Experimental data of a catalytic decolorization of Ponceau 4R dye using the cobalt (II)/NaHCO3/H2O2 system in aqueous solution.

The treatment by Advanced Oxidation Processes (AOPs) of wastewater polluted with dyes is of particular interest in the field of environmental engineering, especially for the removal azo-dyes, representing over 50% of the global annual production of dyes. Unfortunately, most azo-dyes are non-biodegradable and can be toxic to aquatic organisms. This is the first data article that applies the methodology of response surface for the optimization of decolorization of an azo-compound using cobalt in a homogeneous medium as the catalyst of a bicarbonate activated hydrogen peroxide (BAP) system which, in turn, is an emerging technology for wastewater treatment. The Response Surface Methodology (RSM) based on a Central Composite Design (CCD) was used to evaluate and optimize the influence of three experimental variables (stoichiometric dosage of H2O2, molar ratio H2O2/NaHCO3 and cobalt concentration) on the decolorization of Ponceau 4R. Reactions were performed at 25 °C, pH 8.3 with a reaction time of 2 h. Analysis of variance (ANOVA) showed values of R2 and adjusted-R2 of 0.9815 and 0.9648, and experimental data were fit to a second-order regression model. The optimal conditions to achieve a maximum decolorization (96.31%) of a Ponceau 4R aqueous solution of 20 mg/l were: 4.73 times stoichiometric dosage of H2O2, molar ratio H2O2/NaHCO3 of 1.70 and cobalt concentration of 11.16 µM. Under the optimal reaction conditions, the influence of temperature (20, 25, 30 and 35 °C) on decolorization was evaluated and data were adjusted to second order kinetics. To verify the efficiency of the BAP system on the decolorization of Ponceau 4R, under the optimal conditions of reaction, UV–Vis spectra, at different reaction times, were measured. Additionally, blank experiments in order to evaluate the effect of individual factors in the Ponceau 4R decolorization, using BAP system, were carried out. Data showed that the Co(II)-NaHCO3-H2O2 system is a suitable technology for the decolorization of azo-dyes aqueous solutions.


a b s t r a c t
The treatment by Advanced Oxidation Processes (AOPs) of wastewater polluted with dyes is of particular interest in the field of environmental engineering, especially for the removal azo-dyes, representing over 50% of the global annual production of dyes. Unfortunately, most azo-dyes are non-biodegradable and can be toxic to aquatic organisms. This is the first data article that applies the methodology of response surface for the optimization of decolorization of an azo-compound using cobalt in a homogeneous medium as the catalyst of a bicarbonate activated hydrogen peroxide (BAP) system which, in turn, is an emerging technology for wastewater treatment. The Response Surface Methodology (RSM) based on a Central Composite Design (CCD) was used to evaluate and optimize the influence of three experimental variables (stoichiometric dosage of H 2 O 2 , molar ratio H 2 O 2 /NaHCO 3 and cobalt concentration) on the decolorization of Ponceau 4R. Reactions were performed at 25 °C, pH 8.3 with a reaction time of 2 h. Analysis of variance (ANOVA) showed values of R 2 and adjusted-R 2 of 0.9815 and 0.9648, and experimental data were fit to a second-order regression model. The optimal conditions to achieve a maximum decolorization (96.31%) of a Ponceau 4R aqueous solution of 20 mg/l were: 4.73 times stoichiometric dosage of H 2 O 2 , molar ratio H 2 O 2 /NaHCO 3 of 1.70 and cobalt concentration of 11.16 μM. Under the optimal reaction conditions, the influence of temperature (20, 25, 30 and 35 °C) on decolorization was evaluated and data were adjusted to second order kinetics. To verify the efficiency of the BAP system on the decolorization of Ponceau 4R, under the optimal conditions of reaction, UV-Vis spectra, at different reaction times, were measured. Additionally, blank experiments in order to evaluate the effect of individual factors in the Ponceau 4R decolorization, using BAP system, were carried out. Data showed that the Co(II)-NaHCO 3

Value of the data
• This is the first experimental design applying a bicarbonate activated hydrogen peroxide (BAP) system that allowed the development of an empiric model for decolorization of an azo dye (Ponceau 4R). The quadratic model obtained through RSM is adequate to predict the catalytic decolorization of Ponceau 4R in the range of experimental conditions used. • These experimental data can be useful for the development and application of advanced oxidation processes for water and wastewater treatment, with the advantage that the BAP system is a simple, inexpensive alternative and can be used at neutral or basic pH. • Data of the optimal decolorization conditions of Ponceau 4R can be used in equilibrium, kinetics, and mechanism studies of the oxidation of azo-dyes using the BAP system. Additionally, the use of a surface response methodology to establish the effect of variables governing the BAP system, can useful for new research on water and wastewater decolorization. • Data will be useful to researchers and the scientific community interested in the development and application of BAP technology for the treatment of wastewater containing azo-dyes.

Data description
The dataset contains eight Tables and six Figures. Data in Table 1 gives information about some properties of Ponceau 4R dye. The experimental conditions reported in literature, for the Table 1 General properties of Ponceau 4R [1] .   decolorization of organic colorants, using the BAP system are shown Table 2 . Table 3 shows the levels of independent variables (factors) used in the experimental design for the decolorization of Ponceau 4R. The codified and experimental values of runs performed in the experimental design, with the decolorization obtained, are shown in Table 4 . Table 5 summarizes ANOVA for the fitted quadratic model of Ponceau 4R decolorization. Experimental and predicted decolorization data of Ponceau 4R are shown in Fig 1 . Fig. 2 (a)-(c) display, by 3D graphics, the effect of interactions on the process variables of decolorization. Validation data of the empirical model for the Ponceau 4R decolorization, using the BAP system, are presented in Table 6 . UV-Vis absorption spectra of aqueous solution of dye as a function of the reaction time are shown in Fig. 1. Correlation between the experimental and predicted data for decolorization of Ponceau 4R using BAP system.     Fig. 4 illustrates the decolorization data at optimal reaction conditions and blank tests. Total organic carbon (TOC) and total nitrogen (TN) removals for decolorization of Ponceau 4R at optimal conditions and blank tests are summarized in Table 7 . The monitoring of decolorization as a function of reaction time under optimal conditions, at four different tem peratures are shown in Fig. 5 . Fig. 6 represents Arrhenius linear relationship between ln( k ) and 1/ T (K). Table 8 shows the kinetic parameters of the second-order model fit and the coefficient of determination (R 2 ) for the Ponceau 4R decolorization using BAP system at different temperatures.

Materials
Ponceau 4R (89 wt%) was a reagent food-grade purchased from Retema S.A.S.-Colombia, whose properties are summarized in Table 1 . A stock solution of Ponceau 4R (20 mg/l) was made up by accurately dissolving a weighed quantity of the dye in double-distilled water. Cl 2 Co • 6H 2 O, NaOH and NaHCO 3 were of analytical grade, obtained from Merck KGaA (Darmstadt, Germany), while H 2 O 2 (30 wt%) were obtained from Sigma-Aldrich (Saint Louis, MO, USA). 100 ml a stock solution of Co(II) (40 0 0 μM) was made up by dissolving 95.2 mg of Cl 2 Co • 6H 2 O in doubledistilled water, and aliquots of this solution (between 250 and 920 μl) were added to the reactor to obtain the required concentration of cobalt.

Catalytic decolorization tests
The decolorization catalytic reaction was performed in a batch glass reactor, open to atmosphere, thermostated at 25 °C, under constant magnetic stirring at 300 rpm. For each test, the reactor was loaded with 200 ml of aqueous solution at 20 mg/l, plus specific amounts of NaHCO 3 and Co(II). Then, the total H 2 O 2 dosage was added to start the reaction ( t = 0). The dosage of H 2 O 2 was varied in multiples of stoichiometry amount, which is theoretically required to completely oxidize one mole of Ponceau 4R into CO 2 , water (H 2 O) and mineral acids, according to Eq. (1) : Decolorization was measured by monitoring the absorbance of dye in the aqueous medium at its respective maximum absorption wavelength ( λ max = 507 nm), using a UV-Vis spectrophotometer (Mapada UV-1200, China). The concentration interval went from 0 to 20 mg/l, with a correlation coefficient (R 2 ) of 0.9993. Detection limit (DL) and quantification limit (QL) were 0.12 mg/l and 0.36 mg/l, respectively. The decolorization was calculated from Eq. (2) : where C 0 is the dye concentration at t = 0 and C t is the dye concentration at time t .

Experimental design
The central composite design (CCD) is the most popular class of response surface design methodology used for fitting second-order models in the design of experiments [2] . The CCD was used in this work, considering the minimum and maximum levels for H 2 O 2 (from 1.5 to 4.5 times the stoichiometric dosage -SD-), molar ratio of H 2 O 2 /NaHCO 3 (from 0.8 to 2) and cobalt concentration (from 5 to 15 μM). The ranges considered for the three independent variables were chosen from data reported by others authors in the literature ( Table 2 ). Table 3 shows the description of experimental ranges and the relationship between codified and real values [8] . Low and high levels are denoted by −1 and + 1, respectively, and the central points as 0. The ±α value depends on the number of variables and, for three variables, it is ±1.682 [8] .
The list of the 20 experimental runs and decolorization values are shown in Table 4 . The run corresponding to the central point was performed six times (run 5, 7, 8, 11, 15 and 17).
Data analysis of variance (ANOVA), using Design Expert software version 8.0 (StatEase, Inc., Minneapolis, USA) for Ponceau 4R decolorization with 95% confidence level are show in Table 5 .
The quadratic model for catalytic decolorization of Ponceau 4R can be described by Eq. (3) : The coefficients of the response model R 2 and adjusted-R 2 were 0.9815 and 0.9648, respectively. Fig. 1 shows the correlation between the experimental and predicted data for decolorization of Ponceau 4R using BAP system. Fig. 2 shows the 3D surface generated by Eq. (3) and the influence of variables analyzed in the decolorization. By means mathematical optimization of the model (maximization of a Eq. (3) occurs where its derivative is equal to zero), the values of variables to achieve the maximum decolorization (98.13%) were determined, corresponding to 4.73 times the stoichiometric dosage of H 2 O 2 , 1.70 of n H 2 O 2 / n NaHCO 3 and 11.16 μM of cobalt concentration. After carrying out the decolorization reaction under optimal conditions, a decolorization experimental of 96.46 ± 0.166% (error 1.70%) was obtained.
Additional catalytic decolorization tests, under the optimal operating conditions, were carried out in order to validate the quadratic model. The experimental and predicted values with Eq. (3) are shown in Table 6 .

Decolorization monitoring using UV-Vis spectra
The efficiency of the Co(II)-NaHCO 3 -H 2 O 2 system for Ponceau 4R decolorization under the optimal conditions was evaluated by measuring the changes of absorption UV-Vis spectra as a function of the reaction time, and the data are displayed in Fig. 3 .

Blank tests
Blank tests, without H 2 O 2 , NaHCO 3 and Co(II), were performed in order to evaluate the effect of individual factors in the Ponceau 4R decolorization ( Fig. 4 ) under the optimal conditions of the experimental design. Blank tests descriptions are summarized in Table 7 . Besides, the total organic carbon (TOC) and total nitrogen (TN) removals were estimated for each test. The TOC and TN removals were calculated using the Eqs. (4) and ( 5 ): where TOC 0 , TOC f , TN 0 and TN f are the TOC and TN contents at the beginning and end of the reaction ( Fig. 4 ). The contents of TOC and TN were determined by using a TOC/TN analyzer (Multi N/C 3100, Analytik Jena AG, Germany).
Experimental data C t / C 0 was fitted to the model described in Eq. (5) . The values of constant k as a function temperature ( T ) ( Table 8 ) were obtained by using the Levenberg-Marquardt algorithm [12] . The Scilab-6.0.2 R function "lsqrsolve" that minimizes the sum of square differences between experimental and predicted values of the nonlinear kinetic function, for each temperature evaluated, was used. The dependence of k values from the reciprocal of absolute temperature (1/ T ) is shown in Fig. 6 . The calculated apparent activation energy (E a ) from the Arrhenius plot regression ( Fig. 6 ) was 47.88 kJ/mol, a value similar to that obtained in the degradation of Acid Orange 7 by catalytic wet hydrogen peroxide oxidation (E a = 47.30 kJ/mol) [12] .