A Review on Detection and Abatement of Heavy Metals

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 μM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Morpholine-modified polyacrylamides with Polymerization-Induced emission and its specific detection to Cu2+ ions

In this work, three morpholine-modified polyacrylamide derivatives (MMPAm) were successfully prepared by free radical polymerization of monomers with morpholine moiety. The intramolecular aggregation of morpholine rings on macromolecular backbone gives MMPAm a significant polymerization-induced emission (PIE). Particularly, poly(N-morpholine acrylamide) (PNMPA) has the characteristics of strong fluorescence at 450 nm, and its fluorescence quantum yield reaches 2.87 %. The introduction of morpholine moiety, the length of CH2 spacer between morpholine ring and the backbone and the molecular weight play the important roles in PIE properties of PNMPA. Interestingly, PNMPA can recognize and detect Cu2+ specifically even in the presence of 12 other metal ions by thorough fluorescence quenching, and the detection limit of PNMPA is 17.3 μM. Furthermore, the dynamic quenching of PNMPA by Cu2+ ions and the complexation ratio of 1:2 according to JOB's working diagram were confirmed by fluorescence titration. Under the assistance of EDTA, a reversible detection system for Cu2+ is achieved, and a portable test paper from PNMPA for the detection of Cu2+ was also made. In conclusion, PNMPA is endowed with a significant PIE effect by the intramolecular aggregation of morpholine rings along the backbone in the polymerization of non-fluorescent monomer, and is expected to be a promising material for specific detection to Cu2+ ions.

Methods for controlling heavy metals in environmental soils based on artificial neural networks

The problem of heavy metal pollution in soil has become a global environmental problem, and it is very important to predict and manage the heavy metals in the environmental soil in a timely manner. The changes in heavy metal content in soil have characteristics such as nonlinearity and large delay, making it difficult to predict heavy metals in soil using traditional methods. Traditional prediction methods are complex and cumbersome, which can lead to longer treatment time and easy secondary pollution. This article analyzed the Back Propagation neural network (BPNN) in artificial neural networks (ANN) and applied it to the prediction of heavy metals in environmental soils. BPNN has good nonlinear function approximation ability, so it can be well applied to complex problems such as soil heavy metal prediction. The methods of treating soil heavy metals include physical repair method, chemical repair method, microbial repair method, plant repair method, plant microbial combined repair method and so on. The use of BPNN can predict heavy metals in environmental soils through adaptive dynamic learning. However, the training time of the BPNN is relatively long and the convergence speed is relatively slow. Therefore, additional momentum terms were added to adjust the weights and thresholds of the network to improve the BPNN. In the experiment, the prediction performance of the improved BPNN was compared before and after the improvement. This article took 50 monitoring data of heavy metals in the same soil in a certain region in 2021 as sample data and predicted the content of heavy metals in the soil using improved and improved BPNN. Due to time constraints, this article only conducted experimental analysis on heavy metals such as lead and cadmium. In the first experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 75.95% and 89.56%, respectively. In the second experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 77.99% and 89.85%, respectively. The improved BPNN has good prediction accuracy and can effectively predict the status of heavy metals in soil. The analysis in this article can provide scientific basis for the comprehensive prevention and control of heavy metals in regional soil, and also provide reference for the development of pollution-free agriculture and ensuring food safety.

New outlook on hazardous pollutants in the wastewater environment: Occurrence, risk assessment and elimination by electrodeionization technologies

Over the decades, water contamination has increased substantially and has become a severe global issue. Degradation of natural resources is taking place at an alarming rate as a result of the use of chemicals like dyes, heavy metals, fertilizers, pesticides, and many more, necessitating the development of long-term pollution remediation methods/technologies. As a new development in the field of environmental engineering, electrodeionization incorporates both traditional ion exchange and electrodialysis. This communication provides an overview of hazardous contaminants such as dyes, heavy metals, fertilizers, and pesticides, as well as their converted forms, which are present in water. It highlights the risks of water pollutants to public health and the environment. Various electrochemical methods with a focus on electrodeionization for the treatment of wastewater and removal of hazardous contaminants are outlined in this review. Additionally, this review discusses the challenges and the future outlook for the development in this field of research.

Identifying candidates for the phytoremediation of copper in viticultural soils: A systematic review

For many years, copper-based fungicides have been used in viticulture and have contributed to increasing concentrations in soils. Today, it is not uncommon to find vineyard soils with total copper topsoil concentrations above 100 mg kg^-1, which may have consequences for both the environment and human health. Phytoremediation, the use of plants to remove heavy metals from soils, is a promising and environmentally-friendly method to extract copper from soils. The objectives of this study were to review and synthesise the current knowledge on copper phytoremediation in vineyard soils and identify future applications. A systematic literature search in Web of Science was conducted on 19 July 2022 and resulted in twenty-seven papers meeting the inclusion criteria. Approximately one third of the papers were from Brazil and most of the experiments had been carried out in pots. In some studies, the addition of bacteria or chelators was also evaluated. Some species, such as Plantago lanceolata L. or Ricinus communis L., can accumulate copper in their tissues at concentrations above 1000 mg kg^-1. Addition of bacteria and chelators to the soil can also increase the copper uptake capacity by plants. However, most of the species evaluated accumulate copper in the roots, rather than in the shoots, thus limiting the implementation of this method in practice. Further studies are thus needed to find other hyperaccumulator plants. Future research should focus primarily on the ability of plants to accumulate copper in their aerial parts, their ability to transfer copper from roots to shoots, and their biomass production under high soil copper concentrations. Longer-term experiments and more in situ testing are also needed to evaluate the potential for development and use of copper phytoremediation in vineyards. To conclude, species of the Poaceae and Lamiaceae families are the most promising so far for phytoremediation. Identifying plants able to translocate copper from the roots to the aerial parts will be an important factor in the success of this method.

Low Au-content CoAu electrodes for environmental applications

Six cobalt gold (CoAu) electrodes were prepared by electroless deposition using different gold-containing solutions (acidic and weakly acidic) and different Au deposition times. Characterization of CoAu electrodes was done by scanning electron microscopy with energy-dispersive X-ray spectroscopy, N2-sorption, and X-ray powder diffraction techniques. The possibility of using the prepared electrodes in environmental applications, i.e., for the electrochemical sensing of a trace amount of arsenic(iii) in weakly alkaline media was assessed. Employing the CoAu electrode (prepared by immersing Co/Cu into 1 mM HAuCl4 (pH 1.8) at 30 °C for 30 s) under optimized conditions (deposition potential -0.7 V and deposition time of 60 s), a low limit of detection of 2.16 ppb was obtained. Finally, this CoAu electrode showed activity for arsenic oxidation in the presence of Cu(ii) as a model interferent as well as in real samples. Furthermore, the use of CoAu electrode as an anode in fuel cells, namely, direct borohydride - hydrogen peroxide fuel cells was also assessed. A peak power density of 191 mW cm-2 was attained at 25 °C for DBHPFC with CoAu anode at a current density of 201 mA cm-2 and cell voltage of 0.95 V, respectively. The peak power density further increased with the increase of the operating temperature to 55 °C.

Removal of Arsenic from Wastewater by Using Nano Fe3O4/Zinc Organic Frameworks

Efficient removal of arsenic in wastewater is of fundamental importance due to the increasingly severe arsenic pollution. In this study, a new composite adsorbent (Fe₃O₄@ZIF-8) for As(V) removal from wastewater was synthesized by encapsulating magnetic Fe₃O₄ nanoparticles into metal organic frameworks. In order to evaluate the feasibility of Fe₃O₄@ZIF-8 as an adsorbent for As(V) removal, the adsorption properties of Fe₃O₄@ZIF-8 were systematically explored by studying the effects of dosage, pH, adsorption isotherm, kinetics, and thermodynamics. Additionally, the characterization of Fe₃O₄@ZIF-8 before and after adsorption was analyzed thoroughly using various tests including SEM-EDS, XPS, BET, XRD, TG, FTIR, and the properties and arsenic removal mechanism of the Fe₃O₄@ZIF-8 were further studied. The results showed that the Fe₃O₄@ZIF-8 has a specific surface area of 316 m²/g and has excellent adsorption performance. At 25 °C, the initial concentration of arsenic was 46.916 mg/L, and pH 3 was the optimum condition for the Fe₃O₄@ZIF-8 to adsorb arsenic. When the dosage of the Fe₃O₄@ZIF-8 was 0.60 g/L, the adsorption of arsenic by the Fe₃O₄@ZIF-8 can reach 76 mg/g, and the removal rate can reach 97.20%. The adsorption process of arsenic to the Fe₃O₄@ZIF-8 can be well described by the Langmuir isotherm model and the second-order kinetic equation. At pH 3 and temperature 298 K, the maximum adsorption capacity of arsenic by the Fe₃O₄@ZIF-8 was 116.114 mg/g. Through the analysis of thermodynamic parameters, it is proved that the adsorption process of arsenic by the Fe₃O₄@ZIF-8 is a spontaneous endothermic reaction. The Fe₃O₄@ZIF-8 has broad prospects for removing As(V) pollution in wastewater, because of its strong adsorption capacity, good water stability, and easy preparation.

Sustainable Treatment Techniques for Emerging Pollutants—The Case of Personal Hygiene Products

Personal care products (PCPs) enter wastewater primarily through greywater. Treatment plants have not been able to remove this type of contaminant, although PCP abatement techniques have been developed in recent years. The objective of the current study has been to encounter the sustainable technique that keeps the optimal balance between the criteria considered in the comparison. Therefore, a bibliographic review was conducted in scientific databases of the last eight years, demonstrating that co-composting, anaerobic–aerobic sequencing bioreactors and contaminant absorption through the use of carbon nanotubes are the ones with the least environmental impact. Subsequently, the Saaty and Modified Saaty methods were applied, with a comparative criteria of construction costs, maintenance costs, efficiency and the stage of development. The results indicated that the co-composting technique is the best sustainable technique of those studied, with a score of 0.86/1, which means that the criteria analyzed maintain very close values between them. The co-composting technique yields a low environmental impact in eliminating personal care products. This research work constitutes a practical and easy-to-use tool for decision makers, since it allows finding an optimal elimination treatment for PCPs.

Evaluation of the Immobilization of Coexisting Heavy Metal Ions of Pb2+, Cd2+ , and Zn2+ from Water by Dairy Manure-Derived Biochar: Performance and Reusability

Heavy metals including Cd, Pb, and Zn are prevalent stormwater and groundwater contaminants derived from natural and human activities, and there is a lack of cost-effective treatment for their removal. Recently, biochar has been increasingly recognized as a promising low-cost sorbent that can be used to remediate heavy metal contaminated water. This study evaluates the immobilization/release performance of dairy manure-derived biochar (DM-BC) as a sustainable material for competitive removal of coexisting heavy metal ions from water and explains the underlying mechanism for regeneration/reusability of biochar. Results showed that the metal ions exhibited competitive removal in the order of Pb2+ ≫ Zn2+ > Cd2+. The pH played a decisive role in influencing metal ion speciation affecting the electrostatic attraction/repulsion and surface complexation. Higher pH led to greater removal for Pb2+ and Cd2+, whereas Zn2+ showed maximum removal at pH ≈ 7.5. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and X-ray diffraction confirmed the interactions and precipitation reactions of oxygen-containing functional groups (e.g., ─OH, C O 3 2 - , and Si─O) as key participants in metal immobilization. Langmuir, Freundlich, and Redlich-Peterson isotherm modeling data showed varied and unique results depending on the metal ion and concentration. The removal kinetics and model fitting showed that the three steps of intraparticle diffusion might be more representative for describing the immobilization processes of metal ions on the external surface and internal pores. In the flow-through columns, DM-BC effectively retained the mixed metal ions of Cd2+, Pb2+, and Zn2+ showing 100% removal for the duration of the column run over three cycles of regeneration and reuse.

Characteristics and Assessment of Soil Heavy Metals Pollution in the Xiaohe River Irrigation Area of the Loess Plateau, China

Heavy metals in soil are a potential threat to ecosystems and human well−being. Understanding the characteristics of soil heavy metal pollution and the prediction of ecological risk are crucial for regional eco−environment and agricultural development, especially for irrigation areas. In this study, the Xiaohe River Irrigation Area in the Loess Plateau was taken as the study area, and the concentration, as well as their accumulation degree and ecological risk and distribution of soil heavy metals, were explored based on the geo−accumulation index (Igeo) and Hakanson potential ecological risk index methods. The results showed that the concentrations of soil heavy metals were all lower than the second grade Environmental Quality Standard for Soils of China. However, the average concentrations of Cu, Hg, Cd, Pb, Zn, Ni and As were higher than the above−mentioned standard. Compared with the soil background values of Shanxi Province, eight heavy metals of all samples presented different accumulation degrees, with the highest accumulation degree in Hg, followed by Cd, and the values were 11.3 and 4.0 times more than the background value, respectively. Spatially, the distribution of soil heavy metals in the Xiaohe River irrigation area was quite different, generating diverse pollution patterns with significant regional differences and complex transportation routes. The content of soil heavy metals in the Xiaohe River irrigation area was highly affected by land use types. The pollution degree varied with the distance to an urban area, declining from the urban area to suburban farmland, and the outer suburban farmland. Among these heavy metals, Hg and Cd were the principal contamination elements, and transportation, service industry and agricultural activities were the main potential contamination sources. The potential ecological risk of soil heavy metal positioned as follows: Hg > Cd > Pb > Zn > Cu > As > Ni > Cr. As indicated by the Hakanson potential ecological risk index strategies, except for the Wangwu examining site, the other six sampling sites experienced extremely strong risks, and as a whole, the entire study region was in a condition of incredibly impressive perils. Consequently, these results suggest that improving soil environmental investigation and assessment, setting up soil heavy metal contamination prevention and control innovation framework and reinforcing contamination source control are effective approaches for soil heavy metal contamination anticipation and control in irrigated areas of the Loess Plateau.

The potential of Croton lindheimeri to sequester different metals from different mediums: uptake essential element Fe from soils or sequester toxic metal Sr from solutions

Some metals are necessary nutrients for plant health while some are toxic pollutants. In this study, the ability of Croton lindheimeri to uptake essential element Fe or toxic metal Sr was assessed separately. The amounts of iron plaque on the root systems and the levels of Fe in C. lindheimeri collected from an iron-rich field were assessed. The results indicated that Translocation Factor (TF) of Fe in C. lindheimeri was around 1, with similar amounts of Fe in roots and shoots. C. lindheimeri seedlings were cultured in Sr solutions for 3 weeks to determine its potential to accumulate Sr. It was found that the roots of C. lindheimeri cultured in 20 mg/L Sr solutions sequestered 0.05 ± 0.01 mg Sr/g biomass. TF of Sr in C. lindheimeri was >1. Further research is worthwhile to evaluate the potential of C. lindheimeri to remediate Sr contaminated sites.Novelty statementNo study related to the sequester of metals (either essential or non-essential metals) in Croton lindheimeri (goat weed) was found before. It was the first research about metal accumulation in goat weed.Fe plaque formation and iron sequester in the biomass of Croton lindheimeri were never studied in previous research.Very limited information about phytoremediation of Sr contaminated media was reported in previous studies, this study filled the gap by exploring the uptake of Sr in Croton lindheimeri.

Aggregation-induced emission (AIE) from poly(1,4-dihydropyridine)s synthesized by Hantzsch polymerization and their specific detection of Fe2+ ions

As an important metal element widely existing in nature and the human body, the simple and specific detection of Fe2+ ions has always been of interest.

Preclinical studies conducted on nanozyme antioxidants: shortcomings and challenges based on US FDA regulations

The wide prevalence of oxidative stress-induced diseases has led to a growing demand for antioxidant therapeutics worldwide. Nanozyme antioxidants are drawing enormous attention as practical alternatives for conventional antioxidants. The considerable body of research over the last decade and the promising results achieved signify the potential of nanozyme antioxidants to secure a place in the expanding market of antioxidant therapeutics. Nonetheless, there is no report on clinical trials for their further evaluation. Through analyzing in-depth selected papers which have conducted in vivo studies on nanozyme antioxidants, this review aims to pinpoint and discuss possible reasons impeding development of research toward clinical studies and to offer some practical solutions for future studies to bridge the gap between preclinical and clinical stages.

Graphene-Based Macromolecular Assemblies for Scavenging Heavy Metals

The integration of graphene or graphene oxide nanosheets into three-dimensional (3D) graphene-based macromolecular assemblies (GMAs), in the form of sponges, beads, fibres, films, and crumpled nanosheets, has greatly advanced their environmental remediation applications. This is attributed to the outstanding physicochemical characteristics and superlative mechanical features of 3D GMAs, including precise and physically linked permeable networks, enormous surface area, profound porosity, and high-class sturdiness, amongst others. In this review, the recent advancements towards the exploration of 3D GMAs as an exciting new class of high-performance adsorbents, for eliminating toxic heavy metal ions from both wastewater and freshwater, are systematically summarized and discussed, from both fundamental and applied perspectives. In particular, the numerous surface modification techniques that are actively pursued to enrich the metal adsorption capacity of 3D GMAs, are comprehensively examined. Additionally, associated challenges are pointed out and tactical research strategies and improvements are proposed, with an eye on the conceivable future.

Hematite and Magnetite Nanostructures for Green and Sustainable Energy Harnessing and Environmental Pollution Control: A Review

The optoelectrical and magnetic characteristics of naturally existing iron-based nanostructures, especially hematite and magnetite nanoparticles (H-NPs and M-NPs), gained significant research interest in various applications, recently. The main purpose of this Review is to provide an overview of the utilization of H-NPs and M-NPs in various environmental remediation. Iron-based NPs are extensively explored to generate green energy from environmental friendly processes such as water splitting and CO₂ conversion to hydrogen and low molecular weight hydrocarbons, respectively. The latter part of the Review provided a critical overview to use H-NPs and M-NPs for the detection and decontamination of inorganic and organic contaminants to counter the environmental pollution and toxicity challenge, which could ensure environmental sustainability and hygiene. Some of the future perspectives are comprehensively presented in the final portion of the script, optimiztically, and it is supported by some relevant literature surveys to predict the possible routes of H-NPs and M-NPs modifications that could enable researchers to use these NPs in more advanced environmental applications. The literature collection and discussion on the critical assessment of reserving the environmental sustainability challenges provided in this Review will be useful not only for experienced researchers but also for novices in the field.

Using PVA/CA/Au NPs electrospun nanofibers as a green nanosorbent to preconcentrate and determine Pb2+and Cu2+in rice samples, water sources and cosmetics

Polyvinyl alcohol (PVA)/citric acid (CA)/Au NPs electrospun nanofibers was synthesized and applied as a green and efficient sorbent to extract and preconcentrate Pb²⁺and Cu²⁺from water sources, rice samples and cosmetics before FAAS.

Heavy metals, nitrates and radionuclides in milk of cows depending on their stress resistance

The paper presents the results of studies on the content of cesium, strontium, zinc, cadmium, copper, lead and nitrates in the milk of Ukrainian black-and-white milk breed cows with different resistance to stress. The resistance of cows to stress was determined by concentration of cortisol in the blood one hour after a stress effect. The following factors were stressful: fixation of animals for one hour and pre-selection of blood by a veterinarian for general analysis. The objective of the research was establishing a connection between the different adaptive potential of Ukrainian black-and-white milk breeds and the ability of their bodies to excrete via the milk heavy metal salts, nitrates and radioactive elements which enter the body with food and water. The scientific hypothesis was that the state of pressure which occurs in the body under the influence of stress impairs homeostasis. It can affect the quantity and quality of products, it can cause disorders in the metabolic processes, the synthesis of milk components and introduction of some harmful substances into milk, which are differently accumulated in the body of cows with diverse reactions to stress and can be excreted with milk in at different levels. We established that different resistance of cows to stress can affect the concentration of the investigated harmful substances in milk. Concentration of lead, cadmium, zinc and nitrates was lower in milk of more stress-resistant cows (the first group). Their milk had a lower specific activity of 137Cs and 90Sr. For all the seasons, the reliable results were obtained only for nitrates, and 137Cs and 90Sr – in spring, summer and autumn. Thus, milk of cows with higher resistance to stress is safer in terms of contents of the investigated elements. We have drawn a conclusion that stress can affect the ability of the body to excrete via the milk harmful elements which enter the body with food and water. Perspectives of further research are determining the effect of cows’ stress resistance on the suitability of milk for the production of baby food products.