Development of adsorption and electrosorption techniques for removal of organic and inorganic pollutants from wastewater using novel magnetite/porous graphene-based nanocomposites

Tetraethylenepentamine-Grafted Amino Terephthalic Acid-Modified Activated Carbon as a Novel Adsorbent for Efficient Removal of Toxic Pb(II) from Water

In this study, a new composite, tetraethylenepentamine (TEPA), was incorporated into amino terephthalic acid-modified activated carbon (ATA@AC) through a one-pot integration of TEPA with the COOH moiety of ATA@AC. This process resulted in the creation of a TEPA@ATA@AC composite for Pb(II) removal from an aquatic environment. Several techniques, including SEM, EDX, FT-IR, TGA, XRD, and Zeta potential, were employed to emphasize the chemical composition, morphology, and thermal durability of the as-synthesized TEPA@ATA@AC composite. The impact of experimental variables on the adsorption of Pb(II) ions was studied using batch adsorption. The uptake assessment suggested that the TEPA@ATA@AC composite exhibited superior Pb(II) removal performance with high removal efficiency (97.65%) at pH = 6.5, dosage = 0.02 g, equilibrium time = 300 min, and temperature = 298 K. The isotherm data exhibited good conformity with the Langmuir isotherm model, whereas the kinetics data displayed strong agreement with both pseudo-first-order and pseudo-second-order kinetics models. This reflected that the Pb((II) uptake by the TEPA@ATA@AC composite was caused by physisorption coupled with limited chemisorption. The greatest monolayer uptake capacity of the TEPA@ATA@AC composite was 432.8 mg/g. The thermodynamic findings indicated that the Pb(II) uptake on the TEPA@ATA@AC composite was an exothermic and feasible process. After five adsorption-desorption runs, the TEPA@ATA@AC composite maintained a superior uptake capacity (83.80%). In summary, the TEPA@ATA@AC composite shows promise as a potent adsorbent for effectively removing Cr(VI) from contaminated water, with impressive removal efficiency.

Persulfate enhanced removal of bisphenol A by copper oxide/reduced graphene oxide foam: Influencing factors, mechanism and degradation pathway

The CuO/reduced graphene oxide foam (CuO/RGF) with excellent recyclability was prepared via hydrothermal method followed by freeze drying treatment for bisphenol A (BPA) removal via activating peroxydisulfate (PDS). SEM, XRD, XPS, FT-IR, BET, and TG techniques were used to investigate the structure and property of CuO/RGF. The effect of degradation conditions (pH, PDS amount, Cl-, HCO3-, HA and FA) on BPA removal by CuO/RGF were investigated. The result presented that CuO nanosheet was inserted into the RGF carrier with three-dimensional structure. The degradation rate constant of BPA over CuO/RGF (0.00917 min-1) was 1.24 and 6.46 times higher than those of BPA over CuO (0.00714 min-1) and RGF (0.00142 min-1). More importantly, the pore structure of RGF can successfully limit the release of Cu (II) compared to pure CuO. According to quenching test as well as electron spin resonance (EPR) spectra, BPA degradation was triggered by 1O2, •OH and SO4•-, which was the combination of nonradical (1O2) and radical activation of PDS (•OH and SO4•-). The possible degradation route of BPA was proposed based on intermediates obtained by combining solid phase extraction pretreatment technique with high performance liquid-mass spectrometry. After assessing the viability of MCF-7 cells, we can see that the estrogenic activities of treated solution reduced without producing stronger endocrine disruptors.

Environmental Application of Graphene and Its Forms for Wastewater Treatment: a Sustainable Solution Toward Improved Public Health

Public health is seriously jeopardized in developing countries due to poor sanitation and the presence of persistent pollutants in natural water bodies. Open dumping, wastewater discharge without proper treatment and atmospheric fallout of the organic and inorganic pollutants are the main causes behind the poor condition. Some of the pollutants pose a greater risk due to their toxicity and persistence. Such a class of pollutants are known as chemical contaminants of emerging concern (CECC), including antibiotics and drug residues, endocrine disruptors, pesticides and micro- and nano-plastics. Conventional treatment methods cannot treat them properly and are often associated with several disadvantages. However, the chronological development of techniques and materials for their treatment has exhibited graphene as an efficient candidate for environmental remediation. This current review considers the various graphene-based materials, their properties, advancement in synthesis methods with time and their detailed application in removing dyes, antibiotics and heavy metals. It has been discussed how graphene and its derivatives exhibit unique electronic, mechanical, structural and thermal properties. In this paper, the mechanism of adsorption and degradation using these graphene-based materials has also been discussed vividly. In addition to this, a bibliographic analysis was performed to identify the trend of research related to graphene and its derivatives in the adsorption and degradation of pollutants round the globe reflected by the publications. Therefore, this review can be instrumental in understanding the fact that further development of graphene-based materials and their mass production can provide a very effective and economical wastewater treatment method.

Designing novel perlite-Fe3O4@SiO2@8-HQ-5-SA as a promising magnetic nanoadsorbent for competitive adsorption of multicomponent VOCs

Volatile organic compounds (VOCs), which emerge as multicomponent pollutants through many industrial processes, pose a serious threat to human health and the eco-environment due to their volatility, toxicity and dispersion. Hence, the study of competitive adsorption of multicomponent VOCs is of practical and scientific importance. Herein, the perlite-supported Fe3O4@SiO2@8-hydroxyquinoline-5-sulfonic acid (perlite-Fe3O4@SiO2@8-HQ-5-SA) was designed as a novel magnetic nanoadsorbent by a simple strategy and employed for the competitive adsorption of multicomponent toluene, ethylbenzene and xylene in the vapor-phase targeted as VOCs. The successfully prepared perlite-Fe3O4@SiO2@8-HQ-5-SA was characterized by means of SEM, EDX, FT-IR, VSM and BET analyses. Adsorption capacities of 558 mg/g, 680 mg/g and 716 mg/g were achieved for single component toluene, ethylbenzene and xylene, respectively. It was concluded that the adsorption capacities for both binary and ternary components were significantly decreased compared to single component adsorption. The competitive adsorption capacity order of the binary and ternary component VOCs was xylene > ethylbenzene > toluene due to their competitive dominance. The rate-limiting kinetic analysis indicated that the adsorption rates were determined by both the film diffusion and intraparticle diffusion. The analysis of the error metrics demonstrated that the three-parameter isotherm models better described the adsorption data compared to the two-parameter models. In particular, the Toth model provided the closest fit to the experimental equilibrium data. The thermodynamic analysis indicated the spontaneous nature and probability (ΔG° <0), exothermic (ΔH° <0), physical (ΔH° <20 kJ/mol) and a declination in the degree of randomness (ΔS° <0) of the adsorption processes. The reuse efficiency of perlite-Fe3O4@SiO2@8-HQ-5-SA for toluene, ethylbenzene and xylene decreased to only by 88.91%, 88.07% and 87.16% after five recycles. The perlite-Fe3O4@SiO2@8-HQ-5-SA has a significant adsorptive potential compared to other adsorbents reported in the literature, thus it could be recommended as a promising nanoadsorbent for VOCs in industrial processes.

Near Green Synthesis of Porous Graphene from Graphite Using an Encapsulated Ferrate(VI) Oxidant

Graphene oxide (GO) is a conventional yet vital precursor for the synthesis of porous graphene (PG). Several strong oxidizing agents such as potassium permanganate and perchlorates are typically used for oxidization of graphite. However, they expose toxic reactants/products that harm the environment. Therefore, a greener approach is desperately needed to oxidize and exfoliate graphite. This study reports for the first time on successful oxidation of graphite by ferrate(VI) compounds via an encapsulation approach. By further reducing GO prepared from this near green route with vitamin C, PG anticipated by many highly important and expanding areas such as water treatment could be readily achieved. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and UV-vis spectroscopy, and scanning electronic microscopy (SEM) along with energy-dispersive spectroscopy confirmed the high yield of GO from the oxidation of graphite. Raman spectroscopy, XRD, and TEM confirmed the formation of high-quality few-layered PG from the reduction of as-prepared GO. The above results demonstrated the practicality of using encapsulated ferrate(VI) compounds to realize green oxidation of graphite and resolve the paradox about the oxidation capability of ferrate(VI). To further illustrate its potential for the removal of emerging and crucial contaminants from water, as-prepared PG was further examined against the contaminants of methyl orange (MeO) dye and ibuprofen (IBU). Taken together, the results revealed that more than 90% removal efficiency could be achieved at a high PG dosage against MeO and IBU. This ground-breaking greener approach opens the door to risk-free, extensive graphene environmental applications.

Geopolymer composite spheres derived from graphene-modified fly ash/slag: Facile synthesis and removal of lead ions in wastewater

Geopolymer composite spheres derived from potassium-activated graphene-modified slag/fly ash powder were produced in a polyethylene glycol (PEG 400) solvent. The effect of graphene type (graphene oxide (GO) and few-layered graphene (GNP)) on the pore structure and lead ions (Pb²⁺) removal performance of the spheres were evaluated. The results showed that the composite spheres modified with GOs (0.1-0.4 wt%) and GNPs (1-4 wt%) could be spheroidized with an improved performance to adsorb Pb²⁺ in solution. The graphene-containing spheres reached a maximum BET surface area of 68.85 m²/g. Pseudo-second-order and Langmuir isotherm models could express the adsorption process, which was controlled by both monolayer adsorption and chemisorption. The obtained spheres also showed high adsorption capacities for Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ ions. Chemical, physical, electrostatic, ion exchange and cation-π interaction were attributed to the adsorption mechanism of the spheres. The spheres showed good cycling ability compared to those without graphene, which had potential application in heavy metal wastewater treatment.

Electrosorption performance on graphene-based materials: a review

Due to its unique advantages such as flexible planar structure, ultrahigh specific surface area, superior electrical conductivity and electrical double-layer capacitance in theory, graphene has unparalleled virtues compared with other carbon materials. This review summarizes the recent research progress of various graphene-based electrodes on ion electrosorption fields, especially for water desalination utilizing capacitive deionization (CDI) technology. We present the latest advances of graphene-based electrodes, such as 3D graphene, graphene/metal oxide (MO) composites, graphene/carbon composites, heteroatom-doped graphene and graphene/polymer composites. Furthermore, a brief outlook on the challenges and future possible developments in the electrosorption area are also addressed for researchers to design graphene-based electrodes towards practical application.

The translational paradigm of nanobiomaterials: Biological chemistry to modern applications

Recently nanotechnology has evolved as one of the most revolutionary technologies in the world. It has now become a multi-trillion-dollar business that covers the production of physical, chemical, and biological systems at scales ranging from atomic and molecular levels to a wide range of industrial applications, such as electronics, medicine, and cosmetics. Nanobiomaterials synthesis are promising approaches produced from various biological elements be it plants, bacteria, peptides, nucleic acids, etc. Owing to the better biocompatibility and biological approach of synthesis, they have gained immense attention in the biomedical field. Moreover, due to their scaled-down sized property, nanobiomaterials exhibit remarkable features which make them the potential candidate for different domains of tissue engineering, materials science, pharmacology, biosensors, etc. Miscellaneous characterization techniques have been utilized for the characterization of nanobiomaterials. Currently, the commercial transition of nanotechnology from the research level to the industrial level in the form of nano-scaffolds, implants, and biosensors is stimulating the whole biomedical field starting from bio-mimetic nacres to 3D printing, multiple nanofibers like silk fibers functionalizing as drug delivery systems and in cancer therapy. The contribution of single quantum dot nanoparticles in biological tagging typically in the discipline of genomics and proteomics is noteworthy. This review focuses on the diverse emerging applications of Nanobiomaterials and their mechanistic advancements owing to their physiochemical properties leading to the growth of industries on different biomedical measures. Alongside the implementation of such nanobiomaterials in several drug and gene delivery approaches, optical coding, photodynamic cancer therapy, and vapor sensing have been elaborately discussed in this review. Different parameters based on current challenges and future perspectives are also discussed here.

Recent Advances in the Synthesis, Characterization, and Application of Carbon Nanomaterials for the Removal of Endocrine-Disrupting Chemicals: A Review

The large-scale production and frequent use of endocrine-disrupting chemicals (EDCs) have led to the continuous release and wide distribution of these pollutions in the natural environment. At low levels, EDC exposure may cause metabolic disorders, sexual development, and reproductive disorders in aquatic animals and humans. Adsorption treatment, particularly using nanocomposites, may represent a promising and sustainable method for EDC removal from wastewater. EDCs could be effectively removed from wastewater using various carbon-based nanomaterials, such as carbon nanofiber, carbon nanotubes, graphene, magnetic carbon nanomaterials, carbon membranes, carbon dots, carbon sponges, etc. Important applications of carbon nanocomposites for the removal of different kinds of EDCs and the theory of adsorption are discussed, as well as recent advances in carbon nanocomposite synthesis technology and characterization technology. Furthermore, the factors affecting the use of carbon nanocomposites and comparisons with other adsorbents for EDC removal are reviewed. This review is significant because it helps to promote the development of nanocomposites for the decontamination of wastewater.

Removal of organic micropollutans by adsorptive membrane

Various emerging organic micropollutants, such as pharmaceuticals, have attracted the interest of the water industry during the last two decades due to their insufficient removal during conventional water and wastewater treatment methods and increasing demand for pharmaceuticals projected to climate change-related impacts and COVID-19, nanosorbents such as carbon nanotubes (CNTs), graphene oxides (GOs), and metallic organic frameworks (MOFs) have recently been extensively explored regarding their potential environmental applications. Due to their unique physicochemical features, the use of these nanoadsorbents for organic micropollutans in water and wastewater treatment processes has been a rapidly growing topic of research in recent literature. Adsorptive membranes, which include these nanosorbents, combine the benefits of adsorption with membrane separation, allowing for high flow rates and faster adsorption/desorption rates, and have received a lot of publicity in recent years. The most recent advances in the fabrication of adsorptive membranes (including homogeneous membranes, mixed matrix membranes, and composite membranes), as well as their basic principles and applications in water and wastewater treatment, are discussed in this review. This paper covers ten years, from 2011 to 2021, and examines over 100 published studies, highlighting that micropollutans can pose a serious threat to surface water environments and that adsorptive membranes are promising, particularly in the adsorption of trace substances with fast kinetics. Membrane fouling, on the other hand, should be given more attention in future studies due to the high costs and restricted reusability.

Insights into graphene oxide/ferrihydrite adsorption as pretreatment during ultrafiltration: Membrane fouling mitigation and disinfection by-product control

In this study, a novel adsorbent of graphene oxide (GO) incorporated ferrihydrite (FH) was fabricated and integrated with ultrafiltration (UF) to remove natural organic matter (NOM), the crucial cause of membrane fouling and major precursor of disinfection by-products (DBPs). Compared with FH and powdered activated carbon (PAC), GO/FH exhibited superior removal for high molecular weight (HMW) humic- and fulvic-like substances and low molecular weight (LMW) protein. The cake layer formed by GO/FH alleviated the deposition of NOM on membrane surface or inside membrane pores. Therefore, GO/FH reduced 89% and 95% total fouling resistance and irreversible membrane resistance, respectively, together with the lowest increment of transmembrane pressure. Pearson correlation analysis indicated that DOC, rather than specific ultraviolet absorbance (SUVA) and UV₂₅₄, was significantly correlated to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) when SUVA was below 4 L/mg-C.m. Whilst the HMW NOM (1-20 kDa) was highly related to dibromochloromethane (DBCM) (r = 0.98-1), the LMW fraction (< 1 kDa) was correlated with dibromochloromethane (TCAA) and dichloroacetic acid (DCAA) (r = 0.88-0.98). Inspiringly, GO/FH-UF reduced 90% of carbonaceous DBPs, the concentrations of which well met the WHO Guidelines. In summary, GO/FH-UF substantially alleviated membrane fouling and dramatically reduced DBP formation potential.

Salt Removal by Chemically Modified Graphene in Capacitive Deionization (CDI)

Obtaining clean water from salt water by capacitive deionization (CDI) with chemically modified graphene (rGO) was explored in this study. Strong acid (HNO3:H2SO4 = 2:1) was employed to modify rGO to enhance its hydrophilicity and electrochemical properties. Characteristics of rGO with/without acid modification were analyzed by XRD, SEM, FTIR, contact angle, BET, and cyclic voltammetry (CV). Contributions of sulfonic acid groups, hydroxyl groups, and NO2 stretching after acid modification resulted in better wettability and higher specific capacitance of rGO. The contact angle for rGO dropped from 84.9° to 35.1° (am-rGO), indicating improved hydrophilicity of rGO with acid modification. The specific capacitance of am-rGO can reach 150.2 F/g at the scan rate of 1 mV/s. The average NaCl electrosorption capacity of the CDI process with am-rGO was 0.63 mg NaCl/g electrode (10.86 μmol NaCl/g electrode), which indicated rGO with acid modification can enhance the electrosorption capacity by 3.9 times. This study demonstrated that chemical modification can significantly improve the hydrophilicity, electrochemical properties, and electrosorption performance of rGO, which has potential for applications to other carbon-based materials for CDI systems to improve salt removal efficiency.

Fabrication of High Surface Area Microporous ZnO from ZnO/Carbon Sacrificial Composite Monolith Template

Fabrication of porous materials from the standard sacrificial template method allows metal oxide nanostructures to be produced and have several applications in energy, filtration and constructing sensing devices. However, the low surface area of these nanostructures is a significant drawback for most applications. Here, we report the synthesis of ZnO/carbon composite monoliths in which carbon is used as a sacrificial template to produce zinc oxide (ZnO) porous nanostructures with a high specific surface area. The synthesized porous oxides of ZnO with a specific surface area of 78 m2/g are at least one order of magnitude higher than that of the ZnO nanotubes reported in the literature. The crucial point to achieving this remarkable result was the usage of a novel ZnO/carbon template where the carbon template was removed by simple heating in the air. As a high surface area porous nanostructured ZnO, these synthesized materials can be useful in various applications including catalysis, photocatalysis, separation, sensing, solar energy harvest and Zn-ion battery and as supercapacitors for energy storage.

Boron doped Fluorescent Carbon Nano Dots for reduction of ionic dyes and as Encryption and decryption QR code labels

This work discusses the synthesis of fluorescent undoped and boron-doped carbon nanodots (BDCNDs) by a simple hydrothermal approach using Tribulus terretris as carbon precursor and boric acid as boron source....

Fly ash-based geopolymers: an emerging sustainable solution for heavy metal remediation from aqueous medium

Background

The water supplies are hindered because aquatic resources have constrained with natural and man-made pollution activities in terms of releasing huge amounts of contaminants from different point and non-point sources across the globe. The industries like metal plating, batteries, paint, fertilizers, tanneries, textile industries, dyeing industries, mining operations, and paper industries discharge their effluents into the environment directly or indirectly, and hence, they are considered as the key sources of heavy metals contamination in water resources. Heavy metals are inorganic, non-biodegradable, persistent, and having a tendency to get accumulated in biotic and abiotic components of environment as compared to organic pollutants. Some heavy metal cations, for example, mercury, arsenic, cadmium, zinc, lead, nickel, copper, and chromium, are carcinogenic in nature and so, lethal. There are growing health concerns due to toxic impacts of heavy metals on every genre of ecosystem. To deal with the bottleneck situation, it is highly imperative to search a feasible solution for heavy metal remediation in water in context of preventing amalgamation of noxious contaminants in food web. Different methods are exercised for the remediation of such impurities from its solutions. One method, i.e. adsorption is found to be the simplest, economical, efficient, and eco-friendly in this context.

Main body

Geopolymers exhibit heterogeneous amorphous microstructure and wide surface area. The compatibility for depollution and the performance of these materials mainly depend upon their preparation methods, composition, and microstructure. Fly ash-based geopolymer may serve as a better alternate to various cost-effective adsorbents and it will be a proven environmentally viable, waste to money solution by consuming heaps of fly ash waste for the adsorbent modified by using fly ash. The possible utilization of wastes from several industries is a matter of concerned sustainability benefits. This study shows that fly ash-based geopolymers have the potential to cope up with the problems and risk factors associated with the fly ash waste management and it would be the utmost scientific panacea in the field of removing toxins from aqueous medium and maintain environmental health in the future.

Short conclusions

The literature available in different databases is very limited pertaining to heavy metal remediation using fly ash-based geopolymers. Keeping all the factors in mind, this article is an attempt to summarize relevant informations related to work done on fly ash-based geopolymers for treating aqueous solutions comprising heavy metals.

Preparation of Fe/Ni Bimetallic Oxide Porous Graphene Composite Materials for Efficient Adsorption and Removal of Sulfonamides

An iron-nickel bimetallic oxide porous graphene composite material (Fe/Ni-PG) was prepared by a simple partial combustion method, which can be used to effectively remove sulfonamides (SAs) from an aqueous solution. The adsorption performance of Fe/Ni-PG, Fe-PG, and Ni-PG on six kinds of SAs was compared, and the influence of time, temperature, pH, and initial concentration of SAs on the adsorption behavior of SAs of Fe/Ni-PG in an aqueous solution was studied. The adsorption kinetics and thermodynamics exhibited that the Langmuir model and pseudo-second-order kinetics model can describe the adsorption isotherm and kinetics. The maximum adsorption capacities of sulfadiazine (SD), sulfamerazine (SM), sulfamethazine (SDM), sulfathiazole (STZ), sulfapyridine (SPD), and sulfisoxazole (SIZ) calculated by the Langmuir model were 26.3, 50.3, 42.2, 27.3, 34.5, and 41.7 mg/g, respectively, which exceeded those of most reported adsorbents. In the adsorption process, hydrogen bonding, π-π electron donor-acceptor, electrostatic interaction, and bimetallic synergies play a major role, and the entire adsorption process is spontaneously endothermic. In addition, the material has excellent stability, and the Fe/Ni-PG after desorption is consistent with the raw material. This work provides a favorable way for the removal of SAs in the environment.

Hybrid capacitive deionization of NaCl and toxic heavy metal ions using faradic electrodes of silver nanospheres decorated pomegranate peel-derived activated carbon

Capacitive deionization (CDI) is an evolving technology for eradicating salt and toxic heavy metal ions from brackish wastewater. However, traditional CDI electrodes have lower salt adsorption capacity and inadequate adsorption of selective metal ions for long-term operations. Herein, Ag nanospheres incorporated pomegranate peel-derived activated carbon (Ag/P-AC) was prepared and implied to the CDI process for removing NaCl, toxic mono-, di-, and trivalent metal ions. Morphological analysis revealed that the 80-100 nm-sized Ag nanospheres were uniformly decorated on the surfaces of P-AC nanosheets. The Ag/P-AC has a higher specific surface area (640 m² g^-1), superior specific capacitance (180 F g^-1 at 50 mV s^-1) and a lower charge transfer resistance (0.5 Ω cm²). CDI device was fabricated by Ag/P-AC as an anode, which adsorbed anions and P-AC as cathode for adsorption of positively charged ions at 1.2 V in an initial salt concentration of 1000 mg L^-1. An asymmetric Ag/P-AC//P-AC exhibited a maximum NaCl adsorption capacity of 36 mg g^-1 than symmetric P-AC//P-AC electrodes (22.7 mg g^-1). Furthermore, Pb(II), Cd(II), F^-, and As(III) ions were successfully removed from simulated wastewater by using Ag/P-AC//P-AC based CDI system. These asymmetric CDI-electrodes have an excellent prospect for the removal of salt and toxic contaminants in industrial wastewater.

Preparation and characterization of activated carbon from hydrochar by hydrothermal carbonization of chickpea stem: an application in methylene blue removal by RSM optimization

Herein, mesoporous activated carbon (AC) was prepared through potassium hydroxide (KOH) activation of hydrochar derived from the hydrothermal carbonization (HTC) of chickpea stem (CS), and successfully applied to remove methylene blue (MB) dye from aqueous solutions in a batch system. The HTC-CSAC was prepared depending on different impregnation ratios (hydrochar:KOH, 50-150%), impregnation times (12-48 h), activation temperatures (400-600°C) and activation times (30-60 min). To define HTC-CSAC, various analytical techniques such as iodine adsorption number (IAN), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) were used. In the removal process of MB by the best HTC-CSAC with a high IAN of 887 mg g^-1 obtained under conditions including impregnation ratio of 70%, activation time of 45 min, activation temperature of 600°C and impregnation time of 24 h, the effects of adsorption parameters such as pH factor (2-10), adsorbent dosage (50-100 mg), initial MB concentration (40-80 mg/L) and contact time (90-180 min) were studied. Besides, a detailed evaluation of the adsorption mechanism for the removal of MB by HTC-CSAC was performed. The Langmuir model indicated the best isotherm data correlation, with a maximum monolayer adsorption capacity (Q_max) of 96.15 mg g^-1. The adsorption isotherm findings demonstrated that the MB removal process is feasible, and that this process takes place through the physical interaction mechanism. Additionally, the HTC-CSAC adsorbent exhibited a high regeneration and reuse performance in MB removal. After five consecutive adsorption-desorption cycles, HTC-CSAC maintained the reuse efficiency of 77.86%. As a result, the prepared HTC-CSAC with a high BET surface area of 455 m² g^-1 and an average pore diameter of 105 Å could be recommended as a promising and reusable adsorbent in the treatment of synthetic dyes in wastewaters.

Synthesis of sodium lignosulfonate-guar gum composite hydrogel for the removal of Cu2+ and Co2

As an emerging pollutant treatment material, hydrogel is known for its good adsorption capacity and environmental friendliness. In this study, a composite material of acrylic acid as the polymerization monomer grafted sodium lignosulfonate and guar gum was prepared, which provided a channel for adsorbing metal ions with its abundant active functional groups and porous structure. The optimized synthesized product was applied to the removal of Cu²⁺ and Co²⁺ in a one-component system and a multi-component system, and the maximum ion adsorption capacities obtained were determined to be 709 mg g^-1 of Cu²⁺, 601 mg g^-1 of Co²⁺, respectively. The adsorption kinetics and isotherms were well fitted by the pseudo second-order kinetic model and the Langmuir isotherm, showing that the adsorption of Cu²⁺ and Co²⁺ by the adsorbent belongs to the chemisorption on monolayer. XPS results confirmed the successful adsorption of Cu²⁺ and Co²⁺ by GG/SLS. Surface complexation was proposed to be the main mechanism for GG/SLS adsorbent to remove heavy metal ions. In addition, the use of recycling research showed that the adsorbent has good chemical stability. These results provided valuable information for designing highly efficient adsorbents that can be used as a high-quality wastewater treatment material.

Preparation of β-cyclodextrin/graphene oxide and its adsorption properties for methylene blue

Graphene oxide (GO) and GO-based materials have shown excellent adsorption properties because of bounteous structure and rich oxygen functional groups. Many studies have shown that GO are utilized as adsorbents to remove organic dyes from wastewater. GO was prepared by modified Hummers method using graphite powder as raw material. On this basis, β-cyclodextrin/graphene oxide composite (β-CD/GO) was prepared by modifying graphene oxide via β-cyclodextrin(β-CD) crosslinking method. GO and β-CD were characterized by Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray (XRD), scanning electron (SEM) and thermogravimetric analysis (TGA). Their adsorbents properties have been studied with methylene blue (MB) as adsorbate. The factors affecting the study include the temperature, adsorption time, amount of adsorbent and system pH value. Adsorption isotherm and kinetics of the adsorption process are systematically analyzed. The results show that β-CD/GO has a different adsorption capacity from GO under the same adsorption factors. Under the optimized conditions (the reaction temperature is 70 °C, the reaction time is 60 min and the concentration of adsorbent is 0.04 g/L), the removal efficiency of β-CD/GO is 20% higher than that of GO from 70% to 90%. The maximum adsorption capacity of β-CD/GO is 76.4 mg/g. β-CD/GO can be effectively regenerated by elution with absolute alcohol. In these tests, β-CD/GO was suggested to be more efficient than GO in the removal of organic dyes.

Functionalized polyurethane sponge based on dopamine derivative for facile and instantaneous clean-up of cationic dyes in a large scale

Functionalized sponge adsorbent was prepared by a mussel-inspired strategy, which achieved successive modification of material and remained the properties of substrate. The dopamine derivative, DOPAm, was synthesized and adhered to polyurethane (PU) sponge before in situ polymerization with sodium p-styrenesulfonate. The adsorbent showed superior removal efficiency for cationic dyes (98.9 % for methylene blue (MB) at the concentration of 200 μmol/L); it took 1 s only for the adsorbent to adsorb the dyes by swelling and squeezing out the bulk solution simply. Meanwhile, the superior adsorption effect of the adsorbent could be maintained in a wide range of solution pH values from 1 to 13 at room temperature (293 K) in several repeat experiments, due to the slight influence of strong acid and alkali on polysulfonate. With unchanged other experimental conditions, the removal efficiency is still more than 90 % after reusing for 10 times at the different concentrations of MB dye solutions (50, 100, 200 μmol/L). For large-scale wastewater treatment, with the removal efficiency of 80.0 %, the adsorbent could purify 4.1 L wastewater containing MB dye (100 μmol/L) with the maximum flux of 22.2 L/(m³·s) without the assistance of any equipment except for a vacuum pump. Therefore, the adsorbent has great possibilities to be applied in high-efficient and convenient treatment of wastewater in a large scale.

Cytotoxic aquatic pollutants and their removal by nanocomposite-based sorbents

Water is an extremely essential compound for human life and, hence, accessing drinking water is very important all over the world. Nowadays, due to the urbanization and industrialization, several noxious pollutants are discharged into water. Water pollution by various cytotoxic contaminants, e.g. heavy metal ions, drugs, pesticides, dyes, residues a drastic public health issue for human beings; hence, this topic has been receiving much attention for the specific approaches and technologies to remove hazardous contaminants from water and wastewater. In the current review, the cytotoxicity of different sorts of aquatic pollutants for mammalian is presented. In addition, we will overview the recent advances in various nanocomposite-based adsorbents and different approaches of pollutants removal from water/wastewater with several examples to provide a backdrop for future research.

Unified View of Magnetic Nanoparticle Separation under Magnetophoresis

The migration process of magnetic nanoparticles and colloids in solution under the influence of magnetic field gradients, which is also known as magnetophoresis, is an essential step in the separation technology used in various biomedical and engineering applications. Many works have demonstrated that in specific situations, separation can be performed easily with the weak magnetic field gradients created by permanent magnets, a process known as low-gradient magnetic separation (LGMS). Due to the level of complexity involved, it is not possible to understand the observed kinetics of LGMS within the classical view of magnetophoresis. Our experimental and theoretical investigations in the last years unravelled the existence of two novel physical effects that speed up the magnetophoresis kinetics and explain the observed feasibility of LGMS. Those two effects are (i) cooperative magnetophoresis (due to the cooperative motion of strongly interacting particles) and (ii) magnetophoresis-induced convection (fluid dynamics instability originating from inhomogeneous magnetic gradients). In this feature article, we present a unified view of magnetophoresis based on the extensive research done on these effects. We present the physical basis of each effect and also propose a classification of magnetophoresis into four distinct regimes. This classification is based on the range of values of two dimensionless quantities, namely, aggregation parameter N* and magnetic Grashof number Gr_m, which include all of the dependency of LGMS on various physical parameters (such as particle properties, thermodynamic parameters, fluid properties, and magnetic field properties). This analysis provides a holistic view of the classification of transport mechanisms in LGMS, which could be particularly useful in the design of magnetic separators for engineering applications.

Exploration of Energy Storage Materials for Water Desalination via Next-Generation Capacitive Deionization

Clean energy and environmental protection are critical to the sustainable development of human society. The numerous emerged electrode materials for energy storage devices offer opportunities for the development of capacitive deionization (CDI), which is considered as a promising water treatment technology with advantages of low cost, high energy efficiency, and wide application. Conventional CDI based on porous carbon electrode has low salt removal capacity which limits its application in high salinity brine. Recently, the faradaic electrode materials inspired by the researches of sodium-batteries appear to be attractive candidates for next-generation CDI which capture ions by the intercalation or redox reactions in the bulk of electrode. In this mini review, we summarize the recent advances in the development of various faradaic materials as CDI electrodes with the discussion of possible strategies to address the problems present.

Preparation and Photocatalytic Properties of a Bagasse Cellulose-Supported Nano-TiO2 Photocatalytic-Coupled Microbial Carrier

Intimate coupling of photocatalysis and biodegradation (ICPB) has shown promise in removing unwanted organic compounds from water. In this study, bagasse cellulose titanium dioxide composite carrier (SBC-TiO₂) was prepared by low-temperature foaming methods. The optimum preparation conditions, material characterization and photocatalytic performance of the composite carrier were then explored. By conducting a single factor test, we found that bagasse cellulose with a mass fraction of 4%, a polyvinyl alcohol solution (PVA) with a mass fraction of 5% and 20 g of a pore-forming agent were optimum conditions for the composite carrier. Under these conditions, good wet density, porosity, water absorption and retention could be realized. Scanning electron microscopy (SEM) results showed that the composite carrier exhibited good biologic adhesion. X-ray spectroscopy (EDS) results confirmed the successful incorporation of nano-TiO₂ dioxide into the composite carrier. When the mass concentration of methylene blue (MB) was 10 mg L⁻¹ at 200 mL, 2 g of the composite carrier was added and the initial pH value of the reaction was maintained at 6, the catalytic effect was best under these conditions and the degradation rate reached 78.91% after 6 h. The method of preparing the composite carrier can aid in the degradation of hard-to-degrade organic compounds via ICPB. These results provide a solid platform for technical research and development in the field of wastewater treatment.

Enhanced electrochemical performances of peanut shell derived activated carbon and its Fe3O4 nanocomposites for capacitive deionization of Cr(VI) ions

Capacitive deionization (CDI) is one of the most efficient and emerging techniques for the removal of toxic metal ions from aqueous solutions. In this study, mesoporous peanut shell derived activated carbon (PSAC) was prepared by low temperature pyrolysis at 500 °C. Subsequently, a novel iron oxide/PSAC (Fe₃O₄/PSAC) nanocomposite adsorbent was prepared via facile one-pot hydrothermal synthesis method at 180 °C. Nucleation growth mechanism and appropriate characterizations of prepared nanocomposites were investigated. The obtained Fe₃O₄/PSAC possessed a highly mesoporous structure, and a large specific surface area (680 m²/g). The electrochemical analysis showed that the obtained Fe₃O₄/PSAC nanocomposites exhibited higher capacitance (610 F/g at 10 mV/s), good stability and low internal resistance. A batch mode adsorption and CDI based Cr(VI) removal studies were conducted. Effects of solution pH and cycle time on Cr(VI) electrosorption capacity were further investigated. The Fe₃O₄/PSAC based electrodes exhibit a maximum electrosorption capacity of 24.5 mg/g at 1.2 V, which was remarkably larger than other reported materials. The fabricated composite displayed higher electrosorption capacity with rapid time and a favorable reduction of Cr (VI) to Cr(III). Studies indicated that the Fe₃O₄/PSAC based CDI electrode possesses a good potential to be applied for the removal of toxic metal ions from wastewater.

Comprehensive evaluation on removal of lead by graphene oxide and metal organic framework

Graphene oxide (GO) and metal-organic framework (MOF) as adsorbents were applied to removal of Pb(II) with comprehensive characterizations and various experimental conditions. Various characterizations were conducted to clarify the physico-chemical properties of adsorbents. The analyses of adsorption experiments included (i) dosage amounts, (ii) isotherm and kinetic studies, and (iii) several factors related to water chemistry (i.e., solution pH, background ions, and humic acid). The maximum equilibrium adsorption capacity (q_e) for Pb(II) using the GO and MOF was 555 and 108 mg g^-1, respectively, as determined in the optimum dosage experiments. Although the surface area of the MOF (629 m² g^-1) was much larger than that of the GO (19.8 m² g^-1), the adsorption capacity of the MOF was five times lower due to electrical repulsion. Thus, the MOF was utilized as the control group for comparison with the GO to evaluate the adsorption mechanisms in the experiments related to surface charge (i.e., under various pH and humic acid conditions). The adsorption isotherms and kinetics model determined using GO followed the Langmuir model (R² > 0.99) and pseudo-second-order model (R² > 0.99), respectively. Additionally, three adsorption-desorption cycles were conducted with the GO adsorbent to evaluate the maintenance of the removal ratio after regeneration and the equilibrium adsorption capacity was determined. Finally, the adsorption of other heavy metals (i.e., Cu(II), Cd(II), and Zn(II)), separately and in mixtures, was also evaluated to determine the selectivity of the adsorbents.

Graphene-based adsorbents for the removal of toxic organic pollutants: A review

The synthesis and application of efficient materials for remediation of environmental contaminants from water is an emerging area of research. Graphene has received tremendous attention in various fields due to its exceptional properties. Graphene and its derivatives have also been extensively explored for the adsorptive removal of pollutants from water. The recent trends are inclined toward functionalization of graphene-based materials to get the advantage of their improved properties. The functionalized graphene materials are efficient due to their enhanced properties resulting from synergistic effects. This article reviews the synthesis and application of graphene-based adsorbents for the removal of organic pollutants from water. A critical account is provided on synthesis methods, applications, adsorption mechanisms, the figure of merits, and removal performances. The accomplishments, limitations, challenges, and future research directions are also highlighted.

Electro-sorption of ammonium ion onto nickel foam supported highly microporous activated carbon prepared from agricultural residues (dried Luffa cylindrica)

An electrode made of loofah sponge derived activated carbon supported on nickel foam (AC/Ni) was successfully fabricated and used to remove ammonium ion (NH₄⁺) from aqueous solution. A multilayer adsorption isotherm was used to describe ammonium electro-sorption on AC/Ni electrodes at different temperature, initial NH₄⁺ concentration, and electrical field. The cyclic voltammetry (CV) results suggested that the electrical capacitance of AC/Ni electrodes, with the AC being prepared without preheating (OAC) or with low temperature heating (i.e., 300 AC), were higher than those prepared at high preheating temperature (i.e., 400 AC and 500 AC). Increasing the electro-sorption temperature from 10 to 50 °C decreased the monolayer NH₄⁺ adsorption capacity from 5 to ca. 2-3 mg-N g^-1, respectively. Background electrolyte, namely, sodium sulfate, exhibited significant competitive effect on the adsorption of ammonium ion at sodium ion concentration > 10^-2 M. The activation energy and heat of adsorption were 9-23.2 kJ mol^-1 and -3.7--10.7 kJ mol^-1, respectively, indicating a physisorption and exothermic adsorption characteristics. Based on the kinetics and thermodynamics analysis, there was slight increase in the activation energy with elevating preheating temperature, which increased the quantity of micro-pores and surface heterogeneity of the AC materials. Overall, results clearly demonstrated that carbon pyrolysis played a role on the capacitive charging behaviors of electrodes and the efficiency of NH₄⁺ electro-sorption on the AC/Ni electrodes.

Recent progress on carbon nanomaterials for the electrochemical detection and removal of environmental pollutants

Rapid global industrialization and explosive population growth have resulted in an increase in the discharge of harmful and toxic compounds. These toxic inorganic gases, volatile organic compounds, heavy metals, personal care products, endocrine-disrupting chemicals, dyes, and pharmaceuticals are destroying the balance in the Earth and increasing environmental toxicity at an alarming rate. Thus, their detection, adsorption and removal are of great significance. Various carbon nanomaterials including carbon nanotubes, graphene, mesoporous carbon, carbon dots, and boron-doped diamond have been extensively utilized and further proven to be ideal candidates for resolving environmental problems, emerging as adsorbents, electrochemical sensors and electrodes. Herein, we review the recent advances, progress and achievements in the design and properties of carbon nanomaterials and their applications for the electrochemical detection and removal of environmental pollutants.

Aqueous removal of inorganic and organic contaminants by graphene-based nanoadsorbents: A review

Various graphene-based nanoadsorbents, including graphenes, graphene oxides, reduced graphene oxides, and their nanocomposites, have been widely studied as potential adsorbents due to their unique physicochemical properties, such as structural variability, chemical strength, low density, and the possibility of large scale fabrication. Adsorption mechanisms are governed largely by the physicochemical properties of contaminants, the characteristics of nanoadsorbents, and background water quality conditions. This review summarizes recent comprehensive studies on the removal of various inorganic (mainly heavy metals) and organic contaminants by graphene-based nanoadsorbents, and also discusses valuable information for applications of these nanoadsorbents in water and wastewater treatment. In particular, the aqueous removal of various contaminants was reviewed to (i) summarize the general adsorption capacities of various graphene-based nanoadsorbents for the removal of different inorganic and organic contaminants, (ii) evaluate the effects of key water quality parameters such as pH, temperature, background major ions/ionic strength, and natural organic matter on adsorption, (iii) provide a comprehensive discussion of the mechanisms that influence adsorption on these nanoadsorbents, and (iv) discuss the potential regeneration and reusability of nanoadsorbents. In addition, current challenges and future research needs for the removal of contaminants by graphene-based nanoadsorbents in water treatment processes are discussed briefly.