Flexible Nano-TiO2Sheets Exhibiting Excellent Photocatalytic and Photovoltaic Properties by Controlled Silane Functionalization─Exploring the New Prospects of Wastewater Treatment and Flexible DSSCs

Abstract

TiO2nanoparticles surface-modified with silane moieties, which can be directly coated on a flexible substrate without the requirement of any binder materials and postsintering processes, are synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, time-correlated single-photon counting, and transmission electron microscopy. The viability of the prepared surface-modified TiO2(M-TiO2) sheets as a catalyst for the photo-induced degradation of a model dye, methylene blue, was checked using UV-visible absorption spectroscopy. The data suggest that, compared to unmodified TiO2, M-TiO2sheets facilitate better dye-degradation, which leads to a remarkable photocatalytic activity that results in more than 95% degradation of the dye in the first 10 min and more than 99% of the degradation in the first 50 min of the photocatalytic experiments. We also demonstrate that M-TiO2can be recycled with negligible reduction in photocatalytic activity. Further, the photovoltaic properties of the developed M-TiO2sheets were assessed using UV-visible absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and photochronoamperometry. Dye-sensitized solar cells (DSSC) fabricated using M-TiO2as the photoanode exhibited a photoconversion efficiency of 4.1% under direct sunlight. These experiments suggested that M-TiO2sheets show enhanced photovoltaic properties compared to unmodified TiO2sheets, and that, when N-719 dye is incorporated, the dye-TiO2interaction is more favorable for M-TiO2than bare TiO2. The simple solution processing method demonstrated in this paper rendered a highly flexible photoanode made of M-TiO2with superior charge-separation efficiency to an electrode made of bare TiO2. We propose that our findings on the photovoltaic properties of M-TiO2open up arenas of further improvement and a wide scope for the large-scale production of flexible DSSCs on plastic substrates at room temperature in a cost-effective way.