A New Method for Prediction of Wastewater Treatment Efficiency in the Photo catalytic Processes

For the first time, in the present study, a new approach of using the color properties of acid red 18 decolourization behavior by synthetized nano photocatalytic TiO2-Ag2O. In this manner two color system (CIE L*a*b* and CIE L*C*h°) used to calculate the color properties (lightness, Chroma and hue) of samples during the decomposition process. MATLAB software was used to transfer absorbance data obtained from VU-Vis spectrophotometer to L*, a*, b*, C* and h°. Effect of key operator parameters such as pH, catalyst dosage, [H2O2]/Dye=H were evaluated during the process. The results of this research indicated a good correlation between theoretical results (based on color characteristic results) and experimental results. Also decolourization behavior could be predicted using the CIE color system.

Industrial wastewater often contains significant amounts of non-biodegradable organic compounds.The elimination of these contaminants is necessary before a biological treatment of these effluents.Common ways of wastewater treatment include adsorption, sedimentation, chemical analysis, biological methods, and advanced oxidation procedures [1][2][3] .However, these approaches are not without their disadvantages.Biological methods, for example, take much time and cannot degrade complicated dyes 3 .Among the different methods that have been applied to dye degradation advanced oxidation processes (AOPs), in which oxygen-based radicals (°OH -, HO 2 -, and °O2 -) are generated in situ from water and O 2 is considered more appropriate [4][5][6][7] .AOPs methods have been applied for degradation of different colored compounds using UV-Vis light in presence of H 2 O 2 or a mixture of H 2 O 2 and a photocatalyst.This method usually produces a highly reactive hydroxyl (ºOH) and superoxide anion (ºO 2 -) radicals which are responsible of degradation of the dyes into simpler and safer organic compounds such as water-carbon dioxide.Between the different photo catalysts, TiO 2 is one of the most widely used semiconductor photo catalysts; its unique characteristics are well documented.TiO 2 is also used in antifogging and anti-corrosion surfaces, photo catalytic lithography and photo chromic materials 8 .Major limitations such as UV irradiation and fast recombination of hole-electron pairs within nanoseconds, lead in application of additives such as Pt, Pd and Au for improving the photo catalytic efficiency of TiO 2 9-12 .Silver (Ag) is a suitable and nontoxic element which improves the TiO 2 bioactivity because of its inborn antibacterial activity against different microorganisms [13][14][15] .
Using the other science point of prospect could help to have better feedback from research."Color Technology" concerns the science and technology associated with creating, controlling and characterizing the visual appearance of materials, and images 16,17 .Color is one of the most important qualities which is considered in many applications such as foods 18 , cosmetics 19 art, architectural 20,21 , health care 22 and many other applications which affects every moment of our lives.In the present study for the first time, a mathematical relation between color sciences and wastewater treatment is proposed.So, the color properties of C.I. AR18 were measured during the decolourization with TiO 2 -Ag 2 O nano photocatalytic, and process by MATLAB software.

Color attributes and color system
Hue, Chroma, and lightness demonstrate three-dimensional of color.These attributes provide three coordinates that could be applied to "map" color in a color space.CIE Color Systems or Commission International de l'Eclairage (the International Commission on Illumination), is responsible for international recommendations of colorimetry.In 1931, the CIE established standards for a series of color spaces or system that represent the visible spectrum.Using these systems, the varying color spaces of different viewers and devices against repeatable standards are compared.The ultimate destination of the CIE was to develop a repeatable system of color communication standards for manufacturers of paints, inks, dyestuffs, and other applications.These standards' most important purpose was to offer a general framework for color matching.The CIE Color Systems utilize three coordinates to locate a color in a color space.These  16,17,23 .

Catalyst preparation
The sol solution prepared by adding 70 mL of ethanol to 500 mL beaker that had been stirred by a magnetic stirrer then added 5 mL diethanolamin and 20 mL TBOT slowly with mixing the ethanol solution.The mixture was stirred by a magnetic stirrer during addition and for a further 120 min after addition of the precursor at room temperature.Then, mixture of 1mL deionizer water and 15mL ethanol limit was added drop by drop to ethanol solution rotation and kept stirring for 2hr.
The second stage, adding of AgNO 3 in absolute ethanol (with 1:110 M) and stirred with 5 minutes.Then added mixture of ethanol and distilled water (1:2:10 M) slowly with fast mixing and stirred for 15 minutes a transparent sol was obtained.Then added to get Ag 2 O to TiO 2 sol (1:5 M) to obtain Ag 2 O-TiO 2 sol-gel.24hr until was dried to Proximity air and for 10 minutes at 350 º C and 5hr at 500 º C under thermal function.Finlay was cold sample natural to procure nano composite.

Catalyst characterization
The synthesized catalyst was characterized by XRD analysis.The result certifies Ag 2 O-TiO 2 couple production.Using the Deby-Scherrer equation the particle size was measured 25-26 nm.According to SEM analysis the surface morphology was verified as a well-ordered and good size distribution of spherical particles.

Photocatalytic reactor and chemical materials
All of the experiments were evaluated in a batch photocatalytic reactor equipped a low pressure UV lamp (Philips, 15 W) with a total volume of 2L.The colored solution was mixed during the process by a magnetic mixer.All of the chemical materials such as chemical solutions were purchased from Merck.Also Acid red 18 (AR18) was obtained from Saujanya Marketing Company India and the characteristics of the dye was presented in this research.

Spectrophotometric analysis
A VU-Vis spectrophotometer (PerkinElmer, USA) was used for absorbance measurement of samples.Spectral absorbance data of samples, then transformed into CIE L*a*b* and CIE L*C*hº

RESULT ANd dISCUSSION decolorization results
The XRD pattern of synthesized Ag 2 O/TiO 2 photocatalyst is shown in Fig. 2.a.The XRD patterns, the average particle diameter of the synthesized

Photocatalyst experiments
The photocatalytic activities of the prepared catalysts were investigated through degradation of AR18 in a semi-batch photocatalytic reactor and the effects of key operator parameters were studied

The influence of testing parameters
The effect of Ag 2 O on decolourization process was evaluated on 20 mg.L -1 colored solution using 0.01, 0.02, 0.04 and 0.06 gr.L -1 of Ag 2 O as a catalyst the optimum dosage of the catalyst (0.02 gr.L -1 ) obtained in this process.Fig. 3.a, shows Due to the experiments results conducted and observed values, the best efficiency was in 0.02 gr.L -1 of catalyst because larger amount of catalyst can prevent from UV light reaching to the solution, also the effect pH on the dye decolourization was evaluated different values of pH (3 -9) with a fixed amount of catalyst loading (0.02 gr.L -1 ) was investigated occurred.At fig. 3.b presents, the most Adsorption of the dye on the catalyst surface happens at pH of 6.28 that was natural pH of dye.Finally H 2 O 2 concentration effect, (H= [H 2 O 2 /Dye]) on the process efficiency was studied and result were shown in fig.3.c.Decolourization percentage increase with increasing the H amount up to on optimum value and after it, there is not a significant variable [25][26] .

Fig.5: Variation of decolourized solution hue angle during time of treatment
The hue angles of C.I. AR18 solution change from 10 to 72º by a linear equation increasing the time of treatment (fig.5).Those hue angles are related to the real color which are also calculated by MATLAB and illustrate in fig. 5.The logarithmic trend lines equation of a*, L*, and c* show that, increasing the time to more than 10 min is not the useful and proper way to increase the efficiency of treatment.Since as the results show all trend lines become linear after 10 min and it seem that no more change will happen.The processes were evaluated after 10 min of reactions to approve the fitted equations.

Economic study
There are the different important parameters to select a good and effective method for dye removal process.Among of these, economic study has an important role in the different sectors of the industries.
The economic study of this process could be evaluated using the following equation [27][28] : EE= (P×t×1000) ÷ (V×60×Log (TOC o /TOC)) ...( 4) Where: P is power of the lamp, t is time, V is volume and TOC o and TOC are respectively amount ... (7)   The photocatalytic degradation of various organic compounds by means of illuminated photo catalyst is formally described by the Langmuir-Hinshelwood kinetics model: When the adsorption is relatively weak and/or the reactant concentration is low (KC<<1) 29 , neglecting KC in the denominator and integrating with respect to time t, the above equation can be simplified to the pseudo-first order kinetic model equation: where dC/dt is the rate of dye degradation (mol.L -1 .min - ); C 0 =initial concentration of the dye (mol.L -1 ), C=concentration of the dye at time t (mol.L -1 ); t=irradiation time (min), ê=kinetic constant (mol.L -1 .min - ), K=the adsorption coefficient of the dye onto the photocatalyst particle (L.mol -1 ), k app =the apparent rate constant calculated from the curves (min -1 ).According to linear correlation between k app and Ln C 0 /C, EE could be calculated by equation 6 29 .
color spaces include: • CIE XYZ • CIE L*a*b* • CIE L*C*hº Those three-dimensional formats are also a very convenient way to compare the relationship between two or more colors.When a color is expressed in CIE L*a*b*, L* defines lightness, a* denotes the red/green value and b* the yellow/blue value.Fig 1 shows the color-plotting diagram for L*a*b*.A color measurement movement in the +a direction depicts a shift toward red.Along the b* axis, +b movement represents a shift toward yellow.The center L* axis show L = 0 (black or total absorption) at the bottom.At the core of this space is gray.While CIE L*a*b* uses Cartesian coordinates to calculate a color in a color space, CIE L*C*hº uses polar coordinates and can be derived from CIE L*a*b*.The L* defines lightness, C* specifies Chroma (Purity, Saturation) and hº denotes hue angle (Fig 1).Both L*a*b* and L*C*h° attributes could be derived from a measured color's spectral data: L* = 116 (y/yn) 1/3 -16 a* = 500 [(X/Xn) 1/3 -(y/yn) 1/3] b* = 200 [(Y/Yn)1/3 -(Z/Zn)1/3] L* =116 (y/yn)1/3 -16 C* = (a2 + b2)1/2 h° = arctan (b*/a*) Xn, Yn, Zn, are reference white values for the white illumination

Fig. 4 :
Fig. 4: Variation of decolourized solution lightness and Chroma during time of treatment

Fig. 6 .
Fig.6.a.shows the variation of a* during the decolourization.The results show that a* decrease in exponential rate to achieve a constant value.Decreasing the positive value of a* mean that the amount of red color in the solution decreases with time, which, indicate the reduction in dye concentration.The Positive b* value of the samples (fig.6.b)indicates that the presence of impurities in C.I. Acid red 18 with yellow color.TLC chromatography is used to demonstrate the presence of impurities.Fig.6.b. also shows that decreasing the value of b* with time happen in an interesting way.It seems that the impurities in C.I. AR18 resist to treatment until 4s, since b* value does not significantly change.While After 4s, b* value start to reduce which implies the decomposition of impurities.

Fig. 6 :
Fig.6: Variation of decolourized solution a * and b * during time of treatment

CONCLUSION
Using color proper ties of materials (lightness, hue and Chroma) to characterize the properties of them is very common in different industries.The aim of this study is to use the color properties of wastewater to investigate the decolourization behavior of C.I. acid red 18 with synthesized TiO 2 -Ag 2 O nano photocatalytic.The color characteristics show that increasing the time of treatment, increase lightness (L*) and decrease Chroma (C*) of the samples, which both indicate that the concentration of the dye in sample decrease during decolourization.This result also confirmed by a* results.Positive value of a* (which denotes the red color of samples) decreases during the decolourization, which represent the reduction in the amount of red dye in solution.Positive value of b* demonstrate the presence of yellow impurities in C.I. AR18.The existence of impurities is also confirmed by TLC results.The b* value is starting to change after 4 min of decolourization.Therefore, it seems that the impurities resist to decomposition until 4 min.due to the results of the present study, color characteristics could be used to predict of the dye decolourization process in the wastewaters.Apendix1Clc; Close all; Clear all; cd ('D:\') ; [num txt] = xlsread ('Book1.xls','Sheet1','A2:G602');Num = flipud (num); s=find (num (:, 1)==400) ; e=find (num (:, 1)==700) ; R=num(s: 10: e, 2:7); XYZ=my_r2xyz (R, 400, 700,'d65_64'); Lab=xyz2lab (XYZ,'d65_64'); C=makecform ('lab2lch'); lch= applycform (lab, C) ; C = makecform ('xyz2srgb'); rgb= applycform (XYZ/100,C) ; rgb = reshape (rgb,[6 1 3]) ; imtool(rgb)

Table 1
presents the EE/O values of the different dye concentrations as a results, EE/O and electrical cost of the process have a direct relation witch the dye concentration.