High-Silica Zeolites as Sorbent Media for Adsorption and Pre-Concentration of Pharmaceuticals in Aqueous Solutions

Green Synthesis and Efficient Adsorption: Na-X Zeolite vs. C/Mn/SiO2 Composite for Heavy Metals Removal

The studies aimed to test the adsorption capacity of two silica-enriched porous materials, synthetic Na-X zeolite and Mn-containing carbon composite, towards Pb(II) and Zn(II) ions in single and mixed systems and in the presence of diclofenac (DCF) and (or) poly(acrylic acid) (PAA). The synthetic zeolite was characterized by a well-developed surface area of 728 m2/g and a pore diameter of 1.73 nm, while the carbon composite exhibited 268 m2/g and 7.37 nm, respectively. Na-X was found to be more efficient than the carbon composite (75-212 mg/g) in adsorbing heavy metal ions in both single and bimetallic systems (322-333 mg/g). In turn, the C/Mn/SiO2 composite was more effective in removing Pb(II) ions from the systems that simultaneously contained DCF or PAA (480 and 476 mg/g, respectively). The Na-X zeolite demonstrated the greatest stability in all the systems studied. The highest stability was observed in the DCF + Pb(II) mixture, in contrast to the carbon composites where the stability was much lower. To evaluate the possibility of regeneration of the solids, HCl proved to be the best desorbent for heavy metal ions (efficiency of 99%). In general, both adsorbents offer promising potential for solving environmental problems.

Adsorptive removal of micropollutants by natural and faujasite zeolites: Structural effect of micropollutants on adsorption

To effectively characterize natural zeolite powder (ZP) and faujasite zeolite (FAU) as adsorbents to remove a wide variety of organic micropollutants, quantitative structure-activity relationship (QSAR) models for the adsorption of zeolites were developed. For this purpose, batch isotherms were performed to measure the adsorption affinity (Kd) between zeolite and organic micropollutants, and the measured Kd values were used as a dependent variable in the QSAR modeling. In the modeling, the concept of a linear free energy relationship (LFER) was employed and used either empirically measured or in silico calculated descriptors. Modeling results based on empirical descriptors showed that log Kd values for ZP could be predicted with R2 = 0.949 and standard error (SE) = 0.137 log units, and for FAU, R2 = 0.895 and SE = 0.144 log units. A test set was used to validate the models developed by the training set. The predictabilities of the models for the test set were R2 = 0.907 and SE = 0.209 log units for ZP and R2 = 0.784 and SE = 0.236 log units for FAU, indicating that the models have reasonable robustness and predictability. Also, we showed that in silico-based descriptors could be applied to the prediction. These findings may help determine the general coverage of ZP and FAU zeolites and identify suitable applications.

Ordered Mesoporous Silica Prepared in Different Solvent Conditions: Application for Cu(II) and Pb(II) Adsorption

In this work, the synthesis of ordered mesoporous silica of MCM-41 type was investigated aimed at improving its morphology by varying the synthesis conditions in a one-pot process, employing different temperatures and solvent conditions. 2-methoxyethanol was used as co-solvent to ethanol. The co-solvent ratio and the synthesis temperature were varied. The pore morphology of the materials was characterized by nitrogen porosimetry and small angle neutron scattering (SANS), and the particle morphology by transmission electron microscopy (TEM) and ultra-small angle neutron scattering (USANS). The thermal behavior was investigated by simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) measurements. The SANS and N₂ sorption results demonstrated that a well-ordered mesoporous structure was obtained at all conditions in the synthesis at room temperature. Addition of methoxyethanol led to an increase of the pore wall thickness. Simultaneously, an increase of methoxyethanol content led to lowering of the mean particle size from 300 to 230 nm, according to the ultra-small angle scattering data. The ordered porosity and high specific surfaces make these materials suitable for applications such as adsorbents in environmental remediation. Batch adsorption measurements of metal ion removal from aqueous solutions of Cu(II) and Pb(II) showed that the materials exhibit dominantly monolayer surface adsorption characteristics. The adsorption capacities were 9.7 mg/g for Cu(II) and 18.8 mg/g for Pb(II) at pH 5, making these materials competitive in performance to various composite materials.

Hemoperfusion: technical aspects and state of the art

Background

Blood purification through the removal of plasma solutes by adsorption to beads of charcoal or resins contained in a cartridge (hemoperfusion) has a long and imperfect history. Developments in production and coating technology, however, have recently increased the biocompatibility of sorbents and have spurred renewed interest in hemoperfusion.

Methods

We performed a narrative assessment of the literature with focus on the technology, characteristics, and principles of hemoperfusion. We assessed publications in ex vivo, animal, and human studies. We synthesized such literature in a technical and state-of-the-art summary.

Results

Early hemoperfusion studies were hampered by bioincompatibility. Recent technology, however, has improved its safety. Hemoperfusion has been used with positive effects in chronic dialysis and chronic liver disease. It has also demonstrated extraction of a variety of toxins and drugs during episodes of overdose. Trials with endotoxin binding polymyxin B have shown mixed results in septic shock and are under active investigation. The role of non-selective hemoperfusion in sepsis or inflammation remains. Although new technologies have made sorbents more biocompatible, the research agenda in the field remains vast.

Conclusion

New sorbents markedly differ from those used in the past because of greater biocompatibility and safety. Initial studies of novel sorbent-based hemoperfusion show some promise in specific chronic conditions and some acute states. Systematic studies of novel sorbent-based hemoperfusion are now both necessary and justified.

Driving Forces of Cationic Dye Adsorption, Confinement, and Long-Range Correlation in Zeolitic Materials

Zeolitic materials are commonly used to capture emergent contaminants in water or complex aqueous effluents. The efficiency of this adsorption depends strongly on the guest-host interactions and on the surrounding environment with possible coadsorption of the solvent. Only a few experimental techniques are available to probe in situ the sequestration processes at the solid/liquid interface. We propose in the present work to combine the second harmonic scattering technique with isothermal titration calorimetry in order to investigate the adsorption and the confinement of a hemicyanine dye adsorbed inside faujasite materials. The methodology described here permits the quantification of the correlations between the confined dyes in the material and thus gives local information about the organization at the nanometer scale. Various impacts, such as the effect of the solvent type and the silicon to aluminum ratio of the zeolitic adsorbent, are quantitatively estimated and discussed. This work highlights that the most correlated system matches the higher adsorption capacity associated with the lower entropic contribution.

Efficiency in Ofloxacin Antibiotic Water Remediation by Magnetic Zeolites Formed Combining Pure Sources and Wastes

In this work, red mud (RM) and spinel iron oxide nanoparticles (SPIONs) were added to pure silica/alumina sources (SAs) and fly ash (FA) with the aim of synthesizing and investigating the magnetic behavior of different zeolites. SAs were used to synthesize zeolite with LTA topology (zeolite A) with the addition of both red mud and spinel iron oxide nanoparticles. FA and RM were mixed to synthesize sodalite whereas only FA with the addition of SPIONs was used to form zeolite with FAU-topology (zeolite X). All the synthetic products showed magnetic properties. However, zeolites with spinel iron oxide nanoparticles (zeolites A and X) showed ferromagnetic-like behavior. Sodalite was characterized by a reduction in saturation magnetization, whereas zeolite A with red mud displayed antiferromagnetic behavior. For the first time, all the synthetic products were tested for polluted water remediation by a persistent emerging contaminant, ofloxacin (OFL) antibiotic. The four zeolite types showed good adsorption affinity towards OFL under actual conditions (tap water, natural pH). All materials were also tested for OFL removal in real waters spiked with OFL 10 µg L−1. Satisfactory recoveries (90–92% in tap water, 83–87% in river water) were obtained for the two zeolites synthesized from industrial waste materials.

Adsorption Characteristics and Mechanism of Calcium Ions on Different Molybdenite Surfaces via Experiments and DFT Simulations

Calcium ions are common in flotation process water, and have a significant effect on the molybdenite floatability, making separation of molybdenite from other minerals more difficult. Therefore, to improve the separation selectivity, the research of how calcium ions affect the molybdenite surface properties is of great significance. In this study, various methods including flotation tests, contact angle measurements, batch adsorption tests and Density Functional Theory (DFT) simulations were carried out to understand the adsorption characteristics and mechanism. Results of the contact angle measurements showed that the inhibition effects of calcium ions on molybdenite flotation kinetics were mostly attributed to the decrease of the edge surface hydrophobicity, as the contact angle of the edge surface decreased more than the face surface after treatment with calcium ions. While fitting the results of batch adsorption tests with adsorption kinetics and isotherm models, it was found that the Lagergen pseudo-first-order equation and the Freundlich isotherm model nicely follow the experimental trend. Moreover, DFT calculation results indicated that both Ca2+ and CaOH+ preferentially adsorb on the molybdenite (100) surface, particularly the edge surface, which was consistent with the contact angle results. Ca2+ adsorbed on the Mo-top site on the S-(100) surface by forming Ca-S bonds, transferring electrons from Ca 3d orbitals to S 3p orbitals. CaOH+ adsorbed on the S-top site of Mo-(100) surface by forming a strong covalent Mo-O bond and S-Ca bond. The results provide a basis for understanding and improving the separation effect of molybdenite from other minerals in the presence of calcium ions.