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Научни трудове на Съюза на учените в България-Пловдив. Серия В. Техника и технологии, т. XV, ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017. Scientific Works of the Union of Scientists in Bulgaria-Plovdiv, series C. Technics and Technologies, Vol. XV., ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017.
АМПЕРОМЕТРИЧНО ОПРЕДЕЛЯНЕ НА ВОДОРОДЕН ПЕРОКСИД ВАЛКАЛНАСРЕДА С ИЗПОЛЗВАНЕ НАСТЪКЛОГРАФИТ МОДИФИЦИРАН О РОДИЙ ЯмнаЛазаровр, Тонка ТКдеиска
Катедра Органичнахимия иНеорганикнахимия, УХТ, Пловдив
AMPEROMETRIC DETECTION OF HYDROGEN PEROXIDE IN ALKALINE MEDIUM USING RHODIUM-MODIFIED GLASSY
CARBON Yanna Lazarova, Totka Dodevska Department of Organic chemistry and Inorganic chemistry,UFT,Plovdiv
Abstract
The electrocatalytic response of rhodium-modified glassy carbon electrode towards hydrogen peroxide (А2К2) oxidation in alkaline medium (0.1 M NaOH) was studied using cyclic voltammetry (CV) and chronoamperometry. CV experiments yielded evidence that rhodium deposits facilitates hydrogen peroxide electrooxidation. Nhe amaerometric detection of А2К2 was carried out at a constant potential of 0.25 V (vs. Ag/AgCl, 3 M KCl) and the operational parameters of the modified electrode have been defined: electrode sensitivity 231 цА mL-1 cm-2, range of the strict linear concentration dependence of the current signal up to 6.0 mL А2К2 (r2=0.999), response time 15 s.
Keywords: hydrogen peroxide oxidation, alkaline medium, rhodium, modified glassy carbon electrode
Introduction
In recent years, development of sensitive, accurate and simple methods for reliable, fast and low-cost quantitative analysis of hydrogen peroxide (H2O2) over the micro- and nanomolar concentration ranges is practically important and widely investigated (Chen et al., 2012; Chen et al., 2013). H2O2 plays a fundamental role as an oxidising, bleaching, antiseptic and disinfecting agent, therefore it is an essential analyte in pharmaceutical, cosmetic, food and environmental monitoring.
Rhodium (Rh) is an excellent catalyst in hydrogenation reactions, applicable in C-C cross-coupling (Kanuru et al., 2009) and oxidation reactions (Sathe et al., 2011). Rh has a high activity for the catalytic conversion of atmospheric pollutants (Gomez et al., 2004), thus it is a common component of the catalysts used to remove nitrogen oxides, CO and some hydrocarbons from auto exhaust gases. Furthermore, rhodium with its chemical inertness towards acids and bases can withstand even harsh reaction environments, rendering Rh micro- and nanostructures broadly applicable (Sathe et al., 2011). In 2016 research paper, related to the catalytic activity of rhodium, has been reported that Rh nanocrystals with specific morphology may be highly promising alternatives to Pt electrocatalysts for methanol electrooxidation in an alkaline medium (Kang et al., 2016). In this connection, present work deals with the studies on hydrogen peroxide oxidation
in alkaline medium on Rh-modified glassy carbon electrode with respect to quantitative amperometric detection of H2O2. The modified electrode shows well defined, stable voltammetric response at high pH (pH 13, 0.1 M NaOH). Effective electrooxidation of H2O2 at reduced overpotential (0.25 V, vs. Ag/AgCl) was performed using presented here catalyst.
Experimental
Materials
The working electrode was disc from glassy carbon (GC) with diameter of the working surface d=3 mm and visible surface area of ca. 7.07 mm2 (Metrohm). RhCl3.nH20 (Fluka), HCl (Merck), 30% H2O2 (Fluka), NaOH (Fluka) were of analytical grade and used as received. Double distilled water was used to prepare aqueous solutions. Apparatus and measurements
The electrochemical measurements were performed using computer controlled electrochemical workstation EmStat2 (PalmSens BV, The Nederland) in a conventional three-electrode cell, including working electrode, an Ag/AgCl (3 M KCl) reference electrode, and a platinum auxiliary electrode.
The electrochemical measurements were carried out in Ar-purged 0.1 M NaOH at a constant temperature of 25 oC. Cyclic voltammograms (CVs) were recorded at scan rate of 50 mV s-1. Peak intensities of CVs were reported with baseline correction. The chronoamperometric experiment was performed by successive addition of aliquots of freshly prepared 3*10-2 M H2O2 (in 0.1 M NaOH) solution to basic electrolyte 0.1 M NaOH in the cell (30 mL initial volume) with simultaneous registration of the current at a constant potential.
The experimental data were processed by software package "OriginPro 8". Electrochemical deposition of Rh
Before modification, the GC electrode surface was carefully polished with 0.3 and 0.5 ^m alumina slurry on a polishing cloth (LECO, USA), followed by sonication in double distilled water for 3 min in order to remove adsorbed particles. After bath sonication, the electrode was rinsed with double distilled water and allowed to dry at room temperature for few minutes. The rhodium structures were electrodeposited onto the clean working surface of the GC electrode by means of CV - 1 cycle at a scan rate of 0.1 V s-1 from electrolyte containing 2% RhCl3, dissolved in 0.1 M HCl. The electrode surface was seeded with rhodium particles when starting the cycle at -0.3 V, then the scan goes up to 0.9 and back to -0.3 V. The modified Rh/GC was subsequently rinsed twice with double distilled water, dried at ambient conditions and employed for the electrochemical studies.
Results and discussion
The electrocatalytic behaviour of the modified electrode Rh/GC in 0.1 M NaOH was studied using cyclic voltammetry (CV). Fig. 1A presents the CVs recorded in the potential range from -0.2 to 0.4 V in the absence and presence of 1 mM H2O2. It is obvious that the bare GC electrode exhibits low catalytic activity for the electrooxidation of H2O2 in alkaline medium (Fig. 1A inset). The appearance of catalytic wave on the voltammogram for Rh/GC, recorded in the presence of H2O2, provides a proof that the metal phase, deposited onto GC, is electrochemically active. As it can be seen from the CV, upon the addition of H2O2, the electrocatalytic oxidation of H2O2 on modified electrode starts above 0 V (vs. Ag/AgCl). The anodic current increases sharply with further increase of applied potentials and reaches its maximum at a potential around 0.25 V.
In order to evaluate the electrocatalytic activity of Rh particles, the CVs of the modified electrode in the presence of different concentrations of hydrogen peroxide in 0.1 M NaOH were recorded. As shown on Fig. 1B, the anodic peak currents increased gradually with increasing H2O2 concentration and the peak potentials shift to more positive both of which demonstrate that the oxidation current is caused by the electrooxidation of H2O2. The results (inset to Fig. 1B) showed
that the concentration dependence of the catalytic peak currents was linear over the studied range (up to 1.5 mM) with a correlation coefficient of 0.997. It can be inferred from these results that the presence of the electrodeposited Rh on the surface of GC electrode facilitates the detection of H2O2 in alkaline medium.
14n 12 108
1 6 -- 42 0 -2
1 mM H2O2
-0,2 -0,1 0,0 0,1 0,2 0,3 0,4 E, (V)
25 20 15% 1°-50
10 i
8- r2 = . 6 -
p 4 -2 -
0 J-1-1-1-
0 0,5 1 1,5 H2O2 concentration, (mM)
-0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 E, (V)
Fig. 1. CVs of the modified electrode Rh/GC in 0.1 M NaOH: A) in absence and presence of 1 mM H2O2, inset: CVs of the bare GC electrode; B) in presence of various H2O2 concentrations, inset: plot of the anodic peak currents vs. H2O2 concentration; scan rate of 50 mV s-1.
B
A
1,5mM H2O2
1mM H2O2
0,5mM H2O2
Since amperometry under stirred conditions is much more current sensitive than cyclic voltammetry, this method was employed in order to estimate the electrode sensitivity. Fig. 2A displays the typical steady-state catalytic current time response of the modified electrode with successive injection of hydrogen peroxide at a constant applied potential of 0.25 V in 0.1 M NaOH solution. The chronoamperometric record indicates that the oxidative current increased stepwise upon introducing in the background electrolyte aliquots of the analyte stock solution, rapidly reaching a steady-state current in less than 15 s (Fig. 2A). These results demonstrate a stable and efficient catalytic property of Rh electrodeposited on GC electrode. There is a linear relation between response current and peroxide concentration up to 6 mM H2O2; the corresponding calibration curve is presented in Fig. 2B. The linear least squares calibration curve (15 points) is I(^A)=16.299C(mM)-0.423 with a correlation coefficient of 0.999, indicating that the regression line is very well fitted with the experimental data. The electrode sensitivity of 231 ^A mM-1 cm-2 was determined as the slope of the linear portion of the calibration graph, divided by geometric electrode area.
The analytical system is characterized by a relatively simple preparation and wide linear dynamic range of the analyte. The sensitivity of detection (231 ^A mM-1 cm-2) is also a significant advantage, as it is about 4 times as high as the one achieved by Ojani et al. by means of modified electrode type Nikel oxide/CPE (Ojani et al., 2012) obtained at a much higher working potential (0.6 V) and 6 times as high as the sensitivity achieved by Li et al. by means of electrode type MnO2/GO (Li et al., 2010) in a much more shortened concentration range (up to 0.6 mM).
40-,
30
20-
10-
-10
300
400
t, (s)
500
600
140 120 100 80 60 40 20 0
Equation y = a + b*x
Adj. R-Square 0,99901
Value Standard Error
Intercept -0,42281 0,49631
Slope 16,29945 0,13688
1 2 3 4 5 6
H2O2 concentration, (mM)
Fig. 2. A) Authentic record of the amperometric response of modified electrode Rh/GC to successive additions of H2O2 into 0.1 M NaOH at an applied potential of 0.25 V (vs. Ag/AgCl, 3M KCl), temperature 25 oC; B) The corresponding calibration curve (the dependence of the electrode response on the concentration of H2O2).
B
A
0
Conclusions
The quantitative detection of H2O2 in alkaline medium, based on rhodium-modified glassy carbon electrocatalyst, was demonstrated. A Rh/GC catalytic working electrode used as part of a three-electrode system appeared to be effective in electrocatalytic oxidation of the H2O2. This observation was confirmed by the cyclic voltammograms taken in 0.1 M NaOH background electrolyte. Based on this information, H2O2 was detected amperometrically at a constant potential of 0.25 V (vs. Ag/AgCl) within a linear dynamic range up to 6.0 mM with a sensitivity of 231 ^A mM-1 cm-2 (r2=0.999).
References
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