Slow Photon Effect Research Articles

Probing significant light absorption enhancement of titania inverse opal films for highly exalted photocatalytic degradation of dye pollutants

The continuous titania inverse opal (TiO2-IO) films have been prepared by sol–gel infiltration method and calcined at different temperatures. The morphologies of the TiO2 inverse opal films remain unchanged under high temperature treatment. XRD patterns reveal an anatase crystalline phase between 550 and 900°C and a mixture of anatase and rutile phase at 1000°C. Comparing with the mesoporous TiO2 films obtained under the same conditions, all the TiO2 inverse opal films demonstrate a highly enhanced photocatalytic activity in photodegradation of rhodamine B (RhB) as dye pollutant model in aqueous solution. In spite of the fact that the TiO2 inverse opal films with open macroporous structures and possible light scattering effect of the wavelengths can result in the higher photocatalytic activity in the degradation of the dye pollutant, the phenomenon of the slow photon occurring in the TiO2 inverse opal photonic crystals can explain the extraordinary enhancement of the photocatalytic activity. In consequence, the TiO2-IO-700, TiO2-IO-550 and TiO2-IO-800 films show the best photocatalytic performance mainly due to the slow photon effect at the light incident angle at 0°, 20° and 45°, respectively, a direct proof of light absorption enhancement due to the slow photon effect. The slow photon effect in TiO2 inverse opals to enhance light absorption and further to enhance photocatalysis is very important for further potential applications in solar cells and other processes linked to the light absorption.

Titanium Dioxide Photonic Crystals with Enhanced Photocatalytic Activity: Matching Photonic Band Gaps of TiO2 to the Absorption Peaks of Dyes

Photonic crystals have attracted extensive interest for the potential applications in manipulating light by nontraditional ways based on photonic band structure concepts. In this paper, 3D inverse-opal TiO2 photonic crystals (TiO2-PCs) with designed photonic band gaps are prepared. It is worth noting that when the photonic band gaps of the TiO2-PCs are matched with the absorption peaks of the dyes (methyl orange, rhodamine B, and methylene blue), the photocatalytic activity of the corresponding sample is improved under simulated solar light (320 nm < λ < 800 nm) and visible light (420 nm < λ < 800 nm) irradiation. The enhancement could be attributed to the intensified dye sensitization as a result of slow photon effect on the edges of the photonic band gaps. Furthermore, the TiO2-PCs exhibit much higher photocatalytic activity and stability than TiO2 nanoparticle film. It is believed that the presence of inverse opal structure plays an essential role in affecting the dye sensitization and photoreactivity,...

High photocatalytic activity enhancement of titania inverse opal films by slow photon effect induced strong light absorption

The photonic effect on the photocatalytic activity of the continuous titania inverse opal (TiO2-IO) films differing only by the air sphere size (185 and 165 nm) and prepared by a colloid crystal template approach and annealing at different temperatures (700 and 800 °C) has been investigated by aqueous solution degradation of dye pollutants using mesoporous TiO2 thin films as the reference. The high quality of TiO2 inverse opal films has been confirmed by a blue shift of the Photonic Band Gap (PBG) with increasing light incident angle. Excellent agreement was found between theoretical and experimental reflectance spectra, confirming the photonic crystal structure of the samples. The slow photon light absorption enhancement effect inducing highly improved photocatalytic degradation of dye pollutants has been revealed in an aqueous reaction system. When compared with the mesoporous (m-TiO2) films obtained under the same conditions, all the TiO2-IO films demonstrate a much higher photocatalytic activity. At a light incident angle of 0°, the TiO2-IO-700 film (air sphere size: 185 nm) showed a better photocatalytic activity than that of TIO2-IO-800 (air sphere size: 165 nm). Most importantly, with increasing light incident angle, the photocatalytic activity of the TiO2-IO-700 film decreases whilst that of the TiO2-IO-800 film increases sharply due to the enhancement of light absorption related to a slow photon effect, generating more electron-holes. The present work revealed that photocatalytic activity can be dramatically enhanced by utilizing slow photons located at the PBG edges with energies close to the electronic bandgap of the semiconductor. The study using the slow-photon effect on the basis of photonic crystals to improve the photocatalytic activity by enhancing the light absorption could be an important future research direction. The slow-photon effect can open a new exciting avenue to all the fields related to light absorption including solar cells, optical telecommunications and optical computing.

Probing photonic effect on photocatalytic degradation of dyes based on 3D inverse opal ZnO photonic crystal

3D inverse opal ZnO photonic crystals (ZnO-PCs) with designed photonic bandgap (PBG) were prepared to study the pore size and slow photon effect on photocatalytic dye degradation. The PBGs of these ZnO-PC films were tuned experimentally by variation of the polystyrene sphere size of the opal templates. It was found that there is competition between the surface area and mass transport with increasing pore size during photocatalysis. ZnO-PCs exhibited higher photocatalytic activity under visible light irradiation, when the probe molecules were absorbed and well matched with the PBG. The enhancement could be attributed to intensified dye photosensitization as a result of the slow photon effect at the PBG edges, thus leading to a remarkable improvement in the light trapping. The present results provide useful information for developing high performance photocatalysts and photoanodes based on artificial photonic crystal design.

Hierarchical TiO2photonic crystal spheres prepared by spray drying for highly efficient photocatalysis

Hierarchical inverse opal titania photonic crystal (i-TiO2-PC) spheres have been prepared via spray drying and show highly photocatalytic capability in pollutant elimination. The hierarchical i-TiO2-PC spheres integrated a Mie scattering effect of micro-scale spheres and slow photon effect of photonic crystals with a wavelength-scale period structure, which gave birth to remarkable photocatalytic performance. In the photodegradation of methylene blue under irradiation of UV light, the rate constant of the i-TiO2-PC spheres was 1.66 times, on average, higher than that of Degussa P25.

Three‐Dimensionally Ordered Macroporous Titania with Structural and Photonic Effects for Enhanced Photocatalytic Efficiency

The three dimensional photonic crystals concept has been employed for photocatalysis. Slow photons observed in photonic crystal structures will enhance the absorption of materials when the photon energy matches the absorbance of the materials, which would improve the photocatalytic efficiency. In this work, three dimensionally ordered macroporous (3DOM) titania was prepared by applying the colloidal templating method with a range of pore diameters. Calcination at different temperatures to remove the templates resulted in different crystalline phases. The structural and photonic properties were characterized and their effects on photocatalytic activity are presented as well. A strong effect of the pore diameter on the photocatalytic activity was observed and correlated with the photon energy involved in the photodegradation process of organics. A very interesting phenomenon was also observed: the sample prepared by using PS spheres of 250 nm had a high photocatalytic efficiency, which mismatched the effect of pore diameter, probably owing to the slow photon effect.

Photoconductivity in inverse silicon opals enhanced by slow photon effect: Yet another step towards optically amplified silicon photonic crystal solar cells

While silicon photonic crystals have promised revolutionary advances in the field of optical telecommunications and optical computing, it has only recently been realized that their prowess to trap and slow photons could potentially improve the efficiency of silicon solar cells. In this work, spectral responses for the electrical properties of inverse silicon opals are evaluated and show a correlation with photonic bandgaps. In particular, a sign of the enhanced photoelectric generation by the slow photon effect is observed at the edges of photonic bandgaps.

Amplifying fluorescence sensing based on inverse opal photonic crystal toward trace TNT detection

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

Novel N−F-Codoped TiO2 Inverse Opal with a Hierarchical Meso-/Macroporous Structure: Synthesis, Characterization, and Photocatalysis

We reported a new simple route to fabricate N−F-codoped titania inverse opal (IO) films with a hierarchical meso-/macroporous structure, in which the IO structure and the N−F codoping play a role as physical and chemical modifications for titania, respectively. Both modifications are simultaneously achieved via a liquid phase deposition process using a silica colloidal crystal as a template for the first time. The average size of a mesopore in the TiO2 frameworks is 3.2 nm, and that of an interpenetrating aligned macropore is adjusted in the range of 201−315 nm. The N−F-codoped TiO2 IO films exhibit 6.6−7.4 times the methylene blue visible-light photodegradation rate comparing with N−F-codoped TiO2 films without the IO structure. This high visible-light activity was mainly ascribed to a synergetic effect of the hierarchical meso-/macroporous structure and N−F codoping. Furthermore, it was found that the multiple scattering effect of the macroporous structure is more pronounced than the slow photon effect of IOs for facilitating visible-light photocatalysis in our system from the comparison with nonperiodic macroporous N−F-codoped TiO2. The repeated cycling tests revealed that samples showed stable photocatalytic activity.