Metals and Antibiotics as Aqueous Sequestration Targets for Magnetic Polyamidoamine-Grafted SBA-15

In this study, a magnetic generation-5 polyamidoamine (G-5 PAMAM) dendrimer-functionalized SBA-15 (mPSBA) composite was synthesized by coupling amine-functionalized silica (SBA-15-NH₂) and amine-functionalized magnetic nanoparticles (MNP-NH₂) with the G-5 PAMAM, before characterization and aqueous sorption of As(III), Cd(II), tetracycline, and ciprofloxacin using the composite. The mPSBA characterization data exhibited the typical Si-O-Si infrared peaks from the SBA-15 backbone in addition to the acquired characteristic infrared Fe-O and amide-I/II peaks from the MNP and G-5 PAMAM dendrimers, respectively. Postsorption infrared spectra showing shifts for the amide-linked groups indicated the likely points of contaminant attachment on the composite. Its thermal stability was lower than that of SBA-15 but higher than that of SBA-15-NH, while the XRD diffractograms of the backbone SBA-15-NH and MNP were unchanged in the final composite. The mPSBA composite was a better As(III) and Cd(II) adsorbent than SBA-15 by ≈400 and 140%, respectively, with rapid uptake in the first 60 min and equilibrium achieved at 120 min. Sorption was enhanced with increasing pH (until pHpzc) and initial contaminant concentration. The process was spontaneous and endothermic; thus, increasing ambient temperature enhanced Cd(II) sorption. The sorption data fitted better to the homogeneous fractal pseudo-second-order (FPSO) kinetics model and the Brouers-Sotolongo fractal adsorption isotherm models, indicating complex sorption interactions and pore-filling/contaminant trapping within mPSBA. Further experiments using mPSBA for the uptake of tetracycline and ciprofloxacin showed 679% and 325% higher sorption, respectively, compared with that for SBA-15-NH. In addition to the added advantage of easy removal from solution/treated water after the adsorption process, mPSBA sorption capacities for these studied contaminants [As(III): 23.3 mg/g; Cd(II): 74.5 mg/g; tetracycline: 38.4 mg/g; ciprofloxacin: 23.0 mg/g] are better than those of several advanced adsorbents reported in the literature.