Nanostructured materials show unique physical and chemical properties that differ from their bulk materials. This research aims to synthesize new nanostructured materials and to explore their properties. We synthesize different nanostructured materials with new shapes, sizes, and porosities by using conventional or modified methods. We also work to develop "green synthesis" routes for nanomaterials synthesis. Figures below show biosynthesis routes (developed in our lab) for iron oxide (Fe₂O₃) and gold (Au) nanoparticles together with their TEM images. We study physical (optical, magnetic) properties and chemical (catalytic) properties of the nanomaterials followed by their applications in electronic devices, catalysis, wastewater treatment, biodegradable plastic, etc.

(a) Solar to chemical energy conversion
Solar energy can be converted into chemical energy (hydrogen energy) via water splitting by using a semiconductor photocatalyst. In a photocatalytic reaction, water molecules are oxidized by photoholes at the valance band of a semiconductor photocatalyst to form O₂(g) and H⁺. The protons (H⁺) are then reduced by photoelectrons at the conduction band of photocatalyst to produce H₂(g). H₂.generation increases when a co-catalyst (generally, metal nanoparticles, such as Pt ) is used with the photocatalyst (see figure below). To develop a highly active photocatalytic system, we synthesize nano photocatalysts of different sizes and shapes, core-shell type nano structures or nanocomposite materials and evaluate their performances in terms of H₂.production. We also apply photoactive biomolecules (extracted from bacteria) and natural clay (graphite silica) together with the nano photocatalysts and study their mechanisms of activities to further improve the efficiency of hydrogen production. SEM images of some photocatalysts, synthesized in our lab, are shown in the figure below.

Photoelectrochemical reaction is another method of hydrogen production via water splitting. In this method, a semiconductor photocatalyst film is used as a photoanode. Photoholes at the anode react with water molecules to produce O₂(g) and H⁺. Photoelectrons from the anode are transferred to the cathode through an external circuit where H⁺are reduced to produce H₂(g). We fabricate and apply self-aligned 1D and 2D nano structured thin films (see figure below) of various semiconductor oxide materials such as ZnO, TiO₂,.Fe₂O₃.etc., which provide a large surface area and improved charge collection efficiency. Moreover, nanoparticles of CdS, CdSe, Ag, ZnS, amorphous TiO₂,.SiO₂.etc. are used with these films to achieve improved activities under the visible light irradiation or/and improved charge separation.

(b) Solar to electrical energy conversion
The aim of this work is to fabricate a low-cost solar cell, which could replace the expensive Si solar cell. Quantum dots (QDs) solar cell is considered to be one of the potential candidates to replace Si solar cell. QDs are the tiny particles or nanocrystals of semiconductor materials with diameters in the range of 2-10 nm and a central theme in nanotechnology. Due to their unique electronic properties and multi exciton generation effect, the efficiency of QDs solar cell is predicted to be ~70%, which is nearly three times higher than that of conventional Si solar cell. However, the maximum efficiency of QDs solar cells reported so far is 5%. We work to improve the efficiency as well as the stability of QDs solar cells by increasing charge collection and charge separation. For the effective charge collection, we use 1D nanostructured films (instead of nanoparticles film) of TiO₂.or ZnO in a QDs solar cell. Moreover, Ag nanoparticles and ALD (atomic layer deposition) deposited amorphous TiO₂.or SiO₂.coating is used for the efficient charge separation. The SEM image, in the figure below, shows CdS QDs deposited TiO₂.nanowire film fabricated by hydrothermal and SILAR methods.