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Amine-Functionalized GO Decorated with ZnO-ZnFe2O4 Nanomaterials for Remediation of Cr(VI) from Water Shraban K Sahoo, and Garudadhwaj Hota ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b02286 • Publication Date (Web): 15 Jan 2019 Downloaded from http://pubs.acs.org on January 16, 2019
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Amine-Functionalized GO Decorated with ZnO-ZnFe2O4 Nanomaterials for Remediation of Cr(VI) from Water Shraban Ku. Sahoo, and Garudadhwaj Hota* Chemistry Department, NIT Rourkela, Odisha, India, 769008
Abstract: Amine functionalized graphene oxide (NH2-GO) decorated with ZnO-ZnFe2O4 nanomaterials (NH2-GO/ZnO-ZnFe2O4) was successfully synthesized by organic transformation reaction followed by hydrothermal method. The formation, composition, bonding, size, morphology, and surface area of synthesized nanomaterial was analyzed by XRD, FTIR, Raman, XPS, FESEM, HRTEM, and BET analytical techniques. The formation of ZnO-ZnFe2O4 binary phase onto the amine functionalized GO was confirmed by XRD and HRTEM. The surface composition and functionalization of prepared nanocomposite was confirmed by XPS and FTIR analysis. The FESEM images revealed the formation of fine spherical ZnO-ZnFe2O4 nanoparticle on to NH2GO surface. From TEM image, the average particle size of the composite nanomaterials was observed to be 8 nm. From N2 adsorption-desorption study, it was found that, NH2-GO/ZnOZnFe2O4 composite nanomaterials shows higher surface area (122 mg/g) than that of GO/ZnOZnFe2O4 and NH2-GO. The obtained nanocomposite was used as novel adsorbent for remediation of chromium (Cr(VI)) from water. Batch adsorption experimental studies revealed that the Cr(VI) adsorption onto NH2-GO/ZnO-ZnFe2O4 surface was pH dependent and maximum adsorption take place at pH=4. Compared to other prepared nanomaterials, adsorption capacity of NH2-GO/ZnO-ZnFe2O4 was found to be higher because of presence of more surface active sites by functionalizing ZnO-ZnFe2O4 nanomaterials and also introducing amine group on GO surface. Adsorptive removal of Cr(VI) onto nanocomposite surface follows a pseudo second order kinetics. Langmuir model was best fitted to the adsorption data. The process of adsorption was spontaneous and endothermic in nature. The maximum uptake capacity of NH2-GO/ZnOZnFe2O4 was observed to be 109.89 mg/g and was higher than that of NH2-GO and GO/ZnOZnFe2O4 nanocomposites. The mechanism of Cr(VI) adsorption follows electrostatic attraction and formation of chelate with amine groups. ______________________________________________________________________________ Key Words: Graphene oxide, Amine functionalized, Nanocomposites, hexavalent chromium, Adsorbents * Corresponding author Dr. Garudadhwaj Hota Dept. of Chemistry, NIT Rourkela, Orissa, India, 769008 Email:
[email protected],
[email protected] Ph: 91-661-2462655, Fax: 91-661-246265
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1. Introduction Water contagion with toxic heavy metals (As, Cr, Cd, Hg and Pb) above their permissible level is a serious environmental problem, which need an immediate attention for healthy and clean environment. Among different noxious metal ions, chromium(Cr) is one of the extremely harmful heavy metal and is mainly discharged to water body from electroplating, tanneries, metal refining and textile industries1,2. According to US Environmental Protection Agency (USEPA) the maximum acceptable limit of Cr in portable aquatic system is 0.05 mg/L. Concentration of Cr above this permissible level is carcinogenic and mutagenic to ecosystem along with human being. It causes several health problem including lung cancers, kidney problem, liver damage, anemia, ulcer formation etc. Among two stable oxidation states of chromium i.e. Cr(VI) and Cr(III), Cr(VI) is more toxic because of its smaller size, high solubility and larger mobility3–7. Cr(III) is less toxic and also used as an important metal ion in human nutrition8. Hence, Cr(VI) reduction to Cr(III) has also been chosen as an alternative way to reduce its toxicity 9. In recent years, photocatalytic reduction is also considered as a covenant way to change Cr(VI) to Cr(III). Apart from this, numerous techniques like membrane filtration, chemical reduction, adsorption, ion exchange, chemical precipitation, solvent extraction, and electrochemical reduction have been used to reduce the concertation of Cr(VI) from water10,11. Among them, adsorption process is most commonly used technique due to simple setup, easy operation, require less chemical and energy, cost effective and high efficiency12,13. Among different adsorbents, nano-sized metal oxides adsorbents are known to be the promising candidates for removal of inorganic as well as organic toxic pollutants from water14–19. Arising out of their environmental friendly, nontoxicity, cost effective, high surface area nano-sized zinc and iron oxide materials
can be used in various field including catalyst industry20,21, gas
sensors22,23, solar cells24,25, and adsorption26,27. Iron oxides and its derivatives are more popular in adsorbent field28. Zinc oxide was mostly used as an adsorbent to eliminate H2S29,30. Apart from this recently people have found that nano size zinc oxide and its composites could efficiently remove toxic metals ions as well as organic dyes31. For example, Guar gum coated zinc oxide (GG/ZnO) nanocomposites were used to remove Cr(VI) ions from water32. Similarly ZnO–AlOOH and reduced graphene oxide (RGO)/ZnO nanocomposites were used for adsorptive
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removal of Congo Red (CR) and Rhodamine B(RB) respectively17,33. Permethrin pesticide was removed from water by chitosan–zinc oxide nanoparticles34. Nowadays graphene and its derivatives are more popular among all researchers due to their applications potentials in electronics, sensors, adsorption, catalysis, photocatalytic degradation and many other fields. GO is oxidized form of graphene having high theoretical surface area (2620 m2g-1), high functionality (containing C=O, –OH, C–O-C functional groups) and low manufacturing cost that makes GO a promising adsorbent. However, due to certain limitations like difficult to separate GO from the solution and the strong Van der Waals force of attraction between the layers, restricts its direct application as an effective adsorbent. One way to overcome these limitations is to functionalize GO surface with different metal oxides nanoparticles. As a result of which aggregation behavior of graphene nanosheets can be prevented without compromising its high surface area during the adsorption process35–40. Many researchers have been working on the development of GO based metal oxide nanoadsorbents for heavy metals ions removal. Kumar et al., have synthesized GO/MnFe2O4 magnetic nanohybrids and have used for the adsorption of Pb and As from water41. GO based nickel ferrite and RGO-Fe3O4 nanocomposite were used as adsorbent for removal of Cr(III), Cr(VI) and Pb(II) ions42,43. Nanosized magnetic binary oxides of iron and aluminum decorated on GO surface was used as a discerning adsorbent for removal of fluoride44. In order to further improve the adsorbent efficiency modern research focused on the development of functionalized GO based metal oxide nanocomposites. GO is not only providing mechanical support but also its surface functional groups help to maximize the adsorption efficiency. Apart from this, it is also possible to tune its surface for creating a positive or negative change by functionalizing different functional groups on its surface. In recent year, researchers have focused on the surface functionalization of GO with amine groups through organic transformation reaction and used for removal of toxic metal ions. The amine functional groups can form chelate complex with toxic metal ions and hence exhibit high adsorption efficiency45–47. Recently, He et al., have synthesized 3-aminopropyltriethoxysilane functionalized GO for effective Cr(VI) ions adsorption48. Similarly poly diaminopyridine/GO composites doped with sulfuric acid was used to eliminate high concentration of Cr(VI) by Dinda and co-workers49. The amine functional groups are mainly participated in Cr(VI) 3 ACS Paragon Plus Environment
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adsorption by electrostatic interaction along with chelation. Therefore, our main objective in this study is to functionalize GO with increase the number of amine groups along with metal oxide nanocomposite decorated onto GO surface for efficient and improved Cr(VI) removal. In this present paper, we have modified the GO surface with amine groups by converting functional groups (carboxyl, epoxy and hydroxyl) to amine groups by using organic transformation reaction. Then ZnO-ZnFe2O4 binary oxide nanoparticles were decorated onto amine functionalized GO using iron and zinc salt precursors via hydrothermal method. The synthesized nanomaterials were used as novel adsorbent for adsorption study of Cr(VI) from water. Batch adsorption experimental studies were performed by changing different adsorption factors such as effect of dose, pH, time, concentration, and temperature. A suitable mechanism for Cr(VI) removal on to adsorbent surface has been proposed.
2. Experimental Method 2.1. Chemicals and Reagents Graphite powder (
