Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece Stability studies of CdS sensitized TiO 2 nanotubes prepared using the SILAR method Vijila Kalarivalappil a,b , Steven J. Hinder c , Suresh C. Pillai d , V. Kumar b , Baiju Kizhakkekilikoodayil Vijayan e, ⁎ a Basic Science and Humanities Division, Indian Naval Academy, Naval Academy PO, Ezhimala, Kannur, Kerala 670310, India b Centre for Materials for Electronics Technology (C-MET), Department of Information Technology, Government of India, Shoranur Road, M. G. Kavu, Athani P.O., Thrissur, Kerala 680 581, India c The Surface Analysis Laboratory, Department of Mechanical Engineering Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK d Nanotechnology Research Group, Department of Environmental Sciences, Institute of Technology Sligo, Ireland and Centre for Precision Engineering, Materials and Manufacturing Research, Department of Environmental Science, Institute of Technology Sligo, Ash Lane, Sligo, Ireland e Department of Nanoscience/Chemistry, Kannur University, Swami Anandha Theertha Campus, Edat P.O., Payyannur, Kerala 670 327, India ARTICLE INFO Keywords: Titania nanotubes Cadmium sulphide XPS Photocatalysis Solar cell ABSTRACT Titania nanotubes sensitized with CdS nanoparticles of different sizes and amounts were prepared using the successive ionic layer (SILAR) deposition method. UV/visible spectra indicate a red shift in CdS absorption upon increasing the number of SILAR cycles this is due to an increase in amount and size of CdS particles on the surface of titania nanotube. The stability of CdS particle sensitized on the surface of titania nanotubes were monitored using X-ray photoelectron spectroscopy (XPS). The formation of CdSO 4 species on the surface of CdS particles was evident from the XPS analysis. Smaller CdS particles, formed using a lower number of SILAR cycles, are more prone to oxidation than the larger particles formed using a greater number of SILAR cycles. The photocatalytic activity and solar cell efficiency is found to be dependent on the number of SILAR cycles em- ployed. 1. Introduction Well aligned titania nanotubes are gaining considerable interest in a variety of applications such as photocatalysis, batteries and sensors [1–4]. Quantum dot chalcogenides are used widely for the sensitisation of nanostructures for solar cell and photocatalytic applications [5,6]. Semiconductor quantum dots are strongly dependent upon the size of the bandgap and hence their ability to create multiple excitons by the absorption of photons with energies greater than the bandgap [7]. CdS is reported to be one of the most studied chalcogenides due to its small band gap (2.4 eV), its easy tunability and its relatively high absorption coefficient in the visible region of the spectrum [8]. In the physical and chemical method employed in quantum dot deposition the SILAR method has advantages over other techniques due to its simplicity and the low cost of equipment required for the deposition. Therefore the SILAR method is widely used in photocatalytic and solar cell applica- tions [9,10]. A combination of CdS-ZnS coated on the surface of a ti- tania nanoparticle based solar cell is reported to have exhibited an ef- ficiency of 0.66%, however the more costly spiro-OMeTAD material was employed as the hole transport medium [11]. Nanorods of CdS- CdSe and CdSSe have been deposited on titania nanorods by chemical vapour deposition [12]. Titania nanotubes arrays sensitized with Mn and Co doped CdS were used for photoelectrochemical applications [13]. Hydrothermal synthesis of titania nanowires sensitized with CdS using chemical bath deposition has been used effectively for the pho- tocatalytic degradation of methyl orange [14]. A sequential chemical bath deposition technique was employed for the deposition of CdS nanoparticles on the surface of titania nanotubes by Qorbani et al. [15]. Nanocrystalline titania sensitized with optimized compositions of ZnS, CdS and CdSe with CoS and CuS counter electrodes were used to make solar cells with an efficiency of 2.7% [16]. CdS sensitized on vertically aligned single crystalline titania nanorods has been used to fabricate solar cell with an efficiency of 1.8% incorporating a ZnS passivation layer [17]. The layer by layer assembly of titania nanosheet and CdS nanoparticles has been shown to enhance photocurrent generation [18]. Commercially available Hombifine N and Degussa P25 nano- particles were deposited with CdS nanoparticle and used for the gas phase oxidation of ethanol under visible light irradiation [19]. Sonoe- lectrochemical anodisation and sonoelectrochemical deposition were used for the preparation of short titania nanotubes deposited with a CdS https://doi.org/10.1016/j.jece.2018.01.050 Received 10 July 2017; Received in revised form 31 December 2017; Accepted 25 January 2018 ⁎ Corresponding author. E-mail addresses: baijuvijayan@knruty.ac.in, baijuvijayan@gmail.com (B.K. Vijayan). Journal of Environmental Chemical Engineering 6 (2018) 1404–1413 2213-3437/ © 2018 Elsevier Ltd. 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