The removal of aniline as a carcinogen from aqueous environments is highly significant. In the present study, the feasibility of photocatalytic degradation of aniline by CuO nanoparticles was evaluated. A batch reactor with an internal UV lamp was used and the effects of the parameters of pH (3–11), dosage of catalyst (0.01–0.1 g/L), initial concentration of aniline (50–250 mg/L), and duration of reaction (15–90 min) were investigated. The remaining concentration of aniline was determined by spectrophotometer at the wavelength of 198 nm. The Langmuir–Hinshelwood model was used for examining the kinetics of the reaction. The results showed that the degradation of aniline is maximum at pH 7. Also, the removal efficiency of 90.16% after 90 minutes of reaction in the case of initial concentration of 50 mg/L was obtained. The aniline degradation was elevated from 40 to 82% by increasing CuO nanoparticles’ dosage from 0.01 to 0.1 g/L. In addition, the obtained data properly fit with the Langmuir–Hinshelwood kinetic model and showed that the Kapp decreased from 0.029 to 0.016 min−1 by increasing of the initial concentration of aniline. Considering the obtained results, the UV/CuO process can be an effective method for removing aniline from aqueous solution.
The aromatic compounds are among the important chemical materials found in industrial wastewaters which can enter surficial and underground waters directly or indirectly (Casero et al. 1997). These compounds are highly toxic, carcinogenic, and mutagenic, and their existence in water is fatal to aquatic life even at very low concentrations (Saidman et al. 2006). One of the poisonous aromatic compounds is aniline, which is used as raw material or intermediates in certain industries such as the manufacture of plastic materials, dyes, pesticides, and pharmaceutical products. This compound can directly infiltrate the environment through industrial wastewaters or indirectly through degradation of organic compounds (Gómez et al. 2009).
In previous studies, aniline had been treated by certain methods such as advanced oxidation process (Chen & Huang 2015), absorption (An et al. 2009), biological process (Delnavaz et al. 2010), reverse osmosis (Gómez et al. 2009), and electrochemical process (Ferreira et al. 2015). Among different methods, in aqueous environments, advanced oxidation processes are one of the most effective and efficient technologies for degradation and removal of dangerous, resistant, and non-biodegradable organic pollutants (Babaahamdi-Milani & Nezamzadeh-Ejhieh 2016). This method is based on the generation of hydroxyl radical (OH•) which can quickly oxidize organic pollutants. Among advanced oxidation processes, photocatalysis is used as a successful method to degrade various organic pollutants (Xiao et al. 2015). Heterogeneous photocatalysis is a combination of a semi-conductive catalyst such as TiO2, ZnO, ZnS, Fe2O3, CdS, WO3, ZrO2, and CuO and radiation of visible or ultraviolet light (El-Kemary & El-Mehasseb 2010; Behnajady & Eskandarloo 2013). Different studies on aniline removal in aqueous environments have used photocatalytic degradation. For instance, Nitoi et al. (2015); Ku et al. (2010), and Zabihi-Mobarakeh & Nezamzadeh-Ejhieh (2014) used TiO2 semiconductor for removing aniline from aqueous environments. In addition, Karunkaran and Senthilvelan used ZrO2 (Karunakaran & Senthilvelan 2005a) and CdS (Karunakaran & Senthilvelan 2005b), separately, for degradation of aniline.
MATERIALS AND METHODS
Apparatus and materials
All chemical materials required in the present study including NaOH, HCl, dimethyl sulfoxide, aniline (molar mass of 93.13 g/mol and purity of 99.5%), potassium dichromate (K2Cr2O7), silver sulfate (Ag2SO4), mercury (II) sulfate (HgSO4), sulfuric acid (H2SO4), and potassium hydrogen phthalate (KHP) were supplied by Merck Company. In addition, copper oxide nanoparticles (size >50 nm, molecular weight: 79.55 g/mol) were purchased from Sigma-Aldrich Chemical Company. Also, a UV-C lamp with definite power (30 watt) and wavelength (254 nm) was prepared by Philips Company. In addition, a UV-visible spectrophotometer (Labnics, model: LUV-100A) was used for measuring the concentration of aniline in the collected samples while another type of spectrophotometer (HACH, model: Dr5000) was used for measuring chemical oxygen demand (COD). The D5220 method is adopted to determine COD according to Standard Methods for the Examination of Water and Wastewater, 22nd edition (2012).
Methodology and analysis
A batch system was used to conduct the present study. The aniline stock solution and dimethyl sulfate were prepared daily. Then, from the stock solutions, different concentrations were prepared through dilution in deionized water.
The aniline solution was inserted into a Plexiglas reactor and inside the reactor; a 30 watt UV-C lamp was installed for irradiating the aniline solution. For reflection of the UV light output and to increase its efficiency, all around the reactor was covered by aluminum sheets. For homogenization of the solution within the reactor, magnetic stirring was used. At the beginning of each experiment and after adding nanoparticles to the solution, the sample was put in the dark for 30 minutes so as to let the aniline solution and nanoparticles attain equilibrium. All experiments were repeated three times at the laboratory temperature (27 ± 3 °C). For sedimentation and separation of nanoparticles, each sample was centrifuged for 10 minutes at a speed of 3,000 rpm. To ensure complete separation of the nanoparticles, a 10 mL sample was passed through 0.2 μm polytetrafluoroethylene syringe filters.
The effect of different parameters, including pH (3, 5, 7, 9, and 11), duration of exposure (15, 30, 60, and 90 minutes), dose of CuO nanoparticles (0.01–0.1 g/L) and different concentrations of aniline (50–250 mg/L) on the aniline removal efficiency was evaluated. For studying the effect of each parameter, in each round of experiments three parameters were constant and only one parameter varied. The concentration of aniline for each collected sample was measured at the wavelength of 198 nm. In addition, for determining the influence of UV alone on degradation of aniline, in the case of different contact times, 100 mg/L aniline was exposed to UV and the remaining concentration of aniline was measured.
RESULTS AND DISCUSSION
Effect of pH
Effect of CuO nanoparticle concentration
Effect of initial concentration of aniline and reaction time
|C0 (mg/L)||Kapp (min−1)||R2|
|C0 (mg/L)||Kapp (min−1)||R2|
Pathways of aniline removal reactions
In the present study, the feasibility of removing water-soluble aniline through UV/CuO process was investigated. The results of the present study show that the combination method of UV/CuO could degrade aniline in aqueous solution efficiently, such that it could even reach 89% of aniline removal at the initial concentration of 50 mg/L. As well, the obtained data from COD reduction revealed that the proposed method not only can decompose soluble aniline, but it also obviously mineralized this organic pollutant. It was also found that at neutral pH the presented method is more efficient and the kinetics of aniline removal is explained by the Langmuir–Hinshelwood model properly. Finally, the results of the present study proved that photocatalytic degradation using CuO nanoparticles could be used as an effective water treatment process for removal of aniline from polluted waters.
We would like to thank the environmental chemistry laboratory of Zahedan University of Medical Sciences for financial support of this research project.