This article gives an overview of nanotechnologies applied in remediation of water contaminated by poly- and perfluoroalkyl substances (PFASs). The use of engineered nanomaterials (ENMs) in physical sorption and photochemical reactions offers a promising solution in PFAS removal because of the high surface area and the associated high reactivities of the ENMs. Modification of carbon nanotubes (CNTs) (e.g., oxidation, applying electrochemical assistance) significantly improves their adsorption rate and capacity for PFASs removal and opens a new door for use of CNTs in environmental remediation. Modified nanosized iron oxides with high adsorption capacity and magnetic property have also been demonstrated to be ideal sorbents for PFASs with great recyclability and thus provide an excellent alternative for PFAS removal under various conditions. Literature shows that PFOA, which is one of the most common PFASs detected at contaminated sites, can be effectively decomposed in the presence of either TiO₂-based, Ga₂O₃-based, or In₂O₃-based nano-photocatalysts under UV irradiation. The decomposition abilities and mechanisms of different nano-photocatalysts are reviewed and compared in this paper. Particularly, the nanosized In₂O₃ photocatalysts have the best potential in PFOA decomposition and the decomposition performance is closely related to the specific surface area and the amount of photogenerated holes on the surfaces of In₂O₃ nanostructures. In addition to detailed review of the published studies, future prospects of using nanotechnology for PFAS remediation are also discussed in this article.

Mesoporous nanocomposite of MgFe₂O₄ nanoparticles (NPs) and graphene oxide (GO) was synthesized using facile sonication method. Its potential was tested for the removal of Ni (II) and Pb (II) ions from water. The 2:1 w/w ratio of MgFe₂O₄:GO was optimum for the maximum removal of metal ions. Nanocomposite was characterized employing XRD, FT-IR, VSM, SEM-EDX, XPS, TEM and BET analyses. It possessed higher surface area (63.0 m² g⁻¹) than pristine NPs. Batch experiments were performed to study the effect of process parameters viz. pH, dose, contact time, initial metal ion concentration, co-existing ions and temperature. Statistical parameters were also determined. Langmuir, Temkin and Freundlich models were followed in perfect way. Langmuir model showed the monolayer adsorption of metal ions onto the homogeneous surface of nanocomposite with maximum adsorption capacity of 100.0 mg g⁻¹ and 143.0 mg g⁻¹ for Ni (II) and Pb (II) ions respectively, which was higher than the same for MgFe₂O₄ NPs and GO. Kinetic studies demonstrated that the pseudo-second order model well described the adsorption process. The ΔS° and ΔG° values revealed spontaneous nature of adsorption process. Positive ΔH° values using MgFe₂O₄ NPs and nanocomposite indicated endothermic removal; whereas using GO the removal was exothermic. The observed trend for coexisting ions correlated with hydrated ion radii. Efficiency of the adsorbents was also tested for realistic nickel electroplating industrial effluent. Apart from the higher adsorption potential of nanofabricated composite, its magnetic properties are advantageous in utilizing metal loaded nanocomposite for adsorption-desorption cycles for reuse.

Increasing urbanization and industrialization over the world has caused many social and environmental problems, one of which drawing particular concern is the soil pollution and its ecological degradation. In this study, the efficiency of magnetic methods for detecting and discriminating contaminates in the arid and semi-arid regions of northwestern China was investigated. Topsoil samples from six typical cities (i.e. Karamay, Urumqi, Lanzhou, Yinchuan, Shizuishan and Wuhai) were collected and a systematic analysis of their magnetic properties was conducted. Results indicate that the topsoil samples from the six cities were all dominated by coarse low-coercivity magnetite. In addition, the average magnetite contents in the soils from Urumqi and Lanzhou were shown to be much higher than those from Karamay, Yinchuan, Shizuishan and Wuhai, and they also have relatively higher χlf and χfd% when compared with cities in eastern China. Moreover, specific and distinctive soil pollution signals were identified at each sampling site using the combined various magnetic data, reflecting distinct sources. Industrial and traffic-derived pollution was dominant in Urumqi and Lanzhou, in Yinchuan industrial progress was observed to be important with some places affected by vehicle emission, while Karamay, Shizuishan and Wuhai were relatively clean. The magnetic properties of these latter three cities are significantly affected by both anthropogenic pollution and local parent materials from the nearby Gobi desert. The differences in magnetic properties of topsoil samples affected by mixed industrial and simplex traffic emissions are not obvious, but significant differences exist in samples affected by simplex industrial/vehicle emissions and domestic pollution. The combined magnetic analyses thus provide a sensitive and powerful tool for classifying samples according to likely sources, and may even provide a valuable diagnostic tool for discriminating among different cities.

Sediments affected by fluctuations of hydrocarbon contaminated groundwater were studied at a former military site. Due to remediation, groundwater table fluctuation (GWTF) extends over approximately one meter. Three cores were collected, penetrating through the GWTF zone. Magnetic parameters, sediment properties and hydrocarbon content were measured. We discovered that magnetic concentration parameters increased towards the top of the GWTF zone. Magnetite is responsible for this enhancement; rock magnetic parameters indicate that the newly formed magnetite is in a single domain rather than a superparamagnetic state. The presence of hydrocarbons is apparently essential for magnetite to form, as there is clearly less magnetic enhancement in the core, which is outside of the strongly contaminated area. From our results we conclude that the top of the fluctuation zone has the most intensive geomicrobiological activity probably responsible for magnetite formation. This finding could be relevant for developing methods for simply and quickly detecting oil spills.

The non-magnetic capping materials are difficult to be recycled from the water bodies after their application, leading to the increase in the cost of the sediment remediation. To address this issue, a capping material, i.e., magnetic lanthanum/iron-modified bentonite (M-LaFeBT) was prepared by loading lanthanum onto a magnetic iron-modified bentonite (M-FeBT) and used to control the internal phosphorus (P) loading in this study. To determine the capping efficiency and mechanism of M-LaFeBT, the impact of M-LaFeBT and M-FeBT capping on the mobilization of P in sediments was investigated, and the stabilization of P bound by the M-LaFeBT and M-FeBT capping layers was evaluated. Results showed that M-LaFeBT possessed good magnetic property with a saturated magnetization of 14.9 emu/g, and exhibited good phosphate adsorption ability with a maximum monolayer sorption capacity (QMAX) of 14.3 mg P/g at pH 7. Moreover, M-LaFeBT capping tremendously reduced the concentration of soluble reactive P (SR-P) in the overlying water (OL-water), and the reduction efficiencies were 94.7%–97.4%. Furthermore, M-LaFeBT capping significantly decreased the concentration of SR-P in the pore water and DGT (diffusive gradient in thin films)-labile P in the profile of OL-water and sediment. Additionally, most of P bound by the M-LaFeBT capping layer (approximately 77%) was stable under natural pH and reducing conditions. The phosphate adsorption ability for M-LaFeBT was much higher than that for M-FeBT, and the QMAX value for the former was 4.86 times higher than that for the latter. M-LaFeBT capping gave rise to a higher reduction of DGT-labile concentration in the profile of OL-water and sediment than M-FeBT capping. The P adsorbed by the M-LaFeBT capping layer was more stable than that by the M-FeBT capping layer. Results of this study demonstrate that M-LaFeBT is promising for utilization as an active capping material to intercept sedimentary P release into OL-water.

Antibiotics in water and soil are persistent, bioaccumulative and toxic to aquatic organisms and human health. To address it, as one of the new technologies, green synthesized magnetic Fe₃O₄ nanoparticles by Excoecaria cochinchinensis extract used to remove rifampicin (RIF) was investigated in this study. Results showed the adsorption efficiency of RIF reached 98.4% and the maximum adsorption capacity is 84.8 mg/g when 20 mL of RIF at a concentration of 20 M was adsorbed by 10 mg Fe₃O₄ at a temperature of 303 K. The morphology of the green Fe₃O₄ characterized by SEM demonstrated the dimensions ranging from 20 to 30 nm. The N₂ adsorption/desorption isotherms revealed that the surface area of Fe₃O₄ was 111.8 m²/g. In addition, adsorption studies indicated that the kinetics fitted the pseudo second-order and isothermal adsorption conformed to the Langmuir isotherm. Furthermore, due to their magnetic properties, the Fe₃O₄ nanoparticles were easily separated and reused and the mechanism for removing RIF occurred through adsorption rather than chemical redox reaction. Finally, the reusability of Fe₃O₄ for adsorption of RIF showed that the removal efficiency decreased to 61.5% after five cycles.

In this study, carbon nanotube-based adsorbents, oxidized multi-walled carbon nanotube (OMWCNT) with non-magnetic property and OMWCNT-Fe₃O₄ and OMWCNT-κ-carrageenan-Fe₃O₄ nanocomposites with magnetic property, having different structural and surface properties were prepared and their adsorptive properties for the removal of toxic diquat dibromide (DQ) herbicide from water by adsorption were determined in detail. For each adsorption system, the effects of initial DQ concentration, contact time and temperature on the adsorption processes were determined. Equilibrium time was found to be 300 min for DQ solutions. OMWCNT showed faster adsorption and higher maximum adsorption capacity value than magnetic adsorbents. With increasing initial herbicide concentration from 5.43 mg.L⁻¹ to 16.3 mg.L⁻¹, the values of initial sorption rate exhibited a decrease from 29.1 mg.g⁻¹.min⁻¹ to 4.28 mg.g⁻¹.min⁻¹ for OMWCNT-DQ system, from 1.21 mg.g⁻¹.min⁻¹ to 0.823 mg.g⁻¹.min⁻¹ for OMWCNT-Fe₃O₄-DQ system and from 0.674 mg.g⁻¹.min⁻¹ to 0.612 mg.g⁻¹.min⁻¹ OMWCNT-κ-carrageenan-Fe₃O₄ system. Maximum adsorption capacity value of OMWCNT was approximately 2.8-fold higher than magnetic OMWCNT-Fe₃O₄ and 5.4-fold higher than magnetic OMWCNT-κ-carrageenan-Fe₃O₄ at 25 °C. Adsorption kinetic and isotherm data obtained for all adsorption systems were well-fitted by pseudo second-order and Langmuir models, respectively. Thermodynamic parameters indicated that the adsorption of DQ onto carbon nanotube-based adsorbents was spontaneous and endothermic process. Furthermore, OMWCNT having the highest herbicide adsorption capacity could be regenerated and reused at least five times. This study showed that carbon nanotube-based adsorbents with magnetic and non-magnetic property were of high adsorption performance for the removal of DQ from water and could be promising adsorbent materials for the efficient removal of herbicides from wastewaters.

Identifying particulate matter (PM) emitted from industrial processes into the atmosphere is an important issue in environmental research. This paper presents a passive sampling method using simple artificial samplers that maintains the advantage of bio-monitoring, but overcomes some of its disadvantages. The samplers were tested in a heavily polluted area (Linfen, China) and compared to results from leaf samples. Spatial variations of magnetic susceptibility from artificial passive samplers and leaf samples show very similar patterns. Scanning electron microscopy suggests that the collected PM are mostly in the range of 2–25 μm; frequent occurrence of spherical shape indicates industrial combustion dominates PM emission. Magnetic properties around power plants show different features than other plants. This sampling method provides a suitable and economic tool for semi-quantifying temporal and spatial distribution of air quality; they can be installed in a regular grid and calibrate the weight of PM.

Rapid monitoring and discriminating different anthropogenic pollution is a key scientific issue. To detect the applicability and sensitivity of magnetic measurements for evaluating different industrial pollution in urban environment, characteristics of topsoil from three typical fast developing industrial cities (Jinchang, Baiyin and Jiayuguan in Gansu province, northwestern China) were studied by magnetic and geochemical analyses. The results showed that magnetic susceptibility was enhanced near industrial areas, and PSD-MD magnetite dominated the magnetic properties. Magnetic concentration parameters (χlf, SIRM, and χARM) showed different correlations with heavy metals and PLI in the three cities, indicating significantly different magnetic response to different pollution sources. Principal component analysis showed that ferrimagnetic minerals coexist with heavy metals of Fe, As, Cu, Pb, and Zn in Baiyin and Fe, V, Cu, Mn, Pb, and Cr in Jiayuguan. Fuzzy cluster analysis and regression analysis further indicated that the sensitivity of magnetic monitoring to fuel dust is higher than that to mineral dust near non-ferrous metal smelters, and fossil fuel consumption is an important factor for increasing magnetite content. In all the three cities, the sensitivity of magnetic monitoring to pollutants from steel plants is much higher than that from non-ferrous metal plants. Therefore, magnetic proxies provide a rapid means for detecting heavy metal contamination caused by multi-anthropogenic pollution sources in a large scale area, however, the sensitivity was controlled by pollution sources.

Magnetic properties of road dusts from 26 urban sites in Bulgaria are studied. Temporal variations of magnetic susceptibility (χ) during eighteen months monitoring account for approximately 1/3rd of the mean annual values. Analysis of heavy metal contents and magnetic parameters for the fraction d < 63 μm reveal significant correlations (p < 0.05) between χ and Fe, Mn and PLI index. The highest negative correlation (R2 = −0.84) is observed between the ratio ARM/χ and Pb content. It suggests that Pb is related to brake/tyre wear emissions, releasing larger particles and higher Pb during slow driving – braking. Bulk χ values of road dusts per city show significant correlation with population size and mean annual NO2 concentration on a log-normal scale. The results demonstrate the applicability of magnetic measurements of road dusts for estimation of mean NO2 levels at high spatial density, which is important for pollution modelling and health risk assessment.