Adsorption and photophysical properties of fluorescent dyes over montmorillonite and saponite modified by surfactant

A review on transition metal oxides based photocatalysts for degradation of synthetic organic pollutants

This review provides insight into the current research trend in transition metal oxides (TMOs)-based photocatalysis in removing the organic colouring matters from water. For easy understanding, the research progress has been presented in four generations according to the catalyst composition and mode of application, viz: single component TMOs (the first-generation), doped TMOs/binary TMOs/doped binary TMOs (the second-generation), inactive/active support-immobilized TMOs (the third-generation), and ternary/quaternary compositions (the fourth-generation). The first two generations represent suspended catalysts, the third generation is supported catalysts, and the fourth generation can be suspended or supported. The review provides an elaborated comparison between suspended and supported catalysts, their general/specific requirements, key factors controlling degradation, and the methodologies for performance evaluation. All the plausible fundamental and advanced dye degradation mechanisms involved in each generation of catalysts were demonstrated. The existing challenges in TMOs-based photocatalysis and how the researchers approach the hitch to resolve it effectively are discussed. Future research trends are also presented.

A Bibliometric Analysis of Geosmin Removal and Treatment Technologies using Web of Science Database and VOSviewer

In the last few years, the presence of geosmin (GEO) in water bodies has caused serious problems related to water consumption by the population. Many studies focus on its occurrence and detection, but little is discussed about the technologies for treatment and removal of this contaminant. In this way, the present work aims to present a bibliographic search and a bibliometric analysis carried out in the Web of Science database and in VOSviewer software about geosmin remediation, in the last 10 years. 100 articles were found, of which only one, from 2021, was a review. It was possible to assess that the subject has gained greater notoriety in the last 7 years, since the year 2016 marked the increase of publications on the subject, as well as an increasing number of citations. Among the most published countries is the People's Republic of China, with 53% of publications. Bibliometric analysis showed that GEO is directly related to 2-methylisoborneol (2-MIB), since both occur simultaneously in water bodies. In addition, it was possible to identify that adsorptive processes are the most used in the removal of these contaminants, followed by advanced oxidative processes and biological processes, in that order.

Development of an Enzymatic Biosensor Using Glutamate Oxidase on Organic-Inorganic-Structured, Electrospun Nanofiber-Modified Electrodes for Monosodium Glutamate Detection

Herein, dendrimer-modified montmorillonite (Mt)-decorated poly-Ɛ-caprolactone (PCL) and chitosan (CHIT)-based nanofibers were prepared. Mt was modified with a poly(amidoamine) generation 1 (PAMAM_G1) dendrimer, and the obtained PAMAM_G1-Mt was incorporated into the PCL-CHIT nanofiber's structure. The PCL-CHIT/PAMAM_G1-Mt nanofibers were conjugated with glutamate oxidase (GluOx) to design a bio-based detection system for monosodium glutamate (MSG). PAMAM_G1-Mt was added to the PCL-CHIT backbone to provide a multipoint binding side to immobilize GluOx via covalent bonds. After the characterization of PCL-CHIT/PAMAM_G1-Mt/GluOx, it was calibrated for MSG. The linear ranges were determined from 0.025 to 0.25 mM MSG using PCL-CHIT/Mt/GluOx and from 0.0025 to 0.175 mM MSG using PCL-CHIT/PAMAMG₁-Mt/GluOx (with a detection limit of 7.019 µM for PCL-CHIT/Mt/GluOx and 1.045 µM for PCL-CHIT/PAMAMG₁-Mt/GluOx). Finally, PCL-CHIT/PAMAMG₁-Mt/GluOx was applied to analyze MSG content in tomato soup without interfering with the sample matrix, giving a recovery percentage of 103.125%. Hence, the nanofiber modification with dendrimer-intercalated Mt and GluOx conjugation onto the formed nanocomposite structures was performed, and the PCL-CHIT/PAMAM_G1-Mt/GluOx system was successfully developed for MSG detection.

Comparison of microscopic adsorption characteristics of Zn(II), Pb(II), and Cu(II) on kaolinite

In this research, kaolinite was used to investigate the comparative adsorption of copper, lead, and zinc ions through batch control experiments and first principles calculations. Different adsorption conditions were considered as the effect of solution acidity, initial concentration of ions, and contact shaking time. The adsorption system isotherms and kinetic studies were better agreed with the Langmuir and pseudo-second-order kinetic models. They reached adsorption equilibrium within two hours and maximum adsorption capacities of Zn(II), Pb(II), and Cu(II) on kaolinite were 15.515, 61.523, and 44.659 mg/g, respectively. In addition, the microscopic adsorption changes of Zn(II), Pb(II), and Cu(II) on kaolinite were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The results showed that Zn(II), Pb(II), and Cu(II) were most likely to be adsorbed on the kaolinite surface. Furthermore, the adsorption mechanism of [Zn(OH)]+, [Pb(OH)]+, and [Cu(OH)]+ on the kaolinite (001) surface was systematically studied through first-principles density functional calculations. The adsorption characteristics of different ions were evaluated by calculating the adsorption energy of the equilibrium adsorption configuration, state density, and electron density. The adsorption energy of [Zn(OH)]+, [Pb(OH)]+, and [Cu(OH)]+ were − 0.49,  − 1.17, and − 1.64 eV, respectively. The simulation results indicated that new hybrid orbitals were formed between the metal ions and O atoms on the kaolinite surface, with electron transfer occurring the adsorption processes. The charge transfer direction for [Pb(OH)]+ was opposite those for [Zn(OH)]+ and [Cu(OH)]+. [Zn(OH)]+ was more likely to form polydentate complexes with hydroxyl groups on the kaolinite surface than [Cu(OH)]+ and [Pb(OH)]+. This work further elucidated the interaction mechanism between the adsorption systems and provided fundamental theoretical support for the structural modification and optimization of kaolinite, such as increasing the layer spacing of kaolinite and introducing other active groups on its surface to improve the adsorption capacity of heavy metal ions in water treatment and soil remediation.

Honeycomb-like cork activated carbon with ultra-high adsorption capacity for anionic, cationic and mixed dye: Preparation, performance and mechanism

Herein, the cork activated carbon (CAC) with excellent adsorption performance for cationic dye, anionic dye, and mixed dye was obtained by a two-step pyrolysis method. The CAC exhibits a fluffy honeycomb structure consisted of porous carbon nanosheets (100-200 nm), ultra-high specific surface area (3402.68 m²/g), and well-developed hierarchical porous structure, which offers a great deal of adsorption sites and transport channels to dye molecules. The adsorption process of all the dyes onto CAC is better described by Langmuir isotherm model and pseudo-2nd-order kinetic model. The CAC shows ultra-high adsorption capacity for methylene blue (1283.99 mg/g), rhodamine B (4067.57 mg/g), methyl orange (2666.2 mg/g), and congo red (8920.61 mg/g), with an extremely low equilibrium adsorption time (∼10 min). Collectively, this study demonstrated the potential of converting waste cork into high value-added adsorbent for the efficient purification of dye wastewater.

Analytical Characterization of the Intercalation of Neutral Molecules into Saponite

Organo-modified layered materials characterization poses challenges due to their complexity and how other aspects such as contamination, preparation methods and degree of intercalation influence the properties of these materials. Consequently, a deep understanding of their interlayer organization is of utmost importance to optimize their applications. These materials can in fact improve the stability of photoactive molecules through intercalation, avoiding the quenching of their emission at the solid state, to facilitate their use in sensors or other devices. Two synthetic methods for the preparation of saponites with a cationic surfactant (CTABr) and a neutral chromophore (Fluorene) were tested and the obtained products were initially characterized with several complementary techniques (XRPD, SEM, TGA, IR, UV-Vis, Fluorescence and Raman spectroscopy), but a clear understanding of the organization of the guest molecules in the material could not be obtained by these techniques alone. This information was obtained only by thermogravimetry coupled with gas chromatography and mass spectroscopy (TGA-GC-MS) which allowed identifying the species present in the sample and the kind of interaction with the host by distinguishing between intercalated and adsorbed on the surface.

Wastewater Treatment and Biomedical Applications of Montmorillonite Based Nanocomposites: A Review

Background::

Rapid industrialisation, population growth and technological race worldwide have brought adverse consequences on water resources and as a result affect human health. Toxic metal ions, non-biodegradable dyes, organic pollutants, pesticides, pharmaceuticals are among the chief hazardous materials released into the water bodies from various sources. These hazardous contaminants drastically affect the flora and fauna globally leading to health deterioration there by giving rise to new biomedical challenges.

Hypothesis::

Montmorillonite based nanocomposites (MMTCs) have drawn an attention of the researchers to design environmental friendly, advanced and hygienic nanocomposites for wastewater treatment and biomedical purposes. Montmorillonite clay possesses peculiar physical and chemical properties that include enhanced surface reactivity, improved rheological performance, exorbitant miscibility in water due to which it shows highly favourable interactions with polymers, drugs, metals, mixed metals and metal oxides leading to the fabrication of different types of advanced montmorillonite based nanocomposites that have remarkable applications

Methodology::

Here we review the structural characteristics of montmorillonite clay, advances in the synthetic techniques involved in the fabrication of montmorillonite nanocomposites, their applications in waste water treatment and in bio medical field. The recently developed montmorillonite nanocomposites for (1) waste water treatment as nano-adsorbents for the elimination of toxic inorganic species such as metal ions and heterogeneous photo-catalysts for photo degradation of dyes, pesticides and pharmaceuticals (2) biomedical utilization viz drug delivery, wound amelioration, bone cement, tissue engineering etc. are presented

Conclusion::

The review exclusively focuses on recent research on montmorillonite based nanocomposites and their application in wastewater treatment and in biomedical field

Intercalation of a Cationic Cyanine Dye Assisted by Anionic Surfactants within Mg-Al Layered Double Hydroxide

An original route for the intercalation of a 1,1'-diethyl-2,2'-cyanine iodide (PIC) cationic dye, through the use of anionic surfactants as vector/carrier phases, within Mg-Al layered double hydroxide (LDH) was investigated. From the data acquired from complementary techniques (X-ray diffraction, infrared and UV-visible spectroscopies, thermogravimetry, and fluorimetry), it appears that both the intercalation and aggregation states of the cationic dye within the internal structure of LDH mainly depend on both the surfactant state (monomer form or spherical micelle) and its amount. The intercalation of PIC at a low molar ratio to the anionic surfactant leads to the formation of J-aggregates with singular fluorescence properties that mainly depend on the nature of the anionic surfactant used for the co-intercalation process. The results obtained in this study open new routes for the intercalation of cationic species, assisted by anionic surfactants, within LDHs.

Exploration of adsorption mechanism of 2-phosphonobutane-1,2,4-tricarboxylic acid onto kaolinite and montmorillonite via batch experiment and theoretical studies

Two clay minerals, kaolinite (Kaol) and montmorillonite (Mt) with different crystal structures were chosen to investigate the comparative adsorption of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) through batch control experiments and theoretical studies. The systematical isotherm and kinetic studies agreed with Langmuir model and pseudo-second-order model, confirming a monolayer and chemisorption interaction process, respectively. The maximum removal capacities of Kaol and Mt for PBTC were 72.297 mg/g and 121.163 mg/g at pH=3.0 and T=298 K, respectively. Furthermore, the adsorption mechanisms were investigated by molecular dynamic (MD) simulations and density functional theory (DFT). The Interface force field (IFF) was firstly introduced into Materials Studio package to explore the microscopic mechanism of clay mineral interface. The dynamics behaviors verified that the oxygen (O) atom of carboxyl group has stronger affinity at the external surface of Mt, which consistent with the experimental data well. For DFT calculations, quantitative analysis around molecular van der Waals (vdW) surface was adopted to predict reactive sites for the electrophilic reaction. Independent Gradient Model (IGM) and Hirshfeld surface analyses in Multiwfn indicated that the high adsorption effect mainly attributes to hydrogen bond action. These findings improve our ability to explore the related properties occurring at the interface of different clay minerals.

Changes in Optical Properties upon Dye-Clay Interaction: Experimental Evaluation and Applications

The development of hybrid materials with unique optical properties has been a challenge for the creation of high-performance composites. The improved photophysical and photochemical properties observed when fluorophores interact with clay minerals, as well as the accessibility and easy handling of such natural materials, make these nanocomposites attractive for designing novel optical hybrid materials. Here, we present a method of promoting this interaction by conjugating dyes with chitosan. The fluorescent properties of conjugated dye–montmorillonite (MMT) hybrids were similar to those of free dye–MMT hybrids. Moreover, we analyzed the relationship between the changes in optical properties of the dye interacting with clay and its structure and defined the physical and chemical mechanisms that take place upon dye–MMT interactions leading to the optical changes. Conjugation to chitosan additionally ensures stable adsorption on clay nanoplatelets due to the strong electrostatic interaction between chitosan and clay. This work thus provides a method to facilitate the design of solid-state hybrid nanomaterials relevant for potential applications in bioimaging, sensing and optical purposes.

A hydrophobic bio-adsorbent synthesized by nanoparticle-modified graphene oxide coated corn straw pith for dye adsorption and photocatalytic degradation

A novel bio-adsorbent was prepared from corn straw pith (CSP), graphene oxide (GO) and TiO₂ through one-step synthesis for adsorption and photocatalytic reduction of dyes. CSP and GO acted as stent and coat, respectively. TiO₂ nanoparticles attached on the surface of the adsorbent played a role in the degradation of dyes and endowed the adsorbent with hydrophobicity. When the loading of GO and TiO₂ were 5 and 20 wt.% respectively, the adsorbent had quite an ideal structure and satisfactory removal efficiency. There were an electrostatic attraction, hydrophobic and π-π interactions in the process of adsorption. The pseudo-second-order and the Langmuir model described the adsorption behaviour well. The dyes loaded on the adsorbent could be degraded by irradiation with ultraviolet light (UV). After five cycles, the removal efficiency of malachite green, methylene blue and rhodamine b by CSP-5GO-20TiO₂ decreased by 3.77%, 23.89% and 32.01%, respectively. Therefore, the bio-adsorbent has the advantages of economy, environmental protection, and the concept of sustainable development.

Effect of Layer Charge Density on Hydration Properties of Montmorillonite: Molecular Dynamics Simulation and Experimental Study

Four kinds of Ca-montmorillonite with different layer charge density were used to study the effect of charge density on their hydration properties by molecular dynamics simulation and experiments. The research results of Z-density distribution of water molecules, H_w (hydrogen in water molecules), and Ca in the interlayer of montmorillonite show that the hydration properties of montmorillonite are closely related to its layer charge density. If the charge density is low, the water molecules in the interlayers are mainly concentrated on the sides of the central axis about –1.3 Å and 1.5 Å. As the charge density increases from 0.38_semi-cell to 0.69_semi-cell, the water molecules are distributed −2.5 Å and 2.4 Å away from the siloxane surface (Si-O), the concentration of water molecules near the central axis decreases, and at the same time, Ca²⁺ appears to gradually shift from the vicinity of the central axis to the Si-O surface on both sides in the montmorillonite layer. The simulation results of the radial distribution function (RDF) of the Ca-H_w, Ca-O_w (oxygen in water molecules), and Ca-O_t (the oxygen in the tetrahedron) show that the Ca²⁺ and O_w are more tightly packed together than that of H_w; with the increase of the charge density, due to the fact that the negative charge sites on the Si-O surface increase, under the action of electrostatic attraction, some of the Ca²⁺ are pulled towards the Si-O surface, which is more obvious when the layer charge density of the montmorillonite is higher. The results of the RDF of the O_t-H_w show that with the increase of charge density, the number of hydrogen bonds formed by O_t and H_w in the interlayers increase, and under the action of hydrogen bonding force, the water molecules near the central axis are pulled towards the two sides of Si-O surface. As a result, the arrangement of water molecules is more compact, and the structure is obvious. Correspondingly, the self-diffusion coefficient shows that the higher the layer charge density, the lower the self-diffusion coefficient of water molecules in interlayers is and the worse the hydration performance of montmorillonite. The experimental results of the experiments fit well with the above simulation results.

Effect of Layer Charge Characteristics on the Distribution Characteristics of H2O and Ca2+ in Ca-Montmorillonites Interlayer Space: Molecular Dynamics Simulation

The charge characteristics of montmorillonite have significant effects on its hydration and application performances. In this study, a molecular dynamics simulation method was used to study the influence of the charge position and charge density of montmorillonite on the distribution of H2O and Ca2+ in layers. The results showed that when the layer charge is mainly derived from the substitution among ions in the tetrahedron, a large number of Hw and Ot are combined into a hydrogen bond in the interlayer, thus the water molecules are more compactly arranged and the diffusion of water molecules among the layers is reduced. In addition, the Ca2+ are diffused to the sides by a concentrated distribution in the central axis of the layer. As the charge density of the montmorillonite increases, the polarity of the Si-O surface increases, which lesds to the deterioration of the diffusibility of the water molecules and the structure of the water molecules in the interlayers is more stable. The increase in the layer charge density lesds to the expansion of the isomorphic substitution range of the crystal structure, which results in a more dispersed distribution of Ca2+ among the layers under the action of electrostatic attraction between the substituted negative sites and the Ca2+.

Characteristics of Hybrid Pigments Made from Alizarin Dye on a Mixed Oxide Host

This paper describes the fabrication of a new hybrid pigment made from 1,2-dihydroxyanthraquinone (alizarin) on a mixed oxide host (aluminum-magnesium hydroxycarbonate, LH). Various tools were applied to better understand the interactions between the organic (alizarin) and inorganic (LH) components, including ion mass spectroscopy (TOF-SIMS), 27-Aluminm solid-state nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). TOF-SIMS showed that modification of the LH had been successful and revealed the presence of characteristic ions C₁₄H₇O₄Mg⁺ and C₁₄H₆O₅Al^-, suggesting interactions between the organic chromophore and both metal ions present in the mixed oxide host. Interactions were also observed between Al³⁺ ions and Alizarin molecules in ²⁷Al NMR spectra, with a chemical shift detected in the case of the modified LH matrix. Any changes in color following reactions with Mg²⁺ and Al³⁺ ions were observed. Some of the physicochemical properties of alizarin, such as resistance to dissolution and color stability at elevated temperatures, were improved in comparison to the pure dye. This effect can be attributed to strong dye-LH interactions and the effective transformation of alizarin into an insoluble form. Moreover, the pigments exhibited higher thermal resistance and greater color stability in comparison to commercially available alizarin lakes (Alizarin Crimson).

Dual role of layered double hydroxide nanocomposites on antibacterial activity and degradation of tetracycline and oxytetracyline

The antibiotic intercalation inside the layered double hydroxide (LDH) layers was usually considered for water decontamination but rarely for drug delivery. Here, tetracycline (TCH) and oxytetracycline (OXY) were immobilized in Zn₂Al-Cl LDH following two methods: co-precipitation and anionic exchange. The interfacial concentration of antibiotic varies from 0.04 to 0.5 depending the method of immobilization. The antibiotics are not intercalated in the interlayer space allowing their release in 10 Hours. The antibacterial activity against both E. coli and S. epidermidis revealed that the loaded antibiotics are still active but less efficient compared to the free ones. After exposition to UV light or to high temperature storage (30, 60 and 120 °C), their antibacterial activity significantly decreases due to their degradation especially when antibiotic is loaded on material by co-precipitation. These results are promise to reduce antibiotic contamination in waters.

Cetyltrimethylammonium bromide intercalated and branched polyhydroxystyrene functionalized montmorillonite clay to sequester cationic dyes

Herein, Cetyltrimethyl ammonium bromide (CTAB) intercalated and branched polyhydroxystyrene (BPS) functionalized montmorillonite (MMT) nano-composite (BPS-CTAB-MMT) was developed, characterized, and its potential as an adsorbent was tested in sequestering cationic dyes viz. rhodamine B (RB), crystal violet (CV), and methylene blue (MB) from aqueous environment. N₂ adsorption/desorption isotherm showed mesoporous BPS-CTAB-MMT surface with a BET surface area of 273.8 m²/g. The appearance of sharp spikes at 2855 and 2925 cm^-1 (associated with symmetric and asymmetric tensions of C - H bonds) in infra-red spectrum of BPS-CTAB-MMT indicates successful intercalation of MMT with CTAB and functionalization with BPS. The observed crystallite size of BPS-CTAB-MMT was 66 nm. Comparatively greater weight loss for BPS-CTAB-MMT (11%) than MMT (9%) was observed during thermogravimetric analysis. The adsorption of dyes on BPS-CTAB-MMT was pH dependent with maximum uptake was observed in the pH range: 5-6. For initial dyes concentration (C_o) range: 50-150 mg/L, the observed equilibration time for CV was 300 min, whereas for RB and MB the equilibration time varied between 300 and 360 min. Modeling investigations revealed the applicability of Sips isotherm and pseudo-second-order (PSO) kinetic models to dyes adsorption data. Sips maximum adsorption capacity (q_s) values for RB, CV, and MB at 55 °C were 476.5, 438.7, and 432.7 mg/g, respectively. The adsorption of dyes on BPS-CTAB-MMT was thermodynamically favorable. Desorption studies showed 42.1% RB and 41.9% CV recovery with 0.1 M NaOH and CH₃COCH₃, respectively, while only traces of MB were recovered with tested eluents.

Cationic Surfactant-modified Clay as an Adsorbent for the Removal of Synthetic Dyes from Aqueous Solutions

In this study, the potential of hexadecyl trimethyl ammonium bromide modified montmorillonite (HDTMA-Mt) to remove the synthetic dyes Alizarin Red S (ARS) and Bromocresol Green (BCG) from aqueous media was assessed. The effect of different factors including surfactant loading rate onto the clay, contact time, pH, adsorbent dosage and dye concentrations, on the removal of ARS and BCG in batch systems were investigated. The adsorbent was characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). The equilibrium time for ARS and BCG was reached at 40 and 20 min, respectively, under optimized conditions (i.e. pH = 3, adsorbent dosage=1 g/L, surfactant loading rate onto the clay 70% of the cation exchange capacity (CEC) for ARS and 120% of the CEC for BCG, ARS concentration 50 mg/L and BCG concentration 500 mg/L). The adsorption rate of both dyes fitted the pseudo-second-order kinetic model and the equilibrium data was described by the Freundlich isotherm equation. The maximum monolayer adsorption capacities were equal to 666.6 and 1250 mg/g for ARS and BCG, respectively. Therefore, the HDTMA-Mt can be considered as an effective adsorbent for the removal of ARS and BCG from aqueous solutions.

Efficient removal of Acid Green 25 dye from wastewater using activated Prunus Dulcis as biosorbent: Batch and column studies

Biosorbent synthesized from dead leaves of Prunus Dulcis with chemical activation during the synthesis was applied for the removal of Acid Green 25 dye from wastewater. The obtained biosorbent was characterized using Brunauer-Emmett-Teller analysis, Fourier transform-infrared spectroscopy and scanning electron microscopy measurements. It was demonstrated that alkali treatment during the synthesis significantly increased surface area of biosorbent from 67.205 to 426.346 m²/g. The effect of various operating parameters on dye removal was investigated in batch operation and optimum values of parameters were established as pH of 2, 14 g/L as the dose of natural biosorbent and 6 g/L as the dose of alkali treated biosorbent. Relative error values were determined to check fitting of obtained data to the different kinetic and isotherm models. It was established that pseudo-second order kinetic model and Langmuir isotherm fitted suitably to the obtained batch experimental data. Maximum biosorption capacity values were estimated as 22.68 and 50.79 mg/g for natural biosorbent and for alkali activated Prunus Dulcis, respectively. Adsorption was observed as endothermic and activation energy of 6.22 kJ/mol confirmed physical type of adsorption. Column experiments were also conducted to probe the effectiveness of biosorbent for practical applications in continuous operation. Breakthrough parameters were established by studying the effect of biosorbent height, flow rate of dye solution and initial dye concentration on the extent of dye removal. The maximum biosorption capacity under optimized conditions in the column operation was estimated as 28.57 mg/g. Thomas and Yoon-Nelson models were found to be suitably fitted to obtained column data. Reusability study carried out in batch and continuous column operations confirmed that synthesized biosorbent can be used repeatedly for dye removal from wastewater.