A metal-organic framework surrounded with conjugate acid-base pairs for the efficient capture of Cr(VI) via hydrogen bonding over a wide pH range

Adsorption of Ga(III) by Zn2+, quaternary ammonium and polyamine embellished lignin with the crosslinking agent of epichlorohydrin

Cost-effective and eco-friendly extraction of gallium is a technical challenge. Gallium-containing anions can be effectively adsorbed by Zn2+, quaternary ammonium and polyamine. Polyamine can be grafted into adsorbent by formaldehyde and the crosslinking agent of epichlorohydrin. Zn2+/quaternary ammonium/polyamine lignin was constructed for adsorption of Ga(III) through embellishing of Zn2+, quaternary ammonium and polyamine and crosslinking of epichlorohydrin. The adsorbent was characterized by SEM, ICP-MS, BET, BJH, LDM, FTIR and XRD. The effects of pH, initial gallium concentration, adsorption time, dosage of adsorbent and number of cycles on adsorption properties were investigated. The adsorption mechanism was elucidated by SEM, ICP-MS, FTIR and XPS. The results showed that the adsorbent was coarse and contained hydroxyl, polyamine, quaternary ammonium and Zn2+. The adsorption capacity of 0.5 g·L-1 adsorbent for Ga(III) reached 289.20 mg·g-1 at 25 °C, pH of 9, oscillation rate of 200 r/min, initial gallium concentration of 400 mg·L-1 and adsorption time of 540 min. Adsorption followed Langmuir model and quasi-second-order kinetic model. The adsorption capacity decreased by only 10.57 % after five cycles, implying its strong stability and potential reuse. Ga(III) was adsorbed through electrostatic attraction of hydrogen bond and Zn2+, coordination with -NH- and ion exchange between Cl- and Ga(OH)4-.

Insight into the Specific Adsorption of Cu(II) by a Zinc-Based Metal-Organic Framework Mediated via a Proton-Exchange Mechanism

In the context of scarce metal resources, the one-step separation and recovery of high-value copper metal ions from secondary resources is of significant importance and presents substantial challenges. This study identified a Zn-based triazole MOF (Zn(tr)(OAc)) with accessible and noncoordinated terminal hydroxyl groups within its framework. The Zn(tr)(OAc) surpasses most currently reported Cu-specific MOF adsorbents regarding adsorption capacity and Cu2+ selectivity. Furthermore, in the one-step separation and recovery experiment of Cu2+, the Cu2+ concentration was increased from 79.64% in the simulated secondary copper resource solution to 98.62% in the adsorbed phase. Both experimental and theoretical studies indicated that the high ion selectivity for Cu2+ is primarily due to the specific recognition ability of the terminal hydroxyl (-OH) group, enabling only Cu2+ to undergo proton exchange with the hydrogen. The strong adsorption capacity of the material was attributed not only to proton exchange between the hydroxyl groups in the framework and Cu2+ but also to interactions between the nitrogen (N) and oxygen (O) atoms in the heterocyclic rings and Cu2+. In summary, Zn(tr)(OAc) demonstrates great potential in the separation and recovery of Cu2+ from secondary copper resources and provides additional possibilities for enhancing Cu2+ selectivity in MOF-based adsorbents.

Effective removal of Cr(VI) in water by bulk-size polyaniline/polyvinyl alcohol/amyloid fibril composite beads

With the rapid expansion of industrial activities, chromium ions are discharged into the environment and cause water and soil pollution of various extents, which seriously endangers the natural ecological environment and human health. In this study, polyaniline/polyvinyl alcohol/amyloid fibril (PANI/PVA/AFL) composite gel beads (PPA) were prepared from polyaniline and amyloid fibrils with HCl as doping acid and PVA as a cross-linking agent. The results showed that PPA was an irregular composite bead with a diameter of 6 mm. The adsorption of Cr(VI) on the PPA gel beads followed the pseudo-second-order kinetics model, suggesting that chemical reactions were the controlling step in the Cr(VI) adsorption process. Though the Redlich-Peterson isotherm model had the best fit for the adsorption data, the isothermal adsorption process can be simplified using the Langmuir model. The maximum adsorption capacity for Cr(VI) in water was 51.5 mg g-1, comparable to or even higher than some PANI-based nanomaterials. Thermodynamic parameters showed that the adsorption process was a spontaneous, endothermic, and entropy-increasing process. Microscopic analysis revealed that the capture of Cr(VI) on PPA was mainly governed by electrostatic attraction, reduction, and complexation reactions. PPA can be used as a kind of effective remediation agent to remove Cr(VI) in water.

Comprehensive insight into adsorption of chlortetracycline hydrochloride by room-temperature synthesized water-stable Zr-based metal-organic gel/sodium alginate beads

Chlortetracycline hydrochloride (CTC) is one of the prevailing antibiotic pollutants that harm both environmental ecosystem and human health. Herein, Zr-based metal-organic gels (Zr-MOGs) with lower-coordinated active sites and hierarchically porous structures are fabricated via a facile straightforward room-temperature strategy for CTC treatment. More importantly, we incorporated the powder Zr-MOGs into low-cost sodium alginate (SA) matrix to achieve shaped Zr-based metal-organic gel/SA beads for enhancing the adsorption ability and ameliorating the recyclability. The Langmuir maximum adsorption capacities of Zr-MOGs and Zr-MOG/SA beads could reach 143.9 mg/g and 246.9 mg/g, respectively. What's more, in the manual syringe unit and continuous bead column experiments, Zr-MOG/SA beads could achieve an eluted CTC removal ratio as high as 93.6% and 95.5% in the real water sample, respectively. On top of that, the adsorption mechanisms were put forward as a combination of pore filling, electrostatic interaction, hydrophilic-lipophilic balance, coordination, π-π interaction as well as hydrogen bonding interaction. This study outlines a workable strategy for the facile preparation of candidate adsorbents for wastewater treatment.