The Nanosized Dye Adsorbents for Water Treatment

2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

Performance evaluation of facile synthesized CA-PVA-GO composite for the mitigation of Cr(Ⅲ) and C.I. acid violet 54 dye from tannery wastewater

Untreated tannery wastewater contains a large amount of toxic metals, dyes, and other pollutants, which pose adverse effects on the ecosystem and public health. In this work, a calcium alginate-poly vinyl alcohol-graphene oxide (CA-PVA-GO) composite was prepared to remove metals and dyes, particularly Cr(Ⅲ) and CI acid violet 54 (AV54) dye, from tannery wastewater. FESEM, FTIR, and XRD analyses were applied to characterize the GO and CA-PVA-GO. Different operational variables, viz. pH (3.0-5.5 for Cr(III) and 2-7 for dye), dosage (0.164-2.46 g/L), contact time (10-60 min), initial concentration (39, 65, 98, and 201 ppm for Cr(III) and 21.5, 38.5, 54.5, and 61.75 ppm for dye), and temperature (298, 308, 318, and 328 K) were studied to evaluate the efficiency of the CA-PVA-GO composite. The optimum conditions for Cr(Ⅲ) and AV54 dye adsorption were found to be pH (5.0 and 3.0), dosage (0.82 g/L for both), and time (45 and 60 min), respectively, with 35.35 ± 1.43% and 84.63 ± 2.54% removal efficiency. The experimental data was analyzed through the Langmuir and Freundlich isotherms. The maximum adsorption capacity (qm) was observed at 173.01 and 74.68 mg/g for Cr(Ⅲ) and AV54 dye, respectively. The pseudo-second-order kinetic model was fitted better (R2 = 0.981, 0.995, 0.92, and 0.995) than first-order for AV54 dye adsorption. Thermodynamic analyses revealed that the Cr(Ⅲ) and AV54 dye adsorption processes were spontaneous and exothermic. The value of Gibbs free energy (ΔG) for Cr(III) adsorption was obtained at -7.433, -4.508, -2.626, and -1.311 kJ/mol, whereas it was -5.178, -4.867, -4.628, and -4.555 kJ/mol for dye. The values of ΔH and ΔS were -67.257 and -0.198 kJ/mol for Cr(III) and -10.852 and -0.019 kJ/mol for the dye removal. The regenerated CA-PVA-GO composite was reused successfully. Different physicochemical parameters, viz., concentration, pH, TDS, EC, BOD5, and COD of chrome tanning and dyeing effluents, were analyzed before and after the adsorption. The results of chromium and dye removal from tannery wastewater were 53.18% and 93.91%, revealing that the developed eco-friendly CA-PVA-GO composite could be an operative adsorbent for tannery wastewater treatment and possibly scaled up to an industrial level.

Nanoremediation and Antioxidant Potential of Biogenic Silver Nanoparticles Synthesized Using Leucena's Leaves, Stem, and Fruits

Synthetic dyes are persistent organic environmental pollutants that can cause extensive damage to living beings and to the ecosystem as a whole. Cost-effective, sustainable, and efficient strategies to deal with this type of pollution are necessary as it commonly resists conventional water treatment methods. Silver nanoparticles (AgNPs) synthesized using the aqueous extract from the leaves, stem, and fruits of Leucaena leucocephala (Leucena) were produced and characterized through UV-vis, TEM, EDS, SDL, XPS, XRD, and zeta potential, and they proved to be able to promote adsorption to remediate methylene blue and tartrazine pollution in water. The nanoremediation was performed and did not require direct exposure to sunlight or any special lamp or a specific reduction agent. The AgNPs produced using the extract from the leaves exhibited the best performance in nanoremediation and also presented antioxidant activity that surpassed the one from butylated hydroxytoluene (BHT). Consequently, it is an interesting nanotool to use in dye nanoremediation and/or as an antioxidant nanostructure.

Endophytic Aspergillus hiratsukae mediated biosynthesis of silver nanoparticles and their antimicrobial and photocatalytic activities

In the current study, endophytic Aspergillus hiratsukae was used for the biosynthesis of silver nanoparticles (Ag-NPs) for the first time. The characterizations were performed using X ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), and UV-Vis spectroscopy. The obtained results demonstrated the successful formation of crystalline, spherical Ag-NPs with particle diameters ranging from 16 to 31 nm. The FT-IR studied and displayed the various functional groups involved, which played a role in capping and reducing agents for Ag-NPs production. The SEM-EDX revealed that the main constituent of the AS-formed sample was primarily Ag, with a weight percentage of 64.2%. The mycosynthesized Ag-NPs were assessed for antimicrobial as well as photocatalytic activities. The antimicrobial results indicated that the synthesized Ag-NPs possess notable antibacterial efficacy against Staphylococcus aureus, Bacillus subtilis, and Escherichia coli, with minimum inhibitory concentrations (MICs) of Ag-NPs ranging from 62.5 to 250 μg/mL. Moreover, the biosynthesized Ag-NPs demonstrated weak antifungal activity against Aspergillus brasiliensis and Candida albicans, with MICs of 500 and 1,000 μg/mL, respectively. In addition, the mycosynthesized Ag-NPs exhibited photocatalytic activity toward acid black 2 (nigrosine) dye under both light and dark stimulation. Notably, After 300 min exposure to light, the nigrosine dye was degraded by 93%. In contrast, 51% degradation was observed after 300 min in darkness. In conclusion, Ag-NPs were successfully biosynthesized using endophytic A. hiratsukae and also exhibited antimicrobial and photocatalytic activities that can be used in environmental applications.

Advances in two-dimensional transition metal dichalcogenides-based sensors for environmental, food, and biomedical analysis: A review

Transition metal dichalcogenides (TMDCs) are versatile two-dimensional (2D) nanomaterials used in biosensing applications due to their excellent physical and chemical properties. Due to biomaterial target properties, biosensors' most significant challenge is improving their sensitivity and stability. In environmental analysis, TMDCs have demonstrated exceptional pollutant detection and removal capabilities. Their high surface area, tunable electronic properties, and chemical reactivity make them ideal for sensors and adsorbents targeting various contaminants, including heavy metals, organic pollutants, and emerging contaminants. Furthermore, their unique electronic and optical properties enable sensitive detection techniques, enhancing our ability to monitor and mitigate environmental pollution. In the food analysis, TMDCs-based nanomaterials have shown remarkable potential in ensuring food safety and quality. These nanomaterials exhibit high specificity and sensitivity for detecting contaminants, pathogens, and adulterants in various food matrices. Their integration into sensor platforms enables rapid and on-site analysis, reducing the reliance on centralized laboratories and facilitating timely interventions in the food supply chain. In biomedical studies, TMDCs-based nanomaterials have demonstrated significant strides in diagnostic and therapeutic applications. Their biocompatibility, surface functionalization versatility, and photothermal properties have paved the way for novel disease detection, drug delivery, and targeted therapy approaches. Moreover, TMDCs-based nanomaterials have shown promise in imaging modalities, providing enhanced contrast and resolution for various medical imaging techniques. This article provides a comprehensive overview of 2D TMDCs-based biosensors, emphasizing the growing demand for advanced sensing technologies in environmental, food, and biomedical analysis.

Green synthesis of silver nanoparticles using Adhatoda vasica leaf extract and its application in photocatalytic degradation of dyes

The paper describes biogenic synthesis of silver nanoparticles (AgNPs) using Adhatoda vasica leaf extracts at room temperature. The prepared AgNPs were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, powder X-ray diffraction, Energy dispersive X-ray (EDX), High Resolution Transmission Electron Microscope, Scanning Electron Microscopy and Thermogravimetric analyser. The bio reduction method is devoid of any toxic chemicals, organic solvents, and external reducing, capping and stabilizing agent. The synthesized AgNPs had spherical shape with particle size ranging between 3.88 and 23.97 nm and had face centered cubic structure. UV-visible spectral analysis confirmed the formation of AgNPs with a characteristic surface plasmon resonance band at 419 nm. The EDX pattern revealed the presence of elemental Ag in AgNPs. The prepared AgNPs were used for degradation of Amaranth, Allura red and Fast green in aqueous medium, with ≥ 92.6% efficiency within 15 min using 5 mg of AgNPs. The optical bandgap, Eg value of 2.26 eV for AgNPs was found to be effective for rapid photocatalytic degradation of all the three dyes. The degradation process was observed to follow pseudo first order kinetics.

In Situ Synthesis of Crystalline MoS2@ZIF-67 Nanocomposite for the Efficient Removal of Methyl Orange Dye from Aqueous Media

The zeolitic imidazolate framework-67 (ZIF-67) adsorbent and its composites are known to effectively remove organic dyes from aqueous environments. Here, we report a unique crystalline MoS2@ZIF-67 nanocomposite adsorbent for the efficient removal of methyl orange (MO) dye from an aqueous medium. In situ synthetic techniques were used to fabricate a well-crystalline MoS2@ZIF-67 nanocomposite, which was then discovered to be a superior adsorbent to its constituents. The successful synthesis of the nanocomposite was confirmed using XRD, EDX, FTIR, and SEM. The MoS2@ZIF-67 nanocomposite exhibited faster adsorption kinetics and higher dye removal efficiency compared with its constituents. The adsorption kinetic data matched well with the pseudo-second-order model, which signifies that the MO adsorption on the nanocomposite is a chemically driven process. The Langmuir model successfully illustrated the MO dye adsorption on the nanocomposite through comparing the real data with adsorption isotherm models. However, it appears that the Freundlich adsorption isotherm model was also in competition with the Langmuir model. According to the acquired thermodynamics parameters, the adsorption of MO on the MoS2@ZIF-67 nanocomposite surface was determined to be spontaneous and exothermic. The findings of this research open an avenue for using the MoS2@ZIF-67 nanocomposite to efficiently remove organic dyes from wastewater efflux.

A State-of-Art Review of the Metal Oxide-Based Nanomaterials Effect on Photocatalytic Degradation of Malachite Green Dyes and a Bibliometric Analysis

A wide range of hard contaminants in wastewater is generated from different industries as byproducts of the organic compound. In this review, various metal oxide-based nanomaterials are employed for the photocatalytic removal of malachite green (MG) dye from wastewater. Some cost-effective and appropriate testing conditions are used for degrading these hard dyes to get higher removal efficiency. The effects of specific parameters are considered such as how the catalyst is made, how much dye is in the solution at first, how much nanocatalyst is needed to break down the dye, the initial pH of the dye solution, the type of light source used, the year of publications, and how long the dye has to be exposed to light to be removed. This study suggests that Scopus-based core collected data employ bibliometric methods to provide an objective analysis of global MG dye from 2011 to 2022 (12 years). The Scopus database collects all the information (articles, authors, keywords, and publications). For bibliometric analysis, 658 publications are retrieved corresponding to MG dye photodegradation, and the number of publications increases annually. A bibliometric study reveals a state-of-art review of metal oxide-based nanomaterials' effects on photocatalytic degradation of MG dyes (12 years).

Insights into Selective Removal by Dye Adsorption on Hydrophobic vs Multivalent Hydrophilic Functionalized MWCNTs

Hydrophilic functionalized carbon nanotubes (MWCNT-COOH) were developed via hydrothermal glucose-coated carbonization, mixing MWCNTs with glucose in different weight ratios. Methyl violet (MV), methylene blue (MB), alizarin yellow (AY), and methyl orange (MO) were used as dye models for adsorption studies. Comparative dye adsorption capacity onto the pristine (MWCNT-raw) and functionalized (MWCNT-COOH-11) CNTs was evaluated in aqueous solution. These results revealed that MWCNT-raw is capable of adsorbing either anionic or cationic dyes. In contrast, an induced selective cation dye adsorption capacity is significantly enhanced on multivalent hydrophilic MWCNT-COOH, in comparison to a pristine surface. This ability can be tuned to the selective adsorption of cations over anionic dyes or between anionic mixtures from binary systems. An insight into adsorbate-adsorbent interactions shows that hierarchical supramolecular interactions dominate the adsorption processes, which is ascribed to the chemical modification by switching from a hydrophobic to a hydrophilic surface, dye charge, temperature, and potential matching multivalent acceptor/donor capacity between chemical groups in the adsorbent interface. The dye adsorption isotherm and thermodynamics on both surfaces were also studied. Changes in the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were evaluated. Thermodynamic parameters were endothermic on MWCNT-raw, whereas the adsorption process on MWCNT-COOH-11 revealed that adsorption processes were spontaneous and exothermic, accompanied by a significant reduction of entropy values as a consequence of a multivalent effect. This approach provides an eco-friendly, low-cost alternative for the preparation of supramolecular nanoadsorbents with unprecedented properties to achieve remarkable selective adsorption independent of the presence of intrinsic porosity.

Bioinorganic Nanoparticles for the Remediation of Environmental Pollution: Critical Appraisal and Potential Avenues

Nowadays, environmental pollution has become a critical issue for both developed and developing countries. Because of excessive industrialization, burning of fossil fuels, mining and exploration, extensive agricultural activities, and plastics, the environment is being contaminated rapidly through soil, air, and water. There are a variety of approaches for treating environmental toxins, but each has its own set of restrictions. As a result, various therapies are accessible, and approaches that are effective, long-lasting, less harmful, and have a superior outcome are extensively demanded. Modern research advances focus more on polymer-based nanoparticles, which are frequently used in drug design, drug delivery systems, environmental remediation, power storage, transformations, and other fields. Bioinorganic nanomaterials could be a better candidate to control contaminants in the environment. In this article, we focused on their synthesis, characterization, photocatalytic process, and contributions to environmental remediation against numerous ecological hazards. In this review article, we also tried to explore their recent advancements and futuristic contributions to control and prevent various pollutants in the environment.

Quaternary Ammonium Groups Modified Magnetic Cyclodextrin Polymers for Highly Efficient Dye Removal and Sterilization in Water Purification

Water recovery is a significant proposition for human survival and sustainable development, and we never stop searching for more efficient, easy-operating, low-cost and environmentally friendly methods to decontaminate water bodies. Herein, we combined the advantages of β-cyclodextrin (β-CD), magnetite nanoparticles (MNs), and two kinds of quaternary ammonium salts to synthesize two porous quaternary ammonium groups capped magnetic β-CD polymers (QMCDP1 and QMCDP2) to remove organic pollutants and eradicate pathogenic microorganisms effectively through a single implementation. In this setting, β-CD polymer (CDP) was utilized as the porous substrate material, while MNs endowed the materials with excellent magnetism enhancing recyclability in practical application scenarios, and the grafting of quaternary ammonium groups was beneficial for the adsorption of anionic dyes and sterilization. Both QMCDPs outperformed uncapped MCDPs in their adsorption ability of anionic pollutants, using methyl blue (MB) and orange G (OG) as model dyes. Additionally, QMCDP2, which was modified with longer alkyl chains than QMCDP1, exhibits superior bactericidal efficacy with a 99.47% removal rate for Staphylococcus aureus. Accordingly, this study provides some insights into designing a well-performed and easily recyclable adsorbent for simultaneous sterilization and adsorption of organic contaminants in wastewater.

Preparation of Graphite Phase g-C3N4 Supported Metal Oxide Activator and Its Performance in Activating Peroxodisulfate Degradation of Methyl Orange

In order to improve the catalytic activity and recycling performance of semiconductor activators, and improve the activation pathway of persulfate, graphitic carbon nitride (g-C₃N₄) was prepared by calcining melamine, and a composite activator Ag₂O/g-C₃N₄ based on g-C₃N₄ supported metal oxide was prepared using a precipitation method. The morphology, structure, and basic properties of the composites were characterized using SEM, XRD, FT-IR and XPS. The activation efficiency of the Ag₂O/g-C₃N₄ composite activator on peroxodisulfate (PDS) was explored. The results showed that Ag₂O in the composite activator was highly dispersed on the surface of g-C₃N₄ and did not change the molecular structure of g-C₃N₄ significantly. Under different activation systems, the degradation process of MO was best fitted under the pseudo-second-order reaction kinetic model, compared to the separate g-C₃N₄ or Ag₂O activated PDS systems; the activation of the PDS system with Ag₂O/g-C₃N₄ had the best effect on MO degradation; and the composite activator Ag₂O/g-C₃N₄ showed better activation performance. Under the conditions that the mass combined ratio of Ag₂O in the activator was 12%, the initial concentration of PDS was 4 mmol/L, the initial concentration of the activator was 1.25 g/L, and the initial pH was 3, the degradation degree of MO reached 99.4% after 40 min reaction. The free radical quenching experiment proved that the active substances that could degrade MO in the system were SO₄^-· and ·OH, and the effect of SO₄^-· was greater than that of ·OH. The degradation degree of MO in the reaction system remained above 80% after four cycles of use, and the crystal structure of Ag₂O/g-C₃N₄ did not change significantly before and after the reaction. The above results show that Ag₂O/g-C₃N₄ is an efficient and stable composite activator with good application potential in the treatment of dye wastewater by activating PDS.

Recent advances in the removal of dyes from wastewater using low-cost adsorbents

The presence of hazardous dyes in wastewater cause disastrous effects on living organisms and the environment. The conventional technologies for the remediation of dyes from water have several bottlenecks such as high cost and complex operation. This review aims to present a comprehensive outlook of various bio-sorbents that are identified and successfully employed for the removal of dyes from aqueous environments. The effect of physicochemical characteristics of adsorbents such as surface functional groups, pore size distribution and surface areas are critically evaluated. The adsorption potential at different experimental conditions of diverse bio-sorbents has been also explored and the influence of certain key parameters like solution pH, temperature, concentration of dyes, dosage of bio-sorbent and agitation speed is carefully evaluated. The mechanism of dyes adsorption, regeneration potential of the employed bio-sorbents and their comparison with other commercial adsorbents are discussed. The cost comparison of different adsorbents and key technological challenges are highlighted followed by the recommendations for future research.

Green, Sustainable Synthesis of γ-Fe2O3/MWCNT/Ag Nano-Composites Using the Viscum album Leaf Extract and Waste Car Tire for Removal of Sulfamethazine and Bacteria from Wastewater Streams

Multi-walled carbon nanotubes (MWCNTs) decorated with Ag nanoparticles (NPs) are bifunctional adsorbent nanomaterials with antibacterial activity. They can be magnetically recovered from wastewater in case of coupling with γ-Fe₂O₃. In this study, for the first time, an environmentally friendly technique was applied to prepare a nanocomposite (NC) material composed of γ-Fe₂O₃/MWCNT/Ag by using Bridgestone disposable tires and Viscum album leaves extract. γ-Fe₂O₃/MWCNTs/Ag NC was employed for the removal of sulfamethazine (SMT) from aqueous solutions. Under the optimized conditions determined via the Taguchi method, the highest SMT adsorption capacity of the γ-Fe₂O₃/MWCNT/Ag NC was measured to be 47.6 mg/g. The experimental data fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm. The thermodynamic parameters implied that the adsorption process was endothermic. In addition to adsorption of the drug pollutant, the NC demonstrated a superior antibacterial activity against Gram-positive bacteria. The reusability test also showed that over 79% SMT can be removed using γ-Fe₂O₃/MWCNTs/Ag NC even after four adsorption cycles. Taken together, γ-Fe₂O₃/MWCNTs/Ag NC was proven to be a promising antibacterial nano-adsorbent for wastewater treatment.

A comprehensive review on sustainable greener nanoparticles for efficient dye degradation

The effluents released from textile industries mainly consist of dyes, metals and other pollutants. Dyes often are discharged in wastewater streams causing adverse effect on the environment. To eliminate these harmful dyes, various techniques are emerging out of which nanotechnology is the most reliable and safer. Nanotechnology offers convincing applications in case of environmental and economic concerns. The bio-synthesis of nanoparticles has several advantages over conventional methods and approach towards environment concern as well. Biological method of nanoparticles synthesis is concluded to be the most promising and efficient in action. Bio-synthesised nanoparticles could be used for treatment and decolourisation of dyes in an efficient manner. This review comprises the study of number of bio-synthesised nanoparticles utilised for degradation of various dyes present as pollutants in wastewater. Bio-synthesised nanoparticles such as gold, silver, iron, cobalt, zinc, titanium and molybdenum used for degradation of various dyes have been discussed in this review.

Potential applications of spent adsorbents and catalysts: Re-valorization of waste

Water pollution has increased with the growth of human population and its industrial activities. Textile effluents constitute a particular threat due to the presence of heavy metals and dyes. Adsorption is one of the most applied technologies in contaminant removal owing to its high efficiency, low cost, practical implementation and possibility to operate in several experimental conditions. However, this process implies the generation of spent materials, representing a limitation to scale-up. Although the applications of exhausted solids in effluent treatments have not been extensively reviewed before, their reutilization appears to be an environmentally and economically attainable alternative. This work summarizes the potential value of solids post-use. The open literature reports that spent adsorbents based on polysaccharides with iron oxides may adsorb up to 1 g g^-1 of organic pollutants and up to near 100% of metallic ions from wastewater (Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺). The studied conditions vary from 30 to 60 °C, 0,05 to 6 g L^-1 of adsorbent, 10 mg L^-1 to 250 mg L^-1 of organic pollutants (dyes) and pH between 2 and 8. Spent adsorbents in dye removal have proven to have near 95% efficiency in metallic ion adsorption. Otherwise, the spent solids could be applied to remove Ca²⁺ and Mg²⁺ to decrease the hardness of water. Furthermore, at the end-of-life, these materials could be used in cement and ceramic production. To achieve these aims, it is necessary to design the bioadsorbents and biocatalysts considering not only their primary uses (as adsorbent of organic pollutants), but also secondary applications (as toxic metal or hardness removal) and even their final destination (as additive in ceramic or cement production). Finally, further studies are required on the composition, properties, stability at long-term and the life-cycle cost of these materials when they are applied in the construction industry.

Determination of Adsorption of Methylene Blue Dye by Incense Stick Ash Waste and Its Toxicity on RTG-2 Cells

Incense stick ash (ISA) has traces of toxic heavy metals which have an adverse effect on the environment. Every year, tonnes of ISA are disposed of in rivers and other water bodies which leads to water pollution and affects the natural water resources. ISA has several value-added minerals which could be modified or functionalized for environmental cleanup. Here, in the current research work, ISA was transformed into a flower-like noble porous material by mixing ISA and NaOH in a 1 : 1 ratio followed by calcination at 600°C for six hours in a muffle furnace. The developed material was analyzed by sophisticated instruments for the identification of the properties. The microscopic techniques revealed the micron-sized flower-like structure, while the XRD showed peaks at 30–33° which indicates the transformation of the calcite and silicate phases into new-phase mineral. FTIR also revealed bands in regions of 500–1200 cm−1 and new bands near 450 cm−1. EDS confirmed the presence of Na in the sintered product and the transformation of the ISA. Finally, the sintered product potential was assayed for the removal of methylene blue dye from wastewater using an adsorption mechanism. The removal efficiency of dye reached up to 70% within one hour only. It was found that the ISA sintered product has the potential to remove MB dye efficiently from wastewater and also reduce solid waste pollution. Microculture tetrazolium assay (MTT) and lactate dehydrogenase (LDH) assays were performed to evaluate the cytotoxicity of the sintered incense stick ash product on RTG-2 cells. The sintered incense stick ash product induced cytotoxicity on RTG-2 cells in a dose-dependent manner. Sintered ISA products have the potential to remove methylene blue dye efficiently from wastewater and reduce solid waste pollution.

New insights into the selective adsorption mechanism of cationic and anionic dyes using MIL-101(Fe) metal-organic framework: Modeling and interpretation of physicochemical parameters

In the current study, iron-based metal organic framework (MOF) MIL-101(Fe) was successfully prepared via a facile solvothermal method. The as-synthesized MIL-101(Fe) was characterized by XRD, FE-SEM, FTIR, TGA and zeta potential techniques, and then employed as an adsorbent for methyl orange (MO) and methylene blue (MB) dyes. The adsorbed quantities of MO (1067 to 831 mg/g) were higher than those of MB (402 to 353 mg/g) indicating the high selectivity of MIL-101(Fe) towards the anionic dye at all temperatures (20-60 °C). Adsorption processes of MO and MB followed the pseudo-second order kinetics and the Langmuir equilibrium model. The interaction mechanism at a molecular level was analyzed and deeply interpreted via the advanced multilayer adsorption model. Steric parameters indicated that MO molecular aggregation (n) was 0.95-1.33 thus signifying the presence of multi-docking and multi-interactions mechanisms. The aggregated number of MB was superior to unity (i.e., n = 1.17-1.78) suggesting a vertical adsorption position and a multi-interactions mechanism at all operating temperatures. The density of MIL-101(Fe) active sites (D_{M =} 77.33-52.38 mg/g for MB and 149.91-107.07 for MO) and the total adsorbed dye layers (N_t = 3.12-2.49 for MB and 5.36-3.67 for MO) resulted in improving the adsorption capacities of MO dye. The adsorption energies ranged from 8.89 to 33.73 kJ/mol and they displayed that MO and MB uptake processes were exothermic controlled by physical interactions at all temperatures. Regeneration results indicated that this adsorbent can be reutilized without a significant loss in its removal efficiency after five adsorption-desorption cycles. Overall, the adsorption capacity, chemical stability, and regeneration performance of MIL-101(Fe) support its application as a very promising adsorbent for the removal of organic hazardous pollutants from water.

Photosensitized Thermoplastic Nano-Photocatalysts Active in the Visible Light Range for Potential Applications Inside Extraterrestrial Facilities

Among different depollution methods, photocatalysis activated by solar light is promising for terrestrial outdoor applications. However, its use in underground structures and/or microgravity environments (e.g., extraterrestrial structures) is forbidden. In these cases, there are issues related to the energy emitted from the indoor lighting system because it is not high enough to promote the photocatalytic mechanism. Moreover, microgravity does not allow the recovery of the photocatalytic slurry from the depolluted solution. In this work, the synthesis of a filmable nanocomposite based on semiconductor nanoparticles supported by photosensitized copolyacrylates was performed through a bulk in situ radical copolymerization involving a photosensitizer macromonomer. The macromonomer and the nanocomposites were characterized through UV-Vis, fluorescence and NMR spectroscopies, gel permeation chromatography and thermogravimetric analysis. The photocatalytic activity of the sensitized nanocomposites was studied through photodegradation tests of common dyes and recalcitrant xenobiotic pollutants, employing UV-Vis and visible range (λ > 390 nm) light radiations. The sensitized nanocomposite photocatalytic performances increased about two times that of the unsensitized nanocomposite and that of visible range light radiation alone (>390 nm). The experimental data have shown that these new systems, applied as thin films, have the potential for use in indoor deep underground and extraterrestrial structures.

A Facile Review on the Sorption of Heavy Metals and Dyes Using Bionanocomposites

Presently, hazardous metal and dye removal from wastewater is one of the major areas of research focus. For the elimination of these contaminants, many approaches have been devised and applied. However, the accomplishment of various water treatment processes has largely depended on the medium utilized and the associated problem with the leaching of harmful compounds into the water process with most commercial and chemically manufactured materials for water treatment processes. Hence, this study is aimed at reviewing existing studies on the sorption of heavy metals (HMs) and dyes using bionanocomposites (BNCs). The key focus of this review is on the development of eco-friendly, effective, and appropriate nanoadsorbents that could accomplish superior and enhanced contaminant sequestration using BNCs owing to their biodegradability, biocompatible, environmentally friendly, and not posing as secondary waste to the environment. The sorption of most pollutants was observed to be pH, sorbent dosage, and initial contaminant concentration-dependent, with most contaminants’ elimination taking place in the pH range of 2-10. The sorption process of HMs and dyes to various BNCs was superlatively depicted utilizing the Langmuir (LNR) and Freundlich (FL) as well as the pseudo-second-order (PSO) models, suggestive of the sorption process of a monolayer and multilayer and the chemisorption process, the rate-limiting stage in surface sorption. The established sorption capacities for the reviewed sorption process for various contaminants ranged from 1.47 to 740.97 mg/g. Future prospective for the treatment and remediation of contaminated water using BNCs was also discussed.

Novel magnetic nickel ferrite nanoparticles modified with poly(aniline-co-o-toluidine) for the removal of hazardous 2,4-dichlorophenol pollutant from aqueous solutions

Chlorinated organic and phenolic compounds are still purely studied by many researchers because of their severe damage to the aquatic environment and their carcinogenic effect on many living organisms. Therefore, there is a great interest in removing these environmental pollutants from aqueous mediums by easy and inexpensive methods. Herein, novel nickel ferrite (NiFe2O4) nano composite modified with poly(aniline-co-o-toluidine) (PAOT) is prepared, characterized, and used for the removal of 2,4-dichlorophenol (2,4-DCP) as an organic chlorinated environmental pollutant. The morphological properties of the composite are characterized by Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and Brunauer-Emmett-Teller (BET) methods. The prepared composite is tested for the removal of the hazardous dichlorophenol pollutant from aqueous solutions. Under optimized conditions and with effective control of parameters including, contact time, pH of the test solution, adsorbent dose, and temperature, over 83% of the pollutant is adsorbed and removed. The adsorption capacity is 162 mg g-1. Adsorption kinetics, adsorption isotherm and some physicochemical parameters of the reaction are evaluated. The Redlich-Peterson isothermal model is the appropriate model for describing the adsorption process. These results indicate that NiFe2O4/PAOT nanocomposites are promising adsorbents for the removal of persistent organic pollutants (e.g., DCP) from aqueous solutions. The results also reveal that modification of NiFe2O4 particles with poly(aniline-co-o-toluidine) (PAOT) significantly enhances the adsorption capacity of the adsorbent. This is probably due to the electrostatic attraction and non-covalent interactions (e.g. π-π) between the aromatic rings in both dichlorophenol and poly(aniline-co-o-toluidine) copolymer. Advantages offered by using NiFe2O4/PAOT nanocomposites are the high stability, reasonable efficiency, reusability for at least five adsorption-desorption cycles and the ability to remove the adsorbent from aqueous solutions for reuse using an external magnetic field.

A Comprehensive Review of Effective Adsorbents Used for the Removal of Dyes from Wastewater

Aim:

The objective of the review paper aims to explore and to provide the insight of various low-cost adsorbents prepared and used in the removal of hazardous dye pollutants from the contaminated industrial effluents.

Background:

The major untreated discharge from the textile industries constitutes a wide range of organic contaminants with the enhanced concentration of biological oxygen demand and chemical oxygen demand inthe water bodies. Dyes are considered as the major water contaminants and this quest the researchers to adopt various technologies to remove the hazardous dye pollutants from the aquatic environment. Dyes are the chemical compounds that tend to adhere themselves with metal or salts by covalent bond formation or complexes by mechanical retention or physical adsorption so as to impart colours to which it is being applied.

Objective:

Numerous treatment methodologies which have been applied to the degradation of dyes. The current study has been focused on the distinct low cost and cost-effective adsorbents used in the removal of various dye pollutants. Also, the application of nanoparticles in the removal of the hazardous dye pollutants had received great interest because of its size and high reactive nature.

Methods:

The treatment technologies used in the removal of dye pollutants from wastewater have been listed as adsorption, coagulation, electrocoagulation, flocculation, membrane filtration, oxidation and biological treatment.

Results:

The complex structure of the dyes causes a great harmful impact on the aquatic environment. Though numerous treatment technologies have been applied, adsorption has been preferred by various researchers because of its cost-effective nature.

Conclusion:

The various adsorbents are used in the removal of cationic, anionic and non-ionic dyes. The different types of adsorbent from agricultural waste, activated carbons, nanomaterials and biomaterials have been discussed with the advantages and limitations.

Nanomaterials for Remediation of Environmental Pollutants

Today, environmental contamination is a big concern for both developing and developed countries. The primary sources of contamination of land, water, and air are extensive industrialization and intense agricultural activities. Various traditional methods are available for the treatment of different pollutants in the environment, but all have some limitations. Due to this, an alternative method is required which is effective and less toxic and provides better outcomes. Nanomaterials have attracted a lot of interest in terms of environmental remediation. Because of their huge surface area and related high reactivity, nanomaterials perform better in environmental clean-up than other conventional approaches. They can be modified for specific uses to provide novel features. Due to the large surface-area-to-volume ratio and the presence of a larger number of reactive sites, nanoscale materials can be extremely reactive. These characteristics allow for higher interaction with contaminants, leading to a quick reduction of contaminant concentration. In the present review, an overview of different nanomaterials that are potential in the remediation of environmental pollutants has been discussed.

Layered double hydroxide-modified membranes for water treatment: Recent advances and prospects

Layered double hydroxides (LDHs) represent an exciting class of two-dimensional inorganic materials with unique physicochemical properties. They have been widely employed in water treatment due to their high surface areas, excellent ion exchange capacities, and highly tunable structures. They have also been employed in the fabrication and development of membranes for water treatment. 2D nanostructures as well as tailorable "structure forming units", surface functionalization with desired moieties, and interlayer galleries with adjustable heights and internal compositions make them attractive materials for membrane separations. This paper critically overviews the recent advancements in the synthesis and applications of LDH based membranes in water purification. The synthesis techniques and the effect of LDH incorporation into different membrane compositions have been described. LDH-based membranes showed excellent antifouling capability and improved water flux due to enhanced hydrophilicity. Such membranes have been successfully used for the treatment of inorganics, organics from environmental water samples. This review will be useful for understanding the current state of the LDH-based membranes for water purification and defining future research dimensions. In the end, we highlight some challenges and future prospects for the efficient application of LDH-based membranes in water decontamination.

Graphene oxide loaded fibrous matrixes of polyether block amide (PEBA) elastomer as an adsorbent for removal of cationic dye from wastewater

Novel highly porous nanoparticle materials are increasingly being applied in adsorption processes, but they need to be supported by robust matrixes to maintain their functionality. We present a study of hosting graphene oxide (GO) particles on polyether block amide (PEBA) melt electrospun fibers and applying such composite matrix to the adsorption of the cationic dye (crystal violet) from water. Various amounts of GO (from 0.5 to 2.0%) were mixed into pure PEBA and electrospun by melt electrospinning obtaining micro fibrous matrixes. These were characterized for morphology (SEM), chemical composition (FTIR), crystallinity (XRD), and wetting behavior (WCA). The increasing amount of GO adversely affected fiber diameter (reduced from 13.18 to 4.38 μm), while the hydrophilic properties (Water contact angle decrease from 109 to 76°) and overall dye adsorption was increased. Efficient adsorption has been demonstrated, reaching approximately 100 % removal efficiency using a 2% GO composite matrix at a dose of 40 mg/l and pH of 10. Further increase of GO concentration in polymer is not feasible due to instability in the electrospinning process.

MXene-based designer nanomaterials and their exploitation to mitigate hazardous pollutants from environmental matrices

MXenes are a rapidly expanding and large family of two-dimensional (2D) materials that have recently garnered incredible research interests for diverse applications domains in various industrial sectors. Owing to unique inherent structural and physicochemical characteristics, such as high surface area, biological compatibility, robust electrochemistry, and high hydrophilicity, MXenes are appraised as a prospective avenue for environmental-clean-up technologies to detect and mitigate an array of recalcitrant hazardous contaminants from environmental matrices. MXene-based nanoarchitectures are thought to mitigate inorganic pollutants via interfacial chemical transformation and sorption, while three different mechanisms, including i) surface complexation and sorption (ii) catalytic activation and removal and (iii) radical's generation-based photocatalytic degradation, are involved in the removal of organic contaminants. Considering the application performance of MXenes on the incessant rise to expansion, in this review, we discuss the wide-spectrum applicability of diverse MXenes-based hybrid nanocomposites in environmental remediation. A brief description related to environmental pollutants, structural properties, chemical abilities, and synthesis route of MXenes is delineated at the start. Afterwards, the adsorption and degradative robustness of MXene-based designer nanomaterials for various contaminants including organic dyes, toxic heavy metals, pesticide residues, phenolics, antibiotics, radionuclides, and many others are thoroughly vetted to prove their potentiality in the arena of wastewater purification and remediation. Lastly, challenges and trends in assessing the wide-range applicability and scalability of MXenes are outlined. Seeing encouraging outcomes in plenty of reports, it can be concluded that MXenes-based nanostructures could be considered the next-generation candidates for water sustainability.

Advances in the Application of Nanocatalysts in Photocatalytic Processes for the Treatment of Food Dyes: A Review

The use of food additives (such as dyes, which improve the appearance of the products) has become more prominent, due to the rapid population growth and the increase in demand for beverages and processed foods. The dyes are usually found in effluents that are discharged into the environment without previous treatment; this promotes mass contamination and alters the aquatic environment. In recent years, advanced oxidation processes (AOPs) have proven to be effective technologies used for wastewater treatment through the destruction of the total organic content of toxic contaminants, including food dyes. Studies have shown that the introduction of catalysts in AOPs improve treatment efficiency (i.e., complete decomposition without secondary contamination). The present review offers a quick reference for researchers, regarding the treatment of wastewater containing food dyes and the different types of AOPs, with different catalyst and nanocatalyst materials obtained from traditional and green chemical syntheses.

Potential of nanocellulose for wastewater treatment

Wastewater management has significant interest worldwide to establish viable treatment techniques to ensure the availability of clean water. The specialities of nanocellulose for this particular application is due to their high aspect ratio and accessibility of plenty of -OH groups for binding with dyes, heavy metals and other pollutants. This review aggregates the application of nanocellulose for wastewater treatment particularly as adsorbents of dyes and heavy metals, and also as membranes for filtering various other contaminants including microbes. The membrane technologies are proven to be effective relating to their durability and separation effectiveness. The commercial scale application of nanocellulose based materials in water treatment processes depend on various factors like routes of synthesis, surface modifications, hydrophilic/hydrophobic, porosity, durability etc. The recent developments on production of novel adsorbents or membranes encourage the implementation of nanocellulose based cleaner technologies for wastewater treatment.

Toward enhanced catalytic activity of magnetic nanoparticles integrated into 3D reduced graphene oxide for heterogeneous Fenton organic dye degradation

Composite Fenton nanocatalyst was prepared by water-based in situ creation of Fe3O4 nanoparticles integrated within the self-assembly 3D reduced graphene oxide (rGO) aerogel. The hybrid applied for the degradation of Acid Green 25 (AG-25) organic dye in an aqueous solution, in the presence of H2O2. By investigating the conditions that maximize the dye adsorption by the 3D composite, it was found that the pH of the solution should be adjusted between the pKa of the functional groups present on the rGO surface (carboxylic acid) and that of the dye (sulfonic acid) to promote electrostatic interactions dye-3D structure. Performed under these conditions, Fenton degradation of AG-25 in presence of H2O2 was completed in less than 30 min, including all the intermediate products, as demonstrated by MALDI-TOF-MS analysis of the aqueous solution after discoloration. Moreover, this was achieved in a solution with as high a dye concentration of 0.5 mg/mL, with only 10 mg of 3D composite catalyst, at room temperature and without additional energy input. The high performance was attributed to the creation of charge-transfer complex between rGO and Fe3O4 nanoparticles throughout covalent bond C-O-Fe, the formation of which was promoted by the in situ synthesis procedure. For the first time, up to the authors' knowledge, AG-25 degradation mechanism was proposed.

Factors Affecting Synthetic Dye Adsorption; Desorption Studies: A Review of Results from the Last Five Years (2017-2021)

The primary, most obvious parameter indicating water quality is the color of the water. Not only can it be aesthetically disturbing, but it can also be an indicator of contamination. Clean, high-quality water is a valuable, essential asset. Of the available technologies for removing dyes, adsorption is the most used method due to its ease of use, cost-effectiveness, and high efficiency. The adsorption process is influenced by several parameters, which are the basis of all laboratories researching the optimum conditions. The main objective of this review is to provide up-to-date information on the most studied influencing factors. The effects of initial dye concentration, pH, adsorbent dosage, particle size and temperature are illustrated through examples from the last five years (2017-2021) of research. Moreover, general trends are drawn based on these findings. The removal time ranged from 5 min to 36 h (E = 100% was achieved within 5-60 min). In addition, nearly 80% efficiency can be achieved with just 0.05 g of adsorbent. It is important to reduce adsorbent particle size (with Φ decrease E = 8-99%). Among the dyes analyzed in this paper, Methylene Blue, Congo Red, Malachite Green, Crystal Violet were the most frequently studied. Our conclusions are based on previously published literature.

Environmentally benign hybrid nanocomposite beads for azo dye remediation via synchronized dual degradation mechanisms

Practically, 12% of used dyes are excluded as waste in the mobile aqueous environment. Methyl orange (MO), an industrial azo dye, is known to be carcinogenic. Accordingly, this work was engaged to fabrication of a high-efficiency visible light photocatalysts based on Ag-Alginate/Chitosan-coated MgO nanocomposite beads. MgO and Ag were prepared via precipitation and γ-radiation reduction technique as a green physical one, respectively. The degradation mechanisms depended on catalytic reduction by means of sodium borohydride/Ag and photooxidative degradation. XRD proved the periclase crystalline form of MgO of size 20 nm and the formation of face-centered cubic silver crystals of size 15 nm. The degradation yield varied directly with time, MgO, and dye concentration until certain limit. Five and twenty minutes were enough to get clear solution of MO (30 and 15 ppm, respectively) while 60 min was required to achieve the same target for 60 ppm MO solution. The catalysts showed high efficiency for MO of high concentration. The incorporation of Ag into catalytic beads could support both mechanisms as it could elevate the degradation efficiency up to 50% and save the time to a great extent. Thus, this carrier fruitfully converted wastewater into an effluent that can be repaid to the water cycle with minimal strike on the ecosystem.

Biomedical Applications of Antiviral Nanohybrid Materials Relating to the COVID-19 Pandemic and Other Viral Crises

The COVID-19 pandemic has driven a global research to uncover novel, effective therapeutical and diagnosis approaches. In addition, control of spread of infection has been targeted through development of preventive tools and measures. In this regard, nanomaterials, particularly, those combining two or even several constituting materials possessing dissimilar physicochemical (or even biological) properties, i.e., nanohybrid materials play a significant role. Nanoparticulate nanohybrids have gained a widespread reputation for prevention of viral crises, thanks to their promising antimicrobial properties as well as their potential to act as a carrier for vaccines. On the other hand, they can perform well as a photo-driven killer for viruses when they release reactive oxygen species (ROS) or photothermally damage the virus membrane. The nanofibers can also play a crucial protective role when integrated into face masks and personal protective equipment, particularly as hybridized with antiviral nanoparticles. In this draft, we review the antiviral nanohybrids that could potentially be applied to control, diagnose, and treat the consequences of COVID-19 pandemic. Considering the short age of this health problem, trivially the relevant technologies are not that many and are handful. Therefore, still progressing, older technologies with antiviral potential are also included and discussed. To conclude, nanohybrid nanomaterials with their high engineering potential and ability to inactivate pathogens including viruses will contribute decisively to the future of nanomedicine tackling the current and future pandemics.

Advanced Oxidation Processes Coupled with Nanomaterials for Water Treatment

Water quality management will be a priority issue in the near future. Indeed, due to scarcity and/or contamination of the water, regulatory frameworks will be increasingly strict to reduce environmental impacts of wastewater and to allow water to be reused. Moreover, drinking water quality standards must be improved in order to account for the emerging pollutants that are being detected in tap water. These tasks can only be achieved if new improved and sustainable water treatment technologies are developed. Nanomaterials are improving the ongoing research on advanced oxidation processes (AOPs). This work reviews the most important AOPs, namely: persulfate, chlorine and NH₂Cl based processes, UV/H₂O₂, Fenton processes, ozone, and heterogeneous photocatalytic processes. A critical review of the current coupling of nanomaterials to some of these AOPs is presented. Besides the active role of the nanomaterials in the degradation of water contaminants/pollutants in the AOPs, the relevance of their adsorbent/absorbent function in these processes is also discussed.

Recent Advances in Biopolymer-Based Dye Removal Technologies

Synthetic dyes have become an integral part of many industries such as textiles, tannin and even food and pharmaceuticals. Industrial dye effluents from various dye utilizing industries are considered harmful to the environment and human health due to their intense color, toxicity and carcinogenic nature. To mitigate environmental and public health related issues, different techniques of dye remediation have been widely investigated. However, efficient and cost-effective methods of dye removal have not been fully established yet. This paper highlights and presents a review of recent literature on the utilization of the most widely available biopolymers, specifically, cellulose, chitin and chitosan-based products for dye removal. The focus has been limited to the three most widely explored technologies: adsorption, advanced oxidation processes and membrane filtration. Due to their high efficiency in dye removal coupled with environmental benignity, scalability, low cost and non-toxicity, biopolymer-based dye removal technologies have the potential to become sustainable alternatives for the remediation of industrial dye effluents as well as contaminated water bodies.

Tailoring the Effects of Titanium Dioxide (TiO2) and Polyvinyl Alcohol (PVA) in the Separation and Antifouling Performance of Thin-Film Composite Polyvinylidene Fluoride (PVDF) Membrane

In this study, thin-film composite (TFC) polyvinylidene fluoride (PVDF) membranes were synthesized by coating with titanium dioxide (TiO₂)/polyvinyl alcohol (PVA) solution by a dip coating method and cross-linked with glutaraldehyde. Glutaraldehyde (GA) acted as a cross-linking agent to improve the thermal and chemical stability of the thin film coating. The incorporation of TiO₂ in the film enhanced the hydrophilicity of the membrane and the rejection of dyes during filtration. The layer of TiO₂ nanoparticles on the PVDF membranes have mitigated the fouling effects compared to the plain PVDF membrane. The photocatalytic performance was studied at different TiO₂ loading for the photodegradation of dyes (reactive blue (RB) and methyl orange (MO)). The results indicated that the thin film coating of TiO₂/PVA enhanced photocatalytic performance and showed good reusability under UV irradiation. This study showed that nearly 78% MO and 47% RB were removed using the TFC membrane. This work provides a new vision in the fabrication of TFC polymeric membranes as an efficient wastewater treatment tool.

Bi/SnO2/TiO2-graphene nanocomposite photocatalyst for solar visible light-induced photodegradation of pentachlorophenol

In this study, for the first time, a TiO₂/graphene (G) heterostructure was synthesized and doped by Bi and SnO₂ nanoparticles through a hydrothermal treatment. The as-synthesized nanocomposite was employed for photocatalytic degradation of pentachlorophenol (PCP) under visible light irradiation. Structural characterizations such as X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD) proved the valence band alignment at Bi/SnO₂/TiO₂-G interfaces and crystallinity of the nanocomposite, respectively. The as-developed nanocomposite photocatalyst was able to decompose 84% PCP, thanks to the generation of a large number of active OH^•- and O₂^•- radicals. To achieve this optimum photodegradation efficiency, various parameters such as pH, catalyst dosage, and PCP concentration were optimized. The results showed that the PCP photodegradation process followed the first-order kinetic model and the reaction rate constant rose from 0.007 min^-1 (Bi) to 0.0149 min^-1 (Bi/SnO₂/TiO₂-G). The PCP photodegradation efficiency did not decrease significantly after 5 cycles, and the nanocomposite photocatalyst still showed a high efficiency of 68% in the last cycle. The excellent photocatalytic activity of Bi/SnO₂/TiO₂-G is ascribed as well as the heterostructure of the nanocomposite photocatalyst.

A Review on Polymer Nanocomposites and Their Effective Applications in Membranes and Adsorbents for Water Treatment and Gas Separation

Globally, environmental challenges have been recognised as a matter of concern. Among these challenges are the reduced availability and quality of drinking water, and greenhouse gases that give rise to change in climate by entrapping heat, which result in respirational illness from smog and air pollution. Globally, the rate of demand for the use of freshwater has outgrown the rate of population increase; as the rapid growth in town and cities place a huge pressure on neighbouring water resources. Besides, the rapid growth in anthropogenic activities, such as the generation of energy and its conveyance, release carbon dioxide and other greenhouse gases, warming the planet. Polymer nanocomposite has played a significant role in finding solutions to current environmental problems. It has found interest due to its high potential for the reduction of gas emission, and elimination of pollutants, heavy metals, dyes, and oil in wastewater. The revolution of integrating developed novel nanomaterials such as nanoparticles, carbon nanotubes, nanofibers and activated carbon, in polymers, have instigated revitalizing and favourable inventive nanotechnologies for the treatment of wastewater and gas separation. This review discusses the effective employment of polymer nanocomposites for environmental utilizations. Polymer nanocomposite membranes for wastewater treatment and gas separation were reviewed together with their mechanisms. The use of polymer nanocomposites as an adsorbent for toxic metals ions removal and an adsorbent for dye removal were also discussed, together with the mechanism of the adsorption process. Patents in the utilization of innovative polymeric nanocomposite membranes for environmental utilizations were discussed.

Fabrication of the magnetic mesoporous silica Fe-MCM-41-A as efficient adsorbent: performance, kinetics and mechanism

Antibiotics are emerging pollutants and increasingly present in aquaculture and industrial wastewater. Due to their impact on the environment and health, their removal has recently become a significant concern. In this investigation, we synthesized nano zero-valent iron-loaded magnetic mesoporous silica (Fe-MCM-41-A) via precipitation and applied the adsorption of oxytetracycline (OTC) from an aqueous solution. The effects of competing ions such as Na⁺, Ca²⁺ and Cu²⁺ on the adsorption process under different pH conditions were studied in depth to providing a theoretical basis for the application of nanomaterials. The characterization of the obtained material through transmission electron microscopy demonstrates that the adsorbent possesses hexagonal channels, which facilitate mass transfer during adsorption. The loaded zero-valent iron made the magnetic, and was thus separated under an applied magnetic field. The adsorption of OTC onto Fe-MCM-41-A is rapid and obeys the pseudo-second-order kinetic model, and the maximum adsorption capacity of OTC is 625.90 mg g^-1. The reaction between OTC and Fe-MCM-41-A was inner complexation and was less affected by the Na⁺. The effect of Ca²⁺ on the adsorption was small under acidic and neutral conditions. However, the promotion effect of Ca²⁺ increased by the increase of pH. Cu²⁺ decreased the removal efficiencies continuously and the inhibitory effects decrease varied with the increase of pH. We propose that surface complexing, ion-exchange, cationic π-bonding, hydrogen bonding, and hydrophobicity are responsible for the adsorption of OTC onto Fe-MCM-41-A.

Photocatalytic and Antibacterial Properties of Ag-CuFe2O4@WO3 Magnetic Nanocomposite

This study aimed to synthesize a new magnetic photocatalytic nanosystem composed of Ag-CuFe2O4@WO3 and to investigate its photodegradation efficiency for two drug pollutants of Gemfibrozil (GEM) and Tamoxifen (TAM) under Ultraviolet (UV) light irradiation. In this regard, the effect of pH, catalyst dosage, and drug concentration was thoroughly determined. The largest photodegradation level for GEM (81%) and TAM (83%) was achieved at pH 5, a photocatalyst dosage of 0.2 g/L, drug concentration of 5 mg/L, and contact time of 150 min. The drug photodegradation process followed the pseudo first-order kinetic model. In addition to the photodegradation effect, the nanocomposites were proved to be efficient in terms of antibacterial activity, proportional to the Ag doping level. The Ag-CuFe2O4@WO3 nanocomposite exhibited a stable, efficient performance without an obvious catalytic loss after five successive cycles. Taken together, the developed magnetic photocatalyst is able to simultaneously disinfect wastewater streams and to degrade pharmaceutical contaminants and thus shows a promising potential for purification of multi-contaminant water systems.

Gradient Adsorption of Methylene Blue and Crystal Violet onto Compound Microporous Silica from Aqueous Medium

Microporous silica (MS) materials are a kind of an emerging and promising adsorbent precursor. MS prepared from vermiculite has the advantages of easy preparation, low cost, and low layer charge. In this study, organo-MS (OMS) modified by a typical gemini surfactant 1,2-bis(hexadecyldimethylammonio)ethane dibromide (G₁₆) is first synthesized and proved to have effective retention capacity toward cationic dyes. Fourier transform infrared spectroscopy, TG-DTG, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller are used to explore the structural characters of adsorbents. Gradient adsorption of compound MS (MS and OMS) in a binary dye system [methylene blue (MB) and crystal violet (CV)] was investigated. In a single system, the relationship between the adsorption capacity and influencing factors (dye concentration, contact time, temperature, and pH), adsorption kinetics, isotherms, as well as thermodynamics was comprehensively compared to reveal the adsorption mechanism. The adsorption values of MB and CV on MS and OMS are 308 mg g^-1 (R = 77.0%, 15 min) and 250 mg g^-1 (R = 83.3%), respectively, which may be caused by various intermolecular interactions (electrostatic or hydrophobic interactions) between the dye and adsorbent surface. In a binary system, the improved first spectroscopy method is used to calculate the individual concentration of the dye in the binary system. The total removal efficiency of gradient adsorption reaches as high as 89.5% (MB) and 86.4% (CV). In addition, compound MS can be effectively regenerated by HCl solution for several cycles.