Novelties of combustion synthesized titania ultrafiltration membrane in efficient removal of methylene blue dye from aqueous effluent

Photocatalytic degradation of methylene blue at nanostructured ZnO thin films

The photocatalytic degradation of the wastewater dye pollutant methylene blue (MB) at ZnO nanostructured porous thin films, deposited by direct current reactive magnetron sputtering on Si substrates, was studied. It was observed that over 4 photocatalytic cycles (0.3 mg · l^-1MB solution, 540 minUV irradiation), the rate constantkof MB degradation decreased by ∼50%, varying in the range (1.54 ÷ 0.78) · 10^-9(mol·l^-1·min^-1). For a deeper analysis of the photodegradation mechanism, detailed information on the nanostructured ZnO surface morphology and local surface and subsurface chemistry (nonstoichiometry) were obtained by using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) as complementary analytical methods. The SEM studies revealed that at the surface of the nanostructured ZnO thin films a coral reef structure containing polycrystalline coral dendrites is present, and that, after the photocatalytic experiments, the sizes of individual crystallites increased, varying in the range 43 ÷ 76 nm for the longer axis, and in the range 28 ÷ 58 nm for the shorter axis. In turn, the XPS studies showed a slight non-stoichiometry, mainly defined by the relative [O]/[Zn] concentration of ca. 1.4, whereas [C]/[Zn] was ca. 1.2, both before and after the photocatalytic experiments. This phenomenon was directly related to the presence of superficial ZnO lattice oxygen atoms that can participate in the oxidation of the adsorbed MB molecules, as well as to the presence of surface hydroxyl groups acting as hole-acceptors to produce OH· radicals, which can be responsible for the generation of superoxide ions. In addition, after experiments, the XPS measurements revealed the presence of carboxyl and carbonyl functional groups, ascribable to the oxidation by-products formed during the photodegradation of MB.

Recent Advances in the Synthesis and Application of Three-Dimensional Graphene-Based Aerogels

Three-dimensional graphene-based aerogels (3D GAs), combining the intrinsic properties of graphene and 3D porous structure, have attracted increasing research interest in varied fields with potential application. Some related reviews focusing on applications in photoredox catalysis, biomedicine, energy storage, supercapacitor or other single aspect have provided valuable insights into the current status of Gas. However, systematic reviews concentrating on the diverse applications of 3D GAs are still scarce. Herein, we intend to afford a comprehensive summary to the recent progress in the preparation method (template-free and template-directed method) summarized in Preparation Strategies and the application fields (absorbent, anode material, mechanical device, fire-warning material and catalyst) illustrated in Application of 3D GAs with varied morphologies, structures, and properties. Meanwhile, some unsettled issues, existing challenges, and potential opportunities have also been proposed in Future Perspectives to spur further research interest into synthesizing finer 3D GAs and exploring wider and closer practical applications.

Adsorptive removal of organic pollutant methylene blue using polysaccharide-based composite hydrogels

Methylene blue (MB) is categorized as an organic dye (OD) released as effluents after various industrial activities and is one of the most abundant pollutants in the aquatic environment. Significantly, because of its potential toxicity, removing MB from wastewater has been a matter of necessity in recent times. Numerous analytical techniques have been applied, among which polysaccharide-based composite hydrogels appear as the most favorable for MB removal because of their large surface area, excellent mechanical properties, swelling capability, and large-scale production. In this review, the first section gives adequate information about the ODs' adverse effects on the environment and the contribution of polysaccharide-based hydrogels for OD removal, especially MB. Next, various mechanisms such as electrostatic interactions, π-π interactions, hydrogen bonding, hydrophobic interaction, van der Waals force, and coordination interaction involved in the adsorption technique are investigated. The third section extensively describes the MB removal by incorporation of various materials such as monomers, metal oxides, magnetic nanoparticles, and clay into the polysaccharide matrix to produce composite hydrogels. Finally, the current limitations and future perspectives of the polysaccharide-based composite hydrogel techniques are addressed. Overall, this review acknowledged the vital role of polysaccharide-based composite hydrogels for MB adsorption by surveying 110 research articles published in the past five years (2015-2021).

Evaluation of Polyethylene Glycol Crosslinked β-CD Polymers for the Removal of Methylene Blue

The environment is at the heart of global worldwide discussion. This study describes the synthesis of ecofriendly polymers by a crosslinking reaction between β-cyclodextrin as the monomer and polyethylene glycol diglycidyl ether (PEDGE) as well as ethylene diglycidyl ether (EDGE) as the crosslinking agents. The studied polymers were characterized by several techniques, such as SEM, FTIR, TGA-TDA and XRD. Their adsorption properties for methylene blue under various conditions of pH, contact time and initial concentration of dye were assessed in order to find the optimal conditions. The results indicate that the polymers are good nominates for methylene blue adsorption with adsorption capacities up to 15 mg/g. The adsorption mechanism was demonstrated to follow the Langmuir model. Finally, the regeneration of the polymers was investigated using Soxhlet extraction with ethanol. The absorption capacities of the adsorbent were stable after three cycles.

Potential of siltstone and its composites with biochar and magnetite nanoparticles for the removal of cadmium from contaminated aqueous solutions: Batch and column scale studies

The present study is the first attempt to evaluate the pilot and batch scale adsorption potential of siltstone (SS) and its nanocomposites with biochar (EDB/SS), magnetite nanoparticles (MNPs/SS) and MNPs/EDB/SS for Cd removal from contaminated water. The SS, EDB/SS, MNPs/SS and MNPs/EDB/SS were characterized with FTIR, XRD, BET, SEM, TEM, TGA and point of zero charge (PZC). The effects of adsorbent dosage, contact time, initial Cd concentration, pH and presence of competing ions were evaluated on the Cd removal and its adsorption. The order for Cd removal was: MNPs/EDB/SS > MNPs/SS > EDB/SS > SS (95.86-99.72% > 93.10-98.5% > 89.66.98-98.40% > 74.90-90%). Column scale experiments yielded maximum retention (95%) of Cd even after 2 h of injection at 100 mg Cd/L. The exhausted SS, EDB/SS, MNPs/SS and MNPs/EDB/SS were reused without losing significant adsorption potential. Similarly, maximum Cd adsorption (117.38 mg/g) was obtained with MNPs/EDB/SS at dose 1.0 g/L. The results revealed that coexisting cations reduced the Cd removal due to competition with Cd ions. The experimental results were better explained with Freundlich isotherm model and pseudo 2nd order kinetic models. The results revealed that SS and its composites can be used efficiently for the removal of Cd from contaminated water.

Development of a novel three-dimensional magnetic polymer aerogel as an efficient adsorbent for malachite green removal

A novel three-dimensional (3D) magnetic bacterial cellulose nanofiber/graphene oxide polymer aerogel (MBCNF/GOPA) composed of bacterial cellulose nanofibers (BCNFs), Fe₃O₄ nanoparticles, graphene oxide (GO) nano-sheets, and polyvinyl alcohol (PVA) was developed by combining a facile filler-loaded networks method with a vacuum freeze-drying process for the removal of malachite green (MG) dye from aqueous solution. The influence of various factors on adsorption, including initial dye concentration, adsorbent dosage, contact time, temperature, and pH of dye solution, was then investigated. The adsorbent preserved a high adsorption capacity over a wide range of pH conditions. Moreover, the adsorption isotherms data fitted well with the Langmuir isotherm model with a maximum adsorption capacity of 270.27 mg g^-1. Adsorption kinetics followed the pseudo-second-order model, and the thermodynamic parameters showed that the adsorption of MG dye was feasible and endothermic in nature and occurred spontaneously. Therefore, owing to its demonstrated properties such as 3D interconnected porous structure, lightweight, large specific surface area, superparamagnetic behavior at room temperature, excellent adsorbent efficiency (93% removal) and also its simple and eco-friendly synthesis process, MBCNF/GOPA could be considered a promising candidate for removing cationic dye pollutants from aqueous solution, which can easily be collected from aqueous solution by a small magnet. MBCNF/GOPA also showed favorable reusability for MG removal in wastewater treatment, and its application in different water samples for the removal of MG dye molecules from "real" samples was successfully performed.

Sequestrating anionic and cationic dyes from wastewater using spray dried biopolymeric magnetic composite: Experimental and theoretical studies

Spray dried cross-linked chitosan/cobalt ferrite composite was synthesized and applied as an adsorbent for the removal of acid orange II and methylene blue. The composite was structurally, thermally, morphologically and magnetically characterized. The result obtained shows that the magnetic composite was in form of microspheres, while cobalt ferrite was encapsulated in the cross-linked chitosan with saturation magnetization of 10.79 emu g^-1. Adsorption studies revealed that acid orange II adsorbed more favorably on the composite than methylene blue. The adsorption process is spontaneous and exothermic. Liu isotherm model was found to be applicable for the adsorption process. Computational studies showed that the formation of hydrogen bond between acid orange II and the magnetic composite (at both acidic and alkaline pH) contributed to its better adsorption than methylene blue. Adsorption capacity of acid orange II at pH 3 and methylene blue at pH 12 are 542 and 173 mg g^-1 respectively at 303 K base on Liu isotherm model.

A Polyoxoniobate/g-C3N4 Nanoporous Material with High Adsorption Capacity of Methylene Blue from Aqueous Solution

A polyoxoniobate/g-C₃N₄ nanoporous material with functional groups has been synthesized by using carbon nitride (g-C₃N₄) and hexaniobate (K₈Nb₆O₁₉·10H₂O, abbreviated as NbO) as precursors. The structure and compositions of the as-prepared nanomaterials were characterized by XRD, FT-IR, FESEM, TEM, and XPS. These two kinds of materials interact with each other forming a hybrid composite, which can be used as an adsorbent for removing a cationic dye (methylene blue, MB) from wastewater with excellent adsorption capacity. Furthermore, parameters that can affect adsorption process including initial dye concentration, pH and temperature were investigated by bath adsorption experiments. The results indicated that the maximum adsorption capacity of NbO/g-C₃N₄ can reach up to 373.1 mg g⁻¹. Moreover, the equilibrium experiment data fitted Langmuir isotherm well and the adsorption kinetics showed that the pseudo second order model can satisfyingly described MB adsorption kinetics. The thermodynamic analysis indicated that the adsorption was endothermic and spontaneous.

Interfacially crosslinked composite porous membranes for ultrafast removal of anionic dyes from water through permeating adsorption

The dye wastewater is one of the most difficult industrial wastewaters to treat. It keeps a big challenge to realize fast removal of dyes from water by membrane filtration due to the trade-off between separation selectivity and permeation flux for ultrafiltration or nanofiltration (NF) process. Here we report novel composite porous membranes which can remove anionic dyes from water by ultrafast permeating adsorption. A crosslinked polyethyleneimine (PEI) polymer with strong adsorption ability was incorporated onto a nylon microfiltration membrane by the interfacial amidation reaction between PEI and trimesoyl chloride. The obtained composite membranes were used for the decolorization of dye solution by permeation mode. It was shown that the composite membranes were able to nearly completely remove anionic dyes in acidic conditions with high permeation fluxes. In an optimized case, the adsorption capacity of Sunset Yellow for the composite membranes reached 0.7mg/cm² with a high flux of 85L/m²h under a ultralow pressure of 0.01bar. This flux was far much higher than that of NF membranes, about 10L/m²hbar. The pH-dependent electrostatic interaction between PEI and anionic dyes was responsible for the rapid dye removal. The adsorption saturated membranes could be effectively regenerated by a simple alkaline washing.

Optimization of simultaneous ultrasound assisted toxic dyes adsorption conditions from single and multi-components using central composite design: Application of derivative spectrophotometry and evaluation of the kinetics and isotherms

Present study is devoted on the efficient application of Sn (O, S)-NPs -AC for simultaneous sonicated accelerated adsorption of some dyes from single and multi-components systems. Sn (O, S) nanoparticles characterization by FESEM, EDX, EDX mapping and XRD revel its nano size structure with high purity of good crystallinity. Present adsorbent due to its nano spherical shape particles with approximate diameter of 40-60nm seems to be highly effective in this regard. The effects of five variables viz. pH (3.5-9.5), 0.010-0.028g of adsorbent and 0.5-6.5min mixing by sonication is good and practical conditions for well and expected adsorption of MB and CV over concentration range of 3-15mgL^-1. Combination of response surface methodology (RSM) based on central composite design (CCD) and subsequent of analysis of variance (ANOVA) and t-test statistics were used to test the significance of the independent variables and their interactions. Regression analysis reveal that experimental data with high repeatability and efficiency well represented by second-order polynomial model with coefficient of determination value of 0.9988 and 0.9976 for MB and CV, respectively following conditions like pH 8.0, 0.016g adsorbent, 15mgL^-1 of both dyes 4min sonication time is proportional with achievement of experimental removal percentage of 99.80% of MB and 99.87% of CV in batch experiment. Evaluation and estimation of adsorption data with Langmuir and Freundlich isotherm well justify the results based on their correlation coefficient and error analysis confirm that Langmuir model is good model with adsorption capacity of 109.17 and 115.34mgg^-1 in single system and 95.69 and 102.99mgg^-1 in binary system for MB and CV, respectively. MB and CV kinetic and rate of adsorption well fitted by pseudo-second order equation both in single and binary systems and experimental results denote more and favorable adsorption of CV than respective value in single system. The pseudo-second-order rate constant k₂ in binary system larger than single system.

Simultaneous removal of acid green 25 and mercury ions from aqueous solutions using glutamine modified chitosan magnetic composite microspheres

In this current work, the magnetic composite microsphere containing glutamine modified chitosan and silica coated Fe3O4 nanoparticles (CS-Gln-MCM) has been successfully prepared and extensively characterized, which is a kind of biodegradable materials. CS-Gln-MCM shows enhanced removal efficiency for both acid green 25 (AG25), an amphoteric dye, and mercury ions (Hg(2+)) from water in the respective while measured pH range compared with chitosan magnetic composite microsphere (CS-MCM) without modification. It is due to the fact that the grafted amino acid provides a variety of additional adsorption active sites and diverse adsorption mechanisms are involved. In AG25 and Hg(2+) aqueous mixture, the modified adsorbents bear preferential adsorption for AG25 over Hg(2+) in strong acidic solutions ascribed to multiple interactions between AG25 and CS-Gln-MCM, such as hydrogen bonding and electrostatic interactions. While, in weak acidic conditions, an efficient simultaneous removal is observed for different adsorption effects involved in aforementioned two pollutants. Besides, CS-Gln-MCM illuminates not only short equilibrium time for adsorption of each pollutant less than 20.0 min but also rapid magnetic separation from water and efficient regeneration after saturated adsorption. Therefore, CS-Gln-MCM bears great application potentials in water treatment.