Bipolarized intrinsic faradaic layer on a semiconductor surface under illumination.

Interface charge transfer plays a key role in the performance of semiconductors for different kinds of solar energy utilization, such as photocatalysis, photoelectrocatalysis, photochromism and photo-induced superhydrophilicity. In previous studies, different mechanisms have been used to understand interface charge transfer processes. However, the charge transfer mechanism at the solid/liquid interface remains a controversial topic. Here, taking TiO2 as a model, we find and prove, via experiments, the new characteristic of photo-induced bipolarity of the surface layer (reduction faradaic layer and oxidation faradaic layer) on a semiconductor for the first time. Different from energy level positions in the classic surface states transfer mechanism, the potential window of a surface faradaic layer is located out of the forbidden band. Moreover, we find that the reduction faradaic layer and oxidation faradaic layer serve as electron and hole transfer mediators in photocatalysis, while the bipolarity or mono-polarity of the surface layer on a semiconductor depends on the applied potential in photoelectrocatalysis. The new characteristic of bipolarity can also offer new insights into the charge transfer process at the semiconductor/liquid interface for solar energy utilization.

Nutrient Deprivation Coupled with High Light Exposure for Bioactive Chrysolaminarin Production in the Marine Microalga Isochrysis zhangjiangensis.

Chrysolaminarin, a kind of water-soluble bioactive ß-glucan produced by certain microalgae, is a potential candidate for food/pharmaceutical applications. This study identified a marine microalga Isochrysis zhangjiangensis, in which chrysolaminarin production was investigated via nutrient (nitrogen, phosphorus, or sulfur) deprivations (-N, -P, or -S conditions) along with an increase in light intensity. A characterization of the antioxidant activities of the chrysolaminarin produced under each condition was also conducted. The results showed that nutrient deprivation caused a significant increase in chrysolaminarin accumulation, though this was accompanied by diminished biomass production and photosynthetic activity. -S was the best strategy to induce chrysolaminarin accumulation. An increase in light intensity from 80 (LL) to 150 (HL) µE·m-2·s-1 further enhanced chrysolaminarin production. Compared with -N, -S caused more suitable stress and reduced carbon allocation toward neutral lipid production, which enabled a higher chrysolaminarin accumulation capacity. The highest chrysolaminarin content and concentration reached 41.7% of dry weight (%DW) and 632.2 mg/L, respectively, under HL-S, with a corresponding productivity of 155.1 mg/L/day achieved, which exceeds most of the photoautotrophic microalgae previously reported. The chrysolaminarin produced under HL-N (Iz-N) had a relatively competitive hydroxyl radical scavenging activity at low concentrations, while the chrysolaminarin produced under HL-S (Iz-S) exhibited an overall better activity, comparable to the commercial yeast ß-glucan, demonstrating I. zhangjiangensis as a promising bioactive chrysolaminarin producer from CO2.

Photovoltage memory effect in a portable Faradaic junction solar rechargeable device.

Two-electrode solar rechargeable device is one of the promising technologies to address the problem of solar energy storage in large scale. However, the mechanism of dark output voltage remains unclear and the low volumetric energy density also limits its practical applications. Herein, we report that a Si/CoOx/KBi(aq)/MnOx Faradaic junction device exhibits a photovoltage memory effect, that is, the dark output voltage can precisely record the value of the photovoltage in the device. To investigate the mechanism of the effect, we develop an open circuit potential method to real-time monitor the photo charge and dark discharge processes in the Faradaic junction device. This effect leads to minimized interface energy loss in the Faradaic junction device, which achieves much higher performances than the devices without the effect. Moreover, we realize a portable device with a record value of the dark volumetric energy density (∼1.89 mJ cm-3) among all reported two-electrode solar rechargeable devices. These results offer guidance to improve the performance of a solar rechargeable device and design other photoelectric devices for new applications.

Enhanced photoelectrochemical activity of α-Fe2O3/TiO2 nanoheterojunction by controlling hydrodynamic conditions.

Interfacial heterostructuring has appeared to be an efficient strategy to address the efficiency and applicability of the photocatalysts in solar energy conversion. Herein, we developed one-dimensional (1D) α-Fe2O3/TiO2 nanoheterojunction arrays for enhanced photoelectrochemical (PEC) activity. α-Fe2O3 nanotubes were firstly prepared via anodization under controlled hydrodynamic conditions to increase the efficiency. 1D α-Fe2O3/TiO2 nanoheterojunction arrays were then prepared through a hydrothermal treatment and a subsequent annealing process. A controlled anodization by modulating the hydrodynamic conditions, added a fine coating of TiO2 overlayer, to finally give an optimized composition and geometry for improved light absorption and spatial charge separation efficiency. Consequently, the optimized α-Fe2O3 generated a photocurrent of 0.07 mA cm-2 (3.5 times higher than that of pristine α-Fe2O3), and the as-obtained α-Fe2O3/TiO2 nanoheterojunction exhibited a photocurrent intensity of 0.12 mA cm-2 (about 6 times higher than that of pristine α-Fe2O3). A long-term stability can also be ensured. The well-controlled architectures provides a guideline for synthesis of advanced nanomaterials.

Facile synthesis of bimodal macroporous g-C3N4/SnO2 nanohybrids with enhanced photocatalytic activity.

It is of vital importance to construct highly interconnected, macroporous photocatalyst to improve its efficiency and applicability in solar energy conversion and environment remediation. Graphitic-like C3N4 (g-C3N4), as an analogy to two-dimensional (2D) graphene, is highly identified as a visible-light-responsive polymeric semiconductor. Moreover, the feasibility of g-C3N4 in making porous structures has been well established. However, the preparation of macroporous g-C3N4 with abundant porous networks and exposure surface, still constitutes a difficulty. To solve it, we report a first facile preparation of bimodal macroporous g-C3N4 hybrids with abundant in-plane holes, which is simply enabled by in-situ modification through thermally treating the mixture of thiourea and SnCl4 (pore modifier) after rotary evaporation. For one hand, the formed in-plane macropores endow the g-C3N4 system with plentiful active sites and short, cross-plane diffusion channels that can greatly speed up mass transport and transfer. For another, the heterojunctions founded between g-C3N4 and SnO2 consolidate the electron transfer reaction to greatly reduce the recombination probability. As a consequence, the resulted macroporous g-C3N4/SnO2 nanohybrid had a high specific surface area (SSA) of 44.3 m2/g that was quite comparable to most nano/mesoporous g-C3N4 reported. The interconnected porous network also rendered a highly intensified light absorption by strengthening the light penetration. Together with the improved mass transport and electron transfer, the macroporous g-C3N4/SnO2 hybrid exhibited about 2.4-fold increment in the photoactivity compared with pure g-C3N4. Additionally, the recyclability of such hybrid could be guaranteed after eight successive uses.

An ultrasensitive electrochemical immunosensor for Cry1Ab based on phage displayed peptides.

The rapid and widespread adoption of Bacillus thuringiensis (Bt) proteins in genetically modified (GM) crops has raised concerns about the impact of GM crops on environment and food safety. A sensitive and specific method for detecting Bt proteins in GM crops is of great significance for environment and food risk assessment. In this study, using Cry1Ab as a model Bt protein, an ultrasensitive electrochemical immunosensor for Cry1Ab protein has been developed based on phage displayed peptide. Phage displayed peptides against Cry1Ab protein were obtained from a phage displayed peptide library without animal immunization process through biopanning-elution strategy. After modification of electrode with gold nanoparticles, selected phage displayed peptide was applied to electrochemical immunosensor for Cry1Ab. Under the optimized conditions, the peptide-based immunosensor showed a dynamic range of 0.01-100ng/mL and a limit detection of 7pg/mL. Specific measurement of this established method was conducted by testing cross-reactivity of Cry1Ac (88% amino acid sequence homology to Cry1Ab protein), and the result showed that peptide-based immunosensor has negligible cross-reactivity with analogue. In addition, the accuracy and reproducibility of this established immunosensor was evaluated by testing the recovery of spiked samples and assay coefficients of variation, respectively. The results showed that the average recovery of corn and wheat sample was 90-120% and 86.7-120%, respectively; the intra-assay coefficient of variation was 7.4% (n = 6), and the inter-assay coefficient of variation was 6.9% (n = 6) at 1ng/mL Cry1Ab solution. Furthermore, the novel concept of peptide-based immunosensor may provide a potential application in general method for the ultrasensitive detection of various Bt proteins.

Phage-Mediated Immuno-PCR for Ultrasensitive Detection of Cry1Ac Protein Based on Nanobody.

The widespread use of Cry proteins in transgenic plants for insect control has raised concerns about the environment and food safety in the public. An effective detection method for introduced Cry proteins is of significance for environmental risk assessment and product quality control. This paper describes a novel phage mediated immuno-PCR (iPCR) for the ultrasensitive determination of Cry proteins based on nanobodies. Three nanobodies against Cry1Ac protein were obtained from a naïve phage displayed nanobody library without animal immunization process and were applied to the iPCR assay for Cry1Ac. The phage-mediated iPCR for Cry1Ac based on nanobodies showed a dynamic range of 0.001-100 ng/mL and a limit detection of 0.1 pg/mL. Specific measurement of this established method was performed by testing cross-reativity of other Cry1Ac analogues, and the result showed negligible cross-reactivity with other test Cry proteins (Cry1Ab, Cry1F, Cry3B). Furthermore, the phage-mediated iPCR based on nanobody should be easily applicable to the detection of many other Cry proteins.