A novel chelating adsorbent, based on the chemical modification of graphene oxide by functionalization amidinothiourea to form 2-imino-4-thiobiuret-partially reduced graphene oxide (IT-PRGO), is used for the effective extraction of the toxic metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) from wastewater. FTIR and Raman spectroscopy, XRD, and XPS confirm the successful incorporation of the amidinothiourea groups within the partially reduced GO nanosheets through nucleophilic substitution reactions with the acyl chloride groups in the chemically modified GO. The IT-PRGO adsorbent shows exceptional selectivity for the extraction of Hg(II) with a capacity of 624 mg/g, placing it among the top of carbon-based materials known for the high capacity of Hg(II) removal from aqueous solutions. The maximum sorption capacities for As(V), Cu(II), Cr(VI), and Pb(II) are 19.0, 37.0, 63.0, and 101.5 mg/g, respectively. The IT-PRGO displays a 100% removal of Hg(II) at concentrations up to 100 ppm with 90%, 95%, and 100% removal within 15, 30, and 90 min, respectively, at 50 ppm concentration. In a mixture of six heavy metal ions containing 10 ppm of each ion, the IT-PRGO shows a removal of 3% Zn(II), 4% Ni(II), 9% Cd(II), 21% Cu(II), 63% Pb(II), and 100% Hg(II). A monolayer adsorption behavior is suggested based on the excellent agreement of the experimental sorption isotherms with the Langmuir model. The sorption kinetics can be fitted well to a pseudo-second-order kinetic model which suggests a chemisorption mechanism via the amidinothiourea groups grafted on the reduced graphene oxide nanosheets. Desorption studies demonstrate that the IT-PRGO is easily regenerated with the desorption of the metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) reaching 96%, 100%, 100%, 96%, and 100%, respectively, from their maximum sorption capacities using different eluents. The IT-PRGO is proposed as a top performing remediation adsorbent for the extraction of heavy metals from waste and polluted water.
A novel chelating adsorbent, based on the functionalization of activated carbon (AC) derived from water hyacinth (WH) with melamine thiourea (MT) to form melamine thiourea-modified activated carbon (MT-MAC), is used for the effective removal of Hg2+, Pb2+, and Cd2+ from aqueous solution. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) theory confirm the successful functionalization of AC with the melamine thiourea chelating ligand through the amidation reaction between the carboxyl groups of oxidized activated carbon (OAC) and the amino groups of melamine thiourea (MT) in the presence of dicyclohexylcarbodiimide (DCC) as a coupling agent. The prepared MT-MAC exhibited extensive potential for the adsorption of the toxic metal ions Hg2+, Pb2+, and Cd2+ from wastewater. The MT-MAC showed high capacities for the adsorption of Hg2+ (292.6 mg·g–1), Pb2+ (237.4 mg·g–1), and Cd2+ (97.9 mg·g–1) from aqueous solution. Additionally, 100% removal efficiency of Hg2+ at pH 5.5 was observed at very low initial concentrations (25–1000 ppb).The experimental sorption data could be fitted well with the Langmuir isotherm model, suggesting a monolayer adsorption behavior. The kinetic data of the chemisorption mechanism realized by the melamine thiourea groups grafted onto the activated carbon surface have a perfect match with the pseudo-second-order (PSO) kinetic model. In a mixed solution of metal ions containing 50 ppm of each ion, MT-MAC showed a removal of 97.0% Hg2+, 68% Pb2+, 45.0% Cd2+, 17.0% Cu2+, 7.0% Ni2+, and 5.0% Zn2+. Consequently, MT-MAC has exceptional selectivity for Hg2+ ions from the mixed metal ion solutions. The MT-MAC adsorbent showed high stability even after three adsorption–desorption cycles. According to the results obtained, the use of the MT-MAC adsorbent for the adsorption of Pb2+, Hg2+, and Cd2+ metal ions from polluted water is promising.
Polyacrylonitrile nanoparticles grafted on ethylene diamine functionalized partially reduced graphene oxide (PAN-PRGO) was prepared via in situ emulsion polymerization and was further modified to contain amidoxime, amdinoethylene diamine, and carboxylic groups on the surface of the graphene nanosheets via partial hydrolysis of the nitrile groups on the polymer chains of the composite using (4% NaOH, 20 min) (HPAN-PRGO). The properties and morphologies of the prepared composites were compared through FTIR, UV-Vis, Raman spectra, XRD, SEM, TEM, and XPS analysis. The results revealed that polyacrylonitrile nanoparticles were grafted on the surface of the aminated graphene oxide nanosheets via the reaction between the free amino groups of the ethylene diamine modified graphene oxide nanosheets and nitrile groups of acylonitrile (AN). The obtained HPAN-PRGO composite was evaluated for its chelating property with Hg(II) ions. The effect of initial pH, initial concentration of the Hg(II), adsorbent dose, and contact time on the extraction of Hg(II) ions using HPAN-PRGO were investigated. The adsorption experiments indicated that HPAN-PRGO exhibits higher affinity toward Hg(II). The maximum uptake capacity for the extraction of Hg(II) ions on HPAN-PRGO was 324.0 mg/ g at pH 5. The HPAN-PRGO shows a 100% removal of Hg(II) at concentrations up to 50 ppm, and the adsorption is exceptionally rapid showing more than 80.0% removal within 15 min and 100.0% of q e within 1.5 h at 800 ppm concentration. The Langmuir isotherm model and pseudo-second-order kinetic model have showed good fitness with the practical data. The XPS analysis of HPAN-PRGO before and after adsorption revealed the chelation adsorption mechanism between mercury and amine, amide, amidoxime, and carboxylic
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