Nanomaterials in Water Purification: From Pathogens to Microplastics and Heavy Metals

Development of reliable, environmentally safe and economically advantageous methods of water purification from heavy metals is the primary task for environmental protection. The effectiveness of sorption treatment and additional treatment of natural waters from ions of heavy metals with the use of modified magnetite was studied. The samples of magnetite obtained at the ratio of concentrations of iron (II) and iron (III) of 1:2; 1:1 and 2:1 and the samples modified by sodium sulfide were used as a sorbent. Experimental studies revealed that the sorption capacity of magnetite by ions of heavy metals increases at the increase in the ratio [Fe2+]/[Fe3+] from 1:2 to 2:1. The influence of pH of the medium on the effectiveness of sorption of heavy metal ions on magnetite was studied. It was shown that the sorption capacity of magnetite for ions of copper, zinc, nickel and cadmium increases at the increase in pH of the medium from 6.0 to 8.6 due to partial hydrolysis of heavy metal ions. An increase in sorption capacity of magnetite occurs when it is modified by guanidine, thiosemicarbazide and sodium sulfide, which makes it possible to reduce residual concentrations of heavy metals to μg/dm3. The use of magnetite modified by sodium sulfite, obtained at К=2, makes it possible to completely remove cadmium ions from water and reduce copper concentration to 1.2 μg/dm3. This proves the appropriateness of using these sorbents for additional treatment or deep purification of water from ions of heavy metals. It was shown that it is appropriate to use magnetite for extraction of heavy metal ions from water in the presence of hardness ions, which do not affect the selectivity of this sorbent for ions of heavy metals. Thus, based on the obtained results of sorption purification of water from ions of heavy metals while using magnetite, we proposed a fundamental technological circuit for treatment of wastewater of nuclear power plants at discharge to water bodies

The article is devoted to the analysis of reagent methods, selection of reagents and optimal doses for the process of carrying out the purification of industrial wastewater from heavy non-ferrous metal ions, such as copper ammonium, copper sulfate, nickel, hexavalent chromium. Presents data on the cost of each reagent used, as well as a table with the original data. The course of the experimental work, the pH value, the initial metal concentration and the dose of the reagents used are described. The graphic results of experimental work on the purification of wash water containing various non-ferrous metals are given, which show the final concentrations of metals and the cost of cleaning 1 cub m of runoff. As a result of the analysis, conclusions were made about the effectiveness of the various reagents used on heavy non-ferrous metal ions. The criterion for the efficiency of cleaning the wash water was the possibility of achieving the maximum permissible concentration for discharge into the fishery reservoir, the permissible concentration for discharge into the centralized water disposal system of the city and standards for permissible discharge for the enterprise. The optimal conditions for reagent purification of wash water are found, taking into account the possibility of achieving each considered criterion of purification efficiency, with the minimum cost of reagents. The use of reagent purification of wash water requires subsequent neutralization of treated wastewater. The choice of the technological scheme of purification of wash water from heavy non-ferrous metal ions will be determined, on the one hand, from the heavy non-ferrous metal ion contained in the wastewater, and on the other hand, from the need to achieve the required cleaning criterion.

Dynamics of Topology-dependent Water Purification by Siliceous Zeolite Membranes

Uniform well-defined nanostructured BiOBr microspheres have been fabricated via a simple hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG). The heavy metal ion adsorption on the as-synthesized nanostructured BiOBr microspheres was systematically assessed by measuring the residual concentration during the adsorption process using a colorimetric method for Cr(VI) concentration, and an extraction-colorimetric method for Cd(II) and Pb(II) concentrations. The nanostructured BiOBr microspheres showed good removal capacity for heavy metal ions (Cr, Cd, Pb), and excellent adsorption properties for low concentration heavy metal ions, indicating potential applications in water purification. Based on the quick and efficient heavy metal ion removal ability of nanostructured BiOBr microspheres, a continuous filtering-type water purification device was designed and constructed. In using this continuous filtering type water purification device, 1 g of adsorbent can purify about 4900 g of Pb(II) contaminated water, 5900 g of Cd(II) contaminated water, or 21 500 g of Cr(VI) contaminated water having initial concentrations of 200 μg L−1 to successfully attain the World Health Organization standard for drinking water. The good removal capacity can be attributed to the hierarchical nanostructure, which displays a large specific surface area and strong adsorption of heavy metal ions.

"My first experiment was, when I was only 8 years old, studying particles suspended in water exposed to the centrifuge force. When I was eight I already wanted to be a scientist …" Find out more about Raffaele Mezzenga in his Author Profile.

Mangroves are special plant communities that live along intertidal zones in tropical and subtropical areas. They are regarded as one of the most important types of natural ecosystem in the world because of the many ecosystem functions that they perform, of which water purification is the most complex. Mangrove ecosystems are conducive to the deposition and retention of heavy metals. So it is important to understand the impact of heavy metals on mangrove ecosystems, and especially on soil subsystems. We examined the levels of heavy metals in the soil of mangroves in the Dongzhaigang Mangrove National Nature Reserve. Dongzhaigang, the first mangrove nature reserve established in China, is located south of Haikou in Hainan Island and encompasses <TEX>$33.37\;km^2$</TEX>, of which mangroves comprise <TEX>$20.56\;km^2$</TEX>. To assess the impact of human activities, we collected a large number of soil samples in four sampling areas (the protection station, the harbor, a tour area, and Yeboluo island) in the study area. We measured the concentrations of Cu, Pb, Zn and Cd in the soil samples using the spectra of polyatomic molecules. The average concentrations of Cu, Pb, Zn and Cd were <TEX>$5.04\;{\mu}g/g$</TEX>, <TEX>$10.36\;{\mu}g/g$</TEX>, <TEX>$20.06\;{\mu}g/g$</TEX> and <TEX>$0.06\;{\mu}g/g$</TEX>, respectively, and the heavy metal concentrations were lowest in the protected area, highest in the harbor, and intermediate in Yeboluo Island and the tour area. The heavy metal concentrations in the soil collected from different sample plots are related not only to the physical and chemical properties of the soil, but also to the heavy metal emitted by nearby pollution sources. Our analysis indicates that tourist boats are the main pollution sources in the study area.

In this chapter, the emphasis is on biowaste materials generally characterized by various functional groups, such as carboxyl, amine, and hydroxyl, that are used for the removal of heavy metals. The chapter discusses chitosan-based polymeric membranes for water purification, where chitosan-containing polymeric nanocomposites are used for water purification systems, as well as for adsorption of Cu(ii) and Zn(ii) ions in water and for biosorption of organic dyes. It is essential that adsorbent membranes used are effective in the removal of toxic metals, heavy metals, drugs, and dyes. For example, phosphate cellulose as biomaterial under different pH conditions can be used for effective removal of the drug ranitidine from water. The use of biowaste as an adsorbent to effectively remove toxic heavy metals, dyes, and drugs is challenging due to their nature with respect to adsorption, recovery, effectiveness, and recyclability. Biowastes obtained from agriculture, in particular, have been utilized as effective biosorbents in the water purification process. Biosorption is effective for removal of heavy metals from waste water compared with conventional methods. However, chitosan-based polymeric materials possess a high adsorption efficiency compared to biowaste materials, for the effective removal of heavy metals, various drugs, dyes, etc. This chapter also focuses on the mechanisms of adsorption of chitosan-based polymeric materials and biowaste products for effective removal of various heavy metals, drugs, and dyes, and their involvement in high adsorption efficiency, stability, and low cost.

Bioleaching comprises the use of microorganisms for metal-extraction processes from sulphide ores. During these complex processes, sulphides are oxidized to sulphates with the generation of heat. As a result, gold, silver, and other precious metals are liberated from the sulphide matrix, improving their recovery after further processing. A drawback of bioleaching processes is the generation of significant amounts of acid solutions with high heavy metal concentrations. If untreated, these acid solutions may alter the physical and chemical characteristics of water and its surroundings, with high impact to aquatic ecosystems. High heavy metal concentrations in solution may also result in pollution to living organisms. A feasible method to treat bioleaching-generated solutions is selective precipitation. This investigation presents the conditions for a successful individual recovery of the main base metals contained in a bioleaching solution with high copper, zinc, and iron concentrations by pH-based selective precipitation. Tests were made with standard solutions of known concentrations of copper, iron, lead and zinc and by titration the concentrations were checked; which allowed to validate the volumetric titration method. The selective precipitation of heavy metals was carried out in three phases using real acid main drainage and bioleaching solutions generated at the laboratory. The first phase in a pH range of 2 to 4 to recover iron; the second phase in a pH range of 4 to 6 to recover copper; and the third phase in a pH range of 6 to 10 to recover zinc. The selective precipitation allowed the heavy metals to be completely removed from the solution or to achieve concentrations below the maximum allowable limit to be discharged to a body of water or public sewer. Results portray that the variation of pH is an effective method, easy to use and not expensive, feasible to be used in the purification of waters that have been polluted with heavy metals.

Wastewater purification from heavy metal compounds is a complex and urgent task. One of the main sources of pollution of the environment with ions of heavy metals is the wastewater, i.e., washing, of the electro-plating processes. Complex electrolytes based on copper compounds are stable in a wide pH range and, when released into water, cannot be removed by the traditional methods, such as neutralization and precipitation. The study estimated the efficiency of various methods of physicochemical water purification for removing complex ammonia-tartrate copper (II) complexes from water. Findings of research show that titanyl sulfate is most effective in water purification using coagulants. The efficiency of purification with the use of titanium compounds reaches 85 %, which is on average 30--40 % higher than when using traditional coagulants based on aluminum or iron compounds. Electrocoagulation processes make it possible to effectively remove complex copper compounds from water due to a combination of the processes of organic component oxidation and coagulation with iron salts. It was found that advanced oxidation processes, which are based on the reaction with a hydroxyl radical, using hydrogen peroxide, i.e., Fenton processes, make it possible to purify wastewater from copper compounds by 99.9 %. Despite the high efficiency, it is advisable to use adsorption processes only at the stage of additional water purification from previously coagulated and oxidized pollutants

Today the purification of waste water from heavy metals is an actual environmental problem, which is due to the existence of these different forms of pollution (in the form of salts, oxides etc.). The using of environmentally safe materials can be the direction of solution of this problem. One of them is a common natural sorbent - dark brown loam. Large reserves of this material, cheapness, very high adsorption, ion exchange and filtration properties provide the practical and economic feasibility of its use in the process of purification of waste water from chromium (III) ions. The experimental results on improving of sorption properties of dark brown loam by acid activation of sewage treatment from chromium (III) ions have been presented. The optimal conditions for acid activation of the sorbent, at which provides the maximum degree of purification of water from pollution have been defined. Analysis of researches has confirmed the effectiveness of using dark brown loam, modified by sulfuric acid activation, as the sorbent of chromium (III) ions from waste waters.

Heavy metals have caused serious environmental problems and threat to human health. Ultrathin and holey two-dimensional (2D) nanosheets have recently drawn significant attention as superb adsorbent material to remove heavy metal ions due to their unique physicochemical properties. Herein, we report a self-template-directed ultrafast reaction route to synthesis porous hydroxyapatite (Ca10(PO4)6(OH)2) nanosheets via a microwave-assisted hydrothermal method using poly(allylamine hydrochloride) as an additive. The resulting hydroxyapatite nanosheets showed a high specific surface area (92.9 m2 g-1) and excellent adsorption performance for various heavy metal ions including Pb(II), Cu(II), and Cd(II), with maximum adsorption capacities of 210.5, 31.6, and 24.9 mg g-1, respectively. The adsorption kinetics fitted well with the pseudo-second-order equation and the equilibrium data showed a high correlation coefficient with the Langmuir model. Based on the experimental results and analysis, we can conclude that the sorption of heavy metal ions with the hydroxyapatite nanosheets mainly attributes to surface complexation and cation exchange. The present synthetic strategy allows the fast and massive production of porous hydroxyapatite ultrathin nanosheets and may also potentially be applicable to the fabrication of other metal phosphates with assembled or hierarchical porous structures towards various applications such as water purification.

The need for safe and clean water is growing, which has increased the search for sustainable, low-cost, and eco-friendly purification methods. This review explores the application of plants as natural agents in water purification, emphasizing their potential as alternatives to conventional chemical coagulants and disinfectants. Traditional purification techniques such as chlorination, reverse osmosis, and alum-based coagulation, though effective, present environmental, economic, and health challenges including high operational costs, generation of toxic by-products, and potential health risks. In contrast, plant-based coagulants and bioflocculants derived from species such as Moringa oleifera, Opuntia ficus indica, Aloe vera, and Salvia hispanica offer biodegradable, nontoxic, and cost-effective solutions. The mechanisms involved include coagulation-flocculation, adsorption, rhizofiltration, and physical filtration, each contributing uniquely to the elimination of organic contaminants, pathogens, heavy metals, and suspended particles. Case studies from China and India, the United States, and Nigeria demonstrate successful implementation of plant-based purification systems in both natural and constructed wetlands. Despite challenges related to extraction methods, variability in plant efficacy, and large land requirements, ongoing research into nanotechnology, genetic modification, and plant–microbe interactions promise to enhance their efficiency and scalability. Overall, the use of plants in water purification aligns with global goals for sustainable water management, offering a green, accessible, and effective alternative for communities particularly in developing regions.

Carbon's unique properties—abundance, affordability, and exceptional surface area—make it a cornerstone of water purification. Across household filters and large-scale plants, it tackles contaminants like chlorine, heavy metals, and organic pollutants. Researchers constantly improve carbon's water purification capabilities from traditional activated carbon to cutting-edge nanomaterials. This chapter explores various carbon-based materials, their effectiveness against contaminants, and the advantages and limitations of these technologies. The ultimate goal is to enrich the readers with sustainable and efficient methods for clean water access for all.

In recent years, the constant population growth worldwide has put pressure on the need for clean and safe water for human consumption. Magnetic nanomaterials (MNMs) have emerged as a promising material in the past few decades due to their unique physiochemical properties. MNMs possess the desired characteristics for their application in water purification. However, it is important to develop well defined magnetic nanomaterials for efficient removal of water pollutants. This requires effective synthetic methods for the synthesis of shape, size and morphology-controlled nanomaterials. Various physical, chemical and biological methods including ball milling, gas phase deposition, thermal decomposition, hydrothermal, solvothermal, co-precipitation, sol–gel, etc. have been explored over the years for their synthesis. The presence of organic and inorganic pollutants in water even in trace concentration has extreme adverse effects on human and environmental health. Hence, it is the need of the hour to develop effective and economical methods for application in water remediation. In this chapter, the problem of water pollutants, their threatening effects and the use of MNMs in water purification have been addressed. These MNMs are characterized using methods such as UV, IR, XPS, XRD, SEM, TEM, VSM, AFM, RS, 1HNMR, etc. Finally, the application of these materials for water purification have been discussed in detail—highlighting the removal of pesticides, dyes, pharmaceutical drugs, inorganic anions, heavy metals and oil spill from water.KeywordsMagnetic nanomaterialsWater remediationMorphology

Water scarcity issues associated with inadequate access to clean water and sanitation is a ubiquitous problem occurring globally. Addressing future challenges will require a combination of new technological development in water purification and environmental remediation technology with suitable conservation policies. In this scenario, new bioinspired materials will play a pivotal role in the development of more efficient and environmentally friendly solutions. The role of amphiphilic self-assembly on the fabrication of new biomimetic membranes for membrane separation like reverse osmosis is emphasized. Mesoporous support materials for semiconductor growth in the photocatalytic degradation of pollutants and new carriers for immobilization of bacteria in bioreactors are used in the removal and processing of different kind of water pollutants like heavy metals. Obstacles to improve and optimize the fabrication as well as a better understanding of their performance in small-scale and pilot purification systems need to be addressed. However, it is expected that these new biomimetic materials will find their way into the current water purification technologies to improve their purification/removal performance in a cost-effective and environmentally friendly way.