Designer carbon nanotubes for contaminant removal in water and wastewater: A critical review

Evaluating sorbents for reducing per- and polyfluoroalkyl substance mobility in biosolids-amended soil columns

Sustainable reuse of biosolids as fertilizers is being threatened by the presence of per- and polyfluoroalkyl substances (PFAS) in our waste stream warranting research on strategies that will minimize PFAS mobility from land-applied biosolids. Here, we evaluated the ability of waste-derived sorbents aluminum chlorohydrate water treatment residuals (ACH-WTRs, 1 wt%) and biosolids-based biochar (1.5 wt%) to reduce mobility of PFAS in columns with 3 wt% biosolids-amended soils with and without sorbent layered on top of soil only and operated under transient unsaturated conditions. Cycles of simulated rain events of approximately three pore volumes distributed over a 4-day period followed by 3 days of drying were imposed for 6 months. Total PFAS concentrations in collected leachates were lower in the sorbent-treated columns compared to the control columns. Biochar outperformed the ACH-WTR with 41% versus 32% lower total PFAS in leachate, respectively, compared to the control. The most significant mitigation effect was observed with PFOS (perfluorooctane sulfonate) with 68% and 62% less PFOS in the leachates from the columns treated with ACH-WTR or biochar compared to the control, respectively. These results provide a first-of-its-kind assessment of the potential benefit of co-applying WTRs or biochar with biosolids to reduce PFAS mobility in biosolids-amended soils.

Sulfur-Functionalized Single-Walled Carbon Nanotube Buckypaper/MTV-BioMetal-Organic Framework Nanocomposites for Gold Recovery

Developing sustainable, efficient, and selective gold recovery technology is essential to implement the valorization of complementary alternative sources for this precious metal, such as spent e-waste, and to preserve the environment. The main challenge in recovering gold from liquors obtained from leached waste electronics is the low concentration of this precious metal compared to impurities. Here, we report the preparation of a novel multivariate biological metal-organic framework (MTV-BioMOF) as a potential material for the selective recovery of gold metal ions from water, even in the presence of other interfering metals. Moreover, MTV-BioMOF can be incorporated within single-walled carbon nanotube buckypapers (SWCNT-BP) to yield an MTV-BioMOF@HS-SWCNT-BP composite, which combines enhanced mechanical properties and high chemical stability. The thiol-functionalized SWCNT-BP surface and the presence of thioether groups evenly decorating the MTV-BioMOF channels shape a task-specific functional environment that boosts the interactions with gold metal ions. The efficiency of gold recovery reaches values up to 99.5% when MTV-BioMOF@SWCNT-BP is used as an adsorbent for treating Au(III) in very diluted solutions (initial concentration of 5 ppm). This high recovery efficiency, with values as high as 98.0%, is maintained even in the presence of competing metal cations, also demonstrating a noticeable selectivity. This composite material represents a promising paradigm for the selective extraction, enrichment, and purification of gold.

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Heterointerface engineering of MXene: Advanced applications in environmental remediation

Contemporary global industrialization, coupled with the relentless growth of the population, has led to a persistent escalation in the emission and accumulation of various toxic and harmful chemicals in the environment, severely disrupting the ecological balance. The development of efficient environmental cleanup materials is a crucial scientific and technological concern. Since the groundbreaking work on Ti3C2Tx in 2011, there has been a huge growing interest in MXene-based composites developed through heterointerface engineering due to its high surface area, hydrophilicity, eco-friendliness, biocompatibility, easy functionalization, excellent thermal/mechanical properties, metal conductivity and rich electronic density. In the area of environmental remediation, MXene-based composites obtained through heterointerface engineering strategies have the ability to effectively remove and systematically monitor contaminants in comparison to virgin MXene, thanks to the synergistic effects and complementary benefits. Heterointerface engineering strategy increases specific surface area, introduces catalytic sites, constructs heterojunctions/Schottky junctions, and facilitates carrier migration and electron-hole separation. These novel MXene-based composites represent significant advances in MXene research and deserve a comprehensive review. Although several excellent reviews and perspectives on the application of MXene-based composites in environmental remediation have been published, there is still a scarcity of comprehensive and systematic assessments on the reliable data and mechanisms of various MXene-based composite materials for pollutant removal and monitoring. In this focused review, the first part briefly introduces the common preparation strategies and characterization methods of single MXene and MXene-based composites, and the second part details the innovative application of MXene-based composites (involving the amalgamation of MXene with metal oxides, metal sulfide, g-C3N4, layered double hydroxides, metal-organic frameworks, single atom/quantum dots, polymers, etc.) in the field of environmental remediation, including carbon dioxide reduction, nitrogen monoxide and volatile organic compounds removal, antibiotic and heavy metal ions degradation, summarizing the relevant performance and mechanisms. Furthermore, the recent advancements in the utilization of MXene-based composites for the sensing of emerging environmental contaminants (antibiotic and antibiotic resistance genes) are summarized. Finally, an outline of the existing challenges and future prospects on this exciting field was narrated for plausible real-world use. This review will help to inspire the diverse design of MXene-based composites and to advance research related to their application in the environmental sector.

Bio-Inspired Underwater Superoleophobic Aramid Nanofiber-Based Aerogel Membranes for Highly Efficient Removal of Emulsified Oils and Organic Dyes

Effective elimination of insoluble emulsified oils and soluble organic dyes has received extensively attention in wastewater treatment. In this work, a chitosan and polydopamine @ aramid nanofibers (CS&PDA@ANFs) aerogel membrane was fabricated through an integration methodology consisting of phase inversion and successive deposition of PDA and CS. The as-prepared aerogel membrane possessed a satisfactory three-dimensional interpenetrating network architecture with high porosity and desirable mechanical property. Furthermore, due to the synergistic effect of hydrophilic CS and PDA, the resultant membrane exhibited good superhydrophilicity and underwater superoleophobicity associated with favorable oil resistance/antioil fouling properties. The combination of the interconnected porous structures and super wettability endowed the aerogel membranes with desirable oil-in-water emulsion separation performance. Particularly, an extremely high permeation flux (3729 L/m2/h) and a rejection rate (99.3%) were achieved for the CS&PDA@ANFs membrane. Moreover, diverse dyes could be also adsorbed by the resultant membrane, and the equilibrium adsorption capacity of cationic dye malachite green could reach 36 mg/g, with a high rejection rate over 97%. This study indicated that the CS&PDA@ANFs aerogel membrane held great promise for practical applications in complex wastewater remediation.

Magnetic surfactant-modified clay for enhanced adsorption of mixtures of per- and polyfluoroalkyl substances (PFAS) in snowmelt: Improving practical applicability and efficiency

The extensive use of per- and polyfluoroalkyl substances (PFAS) in many industrial and consumer contexts, along with their persistent nature and possible health hazards, has led to their recognition as a prevalent environmental issue. While various PFAS removal methods exist, adsorption remains a promising, cost-effective approach. This study evaluated the PFAS adsorption performance of a surfactant-modified clay by comparing it with commercial clay-based adsorbents. Furthermore, the impact of environmental factors, including pH, ionic strength, and natural organic matter, on PFAS adsorption by the modified clay (MC) was evaluated. After proving that the MC was regenerable and reusable, magnetic modified clay (MMC) was synthesized, characterized, and tested for removing a wide range of PFAS in pure water and snowmelt. The MMC was found to have similar adsorption performance as the MC and was able to remove > 90% of the PFAS spiked to the snowmelt. The superior and much better performance of the MMC than powdered activated carbon points to its potential use in removing PFAS from real water matrices at an industrial scale.

Waste-derived carbon nanostructures (WD-CNs): An innovative step toward waste to treasury

With the growing population, the accumulation of waste materials (WMs) (industrial/household waste) in the environment incessantly increases, affecting human health. Additionally, it affects the climate and ecosystem of terrestrial and water habitats, thereby needing effective management technology to control environmental pollution. In this aspect, managing these WMs to develop products that mitigate the associated issues is necessary. Researchers continue to focus on WMs management by adopting a circular economy. These WMs convert into useful/value-added products such as polymers and nanomaterials (NMs), especially carbon nanomaterials (CNs). The conversion/transformation of waste material into useful products is one of the best solutions for managing waste. Waste-derived CNs (WD-CNs) have established boundless promises for numerous applications like environmental remediation, energy, catalysts, sensors, and biomedical applications. This review paper discusses the several sources of waste material (agricultural, plastic, industrial, biomass, and other) transforming into WD-CNs, such as carbon nanotubes (CNTs), biochar, graphene, carbon nanofibers (CNFs), carbon dots, etc., are extensively elaborated and their application. The impact of metal doping within the WD-CNs is briefly discussed, along with their applicability to end applications.

Advancement in nanomaterials for environmental pollutants remediation: a systematic review on bibliometrics analysis, material types, synthesis pathways, and related mechanisms

Environmental pollution is a major issue that requires effective solutions. Nanomaterials (NMs) have emerged as promising candidates for pollution remediation due to their unique properties. This review paper provides a systematic analysis of the potential of NMs for environmental pollution remediation compared to conventional techniques. It elaborates on several aspects, including conventional and advanced techniques for removing pollutants, classification of NMs (organic, inorganic, and composite base). The efficiency of NMs in remediation of pollutants depends on their dispersion and retention, with each type of NM having different advantages and disadvantages. Various synthesis pathways for NMs, including traditional synthesis (chemical and physical) and biological synthesis pathways, mechanisms of reaction for pollutants removal using NMs, such as adsorption, filtration, disinfection, photocatalysis, and oxidation, also are evaluated. Additionally, this review presents suggestions for future investigation strategies to improve the efficacy of NMs in environmental remediation. The research so far provides strong evidence that NMs could effectively remove contaminants and may be valuable assets for various industrial purposes. However, further research and development are necessary to fully realize this potential, such as exploring new synthesis pathways and improving the dispersion and retention of NMs in the environment. Furthermore, there is a need to compare the efficacy of different types of NMs for remediating specific pollutants. Overall, this review highlights the immense potential of NMs for mitigating environmental pollutants and calls for more research in this direction.

New insights into Co3O4-carbon nanotube membrane for enhanced water purification: Regulated peroxymonosulfate activation mechanism via nanoconfinement

Co-based peroxymonosulfate (PMS) activation system with fascinating catalytic performance has become a promising technology for water purification, but it always suffers from insufficient mass transfer, less exposed active sites and toxic metal leaching. In this work, a carbon nanotube membrane confining Co3O4 inside (Co3O4-in-CNT) was prepared and was coupled with PMS activation (catalytic membrane process) for sulfamethoxazole (SMX) removal. Compared with counterpart with surface-loaded Co3O4 (Co3O4-out-CNT), the Co3O4-in-CNT catalytic membrane process exhibited enhanced SMX removal (99.5% vs. 89.1%) within residence time of 2.89 s, reduced Co leaching (20 vs. 147 μg L-1) and more interestingly, the nonradical-to-radical mechanism transformation (from 1O2 and electron transfer to SO4•- and •OH). These phenomena were ascribed to the nanoconfinement effect in CNT, which enhanced mass transfer (2.80 × 10-4 vs. 5.98 × 10-5 m s-1), accelerated Co3+/Co2+ cycling (73.4% vs. 65.0%) and showed higher adsorption energy for PMS (cleavage of O-O bond). Finally, based on the generated abundant reactive oxygen species (ROS), the seven degradation pathways of SMX were formed in system.

Exploration of functionalizing graphene and the subsequent impact on PFAS adsorption capabilities via molecular dynamics

Per- and polyfluoroalkyl substances (PFAS) are extremely stable compounds due to their strong C-F bonds. They are used in water and stain proof coatings, aqueous film forming foams for fire suppression, cosmetics, paints, adhesives, etc. PFAS have been found in soils and waterways around the world due to their widespread usage and recalcitrance to degradation. Development of selective adsorbent materials is necessary to effectively capture a vast family of PFAS structures in order to remediate PFAS contamination in the environment. The work herein is focused on extracting design principles from molecular dynamics simulations of PFAS with functionalized graphene materials. Simulations examined how PFBA, PFOA, and PFOS interact with graphene, graphene oxide, nitrogen group-functionalized graphene oxide, partially fluorinated graphene flakes, and fully fluorinated flakes. Five flakes were used in each simulation to examine how interactions between flakes may lead to competitive interactions with respect to PFAS or formation of pores. Our study revealed that both the clustering mechanisms of the flakes and functional groups on the flake play a role in PFAS adsorption. The most effective functionalizations for PFAS adsorption are as follows: pristine graphene ≈ fully fluorinated > graphene oxide ≈ partially fluorinated > amine and amide functionalized graphene oxide flake. Long chain PFAS and sulfonate PFAS had higher propensity to adsorb to the materials compared to short chain PFAS and carboxylic head groups.

A cohesive effort to assess the suitability and disparity of carbon nanotubes for water treatment

Population growth, industrialization, and the extensive use of chemicals in daily life have all contributed to an increase in waste generation and an intensified release of organic pollutants into the aquatic environment. To ensure the quality of water (including natural resources), the removal of these pollutants from wastewater has become a challenging task for scientific community. Conventional physical, chemical, and biological treatment methods are commonly used in combinations and are not very effective. Recently, carbon nanotubes (CNTs) emerged as the most reliable and adaptable choice for efficient water treatment due to their extraordinary material properties appearing as a single-step solution for water treatment. High surface area, exceptional porosities, hollow and layered structures, and ease of chemical activation and functionalization are some properties which makes it excellent adsorption material. Hence, this review paper discusses the recent advances in the synthesis, purification, and functionalization of CNTs for water and wastewater treatment. In addition, this study also also provides a quick overview of CNTs-based advance technologies employed in water treatment and carefully assesses the benefits versus risks during large-scale water treatment. Furthermore, it concludes that identified risks to the environment and human health cannot be easily ignored and strict regulatory requirements are a must for producing low-cost innoxious CNTs.

Material Design Strategies for Recovery of Critical Resources from Water

Population growth, urbanization, and decarbonization efforts are collectively straining the supply of limited resources that are necessary to produce batteries, electronics, chemicals, fertilizers, and other important products. Securing the supply chains of these critical resources via the development of separation technologies for their recovery represents a major global challenge to ensure stability and security. Surface water, groundwater, and wastewater are emerging as potential new sources to bolster these supply chains. Recently, a variety of material-based technologies have been developed and employed for separations and resource recovery in water. Judicious selection and design of these materials to tune their properties for targeting specific solutes is central to realizing the potential of water as a source for critical resources. Here, the materials that are developed for membranes, sorbents, catalysts, electrodes, and interfacial solar steam generators that demonstrate promise for applications in critical resource recovery are reviewed. In addition, a critical perspective is offered on the grand challenges and key research directions that need to be addressed to improve their practical viability.

Study of folate-based carbon nanotube drug delivery systems targeted to folate receptor α by molecular dynamic simulations

We designed targeted drug delivery systems containing folate (FOL), the functionalized carbon nanotube (f-CNT) and doxorubicin (DOX), and studied the targeting properties of folate, f-CNT-FOL and DOX/f-CNT-FOL to folate receptor α (FRα). Folate was actively targeted to FRα in molecular dynamics simulations, and the dynamic process, effect of folate receptor evolution, and characteristics were analyzed. On this basis, the f-CNT-FOL and DOX/f-CNT-FOL nano-drug-carrier systems were designed, and the drug delivery process targeted to FRα was studied by 4 times MD simulations. The system evolution and detailed interactions of f-CNT-FOL and DOX/f-CNT-FOL with FRα residues were examined. We found that though the connection of CNT with the FOL could decrease the insertion depth of the pterin of FOL into the pocket of FRα, the loading of drug molecules could reduce this effect. Representative snapshots from the MD simulations were analyzed, showing that the location of DOX on the surface of CNT was constantly changed during the MD simulation, but the surface of the four rings of DOX were almost always parallel to the surface of CNT. The RMSD and RMSF were used to further analyze. The results may provide new insights for the design of novel targeted nano-drug-delivery systems.

Enhancing Cu2+ Ion Removal: An Innovative Approach Utilizing Modified Frankincense Gum Combined with Multiwalled Carbon Tubes and Iron Oxide Nanoparticles as Adsorbent

Aquatic pollution, which includes organic debris and heavy metals, is a severe issue for living things. Copper pollution is hazardous to people, and there is a need to develop effective methods for eliminating it from the environment. To address this issue, a novel adsorbent composed of frankincense-modified multi-walled carbon nanotubes (Fr-MMWCNTs) and Fe3O4 [Fr-MWCNT-Fe3O4] was created and subjected to characterization. Batch adsorption tests showed that Fr-MWCNT-Fe3O4 had a maximum adsorption capacity of 250 mg/g at 308 K and could efficiently remove Cu2+ ions over a pH range of 6 to 8. The adsorption process followed the pseudo-second-order and Langmuir models, and its thermodynamics were identified as endothermic. Functional groups on the surface of modified MWCNTs improved their adsorption capacity, and a rise in temperature increased the adsorption efficiency. These results highlight the Fr-MWCNT-Fe3O4 composites' potential as an efficient adsorbent for removing Cu2+ ions from untreated natural water sources.

The use of chitosan-based composites for environmental remediation: A review

The presence of hazardous pollutants in water sources as a result of industrial activities is a major environmental challenge that impedes the availability of safe drinking water. Adsorptive and photocatalytic degradative removal of various pollutants in wastewater have been recognized as cost-effective and energy-efficient strategies. In addition to its biological activity, chitosan and its derivatives are considered as promising materials for the removal of various pollutants. The abundance of hydroxyl and amino groups in the chitosan macromolecular structure results in a variety of concurrent pollutant's adsorption mechanisms. Furthermore, adding chitosan to photocatalysts increases the mass transfer while decreasing both the band gap energy and the amount of intermediates produced during photocatalytic processes, improving the overall photocatalytic efficiency. Herein, we have reviewed the current design and preparation of chitosan and its composites, as well as their applications for the removal of various pollutants by adsorption and photocatalysis processes. Effects of operating variables such as the pH, catalyst mass, contact time, light wavelength, initial pollutant's concentration, and catalyst recyclability, are discussed. Various kinetic and isotherm models are presented to elucidate the rates, and mechanisms of pollutant's removal, onto chitosan-based composites, and several case studies are presented. Additionally, the antibacterial activity of chitosan-based composites has been discussed. This review aims to provide a comprehensive and up-to-date overview of the applications of chitosan-based composites in wastewater treatment and put forward new insights for the development of highly effective chitosan-based adsorbents and photocatalysts. Finally, the main challenges and future directions in the field are discussed.

Ion Separation Together with Water Purification via a New Type of Nanotube: A Molecular Dynamics Study

We propose a CNT-based concentric twin tube (CTT) as nanochannels for both water purification and ion separation at the nanoscale. In the model, a source reservoir dealing with the solution connects three containers via the CTT that has three subchannels for mass transfer. Before entering the three subchannels, the solution in the separating zone will form three layers (the aqua cations, water, and the aqua anions, respectively) by applying a charged capacitor with the two electrodes parallel to the flow direction of the solution. Under an electric field with moderate intensity, the three subchannels in the CTT have stable configurations for mass transfer. Since the water and the two types of aqua ions are collected by three different containers, the present model can realize both ion separation and water purification. The mass transfer in the subchannels will be sped up by an external pressure exerted on the solution in the source reservoir. The physical properties of the model, e.g., water purification speed, are analyzed with respect to the effects of the electric field, the size of CTT, and the concentration of solute, such as NaCl.

Bisphenol A removal in treated wastewater matrix at neutral pH using magnetic graphite intercalation compounds as persulfate activators

Effluents of municipal wastewater treatment plants (WWTPs) are major sources for releasing contaminants of emerging concern (CECs) into the aquatic environment, which can result in negative effects on aquatic ecosystems and, as a consequence, on humans. Herein, the graphite intercalation concept was used to synthesize heterogeneous catalysts to degrade bisphenol A (BPA) as a model CEC in municipal WWTP effluents at neutral pH. The catalyst was synthesized using the simple molten salt method and showed several benefits, such as iron leaching prevention and stability in environmental matrices. Different methods were applied to describe the catalyst's structural characteristics. The proposed system removed 99.3% of BPA in 75 min using 2 g/L of the synthesized catalyst and 1.19 g/L (5 mM) persulfate at neutral pH. Quenching experiments showed that catalytic activities and BPA removals were significantly aided by both radical and non-radical pathways through the generation of free radicals and singlet oxygen (¹ O₂ ). Furthermore, the reuse of recycled synthesized catalyst was investigated on treated urban wastewater, and the results showed that the catalyst could degrade BPA from the wastewater in consecutive cycles, demonstrating its applicability under real conditions. PRACTITIONER POINTS: BPA was effectively removed from the effluents of municipal WWTPs at neutral pH. A new catalyst (magnetic GIC) was fabricated for heterogeneous catalytic systems. The catalyst activates persulfate to generate free radicals and ¹ O₂ , indicating that radical and non-radical pathways contribute to BPA degradation. The catalyst showed the ability to remove BPA even in the sixth cycle of use, demonstrating its stability and reusability.

Treatment technologies for olive mill wastewater with impacts on plants

Olive mill wastewater (OMW), produced during olive oil production, contains high levels of salt contents, organic matter, suspended particles, and toxic chemicals (particularly phenols), which all result in increased biological and chemical oxygen demand. Olive Oil Mills' Wastes (OMW), which have dark brown color with unpleasant smell, consist mainly of water, high organic (mainly phenols and polyphenols) and low inorganic compounds (e.g. potassium and phosphorus), as well as grease. OMW components can negatively affect soil's physical, chemical, and biological properties, rendering it phytotoxic. However, OMW can positively affect plants' development when it's applied to the soil after pretreatment and treatment processes due to its high mineral contents and organic matter. There are various approaches for removing impurities and the treatment of OMW including chemical, biological, thermal, physiochemical, and biophysical processes. Physical techniques involve filtration, dilution, and centrifugation. Thermal methods include combustion and pyrolysis; biological techniques use anaerobic and aerobic techniques, whereas adsorption and electrocoagulation act as physiochemical methods, and coagulation and flocculation as biophysical methods. In contrast, combined biological treatment methods use co-digestion and composting. A comparison of the effects of both treated and untreated OMW samples on plant development and soil parameters can help us to understand the potential role of OMW in increasing soil fertility. This review discusses the impacts of untreated OMW and treated OMW in terms of soil characteristics, seed germination, and plant growth. This review summarizes all alternative approaches and technologies for pretreatment, treatment, and recovery of valuable byproducts and reuse of OMW across the world.

Fabrication and Characterisation of MWCNT/Polyvinyl (PVC) Polymer Inclusion Membrane for Zinc (II) Ion Removal from Aqueous Solution

Heavy metal pollution has prompted researchers to establish the most effective method to tackle the impacts of heavy metals on living things and the environment, which include by applying nanoparticles. An example is the employment of multi-walled carbon nanotubes (MWCNTs) as an additive in an intermediate membrane or polymer inclusion membrane (PIM). The MWCNTs were added to enhance the properties and reinforce the transport performance of zinc (II) ion (Zn2+) removal from the source phase to the receiver phase by the PIMs. The present study constructed a membrane with a poly(vinyl chloride) (PVC)-based polymer, dioctyl phthalate (DOP) plasticiser, and bis-(2-ethylhexyl) phosphate (B2EHP) carrier incorporated with different concentrations of MWCNTs. The contact angle (CA), water uptake, ion exchange capacity (IEC), and porosity of the fabricated membranes were evaluated. The membrane was also characterised by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and electrochemical impedance spectroscopy (EIS). Subsequently, the fabricated PIM (W1) and mixed matrix (MM)-PIM (W2−W5) samples were assessed under different parameters to acquire the ideal membrane composition and effectiveness. Kinetic modelling of Zn2+ removal by the fabricated PIMs under similar conditions was performed to reveal the mechanisms involved. The average removal efficiency of the membranes was >99% at different parameter conditions. Nevertheless, the W3 membrane with 1.0 wt% MWCNT immersed in a 5 mg/L initial Zn2+ concentration and 1.0 M receiver solution for seven hours at pH 2 demonstrated the highest percentage of Zn2+ removal. The experimental data were best fitted to the pseudo-first-order kinetic model (PFO) in kinetic modelling, and the permeability and flux of the W3 at optimum conditions were 0.053 m s−1 and 0.0532 mol m−2 s−1, respectively. In conclusion, the transport mechanism of Zn2+ was enhanced with the addition of the MWCNTs.

Exploring the significance of nanomaterials and organic amendments - Prospect for phytoremediation of contaminated agroecosystem

Emerging micro-pollutants have rapidly contaminated the agro-ecosystem, posing serious challenges to a sustainable future. The vast majority of them have infiltrated the soil and damaged agricultural fields and crops after being released from industry. These pollutants and their transformed products are also transported in vast quantities which further exacerbate the damage. Sustainable remediation techniques are warranted for such large amounts of contaminants. As aforementioned, many of them have been detected at very high concentrations in soil and water which adversely affect crop physiology by disrupting different metabolic processes. To combat this situation, nanomaterials and other organic amendments assisted phytoremediation ware considered as a viable alternative. It is a potent synergistic activity between the biological system and the supplied organic or nanomaterial material to eliminate emerging contaminants and micropollutants from crop fields. This can be effectively be applied to degraded crop fields and could potentially embody a green technology for sustainable agriculture.

Designing of pretreatment filter technique for reduction of phenolic constituents from olive-mill wastewater and testing its impact on wheat germination

Olive oil extraction produces a great volume of olive mill wastewater (OMW), which is considered a serious ecological challenge. In this study, we have designed and tested a trickling filter consisting of seven different layers of natural material, including (coarse gravel, fine gravel, lime (Ca (OH)₂), sand (SiO₂), carbon char, sponge/mesh), to treat OMW. The filter process involved physical separation, filtration, coagulation and adsorption with the removal of COD (69.8%), BOD (40.2%), Phenolic contents (90%), pH (41%), EC (41.6%) and total suspended solids (TSS) (69%). Our results have shown that treated OMW has a high potential oxidant activity. T7, Untreated OMW at 1:6 dilutions, had the strongest correlation (i.e. 0.97), while untreated OMW had the lowest IC50 (7.62 g ml^-1), which shown the best DPPH radical scavenging capabilities. While pure Untreated OMW has the maximum radical scavenging activity, 63%, treated (1:6) diluted OMW exhibits the lowest value i. e 9% when phosphomolybdate assay was done. HPLC analysis showed that the trickling filter removed the vanillic acid, caffeic acid and reduced the contents of phenolic components such as gallic acid, hydroxytyrosol, vanillin, quercetin and catechol. Filtered OMW was also tested for its germination efficacy at various dilutions (1:0, 1:2, 1:4, 1:6). A remarkable improvement in germination percentage, germination index, seedling length, seedling vigor index, promptness index, stress tolerance index (76.7%, 68.4%, 51.7%, 82.1%, 54.8%, and 66.7%, respectively) has shown the efficiency of treated OMW at 1:6 dilutions. The results from this study show the efficiency of our filter design which can be further used.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Emerging contaminants of high concern for the environment: Current trends and future research

Wastewater is contaminated water that must be treated before it may be transferred into other rivers and lakes in order to prevent further groundwater pollution. Over the last decade, research has been conducted on a wide variety of contaminants, but the emerging contaminants are those caused primarily by micropollutants, endocrine disruptors (EDs), pesticides, pharmaceuticals, hormones, and toxins, as well as industrially-related synthetic dyes and dye-containing hazardous pollutants. Most emerging pollutants did not have established guidelines, but even at low concentrations they could have harmful effects on humans and aquatic organisms. In order to combat the above ecological threats, huge efforts have been done with a view to boosting the effectiveness of remediation procedures or developing new techniques for the detection, quantification and efficiency of the samples. The increase of interest in biotechnology and environmental engineering gives an opportunity for the development of more innovative ways to water treatment remediation. The purpose of this article is to provide an overview of emerging sources of contaminants, detection technologies, and treatment strategies. The goal of this review is to evaluate adsorption as a method for treating emerging pollutants, as well as sophisticated and cost-effective approaches for treating emerging contaminants.

Recovery of Biophenols from Olive Vegetation Waters by Carbon Nanotubes

In this work, the possibility of using carbon nanotubes for the treatment of olive vegetation waters (OVWs) was investigated. In general, the disposal of OVWs represents an important environmental problem. The possibility of considering these waters no longer just as a problem but as a source of noble substances, thanks to the recovery of biophenols from them, was tested. In particular, predetermined quantities of olive vegetation waters were treated with carbon nanotubes. The quantities of adsorbed biophenols were studied as a function of the quantities of carbon nanotubes used and the contact time. The experimental conditions for obtaining both the highest possible quantities of biophenol and a purer adsorbate with the highest percentage of biophenols were studied. After the adsorption tests, the vegetation waters were analyzed by UV spectrophotometry to determine, in particular, the variation in the concentration of biophenols. The carbon nanotubes were weighed before and after each adsorption test. In addition, kinetic studies of the adsorption processes were considered. Carbon nanotubes proved their effectiveness in recovering biophenols.

The combined toxicity and mechanism of multi-walled carbon nanotubes and nano copper oxide toward freshwater algae: Tetradesmus obliquus

Nanoparticles (NPs) are widely used for their special physical properties and released into the natural environment. When two types of NPs exist in the same environment, the presence of one type of NP may affect the properties of the other type of NP. This study investigated the toxic effects of multi-walled carbon nanotubes (MWCNTs) and copper oxide nanoparticles (CuO NPs) on Tetradesmus obliquus. Both NPs had toxic effects on algae, and the toxic effects of MWCNTs were significantly stronger than CuO NPs which the 96-hr median effective concentration to algae were 33.8 and 169.2 mg/L, respectively. Oxidative stress and cell membrane damage were the main reasons for the toxicity of NPs to algae, and they were concentration-dependent, and the existence of CuO NPs in some groups reduced cell membrane damage caused by MWCNTs which may because that CuO NPs formed heteroaggregation with MWCNTs, reducing the contact of nanoparticles with cell membranes, then reducing physical damage. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) results indicated cell damage, the heteroaggregation of MWCNTs-CuO NPs and obvious nanoparticles internalization. In some groups, the presence of CuO NPs significantly reduced reactive oxygen species (ROS) level induced by MWCNTs. However, for the highest concentration group, the ROS level was much higher than that of the two NPs alone treatment groups, which might be related to the high concentration of MWCNTs promoting the internalization of CuO NPs. MWCNTs and CuO NPs affected and interacted with each other, causing more complex toxic effects on aquatic organisms.

Treatment of Wastewater Containing Nonsteroidal Anti-Inflammatory Drugs Using Activated Carbon Material

This study presents an adsorbent material (activated carbon) used in the treatment of wastewater with the role of removing ibuprofen, acetaminophen, diclofenac and ketoprofen pollutants. The wastewater treatment efficiencies of the activated carbon were systematically investigated using adsorption kinetics. The parameters studied were: pH (4 and 6 values of pH), initial concentration of wastewater (1, 5, and 10 mg/L), contact time (10 min), adsorbent quantity (0.1, 0.5, and 1 g), and isotherm models (Langmuir and Freundlich). The highest wastewater treatment efficiency was obtained at the 6 pH value. The determination of four anti-inflammatory drugs, frequently monitored in wastewater, was performed by a simple and fast method using the HPLC-technique-type DAD (diode array detector). The method was linear when the concentration ranged between 0.5 and 20 m/L for all compounds. The equilibrium concentration was obtained after 8 min. The octanol/water coefficient influenced the removal efficiency of the four drugs by the adsorbent material (activated carbon). The dose of activated carbon (0.1 to 1 g) significantly influenced the efficiency of wastewater treatment, which increased considerably when the dose of the adsorbent material increased. Using 1 g of the adsorbent material for the treatment of wastewater containing 1 mg/L initial concentration of pollutant compounds, the efficiencies were 98% for acetaminophen, 92% for diclofenac, 88% for ketoprofen and 96% for ibuprofen.

Heavy metal removal by biomass-derived carbon nanotubes as a greener environmental remediation: A comprehensive review

The concentrations of heavy metal ions found in waterways near industrial zones are often exceed the prescribed limits, posing a continued danger to the environment and public health. Therefore, greater attention has been devoted into finding the efficient solutions for adsorbing heavy metal ions. This review paper focuses on the synthesis of carbon nanotubes (CNTs) from biomass and their application in the removal of heavy metals from aqueous solutions. Techniques to produce CNTs, benefits of modification with various functional groups to enhance sorption uptake, effects of operating parameters, and adsorption mechanisms are reviewed. Adsorption occurs via physical adsorption, electrostatic interaction, surface complexation, and interaction between functional groups and heavy metal ions. Moreover, factors such as pH level, CNTs dosage, duration, temperature, ionic strength, and surface property of adsorbents have been identified as the common factors influencing the adsorption of heavy metals. The oxygenated functional groups initially present on the surface of the modified CNTs are responsible towards the adsorption enhancement of commonly-encountered heavy metals such as Pb²⁺, Cu²⁺, Cd²⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺, and Cr⁶⁺. Despite the recent advances in the application of CNTs in environmental clean-up and pollution treatment have been demonstrated, major obstacles of CNTs such as high synthesis cost, the agglomeration in the post-treated solutions and the secondary pollution from chemicals in the surface modification, should be critically addressed in the future studies for successful large-scale applications of CNTs.

Carbon nanotubes derived from waste cooking oil for the removal of emerging contaminants

Multi-walled carbon nanotube (MWCNT) were synthesized using ethyl acetate and waste cooking oil as more green and sustainable carbon sources, and further successfully applied for the adsorption of norfloxacin and 17α-ethinylestradiol.

Investigation of the interaction mechanism of 3-allyl-2-hydantoin anti-cancer on the pristine and functionalized BC2N nanotubes as an effective drug delivery nanocarriers

One of the exciting aspects of different nanomaterials in biomedical applications is the delivery of a wide range of anti-cancer drugs to mitigate their negative side effects via precise targeting of the tumor cells. In the present study, the DFT B3LYP/6-31G (d, p) level of theory was used to evaluate the capabilities of raw BC₂N nanotubes (BC₂NNTs) and functionalized BC₂NNTs nanostructures as a carrier for an anti-cancer drug (i.e., 3-allyl-2-hydantoin (3-ASH)). It was specified that the existing interaction between 3-ASH and BC₂N nanotubes is weak (-10.97kcalmol^-1). Therefore, the functionalized BC₂NNTs were investigated for 3-ASH interaction. According to our computations, compared with raw BC₂NNTs, the role of hydrogen bonds between 3-ASH molecules' active sites and carboxyl-functionalized BC₂NNTs in the complexes' fixation, adsorption, and thermodynamic energy is of great importance. A considerable transfer of charge between 3-ASH molecule to the functionalized BC₂NNTs was detected via MEP, NBO, and fractional charge transfer analysis. Also, it was found that these nanostructures have high stability on the water medium while their solvation energies have negative values. This negative value is beneficial for the applications of 3-ASH drug delivery. The present work proposes a new method to load 3-ASH drugs with a high density on BC₂NNTs' surfaces.

Mechanisms and biological impacts of graphene and multi-walled carbon nanotubes on Drosophila melanogaster: Oxidative stress, genotoxic damage, phenotypic variations, locomotor behavior, parasitoid resistance, and cellular immune response

The use of graphene and multi-walled carbon nanotubes (MWCNTs) has now become rather common in medical applications as well as several other areas thanks to their useful physicochemical properties. While in vitro testing offers some potential, in vivo research into toxic effects of graphene and MWCNTs could yield much more reliable data. Drosophila melanogaster has recently gained significant popularity as a dynamic eukaryotic model in examining toxicity, genotoxicity, and biological effects of exposure to nanomaterials, including oxidative stress, cellular immune response against two strains (NSRef and G486) of parasitoid wasp (Leptopilina boulardi), phenotypic variations, and locomotor behavior risks. D. melanogaster was used as a model organism in our study to identify the potential risks of exposure to graphene (thickness: 2-18 nm) and MWCNTs in different properties (as pure [OD: 10-20 nm short], modified by amide [NH₂ ] [OD: 7-13 nm length: 55 μm], and modified by carboxyl [COOH] [OD: 30-50 nm and length: 0.5-2 μm]) at concentrations ranging from 0.1 to 250 μg/ml. Significant effects were observed at two high doses (100 and 250 μg/ml) of graphene or MWCNTs. This is the first study to report findings of cellular immune response against hematopoiesis and parasitoids, nanogenotoxicity, phenotypic variations, and locomotor behavior in D. melanogaster.

Sorptive removal of methylene blue from water by magnetic multi-walled carbon nanotube composites

In the present study, five magnetic multi-walled carbon nanotubes (MMWCNTs) with different diameters were prepared and their performance on the sorptive removal of methylene blue (MB) from water was investigated. Transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and vibrating sample magnetometer confirm that the surface of these MMWCNTs has been decorated by Fe₃O₄ nanoparticles, which renders the MMWCNTs superparamagnetic. Thus, these MMWCNTs can be easily separated from water after the adsorption. During the adsorption process, pH slightly affected the removal efficiency of MB and the adsorption performed better under weak alkaline conditions. Adsorption kinetics followed the pseudo-second-order kinetic model well, and the Dubinin-Radushkevich model fitted the isotherms best. The maximum adsorption capacity for MB reached 204.2 mg/g, and the values decreased with increasing diameters of MMWCNTs due to decreasing specific surface areas. The thermodynamics parameters indicated the spontaneous and exothermic nature of the adsorption. The reusability test showed that MMWCNTs could be used for 6 cycles without significant loss of the adsorption capacity. And common ions (K⁺, Na⁺, Ca²⁺ and Al³⁺) and SDS in water did not show greatly effects on the removal efficiency of MB. Hence, MMWCNTs prepared in this study could be promising adsorbents for dyes removal from wastewater.

Modification of regenerated cellulose ultrafiltration membranes with multi-walled carbon nanotubes for enhanced antifouling ability: Field test and mechanism study

Although ultrafiltration (UF) has been extensively employed for drinking water purification, it is crucial to further develop novel membrane materials to improve the antifouling capacity and satisfy the practical usage. Multi-walled carbon nanotubes (MWCNTs) have characteristics that could potentially improve the membrane antifouling performance. Therefore, in this study, modified cellulose UF membranes were prepared using MWCNTs of various outer diameters ranging from 10 to 20 nm to 40-60 nm. The antifouling properties of the modified membrane and natural organic matter (NOM) removal mechanism were investigated while treating water from a local drinking water source river. Overall, the antifouling ability increased by more than one-fold when the nascent cellulose membrane was coated with MWCNTs (outer diameter of 40-60 nm) at a loading of 17.4 g/m². The molecular weight distribution profiles of the NOM in the raw water and permeates suggest the superior performance of the modified membranes in removing two major NOM fractions with molecular weights ranging from approximately 5 k-30 k and 500 k-1000 k. Based on its hydrophobicity, the NOM of the raw water was fractionated into the strong hydrophobic (SHPO), the weak hydrophobic, the strong hydrophilic and the moderately hydrophilic (MHPI) fractions. The WHPO fraction caused the highest fouling compared with the other fractions under consistent experimental conditions. Meanwhile, the modified membranes showed a preference for removing the MHPI and SHPO fractions. These results imply that MWCNTs can be employed to improve the antifouling property of cellulose UF membranes and have the potential to selectively remove moderately hydrophilic contaminants from water.

Toxicity and remediation of pharmaceuticals and pesticides using metal oxides and carbon nanomaterials

The worldwide development of agriculture and industry has resulted in contamination of water bodies by pharmaceuticals, pesticides and other xenobiotics. Even at trace levels of few micrograms per liter in waters, these contaminants induce public health and environmental issues, thus calling for efficient removal methods such as adsorption. Recent adsorption techniques for wastewater treatment involve metal oxide compounds, e.g. Fe2O3, ZnO, Al2O3 and ZnO-MgO, and carbon-based materials such as graphene oxide, activated carbon, carbon nanotubes, and carbon/graphene quantum dots. Here, the small size of metal oxides and the presence various functional groups has allowed higher adsorption efficiencies. Moreover, carbon-based adsorbents exhibit unique properties such as high surface area, high porosity, easy functionalization, low price, and high surface reactivity. Here we review the cytotoxic effects of pharmaceutical drugs and pesticides in terms of human risk and ecotoxicology. We also present remediation techniques involving adsorption on metal oxides and carbon-based materials.

Carbon-based adsorbents for fluoroquinolone removal from water and wastewater: A critical review

This review summarizes the adsorptive removal of Fluoroquinolones (FQ) from water and wastewater. The influence of different physicochemical parameters on the adsorptive removal of FQ-based compounds is detailed. Further, the mechanisms involved in the adsorption of FQ-based antibiotics on various adsorbents are succinctly described. As the first of its kind, this paper emphasizes the performance of each adsorbent for FQ-type antibiotic removal based on partition coefficients of the adsorbents that is a more sensitive parameter than adsorption capacity for comparing the performances of adsorbents under various adsorbate concentrations and heterogeneous environmental conditions. It was found that π-π electron donor-acceptor interactions, electrostatic interactions, and pore-filling were the most prominent mechanisms for FQ adsorption by carbon and clay-based adsorbents. Among all the categories of adsorbents reviewed, graphene showed the highest performance for the removal of FQ antibiotics from water and wastewater. Based on the current state of knowledge, this review fills the gap through methodolically understanding the mechanism for further improvement of FQ antibiotics adsorption performance from water and wastewater.

Degradations of endocrine-disrupting chemicals and pharmaceutical compounds in wastewater with carbon-based nanomaterials: a critical review

Although water occupies 75% of the earth's surface, only 0.0067% of the total water is available for human activities. These statistics further decline with the population growth and consequent multiplication in the amount of annual waste produced. The demand for clean and safe drinking water has always been a prime concern in the global scenario. Among various types of waste materials, endocrine-disrupting chemicals (EDCs) and pharmaceutical effluents have become a constant threat to the aquatic ecosystem and possess challenges worldwide. Endocrine-disrupting chemicals (EDCs) are a mixed group of emerging concern chemicals with the ability to mimic the mechanisms of biosynthesis, transport, and metabolism of hormones. These chemicals pose various health threats such as early puberty, infertility, obesity, diabetes, reproductive disorders, cancerous tumors, and related disorders (immune cells, hormones' activity, and various organs). On the other hand, pharmaceutical compounds such as antibiotics also harm the natural environment, human health, and soil microbiology. Their low concentration, ranging from a few ng/L to μg/L, gives rise to a micro-pollution phenomenon, which makes it difficult to detect, analyze, and degrade in wastewater treatment plants. Activated carbons (ACs) and other adsorbents, including naturally occurring materials (wood, keratin) are considered as nanomaterials (NMs) reference for the separation of organic pollutants. It is generally acknowledged that mass-transfer phenomena control sorption kinetics at the liquid/solid interface, with retention controlled by the sorbent/sorbate properties. Therefore, the type of interaction (strong or weak van der Waals forces) and the hydrophilic/hydrophobic properties of the adsorbent are two crucial factors. Besides, EDCs and pharmaceutical compound sorption on such kinds of nanoporous solids depend on both the molecule size and charge density. The applications of nanomaterials on non-conservative methods, like advanced oxidation processes or AOPs (e.g., photocatalysis and Fenton reaction), are contemplated as more apt in comparison to conservative technology like reverse osmosis nanofiltration, and adsorption, etc. One of the reasons is that AOPs generate free radicals (hydroxyls), which are strong oxidants for the demineralization of organic compounds and the extreme case that hydroxyl radicals can attack any kinds of pollutants with the generation of only water and carbon dioxide as final products. AOPs may imply the use of NMs as either catalysts or photocatalysts, which improve the selective removal of the target pollutant. Therefore, various literature reviews have revealed that there is a timely need to upgrade the efficiency of the remediation approaches to protect the environment against EDCs and pharmaceuticals adequately. There is currently a lack of definitive risk assessment tools due to their complicated detection and associated insufficiency in the health risk database. Hence, our present review focuses on applying carbon-based nanomaterials to remove EDCs and pharmaceuticals from aqueous systems. The paper covers the effect of these pollutants and photocatalytic methods for treating these compounds in wastewater, along with their limitations and challenges, plausible solutions, and prospects of such techniques.

Synthesis of Phosphonated Carbon Nanotubes: New Insight into Carbon Nanotubes Functionalization

Carbon nanotubes were successfully functionalized for the first time in a free radical phosphonylation reaction. Three synthetic protocols were proposed. Carbon nanotubes and diethylphosphite reacted in the presence of known radical initiator, such as azobisisobutyronitrile, single electron oxidant-Mn(OAc)3, or under UV radiation. The functionalized material was fully characterized by means of spectroscopic methods, together with microscopic, surface area and thermogravimetric analyses. UV-illumination was found to be the most effective approach for introducing phosphonates onto carbon nanotubes. X-ray photoelectron spectroscopy analysis showed 6% phosphorus in this sample. Moreover, the method was performed at room temperature for only one hour, using diethylphosphite as a reactant and as a solvent. The functionalized carbon nanotubes showed an improved thermal stability, with a decomposition onset temperature increase of more than 130 °C. This makes it very promising material for flame retarding applications.

Environmental risk of nanomaterials and nanoparticles and EPR technique as an effective tool to study them-a review

Nanotechnologies and different types of nanomaterials belong in present day to intensively studied materials due to their unique properties and diverse potential applications in, e.g., electronics, medicine, or display technologies. Together with the investigation of their desired beneficial properties, a need to investigate and evaluate their influence on the environment and possible harmful effects towards living organisms is growing. This review summarizes possible toxic effects of nanomaterials on environment and living organisms, focusing on the possible bioaccumulation in organisms, toxicity, and its mechanisms. The main goal of this review is to refer to potential environmental risks rising from the use of nanomaterials and the necessity to deal with the possible toxic effects considering the growing interest in the wide-scale utilization of these materials. Electron paramagnetic resonance spectroscopy as the only analytical technique capable of detecting radical species enables detection, quantification, and monitoring of the generation of short-lived radicals often coupled with toxic effects of nanomaterials, which makes it an important method in the process of nanotoxicity mechanism determination.

Nb2O5 nanoparticles decorated with magnetic ferrites for wastewater photocatalytic remediation

Nanotechnology has been studied on environmental remediation processes to foster greater photocatalysts efficiency and reuse in wastewater. This study investigated the photocatalytic efficiency and viability of niobium pentoxide (Nb₂O₅) nanoparticles decorated with magnetic ferrite (cobalt ferrite (CoFe₂O₄) or magnesium ferrite (MgFe₂O₄)) for atrazine photodegradation. Thus, the decorated Nb₂O₅ was synthesized by the polymeric precursor method, forming nanoparticles with sizes ranging from 25 to 50 nm. Nanocomposite elementary analyses showed a homogeneous distribution of elements on all particles surface. Efficient magnetic saturation was observed for pure CoFe₂O₄ (53 emu g^-1) and MgFe₂O₄ (19 emu g^-1) nanoparticles, promoting the magnetic removal of Nb₂O₅:CoFe₂O₄ and Nb₂O₅:MgFe₂O₄ nanocomposites. Photocatalytic assays showed 88% efficiency for atrazine photodegradation with all nanomaterials, which represented a 21% increase compared to photolysis in the 1st cycle. The magnetic nanocomposites when applied to a 5th cycle maintained the atrazine photodegradation activity. In this way, magnetic Nb₂O₅-based nanocomposites decorated with ferrite nanoparticles showed an efficient photocatalytic response, in addition to posterior magnetic removal from the aqueous medium. Therefore, the evaluated magnetic Nb₂O₅ nanocomposites may be an alternative to enhance the wastewater removal process and foster the reuse in advanced oxidative processes.

The Role of Carbon Nanotube Pretreatments in the Adsorption of Benzoic Acid

Four different types of multi-walled carbon nanotubes (MWCNTs) were used and compared for the treatment of benzoic acid contaminated water. The types of nanotubes used were: (1) non-purified (CNTs^UP), as made; (2) purified (CNTs^P), not containing the catalyst; (3) oxidized (CNTs^OX), characterized by the presence of groups such as, –COOH; (4) calcined (CNTs⁹⁰⁰), with elimination of interactions between nanotubes. In addition, activated carbon was also used to allow for later comparison. The adsorption tests were conducted on an aqueous solution of benzoic acid at concentration of 20 mg/L, as a model of carboxylated aromatic compounds. After the adsorption tests, the residual benzoic acid concentrations were measured by UV-visible spectrometry, while the carbon nanotubes were characterized by TG and DTA thermal analyses and electron microscopy (SEM). The results show that the type of nanotubes thermally treated at 900 °C has the best performances in terms of adsorption rate and amounts of collected acid, even if compared with the performance of activated carbons.

Magnetic nanomaterials with unique nanozymes-like characteristics for colorimetric sensors: A review

Colorimetric sensors for the rapid detection of numerous analytes have been widely applied in many fields such as biomedicine, food industry and environmental science due to their highly sensitive and selective response, easy operation and visual identification by naked eyes. In this review, the recent progress of the colorimetric sensors based on the magnetic nanomaterials with unique nanozymes-like catalytic activity (magnetic nanozyme) and their colorimetric sensing applications are presented. Emerging magnetic nanozyme-based colorimetric sensors, such as metal oxide/sulfides-based, metal-based, carbon-based, and aptamer-conjugated magnetic nanomaterials, offer many desirable features for target analytes detection. And due to the unique nanoscale physical-chemical properties, magnetic nanozymes have been used to mimic the catalytic activity of natural enzymes such as peroxidases, oxidases and catalases. This review also highlights the catalytic mechanisms of enzyme-like reactions, and promising colorimetric sensing system for the detection of chemical compounds like H₂O₂, pesticide, ascorbic acid, dopamine, tetracyclines, perfluorooctane sulfonate, phenolic compounds, heavy metal ion and sulfite have been deeply discussed. In addition, the remaining challenges and future directions in utilizing magnetic nanozyme for colorimetric sensors are addressed.