Cationic Organic Dyes Research Articles

Two-Dimensional MXene Flakes with Large Second Harmonic Generation and Unique Surface Responses.

MXenes are a family of two-dimensional (2D) materials with broad and varied applications in biology, materials science, photonics, and environmental remediation owing to their layered structure and high surface area-to-volume ratio. MXenes have exhibited significant nonlinear optical characteristics, which have been primarily explored in the context of photonics applications, yet the second-harmonic generation (SHG) behavior of MXenes remains an unexplored aspect of their optical properties. Herein, we demonstrate and quantify large second-order responses of 2D Ti3C2Tx MXenes both in aqueous solutions and on a silicon substrate for the first time. MXene flakes showed strong second-harmonic scattering (SHS) in a dilute suspension with a sensitivity of less than 0.1 μg/mL. Angle-dependent SHS experiments further found that the second-order responses originate from coherent 2D dipole radiation. Through confocal and atomic force microscopies, we found that the intense SHG signal from free-standing MXene flakes increases exponentially with decreasing thickness, while two-photon fluorescence increases linearly with thickness. The second-order susceptibility of the MXenes was determined to be 3.6 pm V-1 with a thickness of 10 nm, almost twice of that for an often-used SHG crystal, beta barium borate. We further explored surface properties of the MXene sheets by investigating the SHS responses upon addition of organic dye molecules to the system. It was found that the adsorption of crystal violet (CV) obeys a Langmuir adsorption model while the addition of malachite green (MG) resulted in almost no change in SHG intensity, even though the adsorption capacities for both CV (61.3 ± 1.7 mg/g) and MG (54.8 ± 2.8 mg/g) are similar. Such a stark difference in adsorption characteristics between cationic organic CV and MG dyes is likely due to their distinct orientational orderings on the MXene surfaces. This work opens many possibilities for the further employment of the family of 2D materials in photonics, optics, and surface catalysis applications.

Zeolite-decorated black TiOx quantum dots for photocatalytic degradation of organic cationic dyes under LED light irradiation

Defect engineering is a promising strategy to reduce the band gap of semiconductors, enhancing their photocatalytic activity under visible light by introducing intra-bandgap energy states. Among the materials studied, oxygen-deficient black TiOx stands out due to its potential in photocatalytic reduction and hydrogen evolution. However, the valence band edge maximum (VBM) of TiOx is not thermodynamically favorable for the direct oxidation of water to hydroxyl radicals (H2O/•OH). Although the formation of extensive oxygen vacancies is necessary to extend the light absorption of black TiOx to longer wavelengths, a high density of oxygen vacancies (Ov) significantly shortens the diffusion length of charge carriers within the TiOx, leading to increased recombination of electrons and holes (e-/h+), thereby suppressing photocatalytic activity. To overcome these limitations, confining TiOx particles to the quantum dot (QD) size range and constructing heterojunctions with a secondary phase can substantially improve charge carrier separation and photocatalytic performance. In addition to engineering the electronic structure of composite photocatalysts, the preaccumulation of pollutants and their subsequent degradation is an effective strategy. This method decreases the distance between the adsorbed pollutant and the active sites for reactive oxygen species (ROSs) generation, enhancing the efficiency of the photocatalytic degradation process. In this study, we confined TiOx particles to the quantum dot size range by constructing a heterojunction with H-Beta zeolite, which contains defect-induced energy states within its wide band gap. This type of zeolite is particularly effective in adsorbing cationic azo dyes, facilitating pre-accumulation and degradation. The synthesized catalysts were extensively characterized using HRTEM to determine the average size of the TiOx particles and photoluminescence (PL) analysis to investigate charge carrier separation. Our results demonstrated that while TiOx alone showed negligible degradation efficiency, and no •OH were detected, the QD TiOx/Z4 composite achieved complete oxidation of CV by •OH, as confirmed by TOC analysis. The photocatalytic degradation mechanism was proposed based on these experimental findings. These insights could be of significant interest to researchers exploring defective semiconductors for photocatalytic oxidation of organic pollutants in the liquid phase under visible light (LED) irradiation.

Organo cationic dyes adsorption on charged nano-clay: Revealing dual mechanisms through GCS modeling and DFT molecular simulations

This study investigates the adsorption mechanisms of organic cationic dyes, specifically malachite green (MG) and toluidine blue (TB), on sodium montmorillonite clay (Na-MMC). Using montmorillonite sourced from the Nador deposit in Northern Morocco, we aim to model cation exchange with the Gouy-Chapman-Stern (GCS) model. The adsorption capacities are found to be 192.5 meq/100 g for TB and 175.8 meq/100 g for MG at room temperature and uncontrolled pH. X-ray diffraction (XRD) analysis was employed to determine the interlayer spacing of the montmorillonite, contributing to the understanding of adsorption mechanisms. GCS modeling provided insight into the adsorption constants for both dyes, alongside parameters related to the solid/solution interface such as the amount adsorbed per layer, ion concentration in the solution, and clay surface potential. These findings confirmed a significant affinity between the dyes and the clay, aligning with the literature. Moreover, Density Functional Theory (DFT) simulations indicated a stronger affinity of toluidine blue for negatively charged surfaces compared to other dyes.

Enhancing Stability of n-Type Doped Organic Semiconductors through Low Boiling Point Solvent-Assisted Room Temperature Drying.

The development of n-type organic semiconductors (OSCs) has been lagged behind that of p-type OSCs, mainly due to the limited availability of the electron deficient π-conjugated backbones and facile electron trapping by ambient oxidants. Improving the performance of n-type OSCs through n-doping is essential for realizing p-n junction diodes and complementary circuits. Conventional vacuum deposition doping is costly and time-consuming, while solution doping risks thermal damage through necessary annealing. Therefore, the development of a simpler, more affordable n-doping method is crucial. In this study, we have developed a solution-processed n-doping method using an organic cationic dye in a low boiling point solvent that can be dried at room temperature in 1 h, which eliminates the need for annealing. The effects of different organic cationic dyes and reducing agents on the n-type OSC were evaluated. After n-doping, electron mobility and photoresponsivity in the sample increased by 5.5 and 20 times, respectively, compared to undoped samples. Furthermore, there was no significant degradation in the electron mobility of the n-doped samples under ambient conditions after 15 days. Studying n-doping with various organic cationic dyes in different OSC materials, embracing further research into their applications and mechanisms, would advance the field of organic electronics.

A Supramolecular Polymer Network Based on Chitosan and Porphyrin and Its Application as an Adsorbent for Selective Removal of Dyes from Water

AbstractEnvironmentally friendly, high adsorption efficiency, and recyclable adsorbents meet the actual needs of organic dye wastewater treatment. Driven by noncovalent interactions between chitosan (CS) and 5,10,15,20‐tetra(4‐hydroxyphenyl) porphyrin sodium (THPPNa) under acidic conditions, a supramolecular polymer network is constructed. The supramolecular polymer network is applied as an excellent adsorbent for the removal of organic dyes from water with high efficiency. In addition, the supramolecular adsorbent shows excellent selectivity for the removal of organic anionic dyes from the mixtures of organic anionic and cationic dyes in water. Furthermore, the removal efficiency of anionic dyes of the network adsorbent keeps over 95% even after five adsorption–desorption cycles, indicating its reusability. This supramolecular polymer network shows its great potential as a low‐cost, effective, and selective adsorbent for removing organic dyes from water.

In situ construction of Ti3+ self-doped TiO2/Ti3C2 Schottky heterojunctions for highly selective photo-Fenton-like degradation of organic pollutants: Surface/interface effect and mechanism insight

The efficient activation of H2O2 in heterogeneous Fenton-like systems is important for the degradation of organic pollutants. Herein, a Ti3C2 MXene catalyst prepared by a simple HF etching method was used to activate H2O2. Ti3+ self-doped TiO2/Ti3C2 MXene (Ti3+-TiO2/Ti3C2) Schottky heterojunctions were in situ constructed in the photo-Fenton-like system. Owing to the Ti3+-TiO2/Ti3C2 Schottky heterojunctions, abundant multivalence titanium species, and strong surface negative charges, the Ti3C2 catalyst exhibited outstanding photo-Fenton-like performances towards the degradation of cationic organic dyes (methylene blue, rhodamine B, basic fuchsin) in a wide pH range of 3.04–10.02. Radical trapping and electron paramagnetic resonance experiments revealed that surface-bound hydroxyl radicals (OH), superoxide radicals (O2−), and photogenerated holes (h+) were the dominant species in the Ti3C2/H2O2/Visible-light system. Density functional theory calculations confirmed that TiO2/Ti3C2 Schottky heterojunctions not only promoted the separation of photogenerated carriers, but also facilitated the desorption of hydroxyl groups (–OH) from the decomposition of H2O2, thereby increasing the yield of reactive species (OH, O2−, and h+).

Highly active ZnO/Fe3+-TiO2 photocatalysts for visible-light photodegradation application and its colour change behaviour by d-d transition

Highly active novel ZnO/Fe-TiO2 composite catalysts with p-n junction heterostructure have been fabricated by adding commercial ZnO and sol–gel derived Fe-TiO2 nano-powders controlled by grinding and drying. This work reported that doped Fe (III) with TiO2 form a p-type semiconductor and whereas ZnO is an n-type semiconductor. The slight variation of electronegativity between ZnO and TiO2 causes a strong rectifying action for the formation of an interface between ZnO and Fe-TiO2. The occurrence of red shift phenomenon in absorption spectrum of the samples suggest the outcome of d-d transition of Fe3+ (2T2g → 2A2g, 2T1g) and the charge transfer transition between interacting Fe3+ ions (Fe3+ + Fe3+ → Fe4+ + Fe2+). These Fe3+ 3d states in addition to oxygen vacancies and Ti3+ centers create band states, thereby favouring the electronic transition to these levels and resulting in narrowing of TiO2 band gap. A direct confirmation is the increase of Urbach energy with the lowering in the band gap of ZnO/Fe-TiO2.The crystal field splitting of d orbitals (5 degenerate orbitals) of Fe3+ and the approach of free ligand ions which split into two sets and Fe3+ ligand field transition is discussed schematically. The photocatalytic activities of these heterostructure photocatalysts were evaluated by degrading toxic cationic organic dyes such as Methylene Blue (MB) and Malachite Green Oxalate (MG) under visible light. The mechanism of photocatalysis has been recommended which is based on the relative band structure of the semiconductor and integrated heterostructure. The formation of a spike barrier in the CB at the interface gives rise to trap sites that capture the migration of charge carriers and occurs recombination of electron-hole pair at higher Fe(III) doping concentration. The dark adsorption property of the catalysts sample has been also studied.

Melamine Network as a Solution for Significant Enhancement of the Mechanical, Adsorptive, and Surface Properties in a Novel Carbon Nanomaterial-Silica Aerogel Composite.

Silica aerogels exhibit exceptional characteristics such as mesoporosity, light weight, high surface area, and pore volume. Nevertheless, their utilization in industrial settings remains constrained due to their brittleness, moisture sensitivity, and costly synthesis procedure. Several studies have proved that adding nanofillers, such as carbon nanotubes (CNT) or graphene nanoplatelets (GNP), can improve the mechanical strength of the aerogels. The incorporation of nanofillers is often accompanied by agglomeration and pore blockage, which, in turn, deteriorates the surface area, pore volume, and low density. Including flexible melamine foam (MF) as a scaffold for the silica aerogel and nanofiller composite can prevent the restacking of the nanofillers through π-π interaction, hence maintaining the incredible properties of aerogels and improving their mechanical properties. CNT, GNP, and the polymeric silica precursor, polyvinyltrimethoxysilane (PVTMS), were added to a MF, at varying concentrations, to fabricate the MF-aerogel nanocomposites. Surfactant and sonication were utilized to ensure a homogeneous dispersion of the nanofillers in the system. The presence of MF prevented the agglomeration of nanofillers, resulting in lower density and relatively higher surface properties (SBET up to 929 m2·g-1 and pore volume up to 4.34 cc·g-1). Moreover, the MF-supported samples could endure 80% strain without breakage and showed an outstanding compressive strength of up to ∼20 MPa. These aerogel nanocomposites also demonstrated an excellent volatile organic compound (∼2680 mg·g-1) and cationic dye adsorption (∼10 mg·g-1).

Neem biomass derived carbon quantum dots synthesized via one step ultrasonification method for ecofriendly methylene blue dye removal

This article presents a one-step ultrasonication technique for generating biomass carbon dots (BCDs) from neem bark (Azadirachta indica) powder. The BCDs were characterized using modern techniques such as UV–Vis, FTIR, Raman, XRD, HRTEM, FESEM, EDAX, and Zeta potential analyses. Unlike traditional nanocomposite bed systems, this study utilized BCDs as a liquid-phase adsorbent for the regenerative adsorption of the environmentally harmful dye, methylene blue (MB), through an in-situ precipitation reaction. This involved the formation of BCDs-MB adduct via an electrostatic mechanism. The adsorption capacity and percentage of removal were remarkable at 605 mg g–1 and 64.7% respectively, exceeding various solid-based adsorption methods in the literature. The Langmuir isotherm and pseudo-second-order kinetics model provided an excellent fit for this system. The calculated thermodynamic parameter, Gibbs free energy change (ΔG) was negative, indicating a spontaneous, exothermic, and physisorption-based mechanism. The regenerative capacity of our system was further demonstrated by successfully extracting and recovering the MB dye (64%) using ethyl alcohol as the solvent. This method provides an efficient means of recovering valuable cationic organic dye compounds from contaminated environments.

Enhanced photocatalytic activities of LaCoO3 perovskite nanostructures for degrading cationic and anionic dyes

Sustainable and cost-effective technologies are crucial for addressing environmental pollution issues. Perovskite photocatalysts have gained increased attention as a potential solution which could be accounted to their tuneable structural characteristics, flexible bandgap, and superior catalytic properties. In this study, we synthesized Lanthanum Cobaltite (LaCoO3) perovskite nanostructures via co-precipitation for photocatalytic purposes. Morphological analysis revealed LaCoO3 nanoparticles with an average size of ∼33 nm whose crystalline characteristics were investigated as a function of annealing temperatures. We found that the pure and crystalline LaCoO3 phase formed after the post-annealing process at 600°C. Photocatalytic studies showed that the degradation potential of LaCoO3 was significantly improved when hydrogen peroxide (H2O2) was added as co-catalyst system. We achieved degradation efficiencies of up to 91% and 85% for MB and methyl orange (MO), respectively. LaCoO3/H2O2 exhibited excellent photocatalytic potential for degrading both anionic and cationic organic dyes for environmental remediation applications.

Low‐Carbon‐Footprint Plasma‐Functionalized Coconut‐Coir‐Based Porous Carbon as an Efficient and Sustainable Adsorbent

AbstractHerein, the surface of pyrolyzed coconut coir (PCC) dust has been functionalized using atmospheric plasma under non‐equilibrium conditions without utilizing vacuum chambers. The reactive species present in the plasma such as, molecular ions, electrons, and radicals interact with PCC's surface, leading to the introduction of epoxy, carbonyl and amino functional groups on carbon surface. The resulting plasma functionalized carbon (PFC) material was characterized using several advanced material characterization techniques, including PXRD, FTIR, XPS, N2 BET specific surface area, SEM and TEM imaging techniques, etc. Moreover, it has been used in diverse applications in toxic gas removal (CO2, CO, NOx), fluoride (F−) removal from drinking water and cationic organic dye (methylene blue–MB) removal. The reported method for synthesis of functional carbon introduces a platform technology for low carbon footprint, green synthesis of advanced functional materials.

Green synthesis of carbon quantum dots from teak leaves biomass for in situ precipitation and regenerative-removal of methylene blue-dye.

The objective of this study was to completely eliminate environmentally harmful cationic organic dye from aqueous solutions using the one-step ultrasonication method, renowned for its energy efficiency, user-friendliness, and minimal requirement for chemical resources, making it particularly suitable for large-scale applications. To achieve effective environmental remediation, we employed carbon dots derived from teak leaf biomass (TBCDs) layered with graphene oxide. We conducted a thorough characterization of the TBCDs using UV-vis spectroscopy (with absorption peaks at λmax = 208 and 276nm), FTIR spectroscopy (confirming the presence of various functional groups including -OH, -CH, C = O, COO-, C-O-C, and = C-H), Raman spectroscopy (with bands at 1369cm-1 (D-Band) and 1550cm-1 (G-Band), and an intensity ratio (ID/IG) = 0.88, indicating structural defects correlated with the sp3 hybridization sites on the TBCDs), XRD analysis (indicating an amorphous nature of particles), HRTEM imaging (showing homogeneous dispersal of TBCDs with typical sizes ranging from 2 to 10nm), FESEM analysis (showing a flat surface and minuscule particles), and Zeta potential analysis (revealing a surface charge peak at -51.0mV). Our adsorption experiments yielded significant results, with a substantial 50.1 % removal rate and an impressive adsorption capacity of 735.2mg g-1. Theoretical adsorption parameters were rigorously analyzed to understand the adsorption behavior, surface interactions, and mechanisms. Among these models, the Langmuir isotherm in conjunction with pseudo-second-order kinetics provided an exceptional fit (with R2 values closer to 1) for our system. The Gibbs free energy (ΔG) was found to be negative at all temperatures, indicating the spontaneity of the reaction. Regarding mechanism, electrostatic attraction ((+ve) MB dye + (- ve) TBCDs), π-π stacking adsorption facilitated by the graphitic structure, formation of multiple hydrogen bonds due to polar functional groups, and a pore-filling mechanism wherein the cationic MB dye fills the pores of TBCDs with graphene oxide layers, forming an adduct were identified. Furthermore, we demonstrated the regenerative capacity of our system by effectively extracting and recovering the MB dye (with a regeneration rate of 77.1%), utilizing ethyl alcohol as the solvent. These findings not only provide valuable insights into the adsorption capabilities of TBCDs but also highlight the potential of our approach in the recovery of expensive cationic organic dye compounds from polluted environments.

Construction of a carboxyl-functionalized clover-like covalent organic framework for selective adsorption of organic dyes

Covalent organic frameworks (COFs) with designable structure and well-defined aperture are highly desired as novel adsorbents for elimination of dye pollution. Herein, a new carboxyl-functionalized covalent organic framework (TzDABA COF) with clover-like topology was synthesized by the condensation of 1,3,5-tris(4-formyl-phenyl) triazine (Tz) and 3,5-diaminobenzoic acid (DABA) under solvothermal conditions. The obtained TzDABA COF exhibited rapid adsorption kinetics and excellent adsorption capacities toward multiple cationic organic dyes including methylene blue (MB, 315 mg g−1), crystal violet (CV, 533 mg g−1) and malachite green (MG, 1168 mg g−1) owing to the formation of strong electrostatic interaction and π-π interaction between COF framework and organic dye molecules. Remarkably, with particular ABC stacking mode and an abundant of carboxyl functional groups integrated in the clover-like architecture, the anionic TzDABA COF could effectively separate organic dyes in different modes, representing the first case of carboxyl-functionalized clover-like COF for dye separation based on charge effect and size effect. This study paves a new pathway toward construction of carboxyl-functionalized clover-like COFs and reveals their desiring prospect in field of dyes separation and purification.

Exploring the interaction of decavanadate with methylene blue, toluidine blue and rhodamine B

Alkyl pyridinium decavanadate salt interacts with cationic organic dyes in aqueous media. A crystal structure of methylene blue with decavanadate is reported for the first time.

Highly enhanced cationic dye adsorption from water by nitro-functionalized Zn-MOF nano/microparticles and biomolecular binder for improving the reusability

Zinc-metal organic frameworks (Zn-MOFs) of phthalic acid (ZnPA) and nitro-phthalic acid (ZnNPA) microcrystalline particles were fabricated and utilized for the removal of organic cationic dyes (crystal violet (CV), methylene blue...

Removal of methylene blue dye from water with Fe3O4/poly(HEMA-co-AMPS) magnetic hydrogels

In this research, a novel magnetic hydrogel (MHG) adsorbent based on Fe3O4/poly(2-hydroxyethylmethacrylate-co-2-acrylamido-2-methylpropanesulfonic acid) Fe3O4/poly(HEMA-co-AMPS) was synthesized by in situ co-precipitation of Fe3O4 magnetic particles inside poly(HEMA-co-AMPS) hydrogels. This adsorbent was used to adsorb the organic cationic dye methylene blue (MB) from aqueous solutions. The properties of the adsorbent were characterized by FT-IR, TGA, XRD, VSM, and EDX-SEM techniques. The degree of swelling was recorded in water, acidic medium (HCl 0.01 M), and basic medium (NaOH 0.01 M). The results confirmed that Fe3O4 particles were successfully synthesized within the poly(HEMA-co-AMPS) hydrogel structure. Magnetic hydrogels have higher swelling and reach equilibrium faster than hydrogels. The magnetic hydrogel prepared with 3 % crosslinker and 10 % AMPS (MHG3(10)) showed better potential to remove MB dye, adsorption capacity Qmax = 445.35 mg/g, this was obtained under the best conditions at pH 6.5, dose of 1 g/L, and contact time of 10 min. Over the test pHpzc, the surface of the MHG3(10) is predominantly negative at pH values higher than 2.47. The adsorption process of MHG3(10) for MB removal follows the Langmuir model and obeys pseudo-second-order kinetics. In addition, thermodynamic studies performed show that the adsorption process is endothermic (ΔH0 = 75.946 kJ/mol) and spontaneous with a positive value of entropy (ΔS0 = 263.562 J/mol·K). Regeneration experiments showed that MHG3(10) can be reused several times as its removal efficiency is still 94 % after 10 adsorption–desorption cycles. Therefore, the magnetic hydrogel MHG3(10) proved to be a promising adsorbent for the removal of the pollutant MB dye from aqueous media.

Adsorption behavior and mechanism of modified Pinus massoniana pollen microcarriers for extremely efficient and rapid adsorption of cationic methylene blue dye

Herein, a novel biosorbent was successfully fabricated through a two-step process employing Pinus massoniana pollen as raw material. The efficacy of this biosorbent in eliminating methylene blue (MB), a typical organic cationic dye, from highly concentrated industrial wastewater was investigated. The results demonstrated that by adjusting the wettability of pollen microcarriers, it is possible to significantly increase their adsorption capacity for cationic dyes, resulting in a remarkable 25-fold improvement. The modified Pinus massoniana pollen microcarriers (MPPMC) exhibited an optimal adsorption capacity (585 mg/g) under specific conditions and a rapid equilibrium (97.6% in 5 min, uptake 487.8 mg/g) even at room temperature, showing excellent performance in removing MB efficiently and quickly. It is worth noting that the modified microcarriers could be regenerated via a simple pH-controlled adsorption-desorption cycle, maintaining their superior efficiency (> 99%) even after undergoing five cycles, indicating their excellent reproducibility. The MB adsorption process on MPPMC obeyed the pseudo-second-order kinetic model and followed the Langmuir model. Through the introduced modifications, the substantial deprotonation of carboxyl groups notably augmented electrostatic and hydrogen bonding interactions between MPPMC and MB. Overall, this study offers a sustainable, eco-friendly biological adsorbent, and the MPPMC exhibit the considerable potential for efficient and rapid removal of organic cationic dyes in wastewater.

Natural tea extract coated porous MOF nano/microparticles for highly enhanced and selective adsorption of cationic dyes from aqueous medium

A simple, sustainable method was developed for boosting the dye adsorption capability of porous metal organic frameworks (MOFs) by coating them with natural tea extract. Nano/microparticles of zinc-terephthalic acid (ZnTPA) MOFs exhibited only 40% rhodamine B (Rh B) dye adsorption. The dye adsorption capability was strongly enhanced (up to 95%) after coating with natural tea extract and highly selective cationic dye adsorption. The coating of multifunctional biomolecules onto the ZnTPA matrix was expected to facilitate strong intermolecular interaction between MOF surface and organic dyes, which contributed to strongly enhanced dye adsorption. ZnTPA/Tea MOFs not only exhibited enhanced dye adsorption but also showed high retention capability. The broader scope of tea extract coating methodology for cationic dye adsorption was also demonstrated using other MOFs matrix. The exhausted ZnTPA MOF was easily regenerated by sonication followed by re-dipping into tea extract. Tea extract coated ZnTPA MOFs was also used as column packing materials for removing cationic dyes by filtration. Thus, the present work reported a facile strategy for efficient cationic organic dyes removal from the aqueous medium.

Removal of Methylene Blue by adsorption onto natural and purified clays: Kinetic and thermodynamic study

The present work explores the optimization of experimental conditions for the adsorption of the organic cationic dye methylene blue (MB) by natural and purified clays. The adsorption capacities of samples were determinate to evaluate the efficiency of the purification process. At first, we performed mineralogical and textural analysis of the clay minerals, namely, smooth clay (SC), rigorous clay (RC) and bentonite clay (BC), using various techniques, particularly, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). The characterizations data showed that SC and RC are mainly composed of smectite associated with kaolinite, illite and chlorite. While BC is considered a mesoporous and swelling clay with smectite as the major component. The cation exchange capacity (CEC) was determinate as a 6.30 meq/100 g, 10.69 meq/100 g and 32.64 meq/100 g for SC, RC and RC natural samples respectively. It was noticed that the CEC as well as the specific surface area increase once the impurities associated with the clay are removed. A preliminary study was carried out to elucidate the influence of different parameters; such as contact time, exchangeable cation, solute concentration, temperature and pH on MB adsorption in aqueous solution by clays. The adsorption equilibrium data were analyzed by the linear and nonlinear forms of the Langmuir and Freundlich isotherm models. The Langmuir isotherm fitted well with the experimental data, and the pseudo-second-order kinetic model represented appropriately the adsorption kinetics of MB dye. Moreover, purified clays showed improved adsorption capacity for MB compared to pristine ones: 147.64; 257.69 and 1383 mg/g versus 128.75; 193.4 and 681.85 mg/g for SC, RC and BC respectively. This is attributed to a suitable specific surface, ion exchange capacity and electrostatic interactions as result of a more adequate texture and composition of our treated clays. The thermodynamic studies reveled negative Gibbs free energy change (ΔG) values (from -6.293 to -18.608 KJ.mol−1), positive enthalpy change (ΔH) values, exceeding 40 kJ/mol and positive entropy change (ΔS) values confirming the spontaneous, endothermic and chemisorption nature of the MB adsorption process. The results show that the tested purified clays are efficient in MB removal and can be used as an alternative to the commercial adsorbents, which are often relatively expensive.

Green Synthesis of Cerium-Based Metal-Organic Framework (Ce-UiO-66 MOF) for Wastewater Treatment.

Green synthesis of metal-organic frameworks (MOFs) in aqueous solutions under ambient conditions with reduced production costs and environmental effects is an efficient technique to transfer lab-scale production to industrial large scale. Hence, this work proposes a green, low-cost, sustainable, rapid, and innovative synthetic strategy to produce cerium-based (Ce-UiO-66) MOFs under ambient conditions in the presence of water as a green solvent. This synthetic strategy exhibits great potential compared to conventional solvothermal synthetic techniques, and it does not need external activation energy and organic solvents, which can achieve the standards of green chemistry. Ce-UiO-66 MOF was synthesized successfully and utilized as a green adsorbent to efficiently eliminate anionic Congo Red (CR) dye from dye-containing wastewater. The experimental adsorption results were well matched to the pseudo-second-order kinetic and Langmuir isotherm models, in which the maximum CR adsorption capacity was measured to be about 285.71 mg/g. To evidence the applicability of Ce-UiO-66 MOFs in CR adsorption, the CR adsorption reaction was performed in the presence of interfering pollutants [e.g., salts (NaCl, KCl, and MgCl2) and cationic organic dyes (Malachite Green (MG) and Methylene Blue (MB)], where the results prove the promising adsorption performances of Ce-UiO-66 MOFs toward CR dye. Interestingly, the synthesized adsorbent exhibited high structural stability during repeated adsorption-desorption cycles, where the surface area of MOFs decreased from 555 to 376 m2/g after three cycles, while its CR adsorption capacity decreased by only 10% compared to that of the fresh adsorbent. All these outstanding properties indicate that the Ce-UiO-66 MOFs will be an effective adsorbent for water and wastewater treatment applications.