Initial Concentration Ratio Research Articles

Ammonia removal form municipal wastewater by air stripping process: An experimental study

This study was aimed to evaluate ammonia removal efficiency (ARE) in the air stripping process in different operating conditions for wastewater with a low concentration of ammonia such as municipal wastewater treatment plants (WWTPs) on the laboratory scale. The experiments were performed at different pH (9.7 ± 0.26, 10.93±0.16 and 11.94±0.32), temperature (34.25±0.44, 38.57±3.4 and 40.5 ± 7.68 in °C), initial concentration (26.98 -47.34, 19.49 -47.48 and 41–98 in mg/L) and air-water (G/L) ratio (60:1, 70:1 and 80:1). The results showed that ARE in the operating conditions (initial NH4+concentration 26.98 -98 mg/L, pH 9.4–12.38, temperature 34–45.8 °C and G/L 60:1–80:1) was increased from 6.6% to 98% with the range of 1 to 14 h. Based on the results, ARE with 1 standard deviation (SD) increase per unit of pH, temperature and initial NH4+concentration was 13.03%, 3.99% and 2.3%, respectively. Also, based on multivariate regression model at high and low G/L, temperature and pH had the most significant effect on ARE for a synthetic solution as well as a municipal WWTPs stream, respectively. ARE (91%) was obtained during the stripping process of synthetic and actual municipal wastewater.

Molecular Weight Distribution in Ring‐Opening Polymerization of Propylene Oxide Catalyzed by Double Metal Complex: A Model Simulation

AbstractIn the present work, method of moments is used to model the molecular weight distribution (MWD) of polypropylene glycol (PPG) produced with ring‐opening polymerization of propylene oxide catalyzed by double metal complex (DMC), and an explicit expression about the polydispersity index (PDI) of PPG is obtained. The simulated results indicate that decreasing the initial concentration ratio of monomer to total chains (K1) or increasing the rate constant ratio of chain transfer to propagation (K2) leads to smaller PDI. Reducing the concentration of DMC can induce larger PDI. When the PPG's initial PDI (i.e., PDI of initiator) increases, PDI of the final PPG grows up linearly. However, with the increase of monomer conversion, PDI increases first and then decreases, that is, there is a critical conversion. The possible lack of chain transfer at the beginning of polymerization and the insufficient chain transfer caused by increased K1, decreased concentration of catalyst, and decreased K2 will cause larger PDI, namely, broad MWD.

Fabrication of MIL-53(Al)/Ag/AgCl plasmonic nanocomposite: An improved metal organic framework based photocatalyst for degradation of some organic pollutants

Metal organic framework (MOF) based MIL-53(Al)/Ag/AgCl nanocomposite (NC) was synthesized as a novel plasmonic photocatalyst via a facile reflux method. The as-prepared NC was characterized by various techniques. The photocatalytic efficiency of MIL-53(Al)/Ag/AgCl was investigated by photo-degradation of six cationic and anionic dyes. The effect of different factors including weight ratio of NCs, illumination time, and initial dye concentration on the photocatalytic performance of MIL-53(Al)/Ag/AgCl were experimentally investigated. The MIL-53(Al)/Ag/AgCl(10%) exhibited the highest catalytic performance for photo-degradation of different dye contaminants. Results indicated about 80–100% of tested dyes were removed by MIL-53(Al)/Ag/AgCl under LED-light irradiation in 90 ​min. Because of heterojunction between the Ag/AgCl nanoparticles (NPs) and MIL-53(Al), the MIL-53(Al)/Ag/AgCl NC showed higher photocatalytic ability. The results confirmed that due to some considerable features of MIL-53(Al)/Ag/AgCl such as high surface area, surface plasmon resonance effect, and recyclability, the introduced NC acts as a high performance photocatalyst for degradation of dyes in aqueous solutions.

Self-assembly of superstructures at all scales

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

In Situ Preparation of Novel Porous Nanocomposite Hydrogel as Effective Adsorbent for the Removal of Cationic Dyes from Polluted Water.

The use of some hydrogels as adsorbents for pollutants removal from wastewater is limited due to their high swelling properties and the difficulty in recovering them after the adsorption process. To overcome these problems, a new hydrogel nanocomposite based on chitosan-grafted-polyacrylic acid/oxidized electrospun carbon nanofibers (CT-g-PAA/O-ECNFs) was prepared by an in situ grafting polymerization process. The prepared hydrogel nanocomposite was used as a novel effective and highly reusable adsorbent for the removal of methylene blue (MB) from polluted water with low cost. The morphology and the structure of CT-g-PAA/O-ECNFs were investigated by numerous techniques. The effect of incorporating O-ECNFs on the swelling capability of the prepared hydrogel was explored in distillated water and MB solution at normal pH. The effect of parameters including ratio of O-ECNFs, contact time, pH, initial concentration, and temperature on adsorption process were explored. The adsorption isotherm and kinetic were studied by numerous non-linear models. The obtained results confirmed that the incorporation of O-ECNFs into the hydrogel network decreased the swelling capacity and improved its ability towards MB dye removal. The adsorption process depended on the pH value of the dye solution. Additionally, the adsorption and kinetic results were fitted using the Freundlich isotherm model and pseudo second order model (PSO), respectively. Moreover, the new adsorbents can be recycled for at least five cycles keeping its adsorption capacity and can be easily recovered without loss in its initial weight.

Self-Assembly of Fluorescent Photonic Crystal Structures in Binary Water–Glycerol Solvent Droplets

The morphology of photonic-crystal structures formed by the self-assembly of fluorescent marker nanoparticles from evaporating droplets of a binary water–glycerol solvent, the components of which differ appreciably from each other in the viscosity and evaporation rate, being infinitely mutually soluble under normal conditions, was has been studied experimentally for the first time. It has been shown that the main self-assembly disordering factor is Marangoni vortex flows, and the change in the initial concentration ratio between binary mixture components enables the control over the degree of disordering in the solid phase, which is formed after the solvent is evaporated from a droplet and distributed over the substrate. A low initial concentration of any component corresponds to the most ordered distribution, whereas their medium concentrations correspond to the most disordered distribution. The characteristic values of Marangoni numbers in experiments have been calculated. It has been demonstrated that the average radius of the distribution of an ensemble of marker particles over a substrate may serve as a descriptor for the degree of ordering.

In Situ Electrochemical Study of the Coexistence of Eu3+ and Eu2+ in Molten LiCl-KCl by Rotating Disc Electrode

In this study, a graphite rotating disc electrode was successfully designed and applied to conduct electrochemical measurements under flow conditions in molten LiCl-KCl at 773 K. The concentration and diffusion coefficients of Eu3+ and Eu2+ in molten salt were quantitatively measured with this electrode by applying in situ cyclic voltammetry and chronoamperometry techniques. The initial concentration ratio of Eu3+/Eu2+ in LiCl-KCl-0.5 wt% EuCl3 was calculated to be 2.37. The calculated diffusion coefficients of Eu3+ and Eu2+ in the salt were 9.31 ± 0.06 × 10−5 cm2 s−1 and 9.65 ± 0.6 × 10−5 cm2 s−1, respectively. A decrease of the diffusion coefficient of Eu3+ and Eu2+ was observed at a higher concentration of EuCl3, which implies the enhanced Eu-Eu ion interaction. This electrode design is expected to be utilized for the concentration measurement of multivalent ions in a flowing molten salt.

A research into sorption properties of peat briquettes used to remove ions of cadmium, lead and copper from wastewaters

Introduction. At present, the following areas are the subject of intensive research: methods for removing such toxic metals as cadmium, lead, copper, etc. from wastewaters, namely, using new composite sorbents for this purpose; improvement of ion exchange treatment and, for example, sedimentation of sulphides or oxalates; wood ash sorption; biosorption onto plants. It is a future-oriented trend to use peat as a sorbent in a wastewater treatment technology. Extensive peat deposits in the Republic of Belarus can contribute to production of cheap, environmentally friendly sorbents made of modified peat briquettes. The mission of this work is to study the sorption properties of peat briquettes used to remove cadmium, lead and copper ions from wastewater.
 Materials and methods. Physicochemical, technological, mathematical methods are employed.
 Results. The co-authors studied the kinetics of cadmium Cd+2, lead Pb+2, and copper Cu+2 ions sorption onto peat briquettes. They identified that the bigger the grain of peat briquettes, the less efficient the sorption. The sorption process is intensive: it takes cadmium Cd+2, lead Pb+2, and copper Cu+2 ions five minutes to get extracted from the solution; extraction efficiency reaches 91.11; 96.96 and 88.39 %, respectively. 20 minutes is enough to reach degree of equilibrium F = 0.98 for cadmium Cd+2 and lead Pb+2 and F = 0.96 for copper Cu+2. F is equal to 0.99 for all ions in 40 minutes. The multiplicity of extraction, or the ratio of initial concentration to equilibrium concentration reaches 114 for cadmium ions Cd+2, 162 for lead ions Pb+2, and 93 for copper ions Cu+2. In case of saturation, sorption capacity reaches the following values: Сd+2 — 0,0778 mmol/g (8.75 mg/g), Pb+2 — 0.8205 mmol/g (170.00 mg/g), Cu+2 — 2.707 mmol/g (172 mg/g). The co-authors used equations of diffusion and chemical kinetics to establish that the sorption process proceeds in the diffusion mode, and the stage of chemical interaction of metal ions with functional groups of peat contributes to the overall velocity of the process.
 Conclusions. Peat briquettes represent an effective sorbent used to remove cadmium Cd+2, lead Pb+2, and copper Cu+2 ions from wastewater. The sorption process is almost over in 20 minutes.

Understanding monoacylation of symmetrical diamines: A kinetic study of acylation reaction of m-phenylenediamine and benzoic anhydride in microreactor

Monoacylated symmetrical diamines are building blocks or intermediates of several well-established drugs. However, for the symmetrical diamines, the two amine groups located in a similar chemical environment make the selective monoacylation rather difficult and no kinetics study has ever been reported before. To comprehend this kind of reaction more deeply, a continuous flow microfluidic system was developed to evaluate the reaction kinetics of m-phenylenediamine and benzoic anhydride. At first, the reaction order of each reactant, pre-exponential factors and activation energies were determined in turn. The possible reaction mechanism was postulated from the reaction order. Then, a series of validation experiments were designed to show the accuracy and the applied range (concentration and temperature) of the kinetic model. Next, to obtain a controlled selectivity, the effects of initial concentration, reaction temperature and molar ratio on the selectivity were investigated through the model simulation. In the end, under the conditions optimized by the kinetic model, 96.9% selectivity and 92.5% yield were obtained in the microreactor.

Lithium recovery from effluent of spent lithium battery recycling process using solvent extraction

A novel process of lithium recovery from effluent of spent lithium batteries recycling by solvent extraction was proposed. The β-diketone extraction system used in the experiment was composed of benzoyltrifluoroacetone (HBTA), trioctylphosphine oxide (TOPO) and kerosene. The effective parameters such as solution pH value, saponification degree, initial lithium concentration and phase ratio were evaluated by experiments. More than 90% of lithium could be extracted by saponified organic phase through three-stage countercurrent extraction. The loaded organic phase was first eluted by dilute HCl solution to remove nontarget sodium, and then stripped by 6 mol/L HCl at a large phase ratio to obtain lithium-rich solution with 4.322 mol/L lithium. The lithium-rich solution from the process could be used to prepare lithium carbonate or lithium chloride. The stripped organic phase can be recycled and no crud or emulsification was observed during the process. The extraction mechanism of HBTA-TOPO was investigated via FT-IR spectroscopy, and the results indicated the two extractants showed strong synergistic effect. The thermodynamic study revealed lithium extraction is an exothermic process, which meant lower temperature promotes extraction of lithium.This work provided a novel approach to recover lithium from effluent of spent lithium battery recycling.

Spatial and temporal distribution, degradation, and metabolism of three neonicotinoid insecticides on different parts, especially pests' target feeding parts of apple tree.

Neonicotinoid insecticides (NIs) have been recently banned in some countries because of increased pest resistance and deleterious risks to non-target organisms. Recent studies considered all parts of crops as a whole part in plant protection. However, there are few reports focused on the distribution and metabolic trends of NIs on target feeding sites of different pests in apple orchards. The spatial and temporal distribution, absorption, degradation, and metabolism of three NIs, imidacloprid, acetamiprid, and thiamethoxam, on different parts of apple trees were studied under foliar spray and root irrigation treatments. In the spray treatment, the initial average concentration ratios (TCRs) were 31.6% for lower shoots, 23.3% for upper leaves, 23.2% for upper shoots, 21.0% for lower leaves, and 0.5% and 0.4% for upper and lower fruits, respectively. The average half-lives of the three NIs were 2.9 days for shoots, 7.4 days for leaves, and 10.8 days for fruits. The degradation rate of shoots was 2.5 times that of leaves, and 3.6 times that of fruits. Imidacloprid olefin and N-methyl acetamiprid were two of the main metabolites. In the root treatment, both roots and soils had high TCRs during the whole sampling period. Only imidacloprid was transmitted to above-ground parts of the plants, with TCRs of 0.38-50.94%. This study found significant differences in spatial and temporal distribution, degradation, metabolism, and trends of NIs on different pest target sites of apple trees. The data obtained may help promote scientific control of target pests and evaluation of safety for non-target species in orchards. © 2020 Society of Chemical Industry.

Development of a Surfactant-Containing Process to Improve the Removal Efficiency of Phenol and Control the Molecular Weight of Synthetic Phenolic Polymers Using Horseradish Peroxidase in an Aqueous System.

To reduce phenolic pollutants in the environment, many countries have imposed firm restrictions on industrial wastewater discharge. In addition, the current industrial process of phenolic resin production uses phenol and formaldehyde as the reactants to perform a polycondensation reaction. Due to the toxicity of formaldehyde and phenolic pollutants, the main purpose of this research was to design a green process using horseradish peroxidase (HRP) enzymatic polymerization to remove phenols and to produce formaldehyde-free phenolic polymers. In this study, the optimal reaction conditions, such as reaction temperature, pH, initial phenol concentration and initial ratio of phenol, and H2O2, were examined. Then, the parameters of the enzyme kinetics were determined. To solve the restriction of enzyme inactivation, several nonionic surfactants were selected to improve the phenol removal efficiency, and the optimal operation conditions in a surfactant-containing system were also confirmed. Importantly, the molecular weight of the synthetic phenolic polymers could be controlled by adjusting the ratio of phenol and H2O2. The content of biphenols in the products was almost undetectable. Collectively, a green chemistry process was proposed in this study and would benefit the treatment of phenol-containing wastewater and the production of formaldehyde-free phenolic resin in the future.

Synthesis of Chitosan-Ignosulfonate Composite as an Adsorbent for Dyes and Metal Ions Removal from Wastewater.

Sodium lignosulfonate is a polymer with extensive sources and abundant functional groups. Therefore, it has potential value for research and wide utilization. In this study, the adsorption material was prepared by blending sodium lignosulfonate and chitosan, which could adsorb anionic and cationic dyes and metal ions. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetry (TG). The results showed that the composite was cross-linked mainly by the strong electrostatic interaction between the protonated amino group in chitosan and the sulfonate group in sodium lignosulfonate. Moreover, the effects of initial concentration, adsorption time, initial pH, and mass ratio of chitosan to sodium lignosulfonate on the adsorption performance of the composite were investigated. Meanwhile, the adsorption processes were agreed well with the pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption mechanism was that the electrostatic interaction between the protonated amino and hydroxyl groups of the composite with anionic (SO3–) and HCrO4– groups of Congo red and Cr(VI), respectively. In addition, the electrostatic interaction between SO3– of the composite and positively charged group of Rhodamine B played an important role in the adsorption of Rhodamine B.

Obtain and Application of Surface-active Substance on the Base of Products Refination of Cotton Seed Oil

The article the results of investigation on obtaining of surface-active substance -SAS on the waste cotton oil for drilling of wells and intensification of the flotation process are presented. The main component of new SAS are waste, cotton oil refinery and chemical plants. SAS have hudrophobization (waterproof) action on easy-swelling rocks (clays, argellites, alevrolits). Direct water emulsions obtained from reagents have low viscosity, high stability and low filtration index. There reagents have influence at drilling tools (that is they increase the life of drilling bits and diamond bits) [1, 2]. The study flotation enrichments of copper-molybdic ore is revealed characteristic foam-former and collector surface-active substances (NA-1) and is simulation one oily provided creation without minerals fields extraction of gold and color metals has been determined. Optimal conditions of the syntheses: ratio of main components, time of reaction, temperature and concentration have been determined. The comparison of new SAS with other foreing analogies was carried out. The main colloidal-chemical characteristic of synthesized SAS: surface activity, adsorption, viscosity, concentration of micelle- formation have been determined. Technology of obtain of anion surfaceactive substances from local organic raw material was elaborated, which by qualitative characteristics is a substitute of the import reagent collector and foam-former [4, 5]. Dependence on obtained product from the temperature of the process, time of reactions, ratio of initial components optimal concentration of NaOH was investigated. The foam forming ability of the new reagents in comparison with standard reagent T-92 was determined and it was shown that by best ability of forms destruction the methyl syloxane’s liquid and mineral oil have possessed.The intensifications of the process of flotation’s enrichment of copper-molybdic ore with using new obtain reagent NA-1 was offered.

Dynamics of A+B→C reaction fronts under radial advection in three dimensions.

The dynamics of A+B→C reaction fronts is studied both analytically and numerically in three-dimensional systems when A is injected radially into B at a constant flow rate. The front dynamics is characterized in terms of the temporal evolution of the reaction front position, r_{f}, of its width, w, of the maximum local production rate, R^{max}, and of the total amount of product generated by the reaction, n_{C}. We show that r_{f},w, and R^{max} exhibit the same temporal scalings as observed in rectilinear and two-dimensional radial geometries both in the early-time limit controlled by diffusion, and in the longer time reaction-diffusion-advection regime. However, unlike the two-dimensional cases, the three-dimensional problem admits an asymptotic stationary solution for the reactant concentration profiles where n_{C} grows linearly in time. The timescales at which the transition between the regimes arise, as well as the properties of each regime, are determined in terms of the injection flow rate and reactant initial concentration ratio.

Enhanced Population Control in a Synthetic Bacterial Consortium by Interconnected Carbon Cross-Feeding.

Engineered microbial consortia can provide several advantages over monocultures in terms of utilization of mixed substrates, resistance to perturbations, and division of labor in complex tasks. However, maintaining stability, reproducibility, and control over population levels in variable conditions can be challenging in multispecies cultures. In our study, we modeled and constructed a synthetic symbiotic consortium with a genetically encoded carbon cross-feeding system. The system is based on strains of Escherichia coli and Acinetobacter baylyi ADP1, both engineered to be incapable of growing on glucose on their own. In a culture supplemented with glucose as the sole carbon source, growth of the two strains is afforded by the exchange of gluconate and acetate, resulting in inherent control over carbon availability and population balance. We investigated the system robustness in terms of stability and population control under different inoculation ratios, substrate concentrations, and cultivation scales, both experimentally and by modeling. To illustrate how the system might facilitate division of genetic circuits among synthetic microbial consortia, a green fluorescent protein sensitive to pH and a slowly maturing red fluorescent protein were expressed in the consortium as measures of a circuit's susceptibility to external and internal variability, respectively. The symbiotic consortium maintained stable and linear growth and circuit performance regardless of the initial substrate concentration or inoculation ratio. The developed cross-feeding system provides simple and reliable means for population control without expression of non-native elements or external inducer addition, being potentially exploitable in consortia applications involving precisely defined cell tasks or division of labor.

Feasibility of high silica ZSM-5 recovery by ozone with sulfamethoxazole removal from water

This work assessed the feasibility of recovering exhausted high-silica ZSM-5 for the first time. High-silica ZSM-5 (HSZSM-5) loaded with sulfamethoxazole (SMX) was regenerated by water-dissolved ozone. Results showed that 97% recovery of adsorption capacity of regenerated HSZSM-5 was obtained at 2.54 mg/L of ozone after 15 min reaction. Lower SiO2/Al2O3 ratio of HSZSM-5 and initial SMX concentration had a higher recovery ratio of adsorption capacity of regenerated HSZSM-5. The sequential HSZSM-5 adsorption (AD) and ozone oxidation (OZ) experiments were also performed to investigate the effect of pH on the regeneration efficiency of loaded HSZSM-5 and the regeneration mechanism was characterized by fourier-transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. No degraded isoxazole ring of SMX adsorbed in the sinusoidal channels of HSZSM-5 was responsible for the decreased recyclability of HSZSM-5. Higher ozone activity of deprotonated SMX at higher pH (>pKa2) favored the HSZSM-5 regeneration. High silica zeolite-based sequential AD-OZ process may be a sustainable way for the removal of organic micropollutants from water.

Effects of Ca2+ initial concentration on Cu2+ selective adsorption from aqueous solution by modified sugarcane bagasse under batch and column condition

ABSTRACT Tetraethylenepentamine (TEPA) modified sugarcane bagasse (SCB), as a potential biosorbent to selective removal of Cu2+ from high calcium-containing wastewater, was prepared and characterised. Adsorption performances of the modified SCB toward Cu2+ were investigated, and effects of Ca2+ under different initial concentration on Cu2+ adsorption were carried out under both batch and dynamic conditions. Results showed that adsorption isotherm of Cu2+ on modified SCB fitted Sip isotherm model well, and the optimum pH range for Cu2+ adsorption was from 4.0 to 6.0. Dynamic adsorption of Cu2+ on the modified SCB fixed-bed column showed a typical S shape breakthrough curve, which could be predicted well by Bohart-Adams model. Competitive adsorption results in the binary system showed that molar ratio of Cu2+ and Ca2+ adsorbed on the modified SCB was 36.0:1, 15.0:1, 10.7:1, 7.8:1, 6.6:1 and 4.7:1 at of initial concentration ratio of these two metal ions 1:25 1:50 and 1:100 under batch condition, while that was 110:1, 41.7:1, 32.5:1, 27.0:1, 20.9:1 and 16:1 under dynamic condition. Operating at dynamic condition was better than batch condition for Cu2+ selective removal by the modified SCB. Wastewater treatment results showed that the TEPA modified SCB fixed-bed column could recycle Cu2+ from high calcium-containing aqueous solution, and it had great potential in practical application.

Separation of adjacent rare earth elements enhanced by “external push-pull” extraction system: An example for the separation of Pr and Nd

Separation of adjacent rare-earth elements, such as Pr and Nd, is extremely difficult due to the similarity in their physicochemical properties. Enhanced separation of adjacent rare-earth elements based on the “push-pull effect” by addition of water-soluble complexing agents was an effective strategy in traditional organic-aqueous two-phase extraction. However, environmental pollution is serious due to the residual of complexing agent in the extraction raffinates. In present work, a novel “external push-pull” extraction system, composed of three coexisting liquid phases, P507 organic phase, ionic liquid (tributyl-methyl ammonium nitrate, N4441NO3)-rich phase and NaNO3 aqueous solutions, is suggested to improve the separation between Pr and Nd. It is revealed that Nd and Pr can be enriched respectively into the P507 organic top phase and N4441NO3-rich ionic liquid middle phase in the external push-pull extraction system, owing to a so-called “external push-pull effect” from a reversed extraction selectivity of P507 organic phase and N4441NO3 ionic liquid-rich phase towards Nd and Pr, respectively. Compared to traditional organic-water two-phase systems, the separation factor of Pr to Nd in the suggested external push-pull extraction system could increase obviously to 3.5 or even more. Various effects from the aqueous pH, NaNO3 concentration, the initial concentration ratios of Pr to Nd in feed aqueous solutions, and the addition amount of N4441NO3, the volume of P507 organic phase on the separation between Pr and Nd are discussed. In addition, reversal extraction of rare earth ions in the ionic liquid-rich phase is found to be closely related to the complexation behavior of rare earth ions with NO3− ions by using molecular dynamic simulations. Based on this work, a possibility for extraction and separation of 14 rare-earth element ions from their coexisting aqueous solutions using the suggested external push-pull extraction system is also explored. The present work highlights a novel green strategy for improving the separation of adjacent rare-earth elements.

On the Kinetics and Mechanism of the Thiourea Dioxide–Periodate Autocatalysis-Driven Iodine-Clock Reaction

The thiourea dioxide-periodate reaction has been investigated under acidic conditions using phosphate buffer within the pH range of 1.1-2.0 at 1.0 M ionic strength adjusted by sodium perchlorate. Absorbance-time series are monitored as a function of time at 468 nm, the isosbestic point of the I2-I3- system. The profile of these kinetic runs follows either sigmoidal-shaped or rise-and-fall traces depending on the initial concentration ratio of the reactants. The clock species iodine appears after a well-defined but reproducible time lag even in substrate excess, meaning that the system may be classified as an autocatalysis-driven clock reaction. It is also demonstrated that the age of the thiourea dioxide solution markedly shortens the Landolt time, suggesting that the original form of thiourea dioxide (TDO) rearranges into a more reactive form and reacts faster than the original one. The behavior found is consistent with that recently observed in other oxidation reactions of TDO. To characterize the system quantitatively, a 22-step kinetic model is constructed from adapting the kinetic model of the TDO-iodate reaction published recently by supplementing it with six different reactions of periodate. By the help of seven fitted rate coefficients a sound agreement between the measured and calculated absorbance-time traces is obtained.