Enhanced photoluminescence and stability of ZnSe microspheres/Cs4PbBr6 microcrystals/CsPbBr3 nanocrystals composites

A ternary complex combining dual-phase perovskites - Cs₄PbBr₆/CsPbBr₃ (DP-CPB) with ZnSe micropsheres (ZnSe-DP-CPB) was successfully prepared using supersaturated recrystallization technique at room temperature. It was showed that the DP-CPB composites were partially embedded in ZnSe microsphere composed with ZnSe NCs. The light absorption range of ZnSe-DP-CPB composites was extended from visible to near infrared light. Highly enhanced luminescence from ZnSe-DP-CPB composite was observed and the excitation power-dependent photoluminescence showed that the recombination involves excitons. The recombination lifetimes of the ternary composites increased compared with DP-CPB composite, indicating that the non-radiative combination was suppressed which may be possibly due to the decrease of both bulk and surface defects, owing to the passivation of ZnSe, as well as the suitable band alignments of these three components. The ternary complex also showed improved stability of photoluminescence (PL), which opens a new avenue for enhancing the stability of PL and optoelectronic applications for semiconductor-perovskite composites.     

BiOBr microspheres for photocatalytic degradation of an anionic dye

BiOBr microspheres were obtained using a solvothermal synthesis route in the presence of ethylene glycol and KBr at 145 °C, for 18 h. BiOBr microspheres were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen adsorption-desorption isotherms analysis, diffuse reflectance spectroscopy (DRS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Additionally, the theoretical and experimental isoelectric points (IEP) of BiOBr nanostructured microspheres were determined, and pH's influence on the degradation of an anionic dye (methyl orange) under simulated solar radiation was analyzed. Results show that 97% of methyl orange is removed at pH 2 after 60 min of photocatalytic reaction. Finally, DRIFTS studies permit the proposal of a surface reaction mechanism of the photocatalytic oxidation of MO using BiOBr microspheres.     

Enhanced photocatalytic degradation of rhodamine B under visible light irradiation on mesoporous anatase TiO2 microspheres by codoping with W and N

Mesoporous anatase TiO₂ microspheres were prepared via solvothermal method. Ammonium tungstate was used as the W source, and ammonia gas flowing in an ammonothermal reactor as the N source for codoping. TiO₂:(W,N) mesoporous microspheres, which were prepared from solvothermal treatment at 160 °C for 16 h and thermal ammonolysis at 500 °C for 2 h after calcination, have high specific surface area of 106 m² g⁻¹. XPS results indicate the presence of N_O, N_i and W⁶⁺ in the codoped mesoporous TiO₂ microspheres. Monodoping with N shifts the absorption band edge of anatase TiO₂ from ultraviolet region to visible region. Although codoping with W makes the visible light absorbance decrease a little, the photocatalytic degradation of a cationic dye rhodamine B (RhB) on mesoporous TiO₂:(W,N) microspheres is increased to 1.7 times of that on mesoporous TiO₂:N microspheres. This may due to decreasing recombination centers by W-doping charge compensation.     

Synthesis and properties of Au/ZnO nanorods as a plasmonic photocatalyst

It is of great interest to develop plasmonic photocatalysts with high activity and stability recently. In this paper, Au/ZnO nanorods were synthesized via a facile hydrothermal method and used as photocatalysts for methyl orange dye degradation. The results revealed an interesting phenomenon that photocorrosion cracks were produced specially along the c-axis of pure ZnO nanorods for five cycles photodegradation experiments under UV–vis. light irradiation, while Au nanoparticles surface modification can effectively inhibit the occurrence of photocorrosion and improve its photocatalytic activity. The formation of photocorrossion cracks along the c-axis of pure ZnO nanorods verifies the photogenerated charges may follow the route that electrons migrate to Zn-terminated (0001) plane and holes to O-terminated $(000\stackrel{-}{1})$ plane. SPR effect of Au nanoparticles enhances the light absorption ability and the electrons capture ability of Au/ZnO nanorods. Moreover, the surface adsorbed hydroxyl groups content is also increased due to Au nanoparticles modification. As Au nanoparticles can capture photogenerated electrons and hydroxyl groups are the favorable holes scavenger, the charges generation and separation in photocatalysis are strengthened. Especially, the charges separation path in Au/ZnO nanorods have changed, thus inhibiting the occurrence of photocorrosion along the c-axis of ZnO nanorods and improving the photocatalytic activity.     

Engineering oxygen into ultrathin graphitic carbon nitride: synergistic improvement of electron reduction and charge carrier dynamics for efficient photocatalysis

The fast separation rate of photogenerated carriers and the high utilization of sunlight are still a major challenge that restricts the practical application of carbon nitride (g-C₃N₄) materials in the field of photocatalytic hydrogen (H₂) evolution. Here, ultrathin oxygen (O) engineered g-C₃N₄ (named UOCN) was successfully obtained by a facial gaseous template sacrificial agent-induced bottom-up strategy. The synergy of O doping and exfoliating bulk into an ultrathin structure is reported to simultaneously achieve high-efficiency separation of photogenerated carriers, enhance the utilization of sunlight, and improve the reduction ability of electrons to promote photocatalytic H₂ evolution of UOCN. As a proof of concept, UOCN affords enhanced photocatalytic H₂ evolution (93.78 μmol h^?1) under visible light illumination, which was significantly better than that of bulk carbon nitride (named CN) with the value of 9.23 μmol h^?1. Furthermore, the H₂ evolution rate of UOCN at a longer wavelength (λ = 450 nm) was up to 3.92 μmol h^?1 due to its extended light absorption range. This work presents a practicable strategy of coupling O dopants with ultrathin structures about g-C₃N₄ to achieve efficient photocatalytic H₂ evolution. This integrated engineering strategy can develop a unique example for the rational design of innovative photocatalysts for energy innovation.     

Anchoring cobalt single atoms on 2D covalent triazine framework with charge nanospatial separation for enhanced photocatalytic pollution degradation

Covalent triazine frameworks (CTFs) show great potential in photocatalytic fields, while their practical efficiency is still limited due to rapid charge recombination. Here we report a nanospatial separation strategy for photoinduced electron-hole pairs of CTF-1 nanosheets via single-atom Co using facile pyrolysis and phosphorization to form stable Co–N₃ (≈1.60 Å) architecture. HAADF-STEM image demonstrates Co atoms are uniformly dispersed onto ultrathin CTF-1. The local structure surrounding and chemical valent state of Co are systematically investigated by Fourier-transformed EXAFS and K-edge XANES, respectively. Co single atoms as oxidation centers can capture holes transferred from CTF-1, thus resulting in narrow bandgap and improved photo-exciton dissociation in the two-dimensional (2D) direction. The obtained Co/CTF-1 exhibits excellent efficiency of 99.9% for pollutant photodegradation, far outperforming that of pristine CTF-1 (68.8%). Nanospatial separation endows Co/CTF-1 with various micropollution removal capabilities, outstanding cyclic stability, and a widely effective pH range (1.0–11.0) under visible light. Furthermore, active oxidating radicals of h⁺ and ?O₂^? are dominant in photocatalytic degradation for various organic contaminants. This study motivates the atomic design and fabrication of 2D photocatalysts with excellent charge nanospatial separation.     

Discrimination methods for biological contaminants in fresh-cut lettuce based on VNIR and NIR hyperspectral imaging

The rapid detection of biological contaminants such as worms in fresh-cut vegetables is necessary to improve the efficiency of visual inspections carried out by workers. Multispectral imaging algorithms were developed using visible-near-infrared (VNIR) and near-infrared (NIR) hyperspectral imaging (HSI) techniques to detect worms in fresh-cut lettuce. The optimal wavebands that can detect worms in fresh-cut lettuce were investigated for each type of HSI using one-way ANOVA. Worm-detection imaging algorithms for VNIR and NIR imaging exhibited prediction accuracies of 97.00% (RI_547/945) and 100.0% (RI_1064/1176, SI_1064-1176, RSI-I_{(1064-1173)/1064}, and RSI-II_{(1064-1176)/(1064+1176)})_, respectively. The two HSI techniques revealed that spectral images with a pixel size of 1 × 1 mm or 2 × 2 mm had the best classification accuracy for worms. The results demonstrate that hyperspectral reflectance imaging techniques have the potential to detect worms in fresh-cut lettuce. Future research relating to this work will focus on a real-time sorting system for lettuce that can simultaneously detect various defects such as browning, worms, and slugs.     

烟酰胺腺嘌呤二核苷酸在纳米α-氧化铝上的吸附作用

用紫外-可见吸收光谱、X射线衍射、荧光光谱和衰减全反射傅里叶变换红外(ATR-FTIR）光谱等方法,研究了烟酰胺腺嘌呤二核苷酸(NAD+)在纳米α-Al2O3粒子上的吸附行为。 实验结果显示,NAD+的吸附量受pH值和离子强度影响较大,说明NAD+主要通过静电作用吸附在纳米α-Al2O3粒子上。 采用ATR-FTIR光谱分析了不同pH值溶液中及被吸附的NAD+,发现吸附后的NAD+与溶液中NAD+ 的ATR-FTIR光谱相似,但磷酸根的吸收峰向高波数位移,说明磷酸根参与了表面静电作用。 吸附过程符合Langmuir和Freundlich等温式。 荧光实验结果显示,随着吸附剂α-Al2O3用量的变化,NAD+构象也发生变化。     

Interfacial electrostatic phenomena in polyimide Langmuir–Blodgett films in electron tunneling devices

Nanometric electrostatic space charges exist at the metal/molecular film interface due to the displacement of excessive electrons from metal to molecular films. As a result, surface potential is built across the films on metal. The distributions of the displaced electrons and the electronic density of states in films can be determined using the surface potential built. The current–voltage characteristic of tunneling device using polyimide Langmuir–Blodgett films is discussed with taking into account the space charge.     

凹凸棒石/g-C3N4-AgFeO2复合材料制备及其光催化性能

以凹凸棒石(简称凹土,ATP)为基体,通过原位化学法一步直接合成g-C_3N_4薄层材料,并将其有效固载于凹土表面(ATP/gC_3N_4),再通过原位沉淀法引入不同比例AgFeO_2纳米颗粒,构筑系列兼具磁分离特性和高效光催化活性的ATP/g-C_3N_4-AgFeO_2-Y复合光催化剂(Y=wATP/g-C_3N_4/(wATP/g-C_3N_4+wAg FeO_2)×100%,表示ATP/g-C_3N_4在ATP/g-C_3N_4-AgFeO_2复合材料中所占的质量百分数)。采用XRD、SEM、BET、UV-Vis、PL和ICP表征其结构和物化性能,以酸性红G(ARG)为目标降解物,研究其光催化性能。研究发现:通过形成Si-O-C键,g-C_3N_4薄层被均匀固定在凹土表面;AgFeO_2纳米颗粒均匀沉积于ATP/g-C_3N_4表面并形成Z型异质结,ATP/gC_3N_4-AgFeO_2-Y具有比ATP/g-C_3N_4和AgFeO_2更优异的可见光光催化性能,且随着ATP/g-C_3N_4含量的增大呈先升高而后下降的趋势;当Y=57%时复合材料的性能最佳,ATP/g-C_3N_4-AgFeO_2-57%对20 mg·L-1酸性红G的降解率可达97.4%,循环4次使用后,降解率仍保持94.2%。通过自由基捕获实验研究了光催化反应机理,发现·O2-是光催化过程的主要活性物种。