Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV-visible region from 300 to 800 nm by manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV-visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV-visible light for solar fuel production.
These are not the final page numbers! Ü Ü uniform. The low absorption/emission intensity of PNC supernatant is attributed to the low concentration of PNCs. This indicates that the as-formed PNCs can be easily collected by centrifugation (Supporting Information, Figure S5 b), which is desirable for cleaning and postprocessing in various applications.To explain the different capping effects of OA and APTES, we propose the following mechanism based on a dissolution-precipitation model (Figure 4 c). The dissolved precursors precipitate as PNCs at the DMF-toluene interface when the DMF precursor solution is injected into toluene. With OA as the capping ligand, the OA molecules adsorbed on the surface of the formed PNCs and PNSs diffuse from DMF to toluene, along with the products. However, the chain configuration of OA molecules cannot effectively prevent the products from dissolving back into DMF across the DMFtoluene interface and some OA ligands remain in the toluene phase because of their non-polar nature. The loss of OA ligands will result in a lack of ligands in the DMF phase, leading to the formation of large particles in the next round of precipitation. This effect becomes more pronounced when the concentrations of the precursors is high. On the contrary, the strong steric hindrance of APTES and the formation of silica can prohibit the dissolution of the as-formed PNCs back into DMF, which helps to maintain the original structural and optical properties of PNCs. Nevertheless, the PNC APTES-20 sample began to flocculate after standing for a few minutes (Supporting Information, Figure S7) because of hydrolysis of Si-O-C 2 H 5 groups attached to the PNC APTES surface, which generate hydroxy (-OH) groups (as indicated by FTIR spectra), resulting in a change in polarity and hydrogen bonding of the ligands.Water-induced degradation is a major problem for organic metal halide perovskites because protons are captured by methylammonium.[8] Similarly, they are also unstable towards other protic solvents such as alcohols.We hypothesized that PNC APTES may exhibit better stability because of the strong steric hindrance and hydrolysis properties of APTES, which reduces the access of protic solvent molecules to the PNCs surface. To test the stability of PNC APTES in protic solvents, 0.5 mg mL À1 of PNC precipitate capped by different ligands was dispersed in ethanol (Supporting Information, Figure S9 a and b). No emission was observed by the naked eye for PNC OA and PNC OABr dispersed in ethanol, and all XRD peaks (Supporting Information, Figure S9 c) of the decomposed products belong to rhombic PbBr 2 (JCPDS#31-0679). However, the PNC APTES precipitate showed high fluorescence intensity after sonication in ethanol, indicating better stability of PNC APTES in protic solvents.Long term stability tests were also conducted in different protic and polar solvents. As shown in Figure 5 a, the relative PL intensity of the PNC APTES-16 precipitate in isopropanol remained almost 70 % after 2.5 h. However, PNC precipitate showed p...
We demonstrated for the first time that Agnanoparticle-decorated SiO 2 nanospheres (NSs) may display noticeable photocatalytic activities upon surface plasmon resonance (SPR) excitation. The samples were prepared by reacting SiO 2 NSs with AgNO 3 in the seed-mediated growth process, from which the Ag particle size and decoration density can be readily controlled. The dependence of the SPR-mediated photocatalytic performance of Ag-decorated SiO 2 NSs on the Ag morphology was investigated and presented. The as-prepared Agdecorated SiO 2 NSs showed a significantly red shifted and relatively broad SPR absorption when compared with the individually dispersed Ag nanoparticles. Owing to the considerably broad SPR absorption that spanned from the visible to the near-infrared region, Ag-decorated SiO 2 NSs surpassed N-doped P-25 TiO 2 powder and individually dispersed Ag nanoparticles in photocatalytic activity, demonstrating their potential as an active photocatalyst in nearly all the current photocatalysis applications. Furthermore, the result of performance evaluation under natural sunlight shows that the present Ag-decorated SiO 2 NSs can be used as highly efficient photocatalysts that may practically harvest energy from sunlight. The current study provides a new paradigm for designing plasmonic metal nanostructures that can effectively absorb the entire solar spectrum and beyond for solar fuel generation.
Organolead bromide CH3NH3PbBr3 perovskite nanocrystals (PNCs) with green photoluminescence (PL) have been synthesized using two different aliphatic ammonium capping ligands, octylammonium bromide (OABr) and octadecylammonium bromide (ODABr), resulting in PNC–OABr and PNC–ODABr, respectively. Structural studies by X-ray diffraction (XRD) and transmission electron microscopy (TEM) determined that the PNCs exhibit cubic phase crystal structure with average particle size dependent on capping ligand (3.9 ± 1.0 nm for PNC–OABr and 6.5 ± 1.4 nm for PNC–ODABr). The exciton dynamics of PNCs were investigated using femtosecond transient absorption (TA) techniques and singular value decomposition global fitting (SVD-GF), which revealed nonradiative recombination on the picosecond time scale mediated by surface trap states for both types of PNCs. The PL lifetime of the PNCs was measured by time-resolved photoluminescence (TRPL) spectroscopy and fit with integrated SVD-GF to determine the radiative as well as nonradiative lifetimes on the nanosecond time scale. Finally, a simple model is proposed to explain the optical and dynamic properties of the PNCs with emphasis on major exciton relaxation or electron–hole recombination processes. The results indicate that the use of capping ligand OABr resulted in PNCs with a high PL quantum yield (QY) of ∼20% (vs fluorescein, 95%), which have interesting optical properties and are promising for potential applications including photovoltaics, detectors, and light-emitting diodes (LEDs).
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