Graphene oxide/zinc oxide nanocomposite: A superior adsorbent for removal of methylene blue - statistical analysis by response surface methodology (RSM)

Abstract

The graphene oxide was prepared from graphite powder by a modified Hummers method. 29 Briefly, 1 g graphite powder, 6 g KMnO 4 and 1 g NaNO 3 were mixed with 46 mL concentrated sulphuric acid (97 %). The mixture was stirred for 3 h within an ice-bath. After having been removed from the ice-bath, 280 mL deionized water was added and stirred at room temperature for 2 h. Then the sample was stirred at 89°C for 2 h, followed by 6 mL H 2 O 2 which was added dropwise until the colour of the solution turned from dark brown to yellow. The solid product was separated by centrifugation and washed several times with distilled water until the pH of the solution became neutral. The residue was dried at 60°C overnight. The resulting graphene oxide was suspended in water and exfoliated through sonication for 3 h to obtain GO nano sheets. Preparation of Zinc OxideFor the ZnO, 2g ZnSO 4 was dissolved in sodium hydroxide solution and stirred for 12 h. The obtained white product was washed several times with distilled water and was collected by filtration. Finally, it was dried under vacuum to get zinc nano oxide. Preparation of GO/ZnO HybridFor the composite, 5g graphene oxide was dissolved in 20 mL ethanol and kept under ultrasonication for 2 h; it was denoted as GO solution. The as-prepared ZnO nanoparticles (5 g) were dissolved into the mixture of 18 mL methanol and 2mL chloroform and kept under ultrasonication for 2 h; it was denoted as ZnO solution. The GO solution and the ZnO solution were mixed and kept under constant stirring for 24 h. The collected precipitate was obtained by centrifugation and washed with methanol several times. The product was freeze-dried overnight and denoted as GO-ZnO nano composites. The ZnO/CNT composite was synthesized in the same way in order to compare its adsorption performs with GO/ZnO composite. Characterization of the Nano CompositeThe structure and crystal phase of adsorbent was investigated by a powder X-ray diffraction system (XRD6000, Shimadzu) equipped with Cu Ka radiation with a 2 q scanning range of 5-40°. Fourier transform infrared (FT-IR) spectra of samples were recorded by Bruker 27 in the range 400-4000 cm -1 . The morphology of the adsorbents was investigated with a scanning electron microscope (model EQ-C1-1). Determination of pH PZC of the AdsorbentsThe point of zero charge (pH PZC values) is the point at which the net charge on the adsorbent surface is zero. The pH PZC values of GO and GO/ZnO was determined by pH drift method. 30 Briefly, several solutions containing 0.01 M NaCl were supplied. The initial pH (pH i ) of the solutions was adjusted to a value between 2 and 11 using 0.1 M HCl or 0.1 M NaOH. 0.02 g adsorbent was added to the solution. The electrolyte solution with adsorbent was equilibrated for 24 h. After equilibrium, the final pH (pH f ) was recorded. The pH f was plotted against the initial pH (pH i ) values. The pH at which pH i crossovered the (pH f ) was referred to as the pH PZC . The pH PZC of GO and GO/ZnO was determined 7.5 and 8.2, respectively. Adsorpt...

Infrared Absorption Study of Zn–S Hybrid and ZnS Ultrathin Films Deposited on Porous AAO Ceramic Support

“…After ZnS deposition, the dips tend to shift towards a lower energy (enlarged part of the IR spectra in Figure 5b, marked by dotted magenta frame). A weak and broad band appearing at around 484 cm -1 may originate from the Zn-O stretching vibration [33,36,37,45]. In Figure 5, the IR spectrum of the studied samples are presented.…”

“…Characteristic peaks of IR spectra for 1,5-pentanedithiol can be attributed from each as-deposited Zn-S films on AAO indicating MLD type growth [34,35]. The strongest dips at 2927 and 2851 cm −1 were ascribed before to the CH 2 asymmetric (v a (CH 2 )) and symmetric (v s (CH 2 )) stretching vibrational modes, respectively [29,30,[36][37][38]. These dips are also the most intensive ones in the IR spectrum of pure PDT [34,35] and can thus be regarded as chemical fingerprints of this compound.…”

An in-silico layer-by-layer adsorption study of the interaction between Rebaudioside A and the T1R2 human sweet taste receptor: modelling and biosensing perspectives

“…8 was undertaken in a stepwise fashion, with the ZnONPs adsorbed onto the surface of the GO, resulting in an adsorption energy of the ZnONP/GO complex (see Table 2 ) stabilized at − 13.852 kcal/mol. The adsorption performance and sensitivity of ZnONPs have been recently reported in literature 113 , 114 . As much as this study attempted to mimic experimental conditions, it is evident in Fig.…”

Evolution of graphene oxide (GO)-based nanohybrid materials with diverse compositions: an overview

“…In two contemporary publications Hosseini et al 151,152 have reported the preparation of a GO/ZnO composite by the solution method and have applied the same for the removal of a dye (MB) from water following adsorptive and photocatalytic techniques respectively. In the first publication 151 adsorption efficiency was monitored and nanocomposites were observed to exhibit the highest (97%) efficiency of removal of MB at 5 ppm concentration under optimum conditions: pH 6, adsorption time 8.5 min, and adsorbent dosage 0.02 g. But under the same conditions ZnO, GO, pure carbon nanotube (CNT) and ZnO/CNT exhibit 5.165%, 78.82%, 95.42% and 17.13% removal of MB respectively. Therefore, prepared GO/ZnO exhibits the highest dye removal efficiency and it can be used for removal of industrial dyes from waste water via adsorption.…”