Intramolecular charge transfer enhanced optical limiting in novel hydrazone derivatives with a D1-D-Ai-π-A structure.

The present paper investigates one of the hydrazone derivatives (BTH with a D-π-A structure) based on density functional theory. With the computation results of ground state absorption (GSA), excited-state absorption (ESA) and multi-photon absorption (MPA), the optical limiting effect observed in the experiment for the BTH molecule can be well predicted and elucidated by the MPA-ESA mechanism. The analysis of the hole-electron and the electron density differences between two transition states reveal that the main transitions involved in the GSA and ESA of BTH could be recognized as local excitation. Based on these observations, four novel hydrazone derivatives based on the BTH unit with a D1-D-Ai-π-A structure were designed to promote intramolecular charge transfer (ICT). It shows that the ICT effect is well improved by adding the D1 and Ai units. Compared with the original BTH molecule, the main bands of GSA and ESA of D1-D-Ai-π-A molecules are both red-shifted. In addition, GSA, ESA and MPA probabilities are all improved because the obvious charge transfer character results in the transition dipole moment change from localized to delocalized. Accordingly, the optical limiting effect in these hydrazone derivatives is well enhanced. These observations provide guidance for designing novel optical limiting materials based on the hydrazone derivatives.

Occurrence, removal, and risk assessment of polycyclic aromatic hydrocarbons and their derivatives in typical wastewater treatment plants.

Wastewater treatment plants (WWTPs) have a certain removal capacity for polycyclic aromatic hydrocarbons (PAHs) and their derivatives, but some of them are discharged with effluent into the environment, which can affect the environment. Therefore, to understand the presence, sources, and potential risks of PAHs and their derivatives in WWTPs. Sixteen PAHs, three chlorinated polycyclic aromatic hydrocarbons (ClPAHs), three oxidized polycyclic aromatic hydrocarbons (OPAHs), and three methylated polycyclic aromatic hydrocarbons (MPAHs) were detected in the influent and effluent water of three WWTPs in China. The average concentrations of their influent ∑PAHs, ∑ClPAHs, ∑OPAHs, and ∑MPAHs ranged from 2682.50 to 2774.53 ng/L, 553.26-906.28 ng/L, 415.40-731.56 ng/L, and 534.04-969.83 ng/L, respectively, and the effluent concentrations ranged from 823.28 to 993.37 ng/L, 269.43-489.94 ng/L, 285.93-463.55 ng/L, and 376.25-512.34 ng/L, respectively. The growth of heat transport and industrial energy consumption in the region has a significant impact on the level of PAHs in WWTPs. According to the calculated removal efficiencies of PAHs and their derivatives in the three WWTPs (A, B, and C), the removal rates of PAHs and their derivatives were 69-72%, 62-71%, and 68-73%, respectively, and for the substituted polycyclic aromatic hydrocarbons (SPAHs), the removal rates were 41-49%, 31-40%, and 33-39%, respectively; moreover, the removal rates of PAHs were greater than those of SPAHs in the WWTPs. The results obtained via the ratio method indicated that the main sources of PAHs in the influent of WWTPs were the combustion of coal and biomass, and petroleum contamination was the secondary source. In risk evaluation, there were 5 compounds for which the risk quotient was considered high ecological risk. During chronic disease evaluation, there were 11 compounds with a risk quotient considered to indicate high risk. PAHs and SPAHs with high relative molecular masses in the effluent of WWTPs pose more serious environmental hazards than their PAHs counterparts.

Spatial and temporal distribution characteristics of antibiotics and heavy metals in the Yitong River basin and ecological risk assessment.

Due to rapid socioeconomic development, antibiotic pollution and heavy metal pollution are receiving increasing amounts of attention. Both antibiotics and heavy metals in the environment are persistent and toxic, and the interactions between the pollutants create potential long-term hazards for the ecological environment and human health as mixed pollutants. In this study, the surface water of the Yitong River in Changchun was used as the research object, and the hazards associated with antibiotics and heavy metals in the surface water were assessed by analyzing the spatial and temporal distribution characteristics of antibiotics and heavy metals and by using ecological risk assessment and human health risk assessment models. The results showed that ofloxacin (OFL) and norfloxacin (NOR) varied seasonally according to the seasonal climate, with total concentrations ranging from 17.65 to 902.47 ng/L and ND to 260.49 ng/L for OFL and NOR, respectively, and from 8.30 to 120.40 µg/L, 1.52 to 113.41 µg/L and 0.03 to 0.04 µg/L for copper (Cu), zinc (Zn) and cadmium (Cd), respectively. In terms of spatial distribution, the concentration of antibiotics in the urban sections, which had intensive human activities, was higher than that in the suburban sections, while the concentration of heavy metals in the suburban sections, which had intensive agricultural operations, was greater than that in the urban section. Ecological risk evaluation showed that NOR and OFL were present in the water bodies at a high-risk level, Cd was at a low pollution level, and the heavy metal Cd was the primary pollutant associated with health risks toward for adults and children, and it was mainly at a medium risk level. Additionally, both antibiotics and heavy metals posed higher health risks for children than for adults.

Ultrabroadband Photodetectors up to 10.6 µm Based on 2D Fe3 O4 Nanosheets.

The ultrabroadband spectrum detection from ultraviolet (UV) to long-wavelength infrared (LWIR) is promising for diversified optoelectronic applications of imaging, sensing, and communication. However, the current LWIR-detecting devices suffer from low photoresponsivity, high cost, and cryogenic environment. Herein, a high-performance ultrabroadband photodetector is demonstrated with detecting range from UV to LWIR based on air-stable nonlayered ultrathin Fe3 O4 nanosheets synthesized via a space-confined chemical vapor deposition (CVD) method. Ultrahigh photoresponsivity (R) of 561.2 A W-1 , external quantum efficiency (EQE) of 6.6 × 103 %, and detectivity (D*) of 7.42 × 108 Jones are achieved at the wavelength of 10.6 µm. The multimechanism synergistic effect of photoconductive effect and bolometric effect demonstrates the high sensitivity for light with any light intensities. The outstanding device performance and complementary mixing photoresponse mechanisms open up new potential applications of nonlayered 2D materials for future infrared optoelectronic devices.

Large-Scale Ultrathin 2D Wide-Bandgap BiOBr Nanoflakes for Gate-Controlled Deep-Ultraviolet Phototransistors.

Ternary two-dimensional (2D) semiconductors with controllable wide bandgap, high ultraviolet (UV) absorption coefficient, and critical tuning freedom degree of stoichiometry variation have a great application prospect for UV detection. However, as-reported ternary 2D semiconductors often possess a bandgap below 3.0 eV, which must be further enlarged to achieve comprehensively improved UV, especially deep-UV (DUV), detection capacity. Herein, sub-one-unit-cell 2D monolayer BiOBr nanoflakes (≈0.57 nm) with a large size of 70 µm are synthesized for high-performance DUV detection due to the large bandgap of 3.69 eV. Phototransistors based on the 2D ultrathin BiOBr nanoflakes deliver remarkable DUV detection performance including ultrahigh photoresponsivity (Rλ , 12739.13 A W-1 ), ultrahigh external quantum efficiency (EQE, 6.46 × 106 %), and excellent detectivity (D*, 8.37 × 1012 Jones) at 245 nm with a gate voltage (Vg ) of 35 V attributed to the photogating effects. The ultrafast response (τrise = 102 µs) can be achieved by utilizing photoconduction effects at Vg of -40 V. The combination of photocurrent generation mechanisms for BiOBr-based phototransistors controlled by Vg can pave a way for designing novel 2D optoelectronic materials to achieve optimal device performance.

Self-Confined Growth of Ultrathin 2D Nonlayered Wide-Bandgap Semiconductor CuBr Flakes.

2D planar structures of nonlayered wide-bandgap semiconductors enable distinguished electronic properties, desirable short wavelength emission, and facile construction of 2D heterojunction without lattice match. However, the growth of ultrathin 2D nonlayered materials is limited by their strong covalent bonded nature. Herein, the synthesis of ultrathin 2D nonlayered CuBr nanosheets with a thickness of about 0.91 nm and an edge size of 45 µm via a controllable self-confined chemical vapor deposition method is described. The enhanced spin-triplet exciton (Zf , 2.98 eV) luminescence and polarization-enhanced second-harmonic generation based on the 2D CuBr flakes demonstrate the potential of short-wavelength luminescent applications. Solar-blind and self-driven ultraviolet (UV) photodetectors based on the as-synthesized 2D CuBr flakes exhibit a high photoresponsivity of 3.17 A W-1 , an external quantum efficiency of 1126%, and a detectivity (D*) of 1.4 × 1011 Jones, accompanied by a fast rise time of 32 ms and a decay time of 48 ms. The unique nonlayered structure and novel optical properties of the 2D CuBr flakes, together with their controllable growth, make them a highly promising candidate for future applications in short-wavelength light-emitting devices, nonlinear optical devices, and UV photodetectors.

Defect-Induced Epitaxial Growth for Efficient Solar Hydrogen Production.

Epitaxial growth suffers from the mismatches in lattice and dangling bonds arising from different crystal structures or unit cell parameters. Here, we demonstrate the epitaxial growth of 2D MoS2 ribbon on 1D CdS nanowires (NWs) via surface and subsurface defects. The interstitial Cd0 in the (12̅10) crystal plane of the [0001]-oriented CdS NWs are found to serve as nucleation sites for interatomically bonded [001]-oriented MoS2, where the perfect lattice match (∼99.7%) between the (101̅1) plane of CdS and the (002)-faceted in-plane MoS2 result in coaxial MoS2 ribbon/CdS NWs heterojunction. The coaxial but heterotropic epitaxial MoS2 ribbon on the surface of CdS NWs induces delocalized interface states that facilitate charge transport and the reduced surface state. A less than 5-fold ribbon width of MoS2 as hydrogen evolution cocatalyst exhibits a ∼10-fold H2 evolution enhancement than state of the art Pt in an acidic electrolyte, and apparent quantum yields of 79.7% at 420 nm, 53.1% at 450 nm, and 9.67% at 520 nm, respectively.