Ion Concentration In Solution Research Articles

Genetic diversity of VIR Raphanus sativus L. collections on aluminum tolerance.

Radish and small radish (Raphanus sativus L.) are popular and widely cultivated root vegetables in the world, which occupy an important place in human nutrition. Edaphic stressors have a significant impact on their productivity and quality. The main factor determining the phytotoxicity of acidic soils is the increased concentration of mobile aluminum ions in the soil solution. The accumulation of aluminum in root tissues disrupts the processes of cell division, initiation and growth of the lateral roots, the supply of plants with minerals and water. The study of intraspecific variation in aluminum resistance of R. sativus is an important stage for the breeding of these crops. The purpose of this work was to study the genetic diversity of R. sativus crops including 109 accessions of small radish and radish of various ecological and geographical origin, belonging to 23 types, 14 varieties of European, Chinese and Japanese subspecies on aluminum tolerance. In the absence of a rapid assessment methodology specialized for the species studied, a method is used to assess the aluminum resistance of cereals using an eriochrome cyanine R dye, which is based on the recovery or absence of restoration of mitotic activity of the seedlings roots subjected to shock exposure to aluminum. The effect of various concentrations on the vital activity of plants was revealed: a 66-mM concentration of AlCl3 · 6Н2О had a weak toxic effect on R. sativus accessions slowing down root growth; 83 mM contributed to a large differentiation of the small radish accessions and to a lesser extent for radish; 99 mM inhibited further root growth in 13.0 % of small radish accessions and in 7.3 % of radish and had a highly damaging effect. AlCl3 · 6Н2О at a concentration of 99 mM allowed us to identify the most tolerant small radish and radish accessions that originate from countries with a wide distribution of acidic soils. In a result, it was possible to determine the intraspecific variability of small radish and radish plants in the early stages of vegetation and to identify genotypes that are contrasting in their resistance to aluminum. We recommend the AlCl3 · 6Н2О concentration of 83 mM for screening the aluminum resistance of small radish and 99 mM for radish. The modified method that we developed is proposed as a rapid diagnosis of aluminum tolerance for the screening of a wide range of R. sativus genotypes and a subsequent study of contrasting forms during a longer cultivation of plants in hydroponic culture (including elemental analysis of roots and shoots, contrasting in resistance of accessions) as well as reactions of plants in soil conditions.

Molecular dynamics study of sessile ionic nanodroplet under external electric field

Effect of external electric field and surface temperature on the dynamics of a sessile ionic nanodroplet has been investigated using classical molecular dynamics (MD) simulations. The study investigates the spreading, evaporation and deformation behavior of a salt-water nanodroplet on a solid Pt surface in the presence and absence of external electric field. Varying the intensity and direction of the external electric field, a series of MD simulations were carried out considering a moderate concentration of ionic solution to understand these phenomena at molecular level. In the presence of salt ions, effect of hydration becomes more dominant which resists the deformation of the nanodroplet. It was also found that vertical electric field leads to the formation of nanobridge/column like structures beyond some critical field intensities. In addition to the electro-evaporation, the present study probes the effect of surface temperature on the evaporation and spreading process of the sessile ionic nanodroplet.

Enhancing Protein Crystallization under a Magnetic Field

High-quality crystals are essential to ensure high-resolution structural information. Protein crystals are controlled by many factors, such as pH, temperature, and the ion concentration of crystalline solutions. We previously reported the development of a device dedicated to protein crystallization. In the current study, we have further modified and improved our device. Exposure to external magnetic field leads to alignment of the crystal toward a preferred direction depending on the magnetization energy. Each material has different magnetic susceptibilities depending on the individual direction of their unit crystal cells. One of the strategies to acquire a large crystal entails controlling the nucleation rate. Furthermore, exposure of a crystal to a magnetic field may lead to new morphologies by affecting the crystal volume, shape, and quality.

Application of Taguchi Method for Optimization Cadmium Separation by Emulsion Liquid Membrane

A study was carried out to remove cadmium ions from a hydrochloric medium at a concentration of 100 ppm using the emulsified liquid membrane (ELM) technique. Emphasis was placed on assessing process parameters and their effect on changing the concentration of cadmium ions in the hydrochloric solution. To study the performance characteristics of the process, Taguchi method was used with analyzing of signal/noise ratio. Five parameters that affect performance such as (pH of the external phase (1-4), surfactant concentration in the organic layer (4% -10% v / v), carrier concentration in the organic layer (4% -10% v / v), speed of Emulsification (5800-24000) rpm and emulsion volume ratio / outer phase ratio (Eml./Ext ratio) was studied, taking into account the change in the concentration of cadmium ions in the external phase. To obtain the lowest concentration of cadmium ions in the external stage, the values ​​of the optimum parameters were: pH = 3, Surfactant conc. = 4%, Carrier conc. = 8% emulsification speed = 19700 rpm, and Eml./Ext. ratio = 18%. Results of the present work suggested that Eml./Ext. ratio had a major effect on the concentration change, followed by a pH in the outer phase, the emulsification velocity, carrier concentration, and the surfactant concentration respectively.

Theoretical description of the ligand function for ionoselective electrodes reversible to metal anion complexes. 2. Selectivity to foreign ions

Within the framework of the steady-state diffusion model, the equations have been obtained explicitly describing the selective electrode selectivity coefficient to the ligand ion in relation to foreign ions not forming complexes with zinc ions, as a function of fundamental thermodynamic characteristics (exchange constants of tetrathiocyanatozincate for thiocyanate and foreign ion, concentrations of ion exchanger in the membrane and zinc ion in the sample solution), as well as controllable diffusion parameters (thicknesses of solution and membrane phase diffusion layers, governed by stirring mode and measuring time, respectively). Separate attention is given to cases of measurements in presence and in absence of constant background concentration of zinc ions in the sample solution. It has been shown that selectivity of tetrathiocyanatozincate selective electrode to thiocyanate ion in relation to anions not forming complexes with zinc, is several orders of magnitude higher than selectivity of an ordinary thiocyanate-selective electrode containing higher quaternary ammonium thiocyanate as an ion exchanger, and increases regularly with the background concentration of zinc ions. The results obtained are in general agreement with the experimental data given in the literature. It has been shown that variability of selectivity coefficients caused by variations of diffusion parameters within the limits corresponding to real measuring conditions, can be up to 0.3–0.4 orders of magnitude.

Adsorption of Pb(II) ions from contaminated water by 1,2,3,4-butanetetracarboxylic acid-modified microcrystalline cellulose: Isotherms, kinetics, and thermodynamic studies

Microcrystalline cellulose (MCC) has been utilized as an adsorbent material for the removal of Pb(II) ions from aqueous solution after treatment with 1,2,3,4-butanetetracarboxylic acid (BTCA) at elevated temperature to obtain MMCC. The resulting adsorbent was characterized for point of zero point charge (pHZPC), estimation of carboxyl content, Fourier transform infrared spectroscopy (FT-IR), scan electron microscopy (SEM), and textural properties, including surface area, and subsequently utilized for the removal of Pb(II) ions from aqueous solution. The adsorption process was probed by investigating the effect of adsorbent dose, pH of solution, temperature, agitation time, and Pb(II) ion concentration. The results showed successful functionalization of MCC using BTCA, significantly improved the binding properties of the adsorbent towards Pb(II) ions. Isothermal adsorption data was analyzed using Langmuir, Freundlich and Temkin models, evaluated via nonlinear regression analysis. The maximum adsorption capacity was found to be 1155 mg/g (at pH 5 and 30 °C) from Langmuir theory, and appears independent of surface area. The Freundlich model was found to provide the best fit and the constant n was determined to be 2.69, indicating that adsorption of Pb(II) ions onto MMCC is favorable. Kinetic modelling showed good agreement for the pseudo-second order kinetic model, supporting the theory that chemisorption is involved in the adsorption process, which is promoted by a high density of active sites. Thermodynamic analysis showed that the adsorption of Pb(II) ions onto MMCC was endothermic and nonspontaneous; hence, MMCC offers an effective method of Pb(II) ion removal from aqueous solutions, with potential for water remediation processes.

Efficient Removal of Ni(II) from Aqueous Solution by Date Seeds Powder Biosorbent: Adsorption Kinetics, Isotherm and Thermodynamics

Adsorption investigations in batch approaches were performed to explore the biosorption of Ni(II) ions from aqueous solutions on date seeds powder. The effects of pH, particle size, initial concentration of Ni(II) ions, adsorbent mass, temperature, and contact on the adsorption efficacy were studied. The maximum removal obtained was 90% for an original Ni(II) ion solution concentration of 50 ppm was attained at pH 7 after 30 min and with 0.30 g of an added adsorbent. The four adsorption models, namely Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin were examined to fit the experimental findings. The adsorption system obeys the Freundlich model. The system was found to follow the pseudo-second order kinetic model. Thermodynamic factors; entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes were also assessed. Results proved that adsorption of Ni(II) ions is exothermic and spontaneous. Sticking probability value was found to be less than unity, concluding that the process is dominated by physical adsorption.

Cadmium (II) removal from aqueous solution using magnetic spent coffee ground biochar: Kinetics, isotherm and thermodynamic adsorption

Spent coffee grounds are a waste generated in large amounts by the food industry producing instant coffee. While it is used as animal feed, mostly spent coffee grounds are burned. In this study, The spent coffee grounds were modified to be magnetic in order to remove cadmium (II) ion. The magnetic solids are easy to separate from water with a magnet. The biochar was prepared at 400 °C. Several factors that affect the adsorption were studied, such as adsorbent dosage, contact time, initial metal ion concentration and effect of solution pH. At the optimum conditions (the adsorbent dosage 0.1 g l−1, pH 7, time 30 min and the initial concentration 40 mg l−1), the percentage removal of Cd(II) was ∼96%. The surface morphology of the adsorbent showed iron particles with a cubical shape on the adsorbent, with 3–20 μm average diameter. The adsorption data was well fit by a pseudo-second order and a Langmuir isotherm, with the maximum adsorption capacity 10.42 mg/g. The adsorption process was spontaneous and endothermic. The main goal of the study is to re-use the spent coffee grounds waste and use low-cost adsorbent for cadmium (II) removal in aqueous solution. The magnetic biochar was easily manipulated by external magnetic fields after treatment. With good adsorbent performance of the magnetic biochar, spent coffee grounds could be used to treat Cd(II) contamination.

Kinetic study on the copper electroless coating on carbon nanotubes

The present work deals with the kinetics of Cu coating on carbon nanotube by electroless deposition method performed at five temperatures of 10, 25, 50, 75 and 90 °C. A theoretical model for nucleation and growth transformation based on Johnson-Mehl-Avrami equation was applied for determining the kinetics and mechanism of the process. The evolution of the Cu precipitation was assessed by the variation of Cu2+ ion concentrations in the electroless bath solution. The average Avrami exponent was acquired 1.35 which is in agreement with the grain boundary nucleation after saturation with interface controlled growth mode. It was found that raising the temperature of the solution could accelerate the reaction rate. The value of 49.9 kJ mol−1 obtained for the activation energy is of the same order as found in similar surface chemical-controlled processes. The X-ray diffraction result revealed that the crystalline structure of Cu was obtained on CNTs from the electroless process. Field emission scanning electron microscopy results were in agreement with the trends of nucleation and growth mechanism and showed that the CNTs were uniformly covered with Cu after the process. Fourier transform infrared spectroscopy test demonstrated that the functional groups formed by functionalization treatment on the surface of CNTs might act as suitable nucleation sites.

Real-time measurement system for determining metal concentrations in water-intensive processes

Abstract The main purpose of this paper is to demonstrate the potential of time-domain nuclear magnetic resonance (TD-NMR) technology for monitoring the concentrations of metal ions in water-based solutions. The main focus of this work was paramagnetic ions, such as Mn2+, Cu2+, Fe3+, Fe2+, Zn2+ and Ni2+, which are often the principal metal components in mining waters. Laboratory samples of different concentrations of single metals and mixtures of them and samples of real mining water were used in the relaxation rate (R 2) measurements. The measurements of single metal ions were used for the determination of the relaxivities of those ions. The concentrations of the ions in the mining water as a function of pH were also estimated by means of the X-ray fluorescence (XRF) method and ChemEQL software for calculating chemical speciation equilibria. Using these concentration values and the relaxivities of the metal ions, the total relaxation rate (R 2) results were then calculated. Principally, the results of these three different determinations are in relatively good agreement. It can be concluded that TD-NMR has great potential for monitoring metal ion concentrations during water treatment.

Study on the Treatment and Recovery of Acid in Steel Pickling Wastewater with Diffusion Dialysis

Steel pickling wastewater is taken as the subject. A self-made diffusion dialysis reactor is used to recover the acid in the waste fluid. The volume of the diffusion dialysis reactor is 10L and the effective membrane area of the anion exchange membrane is 150cm2. An investigation is performed for the effects of the initial pH, the initial iron concentration, the diffusion fluid flow ratio and the number of cycles of the solution on the acid recovery efficiency. The test results showed that when the concentration of iron ions in the initial solution is 20g/L, the initial pH is 1, and the liquid flow ratio is1:1.5 (dialysis chamber: diffusion chamber), the recovery rate of acid in the waste fluid can reach a maximum of 56%.

Extraction of Cobalt and Lithium from Sulfate Solution Using Di(2-ethylhexyl)phosphoric Acid/Kerosene Mixed Extractant

The solvent extraction behavior of cobalt and lithium from mixed sulfate solution using di(2-ethylhexyl)phosphoric acid (D2EHPA)/kerosene as extractant system has been investigated. The effect of different process parameters such as pH of feed solution, extractant concentration, cobalt and lithium ion concentrations in the feed solution have been studied. Extraction equilibrium constants have been calculated and found to be log Kex Co = –2.01 and log Kex Li = –2.42. The highest separation factor of 292 was achieved using 1.59 M D2EHPA at pH 1.85 from mixed sulfate solution. 93.9% of cobalt and 11.4% lithium was co-extracted from 0.01 M cobalt and lithium sulfate solution. Extraction of cobalt-lithium by D2EHPA is affected by cation exchange mechanism, cobalt is extracted as [Co(HA2)2] and [CoA2] depending on the metal concentration in the feed solution while the lithium is extracted as [Li(A2H)]. Quantitative extraction of cobalt was achieved in two-stage counter-current batch extraction (with McCabe–Thiele plot) using 0.477 M D2EHPA at an O : A phase ratio of 1. The data obtained from loaded organic and raffinate indicate a composition which reveals nearly complete extraction of cobalt and rejection of lithium resulting significant separation of these elements from mixed sulfate solution.

Selective Acid Leaching of Copper and Zinc from Old Flotation Tailings

The goal of the present work was to develop hydrometallurgical method based on acid leaching, which makes it possible to perform selective extraction of non-ferrous metals from old flotation tailings. Leaching was performed with sulfuric acid solutions (from 0.5 to 10%) and distilled water. Leaching was carried out using percolators and bottle agitator. Percolators were loaded with 100 g of old tailings, and leaching was performed with 100 mL of acid solutions. Pulp density during agitation leaching (S: L) was 1: 5. Two samples of old flotation samples were studied. The first sample of flotation tailings contained 0.26% of copper, 0.22% of zinc, and 17.4% of iron; while the second sample contained 0.36% of copper, 0.23% of zinc, and 23.2% of iron. Percolation leaching made it possible to extract up to 43 and 47% of Cu and Zn from the first sample. Extraction rate was maximum during the leaching with 1 and 2.5% sulfuric acid solutions. During the agitation leaching, the maximum extraction rate was reached with a 2.5% sulfuric acid solution (52 and 54% Cu and Zn), but the leaching rate with all solutions and distilled water differed insignificantly. Percolation leaching made it possible to extract up to 54 and 37% of Cu and Zn from the second sample of tailings, while agitation leaching made it possible to extract up to 34 and 68% Cu and Zn, respectively. The rate of non-ferrous metals extraction from the second sample with water did not differ significantly from that of obtained in the experiments with sulfuric acid solutions. In all experiments, the increase in the H2SO4 concentration led to the increase in concentrations of iron ions in productive solutions, which impedes the extraction of non-ferrous metals from solutions. Thus, it was possible to reach selective leaching of non-ferrous metals and to obtain solutions with relatively low concentrations of iron ions.

Effect of Pore Structure and Ion Concentration of Solution on the Formation of Ettringite in Composite Cement Paste

Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO42- and Al(OH)4- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.

Preliminary Study on The Development of Preconcentration Method of Cu(II), Co(II), Ni(II), and Cr(III) Ions in Water Samples Using Nanomagnetite Coated by Carboxymethyl kappa-Carrageenan (CMKC)

Flame Atomic Adsorption Spectrophotometry (FAAS) is one of the instruments that is often used to determine metal ion concentration in solution. FAAS uses simple operational procedure for metal ions concentration determination and produces accurate metal ion concentrations. Unfortunately, the accuracy of metal ion determination test decreases if the concentration of metal ions is too low, whereas the threshold for metal ions in drinking water is very low. Preconcentration is a method for increasing the concentration of metal ions in sample. An effective preconcentration method needs to be studied to improve the accuracy in the determination of metal ions concentration in water at low concentration using FAAS. This research aims to determine the effectiveness of metal ions preconcentration in water samples using nanomagnetite coated by CMKC. The research was conducted in four stages, 1) synthesis of nanomagnetite coated by CMKC; 2) preconcentration of samples containing Cu(II), Co(II), Ni(II), and Cr(III); 3) measurement of metal ion concentration with FAAS; 4) effectivity of preconcentration process and preconcentration optimum conditions. The result showed that nanomagnetite coated by CMKC can be used to preconcentration of metal ions Cu(II), Co(II), Ni(II), and Cr(III) in water samples by utilizing desorption-adsorption mechanism. Desorption was done using 0.1 N HNO3 as a desorption solvent without variation in concentration and desorption time preconcentration optimum conditions for each metal ion were as follows, adsorption condition of Ni(II) was pH 7 and 60 minutes; Cr(III) was pH 7 and 40 minutes; Co(II) was pH 7 and 60 minutes; Cu(II) pH 6 and 40 minutes. The effectiveness of preconcentration at optimum conditions for each metal ions are: %Cr(III) > %Cu(II) > % Co(II) > %Ni(II), successively.

Electrodeposition of zinc plating from zincate electrolyte using galvanostatic mode of pulse electrolysis

The process of electrodeposition of zinc plating in the galvanostatic mode of pulse electrolysis is studied. Having analyzed periodical and reference literature, we selected zincate electrolyte containing ECOMET C1 brightening additive as the research object. Based on the analysis of experimental data, we have revealed dependences of cathode current efficiency of zinc and the deposition rate of coatings on the values of current density in pulse, frequency and duty cycle of a pulse current, temperature, and the concentration of sodium hydroxide and zinc ions in solution. Using the galvanostatic mode of pulse electrolysis made it possible to increase the current density by 25%, and to reduce the concentration of brightening additives with a constant coating quality, in comparison with the stationary mode. Based on the conducted research, the modes of forming high-quality zinc plating at a speed of up to 40 μm/h are recommended.

The Characterization of Nanofet Sensor with Extended Sensing Electrode and Reference Electrode for Biosensor Application

Biosensors based on nano field-effect transistor(nanoFET) have been studied to detect from pH to biomolecules and anion in the air because its potential for label-free detection, rapid response time, low-cost and miniaturization [1-3]. The nanoFET sensor detect target species with a conductance change of nanochannel that is induced by the adsorption of charged substance or the surface potential of the sensing gate electrode. However, the sensing area on top of the nanochannel area is very small, the probability of binding of target molecules on the sensing surface of the device is very low. Therefore, we employ an electrically extended sensing electrode in order to improve adsorption probability of the charged substances and detection sensitivity. Here, we analyzed the behavior of the nanoFET sensor with an extended gate electrode and a reference electrode using pH solution of difference pH levels. It is a fundamental study to understand the behavior of nanoFET sensor with extended gate as biosensors, and it is necessary before applying it to various solution environment.Figure 1 shows the schematics of the nanoFET sensor with the extended gate electrode for pH level sensing of solution. The top gate electrode and the bottom substrate gate of the nanoFET sensor are electrically interconnected with the extended external electrode in order to increase the sensing area. The Ids-Vg characteristics of the nanoFET sensor with extended gate electrode, which is obtained by the voltage sweeping of the gate (Vg) as shown in Figure 2. The threshold voltage of the device is approximately -2.5 V. The electrode of an indium tin oxide(ITO) glass and a Ag/AgCl wire are used for the extended sensing gate electrode and the reference electrode. The connection for gate electrode and the reference electrode are compared with three cases of ITO-Ag/AgCl, Ag/AgCl-ITO and ITO-ITO respectively to compare pH response with the Ids-Vg sweep characteristics of the nanoFET sensor. In the pH sensing experiment, about 50 μL-solution having 4, 7 and 9.2 pH level are used, and it is dropped to a micro well on the extended sensing gate electrode as shown in Figure 1. Figure 3 shows Ids-Vg measurement results of varying the pH level on solution for the three connection cases of extended sensing gate electrode and reference electrode using the same device. Figure 3(a) shows Ids-Vg curve is shifted to the right side as the pH level rises in case of the reference electrode is the Ag/AgCl wire and the extended sensing gate electrode is the ITO glass. The response to pH level is shifted to left side as shown in Figure 3(b) when the electrode connection is reversed for the reference electrode and the extended sensing gate electrode with the ITO glass and the Ag/AgCl wire, respectively. In particular, it is confirmed that the nanoFET device don’t respond to the pH change of solution when both the reference electrode and the extended sensing gate electrode are the ITO glass. We finally conclude that the nanoFET sensor with the extended sensing gate electrode is affected by the surface potential in electrolyte solution induced by varying pH level. The equivalent circuit model of the nanoFET sensor is the series interconnection of two opposing electrolytic capacitors and the MOS capacitor of nanoFET device to the applied gate voltage as shown in Figure 4. Therefore, the nanoFET sensor with the extended gate electrode may not respond to the pH change or ion concentration in electrolyte solution when the interface of liquid-reference electrode is equal to interface of liquid-sensing electrode.In this study, we demonstrated experimentally the working principles of the nanoFET sensor with the extended gate electrode with the response to pH level of liquid solution. We found that the equivalent circuit model is the series connection of two opposing electrolytic capacitors in liquid solution and the MOS capacitor of the nanoFET device. The results suggest that the proper reference electrode should be utilized to measure the pH levels in liquid solution of nanoFET sensor and the other adequate reference electrode might be used to remove the effects induced by pH noise for the biosensor application such as immunosensors.This work was financially supported by the research funds (Grant No. 10076874 and No. 10077599) of the Ministry of trade, Industry and Energy, Korea[1]Matti Kaisti, Detection principles of biological and chemical FET sensors, Biosensors and Bioelectronics, 98 (2017)[2]Benjamin M. Lowe et al. Field-effect sensors-from pH sensing to biosensing: sensitivity enhancement using streptavidin-biotin as a model system, Analyst 142 (2017)[3]K.-N. Lee et al. Chemical gating experiment of a nano-field-effect transistor sensor using the detection of negative ions in air, Sens. Actuators, B 236 (2016) Figure 1

Non-linear adsorption characteristics of modified pine wood sawdust optimised for adsorption of Cd(II) from aqueous systems

Abstract The facile modification of pinewood sawdust, with maleic acid, to produce a sorbent aimed at metal ion adsorption, was tested via the batch adsorption of Cd(II) ions from aqueous solution. The sorbent was characterized for the pH of zero point charge (pHZPC), spectroscopic evaluation of the surface functionalization, structural and morphological features. Factors affecting adsorption behavior, such as adsorbent dose, pH of solution, contact time and Cd(II) ion concentration were investigated. Results obtained show the adsorption rate to be comparatively fast, with equilibrium achieved after ∼35 min. Subsequent analysis, showed Langmuirian behavior and a monolayer adsorption capacity of 180.4 mg g−1, at pH 6; while data derived from two-parameter and three-parameter isotherm models was evaluated using non-linear regression methods, with error analysis, to determine the most appropriate model and allow prediction of optimum parameters. The Sips isotherm model proved the most appropriate in describing the experimental data obtained in the study; with a low level of heterogeneity in the adsorption sites occupied suggesting the interaction of the metal ions is preferential with the added carboxylate moieties only. Additionally, the rate of adsorption was analysed using a range of kinetic models (pseudo-first-order, pseudo-second-order, Bangham and Elovich) in their non-linear forms to provide insight into the adsorption mechanism and showing pseudo-second order behavior is observed, indicating two processes are key in the adsorption process, likely diffusion to the surface and subsequent adsorption on the carboxylate moieties incorporated by chemical modification. In conclusion, the sorbent produced in this study offers high potential for the removal of Cd(II) ions from aqueous solution due to the carboxylic functionalities incorporated into the material, which is optimized by solution pH and adsorbent dose.

Continuous Sorption of Chromium Ions from Simulated Effluents using Citric Acid Modified Sweet Potato Peels

Adsorptive removal of chromium ion in aqueous medium using activated sweet potato peel (SPP) was studied in a laboratory-scale fixed bed column. Specifically, the effect of process parameters such as bed depth, flowrate and chromium ion concentration in aqueous solution, on the adsorption efficiency of the acid modified sweet potato peel was examined. Column adsorption analysis showed that at the flow rate of 0.5 cm3/min, bed height of 6 cm and column influent concentration of 30 mg/dm3, the optimum chromium (VI) ion removal of 87.5% was attained with the equilibrium adsorption capacity of 2.4548 mg/g. Continuous adsorption models such as Yoon-Nelson, Adam-Bohart and the Bed-Depth Service Time (BDST) model, were used to analyse the experimental data and based on correlation coefficient, BDST model best aligned with the obtained experimental data with correlation coefficient, R2, value of 96.43%. The bed capacity, No, and the rate constant, Ka, were calculated as 4.259 mg/dm3 and 0.01045 L/mgmin respectively at optimum column conditions. Results confirmed that acid modified SPP can be used to remove or reduce concentrations of Cr (VI) ions to allowable limits before disposal into water bodies.
 Keywords: Continuous sorption, chromium ions, sweet potato peel, kinetic isotherms, breakthrough curves

Control of solvent exposure of cationic polypeptides in anionic environment

Here we study anionic biphosphate condensation around cationic HIV-1 Tat peptide to understand interaction between charged functional groups with counter-anion. Our all-atom molecular dynamics simulations show that the counter-anion condensation around the basic functional groups and the solvent accessible surface area of the peptide show non-monotonic dependence on biphosphate concentration. There is an optimum concentration of biphosphate ions in solution where the condensation is maximum, while the solvent exposed area is minimum. Thus, we show that the solvent exposure of the macromolecule can be controlled by tuning anion concentration in the solution which may help in designing drug delivery medium.