Solid phase extraction of ultra traces mercury (II) using octadecyl silica membrane disks modified by 1,3-bis(2-ethoxyphenyl)triazene (EPT) ligand and determination by cold vapor atomic absorption spectrometry

A facile and highly efficient method was developed for the preconcentration of the ultra trace amounts of mercury (II) ions. Octadecyl silica membrane disk was modified by the recently synthesized triazene ligand, 1,3-bis(2-ethoxyphenyl)triazene (EPT), and cold vapor atomic absorption spectrometry was used to determine the resultant preconcentrated Hg(II) ions. Solution studies with EPT and a series of metal ions were done in advance, and the results showed a strong affinity of EPT to the mercury ions. To perform solid phase extraction, various parameters such as pH of the sample, flow rates and the amount of the ligand were optimized. A linear calibration curve was obtained in the range of 0.02-1.90 μg L⁻¹ with r² = 0.9990 (n = 8), and the limit of detection (LOD) based on three times the standard deviation of the blank was 10.6 ng L⁻¹. The relative standard deviation (RSD) for the determination of 0.1 μg L⁻¹ Hg(II) found to be 2.9% while a RSD value of 1.1% was obtained for the determination of 1.0 μg L⁻¹ Hg(II) (n = 8). The preconcentration and improvement factors were 380 and 74, respectively. The newly developed method was successfully applied to the determination of mercury ions in real water samples.     

Synthesis and application of chloromethylated polystyrene modified with 1-phenyl-1,2-propanedione-2-oxime thiosemicarbazone (PPDOT) as a new sorbent for the on-line preconcentration and determination of copper in water, soil, and food samples by FAAS

In this paper, we report a simple and sensitive on-line solid phase extraction system for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry (FAAS). This method is based upon the on-line retention of copper at pH 5.0 on a minicolumn packed with chloromethylated polystyrene modified by 1-phenyl-1,2-propanedione-2-oxime thiosemicarbazone (PPDOT) as a new solid-phase extraction (SPE) sorbent. The retained Cu(II) ions were eluted with 1.0 M HNO₃, and transported directly to FAAS for determination. Several chemical and flow variables were studied and optimized for a quantitative preconcentration and determination of copper(II). At the optimized conditions, for preconcentration of 10.0 mL of a sample solution, a linear calibration graph was obtained over the concentration range of 3.00-120.0 μg L⁻¹ for Cu(II). The limit of detection (3σ), limit of quantification (10σ), and enrichment factor are 0.56 μg L⁻¹, 2.0 μg L⁻¹ and 41, respectively. The relative standard deviation (n = 6) at 20 μg L⁻¹ of Cu(II) is 2.0%. This method could be applied for determination of trace amounts of Cu(II) in water, soil, and food samples with satisfactory results.     

Aqueous two-phase systems: a new approach for the determination of p-aminophenol

A new method has been developed for the spectrophotometric determination of p-aminophenol (PAP) in water, paracetamol formulations and human urine samples with a recovery rate between 94.9 and 101%. This method exploits an aqueous two-phase system (ATPS) liquid-liquid extraction technique with the reaction of PAP, sodium nitroprusside and hydroxylamine hydrochloride in pH 12.0, which produces the [Fe₂(CN)₁₀]¹⁰⁻ anion complex that spontaneously concentrates in the top phase of the ATPS (K[Fe₂(CN)₁₀]¹⁰⁻=97.7). The ATPS does not require an organic solvent, which is a safer and cleaner liquid-liquid extraction technique for the determination of PAP. The linear range of detection was from 5.00 to 500 μg kg⁻¹ (R ≥ 0.9990; n = 8) with a coefficient of variation of 2.11% (n = 5). The method exhibited a detection limit of 2.40 μg kg⁻¹ and a quantification limit of 8.00 μg kg⁻¹. The ATPS method showed a recovery that ranged between 96.4 and 103% for the determination of PAP in natural water and wastewater samples, which was in excellent agreement with the results of the standard 4-aminoantipyrine method that was performed on the same samples.     

Emissions of polycyclic aromatic hydrocarbons from fluidized and fixed bed incinerators disposing petrochemical industrial biological sludge

This study investigated the emissions of polycyclic aromatic hydrocarbons (PAHs) from two fluidized bed incinerators (FLBI_A and FLBI_B) and one fixed bed incinerator (FIBI) disposing biological sludge generated from the petrochemical industries in Taiwan. The results of 21 individual PAHs (including low (LM-PAHs), middle (MM-PAHs) and high molecular weight PAHs (HM-PAHs)) were reported. The LM-PAHs mainly dominated the total-PAHs in the stack flue gases, whereas the LM- and HM-PAHs dominated the total-PAHs in the bottom fly, fly ash and WSB effluent. Due to high carcinogenic potencies (= total-BaP_eq concentrations) in the bottom ash (195 ng g⁻¹) and WSB effluent (20,600 ng L⁻¹) of the FIBI, cautious should be taken in treating them to avoid second contamination. Lower combustion efficiency and elevated fuel/feedstock (F/W) ratio for the FIBI led to the highest total emission factor of total-PAHs (38,400 μg kg⁻¹). Lower total-PAH removal efficiencies of wet scrubber (WSB) (0.837–5.89%), cyclone (0.109–0.255%) and electrostatic precipitator (ESP) (0.032%) than those reported elsewhere resulted in high fraction in PAH contributions from the stack flue gases. Lower total-PAH emission factor was found for FLBI_A (2380 μg kg⁻¹ biological sludge) with higher combustion efficiency compared to those for FLBI_B (11,500 μg kg⁻¹) and FIBI (38,400 μg kg⁻¹ biological sludge), implying that combustion efficiency plays a vital role in PAH emissions.     

Sequential eluent injection technique as a new approach for the on-line enrichment and speciation of Cr(III) and Cr(VI) species on a single column with FAAS detection

This paper introduces a sequential eluent injection (SEI) technique combined with an on-line preconcentration/separation system for a fast and sensitive FAAS determination of trace amounts of Cr(III) and Cr(VI) species. The method is based on the simultaneous retention of Cr(III) and Cr(VI) on a single mini-column packed with a chloromethylated polystyrene functionalized with N,N-bis(naphthylideneimino)diethylenetriamine (PS-NAPdien) at pH 6.7. The retained chromium species was eluted by sequential injection of HCl for desorption of Cr(III), and NH₃ and NH₄NO₃ buffer solutions for desorption of Cr(VI). All the chemical and flow injection variables were optimized for the quantitative preconcentration and speciation of Cr(III) and Cr(VI). Under the optimum conditions, the calibration graph obtained is linear over the concentration range of 2.0-60.0 μg L⁻¹ for Cr(III), and 8.0-180.0 μg L⁻¹ for Cr(VI). The preconcentration factors for Cr(III) and Cr(VI) were 70 and 30, respectively. The 3σ detection limits were 0.6 μg L⁻¹ and 2.5 μg L⁻¹ for Cr(III) and Cr(VI), respectively. The relative standard deviations were 2.55% and 0.8%, respectively, for 6 replicate determinations of Cr(III) and Cr(VI) at the 40.0 μg L⁻¹ level. The proposed method was applied for determination of Cr(III) and Cr(VI) in different water samples with satisfactory results.     

Toxicity of mercury on in vitro development of parthenogenetic eggs of a freshwater cladoceran Daphnia carinata

Chronic toxicity test duration of 21 days for daphnid is time consuming and expensive. Therefore, the developmental stages of Daphnia carinata eggs that could be used as potential endpoints for sublethal and chronic toxicity tests have been investigated and defined. Daphnid egg test is simple, easy to conduct and handle in the laboratory, and cost-effective. The 72 h ‘egg arrest’ bioassay system could be an alternative to the classic 21-day chronic test with neonates of daphnid. The main aims of the study were to establish easy to identify stages of D. carinata egg that could be used as potential endpoints for toxicity tests with in vitro cultures of daphnid parthenogenetic eggs. Commonly available Indian freshwater cladoceran Daphnia carinata parthenogenetic eggs in vitro were exposed to water borne mercury concentrations, ranging from 0.1 to 32 μg l⁻¹. Adult female cladoceran D. carinata have eight main developmental stages of parthenogenetic reproduction based on the release of external and internal membranes, formation of cephalic and body regions, appearance of secondary antennae, presence of two pink eyes, than a single black eye, and finally caudal or shell spine separation and finally free-swimming neonate within 65–72 h. At 1, 3.2 and 10 μg l⁻¹ of Hg concentrations; the 25, 50 and 70% embryonic developmental arrests were observed. The lower concentrations of Hg (0.32, 1, and 3.2 μg l⁻¹) tested in the present study are not generally harmful to the neonates and adults daphnid species, but the same are highly toxic to the embryos of D. carinata. The 48 h and 72 h EC₅₀s and their 95% confidence limits for survival and hatchability were lower than previously reported 48 h EC₅₀s for Daphnia magna immobilization assay. The egg of D. carinata turned out to be a suitable alternative model for ecotoxicological and water quality assessment studies.     

Fluoride removal performance of glass derived hydroxyapatite

A novel sodium calcium borate glass derived hydroxyapatite (G-HAP) with different ranges of particle size was prepared by immersion sodium calcium borate glass in 0.1 M K₂HPO₄ solution by the ratio of 50 g L⁻¹ for 7 days. The unique advantage of G-HAP for the adsorption of fluoride ions in solutions was studied. The effects of size and quantity of particles, pH value and adsorption time on adsorption performance were investigated. The maximum adsorption capacity was 17.34 mg g⁻¹ if 5 g L⁻¹, <100 μm G-HAP was added to a solution with an initial pH value of 6.72 and the adsorption time was 12 h. The results showed that the micro-G-HAP could immobilize F⁻ in solution more effectively than commercial nano-HAP, which makes potential application of the G-HAP in removing the fluoride ions from wastewater. The adsorption kinetics and isotherms for F⁻ could be well fitted by a second order kinetic model and Freundlich isotherm model respectively, which could be used to describe the adsorption behavior. The mechanism of G-HAP in immobilizing F⁻ from aqueous solutions was investigated by the X-ray diffraction (XRD), infrared spectra (IR) and scanning electron microscopy (SEM).     

Speciation of selenium in groundwater: seasonal variations and redox transformations

Speciation of selenium in groundwater is essential from the viewpoint of toxicity to organisms and biogeochemical cycling. Selenium speciation in groundwater is controlled by aquifer redox conditions, microbial transformations, dissolved oxygen (DO) and other redox couples. A suburban area of Chennai city in India, where improper waste disposal measures have been practiced is selected for this study. Se(IV), Se(VI) and other hydrochemical parameters were monitored in shallow ground water during pre- and post-monsoon seasons for a period of three years. The objective of the study was to investigate the effect of groundwater recharge on selenium speciation. The concentration of Se(IV), and Se(VI) ranged between 0.15-0.43 μg L⁻¹ and 0.16-4.73 μg L⁻¹, respectively. During post-monsoon period the concentration of Se(IV), and Se(VI) ranged between 0.15-1.25 μg L⁻¹ and 0.58-10.37 μg L⁻¹, respectively. Se(VI) was the dominant species of selenium during the pre- and post-monsoon periods. During the post-monsoon periods, leaching of selenium from soil was more effective due to the increased oxidizing nature of the groundwater as indicated by the DO and redox potential (Eh) measurements. This finding has important implications on the behavior of selenium in groundwater, and also on the health of people consuming groundwater from seleniferous areas.     

Perchlorate removal in Fe0/H2O systems: Impact of oxygen availability and UV radiation

In this study, the removal of perchlorate (0.016 mM ) using Fe⁰-only (325 mesh, 10 g L⁻¹) and Fe⁰ (10 g L⁻¹) with UV (254 nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe⁰-only and Fe⁰/UV reactions, respectively, in a 12 h period. However, under oxic conditions, perchlorate was removed completely in the Fe⁰-only reaction, and reduced by 40% in the Fe⁰/UV reaction, within 9 h. The pseudo-first-order rate constant (k₁) was 1.63 × 10⁻³ h⁻¹ in Fe⁰-only and 4.94 × 10⁻³ h⁻¹ in Fe⁰/UV reaction under anoxic conditions. Under oxic conditions, k₁ was 776.9 × 10⁻³ h⁻¹ in Fe⁰-only reaction and 35.1 × 10⁻³ h⁻¹ in the Fe⁰/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe⁰-only and Fe⁰/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/co-precipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe⁰/UV reaction under oxic conditions increased in the presence of methanol (73%, 9 h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe⁰-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe⁰. The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe⁰/H₂O system.     

L-Aspartic acid/L-cysteine/gold nanoparticle modified microelectrode for simultaneous detection of copper and lead

This paper presents an electrochemical microsensor for simultaneous detection of copper (II) and lead (II) using an l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode. The microelectrode was fabricated by Micro Electro-Mechanical System technique. The complex of gold nanoparticles (AuNPs) and amino acid with carboxyl group was used as the selective ligand for metal ions. The microelectrode was firstly modified with AuNPs to increase the sensitive area of the working electrode. Subsequently, the AuNPs/gold electrode was modified with l-cysteine and then covalently linked with a monolayer of l-aspartic acid using glutaraldehyde. Electrochemical analysis of metal ions was achieved by using square wave voltammetry without stirring. The microsensor exhibited an excellent linear range from 5 μg L^− 1 to 2000 μg L^− 1 with the limit of detection of 1 μg L^− 1. This metal ion detection method based on l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode is simple, sensitive and it could be used for electrochemical analysis of copper (II) and lead (II).     

Accumulation of arsenic and nutrients by castor bean plants grown on an As-enriched nutrient solution

Phytoextraction is a remediation technique that consists in using plants to remove contaminants from soils and water. This study evaluated arsenic (As) accumulation in Castor bean (Ricinus communis cv. Guarany) grown in nutrient solution in order to assess its phytoextraction ability. Castor bean plants were grown under greenhouse conditions in pots containing a nutrient solution amended with increasing doses of As (0, 10, 50, 100, 250, 500 and 5000 μg L⁻¹) in a completely randomized design with four replications. Shoot and roots dry matter production as well as arsenic and nutrient tissue concentrations were measured at the end of the experiment. The results showed that increasing As concentration in nutrient solution caused a decrease in shoot and root biomass but did not result in severe toxicity symptoms in castor bean growing under a range of As concentration from 0 to 5000 μg L⁻¹. The As doses tested did not affect the accumulation of nutrients by castor bean. Although castor bean did not pose characteristics of a plant suitable for commercial phytoextraction, it could be useful for revegetation of As-contaminated areas while providing an additional income by oil production.     

Improved photoelectrochemical detection of mercury (II) with a TiO2-modified composite photoelectrode

The spectrophotometric change of a mercury (II) (Hg²⁺) selective small molecule chemosensor has been successfully converted into a photovoltaic response upon ligating Hg²⁺. The photon excitation was followed by charge separation facilitated by TiO₂ and polyaniline (PANI), resulting in an electron transfer to an electrical back contact. The photoresponse of the Hg²⁺ selective chromophore was converted to an electron current equivalent to the amount of Hg²⁺ in solution. The favourable properties of a Hg²⁺ sensitive chemosensor was combined with the semiconductor capabilities of TiO₂ to construct a sensor that is capable of generating a current in the presence of Hg²⁺ under illumination. A composite of the fluorescent chemosensor rhodamine 6G hydrozone derivative (RS) and PANI was immobilized on indium tin oxide (ITO) plates coated with TiO₂ and subjected to photovoltammetric measurements. The photovoltammetric responses of the coated layers were investigated to determine the sensitivity and selectivity of the immobilized sensor to Hg²⁺ in the presence of background ions. The photo-response increased linearly with increasing Hg²⁺ concentration from 10 to 200 μg L⁻¹ with a limit of quantification (LOQ) of 4 μg L⁻¹. The pH independence for the photoresponse was limited by the TiO₂ layer and was optimal between pH 6 and 7.     

Novel modeling concept for evaluating the effects of cadmium and copper on heterotrophic growth and lysis rates in activated sludge process

A new modeling concept to evaluate the effects of cadmium and copper on heterotrophic growth rate constant (μ_H) and lysis rate constant (b_H) in activated sludge was introduced. The oxygen uptake rate (OUR) was employed to measure the constants. The results indicated that the μ_H value decreased from 4.52 to 3.26 d⁻¹ or by 28% when 0.7 mg L⁻¹ of cadmium was added. Contrarily the b_H value increased from 0.31 to 0.35 d⁻¹ or by 11%. When adding 0.7 mg L⁻¹ of copper, the μ_H value decreased to 2.80 d⁻¹ or by 38%. The b_H value increased to 0.42 d⁻¹ or by 35%. After regression, the inhibitory effect was in a good agreement with non-competitive inhibition kinetic. The inhibition coefficient values for cadmium and copper were 1.82 and 1.21 mg L⁻¹, respectively. The relation between the b_H values and heavy metal concentrations agreed with exponential type well. The heavy metal would enhance b_H value. Using these data, a new kinetic model was established and used to simulate the degree of inhibition. It was evident that not only the inhibitory effect on μ_H but also that the enhancement effect on b_H should be considered when heavy metal presented.     

Optimal exponential feeding strategy for dual-substrate biostimulation of phenol degradation using Cupriavidus taiwanensis

The exponential feeding strategy (EFS) of dual substrates (i.e., phenol and glycerol) was applied to optimize the overall performance of phenol degradation by Cupriavidus taiwanensis R186. Addition of a second substrate (e.g., glycerol) could stimulate the phenol biodegradation efficiency of strain R186. Hence, a feasible EFS was developed for fed-batch phenol biodegradation using the dual-substrate biostimulation technique. The phenol degradation kinetics was well characterized with proposed model and response surface analysis. Our findings quantitatively revealed that glycerol could effectively enhance the phenol degradation performance, as the highest phenol degradation efficiency occurred with the supplementation of 0.8–1.2 g L⁻¹ of glycerol. The optimal dual-substrate EFS was identified via contour analysis and kinetic modeling. With the optimal dual-substrate EFS (i.e., a feeding rate constant (α₁ and α₂) of 0.5 and 0.3, respectively), the shortest time (ca. 13.80 h) for phenol degradation was achieved with a specific growth rate of ca. 0.281 h⁻¹.     

Enhanced thermoelectric properties of NaCo2O4 by adding ZnO

The primary phase present in the as-sintered Na(Co_1 − xZn_x)₂O₄ (0 ≤ x ≤ 0.1) bodies was the solid solution of the constituent oxides with a bronze-type layered structure. The electrical conductivity of the Na(Co_1 − xZn_x)₂O₄ samples significantly increased with an increase in ZnO content. The sign of the Seebeck coefficient for all samples was positive over the whole temperature range (723-1073 K), i.e., p-type conduction. The power factor of Na(Co_0.95Zn_0.05)₂O₄ showed an outstanding power factor (1.7 × 10^− 3Wm^− 1 K^− 2) at 1073 K. The power factor was above four times superior to that of ZnO-free NaCo₂O₄ (0.4 × 10^− 3Wm^− 1 K^− 2). This originates from an unusually large Seebeck coefficient (415 μVK^− 1) accompanied with high conductivity (127Ω^− 1 cm^− 1) at 1073 K.     

Tl-208, Pb-212, Bi-212, Ra-226 and Ac-228 adsorption onto polyhydroxyethylmethacrylate-bentonite composite

The adsorption of naturally occurring radionuclides (²⁰⁸Tl⁺, ²¹²Pb²⁺, ²²⁶Ra²⁺, ²¹²Bi³⁺ and ²²⁸Ac³⁺) onto Polyhydroxyethylmethacrylate-bentonite (PHEMA-B) composite was investigated. Experimentally obtained isotherms were evaluated with reference to Langmuir, Freundlich and Dubinin-Radushkevich (DR) models. The adsorption isotherms were L type of Giles classification proving that PHEMA-B had a high affinity adsorbent for the studied radionuclides. The Langmuir adsorption capacities (X_L) were in the order of ²²⁶Ra (2.8 MBq kg⁻¹)>²¹²Bi (0.4 MBq kg⁻¹)>²¹²Pb (0.3 MBq kg⁻¹)>²²⁸Ac and ²⁰⁸Tl (0.2 MBq kg⁻¹). The adsorption process was physical via complex formation after proton exchanger for which the adsorption energies obtained from DR model was evidence. The enthalpy and entropy changes were positive and the negative free enthalpy change was proof for the spontaneity of adsorption. The reusability tests for PHEMA-B for five uses demonstrated that the adsorbent could be reused after complete recovery of the loaded radionuclide ions by 1 M HCl. The chemical structure of the composite did not change after the reuses and storage foregoing.     

Dependency of microstructure parameters and microhardness on the temperature gradient for directionally solidified Ti–49Al alloy

Intermetallics Ti–49Al (at.%) alloy was directionally solidified with different temperature gradients (G) ranged from 2.8 K mm⁻¹ to 12.5 K mm⁻¹ at a constant growth rate (V = 10 μm s⁻¹) by using a Bridgman-type directional solidification furnace. The microstructure of the directionally solidified specimen is constituted of α₂(Ti₃Al) and γ(TiAl) lamellar structures. The values of the primary dendritic spacing (λ), interlamellar spacing (λ_L) and microhardness (HV) were measured. Dependencies of λ, λ_L and HV on G were determined by using the linear regressing analysis. According to these results, the values of λ and λ_L decrease with the increase of G, and the values of HV increase with the increase of G and with the decrease of λ and λ_L. In addition, these results were compared with the previous similar experimental results of TiAl-based alloys.     

Design and synthesis of immunoconjugates and development of competition inhibition enzyme-linked immunosorbent assay (CIEIA) for the detection of O-isopropyl methylphosphonofluoridate (sarin): an organophosphorous toxicant

Three haptens of the organophosphorus (OP) toxicant ‘sarin’ having different spacer arm were designed and synthesized. Haptens were conjugated with BSA (bovine serum albumin) and ovalbumin (OVA) for raising antibody and coating antigen. High antibody titer with higher specificity was obtained from 4-(4-(isopropoxy(methyl)phosphoryloxy)phenylamino)-4-oxobutanoic acid (hapten B) having reasonable long spacer arm. For the standard curve, an IC₅₀ (inhibitory concentration) of free antigen was found to be 0.415 μg mL⁻¹ on the basis of indirect competitive ELISA. The study revealed that heterology in competition inhibition enzyme immunoassay (CIEIA) produced remarkable improvement in the sensitivity and specificity of the assay. Under the optimized conditions, the quantitative working range was found to be 0.19-1.56 μg mL⁻¹ with a limit of detection (LOD) of 0.05 μg mL⁻¹. The antibodies showed negligible cross reactivity (CR) with other OP toxicants and pesticides, which makes the assay suitable for the selective detection of sarin.     

Relating organic fouling of reverse osmosis membranes to adsorption during the reclamation of secondary effluents containing methylene blue and rhodamine B

Dyes fouling of reverse osmosis (RO) membranes and its relation to adsorption had been investigated by using a crossflow RO filtration setup. Methylene blue (MB) and rhodamine B (RB) were used as model organic foulants. The calculated amount of the irreversible sorption was related to the irreversible flux decline. The characteristic fouling kinetics was accounted by Langmuir-Hinshelwood (L-H) kinetics model for initial fouling, with the fouling rate constant k = 0.0556 μm s⁻¹ min⁻¹ and k = 0.0181 μm s⁻¹ min⁻¹ for MB and RB fouling RO membrane CPA2, respectively. And the subsequent fouling was attributed to the growth of a dye cake. A remarkable correlation was obtained between the quantified irreversible sorption and irreversible flux decline under the solution chemistries investigated. In the presence of divalent cation, the extent of flux decline was related to the competition model.