The importance of ligand speciation in environmental research: a case study

Diverse Surface Chemistry of Cobalt Ferrite Nanoparticles to Optimize Copper(II) Removal from Aqueous Media

Water pollution by heavy metals is one of the most serious worldwide environmental issues. With a focus on copper(II) ions and copper complex removal, in the present study, ultra-small primary CoFe₂O₄ magnetic nanoparticles (MNPs) coated with octadecylamine (ODA) of adequate magnetization were solvothermally prepared. The surface modification of the initial MNPs was adapted via three different chemical approaches based on amine and/or carboxylate functional groups: (i) the deposition of polyethylimide (PEI), (ii) covalent binding with diethylenetriaminepentaacetic acid (DTPA), and (iii) conjugation with both PEI and DTPA, respectively. FT-IR, TGA, and DLS measurements confirmed that PEI or/and DTPA were successfully functionalized. The percentage of the free amine (−NH₂) groups was also estimated. Increased magnetization values were found in case of PEI and DTPA-modified MNPs that stemmed from the adsorbed amine or oxygen ligands. Comparative UV–Vis studies for copper(II) ion removal from aqueous solutions were conducted, and the effect of time on the adsorption capacity was analyzed. The PEI-modified particles exhibited the highest adsorption capacity (164.2 mg/g) for copper(II) ions and followed the pseudo-second-order kinetics, while the polynuclear copper(II) complex Cu_x(DTPA)_y was also able to be immobilized. The nanoadsorbents were quickly isolated from the solution by magnetic separation and regenerated easily by acidic treatment.

A magnetically recyclable superparamagnetic silica supported Pt nanocatalyst through a multi-carboxyl linker: synthesis, characterization, and applications in alkene hydrosilylation

To simplify separation procedures, improve the reusability and decrease the loss of Pt, two Pt catalysts anchored on superparamagnetic silica (Fe₃O₄@SiO₂-EDTA@Pt and Fe₃O₄@SiO₂-DTPA@Pt) were prepared for the first time. The stable magnetic properties made them easily recyclable using a magnet rather than filtration, decantation or centrifugation. After 12 catalytic runs for both 30–50 nm Pt catalysts, the yield of 1-heptylmethyldichlorosilane was still up to 90%. The average loss of Pt in each reaction was only 0.87% for Fe₃O₄@SiO₂-EDTA@Pt and 0.66% for Fe₃O₄@SiO₂-DTPA@Pt owing to the strong interaction between Pt and carboxyl. The unprecedented activity and selectivity of the two Pt nanoparticle catalysts were observed in the hydrosilylation of alkenes. The turnover number in the reaction between 1-hexene and methyldichlorosilane using 5 × 10⁻⁸ mol of the Pt approached 662 733 for Fe₃O₄@SiO₂-EDTA@Pt and 579 947 for Fe₃O₄@SiO₂-DTPA@Pt over 12 h. The corresponding hydrosilylation products in excellent yields were obtained when we employed a broad range of alkenes as substrates, including 5 isomerous hexenes and 14 important industry raw materials. Fe₃O₄@SiO₂-DTPA@Pt showed a better activity. They have potential for catalyzing more reactions and replacing the current homogeneous Pt catalysts in industry.

To simplify separation procedures, improve the reusability and decrease the loss of Pt, two Pt catalysts anchored on superparamagnetic silica (Fe₃O₄@SiO₂-EDTA@Pt and Fe₃O₄@SiO₂-DTPA@Pt) were prepared for the first time.

Scale deposits in kraft pulp bleach plants with reduced water consumption: a review

The general tendency in the pulp industry towards reduced fresh water consumption and minimum effluent causes major deposit problems in mills. Chemical pulp bleach plants are affected by several types of mineral deposits, the most frequent being calcite, barite and calcium oxalate. In this review, the phenomena leading to scaling in chemical pulp bleaching are discussed, together with strategies for limiting deposits. The merits of various chemical methods in estimating scaling risks are compared. Chemical speciation methods are used throughout this review to gain a better understanding and prediction of scaling phenomena. Coupled chemical process simulations are anticipated to be a crucial way of solving deposition problems in bleach plants.

Efeito de inibidores da peroxidase sobre a conservação de raízes de mandioca in natura

A alta perecibilidade da mandioca (Manihot esculenta, Crantz) in natura faz com que o consumo seja feito dentro de um período curto após a colheita. A principal causa de perda se deve à deterioração fisiológica, atribuída à atividade da enzima peroxidase (E.C.1.11.1.7). Este trabalho objetivou avaliar o efeito combinado de diferentes inibidores da peroxidase nas concentrações de 1, 5 e 10 mM em raízes da variedade Cacau Amarela. As raízes foram tratadas por uma hora em soluções com ácido ascórbico, bissulfito de sódio, sódio, Na2-EDTA, L-cisteína e SDS, e armazenadas a 25 °C por seis dias. A cada dois dias, foram realizadas análises visuais e retiradas amostras para posterior avaliação da peroxidase. Todos os tratamentos foram eficientes em aumentar a vida de prateleira das raízes de mandioca in natura em até quatro dias. O tratamento com ácido ascórbico e bissulfito de sódio a 10 mM e L-cisteína a 5 mM foram eficientes em aumentar a vida de prateleira em até seis dias. No segundo dia de armazenamento, houve redução na atividade da peroxidase em relação ao controle, em todas as concentrações dos inibidores aplicados.

Effects of silver nanoparticles on bacterial activity in natural waters

Silver nanoparticles (AgNPs) may be introduced into aquatic ecosystems because of their widespread use as antimicrobial agents. However, few studies have investigated the impacts of AgNPs on natural aquatic microbial activity in an environmentally relevant context. In this study, bacterioplankton were collected from nine aquatic habitats and exposed to six concentrations of carboxy-functionalized AgNP (ViveNano, 10-nm particle size, 20% Ag w/w) over 48 h. After 1 h of exposure, bacterial production and extracellular alkaline phosphatase affinity were significantly reduced in all AgNP-exposed samples. However, across a 48-h exposure, extracellular aminopeptidase affinity was not consistently impacted by AgNPs. After 48 h, bacterial production recovered by 40 to 250% at low AgNP nominal concentrations (0.05 and 0.1 mg/L) but remained inhibited at the two highest AgNP nominal concentrations (1 and 10 mg/L). In contrast, AgNO(3) additions between 0.01 to 2 mg Ag/L fully inhibited bacterial production over the 48-h exposure. At 48-h exposure, the lowest observed effective concentrations and average median effective concentration for bacterial production ranged from 8 to 66 and 15 to 276 µg Ag/L, respectively. Thus, in natural aquatic systems, AgNP concentrations in the nanogram per liter range are unlikely to negatively impact aquatic biogeochemical cycles. Instead, exposures in the low microgram per liter range would likely be required to negatively impact natural aquatic bacterioplankton processes.

Bacterial mer operon-mediated detoxification of mercurial compounds: a short review

Mercury pollution has emerged as a major problem in industrialized zones and presents a serious threat to environment and health of local communities. Effectiveness and wide distribution of mer operon by horizontal and vertical gene transfer in its various forms among large community of microbe reflect importance and compatibility of this mechanism in nature. This review specifically describes mer operon and its generic molecular mechanism with reference to the central role played by merA gene and its related gene products. The combinatorial action of merA and merB together maintains broad spectrum mercury detoxification system for substantial detoxification of mercurial compounds. Feasibility of mer operon to coexist with antibiotic resistance gene (ampr, kanr, tetr) clusters enables extensive adaptation of bacterial species to adverse environment. Flexibility of the mer genes to exist as intricate part of chromosome, plasmids, transposons, and integrons enables high distribution of these genes in wider microbial gene pool. Unique ability of this system to manipulate oligodynamic property of mercurial compounds for volatilization of mercuric ions (Hg2+) makes it possible for a wide range of microbes to tolerate mercury-mediated toxicity.

Capture of Co(II) from its aqueous EDTA-chelate by DTPA-modified silica gel and chitosan

The adsorption of Co(II) by diethylenetriaminepentaacetic acid (DTPA)-modified silica gel and chitosan in the presence of EDTA and other interfering species was studied. Co(II) removal ranged from 93% to 96% from the solutions where Co(II) was totally chelated by EDTA. The amount of oxalate or Fe(II) did not affect the adsorption of Co(II) in the case of DTPA-chitosan. However, increasing the amount of oxalate enhanced the adsorption performance of DTPA-silica gel, probably due to the formation of new active sites on the silica gel surface. DTPA-chitosan was also effective in simulated decontamination solutions. For DTPA-silica gel, the rate of adsorption of free Co(II) was controlled by pore diffusion, but the rate of adsorption of Co(II)EDTA was controlled by the surface chelation reaction, which was attributed to the inhibited diffusion of Co(II)EDTA inside the silica gel mesopores. However, the macroporous structure of DTPA-chitosan enabled pore diffusion of both Co(II) and Co(II)EDTA. The equilibrium isotherms of DTPA-silica gel were best described by a BiLangmuir model, in which there are two different adsorption sites on the silica gel surface assigned to different speciations of DTPA. For DTPA-chitosan, the data fit best with a Sips model, which indicates system heterogeneity. Finally, measurements with capillary electrophoresis showed an increase in dissolved EDTA during adsorption, demonstrating the ability of DTPA-modified adsorbents to release Co(II) from its EDTA chelate. This promising result can provide a basis for applying the studied materials to the treatment of water effluents containing Co(II) chelated by EDTA by a simple one-step adsorption process.

The influence of organic ligands on the adsorption of cadmium by suspended matter in natural waters studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrochemical methods

Natural water carrying a great amount of suspended particulate matter (SPM) was used as a model system for the study of the competition among organic ligands (dietilentetraamine pentaacetic acid, DTPA, nitrilotriacetic acid, NTA, and citrate, Cit) and natural complexants (SPM) for cadmium adsorption. Speciation diagrams at the pH of the natural sample were obtained by electroanalytical techniques, processing the experimental data with the complexation constants and the mass balance of the system. Results show that the adsorption equilibrium SPM-Cd is completely displaced by DTPA but not completely by NTA or Cit. Furthermore, larger Cit concentrations increase the amount of adsorbed Cd(II). The increment of the complexing capacity may be explained on the basis of SPM-Cit-Cd ternary complexes formation. This hypothesis was supported on the results obtained by applying for the first time the MALDI-TOF technique in a mixture of SPM, Cd(II), organic ligands and their complexes.

Oxidation of EDTA with H2O2 catalysed by metallophthalocyanines

The oxidation of ethylenediaminetetraacetic acid (EDTA) and Na, Ca, Zn, Fe, and Mn EDTA complexes with hydrogen peroxide was studied in aqueous solution with the use of several metallophthalocyanines (MePcS) as catalysts. The impact of pH, temperature, and catalyst/substrate ratio were investigated. The most effective catalytic system under neutral conditions was FePcS- H2O2. In these laboratory-scale experiments, a catalyst/substrate/H2O2 molar ratio of 4:100:2000 was found to be optimal, while the effective reaction temperature was 40-60 degrees C. When the impact of metal speciation was studied, metal-specific degradation rates in the removal of these compounds were observed: all EDTA-metal complexes except Zn-EDTA were efficiently oxidized within three hours. The most degradable species was Fe(III)-EDTA. Among the catalysts, FePcS was found to be the most active in EDTA degradation. Over 90% of EDTA was removed in the presence of FePcS as catalyst within three hours of reaction time.

Copper and trace element fractionation in electrokinetically treated methanogenic anaerobic granular sludge

The effect of electrokinetic treatment (0.15 mA cm(-2)) on the metal fractionation in anaerobic granular sludge artificially contaminated with copper (initial copper concentration 1000 mg kg(-1) wet sludge) was studied. Acidification of the sludge (final pH 4.2 in the sludge bed) with the intention to desorb the copper species bound to the organic/sulfides and residual fractions did not result in an increased mobility, despite the fact that a higher quantity of copper was measured in the more mobile (i.e. exchangeable/carbonate) fractions at final pH 4.2 compared to circum-neutral pH conditions. Also addition of the chelating agent EDTA (Cu2+:EDTA4- ratio 1.2:1) did not enhance the mobility of copper from the organic/sulfides and residual fractions, despite the fact that it induced a reduction of the total copper content of the sludge. The presence of sulfide precipitates likely influences the copper mobilisation from these less mobile fractions, and thus makes EDTA addition ineffective to solubilise copper from the granules.

EDTA degradation induced by oxygen activation in a zerovalent iron/air/water system

A method for the removal of ethylenediaminetetraacetic acid (EDTA) at room temperature and 1 atm is demonstrated. EDTA (1 mM, 50 mL) containing 2.5 g of granular zerovalent iron (ZVI) (20-40 mesh) was degraded in 2.5 h. Using a recently developed form of O2 activation, reactive oxygen species are generated in situ, resulting in the degradation of EDTA when complexed with FeII. ESI-MS measurements indicate that degradation of EDTA yields low-molecular carboxylic acids. The presence of oxygen is crucial: the observed pseudo-first-order rate constants for EDTA removal are kobs = 1.02 h(-1) (kSA = 1.85 +/- 0.046 L h(-1) m(-2)) and kobs = 0.04 h(-1) (kSA = 0.00724 +/- 0.002 L h(-1) m(-2)) under air and under N2 purge, respectively. kSA represents surface area normalized rate constants. Large excesses of EDTA in the reaction mixture slowthe rate of degradation. Increasing the concentration of EDTA from 1.0 to 10.0 mM while holding all other parameters constant gave observed rates of kobs = 1.02 +/- 0.26 h(-1) (kSA = 1.85 +/- 0.046 L h(-1) m(-2)) and kobs = 0.044 +/- 0.01 h(-1) (kSA = 0.00796 +/- 0.002 L h(-1) m(-2)), respectively. The rate-limiting step is determined to be homogeneous oxygen activation.

Impact of aminopolycarboxylates on aquatic organisms and eutrophication: overview of available data

Aminopolycarboxylic acids, which include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA), 1,3-propylenediaminetetraacetic acid (1,3-PDTA), beta-alaninediacetic acid (beta-ADA), and methylglycinediacetic acid (MGDA), constitute a class of complexing agents that occur in a wide range of domestic products and that are used intensively as metal sequestrants in several industrial applications. Because they are highly polar and partially nondegradable, aminopolycarboxylates are released into the aquatic environment in significant quantities, mainly via wastewater. The historical and current use of aminopolycarboxylates and their ubiquitous presence in surface waters prompted many studies about their possibly detrimental impact on aquatic organisms. This review summarizes the available data and information on the eutrophication potential and toxicity of aminopolycarboxylates to a multitude of aquatic organisms including vertebrates, invertebrates, algae, bacteria, and protozoa. This article also addresses how the ecotoxic effects of aminopolycarboxylates are dependent on their speciation, that is, on their presence in a free or a metal-complexed form.

Biological and photochemical degradation rates of diethylenetriaminepentaacetic acid (DTPA) in the presence and absence of Fe(III)

The environmental fate of ethylenediaminetetraacetic acid (EDTA) has been extensively studied, while much less is known about the environmental behaviour of diethylenetriaminepentaacetic acid (DTPA). In this study, it was confirmed that DTPA is persistent toward biodegradation. The biodegradability of DTPA was investigated in the absence and in the presence of Fe(III) by using CO2 evolution test and Manometric respirometry test. The CO2 evolution and oxygen uptake of iron-free (DTPA was added as free acid) and Fe(III)DTPA were less than in inoculum blank. Possible inhibitor effect was analysed by testing biodegradation of sodium benzoate with and without iron-free or Fe(III)DTPA in the Manometric respirometry test. Only slight inhibition was observed when DTPA was added as free acid. Photodegradation of iron-free DTPA and Fe(III)-DTPA complex was studied by using sunlight and UV radiation at the range 315-400 nm emitted by black light lamps. The results indicate that DTPA added as free acid degrades photochemically in humic lake water. Fe(III)DTPA was shown to be very photolabile in humic lake water in the summer; the photochemical half-life was below one hour. Photodegradation products were identified by the mass spectrometric technique (GC-MS). It was shown that photodegradation of Fe(III)DTPA does not result in total mineralization of the compound. Diethylenetriaminetetraacetic acid, diethylenetriaminetriacetic acid, ethylenediaminetriacetic acid, N,N'- and/or N,N-ethylenediaminediacetic acid, iminodiacetate, ethylenediaminemonoacetic acid and glycine were identified as photodegradation products of Fe(III)DTPA. Based on these observations, we propose a photodegradation pathway for Fe(III)DTPA.