Removal of PFOA in groundwater by Fe0 and MnO2 nanoparticles under visible light

Unveiling nano-empowered catalytic mechanisms for PFAS sensing, removal and destruction in water

Per- and polyfluoroalkyl substances (PFAS) are organofluorine compounds used to manufacture various industrial and consumer goods. Due to their excellent physical and thermal stability ascribed to the strong CF bond, these are ubiquitously present globally and difficult to remediate. Extensive toxicological and epidemiological studies have confirmed these substances to cause adverse health effects. With the increasing literature on the environmental impact of PFAS, the regulations and research have also expanded. Researchers worldwide are working on the detection and remediation of PFAS. Many methods have been developed for their sensing, removal, and destruction. Amongst these methods, nanotechnology has emerged as a sustainable and affordable solution due to its tunable surface properties, high sorption capacities, and excellent reactivities. This review comprehensively discusses the recently developed nanoengineered materials used for detecting, sequestering, and destroying PFAS from aqueous matrices. Innovative designs of nanocomposites and their efficiency for the sensing, removal, and degradation of these persistent pollutants are reviewed, and key insights are analyzed. The mechanistic details and evidence available to support the cleavage of the CF bond during the treatment of PFAS in water are critically examined. Moreover, it highlights the challenges during PFAS quantification and analysis, including the analysis of intermediates in transitioning nanotechnologies from the laboratory to the field.

Design of nanomaterials for the removal of per- and poly-fluoroalkyl substances (PFAS) in water: Strategies, mechanisms, challenges, and opportunities

Due to their persistent and pervasive distribution and their adverse effects on human health, the removal of per- and polyfluoroalkyl substances (PFAS) from the environment has been the focus of current research. Recent studies have shown that engineered nanomaterials provide great opportunities for their removal by chemical, physical and electrochemical adsorption methods, or as photo- or electrocatalysts that promote their degradation. This review summarizes and discusses the performance of recently reported nanomaterials towards PFAS removal in water treatment applications. We discuss the performance, mechanisms, and PFAS removal conditions of a variety of nanomaterials, including carbon-based, non-metal, single-metal, and multi-metal nanomaterials. We show that nanotechnology provides significant opportunities for PFAS remediation and further nanomaterial development can provide solutions for the removal of PFAS from the environment. We also provide an overview of the current challenges.

Degradation of perfluoroalkyl substances using UV/Fe0 system with and without the presence of oxygen

The wide presence of per- and poly-fluoroalkyl substances (PFAS) in the environment is a global concern, thus their degradation is an imminent task. In this study, oxidative and/or reductive degradation of three representative PFAS - perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorooctane sulfonate (PFOS) was achieved using nanoscale zero-valent iron (Fe⁰ NPs) under ultraviolet (UV) light, both with and without the presence of oxygen. Higher degradation and defluorination rates were obtained for a longer chain PFNA compared to PFOA, and a higher removal of PFAS was achieved without the presence of O₂ compared to that with O₂. The degradation followed first-order reaction kinetics, and obtained the highest rates of 97.6, >99.9, and 98.5% without the presence of O₂ for PFOA, PFNA, and PFOS, respectively. The degradation rates increased with an increase in the nanoparticle concentrations in the range of 1-100 mg/L. In addition to fluoride ions, shorter chain perfluorocarboxylic acids (PFCAs) were detected as the main intermediates during PFAS degradation; PFHpS and 6:2 FTS were also detected during PFOS degradation. Hydroxyl radicals (·OH) and superoxide radicals (·O₂^-) were not involved in the degradation of PFOA, but likely involved in the degradation of PFOS. Emerging contaminants PFAS degradation using the UV/Fe⁰ system is a cost-effective technology owing to the low cost and recyclability of Fe⁰ nanomaterials, low energy consumption in the system, and its capability to degrade PFAS both with and without the presence of oxygen. This technology can be potentially applied to treat PFAS-contaminated waters in the environment.

A systematic review on iron-based nanoparticle-mediated clean-up of textile dyes: challenges and prospects of scale-up technologies

The projected increase of the global textile industry to USD1002.84 billion in 2027 indicates a simultaneous increase in water pollution due to textile dye-rich voluminous effluents highlighting the requirement of source clean-up. This review analyzes the colossal amount of literature on lab-scale nanoremediation technologies involving iron-based nanoparticles and the mechanistic aspects. However, not many studies are in place with regard to execution because there are several bottlenecks in the scale-up of the technology. This review attempts to identify the limitations of scale-up by focusing on each step of nanoremediation from synthesis of iron-based nanoparticles to their applications. The most prominent appears to be the low economic viability of physico-chemical synthesis of nanoparticles, lack of appropriate toxicity studies of iron-based nanoparticles, and dearth of studies on field applications. It is recommended that above studies should be made not only on lab scale but also on field samples preferably utilizing microbial products based green synthesized iron-based nanoparticles and conducting toxicity studies. Besides, immobilization of the nanoparticles on renewable material greatly enhances the sustainability and economic value of the process. Furthermore, since the chemical composition of dye-rich effluents varies among industries, effluent specific optimization of process parameters and kinetics thereof is also a major prerequisite for scale-up. The value of this review lies in the fact that it brings, for the first time, a comprehensive and critical systematization of various aspects needing attention in order to scale-up such effective nanoremediation processes.

Remediation and mineralization processes for per- and polyfluoroalkyl substances (PFAS) in water: A review

Per- and polyfluoroalkyl substances (PFAS) are synthetic organic molecules used to manufacture various consumer and industrials products. In PFAS, the CF bond is stable, which renders these compounds chemically stable and prevents their breakdown. Several PFAS treatment processes such as adsorption, photolysis and photocatalysis, bioremediation, sonolysis, electrochemical oxidation, etc., have been explored and are being developed. The present review article has critically summarized degradative technologies and provides in-depth knowledge of photodegradation, electrochemical degradation, chemical oxidation, and reduction mineralization mechanism. Also, novel non-degradative technologies, including nano-adsorbents, natural and surface-modified clay minerals/zeolites, calixarene-based polymers, and molecularly imprinted polymers and adsorbents derived from biomaterials are discussed in detail. Of these novel approaches photocatalysis combined with membrane filtration or electrochemical oxidation via a treatment train approach shows promising results in removing PFAS in natural waters. The photocatalytic mineralization mechanism of PFOA is discussed, leading to recommendations for future research on novel remediation strategies for removing PFAS from water.

Sequestration and potential release of PFAS from spent engineered sorbents

Per- and poly-fluoroalkyl substances (PFAS) have contaminated land and water at numerous sites worldwide that now require remediation. The most common approach for treating contaminated water currently relies on removal of PFAS by sorption. The spent sorbents loaded with PFAS can potentially be disposed of at landfills, provided the sorbed contaminants remain sequestered and certain risk criteria are met. Hence, it is essential that remediation sorbents (i) rapidly adsorb a large variety of PFAS under varying water chemistry conditions, and (ii) do not release the adsorbed PFAS in due course. This review aims at establishing the current state of knowledge about the potential release of PFAS that may occur during and after treatment. The scientific literature currently provides data for a very restricted range of long-chain PFAS. Our knowledge of the dynamics of PFAS adsorption processes on engineered sorbents is limited, and even less is known about their desorption processes. The sorption of PFAS can be strongly affected by changes in the solution pH, ionic strength and dissolved organic matter content, and the process is also subject to complex competition mechanisms in the presence of other PFAS as well as organic contaminants and inorganic salts. Several studies suggest that changes in one or several of these factors may trigger the release of PFAS from engineered sorbents. This phenomenon is more likely to occur for PFAS with shorter carbon chain lengths (<C8), at high pH and in the presence of other PFAS or other anionic sorbates. The release of PFAS from spent sorbent materials, stored or deposited under conditions that vary over time, is highly undesirable, as they can potentially become a secondary source of PFAS in the environment. Our analysis identifies a number of knowledge-gaps that should be urgently addressed in order to design sustainable remediation solutions, including an improved management of spent sorbent materials.

Adsorption, degradation, and mineralization of emerging pollutants (pharmaceuticals and agrochemicals) by nanostructures: a comprehensive review

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

Synthesis and Application of Zero-Valent Iron Nanoparticles in Water Treatment, Environmental Remediation, Catalysis, and Their Biological Effects

Present and past anthropogenic pollution of the hydrosphere and lithosphere is a growing concern around the world for sustainable development and human health. Current industrial activity, abandoned contaminated plants and mining sites, and even everyday life is a pollution source for our environment. There is therefore a crucial need to clean industrial and municipal effluents and remediate contaminated soil and groundwater. Nanosized zero-valent iron (nZVI) is an emerging material in these fields due to its high reactivity and expected low impact on the environment due to iron's high abundance in the earth crust. Currently, there is an intensive research to test the effectiveness of nZVI in contaminant removal processes from water and soil and to modify properties of this material in order to fulfill specific application requirements. The number of laboratory tests, field applications, and investigations for the environmental impact are strongly increasing. The aim of the present review is to provide an overview of the current knowledge about the catalytic activity, reactivity and efficiency of nZVI in removing toxic organic and inorganic materials from water, wastewater, and soil and groundwater, as well as its toxic effect for microorganisms and plants.