Design of Nickel-Containing Nanocomposites Based on Ordered Mesoporous Silica: Synthesis, Structure, and Methylene Blue Adsorption.

Mesoporous materials containing heteroelements have a huge potential for use as catalysts, exchangers, and adsorbents due to their tunable nanometer-sized pores and exceptionally large internal surfaces accessible to bulky organic molecules. In the present work, ordered mesoporous silica containing Ni atoms as active sites was synthesized by a new low-temperature method of condensation of silica precursors on a micellar template from aqueous solutions in the presence of nickel salt. The homogeneity of the resulting product was achieved by introducing ammonia and ammonium salt as a buffer to maintain a constant pH value. The obtained materials were characterized by nitrogen sorption, X-ray and neutron diffraction, scanning electron microscopy, infrared spectroscopy, and thermal analysis. Their morphology consists of polydisperse spherical particles 50-300 nm in size, with a hexagonally ordered channel structure, high specific surface area (ABET = 900-1200 m2/g), large pore volume (Vp = 0.70-0.90 cm3/g), average mesopore diameter of about 3 nm, and narrow pore size distribution. Adsorption tests for methylene blue show sorption capacities reaching 39-42 mg/g at alkaline pH. The advantages of producing nickel silicates by this method, in contrast to precipitation from silicon alkoxides, are the low cost of reagents, fire safety, room-temperature processing, and the absence of specific problems associated with the use of ethanol as a solvent, as well as the absence of the inevitable capture of organic matter in the precipitation process.

Modification of Thin Film Composite PVA/PAN Membranes for Pervaporation Using Aluminosilicate Nanoparticles.

The effect of the modification of the polyvinyl alcohol (PVA) selective layer of thin film composite (TFC) membranes by aluminosilicate (Al2O3·SiO2) nanoparticles on the structure and pervaporation performance was studied. For the first time, PVA-Al2O3·SiO2/polyacrylonitrile (PAN) thin film nanocomposite (TFN) membranes for pervaporation separation of ethanol/water mixture were developed via the formation of the selective layer in dynamic mode. Selective layers of PVA/PAN and PVA-Al2O3·SiO2/PAN membranes were formed via filtration of PVA aqueous solutions or PVA-Al2O3·SiO2 aqueous dispersions through the ultrafiltration PAN membrane for 10 min at 0.3 MPa in dead-end mode. Average particle size and zeta potential of aluminosilicate nanoparticles in PVA aqueous solution were analyzed using the dynamic light scattering technique. Structure and surface properties of membranes were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle measurements. Membrane performance was investigated in pervaporation dehydration of ethanol/water mixtures in the broad concentration range. It was found that flux of TFN membranes decreased with addition of Al2O3·SiO2 nanoparticles into the selective layer due to the increase in selective layer thickness. However, ethanol/water separation factor of TFN membranes was found to be significantly higher compared to the reference TFC membrane in the whole range of studied ethanol/water feed mixtures with different concentrations, which is attributed to the increase in membrane hydrophilicity. It was found that developed PVA-Al2O3·SiO2/PAN TFN membranes were more stable in the dehydration of ethanol in the whole range of investigated concentrations as well as at different temperatures of the feed mixtures (25 °C, 35 °C, 50 °C) compared to the reference membrane which is due to the additional cross-linking of the selective layer by formation hydrogen and donor-acceptor bonds between aluminosilicate nanoparticles and PVA macromolecules.

Effect of Mg2+ ions on competitive metal ions adsorption/desorption on magnesium ferrite: Mechanism, reusability and stability studies.

The adsorption behavior of magnesium ferrite in single- and multicomponent metal ions solutions in the presence of Mg2+ ions were studied. A dramatic decrease in the adsorption capacity of magnesium ferrite towards Mn2+, Co2+, and Ni2+ ions for comparison study of single- and multicomponent solutions was established. The affinity of the sorbent in accordance with the maximum sorption capacities increases in the following order Cu2+ > Co2+ > Ni2+ > Mn2+. High efficiency of magnesium ferrite regeneration (~100%) with aqueous solutions of magnesium chloride in the concentration range of 0.001-0.1 M was shown. The low degree of toxic metal ions desorption combined with XRD, IR spectroscopy, and EDX analysis data indicate the key role of Mg2+ ion adsorption in the magnesium ferrite adsorbent regeneration. The positive effect of the introduction of Mg2+ ions into multicomponent solutions on metal ions adsorption was established, which is accompanied by an increase in the maximum sorption capacity for all metal ions and especially significant increase in the selectivity towards Cu2+ ions (2.41 mmol/g). The stability of the crystal structure of magnesium ferrite and a low degree of Mg2+ and Fe3+ ions leaching during multiple cycles of adsorption and regeneration of the adsorbent were observed.

Sorption and mechanism studies of Cu2+, Sr2+ and Pb2+ ions on mesoporous aluminosilicates/zeolite composite sorbents.

The research aimed to develop a novel mesoporous aluminosilicate/zeolite composite by the template co-precipitation method. The effect of aluminosilicate (AlSi) and zeolite (NaY) on the basic properties and adsorption capacity of the resultant composite was conducted at different mass ratios of AlSi/NaY (i.e., 5/90, 10/80, 15/85, 20/80, and 50/50). The adsorption characteristics of such composite and its feedstock materials (i.e., aluminosilicates and zeolite) towards radioactive Sr2+ ions and toxic metals (Cu2+ and Pb2+ ions) in aqueous solutions were investigated. Results indicated that BET surface area (SBET), total pore volume (VTotal), and mesopore volume (VMeso) of prepared materials followed the decreasing order: aluminosilicate (890 m2/g, 0.680 cm3/g, and 0.644 cm3/g) > zeolite (623 m2/g, 0.352 cm3/g, and 0.111 cm3/g) > AlSi/NaY (20/80) composite (370 m2/g, 0.254 cm3/g, and 0.154 cm3/g, respectively). The Langmuir maximum adsorption capacity (Qm) of metal ions (Sr2+, Cu2+, and Pb2+) in single-component solution was 260 mg/g, 220 mg/g, and 161 mg/g (for zeolite), 153 mg/g, 37.9 mg/g, and 66.5 mg/g (for aluminosilicate), and 186 mg/g, 140 mg/g, and 77.8 mg/g for (AlSi/NaY (20/80) composite), respectively. Ion exchange was regarded as a domain adsorption mechanism of metal ions in solution by zeolite; meanwhile, inner-surface complexation was domain one for aluminosilicate. Ion exchange and inner-surface complexation might be mainly responsible for adsorbing metal ions onto the AlSi/NaY composite. Pore-filling mechanism was a less important contributor during the adsorption process. The results of competitive adsorption under binary-components (Cu2+ and Sr2+) and ternary-components (Cu2+, Pb2+, and Sr2) demonstrated that the removal efficacy of target metals by the aluminosilicate, zeolite, and their composite remarkably decreased. The synthesized AlSi/NaY composite might serve as a promising adsorbent for real water treatment.