Nanofiber Ion-Exchange Membranes for the Rapid Uptake and Recovery of Heavy Metals from Water

Efficient Immobilization of heavy metals using newly synthesized magnetic nanoparticles and some bacteria in a multi-metal contaminated soil

Simultaneous application of modified Fe3O4 with biological treatments in remediating multi-metal polluted soils, has rarely been investigated. Thus, a pioneering approach towards sustainable environmental remediation strategies is crucial. In this study, we aimed to improve the efficiency of Fe3O4 as adsorbents for heavy metals (HMs) by applying protective coatings. We synthesized core-shell magnetite nanoparticles coated with modified nanocellulose, nanohydrochar, and nanobiochar, and investigated their effectiveness in conjunction with bacteria (Pseudomonas putida and Bacillus megaterium) for remediating a multi-metal contamination soil. The results showed that the coatings significantly enhanced the immobilization of heavy metals in the soil, even at low doses (0.5%). The coating of nanocellulose had the highest efficiency in stabilizing metals due to the greater variety of surface functional groups and higher specific surface area (63.86 m2 g-1) than the other two coatings. Interestingly, uncoated Fe3O4 had lower performance (113.6 m2 g-1) due to their susceptibility to deformation and oxidation. The use of bacteria as a biological treatment led to an increase in the stabilization of metals in soil. In fact, Pseudomonas putida and Bacillus megaterium increased immobilization of HMs in soil successfully because of extracellular polymeric substances and intensive negative charges. Analysis of metal concentrations in plants revealed that Ni and Zn accumulated in the roots, while Pb and Cd were transferred from the roots to the shoots. Treatment Fe3O4 coated with modified nanocellulose at rates of 0.5 and 1% along with Pseudomonas putida showed the highest effect in stabilizing metals. Application of coated Fe3O4 for in-situ immobilization of HMs in contamination soils is recommendable due to their high metal stabilization efficiency and suitability to apply in large quantities.

A Novel Minidumbbell DNA-Based Sensor for Silver Ion Detection

Silver ion (Ag⁺) is one of the most common heavy metal ions that cause environmental pollution and affect human health, and therefore, its detection is of great importance in the field of analytical chemistry. Here, we report an 8-nucleotide (nt) minidumbbell DNA-based sensor (M-DNA) for Ag⁺ detection. The minidumbbell contained a unique reverse wobble C·C mispair in the minor groove, which served as the binding site for Ag⁺. The M-DNA sensor could achieve a detection limit of 2.1 nM and sense Ag⁺ in real environmental samples with high accuracy. More importantly, the M-DNA sensor exhibited advantages of fast kinetics and easy operation owing to the usage of an ultrashort oligonucleotide. The minidumbbell represents a new and minimal non-B DNA structural motif for Ag⁺ sensing, allowing for the further development of on-site environmental Ag⁺ detection devices.

Nanocellulose as green material for remediation of hazardous heavy metal contaminants

Heavy metal pollution generated by urban and industrial activities has become a major global concern due to its high toxicity, minimal biodegradability, and persistence in the food chain. These are the severe pollutants that have the potential to harm humans and the environment as a whole. Mercury, chromium, copper, zinc, cadmium, lead, and nickel are the most often discharged hazardous heavy metals. Nanocellulose, reminiscent of many other sustainable nanostructured materials, is gaining popularity for application in bioremediation technologies owing to its many unique features and potentials. The adsorption of heavy metals from wastewaters is greatly improved when cellulose dimension is reduced to nanometric levels. For instance, the adsorption efficiency of Cr³⁺ and Cr⁶⁺ is found to be 42.02% and 5.79% respectively using microcellulose, while nanocellulose adsorbed 62.40% of Cr³⁺ ions and 5.98% of Cr⁶⁺ ions from contaminated water. These nanomaterials are promising in terms of their ease and low cost of regeneration. This review addresses the relevance of nanocellulose as biosorbent, scaffold, and membrane in various heavy metal bioremediation, as well as provides insights into the challenges, future prospects, and updates. The methods of designing better nanocellulose biosorbents to improve adsorption efficiency according to contaminant types are focused.

De Novo Ion-Exchange Membranes Based on Nanofibers

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

Fluorescent Probe for Ag+ Detection Using SYBR GREEN I and C-C Mismatch

Among heavy metals silver ions (Ag⁺) severely impact water, the environment and have serious side effects on human health. This article proposes a facile and ultrasensitive fluorescent probe for the detection of Ag⁺ ions using SYBR Green I (SGI) and cytosine-rich (C-rich) silver-specific oligonucleotide (SSO). Maximum fluorescent intensities with the highest sensitivity were obtained using a 0.61 dye/SSO base ratio (DBR). The established sensing principle using the optimized parameters for bath temperature, SSO concentration, DBR, ionic strength, pH, reaction time, incubation duration and temperature effect achieved a sensitive limit of detection of 59.9 nM for silver ions (calculated through 3σ, n = 11) with a linear working range of 100–1000 nM and 0.997 R². The total time for one assay is below 10 min; The relative standard derivation for ten repeated measurements is 8.6%. No blatant interferences were observed in the selectivity test when fluorescent probe is evaluated by investigating the effects of 11 common interference factors in the aqueous matrix. In extreme cases, three false-negative factors were observed, including calcium hardness, magnesium hardness, and hypochlorite. The recovery ratios were within the range of 79~110% for three types of diluted water.

Sustainable carboxylated cellulose filters for efficient removal and recovery of lanthanum

Carboxylated cellulose filters were fabricated by oxidation of a cellulose fibrous mat via TEMPO-mediated oxidation. These carboxylated cellulose filters were employed as sustainable filters for removal and recovery of lanthanum ions (La (III)) with high adsorption capability. The surface chemistry of the carboxylated cellulose fibers before and after adsorption of La (III) was investigated systematically. The distribution of La (III) on carboxylated cellulose fibers were explored by EDX mapping approach, which revealed that the adsorption occurred on both the surface and the internal structure of the cellulose fibers. The kinetics and isotherms of the adsorption were conducted to understand the adsorption mechanism of the carboxylated cellulose filter and to learn the maximum adsorption capacity for La (III) which was as high as 33.7 mg/g. The adsorption selectivity of the carboxylated cellulose filter for La (III) was determined when interfering ions including mono- and di-covalent ions were involved. The carboxylated cellulose filter exhibited high adsorption capability and high permeation flux evidenced by the breakthrough curves of the dynamic adsorption of La (III) under an extremely low pressure of 0.07 kPa. A variety of desorption reagents were selected to recover lanthanum from the carboxylated cellulose filter, where the optimized conditions for recovery were explored. Finally, a spiral wound cartridge of the carboxylated cellulose fibrous mat was fabricated and the removal and the recovery of La (III, 2.5 ppm) from massive lanthanum-containing water were demonstrated. It was very impressive that the high rejection ratio of 94.3% was achieved under the low pressure drop of 3.0 kPa remaining throughout the separation process, and the treated solution volume was high up to 21.4 L, which was about six-times higher than that of commercially available nanofibrous adsorption membranes, indicating that the carboxylated cellulose filter could be used as a highly efficient adsorption medium for industrial recovery of rare earth metals.

Isotope metallomics approaches for medical research

Metallomics is a rapidly evolving field of bio-metal research that integrates techniques and perspectives from other "-omics" sciences (e.g. genomics, proteomics) and from research vocations further afield. Perhaps the most esoteric of this latter category has been the recent coupling of biomedicine with element and isotope geochemistry, commonly referred to as isotope metallomics. Over the course of less than two decades, isotope metallomics has produced numerous benchmark studies highlighting the use of stable metal isotope distribution in developing disease diagnostics-e.g. cancer, neurodegeneration, osteoporosis-as well as their utility in deciphering the underlying mechanisms of such diseases. These pioneering works indicate an enormous wealth of potential and provide a call to action for researchers to combine and leverage expertise and resources to create a clear and meaningful path forward. Doing so with efficacy and impact will require not only building on existing research, but also broadening collaborative networks, bolstering and deepening cross-disciplinary channels, and establishing unified and realizable objectives. The aim of this review is to briefly summarize the field and its underpinnings, provide a directory of the state of the art, outline the most encouraging paths forward, including their limitations, outlook and speculative upcoming breakthroughs, and finally to offer a vision of how to cultivate isotope metallomics for an impactful future.

Separation and Recycling of Concentrated Heavy Metal Wastewater by Tube Membrane Distillation Integrated with Crystallization

Tube membrane distillation (MD) integrated with a crystallization method is used in this study for the concurrent productions of pure water and salt crystals from concentrated single and mixed system solutions. The effects of concentrated Zn2+ and Ni2+ on performance in terms of membrane flux, permeate conductivity, crystal recovery rates, and crystal grades are investigated. Preferred crystallization and co-crystallization determinations were performed for mixed solutions. The results revealed that membrane fluxes remained at 2.61 kg·m-2·h-1 and showed a sharp decline until the saturation increased to 1.38. Water yield conductivity was below 10 μs·cm-1. High concentrated zinc and nickel did not have a particular effect on the rejection of the membrane process. For the mixed solutions, membrane flux showed a sharp decrease due to the high saturation, while the conductivity of permeate remained below 10 μs·cm-1 during the whole process. Co-crystallization has been proven to be a better method due to the existence of the SO42- common-ion effect. Membrane fouling studies have suggested that the membrane has excellent resistance to fouling from highly concentrated solutions. The MD integrated with crystallization proves to be a promising technology for treating highly concentrated heavy metal solutions.

Pd/Fe nanoparticle integrated PMAA-PVDF membranes for chloro-organic remediation from synthetic and site groundwater

The poly(methacrylic acid) (PMAA) was synthesized in the pores of commercial microfiltration PVDF membranes to allow incorporation of catalytic palladium/iron (Pd/Fe) nanoparticles for groundwater remediation. Particles of 17.1 ± 4.9 nm size were observed throughout the pores of membranes using a focused ion beam. To understand the role of Pd fractions and particle compositions, 2-chlorobiphenyl was used as a model compound in solution phase studies. Results show H2 production (Fe0 corrosion in water) is a function of Pd coverage on the Fe. Insufficient H2 production caused by higher coverage (> 10.4% for 5.5 wt%) hindered dechlorination rate. With 0.5 wt% Pd, palladized-Fe reaction rate (surface area normalized reaction rate, ksa = 0.12 L/(m2-h) was considerably higher than isolated Pd and Fe particles. For groundwater, in a single pass of Pd/Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics, such as trichloroethylene (177 ppb) and carbon tetrachloride (35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The degradation rate (observed ksa) followed the order of carbon tetrachloride > trichloroethylene > tetrachloroethylene > chloroform. A 36 h continuous flow study with organic mixture and the regeneration process show the potential for on-site remediation.

Composite Membranes Derived from Cellulose and Lignin Sulfonate for Selective Separations and Antifouling Aspects

Cellulose-based membrane materials allow for separations in both aqueous solutions and organic solvents. The addition of nanocomposites into cellulose structure is facilitated through steric interaction and strong hydrogen bonding with the hydroxy groups present within cellulose. An ionic liquid, 1-ethyl-3-methylimidazolium acetate, was used as a solvent for microcrystalline cellulose to incorporate graphene oxide quantum dots into cellulose membranes. In this work, other composite materials such as, iron oxide nanoparticles, polyacrylic acid, and lignin sulfonate have all been uniformly incorporated into cellulose membranes utilizing ionic liquid cosolvents. Integration of iron into cellulose membranes resulted in high selectivity (>99%) of neutral red and methylene blue model dyes separation over salts with a high permeability of 17 LMH/bar. With non-aqueous (alcohol) solvent, iron-cellulose composite membranes become less selective and more permeable, suggesting the interaction of iron ions cellulose OH groups plays a major role in pore structure. Polyacrylic acid was integrated into cellulose membranes to add pH responsive behavior and capacity for metal ion capture. Calcium capture of 55 mg Ca2+/g membrane was observed for PAA-cellulose membranes. Lignin sulfonate was also incorporated into cellulose membranes to add strong negative charge and a steric barrier to enhance antifouling behavior. Lignin sulfonate was also functionalized on the commercial DOW NF270 nanofiltration membranes via esterification of hydroxy groups with carboxyl group present on the membrane surface. Antifouling behavior was observed for both lignin-cellulose composite and commercial membranes functionalized with lignin. Up to 90% recovery of water flux after repeated cycles of fouling was observed for both types of lignin functionalized membranes while flux recovery of up to 60% was observed for unmodified membranes.

An insight into Cadmium poisoning and its removal from aqueous sources by Graphene Adsorbents

Graphene alone, in modified form or its composites had find their explicit position in the field of adsorption technology and hence assist in detection and removal of heavy metals like Cd (permissible limit 0.1 mg/L), which can cause various physiological problems if entered in variety of biota. Attributed to their unique physiognomies graphene-based adsorbent had classed themselves superior as compared to other carbonaceous adsorbent like CNT's or activated carbon, etc. This assessment summarizes the validity of graphene and its composite as a superior adsorbent for decontamination of Cd from aqueous environment; in addition, this evaluation also pronounces the toxicity profile of trace graphene and necessity of regeneration of the adsorbent.