Preparation Of Nanoparticle Modified Electrode Based On Au,Pt And Its Detection For As(â…¢),Cr(â…¥) In Water

The contamination of water with heavy metals is a serious worldwide threat to human health, among which arsenic and chromium have caused wider public concern. It is significant to detect As（Ⅲ） and Cr（Ⅵ） precisely and conveniently for evaluating their ecological harm. So, it is necessary to develop real-time and portable instruments to satisfy site monitoring requirements of As（Ⅲ） and Cr（Ⅵ） contamination. Electrochemical methods are sensitive and simple to operate, easy to miniaturize instrument, thus possessing good application in on-line detection and site monitoring.Three different modified electrodes based on electrocatalytic activity of Au and Pt to As（Ⅲ） and Cr（Ⅵ） were prepared. The fabrication of nanoscale roughened Pt electrode through simple electrochemical method was explored. Further, nanogold was electrodeposited to obtain modified electrodes on two carriers, the roughened Pt electrode and graphene which possessing unique structures and displaying excellent electro catalytic performances. The feasibilities of detections of trace As（Ⅲ） and Cr（Ⅵ） in water samples with the three modified electrodes were studied. The details are summarized as follows:1. Determination of As（Ⅲ） in water samples based on electrochemical roughened Pt electrodePlatinum electrode has been electrochemically roughened in a H₂SO₄ solution for studying the feasibility of detection of As（Ⅲ）. The morphology and electrochemical properties of the fabricated electrode were respectively characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The preparation conditions of the modified electrodes and analytical conditions of As（Ⅲ） were optimized. The results show that: the Pt electrode has higher conductivity and larger specific surface area after being roughened, which increasing its electrocatalytic property. The determination conditions were optimized as follows:roughened time of Pt electrode is 3 s, electrolyte is 0.1mol L^-1 of H₂SO₄, scan rate is 250 mV s-1, pre-concentration potential and pre-concentration time are-0.4 V and 120 s, respectively. The oxidation peak currents of As（Ⅲ） to As（V） at 0.86 V are in proportion to concentra tions of As（Ⅲ） in the range from 0.4 to 80 μmol L^-1 with a detection limit of 0.076 μmol L^-1（S/N = 3）. The recoveries are from 95.4% to 105.0%. The roughened Pt electrode is simple to prepare, easy to refresh, and exhibits good stability and satisfied resistance to interferences especially to C u（II）. The proposed electrode can be applied to detect As（Ⅲ） in water sample satisfactorily.2. Electrochemical study of As（Ⅲ） on gold nanoparticles modified roughened platinum electrodeGold nanoparticles modified roughened platinum electrode（Au/RPE） was prepared by electrodeposition of gold nanoparticles on a roughened platinum electrode with constant potential reduction method. The behavior of As（Ⅲ） on Au/RPE was explored. The morphology and electrochemical properties of Au/RPE were respectively characterized by scanning electron microscop y and cyclic voltammetry. The detection conditions of As（Ⅲ） were optimized. The oxidation peak currents of As（0） to As（Ⅲ） at 0.05 V are in proportion to concentrations of As（Ⅲ） in the range from 0.1 to 4 μmol L^-1 under the optimal conditions of-0.1 V of pre-concentration potential, 100 s of pre-concentration time, 0.1mol L^-1 H₂SO₄ of the electrolyte, square wave stripping voltammetry of the detection method. The limit of detection is 0.03 μmol L^-1（S/N = 3）, the recoveries are from 94.0% to 104.0%; The reductive peak currents of As（Ⅲ） to As（0） at-0.05 V are in proportion to concentrations of As（Ⅲ） in the range from 0.5 to 9 μmol L^-1 under the condition of 0.1 mol L^-1 H₂SO₄ of the electrolyte, square wave voltammetry of the detection method. The limit of detection is 0.17 μmol L^-1（S/N = 3）. The recoveries are from 96.0% to 102.0%. The Au/RPE can achieve effective detection of As（Ⅲ） not only through the oxidation peak of As（0） but also through the reduction peak of As（Ⅲ）. The Au/RPE exhibited good stability, acceptable reproducibility, and can be applied to detect trace amounts of As（Ⅲ） in water sensitively. Further, the detection method based on the reduction peak of As（Ⅲ） has the advantage of better resistance to Cu（II）.3. Determination of Cr（Ⅵ） in water samples based on a graphene/Au nanoparticles composite film modified electrode prepared directly by electrochemical methodElectrochemical reduced graphene oxide and gold nanoparticles composite film（ERGO/Au） modified electrode was prepared by a directly electrochemical method for investigating electrochemical behaviors of Cr（Ⅵ）. The morphology and electrochemical properties of the fabricated electrode were respectively characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The preparation conditions of the modified electrodes and analytical conditions of Cr（Ⅵ） were optimized. The results show that ERGO/Au nanocomposite exhibited large electroactive surface area and excellent electrocatalytic property. The determination conditions are optimized as follows: the deposition potential and deposition time of Au are-0.4 V and 120 s, respectively. The dope of graphene oxide suspension is 3 μL, the electrolyte is 0.1mol L^-1 of HC l. The fabricated electrode exhibits linear ranges from 1 to 100 μmol L^-1 for Cr（Ⅵ） determination by linear sweep voltammetry. The limit of detection is 0.3 μmol L^-1（S/N = 3） The recovery of the standard addition is varied from 95.3% to 104.0%. The proposed electrode shows satisfactory repeatability, reproducibility, selectivity with a convenient preparation procedure and displays excel ent performance for practical samples.