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.
This work reports the feasibility of using pristine and chemically modified coral limestones by acid
and base. Their potential adsorptive capabilities is probed by treatment of toxic Cr(VI), Pb(II) ions
and methylene blue in aqueous solution under different experimental parameters by batch method.
Parameters such as agitation time, concentration, temperature and pH were varied to understand the
sorption behaviour of the adsorbents in each case. The adsorbents were characterized by SEM, XRD
and FTIR. Morphological analysis by SEM micrographs show that the surface of all adsorbents was
irregular in nature. XRD spectra confirmed the orthorhombic structure of aragonite in the pristine
coral limestones (PCL), acid modified coral limestones (ACL) and base modified coral limestones
(BCL). FTIR results affirmed the presence of (CO3
2-) and (-C=O) groups of the carbonate ions and
Ca-O attachment to the surface of PCL and removal of CaCO3 characteristic peaks in ACL and BCL.
However, in the modified adsorbents shifting of Ca-O peaks occurred. The recorded maximum
adsorption capacities of PCL, ACL and BCL for Cr(VI) ions were 69.42, 65.04, 64.88 mg/g, Pb(II)
ions 39.36, 74.11, 78.34 mg/g and methylene blue 37.24, 46.28, 46.39 mg/g, respectively. The uptake
of Pb(II), Cr(VI) ions, methylene blue onto PCL fitted Freundlich model. Also the uptake of Cr(VI)
ions and methylene blue onto ACL and BCL fitted Freundlich isotherm. However, uptake of Pb(II)
ions onto both ACL and BCL fitted Langmuir isotherm. The data revealed that the adsorption of Pb(II)
ions onto PCL and ACL and methylene blue dye onto PCL was exothermic. Whilst the adsorption of
Cr(VI) ions onto PCL, ACL and BCL and methylene blue dye onto ACL and BCL were endothermic
in nature, hence increasing the temperature would enhance the uptake of Pb(II) ions onto BCL, Cr(VI)
ions onto ACL and BCL and methylene blue onto ACL and BCL. The obtained (ΔGº) values at all
studied temperatures for the adsorption of Pb(II), Cr(VI) ions and methylene blue onto PLC, ACL and
BCL indicated a spontaneous process.
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