Magnetic iron oxide nanoparticles functionalized multi-walled carbon nanotubes for toluene, ethylbenzene and xylene removal from aqueous solution

The Sword of Damocles: Microplastics and the molecular dynamics of sulfamonomethoxine revealed

In recent years, the environmental impact of microplastics (MPs) and antibiotics (ATs) as pollutants cannot be ignored. In order to evaluate the carrier effect of MPs in the aqueous environment, three MPs, polyamide (PA), polyethylene (PE) and polyethylene terephthalate (PET), were selected in this study, and their structures were analyzed by means of characterization. A preliminary description of their interactions with sulfamonomethoxine was carried out by adsorption kinetics and isotherm fitting. The dominance of non-bonding capacity (van der Waals and electrostatic interaction forces) in the adsorption process was demonstrated using molecular dynamics (MD) simulations and density functional theory (DFT), with the interaction strengths ranked as PA > PE > PET, respectively. PA is less adsorbent stable at the molecular level but exhibits the largest adsorption capacity influenced by the characterized structure and multiple interaction forces. PET possesses a stronger stability and is not easily replaced by other substances. This will help to further understand the complex effect mechanism between MPs and organic pollutants, and provide an important reference for the prevention and control of environmental pollution.

Evaluation of the difference in adsorption of amphetamine-type drugs on deep eutectic solvent-functionalized graphene oxide/ZIF-67 composite: Experiment and theoretical calculations

Herein, the capture and separation properties of the deep eutectic solvent-functionalized magnetic graphene oxide/ZIF-67 composite (ZMG-DES) towards amphetamine-type drugs (MDMA, MAM and AM) from water were investigated. Kinetic and isotherm models showed that the adsorption behaviors were monolayer chemisorption. Batch experiment results showed that the maximal adsorption of MDMA (933.652 μg⋅g-1) was 2.3 and 2.8 times higher than that of MAM (412.849 μg⋅g-1) and AM (328.652 μg⋅g-1), respectively, and this superiority remained consistent under varied environmental influences (pH, background ion and humic acid). Theoretical calculations and characterization analyses demonstrated the methylenedioxy group of MDMA led to the highly selective adsorption. Electrostatic potential (ESP) distribution indicated that the methylenedioxy added electron-rich areas and provided more adsorption sites. The Independent Gradient Model (IGMH) quantified the adsorption contribution of the functional groups in each system, which the contribution of the methylenedioxy reached 25.23%, significantly exceeding that of -NH- (18.80%) and benzene ring (20.76%), and proved that the H-bonds formed methylenedioxy enhanced adsorption. Furthermore, the Hirshfeld surface analysis proved that the methylenedioxy and -NH- of MDMA acted as H-bond acceptor and donor, respectively, which synergistically promoted the adsorption. The present study will help us to understand the structure-property relationship between amphetamine-type drugs and ZMG-DES.

Carbon nanotube-wastewater treatment nexus: Where are we heading to?

Water treatment is crucial in solving the rising people's appetite for water and global water shortages. Carbon nanotubes (CNTs) have considerable promise for water treatment because of their adjustable and distinctive arbitrary, physical, as well as chemical characteristics. This illustrates the benefits and risks of integrating CNT into the traditional water treatment resource. Due to their outstanding adsorbent ability and chemical and mechanical properties, CNTs have gained global consideration in environmental applications. The desalination and extraction capability of CNT were improved due to chemical or physical modifications in pure CNTs by various functional groups. The CNT-based composites have many benefits, such as antifouling performance, high selectivity, and increased water permeability. Nevertheless, their full-scale implementations are still constrained by their high costs. Functionalized CNTs and their promising nanocomposites to eliminate contaminants are advised for marketing and extensive water/wastewater treatment.

Adsorption Behavior of Diclofenac on Polystyrene and Poly(butylene adipate-co-terephthalate) Microplastics: Influencing Factors and Adsorption Mechanism

To unveil the intricacies surrounding the interaction between microplastics (MPs) and pollutants, diligent investigation is warranted to mitigate the environmental perils they pose. This exposition delves into the sorption behavior and mechanism of diclofenac sodium (DCF), a contaminant, upon two distinct materials: polystyrene (PS) and poly(butylene adipate-co-terephthalate) (PBAT). Experimental adsorption endeavors solidify the observation that the adsorption capacity of DCF onto the designated MPs amounts to Q(PBAT) = 9.26 mg g-1 and Q(PS) = 9.03 mg g-1, respectively. An exploration of the factors governing these discrepant adsorption phenomena elucidates the influence of MPs and DCF properties, environmental factors, as well as surfactants. Fitting procedures underscore the suitability of the pseudo-second-order kinetic and Freundlich models in capturing the intricacies of the DCF adsorption process onto MPs, corroborating the notion that the mentioned process is characterized by non-homogeneous chemisorption. Moreover, this inquiry unveils that the primary adsorption mechanisms of DCF upon MPs encompass electrostatic interaction, hydrogen bonding, and halo hydrogen bonding. An additional investigation concerns the impact of commonly encountered surfactants in aqueous environments on the adsorption of DCF onto MPs. The presence of surfactants elicits modifications in the surface charge properties of MPs, consequently influencing their adsorption efficacy vis-à-vis DCF.

Tuning the Dual Active Sites of Functionalized UiO-66 for Selective Adsorption of Yb(III)

The recovery of rare earth elements (REEs) from discharged electronic devices or mineral waste water is highly essential but still facing challenges. In this work, two amino-functionalized carboxyl-UiO-66 (UiO-66-COOH-TETA and UiO-66-(COOH)₂-ED) prepared via the postmodification method were employed as the adsorbents for Yb(III) capture. The experimental results revealed their superior adsorption capacities of 161.5 and 202.6 mg/g, respectively. Meanwhile, their adsorption processes can be described by the pseudo-second-order kinetic model and Langmuir model. Effects of initial pH and temperature on adsorptions were systematically evaluated, affording an optimal operating condition (i.e., pH of 5.5-6, T of 65 °C, t of 10 h). Moreover, the fabricated materials exhibited great reusability after five adsorption-regeneration cycles. UiO-66-COOH-TETA demonstrated good separation selectivity for Yb(III) over light REEs (i.e., 3.98 of Yb/Ce, 3.51 of Yb/Nd). Based on the density functional theory calculations and characterization analysis (XPS, Zeta, mapping, and IR), the adsorption mechanisms were mainly attributed to significant electrostatic attraction and strong surface complexation between N and O sites and Yb(III).

Adsorption of Pyrethroids in Water by Calcined Shell Powder: Preparation, Characterization, and Mechanistic Analysis

Pyrethroids are common contaminants in water bodies. In this study, an efficient mussel shell-based adsorbent was prepared, the effects of factors (calcination temperature, calcination time, and sieved particle size) on the pyrethroid adsorption capacity from calcined shell powder were investigated via Box-Behnken design, and the prediction results of the model were verified. By characterizing (scanning electron microscopy, X-ray diffraction, Fourier infrared spectroscopy, and Brunauer-Emmett-Teller measurements) the adsorbent before and after the optimized preparation process, the results showed that calcined shell powder had a loose and porous structure, and the main component of the shell powder under optimized condition was calcium oxide. The adsorption mechanism was also investigated, and the analysis of adsorption data showed that the Langmuir, pseudo second-order, and intra-particle diffusion models were more suitable for describing the adsorption process. The adsorbent had good adsorption potential for pyrethroids, the adsorption capacity of the two pesticides was 1.05 and 1.79 mg/g, and the removal efficiency was over 40 and 70% at the maximum initial concentration, respectively.

Adsorption of antibiotics on different microplastics (MPs): Behavior and mechanism

MPs can adsorb antibiotics to coexist and accumulate in the aquatic environment in the form of complexes, resulting in unforeseeable adverse consequences. The adsorption behavior and mechanism of three antibiotics amoxicillin (AMX), ciprofloxacin (CIP), and tetracycline (TC) by four MPs Polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), and polyethylene (PE) were studied. Results showed that the adsorption of antibiotics onto MPs follows the pseudo-second-order kinetic and the Freundlich isotherm model, indicating a multilayer chemical adsorption. Combined with FTIR, XRD, and SEM analyses, the adsorption behavior was simultaneously governed by physical processes. Additionally, the equilibrium adsorption capacity was inhibited in the research concentration range of NaCl from 10 mg/L to 10 g/L. The higher the salt concentration, the more pronounced the inhibition phenomenon was. The high (9) and low (3) pH also inhibited the adsorption of antibiotics to MPs. The humic acid (HA) concentration in the range of 0-20 mg/L generally inhibited the MPs-antibiotics adsorption, but the higher HA concentration showed less inhabitation than the lower one. The adsorption inhibition of TC on the four MPs by SA also followed the above rule. However, the adsorption inhibition of sodium alginate (SA) on AMX and CIP on the four MPs was enhanced with its concentration (0-50 mg/L).

An immobilization of aminopropyl trimethoxysilane-phenanthrene carbaldehyde on graphene oxide for toluene extraction and separation in water samples

A new functionalized Nano graphene with aminopropyl trimethoxysilane-phenanthrene-4-carbaldehyde (NGO@APTMS-PNTCA) as a novel adsorbent was used to extract toluene from water samples by the ultrasound-assisted dispersive solid-phase microextraction procedure (USA-D-SPME). So, 50 mg of NGO@APTMS-PNTCA adsorbent was added to water samples and sonicated for 20 min. After toluene extraction, the NGO@APTMS-PNTCA adsorbent separated from the liquid phase with a Whatman membrane filter (200 nm). Then, the toluene was back-extracted from the adsorbent by 2.0 mL of the acetone/ethanol (1:1, eluent) at 25 °C. Due to the physical properties and structure of toluene, fluorobenzene was used as an internal standard. Finally, the toluene values were measured by a gas chromatography-flame ionization detector (GC-FID). In optimized conditions, the limit of detection (LOD), the working range (WR), and the enrichment factor (EF) were obtained at 2.5 μg L^-1, 0.01-1.2 mg L^-1, and 9.63, respectively (MRSD% = 3.38). Also, the limit of quantification (LOQ) 10 μg L^-1 and extraction recovery of more than 95% was efficiently achieved for toluene. Standard additions of toluene to blank solutions had high recoveries between 95.2% and 104.5% with a relative standard deviation (RSD%) of 0.27-5.2. The absorption capacities of NGO and NGO@APTMS-PNTCA adsorbents for toluene extraction were obtained at 32.8 mg g^-1 and 154.9 mg g^-1, respectively. The USA-D-SPME method was validated by spiking the standard concentrations of toluene. The proposed method demonstrated relevant and suitable statistical results with high accuracy and precision for toluene extraction by a novel adsorbent synthesis.

Sulfonated magnetic multi-walled carbon nanotubes with enhanced bonding stability, high adsorption performance, and reusability for water remediation

In view of the simple and rapid conveniency of magnetic separation, magnetic nanocomposites had notably gained attention from researchers for environmental field applications. In this work, carboxylated magnetic multi-walled carbon nanotubes (c-MMWCNTs) and novel sulfonated MMWCNTs (s-MMWCNTs) were synthesized by a facile solvent-free direct doping method. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, energy dispersive X-ray, vibrating sample magnetometer, and point of zero charge analyses confirmed the successful doping of the Fe₃O₄ nanoparticles into the functionalized MWCNTs to form MMWCNTs. Besides, the bonding stabilities of both c-MMWCNTs and s-MMWCNTs were compared, and results showed that s-MMWCNTs possessed more substantial bonding stability than that of c-MMWCNTs with significantly less leaching amount of Fe₃O₄. The adsorption capacity of s-MMWCNTs was higher than that of c-MMWCNTs owing to the stronger electronegativity sulfonic group in s-MMWCNTs. Moreover, the reusability experiments proved that the adsorbent remained consistently excellent MB removal efficiency (R > 94%) even reused for twelve cycles of batch adsorption. The finding of the present work highlights the simple fabrication of novel s-MMWCNTs and its potential to be served as a promising and sustainable adsorbent for water remediation owing to its enhanced bonding stability, high adsorption performance, magnetic separability, and supreme recyclability.

Carbon Nanostructures-Silica Aerogel Composites for Adsorption of Organic Pollutants

Silica aerogels are a class of materials that can be tailored in terms of their final properties and surface chemistry. They can be synthesized with specific features to be used as adsorbents, resulting in improved performance for wastewater pollutants' removal. The purpose of this research was to investigate the effect of amino functionalization and the addition of carbon nanostructures to silica aerogels made from methyltrimethoxysilane (MTMS) on their removal capacities for various contaminants in aqueous solutions. The MTMS-based aerogels successfully removed various organic compounds and drugs, achieving adsorption capacities of 170 mg⋅g^-1 for toluene and 200 mg⋅g^-1 for xylene. For initial concentrations up to 50 mg⋅L^-1, removals greater than 71% were obtained for amoxicillin, and superior to 96% for naproxen. The addition of a co-precursor containing amine groups and/or carbon nanomaterials was proven to be a valuable tool in the development of new adsorbents by altering the aerogels' properties and enhancing their adsorption capacities. Therefore, this work demonstrates the potential of these materials as an alternative to industrial sorbents due to their high and fast removal efficiency, less than 60 min for the organic compounds, towards different types of pollutants.

Turning a Novel Janus Electrospun Mat into an Amphiphilic Membrane with High Aromatic Hydrocarbon Adsorption Capacity

Aromatic hydrocarbons in water is one of the collateral effects of the petrochemical industry and represents a serious problem both for their toxicity and environmental contamination. In this work, an innovative amphiphilic membrane was developed capable of rapidly removing hydrocarbons (such as BTEX) present in water under the solubility limit. Firstly, a Janus nanostructured membrane was developed from the deposition of superhydrophobic carbonaceous nanoparticles (CNPs) synthesized by radiofrequency plasma polymerization on a hydrophilic electrospun poly(vinyl alcohol) mat. Secondly, this membrane was turned amphiphilic by UV exposure, allowing water to pass through. The surface properties of the membranes were studied through SEM, contact angle, and FTIR analysis. Dead-end experiments showed that the toluene and xylene selective sorption capacity reached the outstanding adsorption capacity of 647 mg/g and 666 mg/g, respectively, and that the membrane could be reused three times without efficiency loss. Furthermore, swelling of the PVA fibers prevented the liberation of NPs. The selective sorption capacity of the UV-exposed CNPs was explained by studying the interfacial energy relations between the materials at play. This work provides a simple, low-cost, and scalable technique to develop membranes with great potential for water remediation, including the removal of volatile organic compounds from produced water, as well as separating oil-in-water emulsions.

N-doped and activated porous biochar derived from cocoa shell for removing norfloxacin from aqueous solution: Performance assessment and mechanism insight

Environmental pollution has worsened as a result of antibiotic overuse. Nitrogen doping of biochar increases its ability to adsorb antibiotics and has been widely applied as an adsorbent. In this study, we synthesized nitrogen-doped biochar (N-A) from cocoa shell wastes calcined with urea and sodium bicarbonate (NaHCO₃) as nitrogen sources and green activators, respectively. An analysis of the biochar morphology, structure, specific surface area, and functional groups provided an understanding of its properties. As indicated by increased surface area, micropores, and surface functional groups, biochar was enhanced in its performance for norfloxacin adsorption when activated using NaHCO₃ and nitrogen doped. Adsorption experiments revealed that N-A biochar at 700 and 400 °C had a high adsorption capacity for NOR of 134 mg/g (N-A-CSB700) and 112.31 mg/g (N-A-CSB400) when compared to pristine biochar at 59.27 mg/g (CSB700) and 56.34 mg/g (CSB400), indicating that N-A doped modification on biochar greatly improved adsorption capacity. The Langmuir model demonstrated better NOR adsorption isotherms. The pseudo-second order and Elovich models closely followed the adsorption kinetics. Further investigations were conducted to determine how environmental factors influence biochar interaction with NOR. The results indicated a stable NOR removal efficiency was kept at a wide pH range, whereas the ionic strength inhibited the NOR adsorption process. The investigation into the sorption mechanism revealed that pore filling, H-bonding, π-π EDA interactions, ion exchange, and electrostatic attraction may all be implicated in the NOR adsorption process. Specifically, pore filling played the dominant role for N-A-CSB700, while N-A-CSB400 sorption occurred mainly via H-bonding. Since N-A-CSB700 doped biochar combines high adsorption capacity with a low inhibition effect of environmental factors (Na⁺/Ca²⁺), it has a high potential for future practical applications as an environmentally sustainable alternative. It uses low-cost solid waste to produce an adsorbent to cope with emerging contaminants such as antibiotics.

Adsorption behaviors and mechanisms of antibiotic norfloxacin on degradable and nondegradable microplastics

The misuse of both antibiotics and plastics significantly increases the environmental pollution problems associated with these contaminants. Moreover, microplastics can adsorb other pollutants in the environment. However, the mechanisms of antibiotic adsorption by degradable and nondegradable microplastics are not completely understood. In this study, we investigated the environmental behavior of norfloxacin (NOR) using polybutylene succinate (PBS), which is a degradable microplastic, and compared it with conventional microplastics, polystyrene (PS) and polyethylene (PE). The order of adsorption capacity was PS > PBS ≫ PE. The adsorption behavior fitted well with the pseudo-second-order kinetic and Langmuir isotherm models, indicating monolayer adsorption. The process is thermodynamically endothermic and non-spontaneous and is controlled by chemical and physical mechanisms, including π-π conjugation, hydrogen bonds, ion exchange, and electrostatic interactions. The adsorption capacity of microplastics was higher when the solution pH was around the pKa value of NOR than at other pH values. Ionic strength and dissolved organic matter inhibited the adsorption process. For PS and PBS, the amount of NOR adsorbed onto MPs initially decreased and then increased with the increase of coexisting heavy metal ions. Zn²⁺ and Pb²⁺ could promote the adsorption of NOR by PE. This study reveals the interaction mechanisms between microplastics and antibiotics and provides a more comprehensive theoretical basis for an ecological environmental risk assessment of different microplastics.

Adsorption of benzene and toluene from aqueous solution using a composite hydrogel of alginate-grafted with mesoporous silica

Hydrogels are often claimed as optimal adsorbents for water treatment; however, their efficiency towards the removal of hydrophobic pollutants is still limited. As an alternative, hydrogels prepared from polymers functionalized with siliceous materials can overcome this issue. Here, a composite hydrogel (denoted as GEL-SBA15) was prepared using alginate grafted with mesoporous silica (SBA15) and poly(vinyl alcohol) for benzene and toluene adsorption from aqueous solutions. Adsorption studies demonstrated that a low dosage of GEL-SBA15 (10 mg) has a high adsorption capacity for benzene (1482.8 mg/g) and toluene (596.6 mg/g) under mild experimental conditions (pH 7.0, at 25 °C). Besides, the adsorption capacities of GEL-SBA15 for both pollutants were enhanced compared to the conventional hydrogel. Kinetic analysis showed that the adsorption of benzene and toluene follows a pseudo-second order model, while the experimental adsorption data were well-fitted by the Freundlich isotherm. According to this isotherm, the adsorption occurs via a collaborative process, and weak physical forces (π-π interactions, van der Waals and hydrophobic) are involved. Hence, the post-utilized GEL-SBA15 can be recycled and reused up to 6 times without losing adsorption performance. Although hydrogels are not common adsorbents for aromatic hydrocarbons, the results reported here rank GEL-SBA15 as a promising adsorbent for the removal of these pollutants from water.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Functionalized Carbon Nanotubes (CNTs) for Water and Wastewater Treatment: Preparation to Application

As the world human population and industrialization keep growing, the water availability issue has forced scientists, engineers, and legislators of water supply industries to better manage water resources. Pollutant removals from wastewaters are crucial to ensure qualities of available water resources (including natural water bodies or reclaimed waters). Diverse techniques have been developed to deal with water quality concerns. Carbon based nanomaterials, especially carbon nanotubes (CNTs) with their high specific surface area and associated adsorption sites, have drawn a special focus in environmental applications, especially water and wastewater treatment. This critical review summarizes recent developments and adsorption behaviors of CNTs used to remove organics or heavy metal ions from contaminated waters via adsorption and inactivation of biological species associated with CNTs. Foci include CNTs synthesis, purification, and surface modifications or functionalization, followed by their characterization methods and the effect of water chemistry on adsorption capacities and removal mechanisms. Functionalized CNTs have been proven to be promising nanomaterials for the decontamination of waters due to their high adsorption capacity. However, most of the functional CNT applications are limited to lab-scale experiments only. Feasibility of their large-scale/industrial applications with cost-effective ways of synthesis and assessments of their toxicity with better simulating adsorption mechanisms still need to be studied.

Characterization and efficient dye discoloration of Algerian diatomite from Ouled Djilali-Mostaganem

A series of naturally occurring diatomaceous earth samples from Ouled Djilali, Mostaganem (Lower Chelif basin, Algeria northwestern), were investigated, which are characterized by the expansion and evolution during the Messinian age. Four varieties of diatomite were distinguished, characterized, and successfully used to adsorb methylene blue dye in aqueous medium. Several properties and characteristics of diatomite have been outlined using analytical methods such as X-ray fluorescence spectrometry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption–desorption (BET), and scanning electron microscopy (SEM), as well as other complementary analysis tests. Results showed that silica and calcium carbonates were the main constituents of the diatomite samples (ranging between 32.8 and 61.5% for SiO2; and 13.8–25.9% for CaO), with a slight difference in chemical composition between selected samples. Typical for all diatomite samples, the XRD analysis suggests a high mass quantity of amorphous phase (Opal); high content of crystal phase was also registered. FTIR allowed determining the basic characteristic silica bands regarding diatomite samples. While the BET and SEM investigations revealed that the studied diatomite material has a highly porous structure and was very rich in diatoms. The maximum adsorption capacity of methylene blue that was calculated from the Langmuir isotherm model was 116.59 mg/g (for Ouled Djilali: OD05 sample) at 25 °C and pH 7.0. The diatomite from Mostaganemian (Ouled Djilali) deposit may find promising applications as low-cost adsorbent for dyes removal from water.

Adsorption behavior of the antibiotic levofloxacin on microplastics in the presence of different heavy metals in an aqueous solution

In recent years, the composite pollution of microplastics with organic pollutants and heavy metal ions in the water environment, including their combined toxicity, has received increasing attention. However, the mechanism underlying the joint effect of antibiotics and heavy metals on the surface behavior of microplastics has not been reported. The primary purpose of this article was to analyze the adsorption of levofloxacin (OFL) onto polyvinyl chloride (PVC) in an aqueous solution. The adsorption behavior was studied using kinetics, thermodynamics, and isotherm models, and the effects of several environmental factors, such as ionic strength, fulvic acid, and heavy metals, were determined. The adsorption kinetics and isotherms models indicated that the whole adsorption process was controlled by both intraparticle and outer diffusion, as well as chemical adsorption, which was the dominant mechanism. Based on the results of the thermodynamic experiment, the adsorption process was a nonspontaneous and exothermic reaction process. Furthermore, the presence of Cu²⁺, Zn²⁺, and Cr³⁺ ions significantly promoted the adsorption of OFL, but the presence of Cd²⁺ and Pb²⁺ ions inhibited its adsorption. At the same time, the presence of the ionic strength and fulvic acid remarkably restricted the adsorption process. These findings confirmed that electrostatic interactions, ion exchange, intermolecular hydrogen bonds, and halogen bond cooperation were the main adsorption mechanisms. This paper mainly discusses the interaction between combinations of pollutants with microplastics, which provides theoretical guidance for the interface behavior, migration and transformation of marine microplastics in the actual environment.

Multifunctional Magnetic Oxide Nanoparticle (MNP) Core-Shell: Review of Synthesis, Structural Studies and Application for Wastewater Treatment

The demand for water is predicted to increase significantly over the coming decades; thus, there is a need to develop an inclusive wastewater decontaminator for the effective management and conservation of water. Magnetic oxide nanocomposites have great potentials as global and novel remediators for wastewater treatment, with robust environmental and economic gains. Environment-responsive nanocomposites would offer wide flexibility to harvest and utilize massive untapped natural energy sources to drive a green economy in tandem with the United Nations Sustainable Development Goals. Recent attempts to engineer smart magnetic oxide nanocomposites for wastewater treatment has been reported by several researchers. However, the magnetic properties of superparamagnetic nanocomposite materials and their adsorption properties nexus as fundamental to the design of recyclable nanomaterials are desirable for industrial application. The potentials of facile magnetic recovery, ease of functionalization, reusability, solar responsiveness, biocompatibility and ergonomic design promote the application of magnetic oxide nanocomposites in wastewater treatment. The review makes a holistic attempt to explore magnetic oxide nanocomposites for wastewater treatment; futuristic smart magnetic oxides as an elixir to global water scarcity is expounded. Desirable adsorption parameters and properties of magnetic oxides nanocomposites are explored while considering their fate in biological and environmental media.

Nanoconfinement-Mediated Water Treatment: From Fundamental to Application

Safe and clean water is of pivotal importance to all living species and the ecosystem on earth. However, the accelerating economy and industrialization of mankind generate water pollutants with much larger quantity and higher complexity than ever before, challenging the efficacy of traditional water treatment technologies. The flourishing researches on nanomaterials and nanotechnologies in the past decade have generated new understandings on many fundamental processes and brought revolutionary upgrades to various traditional technologies in almost all areas, including water treatment. An indispensable step toward the real application of nanomaterials in water treatment is to confine them in large processable substrate to address various inherent issues, such as spontaneous aggregation, difficult operation and potential environmental risks. Strikingly, when the size of the spatial restriction provided by the substrate is on the order of only one or several nanometers, referred to as nanoconfinement, the phase behavior of matter and the energy diagram of a chemical reaction could be utterly changed. Nevertheless, the relationship between such changes under nanoconfinement and their implications for water treatment is rarely elucidated systematically. In this Critical Review, we will briefly summarize the current state-of-the-art of the nanomaterials, as well as the nanoconfined analogues (i.e., nanocomposites) developed for water treatment. Afterward, we will put emphasis on the effects of nanoconfinement from three aspects, that is, on the structure and behavior of water molecules, on the formation (e.g., crystallization) of confined nanomaterials, and on the nanoenabled chemical reactions. For each aspect, we will build the correlation between the nanoconfinement effects and the current studies for water treatment. More importantly, we will make proposals for future studies based on the missing links between some of the nanoconfinement effects and the water treatment technologies. Through this Critical Review, we aim to raise the research attention on using nanoconfinement as a fundamental guide or even tool to advance water treatment technologies.

Magnetic nanoadsorbents' potential route for heavy metals removal-a review

Due to the rapid growth in the heavy metal-based industries, their effluent and local dumping have created significant environmental issues. In the past, typically, removal of heavy metals was handled by reverse osmosis and ion exchange techniques, but these methods have many disadvantages. Therefore, extensive work into the development of improved techniques has increased, especially for heavy metal removal. Many countries are currently researching new materials and techniques based on nanotechnology for various applications that involve extracting heavy metals from different water sources such as wastewater, groundwater, drinking water and surface water. Nanotechnology provides the possibility of enhancing existing techniques to tackle problems more efficiently. The development in nanotechnology has led to the discovery of many new materials such as magnetic nanoparticles. These nanoparticles demonstrate excellent properties such as surface-volume ratio, higher surface area, low toxicity and easy separation. Besides, magnetic nanoparticles can be easily and efficiently recovered after adsorption compared with other typical adsorbents. This review mainly emphasises on the efficiency of heavy metal removal using magnetic nanoadsorbent from aqueous solution. In addition, an in-depth analysis of the synthesis, characterisation and modification approaches of magnetic nanoparticles is systematically presented. Furthermore, future opportunities and challenges of using magnetic particles as an adsorbent for the removal of heavy metals are also discussed.

Preparation and characterization of a new waste-derived mesoporous carbon structure for ultrahigh adsorption of benzene and toluene at ambient conditions

In this work, a series of nanoporous carbon materials were synthesized using Iranian asphaltene as a low-cost carbon source and modified by melamine as a new nitrogen-rich promoter (M-IANC). The adsorption capacity of benzene and toluene on the synthesized M-IANCs was measured at low and high concentrations by an in-house built apparatus. The results demonstrated that the addition of melamine remarkably increased the mesoporous volume (up to 1.61 cm³/g) in the nanoporous carbon structure and, subsequently, created a large surface area (2692 m²/g) and pore volume (1.71 cm³/g). The resulting M-IANC-C nanostructure (melamine:PIA mass ratio of 1:2) depicted 228.18 wt.% and 82.08 wt.% adsorption capacity for benzene and toluene, respectively, which were 19.4 and 2.8 times higher than commercial activated carbon. In addition to the distinguished adsorptive behavior for benzene and toluene removal, M-IANC-C exhibited higher cyclic adsorption capacity than those of unmodified IANC sample after four consecutive cycles. The adsorption mechanism and the role of melamine groups in the adsorption of benzene and toluene were also studied by the density functional theory (DFT) calculations. Besides the inexpensive cost of the carbon source (asphaltene), results also indicate that the M-IANC can be a suitable candidate for VOC adsorption.

Magnetic Multi-walled Carbon Nanotube as Effective Adsorbent for Ciprofloxacin (CIP) Removal from Aqueous Solutions: Isotherm and Kinetics Studies

Nowadays, the presence of antibiotics in the environment has been identified as an important concern for the various life cycle. Thus, this study was conducted to evaluate ciprofloxacin (CIP) adsorption efficiency onto the multi-walled carbon nanotube (MWCNTs) and magnetic multi-walled carbon nanotube (MMWCNTs). In this experimental study, the characteristics of the studied adsorbents were determined using SEM, FTIR and XRD methods. The effects of operational parameters including contact time (10–120 min), initial concentration of CIP (10–100 mg/L), adsorbent dosage (0.1–1 g/L) and pH (3–9) were evaluated. The isotherm and kinetics studies of the CIP adsorption onto the studied adsorbents were also carried out. The adsorption efficiency increases by increasing the contact time and adsorbent dosage, while it increased by increasing the CIP initial concentration. The results showed that higher CIP adsorption efficiency was observed at pH = 7, adsorbent dosage of 0.5 g/L, CIP concentration of 30 mg/L and contact time of 120 min. The isotherm and kinetics studies revealed that the CIP adsorption data were better described by the Langmuir isotherm model and pseudo-second-order kinetics equation model. It can be concluded that both of these adsorbents have suitable potential to remove the CIP from aqueous solution but this ability is greater in MMWCNTs.

Nanotechnology-based sorption and membrane technologies for the treatment of petroleum-based pollutants in natural ecosystems and wastewater streams

Petroleum processing wastewater (PPW) is a complex mixture of free, soluble, and emulsive hydrocarbons that often contain heavy metals and/or solid particles. As these hazardous constituents can accumulate in human beings and the environment, exposure to the PPW can have harmful effects in various respects. The use of environmental nanotechnologies (E-Nano) is considered an attractive option to resolve the problems associated with PPW. Among different treatment technologies, E-Nano-based sorption (adsorption/absorption) and membrane filtration approaches have been proven to have outstanding efficacy in remediation of PPW pollutants. It is, however, crucial to determine the appropriate technological option (e.g., low-cost operational conditions) for the practical application of such technologies. In this review, the potential of E-Nano-based sorption and membrane technologies in the treatment of various PPW pollutants is discussed based on their performances in comparison to traditional technologies. Their suitability is evaluated further in relation to their merits/disadvantages and economic feasibility with the goal of constructing a perspective map to efficiently implement the E-Nano technologies.

Surface modification and characterization of carbonaceous adsorbents for the efficient removal of oil pollutants

In this study, the impact of different oxidizing agents on the structural integrity of activated carbon (AC) and multiwalled carbon nanotubes (MWCNTs) was studied for the removal of BTX from aqueous solution. Seven different combinations of green oxidizing agents (mild organic acids) in conjugation with NaOCl (basic oxidizing agent) were used. The modified adsorbents were analyzed by Brunauer, Emmett, and Teller (BET) surface area analyzer, Fourier transform infrared spectroscopy (FTIR), Boehm titration, Raman spectroscopy, thermal gravimetric analysis (TGA), x-ray diffraction (XRD), zeta potential, and variable pressure field emission scanning electron microscope (VPFESEM). The results suggested that the carbonaceous sorbents modified with combination of citric acid tartaric acid, malic acid and salicylic acid (CTMS-I) showed increased surface area (O-AC: 871.67 m²/g, O-MWCNTs: 336.37 m²/g) and total pore volume (O-AC: 0.59 cm³/g, O-MWCNTs: 0.04 cm³/g), with the significantly improved thermal stability. Preliminary batch adsorption experiments conducted using the present prepared O-AC and O-MWCNTs, showed an improved performance towards the adsorption of BTX, compared with other available reported adsorbents in the literature.

A critical review on organic micropollutants contamination in wastewater and removal through carbon nanotubes

The prevalence of organic micropollutants (OMPs) in various environmental compartments is posing a serious health risks to all kinds of lives on the planet. The levels of OMPs such as polyaromatic hydrocarbons, antibiotics, pesticides, contraceptive medicines, and personal care products in water bodies are increasing with each passing day. It is an urgent need of time to limit the release of OMPs into the environment, and to remove the prevailing OMPs for sustainable environmental management. The majority of the conventional means of water decontamination are either inefficient or expensive. However, due to nanosize, high surface area, and hollow and layered structure, carbon nanotubes (CNTs) serve as excellent sorbents for the removal of a diverse range of OMPs. The occurrence of emerging OMPs and their detrimental effects on human and animal health are collected and discussed in this review. The characteristics and efficacy of various CNTs (pristine and modified) for the efficient removal of different OMPs, and the removal mechanisms have been reviewed and discussed. The literature demonstrated that adsorption of OMPs onto CNTs is very complicated and rely on multiple factors including the properties of adsorbent and the adsorbate as well as solution chemistry. It was found that H-bonding, electrostatic interactions, van der Waals forces, hydrophobic interactions, H-π bongs, and π-π interactions were the major mechanisms responsible for the adsorption of OMPs onto various kinds of CNTs. Despite of higher affinities for OMPs, hydrophobicity and higher costs restrain the practical application of CNTs for wastewater treatment on large scale. However, continuous production may lead to the development of cost-effective, efficient and eco-friendly CTNs technology for wastewater treatments in future.

Carbon-based materials as adsorbent for antibiotics removal: Mechanisms and influencing factors

With the development of the removal of organic pollutants in the soil and water environment, antibiotics have been considered as emerging pollutants and received considerable attention among the scientific community. Thus, there is a need for an effective, economical, fast, operational feasible and environmental-friendly technology to remove antibiotics. Adsorption technology would be one of the most promising option on the basis that it best meets the criteria we set out above. From the most primitive activated carbon to the most innovative modified biochar, carbon-based materials have played a significant role in the adsorption process of antibiotics all the time. This paper reviews the adsorption behavior of some representative antibiotics (e.g., chloramphenicols, sulfonamides, tetracyclines, flouroquinolones) over various carbonaceous materials (i.e., activated carbon, carbon nanotubes, graphene, and biochar). Nevertheless, in addition to the structural characteristics and adsorption capacities of carbon-based materials, a special emphasis was placed on the underlying adsorption mechanisms and roles of different influencing factors in the adsorption process. Moreover, the knowledge gaps and research challenges have been highlighted, including design and optimization of the carbonaceous materials for antibiotics adsorption.

Challenges and opportunities in functional carbon nanotubes for membrane-based water treatment and desalination

Environmental applications of carbon nanotubes (CNTs) have grabbed worldwide attentions due to their excellent adsorption capacities and promising physical, chemical and mechanical properties. The functionalization of CNTs, which involves chemical/physical modification of pristine CNTs with different types of functional groups, improves the capabilities of CNT for desalination and/or removals of waterborne contaminants. This paper intends to provide a comprehensive review of functional CNT materials (f-CNT) and their existing and potential applications in membrane-based water treatment and desalination processes, with focuses on critical evaluation of advances, knowledge gaps and future research directions. CNT nanocomposite membranes have been studied at bench scale to efficiently remove a variety of waterborne contaminants and salts, while future improvement is under way with development in CNT functionalization techniques. The CNT-based membrane applications are found to possess a variety of advantages, including improve water permeability, high selectivity and antifouling capability. However, their applications at full scale are still limited by their high cost. Finally, we highlight that f-CNT membranes with promising removal efficiencies for respective contaminants be considered for commercialization and to achieve holistic performance for the purpose of water treatment and desalination.

Rotating Magnetic Field-Assisted Adsorption Mechanism of Pollutants on Mechanically Strong Sodium Alginate/Graphene/l-Cysteine Beads in Batch and Fixed-Bed Column Systems

Novel, efficient bioadsorbent sodium alginate/graphene/l-cysteine (SA/GR/l-Cys) beads were prepared and used for magnetic field (MF)-assisted adsorption of pollutants. SA/GR/l-Cys has excellent mechanical properties, with a breaking stress of 3.5 MPa at 79.8%, an elastic modulus of 5.0 MPa, low swelling properties (average swelling ratio <300%), and good adsorption properties toward organic pollutants and heavy metal ions. A rotating magnetic field (RMF) was shown to have a better influence than a static magnetic field (SMF) on adsorption, with enhanced adsorption capacities 5-fold greater than those of the SMF. We investigated the different adsorption mechanisms of model contaminants through Fourier transform infrared spectroscopy, ζ potential, and X-ray photoelectrons spectroscopy. Formation of new hydrogen bonds, change in ζ potential, and acceleration in chemical reactions strongly influenced the adsorption process under the RMF. In fixed-bed column adsorption, the breakthrough time for column adsorption increased, and the adsorption capacity improved by 30.66%. The costs and practical applications of SA/GR/l-Cys under RMF were also analyzed. This work demonstrated that SA/GR/l-Cys could serve as a promising adsorbent for water pollutants under RMF exposure and could be used in practical applications.

Efficient removal of tetracycline with KOH-activated graphene from aqueous solution

Activated graphene absorbents with high specific surface area (SSA) were prepared by an easy KOH-activated method, and were applied in absorbing antibiotics, such as tetracycline (TC). After activation, many micropores were introduced to graphene oxide sheets, leading to higher SSA and many new oxygen-containing functional groups, which gave KOH-activated graphene excellent adsorption capacity (approx. 532.59 mg g^-1) of TC. Further study on the adsorption mechanism showed that the Langmuir isotherm model and the pseudo-second-order kinetic model fitted with experiment data. To further understand the adsorption process, the effects of solid-liquid ratio, pH, ionic strength and coexisting ions were also investigated. The results revealed that, compared with pH and ionic strength, solid-liquid ratio and coexisting ions (Cu²⁺, CrO₄^2-) had more significant influence over the adsorption performance. The findings provide guidance for application of KOH-activated graphene as a promising alternative adsorbent for antibiotics removal from aqueous solutions.

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

This review focuses on environmental implications and applications of engineered magnetite (Fe3O4) nanoparticles (MNPs) as a single phase or a component of a hybrid nanocomposite that exhibits superparamagnetism and high surface area. MNPs are synthesized via co-precipitation, thermal decomposition and combustion, hydrothermal process, emulsion, microbial process, and green approaches. Aggregation/sedimentation and transport of MNPs depend on surface charge of MNPs and geochemical parameters such as pH, ionic strength, and organic matter. MNPs generally have low toxicity to humans and ecosystem. MNPs are used for constructing chemical/biosensors and for catalyzing a variety of chemical reactions. MNPs are used for air cleanup and carbon sequestration. MNP nanocomposites are designed as antimicrobial agents for water disinfection and flocculants for water treatment. Conjugated MNPs are widely used for adsorptive/separative removal of organics, dyes, oil, arsenic, phosphate, molybdate, fluoride, selenium, Cr(VI), heavy metal cations, radionuclides, and rare earth elements. MNPs can degrade organic/inorganic contaminants via chemical reduction or catalyze chemical oxidation in water, sediment, and soil. Future studies should further explore mechanisms of MNP interactions with other nanomaterials and contaminants, economic and green approaches of MNP synthesis, and field scale demonstration of MNP utilization.

New magnetic graphene-based inorganic-organic sol-gel hybrid nanocomposite for simultaneous analysis of polar and non-polar organophosphorus pesticides from water samples using solid-phase extraction

A new graphene-based tetraethoxysilane-methyltrimethoxysilane sol-gel hybrid magnetic nanocomposite (Fe₃O₄@G-TEOS-MTMOS) was synthesised, characterized and successfully applied in magnetic solid-phase extraction (MSPE) for simultaneous analysis of polar and non-polar organophosphorus pesticides from several water samples. The Fe₃O₄@G-TEOS-MTMOS nanocomposite was characterized using Fourier transform-infrared spectroscopy, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy and X-ray diffraction. Separation, determination and quantification were achieved using gas chromatography coupled with micro electron capture detector. Adsorption capacity of the sorbent was calculated using Langmuir equation. MSPE was linear in the range 100-1000 pg mL^-1 for phosphamidon and dimethoate, and 10-100 pg mL^-1 for chlorpyrifos and diazinon, with limit of detection (S/N = 3) of 19.8, 23.7, 1.4 and 2.9 pg mL^-1 for phosphamidon, dimethoate, diazinon and chlorpyrifos, respectively. The LODs obtained is well below the maximum residual level (100 pg mL^-1) as set by European Union for pesticides in drinking water. Acceptable precision (%RSD) was achieved for intra-day (1.3-8.7%, n = 3) and inter-day (7.6-17.8%, n = 15) analyses. Fe₃O₄@G-TEOS-MTMOS showed high adsorption capacity (54.4-76.3 mg g^-1) for the selected OPPs. No pesticide residues were detected in the water samples analysed. Excellent extraction recoveries (83-105%) were obtained for the spiked OPPs from tap, river, lake and sea water samples. The newly synthesised Fe₃O₄@G-TEOS-MTMOS showed high potential as adsorbent for OPPs analysis.

Recent advances in nanomaterials for water protection and monitoring

Nanomaterials (NMs) for adsorption, catalysis, separation, and disinfection are scrutinized. NMs-based sensor technologies and environmental transformations of NMs are highlighted.

Adsorptive removal of aqueous bezafibrate by magnetic ferrite modified carbon nanotubes

MFe₂O₄/CNTs were synthesized and successfully applied for the removal of aqueous bezafibrate. The adsorption behavior and mechanism were elucidated in detail.

Efficient boron abstraction using honeycomb-like porous magnetic hybrids: Assessment of techno-economic recovery of boric acid

Porous magnetic hybrids were synthesized and functionalized with glycidol to produce boron-selective adsorbent. The magnetic hybrid (MH) comparatively out-performed the existing expensive adsorbents. MH had a saturation magnetisation of 63.48 emu/g and average pore diameter ranging from meso to macropores. The magnetic hybrids showed excellent selectivity towards boron and resulted in 79-93% boron removal even in the presence of competing metal ions (Na⁺ and Cr²⁺). Experiments were performed in a column system, and breakthrough time was observed to increase with bed depths and decreased with flow rates. The batch experiments revealed that 60 min was enough to achieve equilibrium, and the level of boron sorption was 108.5 mg/g from a synthetic solution. Several adsorption-desorption cycles were performed using a simple acid-water treatment and evaluated using various kinetic models. The spent adsorbents could be separated easily from the mixture by an external magnetic field. The cost-benefit analysis was performed for the treatment of 72 m³/year boron effluent, including five years straight line depreciation charges of equipment. The net profit and standard percentage confirmed that the recovery process is economically feasible.

Photocatalytic discoloration of Acid Red 14 aqueous solution using titania nanoparticles immobilized on graphene oxide fabricated plate

Textile industry consumes remarkable amounts of water during various operations. A significant portion of the water discharge to environment is in the form of colored contaminant. The present research reports the photocatalytic degradation of anionic dye effluent using immobilized TiO2 nanoparticle on graphene oxide (GO) fabricated carbon electrodes. Acid Red 14 (AR 14) was used as model compound. Graphene oxide nanosheets were synthesized from graphite powder using modified Hummer's method. The nanosheets were characterized with field emission scanning electron microscope (FESEM) images, X-ray diffraction (XRD) and FTIR spectrum. The GO nanoparticles were deposited on carbon electrode (GO-CE) by electrochemical deposition (ECD) method and used as catalyst bed. TiO2 nanoparticles were fixed on the bed (GO-CE- TiO2) with thermal process. Photocatalytic processes were carried out using a 500 ml solution containing dye in batch mode. Each photocatalytic treatment were carried out for 120 min. Effect of dye concentration (mg/L), pH of solution, time (min) and TiO2 content (g/L) on the photocatalytic decolorization was investigated.

Adsorptive removal of ciprofloxacin by sodium alginate/graphene oxide composite beads from aqueous solution

Graphene oxide (GO) was encapsulated into environmentally benign sodium alginate (SA) to prepare a GO-SA composite hydrogel and an aerogel, which were then used as adsorbents to remove ciprofloxacin from aqueous solutions. The characteristics of these materials were investigated using scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The characterizations demonstrated that the incorporation of GO improved the pore uniformity of the gels and decreased the pore sizes. Kinetic studies showed that the adsorption capacity of SA composite gels increased approximately seven to nine times after the incorporation of GO, matching with pseudo-second-order models. Non-linear fitting parameters of adsorption isotherm studies indicated that a Langmuir model could precisely represent the adsorption behavior. GO-SA aerogels exhibited high tolerance to changes in pH and ionic strength; changes in these parameters minimally influenced the adsorption capacity of the GO-SA aerogels for ciprofloxacin. This work is especially relevant for environmental applications. These graphene-based composites are environmentally benign adsorbents and can remove organic contaminants from aqueous solutions.

Adsorptive removal of antibiotics from aqueous solution using carbon materials

Antibiotics, an important type of environmental contamination, have attracted many researchers to the study of their removal from aqueous solutions. Adsorption technology is a fast, efficient, and economical physicochemical method that is extensively used in wastewater treatment. From original activated carbon and carbon nanotubes to the latest graphene-based materials, carbon-based materials have been widely used as highly effective adsorbents for contaminant removal from aqueous solution because of their large specific surface area, high porosity, and high reaction activity. In this article, adsorption removal methods for four major types of antibiotic (tetracyclines, sulfonamides, macrolides, and quinolones) are reviewed. We also provide an overview of the application development of carbon materials as adsorbents for antibiotic removal from aqueous solution. The most promising works are discussed, and the main challenges in preparing high-performance adsorbents and the development tendency of adsorbents are also analyzed. This work provides theoretical guidance for subsequent research in the design and modification of carbon materials for applications in the adsorption removal of antibiotics from aqueous solution.