• Vol 10, No 4 (2019)
  • Chemical Engineering

The Influence of Plasmonic Au Nanoparticle Integration on the Optical Bandgap of Anatase TiO2 Nanoparticles

Munawar Khalil, Gita Rahmaningsih, Jarnuzi Gunlazuardi, Aminah Umar

Corresponding email: mkhalil@sci.ui.ac.id


Cite this article as:
Khalil, M., Rahmaningsih, G., Gunlazuardi, J., Umar, A., 2019. The Influence of Plasmonic Au Nanoparticle Integration on the Optical Bandgap of Anatase TiO2 Nanoparticles. International Journal of Technology. Volume 10(4), pp. 808-817
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Munawar Khalil Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
Gita Rahmaningsih Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
Jarnuzi Gunlazuardi Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
Aminah Umar Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia.
Email to Corresponding Author

Abstract
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This work reports an investigation into the influence of the surface plasmon resonance (SPR) phenomenon of plasmonic Au nanoparticles on the optical bandgap of anatase titanium dioxide (TiO2) nanoparticles. In the study, the effect of particle integration on the optical bandgap of TiO2 nanoparticles was studied in two types of binary Au-TiO2 heterostructured materials, namely Janus Au-TiO2 nanostructures and core-shell Au@TiO2, and their optical absorption spectra were compared to the pristine anatase TiO2 nanoparticles. The anatase TiO2 nanoparticles was prepared using the sol-gel method. Well-dispersed Au nanoparticles with particle size diameter in the range of 19-33 nm were successfully synthesized using the seed-mediated method and exhibited unique light absorption due to SPR at 544 nm. Based on the results, the integration of Au nanoparticles was found to be responsible for the alteration of both light absorption behavior and the optical bandgap of TiO2. Spectroscopic analyses revealed that the presence of the SPR phenomenon was able to widen the light absorption range of TiO2 to the visible spectrum. In addition, the optical bandgap of the heterostructures was found to be slightly lower than the corresponding pristine anatase TiO2 nanoparticles.

Au nanoparticles; Bandgap; Kubelka-Munk; Plasmonic; TiO2 nanoparticles

Introduction

Recent advances in the development of nanostructured materials, with precise control in size and shape, have enabled researchers to unlock various new optical, electronic and magnetic properties (Duan et al., 2015; Ahmed et al., 2016). Tremendous efforts have also been made to utilize such technology in the fabrication of new types of material with exceptional physicochemical properties, which can be used in various applications such as electronics, catalysis, oil and gas, biomedical and energy storage/conversion (Sharma et al., 2015; Khalil et al., 2017). Exceptional new functionalities can also be obtained by the formation of hybrid nanostructures, in which two or more nanostructured materials are combined. For instance, enhancement in the optical, electronic and photocatalytic properties of various dielectric oxide and semiconductors can be achieved by integrating them with plasmonic metal nanoparticles to form metal-oxide hybrid nanostructured materials (Hernández-Ramirez et al., 2017).

Over the past decades, nano-sized titanium dioxide (TiO2) has been widely considered as one of the most photoactive materials for catalysis in various photocatalytic reactions, due to its chemical stability, low  toxicity and corrosion resistance (Low et al., 2017). Studies  have shown that multiple forms of TiO2 nanostructures have been extensively used as photocatalytic material in photo-induced solar fuel generation, such as CO2 reduction and water splitting, photo oxidation of pollutants in wastewater remediation, and photovoltaic devices (Ayati et al., 2014; Clavero, 2014; Tahir & Amin, 2015; Sofyan et al., 2017). Unfortunately, the large TiO2 bandgap (~3.2 eV) often limits its application in the development of solar-driven photocatalytic reactions, as it only absorbs in the ultraviolet (UV) region (Dette et al., 2014). Furthermore, the rapid recombination of the photo generated charge carriers, i.e. "the excited hot electrons" and "holes", may also diminish the photocatalytic efficiency of TiO2 (Tan et al., 2011).

It has recently been suggested that hetero structuring of TiO2 with plasmonic particles such as Au or Ag nanoparticles could be used to solve these two aforementioned major issues, and thus enhance the photocatalytic performance of TiO2 (Ran et al., 2018). Generally, the role of plasmonic particles in this hetero structured system is very similar to organic dyes or transition metal complexes, which act as photosensitizers. It is believed that hot electrons generated during the Localized Surface Plasmon Resonance (LSPR) process, which typically occur when plasmonic particles are irradiated using visible light, could be transferred to the TiO2 conduction band, which could further be used to facilitate redox reactions (Hidalgo et al., 2009; Lin et al., 2015). As a result, the photocatalytic activity of TiO2 could be extended to a broader light spectrum, e.g. the visible region, which allows the utilization of such materials for solar-driven photocatalytic processes such as artificial photosynthesis.

Currently, a great deal of effort is being made to fully understand the role of plasmonic particles in the enhancement of the photocatalytic activity of TiO2. However, an only a small fraction of the current interest is being paid to the effect of plasmonic particle integration on the electronic structure of TiO2. Therefore, an investigation into the role of plasmonic Au nanoparticles on the bandgap tuning of anatase TiO­2 nanoparticles is presented in this study. In the study, well-distributed Au and anatase TiO­2 nanoparticles were fabricated using the seed-mediated and sol-gel methods respectively. In addition, two types of binary Au-TiO2 heterostructured materials, namely Janus Au-TiO2 nanostructures and core-shell Au@TiO2 nanostructure, were also synthesized to investigate the effect of the plasmonic phenomenon on the optical bandgap of semiconductors.

Conclusion

An investigation of the effect of plasmonic Au nanoparticles in the absorption behavior and optical bandgap of anatase TiO2 nanoparticles has been presented in this work. Well-dispersed anatase TiO2 nanoparticles were successfully synthesized via a sol-gel method and were easily integrated with plasmonic Au nanoparticles to form two types of heterostructure, namely Janus Au-TiO2 nanostructures and cores-shell Au@TiO2 nanostructures. Based on the results, the integration of Au nanoparticles was found to be responsible for the alteration of both light absorption behavior and the optical bandgap of TiO2. The results also show that the two heterostructures were able to absorb not only in the UV range, but also in the visible light spectrum. In addition, Kubelka-Munk estimation also revealed that the optical bandgap of the heterostructures was slightly lower than that of the corresponding pristine anatase TiO2 nanoparticles.

Acknowledgement

This work was financially supported by the Indonesian Ministry of Research, Technology and Higher Education (Kemenristekdikti RI) through Hibah Penelitian Dasar Unggulan Perguruan Tinggi (PDUPT) No. 375/UN.R3.1/HKP05.00/2018. 

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