Synthesis and characterization of porous magnetic silica composite for the removal of heavy metals from aqueous solution

Fe/Co-MOF Nanocatalysts: Greener Chemistry Approach for the Removal of Toxic Metals and Catalytic Applications

This study describes the preparation of new bimetallic (Fe/Co)-organic framework (Bi-MOF) nanocatalysts with different percentages of iron/cobalt for their use and reuse in adsorption, antibacterial, antioxidant, and catalytic applications following the principles of green chemistry. The prepared catalysts were characterized using several techniques, including X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. These techniques proved the formation of MOFs, and the average crystallite sizes were 25.3-53.1, 27.6-67.2, 3.0-18.9, 3.0-12.9, and 3.0-23.6 nm for the Fe-MOF, Co-MOF, 10%Fe:90%Co-MOF, 50%Fe:50%Co-MOF, and 90%Fe:10%Co-MOF samples, respectively. The nanoscale (Fe/Co) Bi-MOF catalysts as efficient heterogeneous solid catalysts showed high catalytic activity with excellent yields and short reaction times in the catalytic reactions of quinoxaline and dibenzoxanthene compounds, in addition to their antioxidant and antibacterial activities. Furthermore, the nanoscale (Fe/Co) Bi-MOF catalysts efficiently removed toxic metal pollutants (Pb²⁺, Hg²⁺, Cd²⁺, and Cu²⁺) from aqueous solutions with high adsorption capacity.

Removal of Pb(II) ions from aqueous solutions using functionalized cryogels

In this study, a poly(allylamine-co-methacrylamide-co-acrylic acid) (p(AA-co-MA-co-AAc)) cryogel containing amine and carboxyl groups was prepared and subsequently functionalized with thiourea using methyl isothiocyanate. The functionalized p(AA-co-MA-co-AAc) cryogel was then applied to the adsorption of lead (Pb) ions from aqueous solution, and the amount of Pb adsorption was measured. The functionalized p(AA-co-MA-co-AAc) cryogel was analyzed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and its chemical structure, pore shape, pore distribution and specific surface area were confirmed. To determine the effect of the solution pH and initial concentration on Pb adsorption by the functionalized p(AA-co-MA-co-AAc) cryogel, Pb adsorption tests were performed. The functionalized p(AA-co-MA-co-AAc) cryogel exhibited the highest adsorption amount at pH 7 and 400 mg L^-1. The Pb adsorption process was determined to occur through chemical adsorption because the experimental data were fit well by a pseudo-second-order model. In addition, the equilibrium isotherm data fit the Langmuir isotherm better than the Freundlich model, indicating that the functionalized p(AA-co-MA-co-AAc) cryogel surfaces were uniform and that a lead adsorbate monolayer formed at equilibrium.

Development and application of carbon nanotubes reinforced hydroxyapatite composite in separation of Co(II) and Eu(III) ions from aqueous solutions

Multi-walled carbon nanotubes/strontium hydroxyapatite (MWCNT/SH) composite was synthesized, where CNTs were applied to improve the properties of HAP and increase the reinforcement of the composite. The composite CNTs/Sr-HAP and its precursor Sr-HAP were successfully applied in removal of Co(II) and Eu(III) ions from aqueous solutions. Sorption of Co(II) and Eu(III) onto the synthesized sorbents was investigated as a function of contact time and pH. The synthesized sorbents highly removed the studied radionuclides from their aqueous solutions with necessary time of 6 h to reach equilibrium. The maximum sorption capacity was 33.31 and 48.93 mg g−1 for Co(II) sorption onto Sr-HAP and CNTs/Sr-HAP composite at pH 4.5, while it was 115.74 and 127.11 mg g−1 for sorption of Eu(III) onto Sr-HAP and CNTs/Sr-HAP composite at pH 2.5, respectively. Desorption of Co(II) and Eu(III) from loaded samples was studied using various eluents and maximum recovery was obtained using FeCl3 and HCl solutions. Co(II) was completely separated from Eu(III) by a ratio of 85.1 % using Cd(NO3)2 as an eluent in CNTs/Sr-HAP composite packed column.

Fabrication of novel sandwich nanocomposite as an efficient and regenerable adsorbent for methylene blue and Pb (II) ion removal

An adsorbent, which is easy to be separated and reused after adsorption, is very important for the removal of pollutants in aqueous solution. Hence, a novel nanofibrous sandwich structured adsorbent of silica nanofiber/magnetite nanoparticles/porous silica (SNF/MNP/PS) was designed and synthesized for the first time. The magnetite nanoparticles with diameter less than 10 nm were evenly distributed on the surface of silica nanofiber, which was subsequently fully covered by a layer of porous silica. The novel adsorbent was proved possessing good adsorption capacity for both methylene blue (MB) and Pb (II) ion (Pb²⁺), and the adsorption equilibrium could be well described by the Langmuir-isotherm model with the maximum adsorption capacity of 103.1 mg/g for MB and 243.9 mg/g for Pb²⁺ at 288 K. Moreover, in MB-Pb²⁺ mixed system the measured adsorption capacity reached 74.5 mg/g for MB and 202.4 mg/g for Pb²⁺, respectively. The saturated adsorbent could be readily magnetically separated from the solution and then efficiently regenerated by heterogeneous Fenton-like reaction (for MB) or acidic desorption process (for Pb²⁺), respectively. After 5 cycles of adsorption-regeneration, the adsorption capacity of the reused adsorbent still reached 81.0% (for MB) and 70.9% (for Pb²⁺) of the initial value. The SNF/MNP/PS behaves good adsorption properties for different types of pollutants, high magnetic recoverability and regeneration efficiency, which make it applicable to different contaminants removal.

Insight into highly efficient co-removal of p-nitrophenol and lead by nitrogen-functionalized magnetic ordered mesoporous carbon: Performance and modelling

Highly efficient simultaneous removal of Pb(II) and p-nitrophenol (PNP) contamination from water was accomplished by nitrogen-functionalized magnetic ordered mesoporous carbon (N-Fe/OMC). The mutual effects and inner mechanisms of their adsorption onto N-Fe/OMC were systematically investigated by sole and binary systems, and thermodynamic, sorption isotherm and adsorption kinetics models. The liquid-film diffusion step might be the rate-limiting step for PNP and Pb(II). The fitting of experimental data with Temkin model indicates that the adsorption process of PNP and Pb(II) involve physisorption and chemisorption. There exist site competition and enhancement of PNP and Pb(II) on the sorption to N-Fe/OMC. Moreover, N-Fe/OMC could be regenerated effectively and recycled by using dilute NaOH and acetone. These demonstrated superior properties of N-Fe/OMC indicate that it could be applied to treatment of wastewaters containing both lead and PNP.

Preparation, characterization and application of superparamagnetic iron oxide nanoparticles modified with natural polymers for removal of 60Co-radionuclides from aqueous solution

Superparamagnetic iron oxide nanoparticles (IO-MNPs) coated with natural polymers, starch (IO-S MNPs) and dextrin (IO-D MNPs), were synthesized by modified co-precipitation method. IO and hybrid-IO-MNPs were characterized by XRD, SEM, HRTEM, FT-IR spectroscopy, vibrating sample magnetometer (VSM) and zeta potential (ZP). IO-S MNPs and IO-D MNPs have IO core-shell structure with core of 10.8 nm and 13.8 nm and shell of 7.5 nm and 5.9 nm, respectively. The efficiency of the hybrid IO-MNPs for sorption of 60Co(II)-radionuclides from aqueous solution was investigated under varying experimental conditions. Kinetic data were described well by pseudo-second-order mode, sorption isotherms were fitted quite with Freundlich model with maximum adsorption capacity 36.89 (mmol·g−1)/(L·mmol−1)n for IO-S MNPs and 24.9 (mmol·g−1)/(L·mmol−1)n for IO-D MNPs. Sorption of 60Co-radionuclides by IO-S MNPs was suppressed with salinity and most of the adsorbed 60Co onto IO-S MNPs could be remove with 0.1 M HCl solution. IO-S MNPs exhibits superparamagnetic properties, easier separation according to higher saturation magnetization (47 emu/g) and better adsorption for 60Co-radionuclides than IO-D MNPs.

The preparation of modified boehmite/PMMA nanocomposites by in situ polymerization and the assessment of their capability for Cu2+ ion removal

The addition of nanoboehmite as a nanofiller into the polymer matrix led to the improvement of the thermal properties and increased the active sites of nanocomposites for Cu(ii) removal.