Preparation of nanostructured TiO2-based photocatalyst by controlling the calcining temperature and pH

Mohammed Jasim Uddin 0 Md Akhtarul Islam 0 Sheikh Ariful Haque 0 Saidul Hasan 0 Mohammad Shaiful Alam Amin 0 Mohammed Mastabur Rahman 0 0 Department of Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology , Sylhet 3114, Bangladesh Nanostructured TiO2 has been synthesized using one-step sol-gel method and characterized by different characterization techniques (SEM, EDS, XRD, and UV-vis spectroscopy). The photocatalytic degradation of methylene blue (MB) and Congo red (CR) is studied with the synthesized TiO2. The photocatalytic degradation data has been validated using several kinetic models. The TiO2 showed efficient photocatalytic degradation performance on MB and CR. In addition to this, the effect of pH on the photocatalytic degradation has been investigated. The TiO2 showed enhanced photocatalytic performance in basic media than that in neutral or acidic ones. - Background Titanium dioxide is a promising material and is widely used in many applications such as disinfection, medical treatment, environmental purification, and photovoltaic cell [1,2] due to its high photocatalytic activity [3,4], excellent gas-sensitivity [5], and dielectric properties [6]. TiO2 particles, which are smaller than tens of nanometers, are of particular interest for the synthesis of new materials due to their special optical properties, high catalytic activity, and unusual mechanical properties in comparison to their bulk material counterpart [7]. TiO2 can be synthesized into various shapes - nanoporous materials, nanoparticles, nanowires, nanorods, nanotubes, and nanofibers using different preparation methods [5]. Many methods have been developed to control the size of nanoparticles, which include Langmuir-Blodgett films [8], vesicles [9], and reverse micro-emulsion method [10]. The chemical and physical properties exhibited by these materials depend on both the composition and the degree of homogeneity. Therefore, different synthesis strategies have been developed. These studies include coprecipitation, flame hydrolysis, impregnation, and chemical vapor deposition [11,12]. So far, solgel route has demonstrated a high potential for controlling the bulk and surface properties of the oxides [13-15]. Additionally, non-hydrolytic solgel routes have been reported in the literature [16]. The physical and chemical properties of TiO2 in the nanometer size range depend on phase composition, grain size, and dispersity [17]. Nanosized TiO2 crystals, of less than 10 nm, show significant differences with the bulk TiO2 in many aspects due to the quantum size effect [18,19]. The photocatalytic oxidation technology is frequently used for the complete degradation of organic micropollutants (dyes) in water, utilizing sunlight and UV radiation as energy sources [13,20]. However, TiO2 is active only under near-ultraviolet irradiation region, because of its wide-bandgap energy of 3.0 to 3.2 eV. As a result, significant efforts have been made over the last two decades to develop modified TiO2 particles that are functioning under visible-light irradiation ( > 400 nm). TiO2 has been used in a wide range of application including thin films or as submicron powders [21]. In the present paper, 20 g of nanostructured TiO2 powder is synthesized from Ti (O-iC3H7)4 (referred to hereafter as TIP) without the addition of catalyst or stabilizer at room temperature and atmospheric pressure. Under such conditions, nanosized particles (20 to 60 nm) are partly crystallized in the anatase phase. The Figure 1 SEM image of prepared TiO2 nanoparticles. objective of this paper is threefold: (1) to investigate the photocatalytic activity of the synthesized TiO2 on methylene blue (MB) and Congo red (CR), reactive dyes which are mostly used in textile processing industries, (2) to investigate and reveal the photocatalytic degradation kinetics using several mathematical models, and (3) to determine the pH level at which the photocatalytic reaction proceeds with acceptable reaction rate and completion of photocatalytic degradation. Methods Materials Titanium (IV) isopropoxide (Alfa Aesar, USA), 2propanol (Alfa Aesar), MB (Merck, Germany), and CR (Merck) have been used as received. Water used in experiments was triple distilled and produced in laboratory. P25 (Degussa, Germany) was used as a reference photocatalyst (TiO2) throughout this study. Synthesis Nanostructured TiO2 was prepared by following solgel chemistry methods. The solgel method is a promising method, because the morphology of the nanomaterial is Figure 3 EDS analysis of synthesized TiO2 sample. The peak marked with C (carbon, the base peak), O (oxygen), and * (asterisk) represent the support materials of the grid used during the EDS analysis. varied simply by changing the solution composition and deposition condition. The synthesis reactor consists of a three-necked round bottom reactor equipped with a vertical condenser fitted to the middle neck. A separatory fun (...truncated)