Microbial Sensing and Removal of Heavy Metals: Bioelectrochemical Detection and Removal of Chromium(VI) and Cadmium(II).

The presence of inorganic pollutants such as Cadmium(II) and Chromium(VI) could destroy our environment and ecosystem. To overcome this problem, much attention was directed to microbial technology, whereas some microorganisms could resist the toxic effects and decrease pollutants concentration while the microbial viability is sustained. Therefore, we built up a complementary strategy to study the biofilm formation of isolated strains under the stress of heavy metals. As target resistive organisms, Rhizobium-MAP7 and Rhodotorula ALT72 were identified. However, Pontoea agglumerans strains were exploited as the susceptible organism to the heavy metal exposure. Among the methods of sensing and analysis, bioelectrochemical measurements showed the most effective tools to study the susceptibility and resistivity to the heavy metals. The tested Rhizobium strain showed higher ability of removal of heavy metals and more resistive to metals ions since its cell viability was not strongly inhibited by the toxic metal ions over various concentrations. On the other hand, electrochemically active biofilm exhibited higher bioelectrochemical signals in presence of heavy metals ions. So by using the two strains, especially Rhizobium-MAP7, the detection and removal of heavy metals Cr(VI) and Cd(II) is highly supported and recommended.

Recent findings and future directions of grafted gum karaya polysaccharides and their various applications: A review.

Gum karaya is a polysaccharide that has several industrial applications in the pharmaceutical, food, and environmental fields owing to its hydrophilic, anionic, and biocompatible nature. Gum karaya and its modified forms have been assessed for drug delivery, wastewater treatment, and food industry applications. This review provides a comprehensive overview of various synthetic methods of modification of gum karaya, such as grafting initiated through free radical, microwave-assisted grafting, radiation-assisted, and enzyme-assisted modification methods. In addition, the review outlines collective industrial applications of modified gum karaya in drug delivery systems, removal of heavy atoms, dyes, food, and other biological activities, and suggests possible prospects for gum karaya modification and their remarkable industrial applications.

Development of Novel Bead Milling Technology with Less Metal Contamination by pH Optimization of the Suspension Medium.

To develop novel contamination-less bead milling technology without impairing grinding efficiency, we investigated the effect of the formulation properties on the grinding efficiency and the metal contamination generated during the grinding process. Among the various formulations tested, the combination of polyvinylpyrrolidone and sodium dodecyl sulfate was found to be suitable for efficiently pulverizing phenytoin. However, this stabilization system included a relatively strong acid, which raised the concern of possible corrosion of the zirconia beads. An evaluation of the process clearly demonstrated that acidic pH promoted bead dissolution, suggesting that this could be suppressed by controlling the pH of the suspension. Among the various pH values tested, the metal contamination generated during the grinding process could be significantly reduced in the optimized pH range without significant differences in the particle size of the phenytoin suspension after pulverization. In addition, the contamination reduction by pH optimization in the presence of physical contact among the beads was approximately 10-times larger than that without bead contact, suggesting that pH optimization could suppress not only bead dissolution but also the wear caused by bead collisions during the grinding process. These findings show that pH optimization is a simple but effective approach to reducing metal contamination during the grinding process.

Health risk of heavy metals in street dust.

Heavy metals in street dust represent a risk to the human health due to their toxicity, persistence and bioaccumulation. Using the US Environmental Protection Agency (USEPA) assessment, here, we review the human health risks of such dust world-wide. The street dust in such cities is contaminated by As, Cd, Cr, Cu, Hg, Mn Ni, Pb and Zn beyond the median levels of the world soil background values. Among these elements, the median values of the hazard risk indices (non-carcinogenic risk) are highest for As, Cr and Pb and the median values of the risk indices (carcinogenic risk) for As are in the tolerable risk range for children and adults and in the case of Pb, the median value of the carcinogenic risk indices are also in the tolerable range for children. We emphasize that the level of heavy metals in street dust pose a considerable risk to the human health and require monitoring and approaches to reduce such toxic levels.

Metabolite profiling and evaluation of CYP450 interaction potential of 'Trimada'- an Ayurvedic formulation.

ETHNOPHARMACOLOGICAL RELEVANCE: Trimada is well-known polyherbal Ayurvedic formulation used in Indian Traditional medicine since ancient times. It consisted of three inebriant herbs including "Chitraka" (Plumbago zeylanica Linn. Family- Plumabaginaceae), "Musta" (Cyperus rotundus Linn. Family- Cyperaceae) and Vidanga (Embelia ribes Burm. F. Family- Myrsinaceae) in equal ratios as mentioned in Ayurveda. Trimada is traditionally used to increase the functioning of the digestive system and metabolism. Along with these, it also assists in the reduction of cholesterol as well as reduces stomach aches and chest pain. AIM OF THE STUDY: This study is aimed to identify the metabolites present in this polyherbal formulation. Further, the cytotoxicity and interaction potential of the formulation and individual herbs with Cytochrome P450 isozymes (CYP3A4, 2D6, 2C9, 1A2) was evaluated by MTT assay and CYP450 enzyme inhibition. The concentration of heavy metals was also determined. MATERIAL AND METHODS: Ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-QTOF-MS) analysis was performed to detect and identify the phytoconstituents in the formulation. Cytotoxicity of the formulation was evaluated by MTT assay. CYP450 enzyme interaction potential of the individual herbs and the Trimada formulation was carried out through CYP-CO assay and fluorometric high throughput screening (HTS) assay for individual isozymes. The content of heavy metal in the formulation was quantified by Atomic Absorption Spectroscopy. RESULTS: Trimada formulation exhibited lower cytotoxicity to human liver carcinoma cell line (HepG2). CYP-CO assay revealed that the interaction potential of individual herbs and Trimada on the liver microsomes was found to be lesser than the standard inhibitor ketoconazole. Individual herbs and Trimada formulation displayed higher IC50 values than the respective standard inhibitors in the fluorimetric assay. UPLC-QTOF-MS analysis showed the presence of a number of active phytoconstituents including sesquiterpenes, phenolic acids, benzoquinones, triterpenes and flavonoids. The heavy metal concentration in the traditional medicinal herbal formulation was found within the approved limit. CONCLUSIONS: This study suggested that the individual herbs and Trimada formulation exhibited low cytotoxicity and contributes insignificant interaction with CYP450 isozymes. So, the formulation is considered to be safe for its therapeutic management without any potential drug interaction involving CYP 450 isozymes.

Diversity, structure and regulation of microbial metallothionein: metal resistance and possible applications in sequestration of toxic metals.

Metallothioneins (MTs) are a group of cysteine-rich, universal, low molecular weight proteins distributed widely in almost all major taxonomic groups ranging from tiny microbes to highly organized vertebrates. The primary function of this protein is storage, transportation and binding of metals, which enable microorganisms to detoxify heavy metals. In the microbial world, these peptides were first identified in a cyanobacterium Synechococcus as the SmtA protein which exhibits high affinity towards rising level of zinc and cadmium to preserve metal homeostasis in a cell. In yeast, MTs aid in reserving copper and confer protection against copper toxicity by chelating excess copper ions in a cell. Two MTs, CUP1 and Crs5, originating from Saccharomyces cerevisiae predominantly bind to copper though are capable of binding with zinc and cadmium ions. MT superfamily 7 is found in ciliated protozoa which show high affinity towards copper and cadmium. Several tools and techniques, such as western blot, capillary electrophoresis, inductively coupled plasma, atomic emission spectroscopy and high performance liquid chromatography, have been extensively utilized for the detection and quantification of microbial MTs which are utilized for the efficient remediation and sequestration of heavy metals from a contaminated environment.

Thermal characteristics and cadmium binding behavior of EC-ELP fusion polypeptides.

Elastin-like polypeptides (ELPs) are stimulus-responsive protein-based biopolymers that exhibit phase transition behavior. By joining them to synthetic phytochelatin (EC), EC-ELP fusion proteins with temperature sensitivity and metal-binding functionality were generated to remove heavy metal ions biologically. Three different EC domains (EC10, EC20, EC30) were incorporated into the ELP, and the EC-ELP fusion proteins were expressed in E. coli. Their thermal properties and metal binding abilities were then investigated according to the EC length. In addition, the feasibility of reusing EC-ELPs and the cadmium ion binding affinity of reused EC-ELPs were explored.

Carboxymethyl cellulose-based cryogels for efficient heavy metal capture: Aluminum-mediated assembly process and sorption mechanism.

Heavy metal ions pollution is a terrible issue that needs to be efficiently treated as a matter of priority to construct our sustainable society. However, the easy-to-handling of high-performance biomass-derived sorbents with fascinating features like high sorption capacity, favorable separation and recycling remain challenging. Herein, the development of a novel bead-like adsorbent with above features, that is, Al(III)-assembled carboxymethyl cellulose beads were used for the removal of Pb(II), Ni(II) and Co(II) from aqueous solution. Characterization methods like FT-IR, SEM, XPS and TGA were employed to confirm its physicochemical properties. Removal of the three heavy metal ions at different pH values, initial concentration and contact time were discussed at batch adsorption experiments. Meanwhile, regeneration was also discussed deeply. The results revealed that the adsorption capacity of the sorbents for three heavy metals increases with increasing pH and the initial concentration. The adsorption isotherm could be described well by the Freundlich model, and the maximum adsorption capacity for Pb(II), Ni(II) and Co(II) were 550, 620 and 760 mg/g, respectively. Kinetics study indicated that the Pseudo-second-order model described the best correlation with experimental data, this suggested that the complexation may participated in the adsorption process. More significantly, this type of bead-like adsorbents displayed excellent reusability after four sequential cycles.

Novel polymer crafted sugar thiacrown ether and its applications in recovery of metal ions.

Polymeric macrocycles are important as complexation agents in chemistry. The multivalent binding of heteroatoms inside the macrocycle to metals and organic pollutants has gained much interest. A protecting group strategy was applied to synthesise functionalized crown ether based on glucose. The 4,6-position was protected by benzylidene, and arms were introduced on the remaining hydroxyls in 2- and 3-positions. Cyclization was achieved through sodium sulfide in ethanol. The selective cleavage of the benzylidene protecting group left the free hydroxyl group on C-6 position. The propargyl group was introduced and attached the macrocycles to polyvinyl azide by click reaction. The compounds were identified by nuclear magnetic resonance, infrared spectroscopy and mass spectrometry, and the morphology and thermal stability of the polymer were characterized via field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and differential scanning calorimetry. The removal of metal ions Co, Cd and Pb was performed by atomic absorption spectrometry in different experimental conditions. The results indicated that synthesised crown ether can effectively removal such metals and has highly sufficient recyclability.

Salicylaldehyde derivative of nano-chitosan as an efficient adsorbent for lead(II), copper(II), and cadmium(II) ions.

In this study, a biodegradable natural polymer chitosan was modified with salicylaldehyde to prepare salicylaldehyde functionalized chitosan nanoparticles (N-Ch-Sal). The N-Ch-Sal was characterized by atomic force microscopy (AFM), scanning electron microscopy-energy-dispersive X-ray (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The salicylaldehyde functionalized chitosan nanoparticles (N-Ch-Sal) (~80 nm) were then used for the adsorption of three heavy metals viz., Cu(II), Cd(II) and Pb(II) ions. The above-mentioned techniques were also employed for evaluation of changes in N-Ch-Sal after metal adsorption. The parameters affecting the adsorption of metal ions including pH, contact time, amount of adsorbent, initial metal ion concentration and the effect of interfering ions, were studied thoroughly and optimized. The concentration of metal ions remaining in the aqueous system after adsorption experiments was analyzed by ICP-MS. At optimal conditions, sorption capacity of Pb(II) ion was found to be highest i.e., 123.67 followed by Cu(II) (84.60) and Cd(II) (63.71 mg/g). The adsorption process followed the pseudo-second-order kinetic model and fitted well with the Langmuir adsorption isotherm. The adsorption method was applied to a real tap water sample for the quantification and removal of Pb(II) ions. The concentration of Pb(II) ions in the tested sample was 4.88 ppb.

Levels of heavy metals in soil and vegetables and associated health risks in Mojo area, Ethiopia.

Health implications to the population due to the consumption of contaminated vegetables has been a great concern all over the world. In this study, the levels of heavy metals (Cr, Cd, Zn, Fe, Pb, As, Mn, Cu, Hg, Ni and Co) in soil and commonly consumed vegetables from Mojo area in central Ethiopia have been determined using Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) and possible health risks due to the consumptions of the vegetables have also been estimated. The levels of As, Pb, Cd, Zn, Cu, Hg and Co were exceeded the reference level in agricultural soil. Likewise, As, Pb, Cd, Cr and Hg levels exceeded the recommended values in vegetable samples with concentrations ranging from 1.93-5.73, 3.63-7.56, 0.56-1.56, 1.49-4.63 and 3.43-4.23 mg/kg, respectively. It was observed that leafy vegetable (cabbage) has accumulated heavy metals to greater extent compared with tomato. The estimated daily intake (EDI) of toxic metals due to the consumption of the vegetables were below the maximum tolerable daily intake (MTDI). However, the total health quotient (THQ), calculated based on EDI of the heavy metals were found > 1 for As and Hg due to tomato consumption and for As, Hg and Co due to cabbage consumption, suggesting significant health risk. The health index (HI) due to the intake of toxic metals from the consumption of both vegetables were much > 1, with HI values of 7.205 and 15.078 due to tomato and cabbage consumption, respectively. This clearly suggests the possible adverse health effect to adult population from the consumption of tomato and cabbage from the study area. The total cancer risk (TCR) analysis have also revealed the potential adverse cancer risk induced by As, Cd, Hg, and Ni from the consumption of both tomato and cabbage as their TCR values were above the threshold level. Based on the results of this study, there would be a significant health risk (both non-carcinogenic and carcinogenic) to the consumer associated with the consumption of cabbage and tomato being cultivated in Mojo area. Consequently, we recommend a strict regulatory control on the safety of vegetables originated from the study area.

Distribution and speciation of iron in Fe-modified biochars and its application in removal of As(V), As(III), Cr(VI), and Hg(II): An X-ray absorption study.

Characterization of the spatial distribution and speciation of iron (Fe) in Fe-modified biochars is critical for understanding the mechanisms of contaminant removal. Here, synchrotron-based techniques were applied to characterize the spatial distribution and speciation of Fe in biochars modified by FeCl3 or FeSO4 and pyrolyzed at 300, 600, and 900 °C, respectively. Confocal micro-X-ray fluorescence imaging (CMXRFI) results indicated Fe, sulfur (S), and chlorine (Cl) diffused into the basic porous structure of the biochars and aggregated to the surface as pyrolysis temperature increased. Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra revealed maghemite (γ-Fe2O3) as the primary Fe species in the modified biochars and Fe(0) was observed when pyrolyzed at 600 or 900 °C. Unmodified and FeCl3-modified biochars pyrolyzed at 900 °C were evaluated in the removal of arsenate (As(V)), arsenite (As(III)), hexavalent chromium (Cr(VI)) and Hg(II) from aqueous solution and Fe-modification enhanced the removal efficiency from 42.0%, 62.5%, 19.6%, and 97.0%, respectively, to all 99.9%. X-ray absorption spectroscopy results indicate both adsorption and redox reaction contributed to the removal mechanisms. The present study provides a prospective and sustainable material and offers information relevant to tailoring Fe-modified biochars to specific environmental applications.

Foamed urea-formaldehyde microspheres for removal of heavy metals from aqueous solutions.

A simple foaming method was applied to fabricate urea formaldehyde (UF) microspheres with cross-linked porous structures for environmental remediation of heavy metals. The specific surface area and average pore radius of the resultant foamed UF microspheres were 11-29 m2/g and 11-25 nm, respectively, which increased with the increasing molar ratio of formaldehyde to urea. All the foamed UF microspheres showed good removal of heavy metals ions (Pb(II), Cu(II), and Cd(II)) in both single- and mixed-metal solutions. Further investigations of Pb(II) adsorption on a selected UF microspheres showed fast kinetics and relatively high adsorption capacity (21.5 mg/g), which can be attributed to the mesoporous structure and abundance of oxygen surface functional groups of the microspheres. Both experimental and model results showed that chelation or complexation interactions between Pb(II) and the surface functional groups were responsible to the strong adsorption of the heavy metal ions on the microspheres. Hydrochloric acid (0.05 M) successfully desorbed Pb(II) from the post-adsorption microspheres for multiple times and the regenerated microspheres showed high Pb(II) removal rates (>96%) in five adsorption-desorption cycles. With many promising advantages, foamed UF microspheres show great potential as a wastewater treatment agent for heavy metal removal.

Selection of the Optimal Spectral Resolution for the Cadmium-Lead Cross Contamination Diagnosing Based on the Hyperspectral Reflectance of Rice Canopy.

This paper proposed an optimal spectral resolution for diagnosing cadmium-lead (Cd-Pb) cross contamination with different pollution levels based on the hyperspectral reflectance of rice canopy. Feature bands were sequentially selected by two-way analysis of variance (ANOVA2) and random forests from the high-dimensional hyperspectral data after preprocessing. Then Support Vector Machine (SVM) was applied to diagnose the pollution levels using different feature bands combination with different spectral resolutions and cross validation was conducted to evaluate the distinguishing accuracies. Finally, the optimal spectral resolution could be determined by comparing the diagnosing accuracies of the optimal feature bands combination in each spectral resolution. In the experiments, the hyperspectral reflectance data of rice canopy with ten different spectral resolutions was captured, covering 16 pretreatments of Cd and Pb pollution. The experimental results showed the optimal spectral resolution was 9 nm with the highest average accuracy of 0.71 and relatively standard deviation of 0.07 for diagnosing the categories and levels of Cd-Pb cross contamination. The useful exploration provided an evidence for optimal spectral resolution selection to reduce the cost of heavy metal pollution diagnose.

Adsorptive removal of lead (Pb), copper (Cu), nickel (Ni) and mercury (Hg) ions from water using chitosan silica gel composite.

Silica gel chitosan composite was prepared to perform adsorptive experiment of different heavy metal ion solutions. The characterization of chitosan + silica gel (Ch + Sg) composite was done by FTIR and SEM-EDS to understand the presence of active sites and to have an insight on the surface morphology. The adsorption study of heavy metal ions by Ch + Sg composite gives maximum removal percent for Cu, Pb and Ni which were obtained at pH 5 and for Hg at pH 6.The trend of removal by Ch + Sg signifies that maximum removal percent was attained at 120 min. The surface of Ch + Sg is heterogeneous for the adsorption of Hg, Ni and Cu and homogeneous for Pb adsorption. The values obtained for Pb signify that its adsorption best fitted to pseudo first order with the R2 value of 0.986, whereas pseudo second order best fitted to the experimental data of Cu, Ni and Hg as R2 values which are 0.983, 0.819 and 0.957 respectively. The values of change in entropy (⊿S) obtained for Pb, Cu, Ni and Hg are - 69.33, - 118, - 63.33 and - 98.52 J/mol K respectively. Negative values of change in enthalpy, ⊿H in (kJ/mol) are in the range of - 18.2 to - 37.66 which indicates both physical and chemical adsorption involves in the process of adsorption.

Combining potassium chloride leaching with vertical electrokinetics to remediate cadmium-contaminated soils.

This study evaluated the feasibility of combining potassium chloride (KCl) leaching and electrokinetic (EK) treatment for the remediation of cadmium (Cd) and other metals from contaminated soils. KCl leaching was compared at three concentrations (0.2%, 0.5%, and 1% KCl). EK treatment was conducted separately to migrate the metals in the topsoil to the subsoil. The combined approach using KCl leaching before or after EK treatment was compared. For the single vertical EK treatment, the removal of Cd, lead (Pb), copper (Cu) and zinc (Zn) from the topsoil (0-20 cm) was 9.38%, 4.80%, 0.95%, and 10.81%, respectively. KCl leaching at 1% KCl removed 84.06% Cd, 9.95% Pb, 4.34% Cu, and 19.93% Zn from the topsoil, with higher removal efficiency than that of the 0.2% and 0.5% KCl leaching treatments. By combining the KCl leaching and EK treatment, the removal efficiency of heavy metals improved, in particular for the 1% KCl + EK treatment, where the removal rate of Cd, Pb, Cu, and Zn from the upper surface soil reached 97.79%, 17.69%, 14.37%, and 41.96%, respectively. Correspondingly, the soil Cd content decreased from 4 to 0.21 mg/kg, and was below the Chinese standard limit of 0.3 mg/kg soil. These results indicate that 1% KCl + EK treatment is a good combination technique to mitigate Cd pollution from contaminated soils used for growing rice and leafy vegetables.

Multistage remediation of heavy metal contaminated river sediments in a mining region based on particle size.

Sediment pollution is an important environmental problem, and the remediation of heavy metal contaminated sediments is crucial to river ecosystem protection, especially in mining regions. In this work, characteristics of heavy metals (Cu, Zn, Cd, As and Hg) were investigated, including contents and fractions based on particle size (PS) in river sediments. Chemical leaching and stabilization for sediment remediation were performed, and the technology feasibility was assessed. The results indicated that the heavy metals were primarily reserved within fine sediments (PS < 75 µm), comprising 79.8% of the total. For the sequentially extracted fractions, residual fraction dominated the total content in large PS sections (PS > 150 µm), while the oxidizable fraction, reducible fraction and weak acid extractable fraction dominated the total content in fine sediments, except for that of Hg. Chemical leaching can transform most metals in sediments from large-sized particles to fine particles because the metals are absorbed by fine particles in solution rather than complexation. The stabilization suggested that cement could be an effective agent for ecological risk control for heavy metals. In field engineering, a total of 145,000 m3 sediment was divided into various sections by PS and synchronously washed by eluting agents. Finally, clean sediments (PS > 150 µm) were used as building material and clean backfilling; meanwhile, heavily polluted sediments (PS < 150 µm) were buried as general industrial solid waste after stabilization treatment. Over 90% of the contaminated sediments were reused throughout multistep remediation. Furthermore, a reduction in waste and harm, along with resources, was obtained. This study provided a feasible technology for heavy metal contaminated sediment remediation.

Amine-terminated dendritic polymers as a multifunctional chelating agent for heavy metal ion removals.

In this study, amine-terminated hyperbranched PAMAM (polyamidoamine) polymer (AT-HBP) was synthesized as a multifunctional chelating agent to remove two heavy metal ions (Cr(III) and Cu(II)) from the simulated wastewater solutions. The AT-HBP was characterized by Fourier transformed infrared (FTIR), dynamic light scattering (DLS), and proton nuclear magnetic resonance (1H NMR) analysis. The removal process was carried out in two different methods, centrifuged process and ultrafiltration. The concentration of heavy metal ions before and after removal was measured by inductively coupled plasma (ICP) instrument. The removal processes were evaluated by changing different parameters such as solution pH, AT-HBP dosage, and metal ion concentration. To evaluate the extend of binding of heavy metal ions in the presence of AT-HBP the presence of salt in the solution was also examined on the performance of the removal system. The overall results indicated that removal percentages higher than 98% for Cr(III) and 86% for Cu(II) were achieved for heavy metal concentrations of 100 mg/L for both removal process methods. Furthermore, the function of second generation of polypropylenimine (PPI) was compared to AT-HBP. The results reveal that the removal of Cr(III) and Cu(II) ions by AT-HBP were approximately 20% and 10% higher compared to PPI, respectively. Finally, hyperbranched dendritic polymer with lower expenses to synthesize compared to dendrimer underlined favorable properties as a multifunctional chelating agent and enhancement of ultrafiltration process for wastewater treatment. Graphical abstract.

One-step synthesis of versatile magnetic nanoparticles for efficiently removing emulsified oil droplets and cationic and anionic heavy metal ions from the aqueous environment.

Versatile polyethyleneimine (PEI)-coated Fe3O4 magnetic nanoparticles (MNPs) have been synthesized by a one-step solvothermal method. The morphologies, structures, and properties of MNPs prepared for different reaction times have been characterized through various techniques. The synthesized MNPs were then used to separate emulsified oil and cationic and anionic heavy metal ions from the aqueous environment; moreover, the effects of the temperature, pH, and ionic strength of aqueous media, the solvothermal reaction time, and the number of reuse cycles on the removal efficiency have been investigated in detail. The results showed that pseudo-second-order kinetics and the Langmuir isotherm well described the adsorption processes of Cu(II) and Cr(VI). The Langmuir model yielded maximum adsorption capacities of 66.6 mg g-1 for Cu(II) and 54.5 mg g-1 for Cr(VI) at pH 5.0 and 25 °C. The synthetic MNPs could also efficiently separate diesel oil or olive oil droplets stabilized by sodium dodecyl sulfate from aqueous media. Moreover, these MNPs could be recycled five times without showing significant loss in separation efficiency. Notably, the synthesized PEI-coated MNPs could simultaneously separate emulsified oil and cationic and anionic heavy metal ions from multicomponent wastewater. Such versatile PEI-coated MNPs displayed good affinity towards emulsified oil and cationic and anionic heavy metal ions, showing great potential for practical applications in the treatment of complicated industrial wastewater matrices. Graphical abstract Simultaneous separation of emulsified oil and cationic and anionic heavy metal ions from aqueous media by using polyethyleneimine-coated Fe3O4 magnetic nanoparticles.

Nanomaterials as versatile adsorbents for heavy metal ions in water: a review.

Over the years, heavy metal pollution has become a very serious environmental problem worldwide. Even though anthropogenic sources are believed to be the major cause of heavy metal pollution, they can also be introduced into the environment from natural geogenic sources. Heavy metals, because of their toxicity and carcinogenicity, are considered to be the most harmful contaminants of groundwater as well as surface water, a serious threat to both human and aquatic life. Nanomaterials due to their size and higher surface area to volume ratio show some unique properties compared to their bulk counterpart and have drawn significant attention of the scientific community in the last few decades. This large surface area can make these materials as effective adsorbents in pollution remediation studies. In this review, an attempt has been made to focus on the applicability of different types of nanomaterials, such as clay-nanocomposites, metal oxide-based nanomaterials, carbon nanotubes, and various polymeric nanocomposites as adsorbents for removal of variety of heavy metals, such as As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn, U, V, and Zn, from water as reported during the last few years. This work tries to analyze the metal-nanomaterial interactions, the mechanism of adsorption, the adsorption capacities of the nanomaterials, and the kinetics of adsorption under various experimental conditions. The review brings forward the relation between the physicochemical properties of the nanomaterials and heavy metal adsorption on them.