Phenyl-incorporated carbon nitride photocatalyst with extended visible-light-absorption for enhanced hydrogen production from water splitting.

Developing and employing photocatalysts with extended visible-light-absorption has emerged as a fundamental issue for the enhanced capability of photocatalytic H2 evolution from water splitting. Herein, a wide-spectrum light-responsive phenyl-grafted carbon nitride photocatalyst was synthesized. It was found that benzonquanmine-derived g-C3N4 (BCN) exhibits significantly extended light absorption (∼670 nm) compared with conventional melamine-derived g-C3N4 (MCN). Correspondingly, the photocatalytic H2-evolution rate of BCN (2846 µmol h-1 g-1) is five times as that of MCN under visible-light irradiation. Particularly, an impressive H2-evolution rate of 58 µmol h-1 g-1 could be achieved on BCN even under light irradiation beyond 620 nm. The outstanding photocatalytic H2-evolution performance could be not only attributed to the enriched photons generated from the enhanced solar energy harvesting, but also to the distinctly inhibited rapid recombination of photogenerated electron-hole pairs resulting from the incorporation of phenyl groups. This work furnishes a new train of thought for the designing of carbon-nitride-based photocatalysts with enhanced capability of visible-light-utilization.

Bridging regulation in graphitic carbon nitride for band-structure modulation and directional charge transfer towards efficient H2 evolution under visible-light irradiation.

The bridging N atom in g-C3N4 structure plays a decisive role in photo-generated charge transfer because it usually confines photo-generated electrons and holes in each heptazine, thus leading to severe recombination. In this work, a kind of 2-aminoterephthalic acid-derived benzene ring group with rich π-electrons was considered to integrate with bridging N to break the above-mentioned confining effect. On the basis of density-functional theory calculations and experimental analysis, this 2-aminoterephthalic acid-derived bridging structure facilitated to draw photo-generated charge out of heptazine unit, and its polarized asymmetric structure promoted the directional transfer of photo-generated charge carriers across adjacent heptazines, thus efficiently reducing the recombination. Meanwhile, the 2-aminoterephthalic acid-derived bridging structure also reinforced the connectivity of heptazine units in g-C3N4 framework and led to high degree of polymerization, which thus extended the π-conjugated electronic system of g-C3N4 and modulated the band structure favoring photocatalytic hydrogen production. Consequently, a high photocatalytic H2-production activity of 24,595 µmol h-1 gcat-1 was achieved on the bridging regulated g-C3N4 under visible light, with an apparent quantum yield of 48.7% at 425 nm.

Physicochemical impact of bioactive terpenes on the microalgae biomass structural characteristics.

This study aimed to evaluate the functionality of bioactive terpenes on Spirulina (Arthrospira platensis; AP) and Chlorella (Chlorella vulgaris; CV) biomasses. The two microalgae species were treated with 0.01%, 0.05%, and 0.1% of thymol (THY), trans-cinnamaldehyde (TC), menthol (MEN), and vanillin (VAN). Raman micro-spectroscopy (RMS) was correlated with other physicochemical methods to confirm their functional mechanisms. In results, THY (0.1%) decreased (P < 0.05) RMS intensity at 1196 cm-1 that represents the protein's secondary amines wavenumber. Also, VAN (0.1%) decreased significantly A. platensis α-helix to 16.60 ± 0.52% compared to the control with 19.83 ± 0.32%. While, 0.1% TC increased (P < 0.05) the viscosity to 2.52 ± 0.61 Pa.s. This work demonstrated that terpenes could differently affect the physicochemical structure of microalgae biomass. The RMS's uniqueness comes from its ability to evaluate the functionality of terpenes during microalgae cultivation. Besides, chemometrics led to focus on the most important variances.

Quantitative visualization of photosynthetic pigments in tea leaves based on Raman spectroscopy and calibration model transfer.

BACKGROUND: Photosynthetic pigments participating in the absorption, transformation and transfer of light energy play a very important role in plant growth. While, the spatial distribution of foliar pigments is an important indicator of environmental stress, such as pests, diseases and heavy metal stress. RESULTS: In this paper, in situ quantitative visualization of chlorophyll and carotenoid was realized by combining the Raman spectroscopy with calibration model transfer, and a laboratory Raman spectral model was successfully extended to a portable field spectral measurement. Firstly, a nondestructive and fast model for determination of chlorophyll and carotenoid in tea leaf was established based on confocal micro-Raman spectrometer in the laboratory. Then the spectral model was extended to a real-time foliar map scanning spectra of a field portable Raman spectrometer through calibration model transfer, and the spectral variation between the confocal micro-Raman spectrometer in the laboratory and the portable Raman spectrometer were effectively corrected by the direct standardization (DS) algorithm. The portable map scanning Raman spectra of the tea leaves after the model transfer were got into the established quantitative determination model to predict the concentration of photosynthetic pigments at each pixel of the tea leaves. The predicted photosynthetic pigments concentration of each pixel was imaged to illustrate the distribution map of foliar pigments. Statistical analysis showed that the predicted pigment contents were highly correlated with the real contents. CONCLUSIONS: It can be concluded that the Raman spectroscopy was applicable for in situ, non-destructive and rapid quantitative detecting and imaging of photosynthetic pigment concentration in tea leaves, and the spectral detection model established based on the laboratory Raman spectrometer can be applied to a portable field spectrometer for quantitatively imaging of the foliar pigments.

Integrated Z-Scheme Nanosystem Based on Metal Sulfide Nanorods for Efficient Photocatalytic Pure Water Splitting.

Developing efficient metal sulfides for pure water splitting is a challenging topic in the field of photocatalysis. Herein, inspired by natural photosynthesis, an all-solid-state Z-scheme photocatalyst was constructed with Cd0.9 Zn0.1 S (CZS) for water reduction, red phosphorus (RP) for water oxidation, and metallic CoP as the electron mediator. RP@CoP core-shell nanostructures were uniformly attached on the CZS nanorods, which gave rise to multiple monodispersed nanojunctions. The integrated Z-scheme nanosystem exhibited an apparent quantum efficiency of 6.4 % at 420 nm for pure water splitting. Theoretical analysis and femtosecond transient absorption results revealed that the impressive performance was mainly due to efficient hole transfer of CZS, resulting from the intimate atomic contacts between CoP mediator and photocatalysts, together with favorable band alignment. Meanwhile, the multiple monodispersed Z-scheme nanojunctions could provide abundant reaction sites, which was also important for the boosted activity.

Photoinduced Superhydrophilicity of Anatase TiO2 Surface Uncovered by First-Principles Molecular Dynamics.

TiO2 is a prototype of photocatalyst materials. Interfacial water structure is critical to understand the chemical reactivity of TiO2. By performing first-principles molecular dynamics simulations on the TiO2(001)/water interface were performed, we found that the presence of a photogenerated hole at the interface increases the coverage of both the molecular and dissociative water adsorption by increasing the surface acidity and then shapes the layered and ordered water structure by enhancing the interfacial hydrogen bond network. The enhanced attachment of water in contact with the TiO2 surface rationalizes the increase in the intensity of the sum frequency generation spectrum under ultraviolet illumination reported in the experiment. These findings provide a novel interpretation of the electronic effect for the photoinduced hydrophilic conversion of the TiO2 surface at the atomistic level.

First-Principles Investigation of ß-FeOOH for Hydrogen Evolution: Identifying Reactive Sites and Boosting Surface Reactions.

Akaganeite (ß-FeOOH) is a widely investigated candidate for photo(electro)catalysis, such as water splitting. Nevertheless, insights into understanding the surface reaction between water and ß-FeOOH, in particular, the hydrogen evolution reaction (HER), are still insufficient. Herein, a set of first-principles calculations on pristine ß-FeOOH and halogen-substituted ß-FeOOH are applied to evaluate the HER performance through the computational hydrogen electrode model. The results show that the HER on ß-FeOOH tends to occur at Fe sites on the (010) surface, and palladium and nickel are found to serve as excellent co-catalysts to boost the HER process, due to the remarkably reduced free energy change of hydrogen adsorption upon loading on the surface of ß-FeOOH, demonstrating great potential for efficient water splitting.

A self-doping strategy to improve the photoelectrochemical performance of Cu2ZnSnS4 nanocrystal films for water splitting.

A series of self-doped Cu2ZnSnS4 (CZTS) nanocrystal films with Sn ions partially replaced by Zn ions were prepared from their colloidal solutions by electrophoretic deposition. The self-doped CZTS photocathodes yielded higher photocurrents than the pristine one, which was ascribed to the upper shift in the conduction band and the formation of a shallow defect level.

Nondestructive Determination of Diastase Activity of Honey Based on Visible and Near-Infrared Spectroscopy.

The activities of enzymes are the basis of evaluating the quality of honey. Beekeepers usually use concentrators to process natural honey into concentrated honey by concentrating it under high temperatures. Active enzymes are very sensitive to high temperatures and will lose their activity when they exceed a certain temperature. The objective of this work is to study the kinetic mechanism of the temperature effect on diastase activity and to develop a nondestructive approach for quick determination of the diastase activity of honey through a heating process based on visible and near-infrared (Vis/NIR) spectroscopy. A total of 110 samples, including three species of botanical origin, were used for this study. To explore the kinetic mechanism of diastase activity under high temperatures, the honey of three kinds of botanical origins were processed with thermal treatment to obtain a variety of diastase activity. Diastase activity represented with diastase number (DN) was measured according to the national standard method. The results showed that the diastase activity decreased with the increase of temperature and heating time, and the sensitivity of acacia and longan to temperature was higher than linen. The optimum temperature for production and processing is 60 °C. Unsupervised clustering analysis was adopted to detect spectral characteristics of these honeys, indicating that different botanical origins of honeys can be distinguished in principal component spaces. Partial least squares (PLS) and least squares-support vector machine (LS-SVM) algorithms were applied to develop quantitative relationships between Vis/NIR spectroscopy and diastase activity. The best result was obtained through Gaussian filter smoothing-standard normal variate (GF-SNV) pretreatment and the LS-SVM model, known as GF-SNV-LS-SVM, with a determination coefficient (R²) of prediction of 0.8872, and root mean square error (RMSE) of prediction of 0.2129. The overall results of this paper showed that the diastase activity of honey can be determined quickly and non-destructively with Vis/NIR spectral methods, which can be used to detect DN in the process of honey production and processing, and to maximize the nutrient content of honey.

Molten Ag2 SO4 -based Ion-Exchange Preparation of Ag0.5 La0.5 TiO3 for Photocatalytic O2 Evolution.

Ag0.5 La0.5 TiO3 with an ABO3 perovskite structure was synthesized by a newly developed ion-exchange method. Molten Ag2 SO4 instead of traditional molten AgNO3 was used as Ag+ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag+ for Na+ in Na0.5 La0.5 TiO3 with a stable ABO3 perovskite structure at a high ion-exchange temperature (700 °C). Under full-arc irradiation, the O2 -evolution activity of Ag0.5 La0.5 TiO3 was about 1.6 times that of Na0.5 La0.5 TiO3 due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag+ for Na+ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light-response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag+ for Na+ induced a lattice distortion of the ABO3 perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible-light irradiation, Ag0.5 La0.5 TiO3 displayed notable O2 evolution whereas Na0.5 La0.5 TiO3 showed little O2 evolution, thus demonstrating that the substitution of Ag+ for Na+ enabled the use of visible light to evolve O2 photocatalytically. This work presents an effective route to explore novel Ag-based photocatalysts.