Photocatalytic degradation of basic red 51 dye in artificial bathroom greywater using zinc oxide nanoparticles

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Photocatalytic degradation of basic red 51 dye in artificial bathroom greywater using zinc oxide nanoparticles

G. Yashni, Adel AlGheethi

^⇑

, Radin Maya Saphira Radin Mohamed, Siti Nor Hidayah Arifin, Vikneswara Abirama Shanmugan, Amir Hashim Mohd Kassim

Micro-pollutant Research Centre (MPRC), Department of Water and Environmental Engineering, Faculty of Civil and Environmental Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Johor, Malaysia

a r t i c l e i n f o

Article history:

Received 9 September 2019

Received in revised form 19 January 2020 Accepted 22 January 2020

Available online xxxx

Keywords:

Photocatalysis Decolourisation Azo dye Nanoparticles Bathroom greywater

a b s t r a c t

The current work aims to optimise the photocatalytic degradation of Basic Red (BR51) in artificial bathroom greywater (ABGW) using zinc oxide nanoparticles (ZnO NPs). A fixed volume (100 mL) of ABGW was exposed to direct sunlight irradiation for 5.5 h to investigate the degradation of BR51 in ABGW is due to photocatalytic degradation.The factors investigated included ZnO NPs (10–200 mg), pH (3–9) and BR51 concentration (1–10 ppm). In order to confirm the degradation of BR51 in ABGW, initial and final absorbance of BR51 in ABGW were recorded. Reusability of the ZnO NPs was evaluated for the degradation of BR51 in ABGW at optimum conditions. The results revealed that the maximum degradation (89.01%) of BR51 was recorded with 100 mg of ZnO NPs, pH 5 and 1 ppm of BR51. In conclusion, the ZnO NPs are able to degrade the BR51dye in ABGW effectively.

Selection and Peer-review under responsibility of the scientific committee of the 4th International Conference on Green Chemical Engineering and Technology: Materials Science.

1. Introduction

Greywater from the households is one of the water pollutants sources[1]. The composition of greywater varies extensively from household to household based on the cosmetics, detergents, hair dyes and other personal habits of residents[2,3]. This results in the occurrence of xenobiotic organic compounds (XOC) in greywater which can be dangerous to the environment and ecosystem when discharged without efficient treatment [4]. Basic Red 51 (BR51) is a type of XOCs found in greywater resulting from the uti- lization of hair dye products during hair dyeing[5]. Previous works had revealed the existence of dyes and other coloured compounds is the main issue in receiving the social recognition in recycling and reusing greywater. Moreover, most residents believed that the coloured greywater is risky owing to their awful appearance although the greywater has been effectively treated and estab- lished to be safe. Azo dyes have complex structures and show high resistances toward natural, biological and physical degradations [6]. These dyes are not removed by the conventional wastewater

treatment with chemical, physicochemical and biological pro- cesses. However, the coagulation and flocculation-sedimentation, adsorption, biosorption, electrochemical techniques and fungal decolonization are among the methods which have a significant contribution in removing the dyes from the wastewater [7].

Nonetheless, these methods have some limitations in their application such as cost-ineffective as well as generation secondary by- products which needs further treatment[7,8]. Therefore, an appro- priate treatment of bathroom greywater technologies should have the potential to produce high quality of wastewater. Photocatalytic degradation is known as green approach due to its non-selectivity, low temperature and non-energy intensive method for complete mineralization of organic compounds such as azo dyes [9]. The method is acts based on the illumination of semiconductors such as TiO2and ZnO which can be induced to the electron-hole pairs by photons with a proper energy level [10]. The photogenerated electrons react with the dye compounds and degrade them meanwhile the photogenerated holes (h⁺) react with the water to produce hydroxyl radicals on the semiconductor’s surface. The attack of hydroxyl radicals on the dye compounds leads to its total degradation and mineralization, but through involvement of several intermediates [11,12]. Besides, the semiconductor for

Selection and Peer-review under responsibility of the scientific committee of the 4th International Conference on Green Chemical Engineering and Technology: Materials Science.

⇑ Corresponding author.

E-mail address:[email protected](A. AlGheethi).

Materials Today: Proceedings xxx (xxxx) xxx

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Please cite this article as: G. Yashni, A. AlGheethi, R. Maya Saphira Radin Mohamed et al., Photocatalytic degradation of basic red 51 dye in artificial bathroom greywater using zinc oxide nanoparticles, Materials Today: Proceedings,https://doi.org/10.1016/j.matpr.2020.01.395

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photocatalysis should be chemical or biological, inert, stable, inex- pensive, easy to synthesis, and produced without human or environmental risks [13]. To the best of our knowledge, the photocatalytic degradation of BR51 in bathroom greywater by ZnO NPs has not been reported. Thus, in this study, the optimisation of photocatalytic degradation of BR51 in artificial bathroom greywater using ZnO NPs was investigated.

2. Material and methods

2.1. Preparation of ZnO NPs and artificial bathroom greywater (ABGW)

The ZnO NPs were prepared as described in previous work[14].

Artificial Bathroom Greywater (ABGW) was prepared with all the ingredients as specified (Table 1) according to[15].

2.2. Photocatalytic degradation of BR51 in ABGW

A fixed volume (100 mL) of ABGW was transferred into a 500 mL glass beaker which contains ZnO NPs loading in the range of (10–200 mg), pH (3–9) and initial BR51 concentration of (1–

10 ppm). When investigating the influence of ZnO NPs loading, the initial pH of suspension was kept at 7 and initial BR51 concentration was 1 ppm meanwhile when studying the effect of various pH, the ZnO NPs load was 100 mg and initial BR51 concentration was 1 ppm. During the study of influence of different BR51 concentration, the ZnO NPs load was 100 mg and initial pH of suspension was 5. The ABGW was magnetically mixed in the dark room at 400 rpm for 30 min to homogenize with the photocatalyst (ZnO NPs)[16]. The absence of light (dark conditions) was confirmed when the intensity of the light showed as 0 Kflux when measured with Lux meter. The solution was exposed to direct sunlight irradiation for 5.5 h[17]. The intensity of solar light was measured with the average reading of 60–78 Kflux throughout the optimisation process[18]. During the time of irradiation, the ABGW suspension was put on the magnetic stirrer to make the ZnO NPs distributed evenly in the ABGW. The absorbance of BR51 in ABGW was determined before each run at its maximum wavelength of 523 nm. At the end of each experimental run, ABGW sample was centrifuged at 4000 rpm for 20 min to remove the ZnO NPs[19]. The recovered ZnO NPs was reused for the next cycle of the photocatalytic degradation as described inSection 2.3. The reusability of ZnO NPs was identified by reusing for 4 cycles. In order to confirm the degradation of BR51 in ABGW is due to photocatalytic degradation, the photo degradation of BR51 was studied under light source (solar), dark conditions and in the absence of catalyst. The degradation efficiency were calculated according to Equation(1) [20].

Degradationð Þ ¼% A0A A0

x100 ð1Þ

where Aois the initial absorbance of BR51 in ABGW, A is the final absorbance of BR51 in ABGW

2.3. Reusability of ZnO NPs

Reusability of the ZnO NPs was evaluated for the degradation of BR51 in ABGW at optimum conditions. Once the photocatalytic

degradation is completed, the ZnO NPs was separated by centrifu- gation at 4000 rpm. The recovered ZnO NPs was washed with fixed volume (50 mL) of distilled water and dried at 100°C in air oven for 5 h and reused for next run[21].

3. Results and discussion 3.1. Effect of ZnO NPs

In this study, the ZnO NPs loadings of 50–200 mg were investigated for the degradation of 1 ppm of BR51 in ABGW under neutral pH 7. The range for these factors was chosen according to[6,16].

Fig. 1shows the degradation percentage of ABGW with BR51 under different ZnO NPs loadings. It can be noted that the degradation rate of BR51 in ABGW was associated with the increasing of ZnO NPs concentrations, the degradation percentage of BR51 was 74.48% at ZnO NPs loadings of 100 mg compared to 10.17% in the control (without ZnO NPs). The further increases in the ZnO NPs from100 mg to 150 and 200 mg caused drop in degradation rate of BR51 in ABGW. These findings are in agreement with Chong et al.[6]who revealed that the catalyst loading is linearly corre- lated to the degradation rate constant up to the optimum catalyst loading. The reduction in the degradation process at high loadings of ZnO NPs might be due to the low penetration of sunlight and subsequently decreases the accessibility of photon-activated active sites[22]. Furthermore, a high ZnO NPs loading causes aggregation and agglomeration in the photocatalytic degradation system which reduce the UV light transmission in the system[23]. Furthermore, activated molecules with ground state molecules deactivated by collision, controls the reaction which consecutively reduces the photocatalytic degradation rate[24].

3.2. Effect of pH

Four pH conditions (pH 3, 5, 9 and 8.15) were investigated in the current study. At pH 5 (slightly acidic), the maximum degradation percentage of BR51 was 82.61% (Fig. 2). However, at pH 9 (slightly basic), there were drop in the degradation efficiency reaching barely 59.29%. The explanations for these findings might be related to the surface of ZnO NPs which become positively- charged at low pH and exert electrostatic force towards anionic BR51 and thus enhance the adsorption process[25]. In contrast,

Table 1

ABGW composition.

Personal Care Products Amount (g/L) Product Brand

Shampoo 1 Sunsilk

Shower gel 0.55 Lifebuoy

Toothpaste 0.64 Colgate

Soap 1 Palmolive

Detergent 0.63 K1000

50 100 150 200 250 300 350

-20 0 20 40 60 80

Degradation (%)

Time (min)

50 mg 100 mg 150 mg 200 mg Without Catalyst

Fig. 1.Degradation of BR51 in ABGW under with different ZnO NPs loads (50,100,150,200 mg) upon exposure to sunlight. Experimental conditions: [BR51]

= 1 ppm, initial pH of suspension = 7.

2 G. Yashni et al. / Materials Today: Proceedings xxx (xxxx) xxx

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at alkalinity pH, the OH radical production is inhibited by the deprotonation of the [Zn-O-OHO- Zn] intermediate structure and the domination of surface [Zn - O- O^-O- Zn] structure in which case the O2generation is more enhanced[26]. The degradation at pH 3 and pH 8.15 were 68.83% and 61.87% respectively. It can be observed that the degradation rate for pH 3 were slightly lower than pH 5 (acidic medium). This is probably because at high acidic medium (pH 3), UV irradiation promotes less electrons from them to the ZnO NPs valence band, producing fewer OH radicals. More- over, the inevitable rise in acidity will coagulate the photocatalyst and drops its activity[27]. Meanwhile degradation rate for pH 8.15 were slightly higher than pH 9 (basic medium). This is due to at less alkaline medium, adsorption is less inhibited because of its negatively charged ZnO NPs surface.

3.3. Effect of initial BR51 concentration

The degradation of BR51 with different concentrations (1, 5 and 10 ppm) were 89.01%, 78.03% and 59.48% respectively (Fig. 3).

These results indicated that the degradation of BR51 decrease with the increases of initial BR51concentration might be due to the reduction in the penetration length of UV light and subsequently

yield a lower degradation rate of BR51. This is because the increase in the concentration of the BR51 compound will avert the incident light from reaching the surface of the ZnO NPs. The degradation rate is reduced as the number of hydroxyl radical which attacks the compound is reduced. Moreover, the unavailability of active sites on ZnO NPs will then hinder the generation of oxidants, which results in a lower degradation rate of BR51[22].Fig. 4

3.4. Reusability performance of ZnO NPs

The reusability of ZnO NPs was determined by reusing for 4 times in the degradation of BR51 in ABGW under optimised conditions (100 mg of ZnO NPs, pH 5 and 1 ppm of BR51). The degradation efficiency of BR51 in ABGW at the first, second, third, and fourth experimental run was 86.13%, 82.90%, 71.90% and 66.49%

respectively. These results indicate that about 20% decrement in photocatalytic degradation performance of BR51 in ABGW after 4 runs designating that ZnO NPs can be reused multiple times as an effective photocatalyst.

4. Conclusion

It can be concluded that ZnO NPs showed high efficiency for the degradation of BR51 in ABGW. The optimum conditions recorded were 100 mg of ZnO NPs, pH 5 and 1 ppm of BR51 with highest degradation of 89.01%. ZnO NPs has a great potential to be applied in the photocatalytic degradation of dyes in the bathroom greywater.

CRediT authorship contribution statement

G. Yashni:Investigation, Methodology, Writing original draft, conceptualization.Adel AlGheethi: Supervision, Writing - review

& editing. Radin Maya Saphira Radin Mohamed: Supervision, Data curation. Siti Nor Hidayah Arifin: Methodology, Writing - review & editing. Vikneswara Abirama Shanmugan: Formal Analysis, Methodology.Amir Hashim Mohd Kassim: Validation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing finan- cial interests or personal relationships that could have appeared to influence the work reported in this paper.

50 100 150 200 250 300 350

45 50 55 60 65 70 75 80 85

Degradation (%)

Time (min)

pH 3 pH 5 pH 9 pH 8.15

Fig. 2.Degradation of BR51 in ABGW under with different pH (3, 5, 9) upon exposure to sunlight in the presence of ZnO NPs. Experimental conditions: [BR51]

= 1 ppm, ZnO NPs loads = 100 mg.

50 100 150 200 250 300 350

40 50 60 70 80 90

Degradation (%)

Time (min) 1 ppm

5 ppm 10 ppm

Fig. 3.Percentage degradation of BR51 under with different BR51 concentration (1, 5 and 10 ppm) upon exposure to sunlight in the presence of ZnO NPs. Experimental conditions: [ZnO NPs] = 100 mg, initial pH of suspension = 5.

50 100 150 200 250 300 350

40 50 60 70 80 90

Degradation (%)

Time (min)

1st cycle 2nd cycle 3rd cycle 4th cycle

Fig. 4.. Reusability of the ZnO NPs within four experimental runs.

G. Yashni et al. / Materials Today: Proceedings xxx (xxxx) xxx 3

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Acknowledgements

We are gratefully appreciated from the support by the Ministry of Education Malaysia through the research grant FRGS vot K090 and Research Management Centre for providing GPPS Grant (H017).

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