Adsorption of Cationic Dyes onto Bentonite

Agrowaste-carbon and carbon-based nanocomposites for endocrine disruptive cationic dyes removal: A critical review

Dyes are considered to be pollutants that pose a considerable worldwide health risk, as they have been discovered as agents that affect the endocrine system. Adsorption is the most commonly used method for removing different substances since it is sustainable, flexible, affordable, and easy to use. Researchers have investigated the usage of agro-waste-based adsorbents that are ecologically friendly for the process of adsorption. This research has emphasized the potential of these adsorbents in developing carbon-based nanocomposites. Improved surface functionalization, great compatibility, and flexibility are beneficial uniqueness of carbon-based nanocomposites as well as a wide variety of applications. As a result, they are highly successful in removing cationic dyes. This paper specifically examines the environmentally friendly usage of activated carbons obtained from agricultural waste and the development of carbon-based-nanocomposites to adsorb positively charged dyes. Additionally, it offers an in-depth investigation of various cationic dyes, operating parameters, adsorption isotherms, kinetics, processes, and thermodynamic investigations. Further research is necessary to determine the effectiveness of carbon-based nanocomposites in removing new endocrine-disrupting pollutants. Additionally, these nanocomposites have the potential to be widely used in treating industrial effluents.

Removal of cadmium and cobalt from water by Slovak bentonites: efficiency, isotherms, and kinetic study

Slovak bentonite was used as an effective natural adsorbent for the removal of Cd(II) and Co(II). Characterization of the samples was conducted using X-ray diffraction (XRD), high-resolution scanning electron microscopy with an X-ray energy dispersion spectrometer (SEM-EDS), and infrared spectroscopy (FT-IR). Adsorption experiments were carried out for pure water and artificial seawater, each containing cobalt and cadmium cations within the concentration range of 5-60 mg/L. The highest bentonite adsorption capacities of the tested bentonites were 23.5 (Cd) and 32.2 (Co) mg g-1. The kinetics data revealed that, in addition to chemisorption, intraparticle diffusion contributes to metal removal. The physical and structural properties of bentonites play an important role in adsorption. Bentonite P 135 from the Lieskovec deposit showed the highest efficiency for removing both ions, with removal percentages exceeding 90% and 77.5% for pure water and artificial seawater, respectively. The results indicate the suitability of using Slovak bentonites as an alternative sorbent for both metal extractions. The mechanism of metal ion adsorption on bentonite clay can be understood through surface complexation and ion exchange. The examined bentonite deposits show potential as promising natural sorbents for the removal of cobalt and cadmium cations from polluted waters.

Controversial Issues Related to Dye Adsorption on Clay Minerals: A Critical Review

This critical review points out the most serious and problematic issues to be found in the literature on the adsorption of dyes on clay minerals. The introduction draws attention to the fundamental problems, namely the insufficient characterization of adsorbents, the influence of impurities on the adsorption of dyes, and the choice of inappropriate models for the description of the very complex systems that clay minerals and their systems represent. This paper discusses the main processes accompanying adsorption in colloidal systems of clay minerals. The relationship between the stability of the colloidal systems and the adsorption of dye molecules is analyzed. The usual methodological procedures for determining and evaluating the adsorption of dyes are critically reviewed. A brief overview and examples of modified clay minerals and complex systems for the adsorption of organic dyes are summarized. This review is a guide for avoiding some faults in characterizing the adsorption of organic dyes on clay minerals, to improve the procedure for determining adsorption, to evaluate results correctly, and to find an appropriate theoretical interpretation. The main message of this article is a critical analysis of the current state of the research in this field, but at the same time, it is a guide on how to avoid the most common problems and mistakes.

Cellulose nanofibers decorated with SiO2 nanoparticles: Green adsorbents for removal of cationic and anionic dyes; kinetics, isotherms, and thermodynamic studies

Cellulose nanofibers decorated with SiO2 nanoparticles (SiO2-CNF) were prepared by the extraction of cellulose nanofibers from Yucca leaves, followed by modification with SiO2 nanoparticles, and used as efficient materials for the removal of both anionic and cationic dyes from the aqueous solution. Prepared nanostructures were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction powder (XRD), Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and transmission electron microscopy (TEM) analysis. The adsorption capacity of the nanostructures was investigated for the removal of both cationic (Methylene Blue, MB, and Crystal Violet, CV) and anionic (Eriochrome Black-T, EB) dyes. The kinetics of adsorption were investigated using some well-known models, including intraparticular diffusion (IPD), pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich. The adsorption isotherms were also explored using the Langmuir, Freundlich, Temkin, and Redlich-Peterson models. The obtained results revealed that the adsorption processes follow PSO kinetic and Langmuir isotherm models. Thermodynamic parameters of the adsorption were measured at different temperatures, indicating the feasibility and spontaneity of the adsorption. The pH and salt effects on adsorption were also explored. Finally, according to the reusability tests, the prepared adsorbents showed high recoverability without considerable loss in adsorption efficiency after five repeated runs.

Synthesis of bentonite/Ag nanocomposite by laser ablation in air and its application in remediation

In this research, a simple, green, and efficient approach is described to produce novel bentonite/Ag nanocomposite wherein the preparation of Ag nanoparticles (Ag NPs) deployed the laser ablation method in air; Ag NPs are deposited on the bentonite via the magnetic stirring method. The structural and morphological characterization of the as-prepared bentonite/Ag nanocomposite (denoted as B/Ag30, 30 min being the laser ablation time) is accomplished using different methods. Additionally, the catalytic assessment of the ensued composite exhibited excellent catalytic reduction/degradation activity for common aqueous pollutants namely methyl orange (MO), congo red (CR) and 4-nitrophenol (4-NP) utilizing NaBH₄ as reductant. Furthermore, the recycling tests displayed the high stability/reusability of B/Ag30 nanocomposite for at least 4 runs with retention of catalytic prowess.

Interlayer adsorption of cationic dye on cationic surfactant-modified and unmodified montmorillonite

Water pollution by toxic organic dyes is one of the most critical health and environmental problems worldwide. By means of molecular dynamics method, the present work aims to evaluate the applicability of montmorillonite (Mt) modified by hexadecyltrimethylammonium cations (HDTMA⁺) compared to unmodified Na-Mt for the adsorption of cationic methylene blue (MB) dye. The results showed that the adsorption energy of MB on both HDTMA-Mt and Na-Mt absorbent ranged from - 100 to - 250 kJ/mol, indicating the effectiveness of two types of adsorbents in dye water treatment. The highest adsorption energy was found at w = 50% in each adsorbent system. Adsorption mechanisms of MB depend on molecular orientations, which is influenced by the surfactant and water content. The adsorption mechanism of MB is chemisorption dominated by strong electrostatic interaction between CH₃ groups of MB and oxygen atoms of Mt surfaces. Besides, physisorption also plays a minor role in MB orientations. It is found that the existence of cationic surfactants can slightly improve the adsorption capacity of MB only at higher water content through enlarging the interlayer space of Mt and reducing mobility of MB. However, there will be a negative impact on the reduction of adsorption sites for dyes especially at low water content. Our results provide a possible application for swelling clay minerals being a promising adsorbent for dyes-surfactants co-existing wastewater treatment.

Photoinduced movement: how photoirradiation induced the movements of matter

Pioneered by the success on active transport of ions across membranes in 1980 using the regulation of the binding properties of crown ethers with covalently linked photoisomerizable units, extensive studies on the movements by using varied interactions between moving objects and environments have been reported. Photoinduced movements of various objects ranging from molecules, polymers to microscopic particles were discussed from the aspects of the driving for the movements, materials design to achieve the movements and systems design to see and to utilize the movements are summarized in this review.

Application of dye saturated clay adsorbent from dyeing wastewater as textile printing pigment

Background

Adsorption by cheap materials (like clay and activated carbon) is one of the most effective methods for treating dye wastewaters, especially for cationic dyes. Although activated carbon has a black residue, the unique nanostructure of clay adsorbs dye molecules between its layers and produces a colored sludge. Dye intercalated clays were also introduced as possible coloring pigments. This work tries to combine the wastewater treatment and hybrid pigment production processes so that the remaining sludge of the process can be used as a printing pigment.

Results

Bentonite clay was examined for treating real dye wastewater from the textile industry containing four cationic dyes. The adsorption mechanism of all dyes was studied individually, and the results show that bentonite has a minimum adsorption capacity of 467 mg/g for Basic Red 46 dye based on the Langmuir model. The adsorption process decreased the turbidity by about 86% and reduced the total dissolved solids (TDS) and chemical oxygen demand (COD) of wastewater. The produced hybrid showed a nano‐layer structure according to the field emission scanning electron microscopy (FESEM). Differential thermal analysis (DTA) shows that the thermal stability of the pigment improved by about 30 °C compared to the pristine dye. Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) showed that the dye: bentonite ratio should be adjusted at a medium level to control the hydrophilicity of the hybrid and improve its miscibility in binders.

Conclusion

The produced pigment was printed on cotton fabric with a desirable visual color appearance and showed acceptable rubbing and light fastnesses. The result indicates that wastewater sludge from this adsorption process could be applicable as an industrial pigment. © 2022 Society of Chemical Industry (SCI).

Sodium salt-assisted low temperature activation of bentonite for the adsorptive removal of methylene blue

The sodium salt-assisted low temperature activation of bentonite (BB) was attempted. The unique features of the raw bentonite and BB were characterized with respect to the morphological, functional, and textural analysis. The adsorptive behaviour was evaluated by adopting methylene blue (MB) as the model pollutant via batch adsorption experiment. The experimental data were fitted to the non-linear isotherm equations (Freundlich, Langmuir, and Temkin), while the adsorption modelling was interpreted by the pseudo-first order, pseudo-second order and Elovich models. The adsorptive mechanism was ascertained according to intraparticle-diffusion and boyd models. The intercalation of sodium salt into the bentonite surface give rise to the specific surface area and total pore volume from 120.34 to 426.91, m²/g and 0.155 to 0.225 cm³/g, respectively, indicating a large proportion of the newly formed surfaces may be connected to new pore walls, associated with the silanol (≡SiOH), and aluminol (≡AlOH), and hydroxyl (–OH) groups for the possible entrapment MB onto the adsorbent. The equilibrium data was satisfactory described by the Langmuir isotherm and pseudo-second order model, with a monolayer adsorption capacity for MB of 318.38 mg/g, while the thermodynamic study verified spontaneous, feasible, and endothermic of the adsorption process.

Effects of Surface Heterogeneity of α-Quartz and α-Cristobalite on Adsorption of Crystal Violet

Silica minerals are a kind of important minerals and widespread on the earth's surface. They play an irreplaceable role in the whole geochemistry and environment processes. The diversity in the crystal structure of SiO₂ polymorphs might lead to the heterogeneity in their surface microstructures and properties. As two common SiO₂ polymorph minerals in soil and sediments, α-quartz and α-cristobalite have been studied for the effects of their surface heterogeneity on adsorption behaviors toward crystal violet (CV) by batch adsorption experiments in different specific surface areas (SSAs) and at different pH values and temperatures, as well as by X-ray photoelectron spectroscopy (XPS) investigation. Owing to the larger surface site density, the saturated adsorption amount of α-quartz was larger than that of α-cristobalite. It was also indicated by the larger slope of adsorption lines as a function of SSA. The adsorption capacity of both increased with increasing pH and temperature. In the thermodynamic study, the negative ΔG indicated that the adsorption of CV on the surface was spontaneous and the positive ΔH suggested that the reaction was endothermic. The well-fitted Langmuir adsorption isotherms suggested that the CV adsorption was monolayer adsorption. The adsorption interaction force was mainly involved in electrostatic attraction force between the negatively charged surface reactive sites and positively charged N atoms in the dimethylamino groups of CV. The XPS spectra of N 1s showed that the stoichiometric ratio of N_low/N_high changed from lower than 2:1 to about 2:1 as the adsorption changed from the unsaturated to saturated state. The change reflected that the spatial arrangement of adsorbed CV monomer on the mineral surface could be readjusted by lifting the average tilt angle between the average plane of the CV monomer and the sample surface during the adsorption process. Surface heterogeneity of α-quartz and α-cristobalite controlled the different distributions and postures of adsorbed CV monomers on the surface. The CV monomers adsorbed on α-quartz presented a larger average tilt angle because of its larger surface reactive site density, while α-cristobalite did conversely.

Tailoring Mesoporous Titania Features by Ultrasound-Assisted Sol-Gel Technique: Effect of Surfactant/Titania Precursor Weight Ratio

A mesoporous titania structure has been prepared using the ultrasound-assisted sol-gel technique in order to find out a way to tailor its structure. The TiO₂ obtained was compared to the same version of titania but synthesized by a conventional sol-gel method with the objective of understanding the effect of ultrasound in the synthesis process. All synthesis experiments were focused on the preparation of a titania photocatalyst. Thus, the anatase photocatalytic active phase of titania was proven by X-ray diffraction. Additionally, the ultrasonation treatment proved to increase the crystallinity of titania samples, being one of the requirements to having good photocatalytic activity for titania. The influence of surfactant/titania precursor weight ratio on the structural (XRD), textural (N₂-sorption measurements), morphological (TEM), surface chemistry (FTIR) and optical properties (UVDR) was investigated. It was observed that the crystallite size, specific surface area, band gap energy and even photocatalytic activity was affected by the synergism occurring between cavitation effect and the surfactant/titania precursor weight ratio. The study yielded interesting great results that could be considered for further application of ultrasound to tailor mesoporous titania features via sol-gel soft template synthesis, against conventional sol-gel process.

Systematic utilization of layered double hydroxide nanosheets for effective removal of methyl orange from an aqueous system by π-π stacking-induced nanoconfinement

Systematic utilization of carbonated Mg-Al layered double hydroxide (LDH) nanosheets for methyl orange removal was investigated with respect to particle dimensions. LDHs with the smallest dimensions were carefully synthesized to have a small lateral size as well as high dispersibility. The other particles, with medium and large sizes, were prepared by hydrothermal treatment and urea hydrolysis to have larger sizes and higher crystallinity. According to kinetics and isotherm analyses, the smallest LDH showed efficient adsorption of methyl orange (1250 mg/g-LDH), which was remarkably higher than the adsorption by the other LDHs with larger lateral sizes. Unlike the larger lateral-sized LDHs, the small ones were shown to utilize all accessible adsorption sites on the nanosheets, generating nanoconfinement of methyl orange molecules. Transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) patterns indicated that the LDHs with lateral dimensions of ~40 nm fully utilized interlayer nanospace. Monte Carlo simulation suggested that the intercalated methyl orange was stabilized not only through electrostatic interactions with the LDH layer but also by π-π stacking between the methyl orange molecules, which is thought to be the driving force for replacement of carbonate anions.

Double-Silicate Derived Hybrid Foams for High-Capacity Adsorption of Textile Dye Effluent: Statistical Optimization and Adsorption Studies

In this work, a lightweight inorganic-organic hybrid foam adsorbent is processed out of economically cheap "double-silicate" precursors employing natural bentonite and water glass through a facile cross-linking and polymerization technique. Poly(vinyl alcohol) was used to provide structural strength to the three-dimensional framework. The foam adsorbent possessed an apparent density of 0.083 g cm^-3, indicating its internetworks and exposed surface area for the uptake of dyes. The foam was systematically studied for the treatment of textile dye effluent. Multivariate optimization process was carried out using response surface methodology. The Box-Behnken model was used for the design of experiments and to study the interplay between the variables. Batch adsorption and continuous column adsorption studies were carried out at respective levels of initial concentration (200-1000 μM), adsorbent dose (1-10 g L^-1), and contact time (0-120 min). The results revealed that the hybrid silicate foam exhibits adsorption capacity as high as 99.9, 98.9, and 98.2% for 200, 600, and 1000 μM concentrations of methylene blue in 120 min, respectively, and 100% adsorption for 200, 600, and 1000 μM concentrations of crystal violet in 120 min for 10 g L^-1 of adsorbent. Adsorption equilibrium data fitted well to Langmuir isotherm, and the kinetics followed second-order kinetic model. Synthetic industrial effluent with 1000 μM dye concentration was also prepared and studied with continuous column for determining the working capacity of the adsorbent, and the results are presented. The silicate hybrid foam is a cheap adsorbent that does not produce any secondary waste and can be repeatedly used making it attractive for dye industries.

Sorption of Acid Black 1 dye onto bentonite - equilibrium and kinetic studies

The present study shows sorption capacity of bentonite from the Slovak Jelšový Potok deposit for the anionic dye (Acid Black 1) from aqueous solutions and uses it as an effective and economical adsorbent for the removal of anionic dye. The laboratory experiments were carried out in batch method at 3 different sorbent doses (20, 10 and 5 g L^-1) and an initial concentration of dye ranging from 1 to 1,000 mg L^-1. The adsorption equilibria data were fitted by Freundlich, Langmuir, Dubinin-Radushkevich and Temkin isotherms. The Langmuir equation provided the best description for the sorption, indicating that adsorption occurred on a mono-layered surface. The maximum sorption capacity of bentonite has been estimated as 31.29 mg g^-1. Moreover, the results showed that non-linear method could be a better way to obtain the isotherm parameters. The pseudo-first- and pseudo-second-order equations have been applied for the determination of time effect on sorption/removal of dye from solution. The highest determination coefficient values were observed for the pseudo-second-order model, suggesting chemical character of the adsorption process. Acid Black 1 was probably bound through chemisorption by forming hydrogen bonds between the Si-OH and Al-OH groups in the bentonite and the -NH, -NH2 and -OH groups in the dye.

Influence of the Structure and Experimental Surfaces Modifications of 2:1 Clay Minerals on the Adsorption Properties of Methylene Blue

In this work the adsorption capacities of methylene blue on Mg-smectite and sepiolite and its derived material obtained after acid treatment and/or the addition of Fe at its surfaces are studied. Natural smectite with high Mg-content in its octahedral sheet (Mg-smectite) displays higher adsorption capacity than the sepiolite due to the ability of Mg-smectite to expand the basal spacing to accommodate methylene blue cations between adjacent layers and the inability of sepiolite to adsorb these cations within the structural channels. The acid-activation of Mg-smectite causes a clear decrease in the adsorption capacity attributed to the partial loss of the interlayer positions by the loss of the octahedral sheet and subsequent formation of amorphous silica. Moreover, the adsorption of the Mg-smectite decreases even more when iron oxohydroxides species are incorporated in its interlayer spacing making inaccessible the interlayer active sites for the adsorption of methylene blue cations. On the contrary, the microwave-assisted acid treatment of sepiolite causes a slight increase in the adsorption capacity related with the dispersion of fibers. Nevertheless, contrary to that observed with Mg-smectite, higher increasing of adsorption capacities are obtained after the formation of new adsorption centers due to the incorporation of iron oxohydroxides species at the external surfaces of sepiolite.

Novel carboxymethyl cellulose based nanocomposite membrane: Synthesis, characterization and application in water treatment

Significant efforts have been made to develop composite membranes with high adsorption efficiencies for water treatment. In this study, a carboxymethyl cellulose-graft-poly(acrylic acid) membrane was synthesized in the presence of silica gel, which was used as an inorganic support. Then, different amounts of bentonite were introduced to the carboxymethyl cellulose (CMC) grafted networks as a multifunctional crosslinker, and nanocomposite membranes were prepared. The nanocomposite membranes were characterized using Fourier transform infrared spectroscopy, and scanning electron microscopy, which revealed their compositions and surface morphologies. The novel synthesized nanocomposite membranes were utilized as adsorbents for the removal of crystal violet (CV) and cadmium (Cd (II)) ions, which were selected as representatives of a dye and a heavy metal, respectively. We explored the effects of various parameters, such as time, pH, temperature, initial concentration of adsorbate solution and amount of adsorbent, on membrane adsorption capacity. Furthermore, the kinetic, adsorption isotherm models and thermodynamic were employed for the description of adsorption processes. The maximum adsorption capacities of membranes for CV and Cd (II) ions were found to be 546 and 781 mg g(-1), respectively. The adsorption of adsorbate ions by all types of nanocomposite membranes followed pseudo-second-order kinetic model and was best fit with the Freundlich adsorption isotherm. The results indicated that the synthesized nanocomposite membrane is an efficient adsorbent for the removal of cationic dye and metal contaminants from aqueous solution during water treatment.

Recent advances in new generation dye removal technologies: novel search for approaches to reprocess wastewater

In order to control the negative impacts of dyes on living organisms, several techniques and methodologies have been developed for their removal from industry effluents and other water bodies.