Electrochemical Degradation of Reactive Yellow 160 Dye in RealWastewater Using C / PbO 2-, Pb + Sn / PbO 2 + SnO 2-, and Pb / PbO 2 Modi�ed Electrodes

ree modi�ed electrodes (C/PbO2, Pb + Sn/PbO2 + SnO2, and Pb/PbO2) were prepared by electrodeposition and used as anodes for electrochemical degradation of Reactive Yellow 160 (RY160) dye in aqueous solution. Different operating conditions and factors affecting the treatment process including current density, temperature, initial concentration of (RY160), pH, conductive electrolyte and time of electrolysis were studied and optimized.e best degradation occurred in the presence of NaCl (4 g L) as a conductive electrolyte. Aer 15min, nearly complete degradation of RY160 was achieved (97.9%, 96.65 and 95.35% using C/PbO2, Pb+Sn/PbO2 +SnO2, and Pb/PbO2 electrodes, resp.) at pH 7.13. Higher degradation efficiency was obtained at 25 C.e optimum current density for the degradation of RY160 on all electrodes was 50mA cm. e prepared C/PbO2, Pb+Sn/PbO2 + SnO2 and Pb/PbO2 electrodes were found to be highly efficient in the treatment of effluents obtained from dyeing factory which contain RY160 dye with very slight matrix effect.


Introduction
e electrochemical performance and stability of the PbO 2 �lm are related to substrate preparation and electrodeposition conditions, as well as to the organic-and inorganicdoping species that might be used [1,2].New methodologies have led to improved adhesion of the PbO 2 �lm onto the substrate [3], and also to an oxidation power of the PbO 2 anode comparable to that of the boron-doped diamond (DDB) anode [2]; however the most used substrate is still the Ti-Pt [1][2][3][4][5][6].Comninellis and Chen [7] point the possible release of Pb 2+ ions, especially in basic solutions, as the main drawback of PbO 2 anodes; in many instances, a short lifetime might be another important drawback [8].e degradation of reactive dye was studied by wet-air oxidation (WAO) [9], wetperoxide oxidation (WPO) [10], photooxidation [11][12][13], electro-fenton (EF) advanced oxidation [14,15], ozonation [16,17], H 2 O 2 /UV [18,19], catalytic electro-oxidation [20] and electrocoagulation [21,22].e performances of the Ti-Pt/-PbO 2 and the boron-doped diamond (BDD) electrodes in the electro-oxidation of simulated wastewaters containing 85 mg L −1 of the Reactive Orange 16 and Blue Reactive 19 dye were investigated using a �lter-press reactor [1,4].e electrochemical characterization of Ti/SnO 2 -Sb-Pt anodes prepared by thermal decomposition was researched using different techniques.ese results were also compared to those obtained for the Ti/SnO 2 , Ti/SnO 2 -Sb, and deactivated Ti/SnO 2 -Sb-Pt anodes.COD, HPLC, UV-Vis, and potential control measurements were also used to verify the viability of these anodes to degrade and decolorize wastewater solutions containing a reactive dye: C.I. Reactive Orange 4 [23,24].e electrochemical degradation of C.I. Reactive Red 195 (RR195) and 4-chloro-3-methyl phenol (CMP) in aqueous solution on a Ti/SnO 2 -Sb/PbO 2 electrode was investigated.e in�uence of operating variables on the mineralization efficiency was studied as a function of the current density, the initial pH, the initial concentration of the dye, and the addition of NaCl [25].Basic Yellow 28 (SLY) and Reactive Black 5 (CBWB), which are, respectively, methane and sulfoazo textile dyes were individually exposed to electrochemical treatment using diamond-, aluminum-, copperand iron-zinc alloy electrodes.Four different electrodic materials were tested, and presented 95% color removal and COD removal of up to 65-67% in the case of CBWB dye solution treated with the copper and iron electrodes [26].Electrochemical degradation experiments were conducted to degrade a textile dye, namely, Reactive Blue 19 .e oxidation of RB-19 using titanium-based dimensionally stable anode (DSA) takes place in the bulk solution with electrolytically generated chlorine/hypochlorite.Increasing the initial pH and increasing the reaction temperature decreases the de-colorization efficiency.At the same time, increasing the chloride concentration and increasing the current density showed an increase in the color removal.e complete removal of color was achieved within a short period of electrolysis for different concentrations of RB-19.However, the removal of COD and TOC was 55.8% and 15.6%, respectively, for 400 mg L −1 RB-19 with 1.5 g L −1 sodium chloride concentration [27].e electrochemical oxidation of simulated textile wastewater was studied on iron electrodes in the presence of NaCl electrolyte in a batch electrochemical reactor.e simulated textile wastewater was prepared from industrial components based on the real mercerized and nonmercerized cotton and viscon process [28].Electrochemical oxidation of O-Toluidine (OT) was studied by galvanostatic electrolysis using lead dioxide (PbO 2 ) and (BDD) as anodes.e in�uence of operating parameters, such as current density, initial concentration of OT, and temperature were investigated [29].
In this study, an electrodegradation method was applied on Reactive Yellow 160 (RY160) dye (Scheme 1), by using three modi�ed electrodes (C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 ).Different factors including the pH, concentration of electrolyte, conductive electrolyte type, current density, time of electrolysis, initial concentration of RY160 solution, and temperature were studied and optimized for its removal from water.Two main parameters were measured to evaluate the electrochemical treatment efficiency, the remaining pollutant concentration and the chemical oxygen demand (COD).

Experiments
2.1.Chemicals and Instrumentation.Sodium chloride, sodium �uoride, sodium carbonate, sodium sulphate, cal-cium chloride, potassium chloride, sodium hydroxide, sulphuric acid, and potassium dichromate, silver sulfate were of analytical grade and purchased from Merck.Distilled water was used for the preparation of solutions.Standard solutions of potassium dichromate, sulfuric acid reagent with silver sulfate, and potassium hydrogen phthalate (KHP) were prepared to measure the COD.Different standard solutions of RY160 with concentration from 20-200 mg L −1 were prepared to measure its degradation at different conditions.e doublebeam UV-Vis spectrophotometer is from Shimadzu, the DC power supply is model GP4303D, LG Precision CO. Ltd.
(Korea), a pH meter model AC28, TOA electronics Ltd., (Japan) to adjust pH of the solutions and a digital multimeter is kyoritsu model 1008, (Japan) for reading out the current and potential values.A closed re�ux titrimetric unit was used for the COD determination [30].is process has a great application and good penetrating power.en it was treated with an alkali solution, a mixture of sodium hydroxide (50 g L −1 ) and sodium carbonate (20 g L −1 ), to remove any organic materials in the surface, and tri-sodium orthophosphate (20 g L −1 ) and sulphuric acid

Electrodeposition of
(2 g L −1 ) to remove any oxides.Uniform and well-adhesive deposit necessitates a smooth surface with no oxide or scales.To con�rm our preparation, the lead substrate was soaked for 2 min in a pickling solution consisting of nitric acid (400 g L −1 ) and hydro�uoric acid (5 g L −1 ), and then chemically polished in boiled oxalic acid solution (100 g L −1 ) for 5 min [31].
Electrochemical Deposition of  2 .PbO 2 was deposited galvanostatically on the pretreated lead substrate by electrochemical anodization of lead in oxalic acid solution (100 g L −1 ).is acid solution was electrolyzed galvanostatically for 30 min.at ambient temperature using an anodic current density of 100 mA cm −2 .e cathode was stainless steel (austenitic type), and the two electrodes were concentric with the lead electrode axially.is arrangement gave the formation of a regular and uniform deposit [31].

Preparation of Pb + Sn
Preparation and Fabrication of Pb-Sn Alloy Electrodes.Binary Pb-Sn alloy with concentration (1 : 1 w/w) were prepared according to the standard following procedure and the fabrication of the electrodes as discussed in detail elsewhere.Anodic oxidation of alloy electrodes was carried out, and the �lm was characterized for its structure [32].
Electrochemical Deposition of  2 +  2 .ree electrodes assembly was used for making thin �lms, in which the working alloy electrodes was of 1 cm 2 area with Pt (4 cm) as the counter-electrode and saturated calomel electrode (SCE) as the reference.Prior to oxidation, the working electrode surface was successively polished on 1000∼ grit paper on roughing stone using water as lubricant and �nally with methanol-acetic acid mixture.e alloy substrate was cleaned by acetone to remove greases or oils lodged in the metal surface, treated with an alkali solution, a mixture of sodium hydroxide (50 g L −1 ), and sodium carbonate (20 g L −1 ), to remove any organic materials in the surface, and tri-sodium orthophosphate (20 g L −1 ), sulphuric acid (2 g L −1 ) to remove any oxides.To con�rm our preparation, the alloy substrate was soaked for 2 min in a pickling solution consisting of nitric acid (400 g L −1 ) and hydro�uoric acid (5 g L −1 ), and then chemically polished in boiled oxalic acid solution (100 g L −1 ) for 5 min.Potentiodynamic anodization of Pb-Sn alloy was carried out at 80 ∘ C in the potential range from −1.25 V to +2.35 V with a sweep rate 200 mV s −1 .Aer 20 min of continuous anodization [32], the electrode was taken out of the electrolysis bath and washed thoroughly in doubly distilled water followed by drying in air at 120 ∘ C for 2 h.

Preparation of Modi�ed C/PbO 2 Electrode
Carbon Surface Treatment.Pretreatment of carbon rod (8 mm × 25 cm) was carried out following the procedure applied by Narasimham and Udupa [33].e carbon rod was soaked in 5% NaOH solution, washed with distilled water, dried in furnace at 105 ∘ C, and cooked with linseed oil to reduce the porosity of rod.Aer that, the electrode was ready to receive doped PbO 2 .Electrochemical Deposition of  2 .e electrodeposition of PbO 2 was performed at constant anodic current of 20 mA cm −2 in 12% (w/v) Pb(NO 3 ) 2 solution containing 5% (w/v) CuSO 4 ⋅5H 2 O and 3% surfactant.e role of the surfactant is to minimize the surface tension of the solution.Electrodeposition was carried out for 60 min.at 80 ∘ C with continuous stirring [33].

Electrolysis of Reactive Yellow 160 Degradation.
Galvanostatic electrolyses were carried out at C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes, with current density ranging from 0 to 400 mA cm −2 and electrical potential ranging from 1-12 volts.Runs were performed at 10-40 ∘ C. Solutions of 100 mg L −1 of pure RY160 solution were used.e investigations of this study were carried out in the presence of sodium chloride (0.5-20 g L −1 ) and 4 g L −1 of different conductive electrolytes such as; NaCl, CaCl 2 , KCl, Na 2 CO 3 , NaF, NaPO 4 , and Na 2 SO 4 with pH between 1.5 and 12. e electrolysis duration ranges from 0-30 min.e electrochemical degradation of the RY160 solutions was carried out in a 100 mL Pyrex glass cell where the prepared electrodes C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 work as anode and austenitic stainless steel as cathode.e electrodes were connected to a DC power supply, while the current and potential measurements were read out using the digital multimeter.

Analysis.
Two main parameters were measured to evaluate the electrochemical treatment efficiency, remaining pollutants (RY160) concentration was measured with the double-beam UV-visible spectrophotometer from Shimadzu at  max = 415 nm using calibration curve with standard error ±0.5%, and the COD was determined using a closed re�ux titrimetric method [30].

Mechanism of Electrochemical Oxidation of Organic
Pollutants. e electrochemical oxidation of many organic pollutants in aqueous solutions on anode could take place by direct electron transfer or oxygen-atom transfer.In addition to direct oxidation, organic pollutants can also be treated by an indirect electrolysis generating chemical reactant to convert them into less deleterious products.Oxidation of these pollutants might go further to carbon dioxide and water via successive reactions.Each of them could proceed through several steps such as mass transport, adsorption, and direct or indirect reaction at the anode surface [31].e direct electrochemical oxidation of organic compounds could generally occur through the following mechanism in which the �rst step is the oxidation of water molecules on the electrode surface (MO  ).is process may give rise to formation of hydroxyl radicals according to the following equation e produced hydroxyl radicals can be oxidized to a higher state forming the so-called higher oxide as follows e role of the formed higher oxide is the participation in the formation of selective oxidation of the organic pollutants (R) without complete incineration (4): e above route can take place only if the transition of the underlying oxide to a higher oxidation state occurred.e electrodes of this class are called "active electrodes" [34].However, if the product of ( 4) is not obtained, the electrogenerated hydroxyl radicals could directly oxidize the organic compound to carbon dioxide and water, predominantly causing the combustion of the organic compound through hydroxylation of these compounds as follows and this class of electrodes are called "nonactive electrodes" [35].On the basis of the abovementioned mechanism, the lead dioxide anode employed in this investigation is characterized by high oxygen overvoltage on which (OH • ) is generated from the oxidation of water.Hydroxyl radicals (OH • ) are electrosynthesized in aqueous solutions and can react rapidly with aromatic pesticides, leading to a polyhydroxylation reaction, followed by complete mineralization of the initial pollutants [35].However, PbO 2 does not have a higher oxidation state� consequently it is classi�ed as a "nonactive electrode".It was reported that lead dioxide electrode is hydrated one, and the electrogenerated hydroxyl radicals are expected to be more strongly adsorbed on its surface.is behavior makes lead dioxide anode very reactive towards organic oxidation.e degradation of the organic pollutants is completed by reaction with adsorbed hydroxyl radicals forming carbon dioxide and water.Indirect electrochemical oxidation of organic pollutants occurs through the "in situ" electrogeneration of catalytic species with powerful oxidizing property.is process is capable of eliminating the detrimental pollutants from their solutions by converting them into harmless compound.
Although a large number of electrogenerated oxidants can be used such as Fenton's reagent and ozone, the hypochlorite ion is the most widely employed oxidant in wastewater treatment [36].e mechanism of electrogeneration, from a solution, containing chloride ions involves two steps.e �rst one is primary oxidation of chloride ions to chlorine at the anode surface according to [36] the following equation:  hypochlorite tends to chemically decompose to sodium chlorate as follows: So when temperature rises higher than 35 ∘ C, production of NaClO falls.But at higher current densities the rate of hypochlorite decomposition increases with increase in current density.

Effect of Type of Electrolyte.
Electrolytes of 4 g L −1 of the following salts; NaCl, CaCl 2 , KCl, Na 2 CO 3 , NaF, Na 3 PO 4 , and Na 2 SO 4 were studied by three electrodes.As appears in Figure 4, e NaCl, KCl, and CaCl 2 were the most effective conductive electrolytes for the electrocatalytic degradation of the investigated RY160 and COD removal.e Cl − anion is a powerful oxidizing agent.It enhances the degradation of pollutants.erefore, addition of NaCl, KCl, and CaCl 2 provides the effective Cl − ion.is behavior may be due to the small ionic size of K + and Na + which increases the ion mobilities and the loss ability of Cl − ion.Na 2 SO 4 and NaF electrolytes showed the least efficiency in the degradation of pollutant.is may be attributed to the formation of an adherent �lm on the anode surface which poisons the electrode surface.Also, these electrolytes do not contain chloride ions (Cl − ) in their structures and may form stable intermediate species that could not be oxidized by direct electrolysis.ese observations were also con�rmed in other studies [31].

Effect of the Electrolysis Time.
To assess the effect of electrolysis time, experiments were conducted with operating treatment conditions that were consistent with those described for C/PbO electrodes.e maximum removal of RY160 was achieved using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 and Pb/PbO 2 electrodes aer at least 15 min.erefore, this was taken as optimal degradation time for the removal of RY160.e optimal time for COD removal for three electrodes was 270, 340, and 360 min, respectively.

Effect of Temperature.
It is well known that the rate of diffusion of ions increases with increasing temperature.Figure 5 represents the correlation between the concentration of the remaining RY160 dye and COD residual as a function of the solution temperature.e rate of the RY160 degradation and COD removal increase signi�cantly with increasing the solution temperature until 25 ∘ C. erefore, 25 ∘ C was �xed as optimal electrolysis temperature for the next experiments.1 cm was chosen as optimum distance between electrodes for sodium hypochlorite generation.e experiments were carried out under the following conditions: current density 50 mA cm −2 , pH of 7.13, temperature of 25 ∘ C, and the concentration of NaCl 4 g L −1 .e time of electrolysis was 15 min.It is clear that the sodium hypochlorite production increase with decreasing distance down to 1 cm.is is due to drop of electrolyte ohmic potential, and hence the cell voltage [37].e highest hypochlorite production was achieved with narrow distance between the cell electrodes of 1 cm.

Application of the Treatment Process in Real
Wastewater Samples.e treatment of RY160 effluents obtained from dyeing factory was carried out by using the prepared C/PbO 2 -, Pb+Sn/PbO 2 -, + SnO 2 , and Pb/PbO 2 -modi�ed electrodes.e treatment was performed, �rst by collecting actual waste samples from the wastewater effluents of the RY160 dyeing bath.e initial dye-load concentration of these samples was 170 mg/L taken from Hubbub dyeing factory located in the industrial area at Biet Hanon, Gaza Strip, PNA.e dyestuff solutions were treated by the electrocatalytic oxidation technique using the same method as applied to the treatment of RY160 in aqueous solution to investigate the optimum condition for real wastewater containing the dye.Aer the treatment process, the removal percentages of RY160 dye at 15 min using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes were 97.9%, 96.65, and 95.35%, respectively.e removal percentages of COD were 100% at 300, 380 and 400 min for the above electrodes, respectively.ese results indicated that the suggested modi�ed electrodes are highly e�cient in the treatment of effluents containing RY160 dye with very slight effect of matrix.

Conclusion
In this work, three modi�ed electrodes (C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 ) were prepared by elecrodeposition and used as anodes for electrodegradation of RY160 in aqueous solution at different parameters including conductive electrolyte, current density, temperature, initial concentration of RY160, pH, and time.e optimum conditions for three electrodes are: NaCl (4 g L −1 ), temperature at 25 ∘ C, degradation time of 15 min, initial concentration of 100 mg L −1 , current density equals 50 mA cm −2 and 1 cm distance between the three electrodes of the cell.e degradation of RY160 was nearly completed (97.9%, 96.65, and 95.35%) using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes at pH 7.13, respectively.e obtained results indicated high e�ciency of the suggested modi�ed electrodes in the treatment of effluents containing RY160 dye with very slight matrix effect.

S 1 :
e structure formula of RY160.

2. 5 .
Cost Calculation of RY160 Degradation.e cost of electrochemical degradation of RY160 per liter was calculated as follows: Cost = Electrical energy consumption × price in dollars Electrical energy consumption kws −1  =  (1000 × 3600) ,
Different concentrations of NaCl were applied to study their effect on the removal of RY160 and the corresponding COD elimination as indicated in Figure2.e results indicate that an increase of the electrolyte concentration up to 4 g L −1 leads to increase in the RY160 degradation rate and COD removal for three C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.e NaCl solution liberates Cl 2 gas which is considered as the active species for the degradation of organic compound.Further increase of the NaCl concentration has slight effect on the degradation rate of RY160 and COD removal.
e second step is formation of hypochlorous acid as follows Cl 2 + H 2 O  ⟶ HClO + Cl − + H + 3.2.1.Effect of pH Value.epH of the solution was varied while the other conditions where kept constant.As shown in Figure 1, maximum removal of RY160 and COD was achieved at pH 7.13 for C/PbO 2 , Pb+Sn/PbO 2 +SnO 2 , and ) F 2: e effect of NaCl concentration on RY160 and COD removal using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.Pb/PbO 2 , respectively.epHvalues of the solutions were adjusted by adding drops of H 2 SO 4 and NaOH.e reactions were carried out for 15 min for three electrodes under the following conditions: the initial concentration of 100 mg L −1 , a current density of 50 mA cm −2 , a temperature of 25 ∘ C and NaCl concentration of 4 g L −1 .edistance between the two electrodes was adjusted to 1 cm.It was found that the maximum rate of degradation using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes was achieved in neutral medium as the optimal medium.3.2.2.Effect of the NaCl Concentration.degradation and COD removal increase with increasing the applied current density up to 50 mA cm −2 by using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.Further increase of the current density was followed by gradual decrease in RY160 degradation and COD removal due to increase in temperature.Above a temperature 35 ∘ C, sodium KCl Na 2 CO 3 Na 3 PO 4 Na 2 SO 4 NaF F 4: e effect of the conductive electrolyte type on RY160 and COD removal using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.
2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 ) 354]2 , + SnO 2 and Pb/PbO 2 electrodes at 100 mg L −1 was the optimum concentration for the initial load concentration of RY160.As the initial RY160 concentration increase, the degradation efficiency decrease.isevidencethatthegeneration of the powerful oxidizing agent Cl − ions on electrode surface was not increased in constant current density.eoptimumoperatingconditionsfordegradationPbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.RY160 dye for each electrode were determined and summarized in Table 1.At optimized conditions, the percentages of RY160 degradation and COD removal for C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 are 97.9%,96.65,and95.35%,respectively.eresultsindicatethat the C/PbO 2 electrode is more adequate than Pb + Sn/PbO 2 + SnO 2 -and than Pb/PbO 2 -modi�ed electrode for the degradation of RY160.eirbehavior may be attributed to the color and structure of tested electrodes.C/PbO 2 modi�ed electrodes have a black color, while Pb + Sn/PbO 2 + SnO 2 and Pb/PbO 2 modi�ed electrodes have a brown color.It was reported that PbO 2 �lm has two structures, -structure (brown color) and structure (black color)[31].eblackone has a tetrahedral crystal structure which is close-packed and more disordered in comparison with the close-packed structure of the brown -form (orthorhombic).erefore,thesurfacearea in case of tetrahedral structure is more than that of the orthorhombic one, and hence the -PbO 2 form will be more effective than -PbO 2 form.Because the overpotential for oxygen evolution of -PbO 2 is higher than that of -PbO 2 , it is expected that the electrocatalytic properties for C/PbO 2 -modi�ed electrodes are more efficient than that of Pb/PbO 2 -modi�ed electrode[34].In this work, the degradation rate of RY160 was nearly completed and reached 97.9, 96.65, and 95.35percentage using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes, respectively, aer 15 min.Percentage of COD and concentration removal of RY160 on C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes in the optimum conditions.
3.2.8.Effect of Distance between the Cathode and Anode.eeffect of distance between the two electrodes of the cell was studied.It was found from Figure7that there was an increase of hypochlorite generation by decreasing the distance between the two electrodes up to 1 cm for C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.erefore T 1: ) F 6: e effect of initial concentration on RY160 and COD removal using C/PbO 2 , Pb + Sn/PbO 2 + SnO 2 , and Pb/PbO 2 electrodes.