Initial Fast Reaction Research Articles

Resolving Fast Relative Kinetics in Inorganic Solid-State Synthesis.

Solid-state syntheses are generally regarded as being slow, limited by transport, and, as such, are often only stopped to check the products after many hours at high temperature. Here, using a custom-designed reactor to rapidly initiate solid-state syntheses, we are able to capture the earliest stages of a reaction using in situ X-ray scattering. For the reaction of TiO2 and Li2CO3 to form spinel lithium titanate (Li4Ti5O12)─an anode material for fast-charging applications─we capture two distinct kinetic regimes, including fast initial kinetics in the first seconds-minutes of the reaction that account for significant product formation. We use an Avrami model to compare the reaction at high temperatures (700-750 °C), which results in the rapid formation of Li4Ti5O12 within minutes, and lower temperatures (482 °C), consistent with conditions that might be chosen based on "Tamman's rule", a common heuristic. Our analysis reveals characteristic Avrami slopes (i.e., dimensionalities) for each step in the chemical transformation. We anticipate that the fast initial reaction kinetics found here are likely to be common in the synthesis of other materials used in battery electrodes, solid-state electrolytes, ion-conductive membranes, etc. where ion transport is a prerequisite for functionality.

Mutual Activation of Two Radical Trapping Agents: Unusual "Win-Win Synergy" of Resveratrol and TEMPO during Scavenging of dpph• Radical in Methanol.

The reaction of the 2,2'-diphenyl-1-picrylhydrazyl radical (dpph•) with resveratrol in methanol (kMeOH = 192 M-1 s-1) is greatly accelerated in the presence of stable nitroxyl radical TEMPO• (kmixMeOH = 1.4 × 103 M-1 s-1). This synergistic effect is surprising because TEMPO• alone reacts with dpph• relatively slowly (kS = 31 M-1 s-1 in methanol and 0.03 M-1 s-1 in nonpolar ethyl acetate). We propose a putative mechanism in which a mutual activation occurs within the acid-base pair TEMPO•/RSV to the resveratrol (RSV) anion and TEMPOH•+ radical cation, both being extremely fast scavengers of the dpph• radical. The fast initial reaction is followed by a much slower but continuous decay of dpph• because a nitroxyl radical is recovered from the TEMPOnium cation, which is reduced directly by RSV/RSV- to TEMPO• or recovered indirectly via a reaction with methanol, producing TEMPOH subsequently oxidized by dpph• to TEMPO•.

Effective degradation of Direct Red 81 using FeS-activated persulfate process

As a burgeoning advanced oxidation process (AOP), heterogeneous activation of persulfate (PS) for synthetic refractory contaminants decontamination has recently received much attention. In this study, FeS was selected as a heterogeneous PS activator to facilitate the degradation of a typical recalcitrant contaminant of diazo dye Direct Red 81 (DR 81). The results showed that approximately 95% of 0.03 mM DR 81 was removed within 60 min with FeS and PS doses of 1.5 × 10−3 M. The efficient decomposition of DR 81 by the FeS/PS system was assumed to be mainly attributed to the highly reactive SO4−• and •OH, which was related to PS cleavage by both dissolved Fe2+ leached from FeS and Fe2+ bound on the FeS surface. Except for strongly alkaline conditions, DR 81 decolorations by FeS/PS were insignificantly affected by operational parameters such as temperature, initial solution pH, and rotate speed. Meanwhile, the presence of five inorganic anions being studied had distinct impacts on DR 81 degradation and followed a strict order of NO3− < Cl− < SO42− < CO32− < PO43−. However, FeS/PS system was highly adaptable, and FeS, which is used as a PS activator was more stable. GC/MS and TOC data revealed that thorough mineralization of DR 81 by PS/FeS in an initial fast reaction phase to transform DR 81 to aromatic intermediates, followed by a slow reaction phase that mineralized these organic intermediates into carboxylic acids and carbon dioxide through further oxidation.

Biochar Chemistry in a Weathered Tropical Soil: Kinetics of Phosphorus Sorption

The phosphorus (P) chemistry of biochar (BC)-amended soils is poorly understood. This statement is based on the lack of published research attempting a comprehensive characterization of biochar’s influence on P sorption. Therefore, this study addressed the kinetic limitations of these processes. This was accomplished using a fast pyrolysis biochar made from a mix of waste materials applied to a highly weathered Latossolo Vermelho distrofico (Oxisol) from São Paulo, Brazil. Standard method (batch method) was used. The sorption kinetic studies indicated that P sorption in both cases, soil (S) and soil-biochar (SBC), had a relatively fast initial reaction between 0 to 5 min. This may have happened because adding biochar to the soil decreased P sorption capacity compared to the mineral soil alone. Presumably, this is a result of: (i) Inorganic phosphorus desorbed from biochar was resorbed onto the mineral soil; (ii) charcoal particles physically covered P sorption locations on soil; or (iii) the pH increased when BC was added SBC and the soil surface became more negatively charged, thus increasing anion repulsion and decreasing P sorption.

Chlorine immobilization and performances of cement paste/mortar with C-S-Hs-PCE and calcium chloride

Friedel’s salt usually forms in cement paste with CaCl2, however, it is still uncertain whether calcium silicate hydrate seed - polycarboxylate (C-S-Hs-PCE) promotes the formation of Friedel's salt, especially improves the performances of cement paste/mortar with CaCl2. Therefore, in this study, X-ray diffraction (XRD) and differential thermal analysis (DTA) were used to quantify the Friedel’s salt content in pastes with different contents of C-S-Hs-PCE and CaCl2. Simultaneously, their setting times and compressive strengths at 1, 3 and 28 days were comparatively analyzed and the pore size distributions, hydration and chemical shrinkages of all pastes were also carried out to investigate the relative mechanism. The results reveal that C-S-Hs-PCE promotes the formation of Friedel's salt in paste with CaCl2, but this promotion is related to the contents of C-S-Hs-PCE and CaCl2. C-S-Hs-PCE hardly influences the compressive strengths at 1, 3 and 28 days of mortars with less than 2% CaCl2, however, 2% C-S-Hs-PCE significantly improves the compressive strength of mortar with 2% CaCl2. It is worth noting that it increases the specific surface area of pore in paste with CaCl2, but it decreases the volume and average diameter of pore in it. More importantly, it still enhances the heat flow in the initial fast reaction, first deceleration and induction periods of paste with CaCl2. It also advances the merged main exothermic peak and enhances the heat flow at this merged peak. It does not increase the hydration heat during 72 h, but 1–2% C-S-Hs-PCE promotes the hydration of paste with CaCl2 during 72–168 h. It leads to the further decrement in the setting times of paste with CaCl2 for the hydration promotion in the initial fast reaction, first deceleration and induction periods.

Atomistic mechanisms study of the carbonation reaction of CaO for high-temperature CO2 capture

Ca-Looping is a promising technology for capturing CO2. Here, ReaxFF molecular dynamics simulations combined with thermogravimetric analysis (TGA) were employed to provide atomic-level insights into the carbonation reaction of CaO with CO2. Results showed that two fast kinetic stages appear when the temperature increases. To understand this phenomenon, the diffusion, structural evolution as well as the carbonates accumulation were analyzed. It was found that the recovery of the initial fast reaction rate largely stems from the formations of pyrocarbonate anion. On CO2-CaCO3 interface, the solid product molecules are continuously propagated and joined in the existing C2O52− phase with multiple instances of formation and dissociation. Furthermore, surface carbonates can combine with crystal oxygen in the form of metastable corner-linked CO44− tetrahedron to diffuse inward the CaO particle. The increase of temperature greatly accelerates the formation of outer polymeric phases of CO2-CO32− and diffusion of inner CO32−, causing more CO2 molecules to be adsorbed and the carbonation reaction rate rises sharply.

Hydrothermal liquefaction of wood using a modified multistage shrinking-core model

Wood liquefaction in hot compressed water is modeled using the hydrolysis of Cellulose, Hemicellulose, and Lignin. These three components are reacted under catalyst-free subcritical conditions in a temperature range from 553 K to 640 K, and the heating rate ranges from 2 K/min to 6 K/min. Using a simplified reaction scheme, water-soluble products11WSP: - Water soluble products (WSP), Biocrude, char, and gas are generated through intermediates with each wood component. A modified multistage shrinking core model is employed to simulate biomass particle degradation. The reaction and kinetic regime of the hydrothermal liquefaction22HTL: -Hydrothermal Liquefaction (HTL) process are treated separately for each wood component. Although the lack of initial fast reaction kinetic data limits the development of more accurate models, computed results displayed a generous fit to data from the literature. At 593 K for a 2 K/min heating rate and particle size of 0.08 mm, biocrude shows the maximum yield of 26.87% for wood liquefaction. Although lower heating rates show fast initial lignin hydrolysis, for longer residence times, and close to the critical point, yield outputs show similar yields. Meanwhile, char and gas yields of cellulose model show maximums of 55 wt% and 25 wt% respectively at 640 K with a 2 K/min heating rate. Nevertheless, char yield values become very similar at 640 K for different heating rates for the cellulose hydrolysis model. Both cellulose and lignin hydrolysis models show better hydrolysis with smaller particle sizes. Besides, lignin decomposition shows more dependence on the particle size, where it decomposes much faster with 0.08 mm particle and slower than Cellulose with the 1 mm particle.

Insight into the role of polyacrylamide polymer powder on the cracking in plastic period of cement mortar

It is still uncertain whether polyacrylamide polymer powder can restrain the cracking of cement mortar in the plastic period and the mechanisms, which are responsible for this role, still need to be systematically clarified. Thus the different contents of the polyacrylamide polymer powder were mixed and various pastes with polyacrylamide were prepared. The cracking behaviors and water evaporation losses of mortars were evaluated. The bleeding percentages, chemical shrinkages, ions concentrations, ultraviolet visible spectra and the characteristics of hydration heat liberations of cement pastes with polyacrylamide polymer powder were investigated to carry out the insight into the role of polyacrylamide polymer powder on the cracking of cement paste in the plastic period. The experimental results indicate that the polyacrylamide polymer powder improves the mortar resistance to the cracking in the plastic period. It decreases the water evaporation loss and bleeding percentage. But it enhances the chemical shrinkage and the increased chemical shrinkage is mainly attributed to the role of polyacrylamide polymer powder on the promotion of cement hydration in the tested ages, especially in the initial fast reaction and the first deceleration periods. The existence of the intermolecular hydrogen bonds is the main reason for lowering the water evaporation loss and bleeding percentages. Acting forces from the intermolecular hydrogen bonds may be additional contributor to the improved resistance to the cracking of cement mortar in the plastic period. The results from this work will provide a reference for the alleviation of the plastic cracking of cement based paste.

Differences between their influences of TEA and TEA·HCl on the properties of cement paste

It is still uncertain whether there are some differences between their influences of TEA and TEA·HCl on the properties of cement paste. Thus, this work aimed to evaluate the differences between their influences of TEA and TEA·HCl on the properties of cement paste. Then the cement pastes or mortars with 0%, 0.01%, 0.015%, 0.02%, 0.06%, 0.10%, 0.20%, 0.50% and 1.00% TEA and TEA·HCl respectively were prepared and their setting times and compressive strengths were investigated. Meanwhile, the chemical shrinkage, pore size distributions, hydration heat releases, thermogravimetric (TG) characteristics and microstructures of vaious pastes were studied to explore the mechanisms that are responsible for these differences. The results show that less than 0.2% TEA·HCl reduces the initial setting time more significantly, whereas 0.02%, 0.06% and 0.1% TEA·HCl are inclined to shorten the finial setting time as comparing with the same content of TEA. Less than 0.1%, 0.02% and moderate TEA·HCl more significantly enhance the compressive strengths at 3 d, 7 d and 28 d respectively in comparison to the same content of TEA. These pastes with less than 0.2% TEA·HCl have the greater chemical shrinkage at 24 and 72 h, the cement pastes with less than 0.02% TEA·HCl provide the greater rate of hydration liberation in the initial fast reaction period, these pastes with 0.2% TEA·HCl display the more significantly increaseed rate of hydration heat liberation in the acceleration period as well as the more total hydration heat liberation at 72 h, as comparing with the cement pastes with same content of TEA. Besides, TG result indicates that these hardened pastes with TEA·HCl form the more CH at 3 d, whereas these hardened pastes with less than 0.06% TEA have the more CH at 28 d. These hardened pastes with 1%, 0.2% and 0.5% TEA·HCl have the relatively less pore voume as compared with the pastes with same contents of TEA at 28 d. The result of the scanning electron microscope (SEM) image shows that in the presence of same content of TEA and TEA·HCl, TEA·HCl is more liable to alter AFt and CH morphology. These discriminative results in the chemical shrinkage, pore sizes distribution, hydration heat release, TG and SEM provide an envience for the differences between their influences of TEA and TEA·HCl on the properties of cement paste. These results will provide a reference for the selective use of TEA and TEA·HCl as an accelerator.

Ternary complexes containing Copper(II), l-Valinate and α, ά-bipyridyl or 1,10-phenanthroline: Synthesis, characterization, ligand substitution and oxidase biomimetic catalytic activity studies

Ternary copper(II) complexes with the molecular formulae of [CuIILL′]X or [CuIILL′X]; L = l-Valinate; L′ = α, ά-bipyridyl or 1,10 - phenanthroline and X is Cl¯, Br¯, NO3¯, AcO¯, ½SO42− or ClO4¯ were synthesized. Elemental and thermal analysis in addition to electrochemical (molar conductance and cyclic voltammetry), magnetic moment measurements as well spectral (FT-IR, UV–Vis and ESR) techniques were used to characterize the complexes. The spectroscopic results suggested square pyramidal and square planar geometries for the five- and four-coordinate complexes respectively. Powder X-ray diffraction spectral data along with the structure solution program Expo 2014 has been used for structural elucidation of the sulfato complexes 1 and 5. Stopped follow technique was employed to study the substitution of the nonelectrolytic coordinately counter anion ligand by using thiourea (TU) as a function of nucleophile and a biphasic process is proposed. An initial fast reaction is followed by a slower one and the initial one was found to be counter ion dependent. Bio-mimicking the multicopper oxidase enzyme such as catechol oxidase and phenoxazinone synthase is a further goal of the present study. Catalytic examinations displayed that the present complexes are promising candidates as functional mimic of the examined enzymes and the probable mechanistic catalytic sequences are discussed.

A general stirred-flow model for time-dependent adsorption and desorption of heavy metal in soils

Quantitative understanding of kinetics and mechanisms heavy metal adsorption-desorption and transport processes, batch and stirred-flow experiments were carried out with vanadium (V) and molybdenum (Mo) on soils at different reaction conditions and time scale. Batch experiments indicated that adsorption of V and Mo on soils was highly nonlinear and time-dependent, where V and Mo retention showed typical biphasic reaction kinetics. The stirred-flow experiments showed that both V and Mo adsorption consisted of a fast initial reaction, as indicated by the fact that effluent solute concentration was close to zero for the first few minutes. A stirred-flow multi-reaction model (MRM) which accounts for slow as well as fast reactions of the reversible and irreversible type was developed to describe V and Mo adsorption and desorption processes on soils. Based on model simulations and experimental tracer breakthrough curves (BTCs) results, we concluded that the proposed model is valid for stirred-flow conditions. The strong retardation and slow release behaviors of V and Mo from stirred-flow experiments were successfully described using the proposed stirred-flow MRM where retardation and irreversible reactions were necessary. Our work provides a general stirred-flow model which is capable of describing reactive and non-reactive solutes.

Square planar versus square pyramidal copper(II) complexes containing N3O moiety: Synthesis, structural characterization, kinetic and catalytic mimicking activity

In quest of copper complexes having [CuN3O] cores, [Cu(phen)(l–Val)(H2O)]NO3 (1) and [Cu(bpy)(l–Val)]ClO4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). Complex 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structures of 1 and 2 have supramolecular networks formed via inter- and intra-molecular hydrogen bonding interactions. The kinetics and mechanism of ligand substitution of 1 and 2 by thiourea (TU) were studied in detail and showed a biphasic process in which an initial fast reaction is followed by a slower one. The activation parameters for the fast reaction: ΔH# = 68 ± 4 and 73 ± 5 kJ mol−1, ΔS# = 43 ± 10 and 54 ± 9 J K−1 mol−1 for 1 and 2, respectively, supports a dissociative substitution mechanism. Whereas for the slow reaction: ΔH# = 33 ± 6 and 43 ± 3 kJ mol−1, ΔS# = −77 ± 10 and −56 ± 9 J K−1 mol−1 for 1 and 2, respectively, support an associative substitution mechanism. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthase. The model complexes 1 and 2 show catecholase activity of Kcat = 10.9 × 103 and 11.4 × 103 h−1 and phenoxazinone synthase activity of Kcat = 2.1 × 103 and 4.3 × 103 h−1, respectively. Compared to the enzyme itself (Kcat = 8.3 h−1), the model complexes 1 and 2 are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase.

Investigation of Atrazine Sorption to Biochar With Titration Calorimetry and Flow-Through Analysis: Implications for Design of Pollution-Control Structures.

Atrazine is one of the most common broad-leaf herbicides used in the world. However, due to extensive use for many years, atrazine often appears in surface and groundwater. Atrazine transport is inhibited by degradation or sorption to soil components, especially organic matter. Biochar is a charcoal-like material produced from pyrolysis of biomass. Due to the amount and type of functional groups found on biochar, this product has shown potential for sorption of atrazine from solution. There is an interest in developing best management practices utilizing biochar to filter atrazine from non-point drainage with pollution-control structures such as blind inlets. The objective of this study was to explore the kinetics and thermodynamics of atrazine sorption to biochar using two different approaches: flow-through sorption cells and isothermal titration calorimetry (ITC). Twenty-five milligrams of an oak (Quercus spp.)-derived biochar was suspended in water and titrated 25 times (0.01 mL per titration) with atrazine at three different concentrations, and by a single titration (0.25 mL), with heat of reaction directly measured with ITC. A benchtop atrazine sorption study that simulated the titration experiment was also conducted. A continuous flow-through system was used to quantify the impact of contact time on atrazine sorption to biochar. Atrazine sorption to biochar displayed both exothermic and endothermic signals within each titration, although the net reaction was exothermic and proportional to the degree of sorption. Net enthalpy was −4,231 ± 130 kJ mole−1 atrazine sorbed. The existence of both exotherms and endotherms within a single titration, plus observation of an initial fast reaction phase from 0 to 300 s followed by a slower phase, suggested multiple sorption mechanisms to biochar. Results of flow-through tests supported kinetics observations, with the 300 s contact time removing much more atrazine compared to 45 s, while 600 s improved little compared to 300 s. Based on flow-through results, annual atrazine removal goal of 50%, and typical Midwestern U.S. tile drainage conditions, a pollution-control structure implementing this biochar sample would require 32 and 4 Mg for a design utilizing a contact time of 45 and 300 s, respectively. Future work is necessary for estimating degradation of atrazine sorbed to biochar.

Abatement of chlorinated compounds in groundwater contaminated by HCH wastes using ISCO with alkali activated persulfate

In this work, in situ chemical oxidation (ISCO) with alkali activated persulfate has been tested for the elimination of HCH isomers and other chlorinated compounds in groundwater from Sabiñanigo (Sardas landfill), which was contaminated by solid and liquid wastes illegally dumped in the area by a company producing lindane. Due to the site lithology and the type of pollutants found in groundwater (HCHs and chlorobenzenes) alkali (NaOH) activated persulfate (PS) was selected as oxidant.The influence of variables such as PS concentration (42–200mM) and NaOH:PS molar ratio (2:1 to 4:1) on chlorinated compound abatement has been studied and a kinetic model to predict the composition of all chlorinated organic compounds (COCs) in the aqueous phase with time was obtained. It was found that a fast initial hydrodechlorination reaction took place in which HCH isomers reacted to trichlorobenzenes (mainly 1,2,4 TCB) at pH≥12. Mono-, di-, tri and tetrachlorobenzenes remaining were oxidized without producing aromatic intermediates. At the condition tested a first order kinetic model for COCs and PS concentration was obtained. Zero order alkali concentration was obtained while pH was being kept at 12 for the whole reaction time.

Dissipation of pterosin B in acid soils – Tracking the fate of the bracken fern carcinogen ptaquiloside

Bracken ferns (Pteridium spp.) are well-known for their carcinogenic properties, which are ascribed to the content of ptaquiloside and ptaquiloside-like substances. Ptaquiloside leach from the ferns and may cause contamination of drinking water. Pterosin B is formed by hydrolysis of ptaquiloside. In soil, Pterosin B is adsorbed more strongly and it is expected to have a slower turnover than ptaquiloside. We thus hypothesized that pterosin B may serve as an indicator for any past presence of ptaquiloside. Pterosin B degradation was studied in acid forest soils from bracken-covered and bracken-free areas. Soil samples were incubated with pterosin B at 3 and 8 μg g−1 for 10 days, whereas sterile (autoclaved) samples were incubated for 23 days. Pterosin B showed unexpected fast degradation in soils with full degradation in topsoils in 2–5 days. Pterosin B dissipation followed the sum of two-first order reactions. The initial fast reaction with half-lives of 0.7–3.5 h contributed 11–59% of the total pterosin B degradation, while the slow reaction was 20–100 times slower than the fast reaction. Total dissipation half-lives were shorter for loamy sand (4 h) than for sandy loam soils (28 h). No degradation of pterosin B took place under sterile conditions assuming observed dissipation during the first 3 h could be attributed to irreversible sorption. Our results demonstrate that pterosin B is microbially degraded and that pterosin B is as unstable as ptaquiloside and hence cannot be used as an indicator for former presence of ptaquiloside in soil.

Impacts of dyebath auxiliaries on the reductive discoloration of Acid Orange 7 dye by high-carbon iron filings.

This study proposed that the physicochemical effects of common dyebath auxiliaries on the bulk dye solution as well as on the iron surface can influence the reductive discoloration of effluent containing Acid Orange 7 (AO7) dye using high-carbon iron filings. Sodium chloride increased the discoloration rate because of the pitting corrosion on the iron surface, triggered by chloride anion. 'Salting out' effect of ammonium sulfate improved the reaction rate up to a certain concentration, beyond which it could compete with dye molecules for the reactive sites, as revealed by formed sulfite and sulfide. Urea drastically reduced the discoloration rates by its chaotropic effect on the bulk solution and by wrapping around the iron surface. Organic acids, namely acetic acid and citric acid, stimulated iron corrosion to improve the discoloration rates. The discoloration reaction was biphasic with an initial fast reaction phase, where in every case more than 70% discoloration was observed within 5 min of reaction, preceding a slow reaction phase. The experimental data could be well described using biphasic kinetics equation (R(2)> 0.997 in all cases) and a biphasic equation was developed considering the individual impact of co-existing auxiliaries on AO7 discoloration.

Intermetal oxygen atom transfer from an FeVO complex to a MnIII complex: an experimental and theoretical approach.

Oxygen atom transfer (OAT) reaction between an FeVO complex and a MnIII complex resulted in the eventual formation of their corresponding FeIII and MnVO complexes. The reaction proceeded via an initial fast OAT reaction between the FeVO and MnIII complexes, yielding a half equivalent of a MnVO complex and a μ-oxo bridged FeIV dimer. The dimer regenerated the FeVO species via equilibrium, which then reacted with the remaining MnIII complex to produce another half equivalent of the MnVO complex.

Cupric Ferricyanide Reaction in Solution for Determination of Reducing Properties of Plant Antioxidants

To develop an antioxidant assay, the oxidation of phenolics and ascorbic acid by cupric ferricyanide in solution was estimated. Solutions (pH 6.6) were kept clear with citrate and gelatin. Reaction kinetics of the color formation at 480 nm indicated further slow increase after initial fast reaction with a sample. With the active phenolics (tannic acid, quercetin, rutin, chlorogenic acid), sufficiently stable endpoint was reached at 35 °C by 90 min. Calibration showed deviation of 5–10 % from the linearity. Antioxidant mixtures of tannic, chlorogenic, and ascorbic acids indicated small positive interaction between tannic and chlorogenic acids. Extracts from forest trees and green tea responded in the same way as individual phenolics to the oxidation. Common plant osmolytes in excess did not interfere with the analysis of tannic acid for its reducing activity. Due to a poor endpoint with ascorbic acid, a method for stabilizing the endpoint was looked further. Borate, molybdate, and lower pH greatly inhibited the reaction with ascorbic acid during the slow phase. By the presence of copper ions, it was possible that the autoxidation of ascorbic acid produced hydrogen peroxide during the slow phase. However, hydrogen peroxide gave substantial color response. Solvent N-methylpyrrolidone at low level inhibited or decreased the color formation for several analytes, suggesting that an analyte-dependent activation of oxygen could cause decolorization of cupric ferrocyanide. Current findings indicated that the cupric ferricyanide antioxidant reaction can be potentially developed to an assay for estimating reducing activity in extracts from woody plants or green tea.

Pollution and Desorption Kinetics of Heavy Metals at Agricultural Soils in Southeastern Iran

Desorption of heavy metals is an important factor in determining heavy-metal availability in soils. The objective of this research was to determine the applicability of kinetic equations to describe the kinetics of copper (Cu) and cadmium (Cd) desorption at two agricultural soils of Kerman Province in Iran. For Cd and Cu desorption studies, 5 g of the air-dried <2-mm soil fraction was extracted with 25 ml of 0.01 M ethylenediamenetetraacetic acid (EDTA) at pH 7.0 with a shaker for periods of 5 to 2880 min. The desorption patterns of Cu and Cd were generally characterized by an initial fast reaction, followed by a slower continuing reaction. Desorption of Cu and Cd from the two soils was equally well described by the two-constant rate and simple Elovich equations. The results of this study can be used to make better prediction about the mobility and bioavailability of the Cu and Cd in soil.

Potassium-Release Characteristics and Their Correlation with Bean (Phaseolus vulgaris) Plant Indices in Some Calcareous Soils

The rate of potassium (K) release from soils can significantly influence K availability to plants. There are few studies about K-release kinetics and K availability in calcareous soils of central Iran. The objective of this study was to study the release rates in 15 different soils from Chaharmahal-Va-Bakhtiari Province through successive extractions with 10 mM citric acid over periods of 2–2016 h and the correlation of K-release characteristics with bean plant indices. The results showed that there was wide variation in the cumulative K release among soils. The cumulative K release ranged from 169 to 1199 mg kg−1. The amounts of K released after 2016 h was not significantly correlated with bean plant indices. Plots of cumulative amounts of K released show a discontinuity in slope at 168 h. Thus, two equations were applied to segments of the total period (2 to 168 and 168 to 2016 h). The amount of K released after 168 h ranged from 62 to 879 mg kg−1. The amount of K released after 168 h was significantly correlated with bean plant indices. In the segment 1 parabolic diffusion, first-order and power function equations and in the second segment parabolic diffusion, first-order, zero-order, and power function equations described K-release kinetics. Release rate constants in the segment 1 were significantly correlated with bean plant indices; however, in the segment 2 release rate constants were not significantly correlated with bean plant indices. The results of our research showed that K-release characteristics after an initial fast reaction play a role in supplying available K and dilute citric acid solution can be used for estimating of K-release kinetics in the studied soils.