Panpan Sun

Superhydrophobic and Ultraviolet-Blocking Cotton Textiles

Cotton textile was coated with ZnO@SiO(2) nanorods in order to obtain superhydrophobic and ultraviolet (UV)-blocking properties. The coating process was conducted in mild conditions, which involved the low-temperature preparation of ZnO seeds, hydrothermal growth of ZnO nanorods, bioinspired layer-by-layer deposition of a SiO(2) shell on the surface of ZnO nanorods, and hydrophobic modification of ZnO@SiO(2) nanorods with octadecyltrimethoxysilane. Despite the highly curved morphology of cotton fibers, the ZnO@SiO(2) nanorods coated the textile densely and uniformly. The treated cotton textile was found to have a large UV protection factor (UPF = 101.51) together with UV-durable superhydrophobicity, as determined by contact-angle measurement under long-term UV irradiation. The good UV-blocking property can be ascribed to the high UV absorbance and scattering properties of ZnO nanorods, and the UV-durable superhydrophobicity is a result of suppression of the photoactivity of ZnO nanorods by a SiO(2) shell.

Growth of single-crystalline rutile TiO2 nanowire array on titanate nanosheet film for dye-sensitized solar cells

A titanate nanosheet (TN) film is employed as a seed layer for the hydrothermal growth of a single-crystalline rutile TiO2 nanowire array on SnO2:F (FTO) conductive glass for dye-sensitized solar cell (DSSC) applications. TiO2 nanowires grown on a TN film appear to be thinner, more uniform, and well separated from each other, compared with those grown directly on FTO conductive glass. Besides FTO conductive glass, TiO2 nanowires can also be grown on silicon wafers and glass slides when a TN film is involved. Scanning electron microscope observations showed that the TN film underwent surface coarsening and thinning during the nucleation and growth of the TiO2 nanowires, suggesting that the film may act as a sacrificial seed layer. When applied in a DSSC, the nanowire photoanode with a TN film involved is significantly superior to that without the film in terms of all cell parameters, and gave an overall solar energy conversion efficiency of over 3% under AM 1.5G solar irradiation, about 3.4 times greater than that without the TN film. The combination of increased dye loading amount and reduced charge recombination at the FTO glass/electrolyte interface due to the involvement of the TN film should contribute to the significant improvement in cell performance.

Rutile TiO2 nanowires on anatase TiO2 nanofibers: A branched heterostructured photocatalysts via interface-assisted fabrication approach

A water-dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO(2) nanowires (NWs) on electrospun anatase TiO(2) nanofibers (NFs), using highly reactive TiCl(4) as precursor. The water-dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water-dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO(2) heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase-rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures.

Rutile TiO2 nanowire array infiltrated with anatase nanoparticles as photoanode for dye-sensitized solar cells: enhanced cell performance via the rutile–anatase heterojunction

The structural and interfacial design of TiO2 photoanodes plays an important role in improving the solar energy conversion performance of dye-sensitized solar cells (DSSCs). Herein, we report that a rutile nanowire (NW) array infiltrated with anatase nanoparticles (NPs) can combine the advantages of the one dimensional electron transportation and light scattering of a NW array and the large dye-loading capacity of NPs, due to the presence of a rutile–anatase heterojunction. The dye-sensitized NW–NP composite film (1.4 μm thick) with a roughness factor of ∼114.7 displays a significantly improved light harvesting ability than a NW array (roughness factor ∼28.2), as manifested by diffuse transmittance and reflection spectra, and even higher light harvesting than a NP film (1.5 μm thick) with a roughness of ∼414.7. Moreover, the dye-sensitized NW–NP composite film shows slower charge recombination kinetics than both the NW array and NP film, as measured by open-circuit photovoltage decay and transient absorption spectroscopy. As a result, the dye-sensitized TiO2 NW–NP composite photoanode exhibits 2.2 times and 1.5 times higher overall efficiency than NW array and NP film photoanodes, respectively, under AM 1.5G simulated solar irradiation, demonstrating the synergistic effect of rutile NW and anatase NP for photoelectrochemical solar energy conversion.

Enhanced electrochromic properties of a TiO2 nanowire array via decoration with anatase nanoparticles

Construction of a micro-/nanostructured TiO2 film has been considered to be an important way to enhance the electrochemical properties and electrochromic performance of the material. Herein, we investigated the electrochromic properties of a nanocomposite TiO2 film prepared by decorating rutile a TiO2 nanowire (TiO2 NW) array with anatase TiO2 nanoparticles (TiO2 NPs) via a facile two-step synthesis method. Owing to its large active surface area and high transparency, the TiO2 NW–NP composite film supported a greater number of sites for Li+ ion intercalation and extraction. As a result, the TiO2 NW–NP film displayed higher optical contrast, coloration efficiency and transient current density compared with NW and NP films, demonstrating that enhanced electrochromic properties could be achieved using the NW–NP composite structure.

Synthesis of porous Al doped ZnO nanosheets with high adsorption and photodecolorizative activity and the key role of Al doping for methyl orange removal

Porous Al doped ZnO (AZO) nanosheets have been prepared as an efficient multifunctional water treatment material. Their fundamental properties were characterized by various spectroscopic testing methods. The AZO nanosheets displayed very rapid adsorption rate and high adsorption capacity for methyl orange (MO) dye. The kinetics and equilibrium of adsorption process were found to follow the pseudo-second-order kinetic and Langmuir isotherm models, respectively. Furthermore, the AZO nanosheets exhibited superior photodecolorizative activity compared with the commercial P25 TiO2 nanoparticles. It was found that Al doping increased the zeta potential of AZO nanosheets and then significantly enhanced the adsorption capacity for MO dye and, at the same time, retarded the recombination of photoexcited electron–hole pairs, and prolonged the lifetime of the photo-generated carriers, and then improved the semiconductor photocatalytic activity. In addition, the visible-light-driven dye photosensitized degradation was also an important reason for enhanced photodecolorizative activity. Therefore, AZO nanosheets are a potential multifunctional water treatment material combining highly efficient adsorption and photocatalytic degradation.

Bilayer TiO2 photoanode consisting of a nanowire–nanoparticle bottom layer and a spherical voids scattering layer for dye-sensitized solar cells

The structural design of TiO2 photoanodes has proved to be a useful approach in improving the energy conversion efficiency of dye-sensitized solar cells (DSSCs). Herein, a bilayer TiO2 photoanode consisting of rutile nanowires (NWs) infiltrated with anatase nanoparticles (NPs) as a bottom layer and spherical voids (450 nm) in a NP film as the top layer is prepared via a simple one-time spray technique on a 1D TiO2 NW array. The bilayer structure exhibits an excellent dye-loading property and efficient light scattering ability, as confirmed by dye-desorption, diffuse transmittance and reflectance spectra, and incident-photon-to-current conversion efficiency (IPCE) results. As a result, the DSSC based on the bilayer photoanode ((1.6 + 2.6) μm) exhibits remarkably higher photocurrent output and overall energy conversion efficiency (3.2 times and 3.5 times higher, respectively) than a 1D TiO2 NW device (1.6 μm) under AM 1.5G simulated solar irradiation. The enhanced device performance can be ascribed to the synergistic effect of a large surface area for sufficient dye-loading, efficient light scattering for sufficient light harvesting, fast charge transport for efficient charge collection and a highly porous structure of the top spherical voids layer for fast diffusion of the I−/I3− electrolyte in the bilayer TiO2 photoanode. This study provides a facile route towards improving the photovoltaic performance of 1D TiO2 NW array solar cells based on constructing bilayer structures via a simple one-time spray technique.

Vacuum heat treated titanate nanotubes for visible-light photocatalysis

Visible light-active TiO2(B)/anatase heterojunction nanotubes (NTs) are prepared via a process combining a two-step alkaline hydrothermal technique, ion exchange and heat treatment in a vacuum. The TiO2 NTs inherit the skeleton structural features of NT precursors and thereby lead to the formation of NTs with good crystallinity and large surface area (298 m2 g−1 at 350 °C and 279 m2 g−1 at 400 °C). UV-vis diffuse reflectance and PL measurements confirm the distinct visible light absorption due to bandgap defect states introduced by vacuum treatment. Heat treatment in a vacuum at 350 °C and 400 °C induces the formation of TiO2(B)/anatase heterostructure in the TiO2 NTs as confirmed by HRTEM results. As a result, visible light photocatalytic tests demonstrate that TiO2 NTs vacuum treated at 350 °C and 400 °C exhibit significantly better photocatalytic activity for acetaldehyde degradation and CO2 generation in comparison with commercial Degussa P25 nanoparticles. The high photocatalytic activity can be ascribed to the synergistic effect of high surface area, good crystallinity and efficient charge separation promoted by the TiO2(B)/anatase heterojunction. This study provides an effective approach in improving the visible light photocatalytic activity of TiO2 nanostructures based on the introduction of native bandgap defects and heterostructure via vacuum heat treatment.

Efficiency enhanced rutile TiO2 nanowire solar cells based on an Sb2S3 absorber and a CuI hole conductor

Despite the excellent photo-generated charge separation and transport properties of the 1D rutile TiO2 nanowire (NW) array, insufficient light harvesting due to a low surface area is a key factor that limits the photovoltaic performance of TiO2 NW-based solar cells. Herein, we apply the Sb2S3 semiconductor as a light absorber and sprayed p-CuI as a hole conductor for TiO2 NW solar cells. The Sb2S3-sensitized device displays significantly improved light absorption compared to its corresponding dye-sensitized device, with a peak incident-photon-to-current conversion efficiency (IPCE) of 64%. Moreover, CuI film deposited by the spray technique enables improved pore filling and better electrical contact between the Sb2S3 absorber and CuI, as well as CuI crystals themselves, and facilitates hole transfer from Sb2S3 to CuI crystals and hole transportation in the CuI layer. As a result, the TiO2 NW/Sb2S3/CuI-spray/Au device exhibits an overall power conversion efficiency of 1.18% under AM 1.5G simulated solar irradiation, which is about 2.88 times and 2.11 times higher than TiO2 NW/N719/CuI-spray/Au and TiO2 NW/Sb2S3/CuI-drop coating/Au devices, respectively. This study thus demonstrates the superiority of the Sb2S3 sensitizer for TiO2 NW solar cells and the spray technique for the preparation of the p-CuI hole conductor.