A) Biocompatible Nanotubes of Hydroxyapatite
Our research group has been extensively involved in forming high surface area HAp over the last few years. Hydroxyapatite, (Ca10(PO4)6(OH)2) (HAp), is one of the most stable crystal structures in the calcium phosphate family. We have reported the synthesis of single phase, stoichiometrically pure, porous nanotubes of hydroxyapatite. The biocompatibility of the resulting product has been tested on L929 mouse fibroblast cells using MTT assay and the cellular internalization of these nanotubes has also been evaluated using Rhodamine 6G dye tagged nanotubes in the presence of fibroblast cells. These studies suggest that the nanotubes are non-toxic to fibroblasts and can be taken up easily by mammalian cells. Such tubes may serve as vehicles for drugs and growth factors for tissue repair including bone regeneration.
B) Studies in formation of DSSCs (Dye sensitized solar cells)
An easy protocol for improvement in formation of the photoanode in a dye sensitized solar cell has been addressed. Specifically, we have been involved in using a variety of polyol ligands to form new and intriguing TiO2 morphologies. Recently, a novel synthesis for the formation of a TiO2 precursor: Titanium butanediolate was performed. This precursor was found to have higher thermal and temporal stability than commercially available TiO2 precursors and it was successfully employed in the one-pot synthesis of rutile nanowires grown directly on a conducting substrate: fluorine doped tin oxide (FTO). This synthesis was further extended to directly form a mixed phase TiO2 film consisting of rutile nanowires along with anatase spherical particles on FTO and this assembly was used as the photoanode in a dye-sensitized solar cell. The synergistic effect of the two phases provided a net DSSC efficiency of 4.61% with FF of 61%.
C) Visible Light Photocatalysts
Developing a viable photocatalyst that can use visible light efficiently has become the mainstay of materials researchers worldwide. Exclusive visible light photocatalysis has captivated the attention due to its abundance (44-47%) in the solar energy spectrum, whereas UV light accounts for only 3-5%. Over the past year we have have shown that using exclusively visible light, ZnTiO3 can be used as a photocatalyst in the degradation of phenol. Phenol was taken as a model dye which has an optical absorption only in the UV region and so sensitization artefacts have been deliberately avoided. ZnTiO3 was synthesized by a sol-gel method and was characterized by powder-XRD, UV-Vis diffuse reflectance spectroscopy, FESEM and BET-surface area. It was observed that even though ZnTiO3 absorbs predominantly in UV region, it’s absorption tail extends up to 425 nm and the band-gap was found to be 3 eV. The photocatalytic degradation rate using ZnTiO3 was calculated and found to be substantially better than the rate obtained with Degussa P-25 (Commercial TiO2), which is widely considered as a model photocatalyst. NMR and EPR studies were also performed to gain insight into the reason for the improved catalysis.
D) Energy Storage Aspects
Supercapacitors, commonly known as electrochemical capacitors (ECs), are unique energy storage devices due to their high power density compared to secondary batteries and they also have a high energy density when compared to conventional electrostatic capacitors. Depending on charge storage mechanism, these can be classified into two main categories namely, electrical double layer capacitors (EDLC) and pseudocapacitors. The latter derives its energy from fast and reversible faradic reactions that occur at the electrode/electrolyte interface. Since such fast redox reactions usually take place in materials where metal ions have multiple oxidation states, therefore, transition metal oxides are of great importance for pseudocapacitors. Moreover, predominantly in these cases, activated carbon (AC) has been used as the anode material which normally does not contribute substantially to the overall energy density. It has been purported that energy density of the supercapacitors can be improved by replacing the traditional AC with oxides materials which can work as the anode. So far there have been few reports on formation of new anode materials. The work in our lab has systematically investigated the effect of carbon allotropes and other 2D conductive materials and also reduced Graphitic oxide (r-GO) on the electrochemical performance of BiVO4: a material that currently only our group has been evaluating and has a seminal publication on. Moreover we have extended this work to solely pure Bi2O3 and also to Zinc vanadate. From these studies, a paradigm for using vanadates as anode materials is slowly emerging showcasing the important role of the electrochemical aspects of the cation involved, and also the pseudocapacitive behaviour of the vanadate ions involved.
D) Various other projects
In others to listed above, our lab is currently pursuing a variety of other projects involving using sun’s energy in an efficient and cost efffective. The aim is to use it for generation of electricity (via solar cells), for aiding in chemical reactions (via photocatalysis) and also for harnessing and storing it (via the use of batteries/supercapictors). Contact Prof. Deepa Khushalani for all the latest projects available at the time of application.