A number of different synthetic dyes, finishes and detergents have been employed frequently in several industries including textile [1, 2], leather , automobiles , food and beverage , pharmaceutical , furniture , paper industry  and many more. They are preferred over naturally existing dyes and finishes due to their availability in various attractive shades, good wash and light fastness  and superior properties too [10, 11, 12]. However, considerable health issues are connected with them due to their recalcitrant nature [13, 14], high molecular weight and complex structures .
Consequently, a huge amount of these chemicals can be found in industrial effluents, changing the taste, odor and color of water , and reacting with many heavy metals to form stable complexes . Therefore, industrial waste comprises of huge quantities of organic pollutants. They represent high chemical oxygen demand (COD)/total organic carbon (TOC) values  along with low biodegradability of industrial effluents . Hence, their discharge into water bodies without any prior treatment causes serious health issues for aquatic and terrestrial life  due to their toxic and carcinogenic properties .
UV absorbers are excessively utilized in sunscreens  and on clothing  to protect us from the damages of UV radiations. Many organic UV absorbers incorporated in sunscreens, such as 2-phenylbenzimdazole-5-sulfonic acid (PBSA)  and monochlorotriazine based UV absorbers , to combat with UV light. The presence of SO3H enhanced the photostablity of PBSA due to extended conjugation, but due to their high molecular weight and complex structure, their presence in effluents also generates high toxicity to biosphere .
Many physical, biological and chemical treatment methods are reported in literature, dealing with pollutants in industrial wastewater, such as precipitation, adsorption , membrane separation , treatment with bacteria  and oxidation . All these methods convert pollutants in industrial effluents to smaller toxic molecules, resulting in incomplete mineralization . Oxidation of organic pollutants by advance oxidation processes (AOPs) have been utilized to degrade a large variety of organic contaminates like dyes , pesticides  and pharmaceuticals .
The above processes produce hydroxyl radicals that are highly reactive with electrical potential 2.8 V and the organic substances are completely mineralized . The combination of H2O2 with Fe2+ and UV radiation is characterized by a reduced cost and a high efficiency for removing non-biodegradable organic contaminants from water [24, 29]. The decomposition of hydrogen peroxide with Fe2+ and UV light generate reactive species such as OH- and •OH [30, 31, 32] (equation 1-3).
In the current investigation, two new reactive hetrofunctional vinyl sulfone and nitrogen (N-) containing organic UV absorber compounds (1a, 2a) that were designed and synthesized in our previous studies  were selected for mineralization. The degradation study of these UV absorbers has been not reported yet. The comparative degradation study was performed by Fenton and UV/H2O2 processes. The influencing parameters of processes were optimized to improve the degradation process.
2.1 Chemicals and reagents
Both UV absorbers (1a-2a) were synthesized in the laboratory and their structures were confirmed with spectroscopic techniques. Structures of these UV absorbers are shown in Figure 1. H2O2 (30% solution w/w), FeSO4.7H2O (99%), Na2SO3, H2SO4 (1M) and NaOH (1M) were of analytical grade and purchased from Sigma Aldrich. All of the solutions were made in distilled water.
2.2 Fenton procedure
UV absorber solution (500 ppm) was prepared in distilled water and pH adjusted using a digital pH meter with the help of NaOH (1 M) and H2SO4 (1M). The experiments were conducted in a conical flask (500 mL) containing 100 mL of UV absorber solution. The desired amount of FeSO4.7H2O and H2O2 was added into the flask at the start of reaction. The conical flasks were covered by aluminum foil and placed on a water bath shaker (100 rpm) at room temperature (25±1°C) in Fenton process. To evaluate the effect of time, the sample (2 mL) was withdrawn periodically and the reactive species were quenched by Na2SO3 (0.5 mL) and the COD removal (%) of UV absorber solution was analyzed. To examine the possible maximum removal of UV absorber, the effect of different experimental parameters such as pH (2.0, 3.0, 5.0, 7.0 and 9.0), contact time (40, 80, 120, 160 and 200 min), H2O2 dose (100, 300, 500, 700, 900 mg/L) and FeSO4 concentration (5, 10, 15, 20, 25 mg/L) were also assessed .
A UV absorber solution (500 ppm) was prepared and adjusted to the pH of solution using a digital pH meter. A photo-reactor emitting at 254 nm was utilized for this experiment. An aqueous solution of UV absorber (100 mL) was placed under UV lamp and the desired amount of hydrogen peroxide (30%) was added at the start of the reaction and stirred at 100 rpm speed. To evaluate the effect of time, the sample was withdrawn periodically and the COD removal (%) of UV absorber was analyzed. To examine the possible maximum removal of UV absorber by UV/H2O2, the effect of different experimental parameters such as pH (2.0, 3.0, 5.0, 7.0 and 9.0), contact time (40, 80, 120, 160 and 200 min) and H2O2 dose (100, 300, 500, 700, 900 mg/L) were also measured .
2.4 Analytical methods
The concentration of UV absorbers (1a and 2a) was measured by calculating their absorbance at their λmax 292 nm and 282 nm, respectively using Perkin Elmer Lambda (CE-7200)UV/Vis Spectrophotometer . The pH of the solution was measured with the use of a digital pH meter (Hanna Instruments, Europe) . The COD of solution was determined via the colorimetric method using equation 4 
Where, COD0 and CODt are the chemical oxygen demand of UV absorber before and after degradation respectively.
Ethical approval: The conducted research is not related to either human or animals use.
3 Results and discussion
3.1 Generation of reactive species by Fe2+/UV irradiation
The generation of reactive oxygen species (OH-, •OH) by the decomposition of hydrogen peroxide by Fe (II) or UV irradiations plays a central role in degradation of organic contaminants in water [34, 35]. As the generation of reactive oxygen species is enhanced, it ultimately improves the degradation process . For the optimization of influencing factors of the Fenton and UV/H2O2 processes, a number of experiments were conducted and results are discussed here.
3.2 Fenton Oxidation
3.2.1 Effect of pH on COD removal
The efficiency of the oxidative process of organic toxins has been highly affected by pH change in Fenton oxidation [24, 37]. But, there is no such consistency reported regarding the optimum pH, and it varies from one case to another. In the current study, the pH of aqueous solutions of UV absorbers were set at pH 2.0, 3.0, 5.0, 7.0 and 9.0 under constant H2O2 dosage of 100 mg/L, Fe2+ dosage of 5 mg/L and contact time of 120 minutes. Figure 2 (A) demonstrated that the maximum COD removal efficiency (%) was attained at pH of 3.0 in case of both the UV absorbers (1a-2a). With an increase in pH above 3.0, the COD removal efficiency of Fenton process was reduced. When the pH value increased from 2.0 to 3.0, the mineralization of absorbers proportionally increased, and then inversely decreased after pH 3.0. Such behavior of the Fenton process can be explained by a decline in the amount of free ions in solution due to precipitation of iron or reaction of •OH with one another to reduce the quantity of free hydroxyl radical at pH > 4.0. The pH < 3.0 causes the creation of [Fe2+(H2O)]2+ in medium, which slowly reacts with hydrogen peroxide and generates fewer hydroxyl radicals. Kinetically, H2O2 decomposition follows pseudo-first order kinetics .
3.2.2 Effect of H2O2 concentration COD removal
For the optimization of H2O2 dosage, the experiments were performed by varying the concentration of hydrogen peroxide (100, 300, 500, 700 and 900 mg/L) under constant pH of 3.0, Fe2+ dosage 5 mg/L and contact time 120 minutes. Figure 2(B) explained the effect of hydrogen peroxide concentration on the COD removal efficiency (%) of UV absorbers (1a-2a). The results confirmed that maximum COD removal efficiency (%) was achieved with 500 mg/L of hydrogen peroxide in Fenton oxidation. After the optimum level had been reached, no further improvement in COD removal efficiency (%) was achieved. Excess H2O2 produced per-hydroxy radical; having less oxidation potential and starts working as hydroxyl radical scavenger .
3.2.3 Effect of Fe2+ dosage on the COD removal
Figure 2(C) demonstrated that the maximum COD removal efficiency (%) was attained with 15 mg/L of iron dosage for UV absorbers (1a-2a). It was found that the COD removal efficiency of absorbers have a similar changing pattern with an increase of Fe2+ dose. The COD removal was increased considerably as the concentration of iron increased but after a certain level, the COD removal was decreased. As the dose of iron rises, the COD removal efficiency improves. After 15 mg/L, addition of Fe2+ is unproductive. Higher dose of Fe(II) after optimum level would generate other side and competitive reactions, decreases the concentration of free radicals [(reaction (6), (7), (8) and (9)]. Figure 3 shows the absorbance of aqueous solutions of UV absorbers prior and following the degradation via Fenton oxidation.
3.2.4 Effect of reaction time on the COD removal
Figure 2(D) demonstrated that maximum COD removal efficiency (%) was attained at 80 minutes in Fenton process. After the optimum level of time duration, no further improvement in COD removal efficiency (%) was achieved. As the reaction time increased, the improvement in COD removal (%) increased linearly, and then it became constant. This can be explained by the fact that most of the hydrogen peroxide reacted with Fe (II) in the beginning of the reaction. The rate of the reaction was high at start of the reaction than it increased slowly and became constant. A study on the effect of time for the treatment of landfill leachate in terms of COD removal efficiency (%) revealed that organic pollutants were speedily degraded in the first 20 minutes, after which any further increase in time duration became insignificant. Generation of a layer of foam on the surface of solution was observed as the oxidation proceeded due to formation of carbon dioxide .
3.3 UV/H2O2 Oxidation
3.3.1 Effect of pH on COD removal
With the UV irradiation time of 200 minutes and concentration of H2O2 100 mg/L, the effect of pH including 2.0, 3.0, 5.0, 7.0 and 9.0 on the mineralization of synthesized UV absorbers is shown in Figure 4(A). When the pH value increased from 2.0 to 3.0, the mineralization of UV absorbers increased and then linearly decreased. A pH of 3.0 achieved the maximum mineralization of UV absorbers 1a and 2a which were 55.34 and 57.68 respectively. At a pH of 9.0, the COD removal percentage of 1a and 2a were 21.23 and 18.54 respectively.
3.3.2 Effect of H2O2 concentration
In the experiments using a constant irradiation time of 200 minutes and pH of 3.0, hydrogen peroxide dosage were set at 100, 300, 500, 700 and 900 mg/L. The effect of H2O2 concentration on mineralization of UV absorbers is shown in Figure 4(B). The maximum COD removal of both the UV absorbers achieved at a 700 mg/L of H2O2. Particularly, the removals were 55.23 and 57.67 % for UV absorber 1a and 2a respectively.
3.3.3 Effect of irradiation time on the COD removal
Preliminary experiments were performed by varying UV irradiation times to 40, 80, 120, 160 and 200 minutes under constant dosage of H2O2 (100 mg/L) and pH of 3.0. Figure 5 shows the effect of UV irradiation time on mineralization of target UV absorbers (1a and 2a). It is evident from the figure that mineralization increases gradually with time. The COD removal (%) of UV absorbers (1a and 2a) was 54.2 and 57.32 respectively at the irradiation time of 200 minutes. Abdelraheem et al. (2015) mineralized the UV absorber and found that due to strong photostablity of UV absorber, its degradation appeared after 285 minutes of irradiation time. This result showed that degradation of these compounds was due to attack of hydroxyl radicals that were produce through decomposition of H2O2 by UV radiations.
4 Comparison of Fenton and UV/H2O2 oxidation
Comparison of Fenton and UV/H2O2 oxidation based on COD removal percentage (%) shows that, ferrous ions catalyzed the production of •OH from hydrogen peroxide during Fenton oxidation. The generation of hydroxyl free radicals increases as the concentration of ferrous ions increases up to a optimum level, which propagated the oxidation of UV absorbers. However, the generations of hydroxyl free radicals in UV/H2O2 is less due to the presence of photostable organic UV absorbers, ultimately it reduces the efficiency of UV/H2O2 oxidation. Table 1 shows that economically Fenton oxidation is better for mineralization of selected triazine based UV absorbers.
In this study, two new triazine based UV absorbers designed for cotton fabric were degraded by applying two advance oxidation processes (Fenton oxidation and UV/H2O2). The results indicated that Fenton oxidation was more efficient towards mineralization of both the UV absorbers than UV/ H2O2 and results were in agreement with previous literature [20, 30, 35, 40]. Under attained optimum conditions of Fenton oxidation, dose of Fe2+ (15 mg/L), H2O2 (500 mg/L), pH (3.0) and contact time (120 minutes), 75.43% and 77.54% of COD removal were achieved for 1a and 2a, respectively. Whereas, the optimum conditions of UV/H2O2 process were H2O2 (700 mg/L), pH (3.0) and irradiation time (200 minutes) which brought 54.33 and 57.65%. It is concluded that synthesized organic triazine based UV absorbers can efficiently be mineralized and degraded via AOPs.
This study was supported by the Department of Chemistry, University of Agriculture, Faisalabad.
GilPavas, E., Dobrosz-Gómez, I., Gómez-García, M.Á., Coagulation-flocculation sequential with Fenton or Photo-Fenton processes as an alternative for the industrial textile wastewater treatment. J. Environ. Manage., 2017, 191, 189-197. Web of ScienceCrossrefPubMedGoogle Scholar
Mokhtari, J., Phillips, D.A., Taylor, J.A., Synthesis and evaluation of a series of trisazo, monochloro-s-triazinyl (MCT) reactive dyes for cotton. Dyes Pigments., 2004, 63, 51-63. CrossrefGoogle Scholar
Pang, C., Neubauer, N., Boyles, M., Brown, D., Kanase, N., Hristozov, D., Fernandes, T., Stone, V., Wohlleben, W., Marcomini, A., Releases from transparent blue automobile coatings containing nanoscale copper phthalocyanine and their effects on J774 A1 macrophages. NanoImpact., 2017, 7, 75-83 Web of ScienceCrossrefGoogle Scholar
Garcia-Falcón, M., Simal-Gándara, J., Determination of food dyes in soft drinks containing natural pigments by liquid chromatography with minimal clean-up. Food Control, 2005, 16, 293-297. CrossrefGoogle Scholar
Jewitt, J., Great wood finishes: A step-by-step guide to beautiful results. Taunton Press., 2000, 78-102. Google Scholar
Hunger, K., Industrial dyes: chemistry, properties, applications. John Wiley & Sons., 2007, 339-425. Google Scholar
Czajkowski, W., Paluszkiewicz, J., Stolarski, R., Kaźmierska, M., Grzesiak, E., Synthesis of reactive UV absorbers, derivatives of monochlorotriazine, for improvement in protecting properties of cellulose fabrics. Dyes Pigments, 2006, 71, 224-230. CrossrefGoogle Scholar
Patel, D.R., Patel, K.C., Synthesis, antimicrobial activity and application of some novel quinazolinone based monoazo reactive dyes on various fibres. Dyes Pigments, 2011, 90, 1-10. Web of ScienceCrossrefGoogle Scholar
Waring, D.R., Hallas, G., The chemistry and application of dyes. Springer Science & Business Media., 2013, 49-106. Google Scholar
Mahamallik, P., Pal, A., Degradation of Textile Wastewater by Modified Photo-Fenton Process: Application of Co (II) Adsorbed Surfactant-modified Alumina as Heterogeneous Catalyst. J. Environ. Chem. Eng., 2017, 2886-2893. Web of ScienceGoogle Scholar
Chequer, F.M.D., de Oliveira, G.A.R., Ferraz, E.R.A., Cardoso, J.C., Zanoni, M.V.B., de Oliveira, D.P., Textile dyes: dyeing process and environmental impact, Ecofriendly textile dyeing and finishing. InTech., 2013, Ch. 06. Google Scholar
Diao, Z.-H., Liu, J.-J., Hu, Y.-X., Kong, L.-J., Jiang, D., Xu, X.-R., Comparative study of Rhodamine B degradation by the systems pyrite/H2O2 and pyrite/persulfate: Reactivity, stability, products and mechanism. Sep. Purif. Technol., 2017, 184, 374-383. CrossrefWeb of ScienceGoogle Scholar
Khan, S., Malik, A., Environmental and health effects of textile industry wastewater, Environmental Deterioration and Human Health. Springer, 2007, 55-71. Google Scholar
Lapidot, N., Gans, O., Biagini, F., Sosonkin, L., Rottman, C., Advanced sunscreens: UV absorbers encapsulated in sol-gel glass microcapsules. J. Sol-Gel Sci. Techn., 2003, 26, 67-72. CrossrefGoogle Scholar
Abdelraheem, W.H., He, X., Duan, X., Dionysiou, D.D., Degradation and mineralization of organic UV absorber compound 2-phenylbenzimidazole-5-sulfonic acid (PBSA) using UV-254nm/H2O2. J. Hazard. Mater., 2015, 282, 233-240. CrossrefPubMedGoogle Scholar
Li, J., Jin, P., Dai, W., Wang, C., Li, R., Wu, T., Tang, C., Excellent performance for water purification achieved by activated porous boron nitride nanosheets. Mater. Chem. Phys., 2017, 196, 186-193. Web of ScienceCrossrefGoogle Scholar
Pal, P., Chapter 5 - Water Treatment by Membrane-Separation Technology, Industrial Water Treatment Process Technology. Butterworth-Heinemann, 2017, pp. 173- 242. Google Scholar
Módenes, A., Espinoza-Quiñones, F., Manenti, D., Borba, F., Palácio, S., Colombo, A., Performance evaluation of a photo-Fenton process applied to pollutant removal from textile effluents in a batch system. J. Environ. Manage., 2012, 104, 1-8. CrossrefWeb of ScienceGoogle Scholar
Akpan, U., Hameed, B., Parameters affecting the photocatalytic degradation of dyes using TiO2-based photocatalysts: a review. J. Hazard. Mater., 2009, 170, 520-529. Web of ScienceCrossrefPubMedGoogle Scholar
Ikehata, K., Gamal El-Din, M., Snyder, S.A., Ozonation and advanced oxidation treatment of emerging organic pollutants in water and wastewater. Ozone: Sci. Eng., 2008, 30, 21-26. CrossrefWeb of ScienceGoogle Scholar
Klavarioti, M., Mantzavinos, D., Kassinos, D., Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes. Environ. Int., 2009, 35, 402-417. CrossrefPubMedWeb of ScienceGoogle Scholar
Song, W., Ravindran, V., Pirbazari, M., Process optimization using a kinetic model for the ultraviolet radiation-hydrogen peroxide decomposition of natural and synthetic organic compounds in groundwater. Chem. Eng. Sci., 2008, 63, 3249-3270. CrossrefWeb of ScienceGoogle Scholar
Ertugay, N., Acar, F.N., Removal of COD and color from Direct Blue 71 azo dye wastewater by Fenton’s oxidation: Kinetic study. Arab. J. Chem., 2017, 10, 1158- 1163. CrossrefWeb of ScienceGoogle Scholar
Hermosilla, D., Cortijo, M., Huang, C.P., Optimizing the treatment of landfill leachate by conventional Fenton and photo-Fenton processes. Sci. Total Environ., 2009, 407, 3473-3481. PubMedWeb of ScienceCrossrefGoogle Scholar
Kausley, S.B., Desai, K.S., Shrivastava, S., Shah, P.R., Patil, B.R., Pandit, A.B., Mineralization of alkyd resin wastewater: Feasibility of different advanced oxidation processes. J. Environ. Chem. Eng., 2017, https://doi.org/10.1016/j.jece.2017.04.001 Web of Science
Sahar, A., Ali, S., Hussain, T., Irfan, M., Eliasson, B., Iqbal, J., UV absorbers for cellulosic apparels: A computational and experimental study. Spectrochim. Acta A., 2018, 188, 355–361. Web of ScienceCrossrefGoogle Scholar
Huston, P.L., Pignatello, J.J., Degradation of selected pesticide active ingredients and commercial formulations in water by the photo-assisted Fenton reaction. Water Res., 1999, 33, 1238-1246. CrossrefGoogle Scholar
Zhang, Y., Zhuang, Y., Geng, J., Ren, H., Xu, K., Ding, L., Reduction of antibiotic resistance genes in municipal wastewater effluent by advanced oxidation processes. Sci. Total Environ., 2016, 550, 184-191. Web of SciencePubMedCrossrefGoogle Scholar
About the article
Published Online: 2018-08-03
Conflict of interest: There is no conflict of interest.
Citation Information: Open Chemistry, Volume 16, Issue 1, Pages 702–708, ISSN (Online) 2391-5420, DOI: https://doi.org/10.1515/chem-2018-0077.
© 2018 Anum Sahar et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0