Tailoring Nanoadsorbent Surfaces: Separation of Rare Earths and Late Transition Metals in Recycling of Magnet Materials

Natural Silicates Encapsulated Enzymes as Green Biocatalysts for Degradation of Pharmaceuticals

Biocatalytic degradation with the use of enzymes has gained great attention in the past few years due to its advantages of high efficiency and environmental friendliness. Novel, cost-effective, and green nanoadsorbents were produced in this study, using natural silicates as an enzyme host matrix for core-shell immobilization technique. With the natural silicate as a core and silica layer as a shell, it was possible to encapsulate two different enzymes: horseradish peroxidase (HRP) and laccase, for removal and degradation of three pharmaceuticals: diclofenac (DFC), carbamazepine (CBZ), and paracetamol (PC). The biocatalysts demonstrated high oxidation rates for the selected pollutants. In particular HRP immobilized fly ash and perlite degraded DFC and PC completely during 3 days of interaction and also showed high degradation rates for CBZ. Immobilized laccase was successful in PC degradation, where up to 70-80% degradation of the compounds with aromatic rings was reported by NMR measurements for a high drug concentration of 10 μg/mL. The immobilization method played a significant role in this process by providing stability and protection for the enzymes over 3 weeks. Furthermore, the enzymes acted differently in the three chosen supports due to their complex chemical composition, which could have an effect on the overall enzyme activity.

Adsorption of rare earth elements on a magnetic geopolymer derived from rice husk: studies in batch, column, and application in real phosphogypsum leachate sample

There is a growing need to develop new strategies for rare earth element (REE) recovery from secondary resources. Herein, a novel approach to utilize biogenic silica (from rice husk) and metakaolin was employed to fabricate magnetic geopolymer (MGP) by incorporating metallic iron. The fabricated MGP adsorbent material was used to uptake Ce3+, La3+, and Nd3+ from synthetic solutions and real phosphogypsum leachate in batch and column modes. The MGP offers a negatively charged surface at pH above 2.7, and the uptake of REEs rises from pH 3 to 6. The kinetic study validated that the kinetics was much faster for Nd3+, followed by La3+ and Ce3+. A thermodynamic investigation validated the exothermic nature of the adsorption process for all selected REEs. The desorption experiment using 2 mol L-1 H2SO4 as the eluent demonstrated approximately 100% desorption of REEs from the adsorbent. After six adsorption-desorption cycles, the MGP maintained a high adsorption performance up to cycle five before suffering a significant decrease in performance in cycle six. The effectiveness of MGP was also assessed for its applicability in recovering numerous REEs (La3+, Ce3+, Pr3+, Sm3+, and Nd3+) from real leachate from phosphogypsum wastes, and the highest recovery was achieved for Nd3+ (95.03%) followed by Ce3+ (86.33%). The operation was also feasible in the column presenting suitable values of the length of the mass transfer zone. The findings of this investigation indicate that MGP adsorbent prepared via a simple route has the potential for the recovery of REEs from synthetic and real samples in both batch and continuous operations modes.

Upscale Synthesis of Magnetic Mesoporous Silica Nanoparticles and Application to Metal Ion Separation: Nanosafety Evaluation

The synthesis of core-shell magnetic mesoporous nanoparticles (MMSNs) through a phase transfer process is usually performed at the 100-250 mg scale. At the gram scale, nanoparticles without cores or with multicore systems are observed. Iron oxide core nanoparticles (IO) were synthesized through a thermal decomposition procedure of α-FeO(OH) in oleic acid. A phase transfer from chloroform to water was then performed in order to wrap the IO nanoparticles with a mesoporous silica shell through the sol-gel procedure. MMSNs were then functionalized with DTPA (diethylenetriaminepentacetic acid) and used for the separation of metal ions. Their toxicity was evaluated. The phase transfer procedure was crucial to obtaining MMSNs on a large scale. Three synthesis parameters were rigorously controlled: temperature, time and glassware. The homogeneous dispersion of MMSNs on the gram scale was successfully obtained. After functionalization with DTPA, the MMSN-DTPAs were shown to have a strong affinity for Ni ions. Furthermore, toxicity was evaluated in cells, zebrafish and seahorse cell metabolic assays, and the nanoparticles were found to be nontoxic. We developed a method of preparing MMSNs at the gram scale. After functionalization with DTPA, the nanoparticles were efficient in metal ion removal and separation; furthermore, no toxicity was noticed up to 125 µg mL-1 in zebrafish.

Tailoring a bio-based adsorbent for sequestration of late transition and rare earth elements

The demand for new renewable energy sources, improved energy storage and exhaust-free transportation requires the use of large quantities of rare earth (REE) and late transition (LTM, group 8-12) elements. In order to achieve sustainability in their use, an efficient green recycling technology is required. Here, an approach, a synthetic route and an evaluation of the designed bio-based material are reported. Cotton-derived nano cellulose particles were functionalized with a polyamino ligand, tris(2-aminoethyl) amine (TAEA), achieving ligand content of up to ca. 0.8 mmol g^-1. The morphology and structure of the produced adsorbent were revealed by PXRD, SEM-EDS, AFM and FTIR techniques. The adsorption capacity and kinetics of REE and LTM were investigated by conductometric photometric titrations, revealing quick uptake, high adsorption capacity and pronounced selectivity for LTM compared to REE. Molecular insights into the mode of action of the adsorbent were obtained via the investigation of the molecular structure of the Ni(II)-TAEA complex by an X-ray single crystal study. The bio-based adsorbent nanomaterial demonstrated in this work opens up a perspective for tailoring specific adsorbents in the sequestration of REE and LTM for their sustainable recycling.