Advancement in the photocatalytic and biomedical performance of titania based nanocomposites synthesized through new sol-gel approaches

Abstract

Titanium dioxide (TiO2 or titania) has been extensively studied as a semiconductor metal oxide material. TiO2 possesses excellent physical and chemical properties. Photocatalytic removal of pollutants from environment is one significant area of research in TiO2 based materials due to photocatalytic activity owing to the ability of TiO2 to produce reactive species by absorbing light. Reactive species generated by TiO2 in the presence of light are also useful in killing bacteria for antiseptic applications. However, there are serious performance limitations in developing TiO2 based photocatalytic application systems or TiO2 based antibacterial materials. In this work, we have introduced versatile inexpensive materials synthesized through simple procedures to improve the photocatalytic and antibacterial properties of TiO2. We developed three different materials systems; Fe2O3-TiO2, Expanded graphite-TiO2 and CNT-TiO2 systems. Cheap titania source titanium oxychloride (TiOCl2) was used as a TiO2 precursor in all 3 studies. Furthermore, all 3 synthesis schemes were designed to reduce the cost by avoiding the use of supporting chemicals and harsh conditions (high temperatures and high pressures). Investigations on the effects of various factors which can influence the physico-chemical properties of the final materials were carried out by means of contemporary analytical tools. Photocatalytic degradation experiments, antibacterial tests and cytotoxicity evaluations were carried out. A significant improvement in the performance of TiO2 based materials was noted and discussed. Chapter 1 of this dissertation overviews the brief history and current status of research in TiO2 based materials for photocatalytic and biomedical applications. Various morphological and chemical modifications in TiO2 to enhance its properties are critically reviewed. Chapter 2 reports on a sol-gel technique to synthesize Fe2O3-TiO2 nanocomposites with improved structural and photochemical properties. Briefly, nanoparticles with different Fe2O3 contents (2%, 5%, 8%, 15%, 25% and 35%) were prepared by introducing Fe2+ and Fe3+ sources to titania. Titanium oxychloride (TiOCl2) was used as a titania precursor to form composites. Final products were obtained after the sintering of the as-synthesized materials at different calcination temperatures ranging from 400oC t 800oC. The physiochemical properties of the samples were examined by XRD, XRF, SEM, HRTEM, UV-Vis DRS, FTIR, TGA and nitrogen gas physisorption studies analysis. XRD analysis revealed that by varying the doping amount of Fe2O3 a mixture of TiO2 crystals can be formed during sintering. SEM and TEM results revealed the sintered samples consisted of particles with different sizes and morphology as a result of calcination and varying the amount of Fe2O3 in the composites. A simple chemical reaction for degradation of thiazine dye methylene blue was used to determine the photocatalytic activity of the prepared nanocomposites. All the synthesized samples showed photocatalytic activity. This work provides a criterion for the selection of synthesis technique, precursors and dopant concentration to obtain metal oxide composites with desirable properties for heterogeneous photocatalysis. Chapter 3 presents an inexpensive sol-gel technique for the synthesis of expanded graphite-TiO2 (EG/TiO2) hybrid materials. Cheap TiO2 precursor TiOCl2 and relatively cheaper form of conjugated carbons (expanded graphite) were used for obtaining EG/TiO2 hybrid systems with various content of EG. Synthesized materials were characterized by XRD, Raman spectroscopy, XPS, FTIR, BET, DRS and TEM techniques and effects of graphite content on the structure, crystallinity, morphology, chemical state, photocatalytic performance and cell proliferation properties were investigated and discussed. Prepared hybrids showed excellent photocatalytic activity and minimum cell proliferation towards human skin keratinocytes. Chapter 4 introduces the concept of enhancing the antibacterial properties of TiO2 in the absence of light by addition of carbon nanotubes (CNT) and reducing the cytotoxicity of CNT by using the synergistic effect of TiO2-CNT hybrid materials. A reproducible sol-gel method was used to synthesize high performance antibacterial TiO2-CNT materials. Effects of CNT loading amount on antibacterial efficiency, cytotoxicity, surface area, porosity, crystalline structure and chemical state of metal oxides were investigated. The obtained products were analyzed by XRD, Raman spectroscopy, XPS, FTIR, TEM and nitrogen gas physisorption studies. It was found that antibacterial strength of TiO2 materials increases significantly with the increase in CNT loading amount and TiO2-CNT sample with wt.10% or more loading of CNT in TiO2 almost completely removed the E.coli bacteria. Cell proliferation studies of synthesized materials on HaCaT cells showed that the obtained materials exhibited minimum cytotoxicity. Thus, the synthesized samples were highly bioactive and can be used for biomedical applications. The last chapter, Chapter 5, presents the general conclusions of this work.