Hindawi Journal of Chemistry Volume 2021, Article ID 6655070, 9 pages https://doi.org/10.1155/2021/6655070 Research Article Photocatalytic Degradation of Alizarin Red S, Amaranth, Congo Red, and Rhodamine B Dyes Using UV Light Modified Reactor and ZnO, TiO2, and SnO2 as Catalyst Rabia Rehman , Waheed-Uz-Zaman, Asma Raza, Warda Noor, Amna Batool, and Hamna Maryem Institute of Chemistry, University of the Punjab, Lahore 54590, Pakistan Correspondence should be addressed to Rabia Rehman; [email protected] Received 22 October 2020; Revised 21 December 2020; Accepted 31 December 2020; Published 12 January 2021 Academic Editor: Mostafa Khajeh Copyright © 2021 Rabia Rehman et al. 'is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 'e photocatalytic degradation of dyes (alizarin red S, amaranth, congo red, and rhodamine B) present in wastewater was performed with UV lamp. 'e catalysts employed for this investigation were ZnO, TiO2, and SnO2. 'e kinetic studies of dyes degradation followed first order reaction. ZnO was found to be most efficient photo-catalyst for degrading these dyes. 'e optimal −1 2 −1 result for alizarin red S was k � 0.2118 min , t1/2 � 3.27 min, and R � 0.7998, for amaranth was k � 0.146 min , t1/2 � 4.74 min, 2 −1 2 −1 and R � 0.8348, for congo red was k � 0.2452 min , t1/2 � 2.8 min, and R � 0.8382, and for rhodamine B was k � 0.1915 min , 2 t1/2 � 3.6 min, and R � 0.76. 1. Introduction before discharging into the environment. Degradation of dyes is the process in which harmful complex dyes are Textile industries are the major contributor of water pol- converted into simple molecules. Several biological and lution due to releasing a large amount of toxic dyes into physio-chemical techniques are used for decolorization of water bodies [1]. 'e dyeing industry has been reported as dyes [11,12]. Biological methods for treating harmful dyes highly polluting industry by board of central pollution are ecofriendly but many dyes are not biodegraded due to control [2]. Almost 15–20% dyes from industries are directly complex structure [13]. 'e photocatalytic removal of dyes is discharged into rivers that affect aquatic life [3]. Fabric an ecofriendly method that involves the exposure of catalyst industries are heavily dependent on these dyes; however, to UV-visible light [14]. Pakistan, which is an economically developing nation, does 'ere are a number of operational factors that govern the not have a proper disposal system for these dyes effluents; degradation of dyes [15] including dyes load in water, pH therefore, they are mostly disposed of into land pits or water and temperature of the system, catalyst’s quantity, and time resources which leads to their contamination and eventually for degradation. 'e structure and composition of different poses health risks for human health and sea life [4]. dyes respond differently to these factors [16]. 'erefore, it is highly dangerous to discharge these wasted 'e widely used photo-catalysts for removing unwanted dyes without properly dismantling them [5]. dyes are metal oxide semiconductors [17]. 'e most efficient Dyes such as alizarin red S, amaranth, congo red, and and cost-effective catalysts are ZnO, TiO2, and SnO2. 'eir rhodamine B are accounted as extremely dangerous toxi- band energy gap and chemical stability make them ideal [18]. cants. Congo red dye can result in genetic mutation [6] and For instance, TiO2 has a large band gap, which makes it rhodamine B [7] dye can damage skin, eyes, and PNS [8], highly reactive to UV radiations. Some other physical factors while amaranth can result in infertility [9] and alizarin red S such as surface area and zeta potential have huge impact on is a potential allergen [10]. Hence, their removal is necessary degradation potential of these catalysts; zeta potential 2 Journal of Chemistry basically indicates how stable a system is. Greater the value absorbance of Amaranth (mol. formula: C20H11N2Na3O10S3; of the zeta potential (either +ve or −ve), stronger are the molar mass: 604.5 g/mol) was monitored at 523 nm wave- repulsive forces between the catalyst particles which impart length, Alizarin Red S (mol. formula: C14H7NaO7S; molar them more stability. 'e photocatalytic activity of these mass: 360.28 g/mol) at 507 nm, Congo Red (mol. formula: catalysts can also be studied under Vis region of light if we C32H22N6Na2O6S2; molar mass: 696.665 g/mol) at 497 nm, extend their bang gaps by doping them with certain tran- and Rhodamine B (mol. formula: C28H31ClN2O3; molar sition metals or nonmetals. TiO2 can also be used to improve mass: 479.02 g/mol) at 568 nm. catalytic potential of other semiconductors by impregnating them on it; it can be done by techniques such as sol-gel and hydrothermal method. So, these factors are really important 2.5. Degradation of Dyes without Catalyst. 'e 0.4 mM so- in obtaining optimal results. lutions of dyes (Amaranth, Alizarin Red S, Congo Red, and 'is study aims at the degradation of dyes on feasible Rhodamine B) were prepared and exposed to UV light at economic terms. 'e present work focuses on photocatalytic room temperature. 'en, absorption of solutions was degradation of dyes such as Alizarin Red S, Amaranth, monitored after regular time intervals. Congo Red, and Rhodamine B (Figure 1) performed using various factors such as amount of catalyst and dye load. 'e 2.6. Degradation of Dyes with Catalyst SnO . In each pre- tubular UV source is used in this work in such a way that the 2 pared 0.4 mM dyes solution, 4 mg of SnO2 was added and atmospheric gases, especially oxygen’s interference, are re- placed on a hot plate for proper mixing. 'en, solutions were moved entirely which is the novelty of the method. 'e irradiated with UV light for degradation. Absorption of scheme also eliminates the unwanted production of ozone solutions was checked after specific time. under UV light in an open degradation setup [19]. 2. Experimental Work 2.7. Degradation of Dyes with Catalyst TiO2. 'e prepared dyes solutions were taken and mixed with 3 mg of catalyst 2.1. Setup Used. 'e source of light for degrading dyes was TiO2. 'en, solutions were exposed to UV light and ab- tubular UV lamp (Phillips TUV 11W T5), as shown in sorption was measured after regular time intervals. Figure 2(a). 'e dye solution was placed on a hot plate for continuous stirring. Specific wavelength and time absor- bance of dye solution were monitored. 'is is a batch process 2.8.DegradationofDyeswithCatalystZnO. Sample solutions setup. Tubular UV rod provides better results using simple of dyes were prepared and 4 mg of ZnO was added in them. bulb. Further, for continuous degradation process study, a 'e solutions were placed under UV light and degradation setup was designed as shown in Figure 2(b). 'e temperature was observed. 'en, absorbance of the solutions which were was 25°C and the dye solution was used as such without the taken out after regular time was noted by spectrometer. addition of any pH alteration or maintaining reagents. Preliminary experiments were conducted for comparing 3. Results and Discussion the efficiency of both processes, which indicated that the second one is more efficiently removing dyes. So, further 'e photocatalytic degradation of dyes was experimented working conditions were optimized using the second setup. using UV lamp and catalysts. 'e degradation rate and absorbance of dyes were checked and represented graphi- cally. 'e kinetic studies showed that degradation of dyes 2.2. Chemicals. Amaranth, Alizarin Red S, Congo Red, follows first order reaction [20]: Rhodamine B, SnO , TiO , and ZnO all were obtained from 2 2 C Merck (Germany). ln o! � kt; (1) Ct 2.3. Equipment. Tubular UV lamp (11 watts, Phillips TUV where Co is the initial dye amount, Ct is the amount of dye at 11W T5), pH meter, electric balance, UV-visible spectro- time t, and k is the constant. photometer with quartz flow cell, hot plate, and magnetic 'e kinetic data results for degradation of alizarin red S, stirrer were used. amaranth, congo red, and rhodamine B dyes under different conditions (without catalyst and with catalysts ZnO, TiO2, and SnO2) are presented in Table 1. 2.4. Method Used for Photocatalytic Degradation. UV lamp and UV-Vis spectrometer were used for this method. Dye solution was stirred on a hot plate. 'e peristaltic pump 3.1. Case 1: Photolytic Degradation of Dye Alizarin Red S takes this dye solution to bottom of the reactor core where without Catalyst and with Catalysts ZnO, TiO2, and SnO2. the solution was exposed to UV radiations. From its upper 'e results for degradation of alizarin red S under different part, the dye solution was passed into a second peristaltic conditions (without catalyst and with catalysts ZnO, TiO2, and pump. 'en, it was passed into spectrometer for continuous SnO2) are graphically represented in Figure 3 and Table 1. 'ey monitoring of absorbance. 'en, that solution was again indicated that ZnO gives better results among these catalysts for mixed into starting solution. In spectrometer, the degrading alizarin red S. Journal of Chemistry 3 OOH + Na O– OH OOS O S Na+ O– O HN O N O O O S S Na+ –O O– O O Na+ (a) (b) Na+ O– O S O N N NH2 NH2 N N O S O O– Na+ (c) HO O Cl– + N O N (d) Figure 1: Structural formulas of dyes used.