(186m) Defect State Modulation of Wide Band Gap Semiconductor Nanoparticle for Potential Manifold Application

Surface modification of inorganic nanoparticle using different ligand is well-known to enhance different functionality of the nanoparticles (NP), which improves tuning of relevant properties for suitable applications in the field of nanotechnology. As the NPs have very high surface to volume ratio compare to its bulk counterpart, it has higher possibility of having surface defect. Surface defects of wide band gap semiconductors play a crucial role in their properties. Defect mediated recombination of photoinduced electron-hole pair in the semiconductors is very much well known. By modulating the defect state, it is possible to control the defect mediated recombination. Herein, we present a facile synthesis of ZnO nanoparticle followed by surface modification using halide ions by simple precipitation method and demonstrate that proximity of various halide ions to the ZnO NP changes their electronic properties. This kind of surface modification shows very little impact on its surface morphology. On the other hand, the functionalization of halide in the surface of ZnO plays a significant role to modulate its electronic property. This change of electronic property influences their applications in photocatalytic activity or magnetism. The halide attached ZnO NP displays a large reduction of defect state emission. In the present work, we have investigated that for wide bandgap semiconducting oxides, use of anionic halide attachment like Cl^- as surface defect healer proves to be more useful for photocatalytic application than bulk doping using cationic dopant like Mn. We have utilized various microscopic and spectroscopic tools (including picosecond resolved technique) to characterize the nanomaterial and the impact of different halide ions to regulate the light induced charge separation in ZnO NP. Picosecond resolved fluorescence transients reveal a significant annihilation of fluorescence decay, implying an electronic interaction between the NP and the attached halide ions. Upon attachment with a suitable halide ion, room temperature ferromagnetism can be achieved in the nanohybrid system. Finally, the photocatalytic activity of the halide-ZnO NP was carried out under UV light irradiation. To illustrate the impact of defect state and halide ion on the ZnO NP surface, we have carried out first principles DFT calculations using Vienna Ab-initio Simulation package (VASP). It is found that ZnO nanoclusters with surface oxygen vacancy produce trap states within the band gap of the nanoclusters. These states effectively confine the photoinduced electrons and thus essentially reduce the photocatalytic yield with respect to pristine ZnO. However, upon proper halide attachment to the defect states, it is possible to reduce the trap state of the NP recovering the efficacy of reactive oxygen species (ROS) generation in the aqueous solution. We have shown both experimentally and theoretically, that attachment of certain halide ions onto ZnO NP affects its electronic structure and gives rise to a ferromagnetic behaviour even in the absence of magnetic ions. So, the particular halide-ZnO (namely Cl-ZnO) consolidate higher magnetic recovery, thus can be easily separated from water after photocatalysis. In conclusion, modulation of surface defects using chloride can improve various properties of ZnO, demonstrating its utility for functionalization of ZnO NP.