Desorption Research Articles

Mechanistic kinetic modeling of simultaneous electrochemical nitrate reduction and ammonium ion oxidation in wastewater

Two kinetic models, i.e., schemes, surface adsorbed nitrogen as divergent (SND) and surface adsorbed NO as divergent (SNOD) towards NH4+ and N2 production, were developed to model simultaneous electrochemical reduction of the nitrate ion (NO3−) and oxidation of by-products. Experimental data for electrochemical reduction was collected in synthetic nitrate solution and actual wastewater using Al and Ti/RuO2 as cathode and anode, respectively. Sum of square errors (SSE) and Akaike's information criterion (AIC) analysis showed that the SND model well-represented all the concentration profiles of nitrogen species with the variation in all the operating parameters. Desorption of nitrite ion from the cathode surface was the rate-determining step for the SND kinetic model. Mechanistic and kinetic analysis suggested that N2 gas was the main product. However, NO2− gets formed as the by-product in the alkaline environment, whereas, NO2− and NH4+ were the by-products in the acidic environment.

Boosting the performance of flexible in-plane micro-supercapacitors by engineering MoS2 nanoparticles embedded in laser-induced graphene

As an essential miniature energy storage device, flexible in-plane micro-supercapacitors (MSCs) have the advantages of rapid charge and discharge, instantaneously high power output, long cycle stability and easy integration. However, the synthesis of electrode materials, the preparation of patterned microelectrodes and the subsequent modular integration are usually carried out independently, and the steps are very complicated. Accordingly, an effective and fast fabrication process involving laser direct writing technique is introduced to prepare shape-controllable MoS2 nanoparticle-embedded laser-induced graphene (MoS2/LIG) patterned electrodes on various substrates for flexible planar MSCs. The embedding of MoS2 nanoparticles can effectively improve the hydrophobic properties of MoS2/LIG hybrid electrodes, which is more conducive to the adsorption and desorption of aqueous electrolyte ions. Benefiting from the engineering of pseudocapacitive MoS2 nanoparticles uniformly embedded in good conductive LIG with 3D porous structure, our flexible planar MoS2/LIG MSC demonstrates a superior areal capacitance of 35.3 mF cm–2, a high energy density of 4.91 mW h cm–2 at a power density of 0.18 mW cm–2, good cycle stability, outstanding mechanical flexibility, and prominent modular integration. The universal process route developed in this work can be used for controllable assembly of many similar flexible planar integrated MSCs, and may accelerate their potential application in flexible and wearable electronics.

Pullulan based hydrogels for the removal of various metal ions from aqueous solutions

Pullulan-graft-poly(acrylic acid) (pullulan-g-poly(AA)) and pullulan-graft-poly(acrylic acid-co-acrylamide) (pullulan-g-poly(AA-co-AAm)) hydrogels were synthesized by free radical solution polymerization. Fourier Transform Infrared Spectroscopy, Thermal Gravimetric Analysis and Scanning Electron Microscopy were used to further understand the formation and the characteristics of the hydrogels. Additionally, the hydrogels’ swelling capacities and swelling kinetics were investigated. Pullulan-g-poly(AA-co-AAm) was found to have the highest swelling capacity with 461% after optimization. Metal ion adsorption and desorption abilities and the reusability properties of the hydrogels were examined, and both of the prepared hydrogels were found to be efficient adsorbents of cadmium(II), copper(II), mercury(II), nickel(II) and zinc(II) ions. The most adequate hydrogel was found to be pullulan-g-poly(AA-co-AAm) for the adsorption of cadmium(II) ions with 169.79 mg/g followed by pullulan-g-poly(AA) hydrogel for the adsorption of cadmium(II) ions with 137.76 mg/g. The desorption tests were conducted by using hydrochloric acid and the hydrogel with the best desorption ability was found to be pullulan-g-poly(AA) hydrogel with 76% for the desorption of Cd(II) ions. The adsorption-desorption cycles were repeated 3 times and the hydrogel that has the best reusability was found to be pullulan-g-poly(AA-co-AAm) with 169.79 mg/g, 124.78 mg/g and 115.34 mg/g for the adsorption of Cd(II) ions in the first, second and third cycles, respectively. All of the synthesized hydrogels were found to be good candidates for the adsorption and desorption of Cd(II), and Cu(II) ions; and pullulan-g-poly(AA-co-AAm) was able to adsorb and desorb Hg(II) ions for at least three times.

Solid - phase extraction of Lead in saline matrix using by GF- AAS with multivariate optimization

This work presents a novel method investigated in the pre-concentration of lead ion as well as the matrix effect eliminated in high salinity medium using solid phase extraction by graphite furnace Atomic Absorption spectroscopy (GFAAS). Fe 3 O 4 -graphene was used as the sorbent while 1M HNO 3 was used as the extraction solvent. Parameters such as: pH, amount of sorbent, time of adsorption, time of desorption and, stirring rate affecting the extraction efficiency of the method were studied and optimized by utilizing two decent optimization methods; factorial design and central composite design (CCD). The limit of detection and limit of quantification were 4.4 and 14.8 ng/mL, respectively The accuracy of the method was evaluated by analyzing a spiked real sample. Good spiked recoveries over the range 98.8-103.6 % were obtained. Under the optimum conditions, the calibration graph was linear over the range 5-50 ng/mL. The relative standard deviation was 4.4 % for four repeated determinations at a concentration of 20 ng/mL.

STUDY OF THE SORPTION OF AMMONIUM CATIONS ON A FIBROUS CARBOXYLIC SORBENT

Background: Wastewater from the mineral fertilizer production, agribusiness containing ammonium ions causes significant harm to fish farming; therefore, it must be purified before discharge. Ion-exchange sorption is a promising method for isolating ammonium cations. The object of the study was a chemisorption fiber VION KN-1, which has developed surface and high sorption rate. Purpose: To study the sorption kinetics of ammonium cations from aqueous solutions on VION KN-1; to train an ANN to predict the degree of recovery of ammonium ions from wastewater using Statistica Neural Networks Version 13. Methods: The ammonium ion concentration in the solution was established by direct potentiometry. Sorption isotherms were constructed using the method of variable concentrations. To determine the limiting stage, the obtained kinetic dependencies were represented in the coordinates of the Boyd-Adamson equations for internal/external diffusion. Results and Discussion: During sorption from solutions with different ammonium nitrogen contents, the values of distribution coefficients (Kd) are at the level of 2.3ꞏ103 cm3/g, which significantly exceeds this parameter for granular ionites. Experimental sorption data were verified using Freundlich (R2 = 0.9224) and Langmuir (R2 = 0.9996) isotherms. The maximum degree of recovery (over 96 %) was achieved by passing a solution with a concentration of 11.3 mmol/dm3. Using an array of experimental data, the MLP-3-5-1 neural network was trained. The coefficient of determination R2 = 0.999420 obtained for the training sample characterizes high network performance. Conclusions: The Langmuir equation better describes the process of NH4+ sorption on a fibrous sorbent. It is reasonable to use VION KN-1 at the fine treatment stage. Ammonium ion desorption from the fiber was performed by acid solution. The resulting solutions of ammonium salts can be used as liquid fertilizers. The trained neural networks can be used to predict the degree of recovery of ammonium ions by sorbent VION KN-1.

Зависимость вытеснения ионов Са, Мg, Fe, К из почв от продолжительности воздействия Н2О и температуры

In the conducted studies on sod-podzolic soils and ordinary chernozems, a change in the rate of transition of Ca, Md, Fe, K ions from the soil to H2O at temperatures of 0 and 20º, the interaction time of 1 day and 1 week was established. It is shown that the speed of the processes depends on the combination of temperature and duration of reactions, differs for individual soils, horizons and certain cations. The magnitude of the change in the rate of the processes under consideration does not fully correlate with the physico-chemical and thermodynamic patterns of changes in the mobility of ions in soils depending on humidity and temperature, which is associated with the simultaneous course of ion exchange reactions, complex formation, sedimentation. The necessity of studying the kinetics of processes occurring in the soil for a more correct assessment of the agroecological state of soils is proved. Keywords: KINETICS, SOIL, TEMPERATURE INFLUENCE, ION DESORPTION

Simultaneous removal of toxic Pb(II) ions, poly(acrylic acid) and Triton X-100 from their mixed solution using engineered biochars obtained from horsetail herb precursor – Impact of post-activation treatment

The horsetail herb was used as the precursor and was subjected to direct physical activation with steam (800 °C for 1 h). Next two variants of post-activation treatment was applied: (1) two-steps washing procedure, firstly with a hot 10% solution of HCl and later with demineralized water (HBA_HCl sample) and (2) one-step washing procedure only with demineralized water (HBA_H2O sample). The final products were characterized towards its textural structure, acid-base properties and surface morphology. The obtained biochars were used as adsorbents for simultaneous removal of hazardous lead(II) ions, poly(acrylic acid) (PAA) polymer and Triton X-100 nonionic surfactant from their mixed solution.It was shown that Pb(II) and PAA adsorbed amounts (from the single and mixed systems of adsorbates) have the greatest values on the HBA_HCl surface in the double PAA + Pb(II) system (148.8 mg/g and 195.8 mg/g, respectively) and in the triple PAA + TRT + Pb(II) system (183.3 mg/g and 187.7 mg/g, respectively). The nonionic surfactant desorption reaches high level (83–100%), independently from using desorption agent (HNO3 or NaOH). Generally in the case of PAA, NaOH solution turned out to be more effective in adsorbent recovery process (especially from HBA_H2O surface), whereas in the case of Pb(II) ions desorption, HNO3 is more effective desorbing agent (74–96% desorption).

Electrochemical Formation of Oxide Films on the Titanium Alloy of Ti6Al4V in Ethylene Glycol-Water Electrolytes to Produce Bioinert Coatings and Increase the Corrosion Resistance of Medical Implants

The research data on the specific features of the formation of oxide films on the Ti6Al4V alloy in the ethylene glycol-water electrolytes have been given. The kinetic dependences obtained for the alloy allowed us to establish that the specific features of the formation of oxide films during the electrochemical oxidation of the alloy surface depend on the solution composition and the current density. For the water-to-alcohol ratio of 50:50 the kinetic dependences show the sections that correspond to the formation of the barrier oxide layer and also to the formation of the pores due to the desorption of fluoride ions and the growth of the porous portion of oxide. As the water-to- alcohol ratio is decreased the indicated peculiarities of kinetic dependences are met not so often and do not obey any regularity. The obtained data are explained by the fact that an increase in the portion of the organic component of the solution results in a decreased etching capacity of the electrolyte due to the controlled activity of fluoride ions. The anode current density value has a similar effect on the variation of kinetic dependences. Its effect is explained by that an increase in the alloy oxidation rate results in the fast formation of the surface oxide and the specific features of kinetic curves are concealed. The linear relationship between the formation time of oxide of a minimum thickness for given conditions and the current density is unavailable and it is conditioned by the chemical interaction of the oxide film with electrolyte components. The obtained research data can be used for the formation of the individual bioinert and bioactive coatings for the implants of a medical purpose or for the formation of the matrix used for the production of composite coatings.

Anodic stripping voltammetry on a carbon-based ion-selective electrode

In this study, we demonstrated the unique capability of carbon-based ion-selective electrode (ISE) to perform highly sensitive square wave anodic stripping voltammetry, while maintaining all the properties of an ISE, in terms of sensitivity, detection limit, response time and selectivity. Square wave anodic stripping voltammetry involves deposition and dissolution steps of metal ions, which means adsorption and desorption of metal ions on the conductive ion-selective membrane without losing its ion-sensing property. To demonstrate this capability, we chose a Ca2+ ion-selective microelectrode (µISE) as a potentiometric method and Cu2+-stripping voltammetry as an amperometric method. The carbon-based ISE surface is capable of quantifying nanomolar to micromolar Cu2+ in both a standard acetate buffer and a complex water sample. The Ca2+-µISE also showed a Nernstian slope of 29 mV/log [Ca2+] and a detection limit of 1 µM within the linear range of 1 µM to 10 mM. It thus opens an opportunity to use the low detection limit of anodic stripping voltammetry and the high selectivity of ISE-based potentiometry.

Adsorption and Desorption of Decane Using Non-Carbon Adsorbents

Adsorption and Desorption of Decane Using Non-Carbon Adsorbents

Heavy metal remediation by nano zero-valent iron in the presence of microplastics in groundwater: Inhibition and induced promotion on aging effects

Nano zerovalent iron (nZVI) is one of the most broadly applied nanomaterials in the fields of groundwater remediation which benefits from its high reactivity for pollutants. However, its successful application faces challenges due to its tendency to agglomerate or form passive (oxy)hydroxide corrosion. With the emerging microplastics (MPs) pollution in groundwater system in recent years and considerable data vacancy on its potential physicochemical and ecological effects, it complicates the situation for groundwater remediation. Hereby, we investigated the effects on metal removal by nZVI in groundwater in the presence of various MPs. The removal capacity of Cu (II), Cr (VI), Pb (II) and Zn (II) by nZVI was found to be inhibited to different degrees in the presence of MPs. Desorption of metallic ions was observed dependent on various metal species, with the highest desorption rate in Zn (II). Amongst all MPs investigated, including polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), PVC poses the most adverse impact on metal desorption, attributing to its promotion of nZVI aging through electrostatic attraction. This study focused on the impact of MPs to metal remediation, beyond the general aspect of MPs hazard such as its toxic effects or delivery of contaminants. Moreover, groundwater was investigated to make a useful supplement to the research of MPs which primarily focuses on surface water.

Recovery of lanthanum, praseodymium and samarium by adsorption using magnetic nanoparticles functionalized with a phosphonic group

In this work, the synthesis and application of a promising magnetic adsorbent for the recovery of lanthanum, praseodymium, and samarium was studied. To obtain the magnetic adsorbent, magnetite nanoparticles were functionalized with a phosphonic acid group (PA-MNPs) by an efficient and reproducible method. Based on HR-TEM analysis, PA-MNPs present an average diameter of 6.8 nm, have a spherical shape, and a certain degree of agglomeration at approximately 20 to 40 nm. The nanoparticles' magnetic saturation was found to be approximately 55 emu/g, enough to provoke their complete separation from an aqueous raffinate using a common magnet. The XPS and FTIR analyses provided evidence for a phosphonic acid group on the surface of the magnetite nanoparticles. The effect of the pH and the initial concentration of lanthanide ions in the aqueous feed solution and the adsorbent dose on REE adsorption was studied. Maximum lanthanide ion loading capacities in the range of 20–24 mg lanthanide/g adsorbent were measured close to pH 4 (contact time: 5 min.; mass of adsorbent: 200 mg). The PA-MNPs adsorbent presented high mechanical and chemical stability in aqueous solutions with initial pH between 3 and 7. The more efficient desorption (75–100%) of lanthanide ions from the adsorbent was achieved using H2SO4 0.1 M solution. The feasibility of regenerating and reusing functionalized magnetic nanoparticles in five cycles of adsorption/desorption was verified. Freundlich and Langmuir adsorption isotherms fit the experimental equilibrium data well, which would be indicating that the adsorption process would be ruled by a hybrid model. The results of kinetic experiments were well explained by a pseudosecond-order kinetic model, and a very fast initial adsorption rate was observed.

The use of Phanerochaete chrysosporium for modification of bentonite for preconcentration and determination of heavy metals

In this study, a solid phase extraction method was successfully applied in the preconcentration and determination of trace levels of Cu(II) and Cd(II) ions and Phanerochaete chrysosporium (white rot fungus) modified bentonite was used as adsorbent. After the biosorption of Cu(II) and Cd(II) ions, metal concentrations in the samples were determined by atomic absorption spectrophotometry. pH, adsorbent amount, eluent type, sample volume, and flow rate, which are effective in the adsorption of metal ions, have been studied. 1 M HCl was used for desorption of these metal ions retained (recovery 95–100%). In addition, the effect of interfered ions has also been investigated. Sorption data were examined according to Langmuir and Freundlich adsorption equations. The results obtained show that the applied method has a high metal biosorption capacity, and Cu(II) and Cd(II) ions are successfully recovered. It was also successful in applying the proposed enrichment method to real water samples.Recovery values between 92.3% and 97.3% were obtained for the studied metal ions. According to the results, the proposed method can be successfully applied to water analysis at 95% confidence interval.

Adsorption of Pb(II) and Cd(II) from aqueous solutions on polyvinylpyrrolidone modified Kyzylsok natural clay

The present work considers the production of a cheap and effective sorbent based on natural clay from the Kyzylsok deposit (Almaty region) in order to purify wastewater from heavy metal ions (Cd2+, Pb2+). It was found that the starting material is applicable for the extraction of Cd2+ ions (the degree of extraction is (97.00 ± 1.99) %), while for the extraction of Pb2+ ions the initial clay must be modified. The modification was carried out using polyvinylpyrrolidone (PVP). The degree of extraction of Pb2+ ions with modified clay increased from (70.00 ± 1.77)% to (98 ± 1.13)% The influence of PVP concentration in the composite material (modified clay) on its sorption properties was studied: the optimal concentration of PVP was 0.1 % solution. The desorption of metal ions was also investigated in the work, it does not exceed 2%. It was found that the sorption process is described by the monomolecular Langmuir isotherm model and the kinetic model of the pseudo-second order.

Fabrication of a CO2-responsive chitosan aerogel as an effective adsorbent for the adsorption and desorption of heavy metal ions

In the traditional desorption method, strong acid is commonly used as an eluent for the regeneration of adsorbents. It is of critical economic and environmental significance to develop a chemical-free desorption method. In this study, a new CO2-responsive chitosan aerogel adsorbent was synthesized from CO2-responsive poly(acrylic acid-2-(dimethylamino)ethyl methacrylate) and chitosan by physicochemical double crosslinking for the adsorption of Cu2+. Compared with the chitosan aerogel, the adsorption capacity of Cu2+ and mechanical properties of CO2-responsive chitosan aerogel increased by 162% and 660%, respectively. Most importantly, after the adsorption of Cu2+ by CO2-responsive chitosan aerogel, the Cu2+ could be desorbed by CO2 bubbling, and the desorption rate of metal ions was more than 80%. The adsorption of Cu2+ by aerogel was attributed to chelation and complexation. The desorption of porous chitosan/P(AA-co-DMAEMA) aerogels (CPA) by CO2 mainly occurred through charge repulsion of protonated ‒NH2 and ‒N‒ groups. After 6 cycles, the adsorption capacity of CPA for metal ions still reached 70% of the initial adsorption capacity, and the desorption rate reached 75%. This novel CO2-responsive chitosan aerogel is a highly efficient and environmentally friendly adsorbent for the adsorption and recovery of metal ions.

An electrically switched ion exchange system with self-electrical-energy recuperation for efficient and selective LiCl separation from brine lakes

Various electrochemical separation methods have been investigated for the recovery of lithium to satisfy the global demand for lithium. However, most of them are still greatly limited by high energy consumption and deficient selectivity. To overcome these issues, in this study, an electrically switched ion exchange (ESIX) system for efficient and selective LiCl separation from brine lakes was developed based on a strategy of self-electrical-energy recuperation, in which the electric energy generated in the process of LiCl uptake was proposed to compensate the energy consumed for the desorption of ions as well as the regeneration of electrodes. λ-MnO2 film coated electrode and [email protected] film coated electrode were fabricated to capture Li+ and Cl- ions in the brine lake, respectively. In the ion uptake process, the inherent potential difference between the two electrodes was balanced due to the embeddedness of Li+ and Cl- ions, which simultaneously triggered the generation of electric energy. This generated electric energy was automatically stored and provided for the desorption of the Li+ and Cl- ions from the electrodes in the ion releasing process. As a result, this ESIX system featured with extremely low energy consumption (1.007 Wh for separating per mole of LiCl) and excellent selectivity with a LiCl recovery capacity of 10.88 mg/g. It is expected that such an ESIX system with self-electrical-energy recuperation could be a promising alternative to those current electrochemical techniques for the recovery of LiCl from brine lakes.

High-Efficiency and Sustainable Desalination Using Thermo-regenerable MOF-808-EDTA: Temperature-Regulated Proton Transfer.

Adsorption as a desalination approach has the advantages of energy efficiency, low cost, and operational convenience, but its practical application is limited by low desalination capacity, consumption/disposal of strong acids/bases as regeneration reagents, and poor reusability. Herein, we synthesized a thermo-regenerable salt absorbent by grafting ethylenediaminetetraacetic acid (EDTA) onto a metal-organic framework (MOF), MOF-808-EDTA, which could rapidly adsorb NaCl within 30 min from saline water at 25 °C with a desalination capacity as high as 9.4 mmol/g. Moreover, the saturated adsorbent could be facilely regenerated in 80 °C water. Fourier transform infrared spectroscopy and derivative thermogravimetry revealed that temperature-regulated proton transfer between amino and carboxyl groups was the mechanism of thermo-regeneration. EDTA on MOF-808-EDTA appears in a zwitterionic state in water at room temperature, which allowed simultaneous adsorption of Na+ and Cl-. At elevated temperature, it returned to a nonionic state accompanied by the desorption of ions. A similar temperature-dependent adsorption-regeneration process was also observed for other salts, including LiCl, KCl, CaCl2, and MgCl2. Column experiments of brackish groundwater showed that 1 g of MOF-808-EDTA could produce ∼106 mL of fresh water (total dissolved solids < 600 mg/L) without significant capacity loss after 10 successive adsorption-regeneration cycles. This study is the first to propose an EDTA-based MOF for desalination and indicates the potential of MOF-808-EDTA as a green adsorbent for sustainable water desalination.

Desorption/Ionization-MS Methods for Drug Quantification in Biological Matrices and Their Validation Following Regulatory Guidance.

Desorption/ionization (DI) methods play an important role among the panel of mass spectrometric (MS) approaches for the rapid and sensitive quantification of drugs from the surface of solid samples. The possibility to implement these approaches for pharmacokinetic/pharmacodynamic investigations in early phase clinical trials depends on the ability to validate quantification assays according to regulatory guidelines (e.g., US Food and Drug Administration and European Medicines Agency) for bioanalytical method validation. However, these guidelines were designed for the validation of liquid chromatography-MS (LC-MS) methods and ligand binding assays. To apply the validation parameters to DI-MS methods (also referred here as on-surface MS) for drug quantification, it is important to consider the particularities of DI approaches compared to LC-MS methods. In this Perspective, we summarize the various applications of on-surface MS methods for drug quantification with their advantages over other MS methods, and provide our point of view regarding future proper method development and validation.

Electrons on a straight path: A novel ionisation vacuum gauge suitable as reference standard

The consortium of the European project 16NRM05 designed a novel ionisation vacuum gauge in which the electrons take a straight path from the emitting cathode through the ionisation space into a Faraday cup. Compared to existing ionisation vacuum gauges, this has the advantage that the electron path length is well defined. It is independent of the point and angle of emission and is not affected by space charge around the collector. In addition, the electrons do not hit the anode where they can be reflected, generate secondary electrons or cause desorption of neutrals or ions. This design was chosen in order to develop a more stable ionisation vacuum gauge suitable as reference standard in the range of 10−6 Pa to 10−2 Pa for calibration purposes of other vacuum gauges and quadrupole mass spectrometers. Prototype gauges were produced by two different manufacturers and showed predictable sensitivities with a very small spread (<1.5%), very good short-term repeatability (<0.05%) and reproducibility (<1%), even after changing the emission cathode and drop-down tests. These characteristics make the gauge also attractive for industrial applications, because a gauge exchange does not require calibration or re-adjustment of a process.

Enhanced electrokinetic remediation of heavy metals contaminated soil by biodegradable complexing agents

In this study, an electrokinetic technique for remediation of Pb2+, Zn2+ and Cu2+ contaminated soil was explored using sodium alginate (SA) and chitosan (CTS) as promising biodegradable complexing agents. The highest Cu2+ (95.69%) and Zn2+ (95.05%) removal rates were obtained at a 2 wt% SA dosage, which demonstrated that SA significantly improved the Cu2+ and Zn2+ removal efficiency during electrokinetic process. The abundant functional groups of SA allowed metal ions desorption from soil via ion-exchange, complexation, and electrolysis. Pb2+ ions were difficult to remove from soil by SA due to the higher gelation affinity with Pb2+ than Cu2+ and Zn2+, despite the Pb2+ exchangeable fraction partially transforming to the reducible and oxidizable fractions. CTS could complex metal ions and migrate into the catholyte under the electric field to form crosslinked CTS gelations. Consequently, this study proved the suitability of biodegradable complexing agents for treating soil contaminated with heavy metals using electrokinetic remediation.