Eco-friendly synthesis of Cynomorium coccineum extract for controlled production of copper nanoparticles for sorption of methylene blue dye
particular diffusion) and common isotherms equations (Lang-
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particular diffusion) and common isotherms equations (Lang- muir, Freundlich, Temkin, and Dubinin-Radushkevich). The corresponding parameters were computed to better understand the adsorption mechanism. 2. Experimental 2.1. Chemical and reagents All used chemicals and reagents: copper sulfate (precursor salt), ethanol, acetone, etc. were of analytical grade. In this study, methylene blue, supplied from Sigma Aldrich, was used as adsorbate and representative of cationic dyes. Its molecular weight was 319.85 g mol 1 . Their physico-chemical character- istics were summarized in Table 1 . Distilled water was used to prepare aqueous solutions and for finishing experiments (washing and rinsing). The pH was adjusted using 0.1 M HCl or 0.1 M NaOH solutions. 2.2. Preparation of Cynomorium coccineum aqueous extract The fractions of Cynomorium coccineum were collected during the month of March 2019 from Skanes region area (latitude: 35 °75 0 , longitude: 10 °82 0 ), Governorate of Monastir, Tunisia. The collected fractions were thoroughly washed and shade dried for a weak and ground to fine powdered using an electri- cal mixer. Grinded dried Cynomorium coccineum fractions (10 g) were heated in a flask containing 150 mL distilled water for 90 min at 70 °C. After which, it was cooled to room tem- perature and then filtrated with a filter paper. 2.3. Bio-synthesis of copper nanoparticles using Cynomorium coccineum extract The freshly prepared Cynomorium coccineum extract (100 mL) was added to 100 mL of 1 M copper sulfate solution. The mix- ture was constantly stirred at 70 °C for 2 h. The color change of the solution from blue to dark green indicated the formation of the copper nanoparticles ( Fig. 1 ). Afterward, it was cooled to room temperature and then filtrated using a filter paper. Finally, the synthesized nanoparticles were subjected to drying at 100 °C for a period of 12 h. 4264 N. Sebeia et al. 2.4. Characterization techniques Fourier Transform Infrared Spectroscopy was used to identify the functional groups characteristics of the bio-molecules pre- sent in Cynomorium coccineum extract. The FT-IR spectra were recorded on a Perkin Elmer model in the 4000–400 cm 1 region using KBr pellet method. The morphological features of the samples were evaluated by a SEM Hitachi S-2360N. Samples were coated with Au by a vacuum sputter-coater with 20 kV accelerating voltage. EDX measurements were taken on a Phi- lips FEI Quanta 200 for semi-quantitative analysis of elements. X-ray powder diffractograms were obtained at room tempera- ture on a PANalytical X’Pert PRO MPD apparatus. Thermal analysis (TGA) experiments were performed in the air flow at a heating rate of 10 °/min in a Pt crucible with NETZSCH STA 449F3 equipment. 2.5. Bio-sorption batch procedure The batch sorption experiments were carried out in Erlen- meyer flasks containing 0.025 g of the prepared copper nanoparticles and a dye volume of 20 mL. The mixture was agitated at 125 rpm for different periods of time after the equi- librium was reached. The effect of initial pH value on the adsorption of methylene blue was studied in the range 3–10. The nanoadsorbent dosage was investigated in the range 0.0125–0.1 g. The effect of the change of temperature was examined at the range 22–55 °C. The absorbance evolution of the colored solutions was monitored through UV–Vis spec- trophotometer at a wavelength of 664 nm. The adsorbed amount of methylene blue was calculated according to the fol- lowing formula: q mg g ¼ ðc 0 c e Þ m V ð1Þ where c 0 and c e are the initial and residual dye concentration. V is the volume of the used adsorbate during the adsorption experiments and m is the mass of the used adsorbent. 3. Results and discussion 3.1. Copper nanoparticles characterization Fig. 2 showed the different functional groups characteristics of Cynomorium coccineum extract and the associated biolog- ical synthesized copper nanoparticles. In the spectrum of the Cynomorium coccineum extract, the bands at 3223, 2882– 2801, 1593, and 1312–1195 cm 1 were attributed to the O AH stretching of alcohol and phenol, CAH stretching of the aliphatic group, C ‚C stretching of the aromatic ring, and C AO stretching of ester, respectively ( Subbaiya et al., 2014; Tahir et al., 2015 ). The intense absorption band observed at 1014 cm 1 could be assigned to C AOAC stretching vibration ( Tahir et al., 2015 ). The spectrum of the biosynthesized copper nanoparticles did not change much compared with the extract and it showed the main characteristic peaks with band shifting. In fact, the band observed for hydroxyl groups at 3223 cm 1 in the spectrum of the studied extract shifted to a lower value (3199 cm 1 ) in the spectrum of the prepared nanoparticles. This shifting, at this position and the decrease in its intensity, might indicate that the copper ions interacted with OH groups. This trend suggested that the prepared particles were surrounded by different organic bio-molecules. Regarding the spectrum of methylene blue adsorbed onto the prepared nanoparticles, such a shift in the band characteristics proved the interac- tion between the dye molecules and the copper nanoparti- cles. Overall, the results obtained from the FT-IR spectra confirmed that the prepared nanoparticles are coated with bio-molecules that acted as both reducer and coating for copper nanoparticles against oxidation. In fact, the formation mechanism of the copper nanoparti- cles could be explained by the fact that the bio-molecules (i.e. Flavonoids, phenolics, etc.) present in Cynomorium coccineum extract can act as ligation agents. The hydroxyl groups of the bio-molecules form complexing agents with the copper sulfate as precursor salts and therefore ligate with copper ions. This starts the nucleation process that goes into reverse micelliza- tion, which then causes the reduction of the nanoparticles. This system undergoes decomposition when the particles are dried at elevated temperatures leading to the easy release of the CuO nanoparticles from the copper-ellagate complex system ( Yuvakkumar et al., 2014 ). According to literature, the major constituents of cynomorium plants have been identified to be Table 1 Physico-chemical characteristics of methylene blue dye. Name Chemical structure k (nm) in water Molecular weight (g/mol) Empirical Formula Methylene blue 664 319.85 C 16 H 18 ClN 3 S tải về 1.78 Mb. Chia sẻ với bạn bè của bạn:
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