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Reactivity of carb

Department of Chemical Engineering, Facu

50603 Kuala Lumpur, Malaysia. E-mail: mk

Cite this: RSC Adv., 2016, 6, 3690

Received 15th October 2015Accepted 1st December 2015

DOI: 10.1039/c5ra21487d

www.rsc.org/advances

3690 | RSC Adv., 2016, 6, 36903699

on black diamond electrodeduring the electro-oxidation of Remazol BrilliantBlue R

Mohammed A. Ajeel, Mohamed Kheireddine Taeib Aroua*and Wan Mohd Ashri Wan Daud*

This article reports for the first time, the reactivity of Carbon Black Diamond (CBD) electrode using cyclic

voltammetry and electrochemical impedance techniques in 0.25 M H2SO4 solution containing 0.5 mM

K4Fe(CN)6. Three CBD electrodes with different content of carbon black 5% (5CBD), 10% (10CBD), and

20% (20CBD) were used in this study. The reactions of the CBD electrodes were quasi-reversible while

the 5CBD electrode had the best activity compared to 10CBD and 20CBD electrodes. The anodic

oxidation behavior of Remazol Brilliant Blue R (RBBR) was investigated by using cyclic voltammetry and

electrochemical impedance techniques on the 5CBD electrode in different pH solutions. The results

indicated that the RBBR oxidized at 1.3 V, and the electro-oxidation process was more active in the low

pH solution. Furthermore, the removal rate of RBBR on 5CBD attained 99.5% after 4 hours of the

electro-oxidation process.

1. Introduction

The electrode material is one of the most important factorsaffecting an electrochemical oxidation process.1 Many anodematerials, such as F-doped PbO2,2 Ti/Ru0.3M0.7O2,3 b-PbO2/a-PbO2/SbSnO2/TiO2,4 Er-chitosan-PbO2,5 and Pd/PPy/foam-Ni,6

SnSbNi,7 Ti/SbSnO2,8,9 and BDD,10,11 have been tested andimproved for use as anodes for electrochemical oxidationprocesses of organic pollutants. Most previous studies haveattempted to propose an efficient electrode with suitable elec-trochemical properties, long service life, and low cost. A carbonblack diamond (CBD) electrode was proposed for the rst timeby our laboratory for organic pollutant oxidation. This electrodehas an inert surface and suitable oxygen evolution potential thatdepends on the carbon black (CB) percentage in the electrode.The potential window for a CBD electrode with 5% CB is similarto that of a BDD electrode; however, increasing carbon blackpercentage, lead to decrease the potential window of CBDelectrode.12 Cyclic voltammetry and impedance techniques areused to investigate the electrochemical kinetic of the electrode.Redox reaction such as K3Fe(CN)6/K4Fe(CN)6, benzoquinone/hydroquinone, Ce(NO3)3/Ce(NO3)4 and Ru(NH3)

3+/4+ have beenused as probes to observe the change in behavior of electrodesurface.1315 Cyclic voltammetry and electrochemical impedancetechniques had been used by many researchers to characterizethe electrochemical parameters for different electrodes,16 aswell as to investigate the behavior of direct anodic oxidation of

lty of Engineering, University of Malaya,

_aroua@um.edu.my

different organic pollutants, such as chlorophenols,17,18

adenine,19 tetramethylthiourea,20 hydrazine and phenol.21 Dyesand textile wastewater pose a serious environmental threat.Although, many researches have employed various techniques,such as direct and non-direct electrochemical oxidation,electro-Fenton, electro-coagulation, and other methods; veryfew have investigated the behavior of direct anodic oxidation ofdyes via cyclic voltammetry or electrochemical impedancetechniques. In this work, the effects of carbon black content andpolytetrauoroethylene binder on activities of diamondcomposite (CBD) electrode were investigated via cyclic voltam-metry. Apart from that, electrode/electrolyte interface for CBDwas investigated by using electrochemical impedance spec-troscopy. Moreover, RBBR electro-oxidation on 5CBD electrodeand its dependency on the main parameters, such as pH andinitial concentration, were also investigated via cyclic voltam-metry and electrochemical impedance spectroscopy methods.Also, RBBR electro-degradation was performed on 5CBD elec-trodes at different current density. RBBR was chosen as themodel dye molecule for anodic oxidation with CBD because it iscommonly used in textile industry.

2. Material and method2.1 Electrode preparation

Three disks of CBD electrode with three different content ofcarbon black (CB) 5% CB (5CBD), 10% CB (10CBD) and 20% CB(20CBD) have been prepared with surface area 1.1 cm2.Whereas, diamond powder (98.3% purity and average particlesize 6 nanometer, Sigma-Aldrich) was mixed carefully with

This journal is The Royal Society of Chemistry 2016

http://crossmark.crossref.org/dialog/?doi=10.1039/c5ra21487d&domain=pdf&date_stamp=2016-01-05http://dx.doi.org/10.1039/c5ra21487dhttp://pubs.rsc.org/en/journals/journal/RAhttp://pubs.rsc.org/en/journals/journal/RA?issueid=RA006005

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a precise percent of carbon black (99% purity and averageparticle size of 13 nanometers, Alfa). Powder mixture have beenmixed with suspension (60 wt%) in water (Sigma-Aldrich) pol-ytetrauoroethylene as the binder and 1,3-propanediol (98%purity, Sigma-Aldrich) and then dried as described in previouswork.12 In addition to the above mentioned method, electrodeswere prepared but, without using polytetrauoroethylenebinder by press the mixed powders using piston pressing with120 kg cm2.

2.2 Electrode characterization

2.2.1 Scanning electron microscopy analysis (SEM). Themorphological appearances of the CBD electrodes were studiedby scanning electron microscopy (SEM) (Hitachi SU-8000,Japan) equipped with an energy-dispersive X-ray (EDX)analyzer. EDX determined the element content of the electrode.

2.2.2 Electrochemical characterization of electrode. ThreeCBD electrodes with different content of carbon black wereinvestigated by cyclic voltammetry and electrochemicalimpedance technique to select the most efficient electrode foranodic oxidation of RBBR. EC-Lap sp-300 potentiostat with EC-Lap soware V10.12 was used to perform the electrochemistryassays. Cyclic voltammetry runs were carried out in a singlecompartment, three-electrode system, which consisted of a CBDelectrode as the working electrode, Ag/AgCl (3 M KCl) electrodeas a reference electrode, and a platinum wire as counter elec-trode. The cyclic voltammetry runs of the CBD electrodes ina solution of 0.5 M H2SO4 containing 0.5 mM of K4Fe(CN)6 wererecorded at different scan rate 20100 mV s1. Klingler andKochi22 eqn (1) consider a suitable relation to estimate theelectron transfer rate coefficient (ko) for quasirevisablereaction.

ko 2:18ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiDanvF

RT

rexp

a2nF

RT

Eoxp Eredp

(1)

where, ko electron transfer rate coefficient, D diffusivity coeffi-cient (6.2 104 cm2 s1) for K4Fe(CN)6, a is the transfercoefficient, n is the number of electrons transferred per mole. vis the scan rate (V s1), R is the gas constant (8.314 kJ K1

mol1), T is the absolute temperature (K), and Eoxp Eredp is theoxidationreduction peaks separation potential.

The electrochemical impedance spectroscopy experimentswere performed with a potential amplitude of the AC signalwas kept at 10 mV and the measured frequency range was 0.01to 105 Hz.

2.3 Electrochemical oxidation behavior of Remazol BrilliantBlue R

Voltammetric experiments were conducted in one compart-ment of a 100 mL glass cell at 25 C to investigate the electro-chemical oxidation behavior of RBBR (99.5% Sigma-Aldrich) onthe 5CBD electrode (containing PTFE binder). A solution of 0.25M H2SO4 (97% Merck Pro Analysis) as a blank solution, andthree aqueous solutions of 600 400 and 100 mg L1 of RBBRwere prepared. The compositions of the solutions were 0.25 MH2SO4 at pH 1, 0.25 M Na2SO4 at pH 6.5 and 0.25 M KOH at pH

This journal is The Royal Society of Chemistry 2016

11. Milli-Q water was used to prepare the solutions. A platinumwire was used as the counter electrode, and Ag/AgCl was used asthe reference electrode. EC-Lap sp-300 with EC-Lap sowareV10.12 potentiostat performed the electro-oxidation behavioron 5CBD electrode.

2.4 Electro-degradation of RBBR

An electrochemical cell with 100 mL of 100 mg L1 RBBR, 0.25M Na2SO4 as the supporting electrolyte was used for RBBRelectro-degradation experiments on the 5CBD electrode. Theexperiments were conducted at applied current densities of 5,10, or 15 mA cm2, and pH 3 at 25 C temperature. ISO-TECHprogrammable power supply IPS 3202 was used, whereasstainless steel cathode and C-MAG HS 7 magnetic stirrer wereused for solution mixing.

2.4.1 Analysis method. Chemical oxygen demand (COD)was analyzed by the standard method (HACH DRB 200). Theconcentrations of RBBR were determined by Lambda 35 UV-Visspectrophotometer (PerkinElmer, U.S.A) at a wavelength of 590nm. Prior to analysis, all the samples were ltered througha 0.22 mm lter membrane to eliminate the suspended solidthat may affect the analysis process. The decomposition inter-mediates of RBBR during electrolysis was examined by high-performance liquid chromatography (HPLC) using an AgilentTechnology 1200 series. C18 column (4.6 mm 250 mm 5mm) at 20 C was used a