Fine-tuning the dye adsorption capacity of UiO-66 by a mixed-ligand approach

High-efficient removal of methylene blue by zirconium-based organic frameworks modified with 1,3,5-benzenetricarboxylic acid: Characterization, performances, and mechanisms

The vast discharge of methylene blue (MB) dye in industrial effluent, risks the ecological environment, thus making its removal unavoidable. Recently, metal organic frameworks (MOFs) due to their larger pore volume, surface area and easy synthesis have proved to be exceptionally promising materials for contaminant treatment. Based on 1,3,5-benzenetricarboxylic acid (BTC) as a modifier, a new composite material consisting of BTC and Zr-based MOF (UIO-66-BTC) was fabricated for the effective removal of MB from the effluent. Its synthesis and efficient application has been confirmed by characterization analysis. The influencing factors, adsorption isotherms, and adsorption kinetics of MB adsorption by adsorbent were studied. It was demonstrated that the removal rate of MB adsorption by UIO-66-BTC reached 98.45% and the adsorption amount reached 393.80 mg g-1 at temperature (298 K), pH 7, adsorbent dosage (0.5 g L-1), MB initial concentration (200 mg L-1), and contact time of 720 min, respectively. The maximum adsorption of MB by UIO-66-BTC was 20.827 times higher than that of UIO-66 (18.908 mg g-1). The experimental data fits with the pseudo-second-order kinetic model and Langmuir isotherm, implying that the adsorption process is a monolayer chemisorption process. The thermodynamic and regeneration experiments showed that the spontaneous process enhanced the adsorption of MB at lower temperatures and the adsorption efficiency of MB remained above 68% after five successive cycles. The mechanism of MB adsorption on adsorbents is mainly based on electrostatic interactions, pore filling, hydrogen bonding and π-π interactions. It is concluded that this new adsorbent can be effectively used to treat MB in effluents.

Durable and recyclable MOF@polycaprolactone mixed-matrix membranes with hierarchical porosity for wastewater treatment

With the fast-growing global water crisis, the development of novel technologies for water remediation and reuse is crucial. Industrial wastewater especially contains various toxic pollutants that pose an additional threat to the environment; thus, efficient removal of such contaminants can ensure safe reprocessing of industrial wastewater, thereby alleviating the demand for fresh water. Herein, we describe a novel and efficient approach for preparing porous polycaprolactone (PCL) membranes with a hierarchical architecture via a simple solvent/non-solvent methodology. A mixed-matrix membrane (MMM) was further constructed utilizing an amine-functionalized metal-organic framework as the sorbent filler nanoparticles and PCL as the polymer support matrix (MOF@PCL) for wastewater treatment applications. The MOF@PCL MMM demonstrated homogeneous morphology as well as exceptional performance towards the removal of both cationic (methylene blue, MB) and anionic (methyl orange, MO) organic dyes, where the maximum adsorption capacities reached 309 mg g-1 and 208 mg g-1, respectively. Kinetic and thermodynamic investigations revealed that the adsorption process was endothermic with a fast intraparticle diffusion rate constant. The MOF@PCL MMM also displayed excellent mechanical stability and recyclability, where the removal efficiency was maintained after 10 cycles.

Adsorption of Methyl Orange on a Novel Palygorskite/UiO-66 Nanocomposite

Herein, a novel composite material containing UiO-66 and palygorskite (Pal) clay mineral was prepared using a facile one-pot synthesis process. The material was studied using a variety of techniques and applied as did not affect the structure of the metal-organic framework (MOF) part, but induced a small increase in specific surface area. The developed Pal/UiO-66 composite presented excellent adsorption efficiency against MO removal, as evidenced by detailed kinetic and isotherm experiments. An impressive maximum adsorption capacity at equilibrium was evidenced; 340 mg g−1 at pH = 5 and T = 25 °C. This corresponds to a 34.5 % increase compared with pure UiO-66, considering only the MOF content. Furthermore, the Pal/UiO-66 composite was proven stable and highly recyclable, losing less than 9% of the removal capacity after five consecutive cycles. The study highlights the synergistic effect of the coupling of MOF structures with low-cost and abundant clay minerals for the development of advanced absorbents.

Adsorption kinetics and isotherms of binary metal ion aqueous solution using untreated venus shell

Among available technologies to remove heavy metals from wastewater, biosorption has gained more attention due to its high removal efficiency, friendly operation, and inexpensive cost. Despite many studies on metal adsorption from single ion solutions, kinetics and isotherms of binary metal ions simultaneously adsorbed onto biosorbents have not been thoroughly investigated to provide insight on involving mechanisms. This study explored the adsorption potential of untreated venus shells (UVS) that can be utilized in economical and environmentally-friendly ways. In this work, UVS of different sizes were prepared without chemical treatment as a biosorbent. Characterization of UVS was accomplished using nitrogen adsorption isotherm, FTIR, and SEM-EDX. Batch adsorption was carried out to study the effect of initial metal ion concentration, adsorbent dosage, and size on removing Cu(II) and Zn(II) from a binary solution of both metal ions using UVS. The experimental values of maximum adsorption capacities of Cu(II) and Zn(II) were 0.446 and 0.465 mg/g, respectively. The adsorption data were analyzed using the pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion rate equations. The pseudo-second order and the intraparticle diffusion model yielded the best fit to the experimental data for Cu(II) and Zn(II) ions, respectively. The equilibrium isotherm was examined using the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), and Elovich models. The Freundlich model best fits the Cu(II) and Zn(II) equilibrium adsorption data. The results indicated that the adsorption of Cu(II) and Zn(II) onto UVS-600 adsorbent could undergo a chemisorption mechanism. Both metal ions in an aqueous solution were competitively adsorbed onto the heterogeneous active sites available on the shell surfaces. Cu(II) and Zn(II) ions in the binary system could result in ionic interference between the adsorbed ions and the active sites.