Carbonized polymer dots enhanced stability and flexibility of quasi-2D perovskite photodetector.

Quasi-2D perovskites have been demonstrated to be competitive materials in the photodetection fields due to the enhanced moisture stability by large organic cations. However, as the increasing demands of modern technology, it is still challenging to combine the flexibility with the capability of weak light detection in a low-cost way. Here, amides, carboxylic acids, and anhydrides groups-rich carbonized polymer dots (CPDs) were employed to fill in the perovskite grain boundaries, which can passivate the point defects of perovskite by coordinating with the unbonded Pb atoms, and reduce the leakage current. Weak light detection capability was demonstrated by directly resolving light with an intensity of 10.1 pW cm-2. More importantly, the stretchable polymer chains on CPDs strongly interact with perovskite ions through multiple supramolecular interactions, and extend the stretchable properties to the perovskite/CPDs composites, which can maintain the integral structure stability during the deformation of perovskite crystals and restricted any crack by releasing the film strain. Our fabricated devices show extraordinary flexible stability in the bending-dependent response tests. The viscoelasticity of CPDs improves the bending stability of the flexible quasi-2D perovskite photodetectors, and device performance shows no degradation after bending 10000 times, comparable or even outperforming the dominating flexible photodetectors.

Cavitation erosion mechanisms in Co-based coatings exposed to seawater.

The cavitation erosion (CE) of most materials in seawater is more serious than in fresh water due to the onset of corrosion; however, in a previous study we reported results that contradict this widely accepted trend. In this research our objective is to provide fundamental insight into the mechanisms that may be responsible for these earlier results. To accomplish this objective, two types of Co-based coatings, prepared by high velocity oxygen fuel (HVOF) spraying system, were used to further investigate the underlying corrosion-mitigating CE mechanism in seawater. Accordingly, the influence of spraying parameters on microstructure, composition and mechanical properties of the coatings was analyzed on the basis of SEM, XRD, Raman spectroscopy, Vicker's hardness and nano-indentation results. Electrochemical corrosion tests were used to evaluate the corrosion behavior of the Co-based coatings. Their CE performances in seawater and deionized water were comparatively studied by a vibratory apparatus. Results demonstrated that a higher flame temperature facilitated the oxides formation with associated improvements in compactness, hardness and toughness of the coatings. The presence of alumina in combination with the oxides formed in-situ facilitated the formation of an oxidation film on surfaces, and effectively enhanced the charge transfer resistance of the coating, thereby significantly improving the corrosion resistance in seawater. Metallic Co was not only more easily oxidized but also more readily corroded than the alloyed Co. Compactness was identified as an important factor affecting CE resistance of coatings in deionized water, because defects facilitate the nucleation and eventual collapse of bubbles. Moreover, bubble collapse produced a transient high temperature spike in excess of 600 °C that also caused Co and Cr elements to oxidize. Because the CE tests were carried out in seawater, additional Co3O4 and Cr2O3 were generated owing to corrosion that more effectively increased the surface compactness and mechanical properties of the coatings. This behavior was particular notable for coatings with metallic Co and Cr, which should be why seawater corrosion could weaken the CE of Co-based coatings.

Impact of atrazine prohibition on the sustainability of weed management in Wisconsin maize production.

BACKGROUND: Controversy has surrounded atrazine owing to its susceptibility to leaching and run-off, with regular calls for a ban or restrictions on its use. In the context of a decreasing trend in the percentage of US maize using no-till since 2008, coinciding with the trend of glyphosate-resistant weeds becoming problematic in the Midwestern United States, we empirically examine how atrazine use restrictions have impacted the diversity of weed management practices used by Wisconsin maize farmers. RESULTS: Using survey data from farms inside and outside atrazine prohibition areas, we found that prohibiting atrazine did not directly impact tillage practices, but rather it increased the adoption of herbicide-resistant seed, which then increased adoption of conservation tillage systems. We also found that prohibiting atrazine and using herbicide-resistant seed reduced the number of herbicide sites of action used. CONCLUSIONS: The results indicate that prohibiting atrazine reduced the diversity of weed management practices, which increased the risk of herbicide resistance. Our concern is that a regulatory policy to address one issue (atrazine in groundwater) has induced farmer responses that increase problems with another issue (herbicide-resistant weeds) that longer term will contribute to water quality problems from increased soil erosion and offset the initial benefits. © 2016 Society of Chemical Industry.

Aqueous-Processed Inorganic Thin-Film Solar Cells Based on CdSe(x)Te(1-x) Nanocrystals: The Impact of Composition on Photovoltaic Performance.

Aqueous processed nanocrystal (NC) solar cells are attractive due to their environmental friendliness and cost effectiveness. Controlling the bandgap of absorbing layers is critical for achieving high efficiency for single and multijunction solar cells. Herein, we tune the bandgap of CdTe through the incorporation of Se via aqueous process. The photovoltaic performance of aqueous CdSexTe1-x NCs is systematically investigated, and the impacts of charge generation, transport, and injection on device performance for different compositions are deeply discussed. We discover that the performance degrades with the increasing Se content from CdTe to CdSe. This is mainly ascribed to the lower conduction band (CB) of CdSexTe1-x with higher Se content, which reduces the driving force for electron injection into TiO2. Finally, the performance is improved by mixing CdSexTe1-x NCs with conjugated polymer poly(p-phenylenevinylene) (PPV), and power conversion efficiency (PCE) of 3.35% is achieved based on ternary NCs. This work may provide some information to further optimize the aqueous-processed NC and hybrid solar cells.

Measuring farm sustainability using data envelope analysis with principal components: the case of Wisconsin cranberry.

Measuring farm sustainability performance is a crucial component for improving agricultural sustainability. While extensive assessments and indicators exist that reflect the different facets of agricultural sustainability, because of the relatively large number of measures and interactions among them, a composite indicator that integrates and aggregates over all variables is particularly useful. This paper describes and empirically evaluates a method for constructing a composite sustainability indicator that individually scores and ranks farm sustainability performance. The method first uses non-negative polychoric principal component analysis to reduce the number of variables, to remove correlation among variables and to transform categorical variables to continuous variables. Next the method applies common-weight data envelope analysis to these principal components to individually score each farm. The method solves weights endogenously and allows identifying important practices in sustainability evaluation. An empirical application to Wisconsin cranberry farms finds heterogeneity in sustainability practice adoption, implying that some farms could adopt relevant practices to improve the overall sustainability performance of the industry.

Interfacing a tetraphenylethene derivative and a smart hydrogel for temperature-dependent photoluminescence with sensitive thermoresponse.

We report, for the first time, the design and synthesis of thermoresponsive (TR) photoluminescent (PL) hydrogel nanoparticles, with a core consisting of poly[styrene-co-(N-isopropylacrylamide)] (PS-co-PNIPAM) and a PNIPAM-co-PAA shell. PAA represents polyacrylic acid which interacts with our emitting molecule 1,2-bis[4-(2-triethylammonioethoxy)phenyl]-1,2-diphenylethene dibromide (d-TPE). The electrostatic interaction between each water-soluble d-TPE molecule and two AA repeat units activates these d-TPE molecules to exhibit strong PL. Our d-TPE doped PS-co-PNIPAM/PNIPAM-co-PAA particles in water display remarkable TR PL: the emission intensity decreased in the course of heating from 2 to 80 °C and recovered during cooling from 80 to 2 °C. Such linear, reversible, and sensitive TR PL is achieved by the use of both PAA and PNIPAM as the shell polymeric chain and by careful optimization of the d-TPE to AA feed molar ratio. Thus, the emission of the d-TPE molecule is affected sensitively by temperature. In addition to such an exceptionally temperature-dependent PL, the presence of CrO4(2-) resulted in the decrease of the emission intensity, which was also temperature-dependent. The present study provides a unified conceptual methodology to engineer functional water-dispersible hydrogel nanoparticles that are stimuli-responsive with the potential to advance various PL-based applications.

Centrifugation-induced water-tunable photonic colloidal crystals with narrow diffraction bandwidth and highly sensitive detection of SCN-.

Novel opal hydrogels with water-tunable photonic bandgap (PBG) exhibiting responses to external stimuli were self-assembled from polystyrene-co-poly(N,N-dimethylacrylamide) (PS-co-PDMAA) microspheres. The polymeric microspheres with narrow size distribution were successfully prepared in water, consisting of two regions. The inner region is rich in PS which is hard and hydrophobic; the outer region is rich in PDMAA which is soft and hydrophilic. The self-assembly of the PS-co-PDMAA hydrogel microspheres is ready induced by centrifugation and resulted in highly ordered three-dimensional (3D) photonic colloidal crystals (PCCs). With an increase of the amount of water, the PBG of the opal hydrogels shifted from the visible to near-infrared region of the electromagnetic spectrum. The maximum shift of diffraction peak positions could be larger than 500 nm with narrow full width at half maximum (FWHM) in the range of 20 to 40 nm only. The change in color was visible to the naked eye. The remarkable sensitivity to water of the lattice spacing of the opal hydrogels was repeatable after centrifugation. These observations are attributed to a reproducible degree of hydration of the hydrophilic outer region of the polymeric microspheres. Furthermore, the diffraction of the opal hydrogels was particularly sensitive to the presence of thiocyanate (SCN(-)) ions. The interaction between SCN(-) ions and DMAA repeat units is argued to block hydrogen bonds between DMAA and water molecules. Our PS-co-PDMAA opal hydrogels could be a practical system for diffraction-based detections.

Fluorescent silver nanoclusters as effective probes for highly selective detection of mercury(II) at parts-per-billion levels.

Facile preparation of water-soluble and fluorescent Ag nanoclusters (NCs) stabilized by glutathione at room temperature is described. Although the glutathione layer was introduced to prevent the silver nanoparticles from decomposition and increase their water solubility, this simple surface optimization resulted in surprisingly high efficiency of selective Hg(2+) sensing, where the limit of detection (LOD) was as low as 10(-10) M (0.02 ppb, 0.1 nM). This result revealed a simple and practical strategy for Hg(2+) detection using fluorescent Ag NCs as sensor probe, with the lowest detecting limits reported to date.

Dimethyl-ammonium 2-[(2-oxo-2H-chromen-7-yl)-oxy]acetate.

In the title salt, C(2)H(8)N(+)·C(11)H(7)O(5) (-), the acetate group is twisted out of the plane of the coumarin ring system with a C-O-C-C torsion angle of 76.3 (2)°. In the crystal, N-H⋯O hydrogen bonds link the cations and anions into chains propagating in [100].

Supercrystal structures of polyhedral PbS nanocrystals.

The construction of supercrystals with non-spherical building blocks has attracted increasing attention due to their potential applications in the fabrication of novel devices. In this study, we report the large-scale preparation of dimension-controllable supercrystals of polyhedral PbS nanocrystals through a solvent evaporation approach. Because of the capillary flow of the drying droplet on the substrate, nanocrystals self-assemble into three distinct types of supercrystals on specific regions of the substrate during the solvent evaporation: two-dimensional supercrystals appear in the central region; three-dimensional faceted supercrystals and three-dimensional bulk supercrystals are found near the edge of the substrate. Moreover, the formation of superlattice structure of each type of supercrystals can be tuned by changing the shape of building blocks. The influences of experimental factors on self-assembly are investigated as well. We anticipate that our research can provide some new insights into the construction of supercrystals with novel structures and large sizes.

Polymer-mediated growth of fluorescent semiconductor nanoparticles in preformed nanocomposites.

In this study, we investigated the size and photoluminescence (PL) evolution of CdTe nanoparticles (NPs) in different polymer media under thermal annealing. A quick growth and maintenance of strong PL were observed. By analyzing the transmission electron microscopy (TEM) images of NPs in polymer media, we discovered that the size evolution of NPs was the combination of Ostwald ripening and dynamic coalescence throughout the growth process. Moreover, the experimental results also revealed that the nature of polymers determined the dynamic coalescence of NPs from three aspects; the mobility of polymer chains, the compatibility of NPs with polymer media, and the interaction between NPs and polymer network. Thus by altering the glass transition temperature (T(g)) of polymers, the molar mass (M(n)) of the polymers, the phase separation of NPs in polymer media, as well as the interaction between NPs and polymers, the growth rate of NPs was controllable.

Photoinduced cleaning of water-soluble dyes on patterned superhydrophilic/superhydrophobic substrates.

Herein we present a novel but simple method to fabricate photoinduced cleaning substrates with patterned superhydrophobic hierarchical silicon cone arrays (SCAs) and superhydrophilic TiO(2) nanorod clusters (TNCs). In our experiment, the photoinduced cleaning properties of the obtained substrate are investigated by repeatedly adsorbing and decomposing rhodamine B (RhB) molecules for at least six cycles. In addition, we demonstrate that the low-surface-energy coating on the superhydrophobic areas is stable, resulting in the high wettability contrast being well preserved during the renewal process. This straightforward method may open up new possibilities for the practical use of microchips with patterned superhydrophobic and superhydrophilic areas.

Direct synthesis of polymerizable surfactant-stabilized nanoparticles: the macromolecular monomers for fabricating nanoparticle-polymer composites.

Incorporation of inorganic nanoparticles (NPs) into polymers is the current means for enhancing the performance of polymer materials, the key to which is the increase of compatibility between NPs and polymer media. In this paper, the polymerizable surfactant octadecyl-p-vinylbenzyldimethylammonium chloride (OVDAC) is synthesized and used as a capping agent for direct synthesis of various metal NPs, for instance Au, Ag, Pd, and Pt, and semiconductor NPs, for instance ZnS, CdS, and PbS. The preformed OVDAC-stabilized NPs are lipophilic and act as macromolecular monomers in the copolymerization with lipophilic monomers.

Donor-acceptor alternating copolymers as donor materials for bulk-heterojunction solar cells: effects of molecular structure on film morphology and device performance.

Three photovoltaic-applicable donor-acceptor (D-A) alternating copolymers including poly{(9,9-dihexyl-9H-fluorene-2,7-ylene)-alt-2-(2,6-bis((E)-2-(5-bromo-3,4-dihexylthiophen-2-yl)vinyl)-4H-pyran-4-ylidene) malononitrile} (PFTMT), poly{(10-hexyl-10H-phenothiazine-3,7-ylene)-alt-2-(2,6-bis((E)-2-(5-bromo-3,4-dihexylthiophen-2-yl)vinyl)-4H-pyran-4-ylidene) malononitrile} (PPTMT) and poly{(2,20-bithiophene-5,50-ylene)-alt-2-(2,6-bis((E)-2-(5-bromo-3,4-dihexylthiophen-2-yl)vinyl)-4H-pyran-4-ylidene)malononitrile} (PDTTMT), were blended with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) to serve as active layers for photovoltaic applications. The effects of extrinsic (blend ratio and solvent) and intrinsic factors (donor materials) on the morphologies of this series of active layers were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was found that the PFTMT:PCBM active layers show distinct phase segregation with large PCBM clusters above 100 nm and are strongly affected by solvent evaporation rate in higher blend ratios. In contrast, the PPTMT:PCBM active layers are homogeneous and not affected by blend ratios and solvents, while the PDTTMT:PCBM active layers show an interpenetrating network initially formed at the blend ratio of 1:1. These results indicate that the polymer-PCBM repulsions arising from the molecular structure of the polymers play a significant role in determining the resulting morphologies of the blend films. Strong PFTMT-PCBM repulsion leads to large-scale phase segregation, while weak repulsions in PPTMT-PCBM and PDTTMT-PCBM favor small-scale phase segregation only. The best photovoltaic power conversion efficiencies are obtained from PDTTMT-based solar cells with the PDTTMT:PCBM blend ratio of 1:3 and nanoscale phase separation of the active layer, where a good balance is formed between a large donor-acceptor interface and the continuous paths of donor and acceptor phase for opposite charge carrier transport to their corresponding electrodes.

Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change.

Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.