Oxalic acid-based covalent triazine framework for efficient, rapid, and simultaneous adsorption of anionic and cationic dyes from water

Chitosan (CS) is largely employed in environmental applications as an adsorbent of anionic dyes, due to the presence in its chemical structure of amine groups that, if protonated, act as adsorbing sites for negatively charged molecules. Efficient adsorption of both cationic and anionic dyes is thus not achievable with a pristine chitosan adsorbent, but it requires the combination of two or more components. Here, we show that simultaneous adsorption of cationic and anionic dyes can be obtained by embedding Linde Type A (LTA) zeolite particles in a crosslinked CS-based aerogel. In order to optimize dye removal ability of the hybrid aerogel, we target the crosslinker concentration so that crosslinking is mainly activated during the thermal treatment after the fast freezing of the CS/LTA mixture. The adsorption of isotherms is obtained for different CS/LTA weight ratios and for different types of anionic and cationic dyes. Irrespective of the formulation, the Langmuir model was found to accurately describe the adsorption isotherms. The optimal tradeoff in the adsorption behavior was obtained with the CS/LTA aerogel (1:1 weight ratio), for which the maximum uptake of indigo carmine (anionic dye) and rhodamine 6G (cationic dye) is 103 and 43 mg g−1, respectively. The behavior observed for the adsorption capacity and energy cannot be rationalized as a pure superposition of the two components, but suggests that reciprocal steric effects, chemical heterogeneity, and molecular interactions between CS and LTA zeolite particles play an important role.

Microwave synthesis of amino-functionalized MCM-41 from coal gasification fine slag for efficient bidirectional adsorption of anionic and cationic dyes

Construction of C8/threonine-functionalized mesoporous silica aerogel based on mixed-mode and its adsorption properties for both anionic and cationic dyes

Herein, a highly porous bimetal-organic framework (bi-MOF) based on cobalt and nickel was successfully in situ grown on organoclay (OC) clusters by solvothermal method. Accordingly, the hierarchical porous CoNi-MOF/OC composite with a superior specific surface area of 2046m2/g and a large pore volume of 0.763cm3/g was obtained, which facilitated the adsorption of organic dyes. A morphological study using scanning electron microscopy indicated the formation of uniform bi-MOF crystals on the OC plates. Furthermore, the single- and multi-dye adsorption assays were implemented to precisely evaluate the adsorption capacity and selectivity of CoNi-MOF/OC composite to anionic and cationic dyes. The results revealed a high adsorption capacity of 58.61mg/g at an adsorbent content of 15mg, initial dye concentration of 20ppm, and contact time of 25min for MB, which is superior to several existing clay-based adsorbents. The adsorption kinetics study showed that the adsorption of cationic and anionic dyes onto the CoNi-MOF/OC composite followed the pseudo-second-order kinetic model. Interestingly, the regeneration study showed appropriate reusability and stability of the CoNi-MOF/OC composite for the removal of organic dyes with an almost unchanged structure after four regeneration cycles. The results of this study provide new insights for the rational design and fabrication of next-generation clay-based adsorbent by combining the synergistic advantages of bi-MOF with superior specific surface area and pore volume with organoclay composition and structure.

Commercial kaolin from a Polish deposit has been examined as a low-cost adsorbent for effluent remediation using five cationic and five anionic industrial dyes. Methylene Blue dye was also used as a reference. The anionic dyes studied showed no affinity towards the kaolin surface, whereas the experimental isotherms for the adsorption of the cationic dyes could all be well described by the Langmuir equation. The values of the adsorption capacity of kaolin towards the cationic dyes ranged from 4 mg/g to 29 mg/g, being probably dependent on the geometry of the dye molecules. The resulting degrees of decolourization attained values of 85–90% for initial dye concentrations in the range 6–20 mg/dm 3 and for kaolin loadings of 0.5–3 g/dm 3 . Adsorption of the cationic dyes onto kaolin increased at higher solution pH values.

This study investigates the adsorption of cationic (methylene blue, MB) and anionic (methyl orange, MO) dyes onto activated carbon synthesized from almond seed shells (ASS-AC). The adsorbent was produced via carbonization and chemical activation and characterized using FTIR, XRD, SEM, and BET analyses. FTIR results revealed abundant oxygen-containing functional groups that enhanced electrostatic attraction and hydrogen bonding with dye molecules. XRD analysis indicated a predominantly amorphous carbon structure, while BET analysis showed a high surface area of 520 m²/g with dominant microporosity. Batch adsorption experiments evaluated the effects of contact time, initial dye concentration, pH, adsorbent dosage, and temperature. Adsorption kinetics followed a pseudo-second-order model (R² > 0.99), suggesting chemisorption as the rate-limiting step. Thermodynamic parameters (ΔG° < 0, ΔH° > 0) confirmed that the adsorption process was spontaneous and endothermic. Equilibrium studies showed that MB adsorption was best described by the Langmuir model with a maximum adsorption capacity of 162 mg/g, while MO adsorption followed the Freundlich model, indicating heterogeneous multilayer adsorption. Overall, ASS-AC demonstrates strong potential as a sustainable, low-cost adsorbent for efficient removal of both cationic and anionic dyes from wastewater.

Selective adsorption and separation of toxic cationic dyes using hierarchically porous SDBS modified vaterite microspheres (Hr-SMV)

ZIF-8/Chitosan hybrid nanoparticles with tunable morphologies as superior adsorbents towards both anionic and cationic dyes for a broad range of acidic and basic environments

Five kinds of activated carbon (AC1, AC2, AC3, AC4, and AC5) were prepared, and the characteristics (scanning electron microscopy images, specific surface area, pore-volume, pHpzc, surface functional groups, and surface hydroxyl groups) of each activated carbon were investigated. Additionally, the adsorption capability of activated carbons and adsorption mechanisms involved in adsorption of cationic and anionic dyes from the aqueous solution were evaluated. The results suggested that the treatment of activated carbon with silver (AC3), titanium oxide (AC4), or magnetic field (AC5) was not useful for increasing specific surface area and micropore volume. Moreover, the amount of cationic and anionic dyes adsorbed using activated carbon prepared from coconut shells (AC1 and AC2) were higher than that adsorbed using AC3, AC4, and AC5. Subsequently, the adsorption mechanism involved in adsorption of cationic and anionic dyes was also assessed. It was found that the amount of cationic and anionic dyes adsorbed was related to the specific surface area, micropore volume, and acidic or basic functional groups. Finally, the interactions between dyes and AC1 were elucidated in this study. Adsorption of dyes onto the AC1 surface was confirmed by the elemental distribution and X-ray photoelectron spectroscopy analysis. These results provide useful information on the surface interactions between the activated carbon and dyes (high molecular organic compounds).

Nitrogen-rich covalent triazine frameworks for high-efficient removal of anion dyes and the synergistic adsorption of cationic dyes

Influence of porosity and surface modification on the adsorption of both cationic and anionic dyes

Decoration of Fe3+ on carboxyl microporous organic network to fabricate magnetic porous carbon for efficient adsorption and removal of cationic dyes

Efficient removal of organic dyes from contaminated water has become a great challenge and urgent work due to increasingly serious environmental problems. Here, we have for the first time prepared nanolayer-constructed TiO(OH)2 microstructures which can present negative charge by deprotonation of the hydroxyl group to efficiently and selectively remove cationic dyes from aqueous solution through electrostatic interaction and an attraction mechanism. The nanolayer-constructed TiO(OH)2 microstructures achieve a high adsorption capacity of 257 mg g-1 for methylene blue (MB). The adsorption kinetics, thermodynamics, and isotherms of MB over the TiO(OH)2 microstructures have been studied systemically. The experimental measurements and corresponding analyses demonstrate that the adsorption process of MB on TiO(OH)2 microstructures follows a kinetic model of pseudo-second-order adsorption, agrees well with the Langmuir isotherm mode, and is a spontaneous and exothermic physisorption. Fourier transform infrared (FT-IR) spectra confirm that the prepared TiO(OH)2 microstructures possess hydroxyl group which can deprotonate to present negative charge in solution. Further experimental studies evidently demonstrate that the TiO(OH)2 microstructures also can remove other cationic dyes with positive charge such as basic yellow 1, basic green 4, and crystal violet but cannot adsorb anionic dye of methyl orange (MO) with negative charge in aqueous solution. The measurements for FT-IR spectra and the adsorption of cationic and anionic dyes evidently reveal that the adsorption of cationic dyes over the TiO(OH)2 microstructures is achieved by the electrostatic interaction and attraction between TiO(OH)2 and the dye. This work opens a strategy for the design of new absorbents to efficiently remove organic dyes from aqueous solution through an electrostatic attraction-driven adsorption process.

Mechanistic and adsorption kinetics study of sulfonated activated carbon enhanced starch-based aerogel for high efficient adsorption of cationic and anionic dyes.

The discharge of dyes into the water body creates toxicity to aquatic organisms because of their aromatic structure and difficult degradation. So, the treatment of dye-contaminated wastewater is required before releasing it. In the present study, thermally treated (600 °C) and H3PO4 (55%)-functionalized bagasse, henceforth called thermochemically activated bagasse (TCAB), was synthesized as potential adsorbent for the effective removal of selected cationic and anionic dyes from their aqueous stream. TCAB characterization was done employing FT-IR, SEM, XRD, zeta potential, BET, and PZC techniques. The comparative study shows that the relative adsorption on TCAB followed the sequence, methyl red (185 mg/g) > safranin (178 mg/g) > congo red (146 mg/g) > brilliant green (139 mg/g) > malachite green (130 mg/g) > bromocresol green (94 mg/g). The adsorption efficiency was investigated concerning the effect of change in TCAB dose (0.05-0.3 g/100 mL), initial dye concentration (20-200 mg/L), pH (4.0-10.0), ionic strength (0.1-0.5 M KCl), urea concentration (0.1-0.5 M) and temperature (25-45 °C). The representative adsorption isotherms belong to typical L-type. The time-dependent dye removal was best explained by the pseudo-second-order (PSO) kinetic model (R2 = 0.9859-0.9991), while equilibrium data were best explained by the Freundlich model (R2 = 0.9881-0.9961). Thermodynamic study showed the spontaneous (ΔG0 <0) and exothermic nature (ΔH0 <0) of the adsorption of different cationic and anionic dyes. The cyclic adsorption ability of TCAB for different dyes was checked up to three cycles (185 to 168 mg/L for MR, 178 to 165 mg/L for SF, 146 to 130 mg/L for CR, 139 to 127 mg/L for BG, 130 to 114 mg/L for MG and 94 to 80 mg/L for BCG), and no significant decrease in the adsorption capacity was noticed. So, the present study provides valuable insights into the adsorption of cationic and anionic dyes onto H3PO4-functionalized bagasse. Addressing the adsorptive aspects enhances the clarity, reliability and applicability of the study's findings and contributes to its overall scientific impact.