High Light Utilization Efficiency Research Articles

Characteristics of charge transport in nano-sized TiO2 particles/submicron spheres multilayer thin-film electrode

In this work, we design the nano-sized TiO2 particles/submicron spheres multilayer structured photoanode, based on the fact of stronger light scattering properties of TiO2 submicron spheres. Effect of TiO2 submicron-spheres on the charge transport and interfacial properties in multilayer thin-film electrodes are investigated in detail using intensity-modulated photocurrent spectroscopy (IMPS), electrochemical impedance spectroscopy (EIS) and incident photon-to-current conversion efficiency (IPCE). Results obtained from IMPS for dye-sensitized solar cells (DSCs) indicate that submicron-spheres have fewer defects, but the poor contact at the interfaces between submicron spheres hinders the electron transport and makes the transit time longer. EIS results show that there are no obvious differences in interface recombination between the designed electrodes. It is interesting to find that the bottom section of the photoanode composed of nano-sized TiO2 thin film has a higher light utilization efficiency than that composed of submicron-spheres; meanwhile, the Fermi level of TiO2 and the photovoltaic properties of DSCs have been extended. Our results may provide an experiment basis for structure design of high-efficiency DSC photoanode.

Photocatalytic degradation and electricity generation in a rotating disk photoelectrochemical cell over hierarchical structured BiOBr film

A double hierarchical structured BiOBr film was prepared on Ti substrate through hydrolysis of Bi2O3 film in the presence of Br− and H+. The prepared BiOBr film exhibited much better photocatalytic (PC) activity on Rhodamine B (RhB) degradation than Bi2O3 film in a rotating disk PC reactor. The double hierarchical structure could not only enhance the surface area, but also exhibited strong RhB adsorption capacity and high light utilization efficiency due to multiple reflections of incident light. Due to similar hierarchical structure, BiOCl film was also used to compare the PC activity of BiOBr film. Because the band gap energy of BiOBr (2.5eV) was narrower than that of BiOCl (3.2eV), weaker PC activity was obtained for BiOBr film under UV light. However, besides RhB photosensitization degradation, BiOBr could also be excited by part of visible light to generate •OH, resulting in a better RhB removal under visible light. A Pt cathode was further connected to BiOBr/Ti photoanode to establish a rotating disk BiOBr/Ti–Pt photoelectrochemical cell to generate electricity with the degradation of pollutants simultaneously. 0.77 and 0.74V open-circuit voltage, 0.019 and 0.010mAcm−2 short-circuit current density were obtained under UV and visible light irradiation, respectively, with 50mL5mgL−1 RhB as “fuel”. The PC activity was also improved due to the efficient separation of electrons and holes. The total current generated was stable but gradually decreased with treatment time due to the consumption of “fuel”.

Microcavity-enhanced light-trapping for highly efficient organic parallel tandem solar cells.

A high-performance parallel tandem solar cell employing ultra-thin Ag as the intermediate anode is demonstrated, which comprises a semitransparent front sub-cell and a microcavity assisted back sub-cell. In addition to the extended optical field as a result of the tandem architecture, the prominent microcavity resonance formed in the back sub-cell enables such a parallel tandem configuration to possess high light utilization efficiency (the peak EQE value is over 80%) and a high photovoltaic performance of 9.2%. This study establishes an effective architecture that can be generally applicable to all organic materials for improving their performance.

Fabrication of H3PW12O40-doped carbon nitride nanotubes by one-step hydrothermal treatment strategy and their efficient visible-light photocatalytic activity toward representative aqueous persistent organic pollutants degradation

A series of H3PW12O40-doped carbon nitride nanotubes (H3PW12O40/C3N4 NTs) are prepared using one-step hydrothermal treatment, with g-C3N4 and H3PW12O40 as precursors. The morphology, porosity, phase, chemical structure, and optical and electronic properties of H3PW12O40/C3N4 NTs are characterized. Subsequently, the photocatalytic activity of H3PW12O40/C3N4 NTs is evaluated through the degradation of representative aqueous persistent organic pollutants methyl orange and diethyl phthalate under visible-light (λ>420nm) irradiation. The photocatalytic activity of H3PW12O40/C3N4 NTs is significantly enhanced compared with g-C3N4 as a result of its unique tubular nanostructure, enhanced quantum efficiency, and high light utilization efficiency. Finally, the reusability of H3PW12O40/C3N4 NTs is evaluated under four consecutive photocatalytic runs.

Dynamics of fluid and light intensity in mechanically stirred photobioreactor

Turbulent flows in a single-stage and a two-stage impeller-stirred photobioreactor with a simple geometric configuration were analyzed using computational fluid dynamics. The trajectories of the microorganisms entrained in the flow field were traced by the particle tracking method. By projecting these trajectories onto a radial–axial (r−z) plane with a given azimuth angle, we were able to observe four different dynamics zones: circulation, pure rotation, trap, and slow-motion. Within the pure rotation zone, turbulence can be observed near the edges of the impeller. The light intensity and the light/dark cycles subjected by the microorganisms differ significantly in these zones. These differences can be further changed by providing different incident light illuminations on the reactor surface. The dynamics zones can be altered by modifying the geometric configuration of the reactor and the impeller stirring mechanism. In combination with the utilization of different incident light illuminations, the light intensity dynamics and the light/dark cycles subjected by the microorganisms can be controlled such that an optimal photobioreactor design with a high efficiency of light utilization and a high formation rate of the biochemical products can be realized.

Sensitivity of Peatland Herbaceous Vegetation to Vapor Pressure Deficit Influences Net Ecosystem CO2 Exchange

Mountain peatlands in the temperate regions represent a small proportion of the global peatland resource, but play a unique, although less recognized role in the regional water and biogeochemical cycles. We conducted leaf and ecosystem CO2 exchange measurements during the growing period of 2008 to investigate the effects of vapor pressure deficit (VPD) and ground water level (WL) on leaf gas exchange of two dominant herbaceous species, Molinia caerulea (L.) and Carex nigra (L.) in a mountain peatland. Implications of the leaf-level responses for net ecosystem CO2 exchange (NEE) were examined. Fluctuations in WL influenced soil water content (SWC) within the top 5 cm of the peat profile. Although midday leaf water potential during the day (Ψmd) was positively correlated (P 1 kPa regardless of the current WL status. Stomatal conductance was positively correlated with leaf assimilation (A) and root-shoot hydraulic conductance (Ks-l). A decline in NEE during summer was attributed to stomatal closure due to high VPD and low light utilization efficiency (α) of the vegetation. Ecosystem respiration (Reco) was positively correlated with peat temperature at 10 cm depth. Our results suggest that increases in VPD, as a possible scenario of climate change, would lower the photosynthetic capacity of the herbaceous peatland vegetation, despite the high WL, and hence lower the potential of such peatlands as sinks for atmospheric CO2.

Analysis of Vertical Distributions of Chlorophyll Fluorescence Parameter (Fv/Fm), SPAD Value and Chlorophyll Concentrations within Tomato Plant Canopy in a Large-scale Greenhouse

In our previous study, it has been proved that photosynthetic abilities in leaves, e.g. maximum net photosynthetic rate, decreases with depth from the top of the year-round cultured tomato plant canopy in a large-scale greenhouse. In this study, we assessed the distribution of photosynthetic abilities within tomato plant canopy by measuring chlorophyll fluorescence parameter (Fv/Fm), SPAD value and chlorophyll concentrations and then investigated the relationships among these parameters. Maximum net photosynthetic rates in leaves within middle and lower layers decreased to half and seventh parts of that within upper layer, respectively. Fv/Fm significantly increased with depth in the canopy, however, SPAD value and chlorophyll a/b ratio significantly decreased with depth in the canopy. Low chlorophyll a/b ratio and high Fv/Fm in leaves within the lower layer suggested that these leaves acclimated to the low light condition and had high light-utilization efficiency for photosynthesis. These results indicated that the decreases in the photosynthetic abilities in leaves with depth in the tomato plant canopy are caused by the low-light acclimation. Furthermore, the correlations between chlorophyll a/b ratio and Fv/Fm, and SPAD value were observed. This result suggested that the measurements of Fv/Fm and SPAD value can be used as a rapid and concise tool to assess the photosynthetic abilities in leaves within tomato plant canopies.

Computer-generated holographic diffuser for color mixing

An iterative algorithm for multiple incoming wavelengths is proposed to design a computer-generated holographic diffuser with the features of high light utilization efficiency and uniform color mixing. The amplitude transmittance of this computer-generated holographic diffuser is constant, while the phase transmittance consists of multiple phase levels. This diffuser is designed according to the Fraunhofer diffraction theory and can uniformly spread the different input light at the same time. The simulation results show that over 88% average far field amplitude transmission efficiency is achieved for each input light and the output uniformity is within 12.4%.

Competition for light between velvetleaf (Abutilon theophrasti) and soybean (Glycine max)

Summary:We examined factors affecting conversion of light into dry matter of velvetleaf (Abutilon theophrasti) and soybean (Glycine max) grown in a replacement series near Ames, Iowa, U.S.A. in 1986 and 1987. Velvetleaf was taller than soybean over most of the growing season and had more branches, especially at the top of the canopy. Velvetleaf had greater light interception than soybean in the upper part of the canopy, particularly early and late in the day, although total light interception by canopies of the two species was similar on most sample dates. Velvetleaf had higher light utilization efficiency, or conversion of intercepted light into dry matter, in the middle and later part of the growing season. This combination of traits appears to give velvetleaf an advantage over soybean in competition for light.

Regulatory Effect of pH and Incident Irradiance on the Levels of Nitrogenase Activity in the Cyanobacterium Nostoc UAM 205

Summary Physiological response of Nostoc UAM 205 to the combined influence of pH and light intensity was examined. Increase in light intensity from 10 to 100μE · m−2 · s−1 had no stimulatory affect on growth rates of cultures grown at pHs 6 and 7, but enhanced growth at alkaline pH. Chlorophyll concentration of cells grown at alkaline pH was higher than that of cells grown at pHs 6 and 7. Chlorophyll concentration decreased with increasing light intensity. The light-saturated photosynthetic rate normalized to chlorophyll was slightly higher in cells grown at high light intensity than in cells grown at low light intensity. The photosynthetic rate did not change with pH. Major physiological changes in response to variations in external pH and irradiance were observed in nitrogenase activity. Optimal rates of nitrogenase activity were found at alkaline pH. Nitrogenase activity showed a negative correlation with the irradiance at which cultures were grown. Cells grown at low light intensity showed a higher maximal rate of dinitrogen fixation and a higher light utilization efficiency than cells grown at high light intensity. These results suggested a special role of light in regulating nitrogenase activity in cyanobacteria.

Light responses of a scleractinian coral (Plerogyra sinuosa)

During daytime Plerogyra sinuosa Dana displays globular expandable tentacles (“bubbles”) which foster the photosynthetic ability of the coral. Adaptational responses of this coral to different depths (5–25 m) and light conditions were investigated by photosynthetic pigment analysis, insitu measurements of oxygen production, transplantation and shading experiments. Pigment concentrations per unit tissue dry weight were variable, but unrelated to depth. Pigment concentrations per zooxanthellae cell remained constant and bubble size increased with depth. Light intensity at 25 m was 20 to 25% of the 5-m value, but daily integrated rates of photosynthesis were 65% of the 5-m rates, indicating a higher light utilization efficiency in deeper corals. Coral heads transplanted from 25 to 5 m died within 20 d if not protected against UV-radiation, but corals transplanted from 5 to 25 m acclimatized to the new light condition. Photosynthetic oxygen production and bubble size increased in shaded, sun-adapted corals within 60 min and decreased in sun-exposed, shade-adapted corals. The variable bubble size is interpreted as an adaptational mechanism to optimize light exposure of zooxanthellae.