Photodegradation of bromophenol blue in aqueous medium using graphene nanoplates-supported TiO2

Applied Water Science (2019) 9:105 https://doi.org/10.1007/s13201-019-0983-z ORIGINAL ARTICLE Photodegradation of bromophenol blue in aqueous medium using graphene nanoplates‑supported TiO2 Tariq Shah1 · Tamanna Gul2 · Khalid Saeed1,2 Received: 1 March 2019 / Accepted: 15 May 2019 © The Author(s) 2019 Abstract The bromophenol blue dye in aqueous medium was photodegraded (under UV irradiation) by graphene nanoplates-supported titanium oxide (TiO2/GNP). The determination of various elements (percentage) and morphological study was performed using energy-dispersive X-rays and scanning electron microscopy, while the photodegradation study of dye was done by UV–visible spectrophotometer. The morphological study showed that the TiO2 particles were dispersed well on the surface of GNP. The sizes of TiO2 particles were below 500 nm. The photodegradation study was performed as function of time, and it was found that the photodegradation of dye in aqueous medium was increased as the time duration of UV irradiation increased. It was found that about 86% of dye was degraded within 8 h. The degradation of bromophenol blue is pHdependent, and the photodegradation rate was increased as the pH of solution increased. The increase in dye degradation might be due to the formation of more hydroxyl radical at higher pH. The degradation of dye at pH 2, 4, 6 and 8 was about 70, 79, 90 and 95%, respectively. Keywords Photodegradation · TiO2 · Bromophenol blue · Graphene sheet Introduction The effluents were released from food processing, leather, paper, textile and dyes manufacturing industries containing various types of coloring materials, which generate nonaesthetic pollution and eutrophication. The majority of dyes is toxic and carcinogenic, non-biodegradable (large size and complex structures) and may contribute to the formation of dangerous by-products through the chemical reactions that take place in the wastewater bodies (oxidation, hydrolysis, etc.) (Ramírez et al. 2012). These coloring materials can be removed from the industrial effluents by using various chemical and physical techniques such as advance oxidation process, adsorption and coagulation, reverse osmosis and ultrafiltration (Ladakowicz et al. 2001; Lee et al. 2006; Nataraj et al. 2009; Zhao et al. 2012). Most of these techniques are nondestructive and transfer only pollutants from * Khalid Saeed 1 Department of Chemistry, University of Malakand, Chakdara, Dir (L), Khyber Pakhtunkhwa, Pakistan 2 Department of Chemistry, Bach Khan University, Charsadda, Khyber Pakhtunkhwa, Pakistan aqueous medium to another medium or convert them into products, which have low toxicity. Currently, semiconductor photocatalysis extensively used for the organic pollutants/ organic dyes degradation. The photocatalytic degradation process is normally based on the production of hydroxyl radical and that radicals are responsible for the organic pollutants degradation (Moghaddam and Yangjeh 2011; Khan et al. 2016). TiO2 has attractive applications in cosmetics and in the production of electrochemistry electrodes, capacitors, solar cells and catalysis (Ghorai and Biswas 2013). Also, TiO2 is widely used as a photocatalyst for the degradation of organic and inorganic substances because of low cost, high stability against corrosion and non-toxicity. When titanium oxide is irradiated by UV, the electrons on the surface of TiO2 are excited from the valence band to the conduction band and that result a positive hole in the valence band. The excited electron may react with hydroxyl/water to generate hydroxyl radicals (strong oxidizing agent), which is responsible for the destroying of organic compounds. It was also reported that the organic compound is directly destroyed by positive hole (Tang et al. 1997). In the present study, an attempt was made for the photodegradation of bromophenol blue using T iO2/GNP. The 13 Vol.:(0123456789) 105 Page 2 of 7 bromophenol blue was selected because it is commonly used as a pH indicator and as a dye. It is also used for the determination of trace quantity of manganese(II), silver(I) and vanadium(V). The contact or inhalation of bromophenol blue may cause skin, eye and respiratory tract irritation. It may cause reproductive and fetal effects. It was also reported that the prolonged exposure may cause liver, kidney and heart damage (http://cdn2.lasecsa.co.za/pdf/sds/Bromo phenol%20blue%20indicator.pdf. 2019). While the GNP exhibits large specific surface area, high mechanical and thermal conductivity and stable in air showed (Anastassia and Vagelis 2013). Due to these outstanding properties, the GNP showed wide potential applications in sensors, supercapacitors, filler in polymeric materials and photocatalysis (Xu and Zhang 2000; Fang et al. 2014). In our present work, the GNPs are used as support for the T iO2 and then used as a photocatalyst for the degradation of dye. The T iO2/GNP was characterized by SEM and EDX. The UV–Vis spectrophotometer was used for the determination of dye degradation. The photodegradation of dye was also performed at a different pH in order to study the effect of pH on degradation of dye. Applied Water Science (2019) 9:105 dried graphene nanoplates-supported titanium oxide ( TiO2/ GNP) sample was stored for further use. Photodegradation of bromophenol blue 0.02 g of GNP/TiO2 was added to 10 mL of 100 ppm bromophenol blue solution. The dye solution was then irradiated under UV light (254 nm, 15 W) for various time durations with constant stirring. After the specific irradiation time, the TiO2/GNP was separated by centrifugation and then the UV–Vis absorption measurements were taken using UV–visible spectrophotometer. The degradation rate of bromophenol blue dye was calculated by using the following equation (Ameen et al. 2010): Degradation rate (%) = Degradation rate (%) = ( Co − C ) Co ( ) Ao − A Ao × 100 × 100 Experimental work where Co is the initial concentration of dye, C is the dye concentration after UV irradiation, Ao shows the initial absorbance, and A is the dye absorbance after UV irradiation. Materials Instrumentation HNO3 and bromophenol blue were purchased from SigmaAldrich and used as received. The GNPs are purchased from Chengdu Organic Chemicals Co., Ltd., Chinese Academy of Sciences. The thickness and diameter of graphene nanoplates are 4–20 nm and 5–10 µm, respectively. The morphological study of gold-coated GNP and T iO2/ GNP was analyzed using JEOL, JSM-5910 scanning electron microscope. The energy-dispersive X-rays (EDX) spectrometric study analysis of T iO2/GNP was performed on EDX (Model INCA 200/Oxford Instruments, UK, company oxford), in order to investigate the elemental composition of the samples. The FT-IR study was performed by FT-IR spectrometer (PerkinElmer, serial number 95120), where IR beam was pass through solid-dried TiO2/GNP sample. The photodegradation study of bromophenol blue was performed using UV–visible spectro (...truncated)