Contents lists available at ScienceDirect FlatChem journal homepage: www.elsevier.com/locate/flatc Sonochemical synthesis of nanospherical TiO 2 within graphene oxide nanosheets and its application as a photocatalyst and a Schottky diode Moushumi Dutta Purkayastha a , Sayantan Sil b , Nisha Singh c , Partha Pratim Ray b , Gopala Krishna Darbha c,d , Sudipta Bhattacharyya e , Amirul Islam Mallick e , Tapas Pal Majumder a, ⁎ a Department of Physics, University of Kalyani, Kalyani 741235, West Bengal, India b Department of Physics, Jadavpur University, Kolkata 700032, West Bengal, India c Department of Earth Sciences, Indian Institute of Science, Education and Research Kolkata, Mohanpur 741246, West Bengal, India d Centre for Climate and Environmental Sciences, Indian Institute of Science, Education and Research Kolkata, Mohanpur 741246, West Bengal, India e Department of Biological Sciences, Indian Institute of Science, Education and Research Kolkata, Mohanpur 741246, West Bengal, India ARTICLEINFO Keywords: Sonosynthesis Schottky barrier diode Photoactivity Stability Recyclability ABSTRACT The hybrid of graphene oxide (GO) nanosheets with well embedded nanospherical TiO 2 was prepared through mechanical mixing using ultrasound. This modifed TiO 2 -GO (TGO) composite exhibits reduced recombination of charge carriers. Benefting from unique morphology and surface area (92 m 2 g −1 ), the TGO composite showed remarkable catalytic activity for the photodegradation of congo red (CR) and methyl orange (MO). The rate constant values were 0.0652 min −1 (pseudo frst order) for CR (5 ppm) and 0.0631 min −1 for MO (5 ppm). The stability and aggregation behavior of TGO was examined using the dynamic light scattering (DLS) technique. The key parameter afecting photocatalytic performance is electron-hole separation. To illustrate this issue, a Schottky diode has been fabricated with TGO composite, in contact with aluminium. Important diode para- meters i.e. ideality factor, series resistance, barrier height have been estimated from forward current-voltage (I- V) characteristics. Space charge limited current (SCLC) theory was employed to provide insight into the carrier transport properties of TGO and enhanced carrier mobility (2.11.10 −6 m 2 V −1 s −1 ) and low transit time (0.237.10 −6 s) under illumination was obtained. The composite appears suitable for energy and photocatalytic applications. 1. Introduction The enormous energy demand of the human civilization has in- troduced several challenges in the energy utilization and environment protection sectors. Industrial as well as agricultural activities disturb the ecological balance by incorporating pollutants into air as well as water. The treatment plants constructed to deactivate the pollutants employ nano-sized particles, the separation of which becomes complex as well as expensive. Graphene, irrespective of its recent discovery [1], has attracted tremendous attention in various felds; encompassing sensors [2], solar cells [3], electronics [4], storage of energy [5], functional composites [6], biomedicine [7] and catalysis [8,9]. It is characterized by a stable 2D morphology with sp 2 -bonded carbon atoms arranged in a honeycombed network. The large specifc areas [10], coexistence of hydrophobic aromatic carbon and hydrophilic oxygen-containing groups in graphene based materials make them suitable support materials [11] and a platform to immobilize several active species and nanoparticles [12–15]. In the feld of electronics, graphene due to its quick photo-switching ability [16] and lower switch-on voltage is favored as Schottky devices. Graphene being readily process able from aqueous and polar solvents has been con- sidered as a potential base material for semiconducting particles to improve the performance of optoelectronic and energy conversion de- vices [17,18]. Nevertheless, its practical applicability is somewhat re- duced due to insulating nature, and the presence of structural defects, poor dispersion and agglomeration due to re stacking and multilayer thickness [19,20]. The only way to tailor the physical and chemical properties of graphene is through chemical modifcation or functiona- lization. Till date, a variety of semiconductors photocatalysts forming composites with graphene has been reported [21–24]. In the present https://doi.org/10.1016/j.fatc.2020.100180 Received 27 April 2020; Received in revised form 15 June 2020; Accepted 17 June 2020 Confict of Interest: The authors declare that they have no known competing fnancial interests or personal relationships that could have appeared to infuence the work reported in this paper. ⁎ Corresponding author. E-mail address: tpm@klyuniv.ac.in (T.P. Majumder). FlatChem 22 (2020) 100180 Available online 24 June 2020 2452-2627/ © 2020 Elsevier B.V. All rights reserved. T