Comparison of adsorption properties for anionic dye by metal organic frameworks with different metal ions

A pH-dependent and charge selective covalent organic framework for removal of dyes from aqueous solutions

A novel imine-linked COF is synthesized by the condensation of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and 2-hydroxy-5-methoxyisophthalaldehyde (HMIPA) under solvothermal conditions. This COF adsorbs preferentially the neutral dye Neutral Red (NR) over the positively charged dye Methylene Blue (MB) at pH 7, and the negatively charged Methyl Orange (MO) over the positively charged Methylene Blue (MB) at pH 3. The maximum adsorption capacities (qe) obtained within very short times (11-60 min) under optimized conditions were 108, 185 and 429 mg.g-1 for the MB, MO, and NR dyes, respectively. These adsorptions obey the Langmuir isotherm and pseudo-second-order kinetics. The prepared TAPT-HMIPA-COF is used successfully for the removal of the dyes from real water and treated wastewater samples. The adsorption data, BET, FTIR, and zeta potential measurements show that the electrostatic, π-π stacking and hydrogen bond interactions are responsible for the adsorption of organic dyes on the surface of the prepared COF. Due to recyclability, high capacity and efficiency for the adsorption of positive, negative and neutral organic dyes, this COF can be considered promising for simultaneous removal of various dyes from aqueous solutions at adjusted pHs.

Polydopamine Enhanced Interactions of Graphene Nanosheets to Fabricate Graphene/Polydopamine Aerogels with Effectively Clear Organic Pollutants

Graphene/polydopamine aerogels (GPDXAG, where X represents the weight ratio of DA·HCl to GO) were prepared by the chemical reduction of graphene oxide (GO) using dopamine (DA) and l-ascorbic acid as reducing agents. During the gelation process, DA was polymerized to form polydopamine (PDA). The introduction of PDA in the gelation of aerogels led to a deeper reduction of GO and stronger interactions between graphene nanosheets forced by covalent cross-linking and noncovalent bonding including π-π stacking and hydrogen bonding. The weight ratio of DA·HCl to GO influencing the formation and morphology of GPDXAG was explored. With the increasing content of DA in gelation, the reduction of GO and the cross-linking degree of graphene nanosheets were enhanced, and the resulting GPDXAG had a more regular pore distribution. Additionally, introducing PDA into GPDXAG improved its hydrophobicity because of the adhesion of PDA to a network of aerogels. GPDXAG exhibited a higher removal efficiency for organic pollutants than the controlled graphene aerogels (GAG). Specifically, the adsorption capacity of GPDXAG for organic solvents was superior to that of GAG, and organic solvent was completely separated from the oil/water mixture by GPDXAG. The equilibrium adsorption capacity of GPDXAG for malachite green (MG) was measured to be 768.50 mg/g, which was higher than that for methyl orange (MO). In MG/MO mixed solutions, aerogels had obvious adsorption selectivity for the cationic dye. The adsorption mechanism of aerogels for MG was also discussed by simulating adsorption kinetic models and adsorption isothermal models.

Recent Advances in MOF-Based Adsorbents for Dye Removal from the Aquatic Environment

The adsorptive removal of dyes from industrial wastewater using commercially available adsorbents is not significantly efficient. Metal–organic frameworks (MOFs) offer outstanding properties which can boost the separation performance over current commercial adsorbents and hence, these materials represent a milestone in improving treatment methods for dye removal from water. Accordingly, in this paper, the recent studies in the modification of MOF structures in dye removal from the aquatic environment have been discussed. This study aims to elaborate on the synthetic strategies applied to improve the adsorption efficiency and to discuss the major adsorption mechanisms as well as the most influential parameters in the adsorptive removal of dyes using MOFs. More particularly, the advanced separation performance of MOF-based adsorbents will be comprehensively explained. The introduction of various functional groups and nanomaterials, such as amine functional groups, magnetic nanoparticles, and carbon-based materials such as graphene oxide and CNT, onto the MOFs can alter the removal efficiency of MOF-based adsorbents through enhancing the water stability, dispersion in water, interactions between the MOF structure and the contaminant, and the adsorption capacity. Finally, we summarize the challenges experienced by MOF-based materials for dye removal from water and propose future research outlooks to be considered.

Four Anderson-type [TeMo6O24]6−-based metal–organic complexes with a new bis(pyrimidine)-bis(amide): multifunctional electrochemical and adsorption performances

Four isostructural Anderson-type POM-based metal–organic complexes derived from a new bis(pyrimidine)-bis(amide) ligand were synthesized, showing multifunctional electrochemical sensing activities and good adsorption performances for organic dyes.

Synthesis of a 2D copper(II)-carboxylate framework having ultrafast adsorption of organic dyes

Two-dimensional (2D) coordination polymers are very interesting materials for their attractive applications. A novel 2D metal-organic framework (MOF) was derived from copper(II) and amino benzoic acid under both room temperature and solvothermal reaction conditions using different solvents. From both of the synthesis methods, an identical MOF was crystalized with monoclinic crystal system having P2₁/c space group. Hirshfeld surface analysis is carried out to explore the non-covalent interactions obtained from single crystal XRD investigation in terms of percentage contribution of each interatomic contact involved in packing of molecules into MOF structure. The microstructure analysis and surface morphology studies revealed the 2D layered regular pattern of rhombus disks of ~5 μm thickness throng together via clustering of these rhombic shaped flakes as flowers (ranging 50-100 μm in size) having uniform elemental composition. This 2D MOF efficiently adsorbed organic dyes (methylene blue, methyl orange, and methyl red) from their aqueous solutions. The 2D copper-carboxylate framework (1.2 g/L) exhibited high adsorption rates for organic dyes (0.15-0.19 mM), and >90% of these dyes could be captured as soon as they are exposed to MOF suspension (1 min) in each case. The dye removal efficiency is credited to synergy among structure, ionic strength, shapes and dimensions of dyes with respect to MOF structure. The microstructure of MOF along with electronic interactions like electrostatic, hydrogen bonding, π-π interactions and coordination to open metal sites, might contribute to the ultrafast dye adsorption process by MOF. The adsorption phenomenon is spontaneous and followed the pseudo-second order kinetic mechanism. DFT calculations revealed important electronic parameters of the dyes and model MOF systems, and novel insights with respect to possible dye-MOF interactions. The MOF remained quite stable during the dye adsorption and was regenerated easily for the successful subsequent use.