Adsorption-desorption Phenomena Research Articles

Phosphorus Availability from Rock Phosphates and Adsorption-Desorption Phenomenon in Red and Alluvial Soil as Affected by Phosphorus Solubilizing Bacteria (PSB), FYM and Vermicompost Application

ABSTRACT Phosphorus (P) is typically fixed in red soils (as Fe-P and Al-P). P release from different sources i.e. Rock-phosphate (RP), Farm Yard Manure (FYM), and Vermicompost (VC) is mainly governed either by adsorption, desorption, fixation, or ligand exchange. The present study was undertaken using phosphorus solubilizers Burkholdaria cariabensis (PSB1) and B. cepacia (PSB2), inorganic sources Udaipur Rock-phosphate (RP1) and Purulia Rock-phosphate (PR2) and organic sources (FYM and VC) applied in red and alluvial soils. Results showed that pH statistically on par and available P content were significantly varied in both soil type under laboratory incubation experiment at 15, 30, 45, and 60 days intervals. P adsorption and desorption experiments were also carried out taking heavy suspension of two P-solubilizers. Results showed that higher soluble P was recorded in FYM amended soils (T8, T9, T10 and T11) over the VC treated soils (T12, T13, T14 and T15) in both soils. Data showed that the RP1 have higher (34.00%) total P concentration as compared to RP2 (10.87%). Meanwhile, it was observed that higher P adsorption observed in red soils as compared to alluvial soils and vice-versa in case of desorption maxima, similarly higher P adsorption in PSB1 as compared to PSB2. A quantitative and qualitative study on organic acid secretions by Burkholdaria cariabensis and Burkholdaria cepacia needs to be carried out in the future.

Ruthenium-doped cobalt sulphide electrocatalyst derived from a ruthenium-cobalt Prussian blue analogue (RuCo-PBA) for an enhanced hydrogen evolution reaction (HER).

The designing of efficient electrocatalysts for hydrogen generation is essential for the practical application of water-splitting devices. With numerous electrochemical advantages, transition metal sulphides are regarded as the most promising candidates for catalysing the hydrogen evolution reaction (HER) in acidic media. In the present study, Ru-doped cobalt sulphide nanosheets, termed Co9S8/Ru@t (t = 24 h, 48 h, and 72 h), were obtained by varying the reaction time from 24 h to 72 h from a RuCo-PBA precursor. The role of the time period for the synthesis of Co9S8/Ru@48h is vital in increasing the number of electroactive sites and optimising the hydrogen adsorption-desorption phenomena leading to an increment in the HER activity. The electrochemical outcomes demonstrate that the optimized Co9S8/Ru@48h requires a low overpotential of just 94 mV to produce 10 mA cm-2 current density, and also exhibits a lower Tafel slope value of 84 mV dec-1 defining its faster reaction kinetics. The as-synthesized Co9S8/Ru@48h was stable for up to 20 h of constant electrolysis signifying its outstanding durability. The optimized synthetic approach and impressive electrochemical results make Co9S8/Ru@48h a suitable alternative to noble-metal-based electrocatalysts for the HER.

Enhancement of the Texture & Morphology of Nano γ-Alumina as a Support for Naphtha Reforming Catalyst

The morphology of nano gamma alumina affects the molecule adsorption-desorption phenomena. In this case, manipulating the surface area, pore volume, and pore size by the technique of preparation to control the morphology and textural properties of gamma alumina. Washing of the synthesized boehmite gel with methanol has a significant effect. The co-precipitation method was used to prepare nano gamma alumina, which is involved by adding drop-by-drop ammonium hydroxide and aluminum nitrate nonahydrate solutions to a cetyltrimethylammonium bromide (CTAB) cationic surfactant solution at 30 C and adjust PH to 8. Nitrogen adsorption-desorption analysis (ASAP 2020), Atomic Force Microscope (AFM), and X-Ray Diffraction (XRD) were used to examine the obtained material. Surface area (362 m2/g), pore volume (0.51 cm3/g), pore size (5.2 nm), and narrow pore size distribution were obtained.

Role of the Number of Adsorption Sites and Adsorption Dynamics of Diffusing Particles in a Confined Liquid with Langmuir Kinetics

In this work, we investigate the effect of the number of available adsorption sites for diffusing particles in a liquid confined between walls where the adsorption (desorption) phenomena occur. We formulate and numerically solve a model for particles governed by Fickian’s law of diffusion, where the dynamics at the surfaces obey the Langmuir kinetic equation. The ratio between the available number of adsorption sites and the number of total particles are used as a control parameter. The investigation is carried out in terms of characteristic times of the system for different initial configurations, as well as the cases of identical or non-identical surfaces. We calculate the bulk and surface densities dynamics, as well as the variance of the system, and demonstrate that the number of sites affects the bulk, surface distributions, and diffusive regimes.

Reversibility of glyphosate sorption in pampean loess-derived soil profiles of central Argentina

There is a growing concern about glyphosate's behavior in the environment. Herbicide behavior in soils greatly depends on adsorption-desorption phenomena, which have shown great variability in soils, although the reversibility of this process has been less examined. The adsorption-desorption behavior of glyphosate was measured on representative soil profiles of the northeast region of Argentinean Pampas, a semi-arid crop cultivating region. Two soil profiles samples (P1 and P2, both Entic Haplustoll) were collected and segmented into depth increments of 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Batch adsorption/48 h-desorption isotherms were performed in a controlled setup. Soil samples had a high sand content (77–92%), and a low content of clay (<3%), but markedly differing in the available P content, especially in the upper layers of soil profiles (0–40 cm, P1 range 133–170 ppm; P2 range 7–43 ppm). Adsorption-desorption isotherms showed a similar range of variation, between 150 and 1400 L kg −1for KFads and 450–1400 L kg −1for KFdes, without appreciable evidence of hysteresis (0.95 ± 0.05). Sorption capacity parameters showed a distinct behavior with depth, P1 exhibiting a U-shape with minimum values at intermediate depths (20–60 cm), while P2 decreases sharply between 0 and 40 cm. General linear models considering the specific surface area (SSA) of each sample and the spatial correlation structure for soil profiles showed a main positive association of KFads and KFdes with the soil organic matter, together with a positive association with iron content (KFads), and a negative association of KFdes with available P content. These results indicate high adsorption extents and sorption reversibility of glyphosate to sandy loam soils of the region, which implies the potential for the herbicide to be available for leaching or degradation under a scenario of intensive use.

Half-cell and noise voltages at a metal-electrode and dilute solution interface

The detection of bioelectric signals is usually based on an electrode-skin contact that is often mediated by a layer of conductive gel. This interface produces a DC voltage (half-cell potential) and a random noise voltage whose relationship is not well known. The first may cause amplifier saturation and the second posits a limit to the detection of small signals. This work investigates the mechanisms of generation of these two voltages in the simpler case of a metal-electrolyte junction and finds a theoretical expression for both, under a few simplifying hypotheses. An expression is found that relates the two voltages to the ionic concentration and to the parameters defining the dynamics of the adsorption–desorption phenomena taking place at the interface. A relationship is found between the two voltages that is in qualitative agreement with experimental findings reported in the literature. This theoretical background provides a basis for further investigation of the metal-gel and of the gel-skin interfaces not addressed in this work.

Desorption of micropollutant from superfine and normal powdered activated carbon in submerged-membrane system due to influent concentration change in the presence of natural organic matter: Experiments and two-component branched-pore kinetic model

Submerged-membrane hybrid systems (SMHSs) that combine membrane filtration with powdered activated carbon (PAC) take advantage of PAC's ability to adsorb and remove contaminants dissolved in water. However, the risk of contaminant desorption due to temporal changes in the influent concentration of the contaminant has not been thoroughly explored. In this study, we used a SMHS with conventionally-sized PAC or superfine PAC (SPAC) to remove 2-methylisoborneol (MIB), a representative micropollutant, from water containing natural organic matter (NOM), with the goal of elucidating adsorption–desorption phenomena in the SMHS. We found that 20–40% of the MIB that adsorbed on PAC and SPAC while the influent was contaminated with MIB (6 h, contamination period) desorbed to the liquid phase within 6 h from the time that the MIB-containing influent was replaced by MIB-free influent (no-contamination period). The percentage of desorption during the no-contamination period increased with increasing MIB breakthrough concentration during the contamination period. These findings indicate that the PAC/SPAC in the SMHS should be replaced while the breakthrough concentration is low, not only to keep a high removal rate but also to decrease the desorption risk. SPAC is fast in removal by adsorption, but it is also fast in release by desorption. SPAC (median diameter: 0.94 µm) showed almost the same adsorption-desorption kinetics as PAC (12.1 µm) of a double dose. A two-component branched-pore diffusion model combined with an IAST (ideal adsorbed solution theory)–Freundlich isotherm was used to describe and analyze the adsorption–desorption of MIB. The diffusivity of MIB molecules in the pores of the activated carbon particles decreased markedly in a short period of time. This decrease, which was attributed to fouling of the activated carbon in the SMHS by coagulant-treated water containing NOM, not only reduced the rate of MIB removal during the contamination period but also hindered the rate of MIB desorption during the no-contamination period and thus prevented the effluent MIB concentration from becoming high. On the other hand, coagulation did not change the concentration of NOM that competes with MIB for adsorption sites.

A Model for Bias Potential Effects on the Effective Langmuir Adsorption–Desorption Processes

We discuss the foundations of a model based on an extension of the Langmuir approximation for the adsorption–desorption phenomena, in which the phenomenological coefficients depend on the bias potential, in addition to their dependence on the adsorption energy. The theoretical analysis focuses on the effect of these effective coefficients on the electrical response of an electrolytic cell to an external electric field, as predicted by the Poisson–Nernst–Planck model. Kinetic balance equations govern the current densities on the electrodes when the adsorption phenomenon occurs in the presence of an electric bias. The influence of the phenomenological parameters entering the model, as well as of the symmetry of the cell on the cyclic voltammetry, is investigated.

Diffusion and adsorption-desorption phenomena in confined systems with periodically varying medium

We study diffusing particles in a confined liquid whose diffusion coefficient periodically varies across the sample. The limiting substrates may adsorb-desorb particles when memory effects are also considered. We show how the bulk modulation (amplitude and number of turns) affects bulk and surface distributions. The diffusing regimes are also studied in terms of the physical parameters governing the system, and we show that, by controlling the modulation (amplitude and frequency) in such limited system, might lead to superdiffusive, usual, or subdiffusive regimes. In other words, increasing the number of turns and the amplitude of modulation changes how the mean square displacement changes over time. Fewer turns with large negative amplitude favors faster diffusion whereas higher number of turns and large positive amplitudes favor slower diffusion. This simple model might help understanding diffusing behavior in modulated and crowded systems such as in cholesteric and smectic liquid crystals and other lamellar systems.

Frequency dispersion in the fractional Langmuir approximation for the adsorption–desorption phenomena

We propose that a kinetic equation of fractional order may be used to account for the frequency dispersion of the effective parameters in the framework of the Langmuir approximation for the adsorption–desorption phenomena. A frequency dependence of these parameters naturally arises in this formalism, indicating that it may play a similar role of a generalization of the Langmuir isotherm obtained from a homogeneous distribution of relaxation times. The fractional approach formalism opens the possibility to consider different relaxation regimes characterizing the interfacial behaviour of electrolytic cells, and may be a powerful tool to interpret complex impedance spectroscopy data.

Extended adsorbing surface reach and memory effects on the diffusive behavior of particles in confined systems

The adsorption-desorption phenomena play a pivotal role in several industrial and scientific processes, deserving attention from research groups across several fields of knowledge. In this article, we study adsorption-desorption of neutral particles scattered in a confined liquid when memory effects are present in both processes, the adsorption and desorption phenomenon. On contrary to previous studies, in which kernels representing memory effects were added to kinetic equations in the desorption term, resulting in considerable change in the dynamics of adsorbed particles, in this work we study the insertion of memory effects on the adsorption process. Such memory means that the preceding state of the particle in the bulk is relevant to the adsorption process, thus heavily affecting how particles are distributed in the bulk and making the reach of the surfaces far greater than when these effects are not considered. We firstly study a case where memory effect occurs only on the adsorption case, and then we analyze situations in which memory effects are included on both adsorption and desorption, and the distinct diffusion regimes in these systems. Our results could be potentially applied and easily adapted to model systems with complex geometries where diffusion and adsorption are present, such as occurs in slit pores.

Phosphorus Sorption and Desorption in Soils Amended with Subabul Biochar

Phosphorus sorption mechanism after biochar application is important to understand the bioavailability of P to crops. The knowledge on P adsorption mechanism on biochar is still poorly understood, and therefore the present study was undertaken with varying biochar rates (0, 1, 3, 5%) on two soils, i.e., one taken from control plot (S1) and another from 100% NPK (S2) plots under long-term fertilizer experiment of red soils by fitting the equilibrium solution and sorbed concentrations of P using adsorption isotherms. Results showed that P sorption increased with higher biochar application rates and soils of S2 (701.8–840.1 mg kg−1) sorbed more P than S1 (534.7–742.4 mg kg−1) with 0–5% biochar rate. Phosphate adsorption on biochar was satisfactorily described by the Langmuir equation (r2 = 0.97–0.99, P = 0.01) and Freundlich equation (r2 = 0.89–0.99, P = 0.01). Phosphorus sorption increased with biochar application rates (0–5%). Desorption experiment showed lower P release and suggests a partial or slow irreversibility of the adsorption–desorption phenomena upon biochar addition to soil. In fertilizer-applied soil (S2) loaded with 60 mg P kg−1 (as KH2PO4), desorption increased with increase in biochar application rates. Biochar application thus alters P availability depending upon P sorption and desorption capacities of soils which have implications for improving P use efficiency in soils.

High performance CO2 gas sensor based on noble metal functionalized semiconductor nanomaterials for health and environmental safety

Design, synthesis and fabrication of novel p-n type semiconducting Pd incorporated MoO3: NiO (MNP) nanocomposite via Hydrothermal protocol and Impregnation method as Carbon-dioxide (CO2) gas sensing material was demonstrated with efficient conductivity and superior stability. The formation of nanocomposites MoO3:NiO and MoO3: NiO: Pd was systematically reviewed and confirmed by x-ray Diffraction (XRD) pattern, x-ray Flurescence Spectroscopy (XRF) and Transmission Electron Microscopy (TEM). A plausible gas sensing mechanism was deduced in terms of adsorption—desorption phenomenon, thus addressing the feasibility and potentiality of MNP nanocomposite engineered for the development of sensitive (S = 96%), selective and stable CO2 gas sensor.

The Flotation by Selected Depressants as an Efficient Technique for Separation of a Mixed Acrylonitrile Butadiene Styrene, Polycarbonate and Polyoxymethyleneplastics in Waste Streams

The virgin acrylonitrile butadiene styrene (ABS), polycarbonate (PC) and polyoxy methylene (POM) available in a plastic mix were separated from each other by a flotation technique with the aid of several depressants. Also, a Design-Expert® statistical software was used to predict plastics flotation using input data including conditioning time, flotation tank temperature and pH and depressants concentration. It revealed that the flotation technique was effective for separation of studied plastics by selected depressants. Understanding the adsorption–desorption phenomena and effective parameters on this process was crucial to explain the activity and selectivity of a depressant on a plastic surface. The increasing conditioning time up to 15 min had adverse effect on the floatability of the all studied plastics conditioned with tannic acid (TA). TA and methyl isobutyl carbinol (MIBC) had not any effect on floatability of PC and POM in all studied depressant concentrations. The flotation of ABS reached to 85% for flotation tank pH of 6.5 with 15 min depressant conditioning at 35 °C as flotation tank temperature. A complicate phenomenon involved and predominated in flotation of studied plastics. Proposed equations by Design-Expert® predicted close plastic flotation values when compared with corresponding experimental values.

Asymmetric adsorption in an open electrolytic cell

We investigate the effect of adsorption–desorption phenomenon of ions in an asymmetric electrolytic cell at open circuit conditions. Our approach is based on the Poisson–Nernst–Planck theory for electrolytes and the kinetic model of Langmuir for the description of adsorption–desorption phenomena on the electrodes. When the electrodes are immersed into the solution, selective ion adsorption takes place. It is shown, that the selective ion adsorption is responsible for generating an electrical potential difference between the electrodes of the cell. The analytical expressions for the potential difference and for the charge distribution are calculated. Finally, the time evolution of the system is investigated and the relaxation times of the problem are deduced numerically.

Adsorption-desorption and hysteresis phenomenon of tebuconazole in Colombian agricultural soils: Experimental assays and mathematical approaches

The adsorption-desorption, hysteresis phenomenon, and leachability of tebuconazole were studied for Inceptisol and Histosol soils at the surface (0–10 cm) and in the subsurface (40–50 cm) of an agricultural region from Colombia by the batch-equilibrium method and mathematical approaches. The experimental Kfa and Kd (L kg−1) values (7.9–289.2) decreased with depth for the two Inceptisols and increased with depth for the Histosol due to the organic carbon content, aryl and carbonyl carbon types. Single-point and desorption isotherms depended on adsorption reversibility and suggested that tebuconazole showed hysteresis; which can be adequately evaluated with the single-point desorption isotherm and the linear model using the hysteresis index HI. The most suitable mathematical approach to estimate the adsorption isotherms of tebuconazole at the surface and in the subsurface was that considering the combination of the n-octanol-water partition coefficient, pesticide solubility, and the mass-balance concept.Tebuconazole had similar moderate mobility potential as compared with the values of other studies conducted in temperate amended and unamended soils, but the risk of the fungicide to pollute groundwater sources increased when the pesticide reached subsurface soil layers, particularly in the Inceptisols.

Symmetry breaking in an electrolytic cell under AC field and non-identical adsorbing electrodes

Broken symmetry of any kind in natural or synthetic systems is a burgeoning area of science. In this article, the temporal behavior of the bulk density, electric potential inside the sample, and the adsorbed ionic particles density in an electrolytic cell are shown to be non-symmetric and strongly affected by the surfaces dynamics. These parameters are analytically calculated by considering electrodes surfaces with non-identical adsorption-desorption phenomena. The system is submitted to an applied external voltage in the limit of small amplitude, where the time scales involved allow strong surface effects. The influence of the surfaces on the ionic distribution is performed in the framework of the Poisson-Nernst-Planck model by taking into account non-identical boundary conditions on the electrodes and on the electric potential, described by distinct kinetic equations. Such approach may be directly applied to explain strong surface dependence on the impedance spectroscopy, in hybrid aligned liquid crystal cells, fuel cells, biological and condensed matter systems in general.

Electrochemical analysis of interface adsorption phenomena on three-dimensional nano-nickel electrode deposited on silicon microchannel plate

The electrochemical double-layer capacitance and adsorption-desorption phenomena of the three-dimensional (3D) nano-nickel electrode on silicon microchannel plate is investigated electrochemically in the neutral aqueous solution. The electrochemical double-layer capacitance of the 3D electrode increases due to the porous structure of the nickel electrode and 3D architecture of the silicon microchannel plate and the charging process can be completed in a shorter time due to the special 3D architecture. The specific monolayer adsorption, electrochemical double-layer adsorption, and diffusion-limited electrochemical processes can be identified clearly on account of the larger surface area and described by an exponential relationship. Different adsorption quantities are also observed from cations and anions on account of the small channels in the 3D nano-nickel electrode.

Electrochemical Behavior of Atorvastatin at Glassy Carbon Electrode and its Direct Determination in Pharmaceutical Preparations by Square Wave and Differential Pulse Voltammetry

A simple and rapid electrochemical methods for the determination of atorvastatin in pharmaceutical preparations was developed. The anodic peak at 1.07 V obtained in a buffer on glassy carbon electrode was used for analysis. The peak current and peak potential depends on pH, scan rate and initial potential. Decrease of the anodic peak with increasing pH, as well as deviations from linear plots of ip = f(C) and ip = kv1/2 indicate that this peak at higher concentrations is affected by adsorption-desorption phenomena. The calibration curves were linear for atorvastatin at the concentration range of 1-50 µg/ml or square wave and differential pulse voltammetry methods, respectively. Intra and interday precision values for atorvastatin were less than 3.17, and accuracy (relative error) was better than 1.93%. The mean recovery of atorvastatin was 100.4% for pharmaceutical preparations. Limits of detection were 0.3 µg/ml and 0.2 µg/ml for square wave and differential pulse voltammetry, respectively. Developed methods in this study are accurate, precise and can be easily applied to Ator, Cholvast and Lipitor tablets as pharmaceutical preparation.

Role of cell wall deconstructing enzymes in the proanthocyanidin–cell wall adsorption–desorption phenomena

The transference of proanthocyanidins from grapes to wine is quite low. This could be due, among other causes, to proanthocyanidins being bound to grape cell wall polysaccharides, which are present in high concentrations in the must. Therefore, the effective extraction of proanthocyanidins from grapes will depend on the ability to disrupt these associations, and, in this respect, enzymes that degrade these polysaccharides could play an important role. The main objective of this work was to test the behavior of proanthocyanidin–cell wall interactions when commercial maceration enzymes are present in the solution. The results showed that cell wall polysaccharides adsorbed a high amount of proanthocyanidins and only a limited quantity of proanthocyanidins could be desorbed from the cell walls after washing with a model solution. The presence of enzymes in the solution reduced the proanthocyanidin–cell wall interaction, probably through the elimination of pectins from the cell wall network.