ABSTRACT
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.
ABSTRACT
Graphene oxide (GO) was functionalized using two silanes ((3-aminopropyl)-triethoxysilane and (3-mercaptopropyl)-triethoxysilane) to obtain, separately, the eco-friendly amine-functionalized GO (GONH) and thiol-functionalized GO (GOSH). Both silanes were also used together to obtain the amine-thiol dual-functionalized GO (GOSN). Various physicochemical characterizations were obtained including spectra from using Fourier-transform infrared (FTIR) spectrometer, thermogravimetric analyzer, and X-ray diffractometer. The adsorbents were used for a comparative study of Cr adsorption from aqueous solution. The obtained data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models, the homogeneous fractal pseudo-second order (FPSO), and the Weber-Morris intraparticle diffusion (IPD) kinetics models. Model parameters of the Langmuir and Freundlich adsorption isotherm models, as well as the thermodynamics, were calculated. Characterization results showed successful functionalizations. The GONH, GOSH, and GOSN exhibited alkaline, acidic, and neutral pH, respectively, in water. Amine and thiol functional groups were observed in the new adsorbents, as well as reduced orderliness. The adsorbents had higher density per unit weight and better thermal stability than pristine GO. Equilibrium Cr adsorption was attained within 60 min for all adsorbents. The PSO and FPSO described the rate data better. The Cr adsorption decreased as solution pH increased; optimum adsorption was recorded at pH 2. Equilibrium adsorption data fitted the Langmuir adsorption isotherm model for the GONH, while it fitted the Freundlich for both GOSH and GOSN. The adsorption process was theoretically exothermic process that was spontaneous processes. The Cr adsorption capacities of these adsorbents are 114, 89.6, and 173 mg/g for GONH, GOSH, and GOSN, respectively, and these were better than several reported graphene-based adsorbents and suggest the potential of these adsorbents for water treatment. PRACTITIONER POINTS: Graphene oxide was mono and dual-functionalized with amine and thiol groups for Cr adsorption. The adsorption capacities of these adsorbents were better than several earlier reported. These adsorbents may be used for real contaminated water treatment.
