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Fabrication of Nano-sensing Materials and Sensing Performance

Author: ZengFanWu
Tutor: LiuXiaoXia
School: Northeastern University
Course: Analytical Chemistry
Keywords: polyaniline nanofiber graphite foil Graphene oxide nano sheets gas sensor electrochemical sensor
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Type: PhD thesis
Year: 2010
Downloads: 178
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Abstract


Polyaniline (PANI) nanofibers were prepared through in situ chemical and electrochemical polymerization of aniline. PANI nanofibers were fabricated onto screen-printed electrode (SPE) and graphite foil (GF) to construct sensors of Nano-PANI/SPE and Nano-PANI/GF respectively. Graphene oxide nano sheets (GONS) were prepared by electrochemical exfoliation of graphite foil.Nano-PANI/SPE sensor was constructed by in situ chemical polymerization of aniline on the insulate gap of the SPE by drop coating method, using iron chloride as oxidant. The morphologies of the PANI on the gap were investigated by scanning electron microscopy (SEM). It can be seen from the SEM images that the film was composed of interconnected nanofibers of ca.60nm in diameter to form pores of ca.300-400nm in diameter.The responses of the Nano-PANI/SPE sensor upon exposure to common volatile organic compounds (VOCs) and ammonia were investigated. It was found that the sensor responsed quickly on exposure to chloromethane, small molecular alcohols, toluene, triethylamine and ammonia. The sensor has higher sensitivity and lower detection limit (0.45ppb) when it was used in sensing ammonia because of the strong de-protonation of PANI by ammonia. The Nano-PANI/SPE sensor has better stability, the resistant of the sensor increased only about3.86%when it was on exposure to air for one week.Polyaniline nano fiber (Nano-PANI) modified graphite foil (GF), Nano-PANI/GF was prepared by electrochemical polymerization of aniline on GF electrode in a solution of0.2mol·dm-3aniline and1.0mol·dm-3HCl. The polymer on the modified electrode Nano-PANI/GF was characterized by FTIR. The morphologies of the modified electrode were investigated by SEM. The electrochemistry activity of Nano-PANI/GF was investigated in0.1mol·dm-3phosphate buffer solution (pH6.9) by cyclic voltammetry (CV). The electrochemistry activity of Nano-PANI/GF increased along with the cyclic number of CV for the electropolymerization of aniline in the first six cycles as the electroactivity was related to charge transfer between graphite foil and PANI.The electrocatalytic properties of the Nano-PANI/GF modified electrode towards ascorbic acid (AA) oxidation were studied through cyclic voltammetry. The current for AA oxidation on the modified electrode at0.2V showed linear response to the concentration of AA in the range of1.7～2.0×103μmol·dm-3. The linear equation is i(mA)=0.0031+0.00013[AA](mmol·dm-3), R2=0.9994and the sensitivity is0.13mA·cm-2·mmol-1·dm3. The detection limit of AA on the modified electrode is1.7μmol·dm-3Graphene oxide nano sheets (GONS) were prepared by electrochemical exfoliation of graphite foil. The composition of GONS was analyzed by XPS and FTIR, and the morphologies were investigated by SEM. It can be seen from the SEM images that the thickness of GONS is as thin as4nm.The electrocatalytic properties of GONS towards AA oxidation were studied through cyclic voltammetry. The current for AA oxidation on GONS at0V showed linear response to the concentration of AA in the range of5.0×10-4～1.0mmol·dm-3. The linear equation is i(mA)=0.0022+0.10[AA](mmol·dm-3), R2=0.9967, and the sensitivity is0.10mA·cm-2·mmol-1·dm3. The detection limit of AA on GONS is0.5μmol·dm-3. The relative standard deviation (RSD) is3.8%for three times detection of0.25mmol·dm-3AA. Common interfering substances (such as citric acid (CA), glucose (Glu), lactic acid (LA), uric acid (UA) and dopamine (DA)) have higher oxidation potential on GONS than AA, so they have no obvious influence on AA sensing. AA in three kinds of beverage were detected by GONS, the results showed the recovery of the additional standard sample was92.0～100.5%。The CV and differential pulse voltammetry (DPV) experimental results showed that GONS also had good current responses to dopamine (DA), uric acid (UA) and acetaminophen (APAP). The oxidant current of DA on GONS shows linear response to the concentration of DA in the range of25～200μmol·dm-3. The linear equation is ip (μA)=4.6+0.90[DA](μmol·dm-3), R2=0.9908, and the sensitivity is0.90μA·cm-2μmol-1·dm3. The detection limit of DA on GONS is4.6μmol·dm-3. The RSD is2.3%for three times detection of80μmol·dm-3DA. The oxidant current of UA on GONS shows linear response to the concentration of DA in the range of25～130μmol·dm-3. The linear equation is ip(μA)=0.010+0.90[UA](μmol·dm3), R2=0.9975, and the sensitivity is0.90μA·cm2·μmol-1·dm3. The detection limit of UA on GONS is2.4μmol·dm-3. The RSD is4.3%for three times detection of80μmol·dm-3UA.The oxidant current of APAP on GONS shows linear response to the concentration of APAP in the range of40～200μmol·dm-3. The linear equation is ip(μA)=-0.055+1.8[APAP](μmol·dm-3), R2=0.9961, and the sensitivity is1.8μA·cm-2·μmol-1·dm3. The detection limit of APAP on GONS is1.9μmol·dm-3. The RSD is4.4%for three times detection of200μmol·dm-3APAP.The oxidation potential on CV and DPV curves of AA, DA, UA and APAP on GONS were separated by more than70mV for each other. Based on the peak separations, simultaneous analysis of all these bioactive molecules is possible in0.1mol·dm-3phosphate buffer solution (pH6.9).

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