Yulong Liao

Controllable synthesis of brookite/anatase/rutile TiO2 nanocomposites and single-crystalline rutile nanorods array

The synthesis of nano-TiO2 materials have attracted intense interest due to their importance in a wide area of applications. In this study, we report a facile method to synthesize mixed-phase TiO2 nanocomposites by using a one-step approach under mild solvothermal conditions. Differently from previous reports, this method not only yields rutile/brookite/anatase TiO2 nanocomposites with high photocatalytic activities, but also can obtain highly oriented single-crystal rutile nanorod arrays selectively deposited on FTO. These products were characterized by XRD, FTIR, FESEM, TEM, HRTEM, and BET. Results indicate that in the brookite/anatase/rutile coexisting nanopowders, the brookite and anatase phases were crystallized into irregular nanoparticles <20 nm in diameter, whereas the rutile phase was crystallized into single-crystalline nanorods ∼20 nm in diameter and 100 to 500 nm in length. The single-crystalline rutile nanorods could form a film with controllable thickness up to ∼7 μm. The sample with 29.9% anatase, 27.9% brookite, 42.2% rutile was shown to have the highest photocatalytic activity, yielding over 90% bleaching of methyl orange solution in 20 min. The degradation rate constant k of this sample was 0.10180 min−1, almost twice as high as that of P25 (k = 0.05397 min−1). DFT calculations were used to confirm the band structures and density of states in brookite, anatase, and rutile phases.

Enhanced electron collection in photoanode based on ultrafine TiO2 nanotubes by a rapid anodization process

The separated and ultrafine TiO2 nanotubes are fabricated by a modified rapid anodization method, which cannot be achieved through conventional anodization. Then, model dye-sensitized solar cells based on the prepared TiO2 nanotubes and commercial TiO2 nanoparticles (P25) are investigated, and a discrepancy is discovered between the light-harvesting capability and the power conversion efficiency. The charge transport and recombination are studied by the electrochemical impedance spectroscopy and the open-circuit voltage decay technique. Results show that the nanotube photoanode owns a longer electron diffusion length and a larger electron lifetime than the nanoparticle one, which can compensate for the loss of light absorption. The enhanced electron collection efficiency observed is attributed to the facilitated charge carrier pathways in the photoanode composed by the separated TiO2 nanotubes fabricated in this work. Therefore, the TiO2 nanotubes synthesized by this method are verified to have good electronic properties, which might find applications not only in photovoltaic, but also in catalysis, sensors, and other areas.

Origin of the boosted exciton separation at fullerene molecule modified poly(3-hexylthiophene)/ZnO interfaces

In this work, we investigate the multifaceted properties at the poly(3-hexylthiophene) (P3HT)/ZnO interface functionalized by a self-assembled monolayer (SAM) of the fullerene derivative C60 pyrrolidine tris-acid (C60-PTA), using a model sandwich structure which allows better mechanistic understanding in comparison to using a more complicated bulk heterojunction (BHJ). Results show that the C60-PTA modification induces fibril-like P3HT nanodomains at the interfaces which were not seen or reported before, yet the increase of work function on the modified ZnO surface is not pronounced. Besides, the quenching efficiency of the P3HT photoluminescence of the modified sample is nearly 7-fold higher than that of the unmodified one, leading to a more efficient exciton separation after the C60-PTA modification. Thus, we believe that the change in P3HT morphology at the interface might have contributed significantly to the substantially improved exciton separation efficiency observed, which was neglected in similar fullerene modified conjugated polymer/metal oxide systems previously. We further investigate the charge transport and recombination as well as the photovoltaic (PV) response in the C60-PTA modified BHJ sample based on vertical ZnO nanorod arrays (NRAs). Results indicate that the mechanistic understanding underlying the model sandwich structure is also applicable in the buried BHJ interfaces. The present study provides a new insight into the origin of the boosted exciton separation in the conjugated polymer/metal oxide heterojunction modified by fullerene molecules, which might be useful for rationally designing three-dimensional organic–inorganic heterojunctions with enhanced splitting capability of photo-excited excitons from the aspect of interfacial morphologies.

Ag–ZnO composite nanocrystals: synthesis, characterisation and photocatalytic properties

Abstract Ag–ZnO composite nanocrystals were prepared by a simple hydrolysis process of zinc acetate dihydrate together with a reduction of the Ag ions in diethylene glycol. Different contents of sodium hydroxide were added into the initial reaction mixture so as to form an effective contact between Ag and ZnO. X-ray diffraction analysis, ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and transmission electron microscopy were used to characterise the structural and morphological properties of the derived nanoparticles. The effects of the content of sodium hydroxide on the structural and morphological properties of the derived nanoparticles were discussed in detail. Photocatalytic measurement was also conducted, and the results indicate that the sample derived from 0·2M NaOH has the best ultraviolet photocatalytic activity for the degradation of the methyl orange aqueous solution among all the samples, which should be ascribed to the heterostructure formed between Ag and ZnO as well as a good dispersity of the nanoparticles.