Raja Vahini, Puvaneswaran Senthil Kumar, Swaminathan Karuthapandian*

Bandgap tailored NiO nanospheres: An efficient photocatalyst for the degradation of crystal violet dye solution

Raja Vahini, Puvaneswaran Senthil Kumar, Swaminathan Karuthapandian*

Department of Chemistry, VHN Senthikumara Nadar College, Virudhunagar – 626 001, Tamilnadu, India.

Supplementary Information

1. Experimental methods

All the chemicals were purchased from the Merck chemicals, India and used without further purification. Deionized water was used throughout the experiment.

2.1 Synthesis of NiO nanospheres

NiO nanospheres were prepared by simple precipitation method. 20 mL of 0.5 M sodium hydroxide solution and 10 mL of 0.5 M of glucose was simultaneously added drop wise to the 100 mL of 0.5 M NiCl2.6H2O solution under vigorous stirring. The black colour precipitate was observed and it was washed alternately with deionized water and ethanol five times to remove the impurities. Finally, the precipitate was dried in hot air oven at 120 0C for 12 h and then calcinated at 500 0C for 4 h to obtain pure NiO nanospheres.

2.2 Characterization Techniques

X-ray diffraction (XRD) was performed to examine the crystal structure of the NiO. The crystallinity of nanoparticle was recorded with a Philips PW- 1710 X-ray diffractometer (Eindhoven ,The Netherlands) with crystal monochromated CuKα radiation (λ=1.540598 A0) in an angular range of 10-800(2θ) with an accelerating voltage of 40 kV and a current of 20 mA. SEM-EDX was carried out with a (Model SUPRA 40 Scanning Election Microscope) acceleration voltage at 3-5 kV with a working distance of 5-9 mm. TEM was taken on model Tecnai G2,F30 acceleration voltage 300kV. UV Vis-1800 spectrometer was used to analyze the various hybrid samples. Photoluminescence spectra (PL) collected using Horiba Jobin Yvon Fluorolog 3 spectrophotometer having a 450 W Xenon lamp, which has been used as excitation source.

2.3.Adsorption of dye solution onto the NiO photocatalyst surface

Since the photo-oxidation reaction usually takes place on the photocatalysts surface, the adsorption of the pollutant on photocatalysts are important for the photocatalytic process. 50 mg of NiO nanospheres was added to 100 mL of Crystal violet dye [CV] solution (10 ppm of initial concentration). The adsorption system was continuously stirred in the dark. The supernatant was withdrawn periodically and analyzed using maximum absorption wavelength (λmax) of 582 nm with the help of UV-Visible spectrometer.

2.4.Photocatalytic activity of NiO nanospheres

The photocatalytic activity was evaluated by employing a multiwavelength multiamp photo reactor fitted with 8 W mercury lamps of wavelengths 365 nm and 254 nm (Heber, India) and a highly polished anodized aluminium reflector. 50 mg of NiO nanospheres was added to 100 mL of the CV dye solution in a 150 mL reaction vessel. At certain intervals, 5 mL of aliquots were collected. The degraded solutions were analyzed using the absorption peaks at 582 nm. After the degradation the catalyst was separated from the reaction mixture and dried to carry out the reusability tests. Prior to irradiation, the suspensions were magnetically stirred in the dark for 1 h to ensure the equilibrium of the working solution.

Results and Discussion

Adsorption of dye solution onto the NiO nanospheres surface

Prior to the irradiation the CV dye solution with NiO photocatalyst, it was stirred for the adsorption-desorption equilibrium. Adsorption efficiency of the catalyst is shown in Figure S1. It shows the NiO photocatalyst has the some short of adsorption efficiency and the C/C0 was decreased a bit.

Figure S1

Figure S1: Adsorption and photodegradation of CV dye solution on NiO nanospheres.