用新型的二氧化硅改性的热还原石墨烯为吸附剂采用固相萃取法和紫外可见分光光度法痕量测定环境水样中的铬vi含量.ppt

Trace determination of chromium(VI) in environmental water samples using innovative thermally reduced graphene (TRG) modified SiO2 adsorbent for solid phase extraction and UVvis spectrophotometry 用新型的二氧化硅改性的热还原石墨烯为吸附剂采用固相萃取法和紫外可见分光光度法痕量测定环境水样中的铬(VI)含量,姓名：汤娟 专业：化学工程,Abstract,An innovative thermally reduced graphene (TRG) modified silica-supported 3-aminopropyltriethoxysilane (SiO2-APTES) composite was synthesized and characterized using Fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy SEM techniques. The adsorbent was then used in the solid phase extraction (SPE) of Cr (VI) as the Cr (VI)-diphenylcarbazide (DPC) complex with the subsequent measurement by UVvis spectrophotometry. The adsorbent surface was activated by addingsodium dodecyl sulfate (SDS) to the sample solution. The effect of the main experimental parameters such as type and volume of the extraction solvent, pH, dosage of DPC, SDS, the adsorbent, time of the extraction, and salt concentration on the extraction efficiency were investigated and optimized. A linear dynamic range of 1.3-40 ng mL-1 with a satisfactory determination coefficient (R2) of 0.9930 was obtained. A detection limit of 0.4 ng mL-1 Cr (VI) was attained when a sample volume of 25 mL was used. Intraday and inter-day precisions were obtained equal to 2.3% and 7.9%, respectively. The enrichment factor (EF) was calculated to be equal to 167. The technique was applied successfully to the determination of Cr (VI) at trace levels in tap, river, sewage and ground water samples and the relative recoveries of the added chromium were in the range of 92.6109.9%.,Introduction,In recent years, large number of carbon-based nanomaterials including fullerene, carbon nanotubes, graphene and graphene oxide have been investigated as adsorbent in SPE due to their excellent adsorption capacity, large surface area, ease of surface modification, chemical stability, durability, corrosion resistance,unique mechanical and electrochemical properties. Graphene(G) is a two-dimensional monolayer of carbon atoms that has ultrahigh surface area and high chemical stability. Strong vander waals interactions between G sheets reduce its solubility insolvents and consequently reduce the adsorption of organic compounds or metal ions. Graphene oxide (GO) is the oxidized derivative of G which contains oxygen atoms (as epoxy,hydroxyl, and carboxyl groups) on the surface of carbon sheets. Therefore, GO is much more hydrophilic than G and can provide formation of hydrogen bonding or electrostatic interactions with organic compounds or metal ions. In order to use both ultrahigh surface area of G and oxygen containing groups of GO,using thermally reduced GO (TRG) sheets is a good idea. TRG is a single or few-layer oxygen-functionalized graphene sheets which has far less amount of oxygen-containing groups compared to GO and takes the advantages of both G and GO.,In this work, we prepared a novel adsorbent by attaching TRG on silica-supported 3-aminopropyltriethoxysilane (SiO2-APTES)surface, and used for extraction of Cr (VI) in environmental water samples. The selectivity of the adsorbent toward the Cr (VI) species was improved by formation of a Cr (VI)-diphenylcarbazide complex prior to the adsorption. Complex formation between Cr(VI) and DPC is an interesting reaction for spectrophotometric determination of Cr(VI). This reaction has high selectivity for Cr (VI) versus Cr (III). The adsorbent has surface characteristics of graphene and graphene oxide such as large contact surface area and high amounts of polar groups on the surface. These properties results in high water-dispersibility of the adsorbent and provide a rapid adsorption process. The detection of the extracted Cr (VI) was performed with UVvis spectrophotometry. The violet Cr (VI)-DPC complex exhibits a maximum absorption at 543 nm.,Experimental,Preparation of the adsorbent At first, silica-supported 3-aminopropyltriethoxysilane (SiO2-APTES) was prepared based on the literature. A portion of GO(0.4g) was added to 40 mL of distilled water and then, sonicated for 30min. Next, SiO2-APTES (20g) was placed in a beaker and the solution containing GO was added to it gradually (SiO2-APTES should not be dried in this step). Then, the mixture was heated up to 15C for 20min.,The precedure,At first, pH of 25mL of the sample solution containing Cr (VI)(10ng mL-1) was adjusted at 1.7 by adding 0.5mL H2SO4(0.5 molL-1). Then, 150L of DPC solution (10-2 mol L-1 in MeOH) was added to it to form the Cr (VI)-DPC complex. After 5 min, 0.5mL of SDS (1% w/v) was added to the sample solution.After that, 20 mg of the adsorbent was transferred to the sample solution and the mixture was sonicated for 1min. Subsequently,the solution containing the adsorbent was stirred for 3min. Next,the adsorbent was detached from the solution by centrifugation at 5500rpm for 3min, and then the supernatant was removed. After that, the desorption solvent (EtOH) was added to it and the mixture was sonicated for 2min to disperse the adsorbent in EtOH.Finally, the mixture was centrifuged at 6000rpm for 3min, and the supernatant was analyzed with UVvis spectrophotometer.,优化结果：,1.the highest extraction recovery was obtained using acetone as desorption solvent but because of its high volatility, analyte concentration changes quickly over time and may cause unrepeatable results. The best choice after acetone was EtOH. Hence, it was chosen as the desorption solvent for further experiments. 2.it was found that at pH 1.7 the extraction recovery was maximum。 3.150 L was chosen as the optimum amount of DPC。 4. 5 mg (500 L, 1% w/v) was used as the optimum amount of SDS. 5. the maximum extraction recovery was obtained using 20 mg of the adsorbent for extraction from 25 mL of sample solution. 6.With increasing the salt concentration, the extraction recovery decreased . 7.3 min was chosen as the extraction time.,Conclusions,In the present study, a TRG modified SiO2-APTES composite was synthesized and used as an adsorbent for extraction and preconcentration of Cr (VI) in environmental water samples. In order to improve the selectivity of detection for Cr (VI), in the presence of Cr (III) and the other metal ions, it was complexed with diphenylcarbazide (DPC) before performing the extraction process. This adsorbent with the adsorptive characteristics of both graphene and graphene oxide provided a rapid adsorption rate as a result of good dispersibility in water and large contact surface area. Microvolume UVvis spectrophotometry was used for rapid determination of the preconcentrated Cr (VI)-DPC. The method offered advantages such as a relatively low cost and simple procedure, good accuracy (recoveries 93110%), low limit of detection(0.4 ng/L), high preconcentration factor (167) and good precision (2.3%). In addition, is an environmental friendly method due to low organic solvent consumption (150 L) in the desorption step. The results demonstrated that this method can be used for determination of Cr (VI) at low concentrations in real samples.Comparison of analytical features of this method with some other techniques indicates that limit of detection and enrichment factor are better than most of the other methods. In addition, this method needs lower time in comparison to most of the other methods.,THANK YOU !,