Surface modification of titanium oxide nanoparticles with chelating molecules: New recognition devices for controlling the selectivity towards lanthanides ionic separation

Recovery of rare earth elements from mine wastewater using alginate microspheres encapsulated with zeolitic imidazolate framework-8

There is increasing demand and interest in efficient methods for the recovery of rare earth elements (REEs) from wastewater because of the growing concerns associated with the negative impacts of REEs-rich waste discharged on pristine ecosystems. Here, we designed a ZIF-8@ALG composite hydrogel by encapsulating zeolitic imidazolate frameworks-8 (ZIF-8) into sodium alginate and poly (vinyl alcohol) double cross-linked networks (ALG) for the recovery of REEs from mine wastewater. ZIF-8@ALG showed exceptional REEs adsorption performance with the most superior separation factor (Ho/Mn) of 597.5. For the REEs considered, the ZIF-8@ALG composite exhibited a preference for heavy REEs with high adsorption efficiencies (65.3 ∼ 97.2%) and distribution coefficients (2045.5 ∼ 28500.0 mL·g-1). Adsorption involved a combination of electrostatic attraction, complexation and ion exchange mechanisms. REEs adsorbed on ZIF-8@ALG could also be desorbed using sodium citrate via ion-exchange and complexation, thus achieving efficient REEs recovery. In addition, ZIF-8@ALG was stable and reusable, maintaining effective adsorption in wastewater over four consecutive cycles, where the optimal adsorption efficiency reached 80.0%. Overall, this study provided an effective and feasible method for the recovery of REEs in mine wastewater, and confirmed that ZIF-8-based materials have significant potential for REEs recovery applications in wastewater engineering treatment.

Novel benzylphosphate-based covalent porous organic polymers for the effective capture of rare earth elements from aqueous solutions

It has been a major challenge to develop stable and cost-effective porous materials that efficiently recover heavy rare earth elements (HREEs) due to ever-increasing demand, low availability and high cost of HREEs. This study presents two novel benzylphosphate-based covalent porous organic polymers (BPOP-1 and BPOP-2) that were prepared by facile one-pot Friedel-Crafts reactions. Various analytical techniques are used to investigate the successful syntheses of BPOP materials and establish their material properties, which include an unusual crystalline nature, large surface area, hierarchical pore structure, and superior chemical stabilities. The BPOPs effectively adsorb, and thus remove HREEs from aqueous media. In particular, BPOP-1 had higher phosphate content and exhibits superior adsorption capacities (Eu³⁺: 289.5; Gd³⁺: 292.7; Tb³⁺: 294.4; Dy³⁺: 301.9 mg/g) than BPOP-2, while BPOP-2 had higher mesoporosity and correspondingly supports faster adsorption kinetics. Remarkably, both BPOP materials exhibit some of the highest HREE adsorption capacities reported to date, the selective capture of Dy³⁺ ions, and excellent cyclic adsorption/desorption properties. We provide a potential adsorption mechanism for Dy³⁺ capture by the BPOP adsorbent. These demonstrate that introducing phosphate functionality into a robust porous polymer backbone with high surface area is a promising strategy for selective HREEs capture from wastewater.

New insights into the radiolytic stability of metal(iv) phosphonate hybrid adsorbent materials

Stable metal(iv) phosphonate hybrids are a promising class of materials for the critical issue of nuclear waste cleanup. However, to be of practical use, adsorbent materials must demonstrate radiolytic stability and this property remains poorly understood. Therefore, the radiolytic stabilities of post-functionalised mesoporous zirconium titanate and zirconium phosphonate coordination polymers were compared. For the first time, solid-state ³¹P MAS-NMR was used to probe the radiolytic degradation of metal(iv) phosphonates and provide mechanistic insight. Polyphosphonate-functionalized hybrids were more stable than monophosphonate hybrids, as the monophosphonate readily detached from the oxide surface. The zirconium phosphonate coordination polymer (Zr-ATMP) demonstrated the greatest radiolytic stability, attributed to its high ligand loading and intimately mixed structure. Zr-ATMP maintained highly efficient sorption from strongly acidic solutions even after receiving doses of gamma radiation up to 2.9 MGy.

Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials

The 'bottom-up' synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.

Transforming lanthanide and actinide chemistry with nanoparticles

Lanthanides and actinides are used in a wide variety of applications, from energy production to life sciences. To address toxicity issues due to the chemical, and often radiological, properties of these elements, methods to quantify and recover them from industrial waste are necessary. When used in biomedicine, lanthanides and actinides are incorporated in compounds that show promising therapeutic and/or bioimaging properties, but lack robust strategies to target cancer and other pathologies. Furthermore, current decorporation protocols to respond to accidental actinide exposure rely on intravenous injections of soluble chelating agents, which are inefficient for treatment of inhaled radionuclides trapped in lungs. In recent years, nanoparticles have emerged as powerful tools in both industry and clinical settings. Because some inorganic nanoparticles are sensitive to external stimuli, such as light and magnetic fields, they can be used as building blocks for sensitive bioassays and separation techniques. In addition, nanoparticles can be functionalized with multiple ligands and act as carriers for selective delivery of therapeutic and contrast agents. This review summarizes and discusses recent progress on the use of nanoparticles in lanthanide and actinide chemistry. We examine different types of nanoparticles based on composition, functionalization, and properties, and we critically analyze their performance in a comparative mode. Our focus is two-pronged, including the nanoparticles free of lanthanides and actinides that are used for the detection, separation, or decorporation of f-block elements, as well as the nanoparticles that enhance the inherent properties of lanthanides and actinides for therapeutics, imaging and catalysis.

TiO₂-Based Hybrid Nanocomposites Modified by Phosphonate Molecules as Selective PAH Adsorbents

A robust sol-gel process was developed for the synthesis of surface-functionalized titania nanocrystallites bearing unsaturated groups starting from molecular heteroleptic single-source precursors. Molecules and nanomaterials were thoroughly characterized by multinuclear liquid and solid-state nuclear magnetic resonance (NMR), infra-red (FT-IR, DRIFT) spectroscopies. Nitrogen adsorption-desorption (BET), thermogravimetric (TG) and elemental analyses demonstrated the reliability and the fine tuning of the surface functionalization in terms of ratio TiO₂:ligand. The as-prepared materials were used as nano-adsorbents to remove mixture of 16 polycyclic aromatic hydrocarbon (PAHs) from aqueous solutions. Adsorption kinetic experiments were carried out for 24 h in solutions of one PAH [benzo(a)pyrene, 220 ppb] and of a mixture of sixteen ones [220 ppb for each PAH]. Most kinetic data best fitted the pseudo-second order model. However, in PAHs mixture, a competition process took place during the first hours leading to a remarkable high selectivity between light and heavy PAHs. This selectivity could be fine-tuned depending on the nature of the unsaturated group of the phosphonate framework and on the nanomaterial textures.