A comprehensive investigation of zeolite-rich tuff functionalized with 3-mercaptopropionic acid intercalated green rust for the efficient removal of HgII and CrVI in a binary system.

In this study, the 3-mercaptopropionic acid (MA) was chosen to achieve the anionic intercalation into the green rust (GR) materials (MA-GR). The zeolite-rich tuff functionalized with the MA-intercalated GR (MA-GR-tuff) was subsequently synthesized and used to remove both HgII cations and CrVI anions in a binary system. MA-GR-tuff showed the best adsorption capacities to both HgII and CrVI among the adsorbent materials. The optimal combination of parameters was determined as the molar ratio of FeII to FeIII of 3.5, the molar ratio of OH- to the total iron of 3.75, the molar ratio of MA to the total iron of 2.5, and the mass ratio of the total iron to the tuff of 1.25. The pseudo-first-order kinetic model was appropriate in describing the kinetic sorption of CrVI by MA-GR-tuff. Both the pseudo-first-order kinetic model and Elovich were suitable for explaining HgII sorption. The maximum monolayer adsorption capacities of MA-GR-tuff towards CrVI and HgII were 185.19 mg/g and 72.99 mg/g, respectively. More flocs and plumes were formed in the MA-GR while the intercalation and more pores and crevices of different sizes were found in the MA-GR-tuff. Sulfhydryl complexation and the molecular sieve of tuff obviously both played a role in influencing the adsorption process. This study directly overcomes the drawback brought by the natural tuff to the treatment of a cationic-and-anionic binary system and supplies a new kind of tuff-based adsorbent for the potential use for the remediation of HM-contaminated wastewater.

Geochemical and Dietary Drivers of Mercury Bioaccumulation in Estuarine Benthic Invertebrates.

Sediments represent the main reservoir of mercury (Hg) in aquatic environments and may act as a source of Hg to aquatic food webs. Yet, accumulation routes of Hg from the sediment to benthic organisms are poorly constrained. We studied the bioaccumulation of inorganic and methylmercury (HgII and MeHg, respectively) from different geochemical pools of Hg into four groups of benthic invertebrates (amphipods, polychaetes, chironomids, and bivalves). The study was conducted using mesocosm experiments entailing the use of multiple isotopically enriched Hg tracers and simulation of estuarine systems with brackish water and sediment. We applied different loading regimes of nutrients and terrestrial organic matter and showed that the vertical localization and the chemical speciation of HgII and MeHg in the sediment, in combination with the diet composition of the invertebrates, consistently controlled the bioaccumulation of HgII and MeHg into the benthic organisms. Our results suggest a direct link between the concentration of MeHg in the pelagic planktonic food web and the concentration of MeHg in benthic amphipods and, to some extent, in bivalves. In contrast, the quantity of MeHg in benthic chironomids and polychaetes seems to be driven by MeHg accumulation via the benthic food web. Accounting for these geochemical and dietary drivers of Hg bioaccumulation in benthic invertebrates will be important to understand and predict Hg transfer between the benthic and the pelagic food web, under current and future environmental scenarios.

A potent multifunctional MnS/Ag-polyvinylpyrrolidone nanocomposite for enhanced detection of Hg2+ from aqueous samples and its photocatalytic and antibacterial applications.

The development of nanotechnology for hazardous heavy metal detection with nanoparticles (NPs) created an interest for the preparation of MnS/Ag nanocomposite. Here, MnS/Ag-polyvinylpyrrolidone (PVP) nanocomposite was developed for the detection of mercury. The prepared composite was analyzed using particle size analyzer, X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), Ultraviolet-visible (UV-vis) spectroscopy, zetasizer, high resolution transmission electron microscope (HRTEM) and Fourier-transform infrared spectroscopy (FTIR). The λmax of MnS/Ag-PVP nanocomposite was observed at 404 nm. The particle size was determined to be 21 ± 1.7 nm and the surface charge was -31.19 ± 3 mV. The brownish yellow colour of the nanocomposite changed into colourless when Hg2+ was added. The different metal ions present with the analyte did not show any interference on detection of Hg2+. The MnS/Ag-PVP nanocomposite incorporated paper and gel exhibited visual detection of Hg2+ from aqueous sample. There was an excellent linearity (y = -0.0015x + 0.8744) found in plot of 20 to 100 nM Hg2+ concentrations versus absorbance at 404 nm and the LOD was calculated to be 16 nM. The probe was applied to quantify Hg2+ from spiked environmental sample and the results were further confirmed with atomic absorption spectrophotometric analysis. Hence, the investigation suggests that the present probe could efficiently detect and quantify Hg2+ at nano molar level. In addition, the study suggests that MnS/Ag-PVP nanocomposite exhibit multifunctional property including efficient photocatalytic and antimicrobial activity. The antibacterial activity was evaluated against both gram positive and gram negative bacteria.

Facile colorimetric detection of Hg (II), photocatalytic and antibacterial efficiency based on silver-manganese disulfide/polyvinyl alcohol-chitosan nanocomposites.

The application of nano materials for removal and detection of hazardous metal detection with nanoparticles is important for researcher. In this paper, the silver-manganese disulfide/chitosan-polyvinyl alcohol (Ag-MnS2/CSPVA) nanocomposites was prepared for the detection of toxic heavy metal. The synthesized nano materials was experimented through the various analysis methods to structural and morphological evaluation. The surface charge of the Ag-MnS2/CSPVA was -25.0 ± 0.1 mV. The various metal ions have not effect on detection of mercury (II). The result shows the excellent linearity was found the mercury concentrations changing with limit of detection of 9.0 nM (nano molar level). The condition of detection was conducted at pH 5 and room temperature. Moreover, the photocatalytic properties of the Ag-MnS2/CSPVA nanocomposites was analyzed for degradation of malachite green under visible light irradiation. The complete malachite green degradation reached up to 97.29% after 30 min of photocatalytic reaction. The antibacterial efficiency was studied versus both Escherichia coli and Staphylococcus aureus bacteria. The outcome depicts that the Ag-MnS2/CSPVA nanocomposites has an excellent property in antibacterial activity.

Countereffect of glutathione on divalent mercury removal by nanoscale zero-valent iron in the presence of natural organic matter.

Although there have been multiple studies on the effects of natural organic matter (NOM) on zero-valent iron (ZVI) removal of several regulated heavy metal ions from contaminated water, the role of NOM on Hg(II) removal by nanoscale ZVI (nZVI) has not yet been studied. The experimental results showed that in the presence of 100 mg L-1 of Suwannee River NOM (SRNOM), the Hg(II) removal ratio by nZVI decreased from 89% to 36% after 80 min of reaction. Similar trends were observed in the long-term test maintained for 15 days, attributable to the surface passivation of nZVI by SRNOM. In contrast, addition of 100 µM glutathione (GSH) to the nZVI suspensions increased the Hg(II) removal ratio from 85% to 96% after 15 days of reaction. Furthermore, adding 100 µM of GSH to the nZVI and SRNOM suspensions largely improved the removal efficiency of Hg(II) to be > 99% after 9 days of reaction, related to the enhanced dissolution of Fe(II) and consequent formation of lepidocrocite and maghemite on the nZVI surface. The addition of thiolic compounds is suggested as a promising step in overcoming the inhibitory effect of SRNOM for the remediation of Hg(II) using nZVI technology.

Biosorption Characteristics of Hg(II) from Aqueous Solution by the Biopolymer from Waste Activated Sludge.

The divalent mercury ion (Hg(II)) is one of the most hazardous toxic heavy-metal ions, and an important industrial material as well. It is essential to remove and recover Hg(II) from wastewater before it is released into the environment. In this study, the biosorption characteristics of Hg(II) from aqueous solution by the biopolymer from waste activated sludge (WAS) are investigated. The major components of the biopolymer consisted of proteins, carbohydrates, and nucleic acids. The adsorption kinetics fit for the pseudo-second-order kinetic model, and the adsorption isotherms were well described by Langmuir equation. The adsorption capacity of the biopolymer increased along with rising temperature, and the maximal adsorption capacity was up to 477.0 mg Hg(II)/g biopolymer at 308 K. The infrared spectroscopy analyses showed that the complexation of Hg(II) by the biopolymer was achieved by the functional groups in the biopolymer, including hydroxyl (-OH), amino (-NH2), and carboxylic (-COOH). From the surface morphology, the special reticulate structure enabled the biopolymer to easily capture the metal ions. From the elemental components analyses, a part of Hg(II) ions was removed due to ion exchange with the Na+, K+, and Ca2+, in the biopolymer. Both complexation and ion exchange played key roles in the adsorption of Hg(II) by the biopolymer. These results are of major significance for removal and recovery of Hg(II) from wastewater.

Experimental rainwater divalent mercury speciation and photoreduction rates in the presence of halides and organic carbon.

Mercury (Hg) photochemical redox reactions control atmospheric Hg lifetime and therefore play an important role in global Hg cycling. Oxidation of Hg(0) to Hg(II) is currently thought to be a Br-initiated two-stage reaction with end-products HgBr2, HgBrOH, HgBrONO, HgBrOHO. Atmospheric photoreduction of these Hg(II) compounds can take place in both the gas and aqueous phase. Here we present new experimental observations on aqueous Hg(II) photoreduction rates in the presence of dissolved organic carbon and halides and compare the findings to rainfall Hg(II) photoreduction rates. The pseudo first-order, gross photoreduction rate constant, kred, for 0.5 µM Hg(II) in the presence of 0.5 mg/ L of dissolved organic carbon (DOC) is 0.23 h-1, which is similar to the mean kred (0.15 ±â€¯0.01 h-1(σ, n = 3)) in high altitude rainfall and at the lower end of the median kred (0.41 h-1, n = 24) in continental and marine waters. Addition of bromide (Br-) to experimental Hg(II)-DOC solutions progressively inhibits Hg(II) photoreduction to reach 0.001 h-1 at total Br- of 10 mM. Halide substitution experiments give Hg(II)Xn(n-2) photoreduction rate constants of 0.016, 0.004 h-1, and < detection limit for X = Cl-, Br-, and I- respectively and reflect increasing stability of the Hg(II)-halide complex. We calculate equilibrium Hg(II) speciation in urban and high-altitude rainfall using Visual Minteq, which indicates Hg(II)-DOC to be the dominant Hg species. The ensemble of observations suggests that atmospheric gaseous HgBr2, HgCl2, HgBrNO2, HgBrHO2 forms, scavenged by aqueous aerosols and cloud droplets, are converted to Hg(II)-DOC forms in rainfall due to abundant organic carbon in aerosols and cloud water. Eventual photoreduction of Hg(II)-DOC in aqueous aerosols and clouds is, however, too slow to be relevant in global atmospheric Hg cycling.

Solid-state polymer membranes for simple, sensitive, and low-cost monitoring of mercury in water.

Solid-state Hg(II) selective membranes were produced and assessed by means of X-ray absorption near edge structure in the total reflection X-ray fluorescence (TXRF-XANES) setup and by the energy dispersive X-ray fluorescence (EDXRF) technique. Membranes were functionalized using four promising ligands for mercury complexation, i.e.: i) 4-(2-Pyridylazo) resorcinol (PAR), ii) thiourea, iii) calconcarboxylic acid (CCS), and iv) dithizone. A simple analytical procedure was followed, using miniscule reagent quantities, thus suggesting the process is also cost-effective. TXRF-XANES revealed that mercury complexes with the ligands, and is not simply adsorbed onto the PVC matrix, while the complexation was found to not be affected by the matrix existence. Mercury exhibited an increased oxidation grade and was covalently bound to the ligand functional groups, via a strong chemical bond. EDXRF revealed that the solid-state membranes can be used for mercury speciation and trace analysis from environmentally relevant matrices, such as tap water. The membranes could be a promising alternative to polymer inclusion membranes (PIMs), due to their simple configuration and high Hg (II) selectivity in aqueous media, but more research is needed. PAR appears to be the most promising ligand, followed by dithizone and thiourea. CCS had a minuscule preconcentration efficiency since it was preferably bound with Cu in tap water, indicating limited usefulness for mercury preconcentration. However, results suggest that, depending on the ligand, the solid-state membranes could be also possibly used for multi-elemental heavy metals analysis in water.