Selective solid phase extraction of mercury(II) by silica gel-immobilized-dithiocarbamate derivatives

Highly efficient removal of trace heavy metals by high surface area ordered dithiocarbamate-functionalized magnetic mesoporous silica

The study describes synthesizing and characterizing a novel dithiocarbamate-functionalized magnetic nanocomposite. This nanocomposite exhibits several desirable properties, including a large pore diameter of 2.55 nm, a high surface area of 1149 m2/g, and excellent capturing capabilities. The synthesis process involves the preparation of highly porous magnetic nanocomposites, followed by functionalization with dithiocarbamate functional groups through a reaction with carbon disulfide and amine. The synthesized nanocomposite was thoroughly characterized using various techniques, including X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The performance of the mesoporous nanocomposite as an adsorbent for removing Pb(II), Cd(II), and Cu(II) cations from contaminated water was evaluated. The study finds that the maximum removal efficiency for Pb(II), Cd(II), and Cu(II) cations is achieved at pH values above 4. The optimal contact time for achieving 100% removal efficiency of the mentioned cations ranged between 60 and 120 min. Within this time range, the adsorbent exhibited efficient capture of the heavy metal cations from contaminated water. Additionally, the appropriate amount of adsorbent required for complete elimination of the heavy metal cations is determined. For Cd(II), the optimal dosage was found to be 50 mg of the adsorbent. For Cu(II), the optimal dosage was determined to be 40 mg. Finally, for Pb(II), the optimal dosage was 30 mg. The adsorbent's regeneration capability was demonstrated, showing that it could be reused for five consecutive runs.

The present and potential future of aqueous mercury preservation: a review

Mercury is considered to be one of the most toxic elements to humans. Due to pollution from industry and artisanal gold mining, mercury species are present globally in waters used for agriculture, aquaculture, and drinking water. This review summarises methods reported for preserving mercury species in water samples and highlights the associated hazards and issues with each. This includes the handling of acids in an uncontrolled environment, breakage of sample containers, and the collection and transport of sample volumes in excess of 1 L, all of which pose difficulties for both in situ collection and transportation. Literature related to aqueous mercury preservation from 2000-2021 was reviewed, as well as any commonly cited and relevant references. Amongst others, solid-phase extraction techniques were explored for preservation and preconcentration of total and speciated mercury in water samples. Additionally, the potential as a safe, in situ preservation and storage method for mercury species were summarised. The review highlighted that the stability of mercury is increased when adsorbed on a solid-phase and therefore the metal and its species can be preserved without the need for hazardous reagents or materials in the field. The mercury species can then be eluted upon return to a laboratory, where sensitive analytical detection and speciation methods can be better applied. Developments in solid phase extraction as a preservation method for unstable metals such as mercury will improve the quality of representative environmental data, and further improve toxicology and environmental monitoring studies.

Fabrication and characterization of 3,4-diaminobenzophenone-functionalized magnetic nanoadsorbent with enhanced VOC adsorption and desorption capacity

The present study, for the first time, utilized 3,4-diaminobenzophenone (DABP)-functionalized Fe₃O₄/AC@SiO₂ (Fe₃O₄/AC@SiO₂@DABP) magnetic nanoparticles (MNPs) synthesized as a nanoadsorbent for enhancing adsorption and desorption capacity of gaseous benzene and toluene as volatile organic compounds (VOCs). The Fe₃O₄/AC@SiO₂@DABP MNPs used in adsorption and desorption of benzene and toluene were synthesized by the co-precipitation and sol-gel methods. The synthesized MNPs were characterized by SEM, FTIR, TGA/DTA, and BET surface area analysis. Moreover, the optimization of the process parameters, namely contact time, initial VOC concentration, and temperature, was performed by applying response surface methodology (RSM). Adsorption results demonstrated that the Fe₃O₄/AC@SiO₂@DABP MNPs had excellent adsorption capacity. The maximum adsorption capacities for benzene and toluene were found as 530.99 and 666.00 mg/g, respectively, under optimum process parameters (contact time 55.47 min, initial benzene concentration 17.57 ppm, and temperature 29.09 °C; and contact time 57.54 min, initial toluene concentration 17.83 ppm, and temperature 27.93 °C for benzene and toluene, respectively). In addition to the distinctive adsorptive behavior, the Fe₃O₄/AC@SiO₂@DABP MNPs exhibited a high reproducibility adsorption and desorption capacity. After the fifth adsorption and desorption cycles, the Fe₃O₄/AC@SiO₂@DABP MNPs retained 94.4% and 95.4% of its initial adsorption capacity for benzene and toluene, respectively. Kinetic and isotherm findings suggested that the adsorption mechanisms of benzene and toluene on the Fe₃O₄/AC@SiO₂@DABP MNPs were physical processes. The results indicated that the successfully synthesized Fe₃O₄/AC@SiO₂@DABP MNPs can be applied as an attractive, highly effective, reusable, and cost-effective adsorbent for the adsorption of VOC pollutants.Graphical abstract.

Enhanced Pb(II) adsorption onto functionalized ordered mesoporous carbon (OMC) from aqueous solutions: the important role of surface property and adsorption mechanism

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO₃ and H₃PO₄ to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pH_pzc, the main Pb(II) existing species of Pb(II) and Pb(OH)⁺ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

Engineering β-ketoenol structure functionality in hybrid silica as excellent adsorbent material for removal of heavy metals from water

A chelating adsorbent based on the chemical modification of silica by an efficient host able to capture toxic metals, is presented.

Heavy Metal Ion Adsorption Properties of Methacrylamidocysteine-Containing Porous Poly(Hydroxyethyl Methacrylate) Chelating Beads

Details of the adsorption performance of poly(2-hydroxyethylmethacrylate–methacrylamidocysteine) [p(HEMA–MAC)] beads towards the removal of heavy metal ions from aqueous solution were studied. The metal-complexing ligand and/or co-monomer MAC was newly synthesized from methylacrylochloride and cysteine. Spherical beads of average size 150–200 mm were obtained by the radical suspension polymerization of MAC and HEMA conducted in an aqueous dispersion. The p(HEMA–MAC) beads obtained had a specific surface area of 18.9 m2/g.

p(HEMA–MAC) beads were characterized by swelling studies, FT-IR spectroscopy and elemental analysis. Such beads with a swelling ratio of 72%, and containing 3.9 mmol MAC/g, were used for heavy metal removal studies. The adsorption capacities of the beads for selected metal ions, i.e. CdII, AsIII, CrIII, HgII and PbII, were investigated in aqueous media containing different amounts of these ions (10–750 mg/l) and at different pH values (3.0–7.0). The adsorption rate was fast in all cases. The maximum adsorption capacities of the p(HEMA–MAC) beads were 1058.2 mg/g for CdII, 123.4 mg/g for AsIII, 199.6 mg/g for CrIII, 639.1 mg/g for PbII and 1018.6 mg/g for HgII. On a molar basis, the following affinity order was observed: CdII > HgII > CrIII > PbII >AsIII. The adsorption capacity of the MAC-incorporated beads was affected significantly by the pH value of the aqueous medium.

The adsorption of heavy metal ions from artificial wastewater was also studied. In this case, the adsorption capacities were 52.2 mg/g for CdII, 23.1 mg/g for CrIII, 83.4 mg/g for HgII, 62.6 mg/g for PbII and 11.1 mg/g for AsIII at an initial metal ion concentration of 0.5 mmol/l. The chelating beads could be regenerated easily with a higher effectiveness by 0.1 M HNO3. These features make p(HEMA–MAC) beads potential candidates for heavy metal ion removal at high capacity.

Catalytic properties of N-hydroxyphthalimide immobilized on a novel porous organic polymer in the oxidation of toluene by molecular oxygen

A novel porous organic polymer pSt was prepared based on silica gel and used for the immobilization of NHPI. The obtained heterogeneous catalyst could adsorb toluene and oxidize it to benzoic acid using a co-catalyst Co(OAc)₂ and molecular oxygen.

Switchable solvent based liquid phase microextraction of mercury from environmental samples: a green aspect

A novel and environmental friendly approach using switchable solvent based liquid phase microextraction (SPS-LPME), followed by UV-vis-spectrophotometric determination has been developed for the preconcentration and determination of mercury.

Multicomponent synthesis of dithiocarbamates starting from vinyl sulfones/sulfoxides and their use in polymerization reactions

Synthesis of dithiocarbamates from vinyl sulfones/sulfoxides and the corresponding polymers with a dithiocarbamate backbone using divinyl sulfone and diamines is reported.

Functionalized Silica Gel as Green Material for Metal Remediation

Advancement in industrialization and urbanization is a good indicator of the progress of humanity. However, it has an evil side as well. This advancement is identified as being responsible for deleterious effects on the health of human beings and aquatic biodiversity. Anthropogenic activities like mining and disposal of treated/untreated waste effluents containing toxic metals have resulted in severe deterioration of water quality, rendering serious environmental problems. The basic problem is that the wastewater generated through industries is not given the necessary pretreatment and is discharged directly into water resources. The metals beyond their permissible limits cause maximum negative impacts owing to their long biological half-lives and nondegradable nature. The condition is further worsening in economically deprived countries, where this metal-contaminated wastewater is directly used in various agricultural and day-to-day practices. As a solution to this, the extraction and removal of toxic metal ions from these polluted water resources at an industrial level is of paramount importance. This chapter provides the enthusiastic efforts of the scientific community to disseminate the fundamentals and practices of green analytical methods for metal removal. These methods are based on solid-phase extraction using functionalized silica gel for the separation and preconcentration of metal ions in polluted water resources. Ease of synthesis and extensive application of these organic-inorganic hybrid materials helps to fulfil the commitment of continual environmental improvement by remediating the wastewater.

Synthesis of a novel silica-supported dithiocarbamate adsorbent and its properties for the removal of heavy metal ions

Silica-supported dithiocarbamate adsorbent (Si-DTC) was synthesized by anchoring the chelating agent of macromolecular dithiocarbamate (MDTC) to the chloro-functionalized silica matrix (SiCl), as a new adsorbent for adsorption of Pb(II), Cd(II), Cu(II) and Hg(II) from aqueous solution. The surface characterization was performed by FT-IR, XPS, SEM and elemental analysis indicating that the modification of the silica surface was successfully performed. The effects of media pH, adsorption time, initial metal ion concentration and adsorption temperature on adsorption capacity of the adsorbent had been investigated. Experimental data were exploited for kinetic and thermodynamic evaluations related to the adsorption processes. The characteristics of the adsorption process were evaluated by using the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption isotherms and adsorption capacities were found to be 0.34 mmol g(-1), 0.36 mmol g(-1), 0.32 mmol g(-1) and 0.40 mmol g(-1) for Pb(II), Cd(II), Cu(II) and Hg(II), respectively. The adsorption mechanism of Hg(II) onto Si-DTC is quite different from that of Pb(II), Cd(II) or Cu(II) onto Si-DTC, which is demonstrated by the XPS and FT-IR results.

WITHDRAWN: Preparation and characterization of silica gel/chitosan composite for the removal of Cu(II) and Pb(II)

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New solid-phase-nanoscavenger for the analytical enrichment of mercury from water

A nanoscavenger of mercaptopropyl-modified silica microparticles has been developed for the determination of trace levels of mercury(II) in water. The synthesis of silica microparticles nanoscavengers is carried out by modification of pre-formed silica particles with mercaptopropyltrimethoxysilane or by incorporating the thiol modification agent during the growth of the silica particles. The silica nanoscavengers were characterized by SEM, TGA, particle analyzer, IR and the parameters influencing the extraction and recovery phases of the preconcentration process were performed by AAS. The results show that careful choice of particle size and surface characteristics produce a new mercapto-silica-nanoscavenger that disperses in water as a quasi-stable sol. This permits the facile recovery of the mercury-loaded nanoscavenger particles. No agitation is required during the mercury extraction as the dispersion is maintained by Brownian motion and slow gravitational sedimentation. The technique overcomes a number of problems, such as cross-contamination and decreases in mercury concentration during sample transportation to the laboratory. Recovery achieved reaches >97 ± 4% over a wide range of preconcentration factors. At a preconcentration factor of 50 the limit of detection (3σ) was 0.19 ng mL(-1). The method is environmentally friendly as only 300 mg of mercapto-nanoscavenger is used, no organic solvent is required for the extraction and the experiment is performed without the need for manual or mechanical agitation.

Copper removal by carbon nanomaterials bearing cyclam-functionalized silica

The synthesis of metal (Fe, Co, Ni)-encapsulated carbon nanomaterials coated with cyclam-bonded silica has been described. The organic layer was identified by Fourier transform infrared spectroscopy and elemental analysis. The functionalized magnetic nanomaterials were employed to extract the divalent cations: copper, calcium, cobalt, manganese and nickel from aqueous solutions. Their adsorption capacities were studied by the batch procedure. The concentration of cations extracted was determined by inductively coupled plasma mass spectrometry. Influence of different parameters viz. pH, amount of the compound studied, contact time, on the cation extraction was investigated. Under optimum conditions copper extraction was significantly more efficient when compared with other coexisting ions.

Silica coated magnetite particles for magnetic removal of Hg2+ from water

The magnetic removal of Hg(2+) from water has been assessed using silica coated magnetite particles. The magnetite particles were first prepared by hydrolysis of FeSO(4) and their surfaces were modified with amorphous silica shells that were then functionalized with organic moieties containing terminal dithiocarbamate groups. Under the experimental conditions used, the materials reported here displayed high efficiency for Hg(2+) uptake (74%) even at contaminant levels as low as 50 μg l(-1). Therefore these eco-nanomagnets show great potential for the removal of heavy metal ions of polluted water, via magnetic separation.

Sodium dodecyl sulfate coated poly (vinyl) chloride: an alternative support for solid phase extraction of some transition and heavy metals

A simple and relatively fast approach for developing a solid phase extraction has been described and used for determination of trace quantities of some heavy and transition metal ions with sodium dodecyl sulfate (SDS)-coated poly vinyl chloride (PVC) modified with bis(2-hydroxyacetophenone)-1,4-butanediimine (BHABDI) ligand. The adsorbed ions were stripped from the solid phase by 10 mL of 3M nitric acid as eluent. The eluting solution was analyzed for metals content (cadmium, chromium, cobalt, copper, lead and zinc) by flame atomic absorption spectrometry (FAAS). The main factors such as pH, amount of ligand and PVC, amount and type of surfactant, and condition of eluting solutions on the sorption recovery of metal ions have been investigated in detail. The relative standard deviation was found in the range of 1.0-3.2% for 0.2 microg mL(-1)of metals ions. After optimization of the extraction condition and the instrumental parameters, a detection limit was found to be in the range of 1.2-3.1 microg L(-1), with enrichment factor of 50 was achieved. The method was successfully applied for the determination of these metals contents in real samples with satisfactory results.

The removal of mercury from water by open chain ligands containing multiple sulfurs

Mercury pollution is a serious challenge faced by environmental chemists over the world. For several years now, our group has been developing new compounds to precipitate and thereby remove mercury from water. In this paper, we present a new family of alkyl thiol mercury chelates to add to the aromatic ligands we have previously reported. These new compounds are effective at precipitating mercury from water and with an excess of the best compound, removal is quantitative. Furthermore, the precipitates are stable and released little to no mercury back into solution during leaching studies.

Functionalized HMS mesoporous silica as solid phase extractant for Pb(II) prior to its determination by flame atomic absorption spectrometry

In this work, a mesoporous silica has been chemically modified with 5-mercapto-1-methyl-1-H-tetrazol using the homogeneous route (MTTZ-HMS). This synthetic route involved the reaction of 5-mercapto-1-methyl-1-H-tetrazol with 3-chloropropyltriethoxysilane, prior to immobilization on the support. The resulting material has been characterized and employed as solid phase extractant for Pb(II). The effect of several variables (stirring time, pH, temperature, metal concentration, presence of other metals) has been studied using batch and column techniques. In batch experiments, 15 min stirring time, 55 degrees C and pH 8 were the optimal conditions for Pb(II) adsorption. In column experiments, sorption was quantitative for 1000 mL of 2.41 x 10(-4 )mM of Pb(II) solution and adsorbed ions were eluted out by 5 mL of 1 M HCl (preconcentration factor of 200). Spiked tap water was used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 100% recovery was obtained. The LOD and LOQ values of the proposed method were found to be 3.52 x 10(-3) and 4.20 x 10(-3 )mM, respectively. The RSD for three preconcentration experiments was found to be <or= 2%. The linear working range for measurements was between 2 x 10(-3 )and 0.14 mM (y = 0.0136x + 0.0007, R(2 )= 0.9999).

Principais rotas de síntese de resinas complexantes de mercúrio

A recuperação de espécies contendo mercúrio utilizando resinas complexantes obtidas a partir da modificação de suportes poliméricos vem atraindo cada vez mais a atenção dos pesquisadores. São muitas as combinações de suportes e grupos complexantes para a síntese desses materiais. Assim, este trabalho apresenta uma revisão sobre os principais grupos funcionais avaliados, bem como as rotas de síntese adotadas para a imobilização desses grupos nos suportes. É abordada também a problemática da síntese de uma resina eficiente, produzida a partir de um processo limpo e acessível às indústrias que utilizam mercúrio em seus processos.