IEEE SENSORS JOURNAL, VOL. 18, NO. 23, DECEMBER 1, 2018 9477 Pre-Adsorbed Methylene Blue at Carbon-Modified TiO 2 Electrode: Application for Lead Sensing in Water Khadijeh Nekoueian, Shila Jafari, Mandana Amiri , and Mika Sillanpää Abstract—Carbon modified titanium dioxide nanostructured (CMTN) was successfully fabricated by ethanol carbonization method and applied to modify the surface of glassy carbon elec- trode. This modified electrode was employed in the extraction and the electrochemical determination of methylene blue. The con- siderable increment in the voltammetric signal for pre-adsorbed methylene blue compared with those for solution, demonstrated a strong tendency of methylene blue to CMTN which was rooted in porous structure of CMTN and the electrostatic interaction between cationic methylene blue with negative surface of the CMTN. By applying differential pulse voltammetry, a calibration curve is obtained for methylene blue in the range of 1.0 × 10 -8 to 1.0 × 10 -5 M and the limit of detection was evaluated to be 3.0 × 10 -9 M. In addition, the pre-adsorbed methylene blue on the surface of the modified electrode performed well in the determination of the trace amounts of lead in the real samples such as lake and tap water. Dynamic linear range for lead was investigated in the range of 1.0 × 10 -7 to 5.0 × 10 -4 M and the limit of detection was calculated to be 3.0 × 10 -8 M. Index Terms— Lead, titanium compounds, nanocomposite, amperometric sensors, chemical analysis. Manuscript received February 24, 2018; revised September 12, 2018; accepted September 17, 2018. Date of publication September 20, 2018; date of current version November 13, 2018. The associate editor coor- dinating the review of this paper and approving it for publication was Prof. Venkat R. Bhethanabotla. (Corresponding authors: Khadijeh Nekoueian; Mandana Amiri.) K. Nekoueian and S. Jafari are with the Laboratory of Green Chemistry, Fac- ulty of Technology, Lappeenranta University of Technology, 50130 Lappeen- ranta, Finland (e-mail: kh.nekoueian@gmail.com). M. Amiri is with the Department of Chemistry, University of Mohaghegh Ardabili, Ardabil 5619911367, Iran (e-mail: mandanaamiri@yahoo.com). M. Sillanpää is with the Department of Civil and Environmental Engi- neering, Florida International University, Miami, FL 33174 USA (e-mail: mika.sillanpaa@lut.fi). This paper has supplementary downloadable multimedia material available at http://ieeexplore.ieee.org provided by the authors. The Supplementary Material includes materials and Instruments Sections: S1. (A) Nitrogen adsorption/desorption isotherms of CMTN and TiO 2 precursor, (B) ZP vs. pH for CMTN. S2. The optimization of various parameters such as A) time, B) pH and C) stirring rate on adsorption of MB and response peak by CMTN/GCE. S3. Investigation of optimum conditions for extraction and detection of Pb(II) as (A) time, (B) agitation rate and (C) MB concentration. S4. (A) Cyclic voltammograms of 1×10 -4 M Pb(II) at GCE/CMTN/MB in various υ (10, 20, 4, 60, 80, 100, 150 and 200 mV s -1 ). (B) Plot of the anodic and cathodic peak currents versus different υ (GCE/CMTNwas immersed for 4 min in the solution of 1×10 -6 M MB pH 7.0 for pre-adsorption then rinsed and immersed for 4 min in the solution of 1×10 -4 M Pb(II) acetate buffer pH 5.0 for adsorption then rinsed and transferred to phosphate buffer solution pH 7.0 for analysis. S5. (A) DPVs of various concentration of Pb(II) (5×10 -4 , 1×10 -4 ,5×10 -5 ,1×10 -5 ,1×10 -6 and 1×10 -7 M) on the surface of GCE/CMTN/MB. υ was 100 mV s -1 . (B) Calibration curve under optimum conditions for Pb(II) in the concentration range of 5×10 -4 to 1×10 -7 M. S6. Investigation of interference effect. This material is 718 KB in size. Digital Object Identifier 10.1109/JSEN.2018.2871437 I. I NTRODUCTION T HE demand for environmental monitoring has encour- aged researchers to investigate efficient methods to detect trace and ultra-trace amounts of organic and inorganic pol- lutants in water samples such as waste water, ground water and surface waters [1]. Among water pollutants, dyes and heavy metal ions have been concerned extensively due to their neglecting will cause severe damage on nature as well as human health and hygiene [2]. Among industrial dyes, methylene blue (MB) as a cationic organic dye is commonly applied in textile industry [1]. The released MB-containing wastewaters into aquatic environ- ment causes harmful impacts on humans such as increasing heart rate, vomiting, shock, Heinz body formation, cyanosis, jaundice, quadriplegia and tissue necrosis [1]. On the other hand, MB demonstrates an effective role in various areas of medicine, biology and chemistry. As a biological stain [3], as a redox mediator for facilitating the process of the electron transfer in electrocatalytic and biological systems [4], [5], as a bio-label for electrochemical marking due to its well-defined redox peaks [6] and MB has been utilized in fabrication of electrochemical sensors due to its interesting electrocat- alytic and adsorption properties [5]–[7]. A few analytical methods have been reported for determination of MB using techniques such as ultraviolet-visible spectroscopy [8], [9], liquid chromatography tandem mass spectrometry [10], capillary electrophoresis [11] and surfaces-enhanced Raman spectroscopy [12]. MB has been determined by voltammet- ric methods using nafion stabilized ibuprofen derived gold nanoparticles electrode [13], gold electrode [14] and thiol functionalized clay modified carbon paste electrode [15]. Among the different hazardous environmental contaminates, monitoring of heavy metals especially lead (Pb(II)) in water resources has been considered remarkably due to the high affinity of Pb(II) to accumulate in environmental matrices and living organism which has severe influence on immune, ner- vous, reproductive and gastrointestinal systems [16]. Various sensitive techniques have been improved for monitoring of Pb(II), such as; atomic absorption spectroscopy (AAS) [17], flame atomic absorption spectroscopy (FAAS) [18], induc- tively coupled plasma mass spectroscopy (ICP-MS) [19] and inductively couple plasma optical emission spectroscopy (ICP-OES) [20]. However, these techniques are mostly con- cerned as expensive methods, which are time consuming, 1558-1748 © 2018 IEEE. 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