Cellulose-based aerogels prepared by freeze-drying for selective adsorption of cationic/anionic dyes

Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: Adsorption performance and mechanisms

Hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeletons for highly efficient and selective adsorption of anionic dyes from water

This study aimed at synthesizing a fast-responsive chemically modified cellulose (MC) adsorbent for removing organic pollutants, such as cationic dyes, namely, methylene blue (MB), crystal violet (CV), brilliant green (BG), and malachite green (MG), from wastewater. The MC adsorbent was prepared by the chlorination of cellulose using phosphorous oxychloride (POCl3) to produce chlorodeoxy–cellulose (cellulose–Cl), followed by the nucleophilic attack of 2-(2-aminothiazol-4-yl)acetohydrazide. The prepared material was characterized extensively. The adsorption of dyes onto MC was investigated, individually and in a mixture, in a batch mode under variable experimental conditions, such as pH, contact time, initial dye concentration, temperature, and adsorbent dose, to optimize the adsorption process. From the kinetic investigations, with high R2 values and lower error functions ((χ2), (SSE), and (MSE)), the adsorption of MB and CV dyes matched well with the pseudo-second-order kinetic model, while the adsorption of BG and MG dyes matched well with the pseudo-first-order kinetic model. In addition, the Temkin model best fitted the adsorption isotherm data for MB, CV, and BG, while the adsorption data of the MG dye fitted well with the Langmuir isotherm model, with the maximum adsorption capacities of 173.00 mg g−1, 171.80 mg g−1, 188.60 mg g−1, and 82.17 mg g−1 for MB, CV, BG, and MG, respectively, at 308 K. Thermodynamic studies revealed the spontaneous and exothermic nature of the adsorption of these cationic dyes onto MC. The MC adsorbent exhibited good recycling performance. After five regeneration and adsorption cycles, the MC adsorbent still had a removal effect greater than 90% for the studied dyes, which indicated its high structural stability. The prepared MC was successfully applied for the removal of cationic dyes from real water samples and synthetic mixtures, with a recovery (R%) of higher than 97%. The adsorption mechanism of MB, CV, BG, and MG onto the adsorbent was elucidated. Ultimately, this study demonstrated that the fast-responsive MC adsorbent can be effectively utilized to eliminate MB, CV, BG, and MG cationic dyes from a wide range of real water sources. Collectively, the results indicated that the as-prepared MC adsorbent is promising for cationic pollutant adsorption, and our mechanistic results are of guiding significance for environmental cleanup. This work contributes significantly to understanding how experimental conditions influence the mechanism of MB, CV, BG, and MG dye adsorption by the MC adsorbent, offering valuable and new insights for future applications and optimizations in the treatment of effluent-containing cationic species.

Carbon-based nanomaterials have always been in high demand because of their efficient adsorption capabilities. Herein, we synthesized water-dispersible carboxylic acid-terminated carbon nanoflakes (CNFs) by simple acid treatment in aqueous solution of glucose. The as-synthesized CNFs have been used for the adsorption of multiple water-soluble cationic dyes and even from a mixture of spiked industrial wastewater. Here, we have used six water-soluble model dyes methylene blue (MB), crystal violet (CV), rhodamine B (RhB), congo red (CR), methyl orange (MO), and metanil yellow (MY) for adsorption studies. CNFs show significant adsorption capacity toward cationic dyes (MB, CV, and RhB) compared to anionic dyes (CR, MO, and MY). Selectivity in adsorption of cationic dyes on negatively charged CNFs adsorbents has occurred via electrostatic interaction. The adsorption capacities of CNFs toward three cationic dyes (MB, CV, and RhB) are ∼148, ∼132, and ∼118 mg g –1, respectively. More importantly, it is observed that CNFs have performed as better adsorbents than the well-known commercially available activated charcoal for the tested dyes. The adsorption process has been studied by varying different regulating parameters such as pH of the solution, initial dye concentration, temperature, and the concentration of CNFs and analyzed in terms of kinetic and isotherm models. Moreover, the adsorbed dyes could be desorbed completely from nanoflake surfaces and are efficient for multicyclic use.

Selective removal of cationic organic pollutants using disulfide-linked polymer

Preparation of amino/hydroxy dual-functionalized hypercrosslinked polymers for effective removal of organic dyes from water.

Under the guidance of self-assembly, a series of Cu(I)/Cu(II) metal–organic complexes (MOCs), [Cu3(TCPB)2(H2O)3]·2H2O (1), {[Cu2(TCPB) (DMA)(H2O)]·H2O}n (2), [(Cu8I8) (Cu6I6)0.5(DABCO)3·2H2O]n (3), and [(Cu4I8) (DABCO)2·6H2O]2n (4) (H3TCPB = 1,3,5-tris(4-carbonylphenyloxy)-benzene, DABCO = 1,4-diazabicyclo[2.2.2]octane) have been synthesized and characterized. Complexes 1 and 2 are driven by noncovalent interactions to assemble into supramolecular metal–organic frameworks. Considering H3TCPB ligand with different geometrical structures, 1 forms an Eiffel Tower shaped supramolecular cage based on equilateral triangle shaped trinuclear [Cu3(CO2)3] unit, which possesses effective free volume about 24.7%. Changing the solvent, 2 displays 1D chain structure based on linear bivalent copper trinuclear {Cu3(CO2)2(H2O)2}. When inducing auxiliary ligand DABCO, H3TCPB serves as additive agent and 3 consists of mixed CuI clusters (Cu6I6 and Cu8I8) and plays a 2D layer, which is a rare example. Without additive agent, 4 exhibits a 2D cuprous iodide layer, where 3 and 4 are two novel copper-iodide supramolecular isomers. Owing to large voids in the framework, 1 can serve as a host for use in dye adsorption. The experiment results show that different dyes, including “just right size” Crystal Violet (CV) can be rapidly adsorbed by 1, but smaller Indigo Blue (IB), Methylene Blue (MEB), Methyl Orange (MO), and larger Rhodamine B (RB) and Methyl Blue (MB) can hardly be adsorbed. Surprisingly, 1 also preferentially adsorbs (or separates) CV from MO and CV in their mixed aqueous solution with fast response and high sensitivity (<16.13 s) by the theoretical calculation. Moreover, absorption spectra demonstrate the band gaps of 3 and 4 are 2.37 and 1.98 eV, respectively. When increasing the dimensions of inorganic compositions in cluster–organic complexes, it could exert a remarkable influence on the band gap.

Controlled surface functionalization of Ni-S nanostructures for pH-responsive selective and superior pollutants adsorption

Adsorption of anionic and cationic azo dyes from wastewater using novel and effective multicomponent adsorbent

This work presents the preparation of inorganic-organic hybrid nanocomposites, namely three-dimensional polyaniline (Pani)/activated silica gel (ASG) (3D Pani@ASG), their characterization, and in removing application as a potential adsorbent for cationic brilliant green (BG), crystal violet (CV), and anionic Congo red (CR), and methyl orange (MO) dyes. Pani@ASG nanocomposites have been prepared by the in situ polymerization method and characterized using various techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with selected area electron diffraction, thermogravimetric analysis with derivative thermogravimetry, zeta potential analyses, and Brunauer-Emmett-Teller (BET). The scanning electron microscopy (SEM) study confirms the average particle size of the Pani@ASG nanocomposite is in the range of 5 nm. FESEM, TEM, FTIR, and XRD analysis proved the successful decoration of ASG over Pani. The BET result of Pani@ASG shows a mesoporous nature with a pore diameter of less than 3 nm and a surface area of 423.90 m2 g-1. Both SEM and TEM analyses show the proportional distribution of ASG over Pani's surface. The adsorption trend of BG and MO on the studied materials at pH 7 was found as follows: Pani@ASG > Pani > ASG. The highest sorption capacities of MO and BG on Pani@ASG were 161.29 and 136.98 mg/g (T = 298.15 K, and Pani@ASG dose: 0.04 g for MO and 0.06 g for BG), which were greater compared with bare Pani and bare ASG, respectively. The interaction mechanism behind the adsorption of BG and MO dyes onto the Pani@ASG nanocomposite includes electrostatic interaction, π-π interaction, and hydrogen bonding. The mechanistic pathway and the interactions between the targeted dyes and Pani@ASG were further studied using adsorption isotherm, adsorption kinetics, and thermodynamics.

High adsorption of cationic dyes from aqueous solution using worm-like porous nanosilica: Isotherm, kinetics and thermodynamics

A simple method for organically modifying a natural acid clay (Japanese acid clay) rapidly with alkylamine has been developed. Japanese acid clay mainly consists of acidic montmorillonite and was successfully modified with decylamine in water at room temperature for a short time period (10 min) using an ultrasonic bath without any pretreatments. The structure of the modified clay changed from exterior surface modification to intercalation with an increase in the decylamine content. The equilibrium adsorption capacity for the anionic dye methyl orange (MO) increased with increasing decylamine content. The adsorption kinetics and isotherm were well described by the pseudo-second-order and Langmuir models, respectively. Better MO adsorption was obtained under the conditions of high dosage, low pH value, and low temperature. The adsorbent was also found to have good adsorption for not only MO but also other anionic dyes (Congo red and eosin Y) and cationic dyes (methylene blue, crystal violet, and rhodamine B). In particular, the decylamine-intercalated clay adsorbent exhibited a high level of adsorption capacity for Congo red and crystal violet. The results demonstrate that the synthesis process can provide a simple and cost-effective organoclay as an adsorbent with high performance for the removal of anionic and cationic dyes.

Enhanced and rapid adsorptive removal of toxic organic dyes from aqueous solution using a nanocomposite of saponified polymethyl acrylate grafted dextrin with embedded nanosilica

The discharge of industrial printing and dyeing wastewater is one of the main reasons for the increasing water shortage and deterioration. The treatment of dyestuff wastewater is an issue and needs to be urgently solved. In this work, anionic ionic liquid functional covalent organic materials (COMs) were firstly synthesized and used for the selective adsorption of cationic dyes. First, a series of sulfonic acid group (SO3H)-functionalized anionic TpPa-SO3, TpBd-(SO3)2, and TpCR-(SO3)2 were prepared, respectively, and then imidazole was grafted onto TpBd-(SO3)2 to obtain ImI@TpBd-(SO3)2. The full characterization using X-ray diffraction, FT-IR spectroscopy, 13C cross-polarization magic-angle spinning NMR spectroscopy, zeta-potentials, BET surface and pore analysis indicated that these COMs and ImI@TpBd-(SO3)2 exhibited different morphologies, porosities, and potentials. The effects of the type of dye, adsorption time, initial dye concentration, and pH on the adsorption of dyes on ImI@TpBd-(SO3)2 were systematically investigated, respectively. The results revealed that ImI@TpBd-(SO3)2 possessed good adsorption performance for nine different cationic dyes with adsorption capacities in the range from 2865.3 mg g−1 for methylene blue (MB) to 597.9 mg g−1 for basic orange 2 (BO), but little adsorption for anionic and neutral dyes, revealing charge selectivity. The adsorption ratio of ImI@TpBd-(SO3)2 for MB was as high as 74.0% at 10 min by using 1.0 mg material, owing to the post modification of TpBd-(SO3)2 with imidazole. The adsorption of MB on ImI@TpBd-(SO3)2 was pH dependent. The adsorption isotherm and kinetics fitted well with the Freundlich and pseudo second-order kinetic model, respectively. Finally, the very outstanding advantages of superior selective adsorption, desorption, convenient preparation, and low density of ImI@TpBd-(SO3)2 predicted its research and application potential in dye wastewater recovery.

Selective adsorption and separation of organic dyes using functionalized cellulose nanocrystals