The main objective of this study was to investigate the photodegradation of azo dye Cibacron Brilliant Yellow 3G-P using Anatase, Degussa-P25 and ZnO. These semi-conductors were characterized using XRD, BET and TEM-EDX. The variation of the amount of semi-conductors significantly affect the rate of color removal. The decolorization rate increased as the catalyst dosage was increased. Other parameters were also studied, such as stirring speed, pH, and initial dye concentration. It was found that the rate of decolorization increases with the increase of stirring speed. Decolorization of about 30, 60 and 80% was respectively achieved in the case of Anatase, Degussa-P25 and ZnO at low stirring speed (50rpm). At pH = 3, the degradation rate was found to be higher than the alkaline pH, about 95.58 and 85.71% of color has been decolorized with Anatase and Degussa-P25 respectively. While using ZnO, the color removal reached maximum in acidic and alkaline solutions, more than 95% of dye was decolorized. The concentrations dye solutions less than 80ppm led to the removal rate of about 95% in the case of ZnO, while it was only about 8–15% in the case of TiO2 with the concentration more than 20 ppm.
Decolourization and photocatalytic degradation of Cibacron Brilliant Yellow 3G-P under UV light radiation.
Anatase displayed higher photocatalytic efficiency than Degussa-P25 and ZnO.
The photocatalytic degradation efficiency of Anatase and Degussa-P25 was observed to be higher at pH = 3.
There are several varieties of dyes generated from the textiles industries and used such as reactive dyes, direct dyes, disperse dyes, acid dyes, basic dyes, and vat dyes. Almost 45% of textiles products in the world belong to the reactive dyes (Jalali Sarvestani & Doroudi 2020). The presence of too small amounts of dyeing components from textiles industries in water is one of the main sources of severe pollution, which may cause higher visibility and has a significant effect on the photosynthetic activity, and this is a matter of concern for the effects on aquatic ecosystem and is likely to cause economic and ecological harm or harm to human health such as liver, brain and dysfunction of the kidneys (Salleh et al. 2011; Berradi et al. 2019). Reactive dyes are one of the most commonly used in the textiles industries due to their wide range of shaède gamut, their flexibility in meeting the various applications and they are thus characterized by their excellent fastness properties they may offer when they have been dyed on wool, silk, cotton and regenerated cellulose fibers (Yaseen & Scholz 2019). The presence of these substances in the environment remains a major concern. Reactive dyes are highly resistant to environmental degradation due to their fused aromatic structures, low biodegradability and thus they remain colored in wastewater for an extended period. Therefore, the increasing use of reactive dyes has highlighted the need to use a process that allows not only the possibility of dye removal and to know how about the operational conditions can be affected the but also the products that can be generated. There are different physical, chemical, and biological methods currently in use which treat the polluted water from textiles colored with dyes (Dajic et al. 2019), the choice of adequate techniques of wastewater treatment primarily depends on a variety of parameters such as type of pollutant and concentration. Advanced oxidation processes (AOP) are alternative methods developed to treat wastewaters based on the use of hydroxyl radicals (OH•) which present high oxidation potential when they are in the contact with organic pollutant to achieve complete elimination. Several researchers have investigated the use of these processes for decolorization of colored waste effluents (Ghribi et al. 2020; Dong et al. 2022; Rayaroth et al. 2022). Heterogeneous photocatalysis belongs to AOP and it has been proved to be a promising method for the treatment of wastewater contaminated with organic and inorganic pollutants. It produces more compounds which are readily biodegradable and have less toxic substances (Aoudjit et al. 2020; Olatunde et al. 2020). In photocatalytic processes, destroying organic recalcitrant compounds is governed by the combined actions of a photocatalyst comprising of an inorganic semi-conductor, a source of radiation and an oxidizing agent. Most of these investigations have used aqueous suspensions of semi-conductors (e.g., TiO2, ZnO), illuminated by UV light to photodegrade the pollutants. Cibacron Brilliant Yellow 3G-P (CBY 3G-P) are widely used in dyeing processes due to their characteristics: bright color, effective application techniques, low energy consumption for the dyeing process and high water solubility. In terms of history, photocatalysis has attracted several researchers and Fujishima & Honda in (1972) showed that when TiO2 is excited by light, the water is able to decompose into hydrogen and oxygen.
This study investigates the removal of anionic Cibracorn Brilliant Yellow 3GP reactive dye from synthetic aqueous solutions by using a heterogeneous photocatalysis process. Three various semi-conductor oxides of pure Anatase, Degussa-P25 TiO2 and ZnO were characterized to investigate their influence for removal of colors and dye by photocatalytic degradation. The various parameters influencing photodegradation such as stirring speed, initial dye concentration and pH were studied.
MATERIALS AND METHODS
Chemicals and reagents
CBY 3G-P is a synthetic azo dye and was supplied by Sigma-Aldrich®. Table 1 shows some of the dye's general characteristics. Chemical compounds, NaOH and HCl were of analytical grade. The photocatalysts TiO2 and ZnO were also supplied by Sigma-Aldrich®. The electrical conductivity of the demineralized water used throughout the preparation of all aqueous solutions must not exceed the value of 23.2 μS/cm.
|Molar weight||872.97 g·mol−1|
|Molar weight||872.97 g·mol−1|
Determination of the maximum absorption wavelength of CBY 3G-P
Determination of the point of zero charge
Photocatalytic degradation of CBY 3G-P was performed in solution using pyrex beakers of 250 mL capacity as batch reactor. All the experiments were carried out at room temperature and pressure. The reactor was shaken mechanically using Jar Tests (stuart floculateur SW6) which has stirrers with variable stirring speeds to meet the same operating conditions and to obtain accurate data and reproducible results. The reactor was illuminated from the outside with a 24W medium pressure mercury vapor lamp (for UV radiation); this light source was assembled on a support so as to be parallel to the plan of reactor.
Procedure and analysis
CBY 3G-P solutions were prepared by stirring a weighed amount of CBY 3G-P in distilled water at room temperature and pressure. Two hundred and fifty mL of CBY 3G-P solution was put into the photoreactor. Firstly, photolysis was investigated; an experiment was performed without catalysts under UV irradiation only. Secondly, the photocatalysis was studied; semi-conductors were added to the dye solutions. The reaction system was continuously stirred under controlled speed to achieve a homogeneous suspension and increase the oxygen transfer to the solution. The suspensions were stirred for at least 30 min in the dark to allow adsorption equilibrium of the system prior to irradiation. After UV light radiation, a Millipore 0.45-μm membrane filter was used to separate semi-conductors from suspension. Cibacron Brilliant Yellow concentrations during irradiation at selected time intervals were analyzed by UV visible spectrometry LAMBDA™ 25 from PERKIN-ELMER. To adjust the pH of different solutions, 0.1 M HCl or 0.1 M NaOH was added; pH was measured by STARTER 3100 pH meter. Similar experiments were carried out by varying the stirring rate (50–150 rpm), dye concentration (10–100 ppm), catalyst amount (0.1–1.5 g/L) and pH of solution (3–11).
RESULTS AND DISCUSSION
The XRD analysis
Surface area analysis
BET surface area analysis reveals that TiO2 Anatase has a surface area of 54 m2 g−1 which is higher than those of TiO2-P25 Degussa (49 m2 g−1) and ZnO (40 m2 g−1).
Transmission electron microscopy analysis
OPTIMIZATION OF PHOTOCATALYTIC PROCESSES
Effect of catalyst loading
Effect of stirring speed
Effect of initial pH on the photocatalysis of CBY 3G-P
Effect of initial concentrations of CBY on the photocatalytic degradation rate
Kinetic study of photocatalytic degradation of CBY
|[CBY 3G-P]0 (mg/L) .||kapp (min−1) .||R2 .||kapp (min−1) .||R2 .|
|[CBY 3G-P]0 (mg/L) .||kapp (min−1) .||R2 .||kapp (min−1) .||R2 .|
Decolorization of CBY 3G-P in aqueous solution has been studied using two different processes: photolysis (without semi-conductor) and heterogeneous photocatalysis in the presence of three semi-conductors (Anatase, Degussa P25 and ZnO). The results show that the presence of catalyst is more essential for efficient dye removal. Operational parameters, namely stirring speed, catalysts dosage, dye concentration, pH of solution and initial dye concentration, affect the rate of dye decolorization. Decolorization of dye is very effective at high stirring speed, the results indicate that there exists an optimum catalysts loading (0.5 g/L for both catalysts: Anatase, ZnO and 1 g/L for Degussa P25) where the color removal rates reaches a maximal value. From an efficiency catalytic standpoint, ZnO showed a better activity for color removal by heterogeneous photocatalysis compared to Anatase and Degussa P25. The decolorization rate increases with a decrease in the initial dye concentration. The experimental results showed that the kinetics of photocatalysis color removal follows a pseudo-first-order kinetic and depends on the initial dye concentration. The apparent rate constant increased when decreasing the concentration of initial dye concentration.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.