Construction of 3D-Printed Sodium Alginate/Chitosan/Halloysite Nanotube Composites as Adsorbents of Methylene Blue

In this study, sodium alginate/chitosan/halloysite nanotube composites were prepared by three-dimensional printing and characterized in terms of morphology, viscosity, thermal properties, and methylene blue (MB) adsorption performance. The high specific surface area and extensively microporous structure of these composites allowed for effective MB removal from wastewater; specifically, a removal efficiency of 80% was obtained after a 60 min treatment at an adsorbent loading of 1 g L-1 and an MB concentration of 80 mg L-1, while the maximum MB adsorption capacity equaled 376.3 mg g-1. Adsorption kinetics and isotherms were well described by quasi-second-order and Langmuir models, respectively. The composites largely retained their adsorption performance after five adsorption-desorption cycles and were concluded to hold great promise for MB removal from wastewater.

Preparation of KHA/SA/MMT composites and their adsorption properties for Rhodamine B

Two natural adsorbent materials, potassium humate (KHA) and montmorillonite (MMT), were successfully prepared by embedding them in sodium alginate (SA) gel spheres through physical cross-linking with CaCl2. And CaCO3 was used as a porogenic agent to prepare the porous composites, KHA/SA/MMT. The materials were characterized by using XRD, TGA, SEM, and N2 adsorption/desorption equipment. The results showed that MMT and KHA were successfully embedded in the SA gel; the introduction of MMT increased the thermal stability of the composites and the embedding of MMT, and the porogenic effect of CaCO3 increased the specific surface area of the composites substantially, which provided favorable conditions for adsorption and treatment of pollutants. In addition, a one-way exploratory experiment yielded a higher removal rate of Rhodamine B (RhB) at D = 0.6 g/L, pH = 5, C0 = 100 mg/L, and t = 360 min. The adsorption kinetics and adsorption isotherm conformed to the secondary kinetic model and Langmuir model, respectively, and the maximum adsorption of RhB by KHA/SA/MMT could reach up to 884.96 mg/g at 303 K. The adsorption mechanism for RhB was shown by FT-IR and XPS analyses to be possibly bound by non-covalent bonding forces. After seven consecutive adsorption-desorption cycles, the adsorption of RhB by KHA/SA/MMT still reached 80.75%. Therefore, the prepared gel spheres have the advantages of easy regeneration and efficient reuse and great potential for application in purifying RhB from wastewater.

An Updated Overview of Magnetic Composites for Water Decontamination

Water contamination by harmful organic and inorganic compounds seriously burdens human health and aquatic life. A series of conventional water purification methods can be employed, yet they come with certain disadvantages, including resulting sludge or solid waste, incomplete treatment process, and high costs. To overcome these limitations, attention has been drawn to nanotechnology for fabricating better-performing adsorbents for contaminant removal. In particular, magnetic nanostructures hold promise for water decontamination applications, benefiting from easy removal from aqueous solutions. In this respect, numerous researchers worldwide have reported incorporating magnetic particles into many composite materials. Therefore, this review aims to present the newest advancements in the field of magnetic composites for water decontamination, describing the appealing properties of a series of base materials and including the results of the most recent studies. In more detail, carbon-, polymer-, hydrogel-, aerogel-, silica-, clay-, biochar-, metal-organic framework-, and covalent organic framework-based magnetic composites are overviewed, which have displayed promising adsorption capacity for industrial pollutants.

Kinetic adsorption of methyl blue dye from aqueous solution by PVC/PVC-based copolymer containing quaternary amine

The present study has investigated the use of a blend polymer polyvinyl chloride/polyvinyl chloride-graft-poly[2-(dimethylamino) ethyl methacrylate containing a quaternary amine in its structure (PVC/PVC-g-PDMAEM(N⁺)) as an adsorbent for the removal of methyl blue dye from aqueous solution. The synthesized polymer blend has been characterized by Fourier Transform Infrared Spectroscopy (FT-IR), scanning Electron Microscope-energy-dispersive spectroscopy (SEM-EDX), and the scanning Spectrophotometer Ultraviolet-visible (UV-Vis). The adsorption studies have been performed by batch experiments. Moreover, the pH effect, adsorbent dose, initial dye concentration, and contact time effect have been explored. Furthermore, the kinetic experimental data have been analyzed using pseudo-first and pseudo-second-order models. The results have shown that the adsorption process is more described by the pseudo-second-order model with a high determination coefficient. The equilibrium adsorption data have been analyzed using three widely applied isotherms: Langmuir, Freundlich, and Tempkin. The best fit was found to be Freundlich isotherm with maximum monolayer adsorption of Methyl Blue (MB) equal to 142.86 mg/g, which was observed at pH = 7. The results have indicated that the PVC/PVC-g-PDMAEM(N⁺) blend polymer is an efficient adsorbent for removing anionic dyes from wastewater.

Matrix-dispersed PEI-coated SPIONs for fast and efficient removal of anionic dyes from textile wastewater samples: Applications to triphenylmethanes

Textile industries produce a massive amount of wastewater that should be cleaned from toxic substances such as fats, colors and any chemicals used during the production steps. Water-treatment methods should be facile, economic, fast and efficient. Here, we report the synthesis, characterization and application of matrix-dispersed superparamagnetic iron oxide nanoparticles (SPIONs) for the removal of anionic dyes from wastewater released from textile industrial plants. The matrix-dispersed SPIONs were synthesized via a solvothermal method in which a polyethyleneimine (PEI) shell was deposited onto SPIONs in order to add positive charges to their surfaces. TEM images revealed that the size of PEI-coated and uncoated SPIONs is 30-50 and 15-30 nm, respectively. Moreover, TEM images depicted that the as synthesized PEI-coated SPIONs show matrix-dispersed structures. Furthermore, the particle size obtained with DLS measurements was found to be 87.93 and 158.9 nm for uncoated and PEI-coated SPIONs, respectively. Bromophenol blue (BPB) and bromocresol green (BCG), two triphenylmethanes, were used as model anionic dyes. FTIR spectroscopy revealed the interaction between the PEI surface coating and the anionic dyes. The apparent ζ-potential measurements showed that the surface negative charges decreased from -13.5 to -4.03 mV upon coating with PEI. In order to investigate the anionic dyes removal/entrapment efficiency of SPIONs, a new derivative visible spectrophotometric method was developed for the simultaneous quantification of BPB and BCG before and after treatment where the linear ranges were 6.98-27.9 and 6.70-26.8 μg/mL and the recovery values were in the ranges of 98.10-101.7% and 99.55-104.8% for BCG and BPB, respectively. It was found that the uptake/adsorption capacity of PEI-coated SPIONs is ca.15.5 and 11.3 mg/g for BCG and BPB, respectively. The calculated thermodynamic parameters for the adsorption of BCG (ΔH = 37.08 J/mol and ΔS = 120.89 J/mol K) and BPB (ΔH = 181.26 J/mol and ΔS = 596.46 J/mol K) and the negative ΔG values indicate that the adsorption is thermodynamically favored. The adsorption processes were found to follow the pseudo-second-order kinetic model with r² values of 0.9982 and 0.9956 for BCG and BPB, respectively.

Preparation of Silicone Emulsion Defoamer with Easy Separation of Magnetic Hydrophobic Nanoparticles

To prepare lyophobic magnetic nanoparticles (LMNs) with core/shell structure to be applied in silicone emulsion defoamer, magnetic nanoparticles covered with silica (MNS) were prepared in a one-step process from FeCl3 · 6H2O, FeCl2 · 4H2O and tetraethyl orthosilicate and then modified with poly (methylhydrosiloxane). X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis (TGA), and contact angle tests were performed to characterize the nano-particles, and the droplets of the defoamer emulsion were observed with a microscope. The foam breaking and foam inhibition properties of the defoamer and the magnetic separation of the particles were observed and recorded by a camera. It was found that the silicone emulsion defoamer exhibited good foam breaking and foam inhibition properties for foaming systems with anionic, cationic and non-ionic surfactants, respectively. The solid particles in the defoamer could be easily separated from the defoamed systems by a magnet.

Adsorption properties of β-cyclodextrin modified hydrogel for methylene blue

With the development of dye and printing, production wastewater has become one of the most primary pollution sources of water and soil pollution. Most of the dyes are toxic substances, which have the "three-way" effect of carcinogenic, teratogenic and mutagenic. Therefore, it is a very difficult but significant issue to deal with the dye in the wastewater. Here, we report a study on low-cost, high-capacity hydrogels that remove water-soluble dyes. The hydrogel is prepared by crosslinking the β-cyclodextrin and functional monomer: acrylamido and 2-acrylamide-2-methylpropane sulfonic acid by aqueous solution polymerization, meanwhile, alkaline hydrolysis is also an important step for adsorption performance. After alkaline hydrolysis, the amide and sulfonic groups in the hydrogel were converted into carboxylate and sulfonate, which was beneficial to the adsorption of cationic dyes. This polymer could remove 96.58% methylene blue (400 mg/L) and only requires 0.02 wt%. Its maximum adsorption capacity for methylene blue could reach 2638.22 mg/g under equilibrium condition. It is the most powerful adsorbent used to treat dye wastewater, according to the report. It also provides some references for hydrogel treatment of dye wastewater.

Alkali-cation-incorporated and functionalized iron oxide nanoparticles for methyl blue removal/decomposition

Enhancing the rate of decomposition or removal of organic dye by designing novel nanostructures is a subject of intensive research aimed at improving waste-water treatment in the textile and pharmaceutical industries. Despite radical progress in this challenging area using iron-based nanostructures, enhancing stability and dye adsorption performance is highly desirable. In the present manuscript alkali cations are incorporated into iron oxide nanoparticles (IONPs) to tailor their structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for IONPs incubated in alkali chloride and hydroxide solutions are based on structural investigation and correlated with the removal/adsorption capabilities. The MB adsorption kinetics of the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only are the functional groups of -OH and -Cl attached to the surface of the NPs, the present investigation also reveals that the presence of alkali cations significantly influences the MB adsorption kinetics and correlates with the cation content and atomic polarizability.

Nanomaterials with Tailored Magnetic Properties as Adsorbents of Organic Pollutants from Wastewaters

Water quality has become one of the most critical issue of concern worldwide. The main challenge of the scientific community is to develop innovative and sustainable water treatment technologies with high efficiencies and low production costs. In recent years, the use of nanomaterials with magnetic properties used as adsorbents in the water decontamination process has received considerable attention since they can be easily separated and reused. This review focuses on the state-of-art of magnetic core–shell nanoparticles and nanocomposites developed for the adsorption of organic pollutants from water. Special attention is paid to magnetic nanoadsorbents based on silica, clay composites, carbonaceous materials, polymers and wastes. Furthermore, we compare different synthesis approaches and adsorption performance of every nanomaterials. The data gathered in this review will provide information for the further development of new efficient water treatment technologies.

Low-Temperature Synthesis of Magnetic Carbonaceous Materials Coated with Nanosilica for Rapid Adsorption of Methylene Blue

This work reports the synthesis of nanosilica-coated magnetic carbonaceous adsorbents (MCA@SiO₂) using low-temperature hydrothermal carbonization technique (HCT) and the feasibility to utilize it for methylene blue (MB) adsorption. Initially, a carbon precursor (CP) was synthesized from corn starch under saline conditions at 453 K via HCT followed by the magnetization of CP again via HCT at 453 K. Subsequently, MCA was coated with silica nanoparticles. MCA and MCA@SiO₂ were characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy/energy-dispersive spectroscopy, transmission electron microscopy, and Brunauer-Emmett-Teller (BET) N₂ adsorption-desorption isotherms. The BET surface area of MCA and MCA@SiO₂ were found to be 118 and 276 m² g^-1, respectively. Adsorption of MB onto MCA@SiO₂ was performed using batch adsorption studies and in the optimum condition, MCA@SiO₂ showed 99% adsorption efficiency with 0.5 g L^-1 of MCA@SiO₂ at pH 7. Adsorption isotherm studies predicted that MB adsorption onto MCA@SiO₂ was homogeneous monolayer adsorption, which was best described using a Langmuir model with the maximum adsorption capacity of 516.9 mg g^-1 at 25 °C. During adsorption kinetics, a rapid dye removal was observed which followed pseudo-first- as well as pseudo-second-order models, which suggested that MB dye molecules were adsorbed onto MCA@SiO₂ via both ion exchange as well as the chemisorption process. The endothermic and spontaneous nature of the adsorption of MB onto MCA@SiO₂ was established by thermodynamics studies. Mechanism of dye diffusion was collectively governed by intraparticle diffusion and film diffusion processes. Furthermore, MB was also selectively adsorbed from its mixture with an anionic dye, that is, methyl orange. Column adsorption studies showed that approximately 500 mL of MB having 50 mg L^-1 concentration can be treated with 0.5 g L^-1 of MCA@SiO₂. Furthermore, MCA@SiO₂ was repeatedly used for 20 cycles of adsorption-desorption of MB. Therefore, MCA@SiO₂ can be effectively utilized in cationic dye-contaminated wastewater remediation applications.

Facile design of a dextran derived polyurethane hydrogel and metallopolymer: a sustainable approach for elimination of organic dyes and reduction of nitrophenols

This work reports a sustainable approach for fabrication of a highly cost-effective and operation-convenient adsorbent derived from dextran and its valorization to a metallopolymer photocatalyst.

Continuous Flow Removal of Anionic Dyes in Water by Chitosan-Functionalized Iron Oxide Nanoparticles Incorporated in a Dextran Gel Column

This paper describes a novel chromatographic method for efficient removal of anionic dyes from aqueous solutions. Chitosan-coated Fe₃O₄ nanoparticles can easily be immobilized on a dextran gel column. Single elution of Evans Blue (EB) solution to the nanoadsorbent-incorporated columns provides high removal efficiency with a maximum adsorption capacity of 243.9 mg/g. We also investigated the influence of initial concentration and solution pH on the removal efficiency of EB. The electrostatic interaction between the adsorbent surface and negatively charged sulfate groups on EB molecules promotes the efficient adsorption of dyes. The equilibrium data matched well with the Langmuir isotherm model, which indicated monolayer dye adsorption onto the adsorbent surface. To extend the application of the current method, we performed further adsorption experiments using other anionic dyes of different colors (Cy5.5, Acid Yellow 25, Acid Green 25, and Acid Red 1). All of these molecules can efficiently be captured under continuous flow conditions, with higher removal efficiency obtained with more negatively charged dyes. These findings clearly demonstrate that the present approach is a useful method for the removal of anionic dye contaminants in aqueous media by adsorption.

Iron-based metal–organic framework as an effective sorbent for the rapid and efficient removal of illegal dyes

A metal organic framework (MOF-235) was fabricated by a simple solvothermal method and utilized as an adsorbent for the selective removal of electron-rich conjugated dyes.