-dimensional (2D) ZnO, as it loses it buckled structure and becomes graphitic. As a consequence, ultrathin 2D ZnO sheets are not suitable for nanoscale devices that rely on a piezoelectric response. In this work, we show that defects, specifically, zinc and oxygen vacancies, and adsorbed oxygen, can restore the wurtzite structure and piezoelectric response of free standing 2D ZnO sheets at specific thicknesses. Using density functional theory calculations, we show that both a 1 monolayer (ML) surface coverage of oxygen and a 25% concentration of zinc vacancies can restore the buckling in few-layer 2D ZnO nanosheets. For a 1.48 nm thick sheet with a 25% Zn vacancy concentration, an e33 value of 1.26 C/m2 can be achieved, which is 120% enhancement compared to the bulk value. These findings provide a methodology for screening piezoelectric properties of other materials and demonstrate that defects can be used to restore the wurtzite structure and dielectric properties of ultrathin 2D ZnO sheets that would allow them to be used in nanoscale piezoelectric devices.

Biosynthesis of aluminium oxide nanobiocomposite and its application for the removal of toxic metals from drinking water

This work aimed to synthesize the aluminium oxide nanoparticles using Ixoro coccinea leaf extract. Furthermore, the synthesized Ixoro coccinea aluminium oxide nanoparticles (I–Al2O3-NPs) and nanocomposites (I–Al2O3-NC), including them as the fillers in a chitosan matrix were characterized, and I–Al2O3-NC was applied to remove the toxic metals (TMs) including Cd, Ni, and Pb from water. Optimization of different batch experimental adsorption parameters (pH, concentration of TMs, dose of I–Al2O3-NC, temperature, and time of contact) was done to check the feasibility of I–Al2O3-NC for maximum removal of TMs from water. The extreme adsorption capacities using nanocomposites for Cd, Ni, and Pb were 66.0, 60.0, and 66.4 mg g−1, respectively. The I–Al2O3-NC followed the Freundlich isotherm model for removing Cd and Ni while showing the monolayer surface coverage for the removal of Pb. For this process, the best-fitted kinetic model was the pseudo-second-order equation. The enthalpy, entropy, and free energy of metal ion adsorption, among other parameters of thermodynamics, were estimated. The process was found to be exothermic, advantageous, and spontaneous. Kinetic studies show that intra-particle diffusion is essential for eliminating TMs. In addition, I–Al2O3-NC was applied for the adsorption of TMs from surface water and determined to be effective in removing these contaminants up to an acceptable drinking water standard. Regeneration of adsorbent suggested that green synthesized I–Al2O3-NC may be an active tool for removing Cd, Ni, and Pb ions from contaminated water.

Voltammetric quantitative analysis of vildagliptin in bulk form and spiked human serum at a modified electrode

The electrochemical behavior of Vildagliptin (VILD) was studied using the cyclic voltammetric technique in an aqueous Britton–Robinson (BR) universal buffer solution of various pH levels between 4.0 and 10 at a 5% calcium-montmorillonite clay modified with carbon paste electrode surface (5% Ca-MMT/CPE). The results exhibited an irreversible anodic peak at about 1.238 V versus Ag/AgCl, KCl (3 mol L−1). The anodic peak was found to be diffusion–adsorption controlled. The possible reaction mechanism is estimated taking into consideration of the calculated electrons and protons number transferred on the electrode/electrolyte interface using the cyclic voltammetric technique. VILD was found to adsorb onto the surface of 5% Ca-MMT/CPE in a monolayer surface coverage of 3.0 × 10−12 mol cm−2. A validated square wave voltammetry (SWV) technique for VILD determination was performed. The calibration curve of VILD onto the 5% Ca-MMT/CPE surface was linear in the concentration range of 1.0–110 nmol L−1 with the mean limits of detection and quantification was 0.285 and 0.950 nmol L−1, respectively, in the bulk form. The proposed procedure for the assay of VILD in bulk form, dosage form, and spiked human serum has the advantage of being simple, rapid, sensitive, and inexpensive compared to other analytical methods. The described method showed an excellent performance for the trace determination of VILD in its formulation without interference from excipients.Graphical abstract

Zinc-doped titanium oxynitride as a high-performance adsorbent for formaldehyde in air

The potential utility of titanium oxynitride doped with 5% zinc (ZnTON) has been investigated as an adsorbent for the treatment of gaseous formaldehyde (FA) using a fixed-bed adsorption system. The adsorption capacity of ZnTON, when estimated at 10%/100% breakthrough (BT) levels from a dry feed gas consisting of 10 Pa FA, was far superior to two reference materials (i.e., commercial P25-TiO2 and activated carbon (AC)) by factors of 1.7/1.3 and 10/2.5, respectively. The adsorption capacity of ZnTON increased with the increase in the initial feeding concentration of FA (5–12.5 Pa), while decreasing with the rising temperature (25–100 oC). An increase in moisture level (0–100% relative humidity) also led to 5.4- and 2.5-fold reductions in adsorption capacity of ZnTON at 10% and 100% BT levels, respectively. Thermodynamically, the adsorption of FA onto ZnTON is an exothermic (ΔHo = - 9.69 kJ.mol-1) to be feasible in nature based on physisorption mechanism. Further, the adsorption of FA onto ZnTON was governed by surface interactions and monolayer surface coverage (Van der Waal's force/electrostatic attraction), as it obeyed the Langmuir isotherm and pseudo-second-order kinetic models. Regeneration tests indicated a positive effect of moisture on FA desorption and durability of ZnTON (i.e., over three adsorption-desorption cycles). This study offers valuable mechanistic insights into the synthesis of an advanced adsorbent for the efficient removal of hazardous volatile organic compounds under near-ambient conditions.

The impact of drug-loading factors on the solid-state form of ritonavir-mesoporous silica systems

Among the formulation techniques used to enhance thesolubility and dissolution rate of poorly, aqueous-soluble drugs, mesoporoussilica drug delivery systems have shown promise. A range of processes areemployed to load drugs onto silica and solvent-based approaches are widelyemployed. This study aims to understand the influence of drug concentration insolvent and drug-silica ratio on drug solid-state form and amorphization withinsilica. Ritonavirwhich belongs to &amp;nbsp;BCS Class II was used asa model drug. Ritonavir wasloaded into Syloid®244FP using a solvent evaporationmethod. Ritonavir loading percentage was calculated based on the assumptionthat the entire specific surface area of silica is exposed and available fordrug adsorption.&amp;nbsp; Ethanolsolutions with 3 different ritonavir concentrations; 70%, 32% and 20% saturatedsolubility at 25°C were employed. Ritonavir was loaded into silica at 1:1, 1:2and 1:3 ritonavir:silica ratios.&amp;nbsp; Allsystems included ritonavir loaded beyond monolayer surface coverage. Ritonavir- Syloid®244 FP formulations were characterisedusing DSC, PXRD, FT-IR, and TGA. The results showed that all ritonavir-Syloid®244 FP systemsprepared contained ritonavir in a non-crystalline state.

Effect of the surface coverage of an alkyl carboxylic acid monolayer on waterborne and cellular uptake behaviors for silicon quantum dots

This article reports the development of highly waterborne silicon quantum dots (Si QDs) terminated with a reactive group for grafting of biomolecules. Hydrogen-terminated QDs were prepared by thermal disproportionation of amorphous hydrogen silsesquioxane derived from triethoxysilane followed by hydrofluoric etching. Next, the hydrogenated Si surfaces were exposed to 10-undecenoic acid at different temperatures in Ar atmosphere, yielding the termination of the QDs with a carboxyl group. The thermal hydrosilylation of 10-undecenoic acid yielded the termination of the QDs with a carboxyl group. An increase in molecular coverage of an undecanoic acid (UA) monolayer resulted in both the enhanced increase of zeta-potential in a negative direction for a greater water-dispersity and the increase of absolute quantum yield (QY) of photoluminescence (PL). PLQY improved for ~ 1% to 26% with increasing UA coverage. We assessed the molecular interaction between the UA-SiQDs and HeLa cells by means of cellular uptake experiments using the QDs with different UA coverages. Results showed that the QDs with the highest dispersity in water were not internalized in the cells under confocal fluorescence microscopic observation. In contrast, the QDs with lower coverage of UA monolayer were internalized by endocytosis when incubated with HeLa cells. This contrasting observation opens the possibility of successfully preparing carboxy-capped SiQDs that do not allow cellular uptake but are targeted to specific cells by appropriate conjugation with biomolecules.

The effect of the density difference between supercritical CO2 and supercritical CH4 on their adsorption capacities: An experimental study on anthracite in the Qinshui Basin

Deep unmineable coals are considered as economic and effective geological media for CO2 storage and CO2 enhanced coalbed methane (CO2-ECBM) recovery is the key technology to realize CO2 geological sequestration in coals. Anthracite samples were collected from the Qinshui Basin and subjected to mercury intrusion porosimetry, low-pressure CO2 adsorption, and high-pressure CH4/CO2 isothermal adsorption experiments. The average number of layers of adsorbed molecules (ANLAM) and the CH4/CO2 absolute adsorption amounts and their ratio at experimental temperatures and pressures were calculated. Based on a comparison of the density of supercritical CO2 and supercritical CH4, it is proposed that the higher adsorption capacity of supercritical CO2 over supercritical CH4 is the result of their density differences at the same temperature. Lastly, the optimal depth for CO2-ECBM in the Qinshui Basin is recommended. The results show that: (1) the adsorption capacity and the ANLAM of CO2 are about twice that of CH4 on SH-3 anthracite. The effect of pressure on the CO2/CH4 absolute adsorption ratio decreases with the increase of pressure and tends to be consistent. (2) A parameter (the density ratio between gas free and adsorbed phase (DRFA)) is proposed to assess the absolute adsorption amount according to the supercritical CO2/CH4 attributes. The DRFA of CO2 and CH4 both show a highly positive correlation with their absolute adsorption amounts, and therefore, the higher DRFA of CO2 is the significant cause of its higher adsorption capacity over CH4 under the same temperature and pressure. (3) CO2 adsorption on coal shows micropore filling with multilayer adsorption in the macro-mesopore, while methane exhibits monolayer surface coverage. (4) Based on the ideal CO2/CH4 competitive adsorption ratio, CO2 storage capacity, and permeability variation with depth, it is recommended that the optimal depth for CO2-ECBM in the Qinshui Basin ranges from 1000 m to 1500 m.

Interfacial Effects of the Photophysics of Rhodamine 6G Ultra-Thin Films on a Poly(methylmethacrylate) Surface

The absorbance, excitation, and emission spectra of ultra-thin films of rhodamine 6G (Rh6G) spin-cast on poly(methylmethacrylate) (PMMA)-coated glass slides are examined as a function of both PMMA and Rh6G thickness. The thickness of PMMA has a little effect on the absorption or emission properties of Rh6G. At low surface coverage, the spectral properties of Rh6G are dominated by isolated molecules. As the Rh6G thickness increases, there is no evidence for exciton formation. Instead, the Rh6G molecules aggregate, which is responsible for the observed absorption and emission spectra. The aggregates significantly quench the emission so that the maximum emission intensity is found just below a monolayer surface coverage. The lack of exciton formation, which is unexpected, is attributed to the surface morphology of PMMA, which has a periodic surface structure.

Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells.

Metal halide perovskites have attracted tremendous attention due to their excellent electronic properties. Recent advancements in device performance and stability of perovskite solar cells (PSCs) have been achieved with the application of self-assembled monolayers (SAMs), serving as stand-alone hole transport layers in the p-i-n architecture. Specifically, phosphonic acid SAMs, directly functionalizing indium–tin oxide (ITO), are presently adopted for highly efficient devices. Despite their successes, so far, little is known about the surface coverage of SAMs on ITO used in PSCs application, which can affect the device performance, as non-covered areas can result in shunting or low open-circuit voltage. In this study, we investigate the surface coverage of SAMs on ITO and observe that the SAM of MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid) inhomogeneously covers the ITO substrate. Instead, when adopting an intermediate layer of NiO between ITO and the SAM, the homogeneity, and hence the surface coverage of the SAM, improve. In this work, NiO is processed by plasma-assisted atomic layer deposition (ALD) with Ni(MeCp)2 as the precursor and O2 plasma as the co-reactant. Specifically, the presence of ALD NiO leads to a homogeneous distribution of SAM molecules on the metal oxide area, accompanied by a high shunt resistance in the devices with respect to those with SAM directly processed on ITO. At the same time, the SAM is key to the improvement of the open-circuit voltage of NiO + MeO-2PACz devices compared to those with NiO alone. Thus, the combination of NiO and SAM results in a narrower distribution of device performance reaching a more than 20% efficient champion device. The enhancement of SAM coverage in the presence of NiO is corroborated by several characterization techniques including advanced imaging by transmission electron microscopy (TEM), elemental composition quantification by Rutherford backscattering spectrometry (RBS), and conductive atomic force microscopy (c-AFM) mapping. We believe this finding will further promote the usage of phosphonic acid based SAM molecules in perovskite PV.

Morphology and Charge Transport Properties of P(NDI2OD-T2)/Polystyrene Blends

While the strategy of blending commodity insulating polymers with conjugated polymers has been previously applied to modify the properties of organic field-effect transistors (OFETs), comprehensive studies on the evolution of morphology and OFET performance with film composition are scarce. In this contribution, films comprising the n-type semiconducting polymer P(NDI2OD-T2) and the insulating polymer polystyrene (PS) are explored in detail. In particular, the electrical properties and film morphology of blends with a P(NDI2OD-T2) concentration ranging from 0.125 to 100 wt % are studied. Two regimes characterized by distinct dependencies of device mobility as a function of P(NDI2OD-T2) content are observed: Above 12.5 wt % P(NDI2OD-T2), the OFET mobility exhibits a weak dependence on P(NDI2OD-T2) concentration despite the presence of strong lateral phase separation, while below 12.5%, the device mobility is observed to decrease strongly with decreasing P(NDI2OD-T2) concentration attributed to disrupted surface connectivity of the P(NDI2OD-T2) phase. UV–vis absorption spectroscopy and grazing incidence wide-angle X-ray scattering (GIWAXS) measurements indicate that the aggregation and crystalline packing are not strongly affected by the presence of PS. Atomic force microscopy and scanning transmission X-ray spectro-microscopy reveal lateral phase separation for blends with compositions of 87.5 to 25 wt % P(NDI2OD-T2). Enrichment of P(NDI2OD-T2) at the film surface is confirmed by near-edge X-ray absorption fine structure spectroscopy, with a high P(NDI2OD-T2) surface composition (>80 wt %) maintained down to an overall blend composition of 12.5 wt % P(NDI2OD-T2). The strong decrease in OFET mobility for P(NDI2OD-T2) concentration less than 25 wt % is attributed to a loss of P(NDI2OD-T2) surface connectivity at low P(NDI2OD-T2) loading. We also observe a transition from face-on to edge-on dominated configuration at low P(NDI2OD-T2) content with GIWAXS, consistent with an edge-on surface layer that persists down to monolayer surface coverage.

Facile Fabrication of Hierarchical Nanoporous Gold Electrode for Biosensing Applications

Nanobiotechnology is a discipline wherein tools from nanotechnology are applied to study biological phenomena. In application to biosensor development, the technically designed nanomaterial serves the purpose of signal amplification when the binding event takes place. In recent years, the use of metal-based nanomaterials has expanded in various biomedical applications due to the scope of facile synthesis and functionalization, high surface area, and extensive stability. Among the noble metal candidates, gold nanoparticles have been employed in the field of biosensor studies.Nanoporous gold is one of the most extensively investigated materials owing to its unique properties which are highly dependent on its microstructure and feature size. In an effort, to improve the current design, nanoporous gold was electrochemically engineered to incorporate two distinguishable scales of ligament and pore sizes giving rise to a hierarchical nanoporous gold (hNPG) structure. We have chosen to take advantage of the surface architectures of hNPG due to the presence of a large specific surface area for functionalization and rapid transport pathways for faster response. Here small-sized pores are exploited for immobilization and a network of larger pores helps in transport. We present here the fabrication of hNPG using a procedure involving electrochemical dealloying-annealing-chemical dealloying to yield a structure of larger pores of several hundred nanometers and smaller pores below 100 nm in size. Different compositions of alloys were used as precursors to generate the desired material of interest. We have used several analytical techniques to characterize the fabricated electrode such as scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, cyclic voltammetry (CV), and thermogravimetric analysis (TGA). SEM-EDX colored images show the atomic percentage of silver left after each dealloying step. The essential role of two-step dealloying and annealing can be seen in cyclic voltammograms. The area under the gold oxide reduction peak was integrated to evaluate the electrochemically active surface area (ECSA) which is significantly higher for the hNPG. Surface coverage of self-assembled monolayers on hNPG was compared with NPG using TGA and reductive desorption. The loading performance of the electrodes was evaluated based on the solution depletion technique which was used to quantify the molecules of interest from the solution into hNPG and NPG. The enhanced catalytic response was seen through the technique of chronoamperometry. Chronoamperometric response of hNPG and NPG was recorded at an applied potential upon successive additions of glucose. Glucose sensing properties of hNPG were largely improved when compared with NPG.The electrochemical detection of the glycoproteins using electrochemical assays based on lectin binding interactions is a current interest for use of this material. hNPG is a material of great promise for biosensor development as it enhances the scaling relations between volume and accessible surface area. Figure 1

A Machine-Learning Approach to Correcting Non-Ideal Background Currents in Disordered Self-Assembled Monolayers

In traditional studies of electroactive molecules tethered to metal surfaces through well-ordered self-assembled monolayers (SAMs), cyclic voltammetry is the primary tool used to measure the coverage of the tethered molecules. The charge under the peak in the voltammogram is directly proportional to the coverage of the redox-active molecules. Accurate coverage measurements are possible because well-ordered SAMs exhibit ideal background currents which are easy to subtract from the total current to isolate the SAMs faradaic current. However, for disordered electroactive SAMs with poor surface blocking properties, specific interactions with the metal substrate create non-ideal background currents which are difficult to separate from the SAMs faradaic current. Although analytical approaches exist to account for background currents in other electrochemical systems, they have some fundamental limitations that impede their practical application to electroactive SAMs. In our work, we propose a simple machine-learning approach to empirically correct for background currents in disordered SAMs, and we apply this approach to determine the surface coverage of partially-desorbed ferrocene-terminated monolayers (Fc-SAMs) from gold surfaces. We use LASSO regression and an ensemble of background scans from partially-desorbed unfunctionalized decanethiol SAMs to approximate the Fc-SAM background currents. Using the approximated background, we estimate the coverage of Fc-SAMs after background correction. This technique allows us to explore Fc-SAM coverage as a function of potential when applying potentials near and beyond the onset of the so-called reductive desorption potential of the SAM which induces non-ideal background currents. To verify the accuracy of the coverages determined using our LASSO method, we used two verification methods: 1) backfilling with decanethiol and 2) chemical stripping of the disordered SAM followed by inductively-coupled plasma-mass spectrometry (ICP-MS). The pros and cons of both confirmation methods will be discussed along with a comparison of error rates and limits of detection between traditional background subtraction method and the LASSO method. We propose that this new approach will enable a more quantitative description of disordered SAM films after reductive desorption events.

Magnetically-propelled fecal surrogates for modeling the impact of solid-induced shear forces on primary colonic epithelial cells

The colonic epithelium is continuously exposed to an array of biological and mechanical stimuli as its luminal contents are guided over the epithelial surface through regulated smooth muscle contraction. In this report, the propulsion of solid fecal contents over the colonic epithelium is recapitulated through noninvasive actuation of magnetic agarose hydrogels over primary intestinal epithelial cultures, in contrast to the vast majority of platforms that apply shear forces through liquid microflow. Software-controlled magnetic stepper motors enable experimental control over the frequency and velocity of these events to match in vivo propulsive contractions, while the integration of standardized well plate spacing facilitates rapid integration into existing assay pipelines. The application of these solid-induced shear forces did not deleteriously affect cell monolayer surface coverage, viability, or transepithelial electrical resistance unless the device parameters were raised to a 50× greater contraction frequency and 4× greater fecal velocity than those observed in healthy humans. At a frequency and velocity that is consistent with average human colonic motility, differentiation of the epithelial cells into absorptive and goblet cell phenotypes was not affected. Protein secretion was modulated with a two-fold increase in luminal mucin-2 secretion and a significant reduction in basal interleukin-8 secretion. F-actin, zonula occludens-1, and E-cadherin were each present in their proper basolateral locations, similar to those of static control cultures. While cellular height was unaffected by magnetic agarose propulsion, several alterations in lateral morphology were observed including decreased circularity and compactness, and an increase in major axis length, which align with surface epithelial cell morphologies observed in vivo and may represent early markers of luminal exfoliation. This platform will be of widespread utility for the investigation of fecal propulsive forces on intestinal physiology, shedding light on how the colonic epithelium responds to mechanical cues.

Environmentally benign Prosopis juliflora extract for corrosion protection by sorption - Gravimetric, mechanistic and thermodynamic studies

Environmentally benign plant extract compounds have gained significant attention in the corrosion prevention applications due to their biodegradability and eco-friendliness. The adsorptive corrosion control action of Prosopis juliflora plant extract was investigated using differential mass change experiments and the mechanism was validated using Tafel and Nyquist plots. The effect of green corrosion inhibitor concentration (0–800 ppm) on corrosion rate at different solution temperatures (305.15, 310.15 and 315.15 K) in 1 M HCl was studied. The corrosion inhibitor exhibited monolayer surface coverage and confirmed by Langmuir isotherm (R2 > 0.970). The negative values of Gibbs free energy (<20 kJ/mol) proved the electrostatic interaction between the inhibitor and metal surface. The enhanced energy barrier for the corrosion process was confirmed by changes in Ea in the presence of biomass-based inhibitor on the mild steel surface. Electrochemical impedance study proved that the double layer capacitance (Cdl) decreased and the resistance increased with increase in corrosion inhibitor concentration. The surface modifications on the metal were observed using scanning electroscope imaging. ATR studies were conducted for functional group identification of the corrosion inhibitor.

Removal of hexavalent chromium via an adsorption coupled reduction mechanism using olive oil derived carbon nano-onions

Carbon nano-onions (CNOs) were obtained in gram-scale by a simple flame pyrolysis method using olive oil. The olive oil carbon nano-onions (OCNOs) obtained had a quasi-spherical chain like onion structure with an average diameter of 46 ± 5.4 nm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis were employed to determine the existence of surface functional groups (−OH, −COOH) on the OCNOs. The OCNOs were applied as adsorbents for the elimination of Cr(VI) ions from aqueous solutions using batch experiments. The ideal conditions for the sequestration of Cr(VI) ensued at pH = 2, T =25 °C, m =0.05 g, t =720 min, and CO =10 mg/L. The XPS data for Cr after adsorption on the OCNOs revealed that Cr(III) ions were produced in the reaction, consistent with the adsorption coupled reduction mechanism. The sequestration of Cr(VI) proceeded via monolayer surface coverage (Langmuir isotherm), with the kinetic information in line with the pseudo-second-order model. The thermodynamic features showed that the removal progression was viable, exothermic, and involved an associative mechanism. After the adsorbent regeneration, the removal of Cr(VI) ions was improved owing to the −OH ions added by the NaOH (regeneration solution). The CNOs produced by flame pyrolysis gave similar Cr(VI) removal data to that observed using more sophisticated CNO synthesis methods.