Visible‐Light‐Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle‐Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal‐oxide‐supported gold nanoparticles (NPs) have emerged as a new type of visible‐light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible‐light irradiation (λ>430 nm) of TiO₂‐supported Au NPs with a bimodal size distribution (BM‐Au/TiO₂) gives rise to the long‐range (>40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO₂. As a result of the enhancement of charge separation, BM‐Au/TiO₂ exhibits a high level of visible‐light activity for the one‐step synthesis of azobenzenes from nitrobenzenes at 25 °C with a yield greater than 95 % and a selectivity greater than 99 %, whereas unimodal Au/TiO₂ (UM‐Au/TiO₂) is photocatalytically inactive.     

Size‐Dependence of the Activity of Gold Nanoparticle‐Loaded Titanium(IV) Oxide Plasmonic Photocatalyst for Water Oxidation

Mesoporous TiO₂ nanocrystalline film was formed on fluorine‐doped tin oxide electrode (TiO₂/FTO) and gold nanoparticles (NPs) of different sizes were loaded onto the surface with the loading amount kept constant (Au/TiO₂/FTO). Visible‐light irradiation (λ>430 nm) of the Au/TiO₂/FTO photoanode in a photoelectrochemical cell with the structure of photoanode|0.1 m NaClO4 aqueous solution|Ag/AgCl (reference electrode)|glassy carbon (cathode) leads to the oxidation of water to oxygen (O₂). We show that the visible‐light activity of the Au/TiO₂/FTO anode increases with a decrease in Au particle size (d) at 2.9≤d≤11.9 nm due to the enhancement of the charge separation and increasing photoelectrocatalytic activity.     

Control of Surface Plasmon Resonance of Au/SnO2 by Modification with Ag and Cu for Photoinduced Reactions under Visible‐Light Irradiation over a Wide Range

Gold particles supported on tin(IV) oxide (0.2 wt % Au/SnO₂) were modified with copper and silver by the multistep photodeposition method. Absorption around λ=550 nm, attributed to surface plasmon resonance (SPR) of Au, gradually shifted to longer wavelengths on modification with Cu and finally reached λ=620 nm at 0.8 wt % Cu. On the other hand, the absorption shifted to shorter wavelength with increasing amount of Ag and reached λ=450 nm at 0.8 wt % Ag. These Cu‐ and Ag‐modified 0.2 wt % Au/SnO₂ materials (Cu‐Au/SnO₂ and Ag‐Au/SnO₂) and 1.0 wt % Au/SnO₂ were used for mineralization of formic acid to carbon dioxide in aqueous suspension under irradiation with visible light from a xenon lamp and three kinds of light‐emitting diodes with different wavelengths. The reaction rates for the mineralization of formic acid over these materials depend on the wavelength of light. Apparent quantum efficiencies of Cu‐Au/SnO₂, Au/SnO₂, and Ag‐Au/SnO₂ reached 5.5 % at 625 nm, 5.8 % at 525 nm, and 5.1 % at 450 nm, respectively. These photocatalysts can also be used for selective oxidation of alcohols to corresponding carbonyl compounds in aqueous solution under visible‐light irradiation. Broad responses to visible light in formic acid mineralization and selective alcohol oxidation were achieved when the three materials were used simultaneously.     

Sunlight‐Driven Hydrogen Peroxide Production from Water and Molecular Oxygen by Metal‐Free Photocatalysts

Design of green, safe, and sustainable process for the synthesis of hydrogen peroxide (H₂O₂) is a very important subject. Early reported processes, however, require hydrogen (H₂) and palladium‐based catalysts. Herein we propose a photocatalytic process for H₂O₂ synthesis driven by metal‐free catalysts with earth‐abundant water and molecular oxygen (O₂) as resources under sunlight irradiation (λ>400 nm). We use graphitic carbon nitride (g‐C₃N₄) containing electron‐deficient aromatic diimide units as catalysts. Incorporating the diimide units positively shifts the valence‐band potential of the catalysts, while maintaining sufficient conduction‐band potential for O₂ reduction. Visible light irradiation of the catalysts in pure water with O₂ successfully produces H₂O₂ by oxidation of water by the photoformed valence‐band holes and selective two‐electron reduction of O₂ by the conduction band electrons.     

Dual Mechanism of an Intramolecular Charge Transfer (ICT)–FRET‐Based Fluorescent Probe for the Selective Detection of Hydrogen Peroxide

A dual‐mechanism intramolecular charge transfer (ICT)–FRET fluorescent probe for the selective detection of H₂O₂ in living cells has been designed and synthesized. This probe used a coumarin–naphthalimide hybrid as the FRET platform and a boronate moiety as the recognition group. Upon the addition of H₂O₂, the probe exhibited a redshifted (73 nm) fluorescence emission, and the ratio of fluorescence intensities at λ =558 and 485 nm (F ₅₅₈/F ₄₈₅) shifted notably (up to 100‐fold). Moreover, there was a good linearity (R ²=0.9911) between the ratio and concentration of H₂O₂ in the range of 0 to 60 μm , with a limit of detection of 0.28 μm (signal to noise ratio (S/N)=3). This probe could also detect enzymatically generated H₂O₂. Importantly, it could be used to visualize endogenous H₂O₂ produced by stimulation from epidermal growth factor.     

Prolonged Hot Electron Dynamics in Plasmonic‐Metal/Semiconductor Heterostructures with Implications for Solar Photocatalysis

Ideal solar‐to‐fuel photocatalysts must effectively harvest sunlight to generate significant quantities of long‐lived charge carriers necessary for chemical reactions. Here we demonstrate the merits of augmenting traditional photoelectrochemical cells with plasmonic nanoparticles to satisfy these daunting photocatalytic requirements. Electrochemical techniques were employed to elucidate the mechanics of plasmon‐mediated electron transfer within Au/TiO₂ heterostructures under visible‐light (λ>515 nm) irradiation in solution. Significantly, we discovered that these transferred electrons displayed excited‐state lifetimes two orders of magnitude longer than those of electrons photogenerated directly within TiO₂ via UV excitation. These long‐lived electrons further enable visible‐light‐driven H₂ evolution from water, heralding a new photocatalytic paradigm for solar energy conversion.     

Au‐TiO2/Graphene Nanocomposite Film for Electrochemical Sensing of Hydrogen Peroxide and NADH

We describe a simple method for preparing Au‐TiO₂/graphene (GR) nanocomposite by deposition of Au nanoparticles (NPs) on TiO₂/GR substrates. The as‐prepared Au‐TiO₂/GR was characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The presence of Au NPs on TiO₂/GR surface remarkably improves the electrocatalytic activity towards the oxidation of hydrogen peroxide (H₂O₂) and β‐nicotinamide adenine dinucleotide (NADH). The Au‐TiO₂/GR modified glassy carbon (GC) electrode exhibits good amperometric response to H₂O₂ and NADH, with linear range from 10 to 200 µM and 10 to 240 µM, and detection limit of 0.7 and 0.2 µM, respectively.     

Enantioselective Intramolecular [2+2] Photocycloaddition Reactions of 4‐Substituted Coumarins Catalyzed by a Chiral Lewis Acid

Eight coumarins, which carry a terminal alkene tethered by a CH₂XCH₂ group to their 4‐position (X=CH₂, CMe₂, O, S, NBoc, NZ, NTs, NBn), were synthesized in overall yields of 51–80 %. Starting materials for the syntheses were either commercially available 4‐hydroxycoumarin or 4‐formylcoumarin. The intramolecular [2+2] photocycloaddition of these coumarins gave diastereoselectively products with a tetracyclic 3,3a,4,4a‐tetrahydro‐1H‐cyclopenta[2,3]cyclobuta[1,2‐c]chromen‐5(2H)‐one skeleton. Direct irradiation at λ=300 nm in dichloromethane (c=10 mM ) led to product formation in good yields for most substrates, presumably via a singlet excited state intermediate. Due to the low coumarin absorption at λ >350 nm the photocycloaddition was slow upon irradiation at λ=366 nm. Addition of a chiral oxazaborolidine‐based Lewis acid (50 mol %) increased the reaction rate at λ=366 nm and induced a significant enantioselectivity in the [2+2] photocycloaddition. Six out of eight coumarin substrates (X=CH₂, CMe₂, O, NBoc, NZ, NTs) gave the respective products in yields of 72–96 % and with 74–90 % enantiomeric excess (ee) upon irradiation in dichloromethane (c=20 mM ) at ?75 °C. The Lewis acid presumably acts by coordination to the coumarin carbonyl oxygen atom, which leads to a bathochromic shift (redshift) of the UV absorption and which increases the singlet state lifetime. A second electrostatic interaction of the hydrogen atom at C3 with the oxygen atom of the oxazaborolidine is likely.     

FRET‐Based Mitochondria‐Targetable Dual‐Excitation Ratiometric Fluorescent Probe for Monitoring Hydrogen Sulfide in Living Cells

Hydrogen sulfide (H₂S) is connected with various physiological and pathological functions. However, understanding the important functions of H₂S remains challenging, in part because of the lack of tools for detecting endogenous H₂S. Herein, compounds Ratio‐H₂S 1/2 are the first FRET‐based mitochondrial‐targetable dual‐excitation ratiometric fluorescent probes for H₂S on the basis of H₂S‐promoted thiolysis of dinitrophenyl ether. With the enhancement of H₂S concentration, the excitation peak at λ≈402 nm of the phenolate form of the hydroxycoumarin unit drastically increases, whereas the excitation band centered at λ≈570 nm from rhodamine stays constant and can serve as a reference signal. Thus, the ratios of fluorescence intensities at λ=402 and 570 nm (I₄₀₂/I₅₇₀) exhibit a drastic change from 0.048 in the absence of H₂S to 0.36 in the presence of 180 μM H₂S; this is a 7.5‐fold variation in the excitation ratios. The favorable properties of the probe include the donor and acceptor excitation bands, which exhibit large excitation separations (up to 168 nm separation) and comparable excitation intensities, high sensitivity and selectivity, and function well at physiological pH. In addition, it is demonstrated that the probe can localize in the mitochondria and determine H₂S in living cells. It is expected that this strategy will lead to the development of a wide range of mitochondria‐targetable dual‐excitation ratiometric probes for other analytes with outstanding spectral features, including large separations between the excitation wavelengths and comparable excitation intensities.     

UV‐Assisted Removal of Inactive Peroxide Species for Sustained Epoxidation of Cyclooctene on Anatase TiO2

Epoxidation of olefins with H₂O₂ is one of the most important reactions in organic synthesis. We found that anatase TiO₂ can be a good catalyst for the epoxidation of cyclooctene with H₂O₂ at room temperature. However, the catalyst deactivated quickly in the presence of excess amount of H₂O₂ because of the formation of inactive side‐on Ti‐η²‐peroxide species on the surface of TiO₂, the presence of which was confirmed by isotope‐labelled resonance UV Raman spectroscopy and kinetics studies. Interestingly, the epoxidation reaction could be dramatically accelerated under irradiation of UV light with λ≥350 nm. This phenomenon is attributed to the photo‐assisted removal of the inactive peroxide species, through which the active sites on the surface of anatase TiO₂ are regenerated and the catalytic epoxidation of cyclooctene with H₂O₂ is resumed. This finding provides an alternative for sustained epoxidation reactions on TiO₂ at room temperature. Moreover, it also has significant implications on the deactivation pathway and possible solutions in Ti‐based heterogeneous catalysis or photocatalysis.     

Au改性TiO2纳米复合物对人结肠癌细胞的光催化杀伤作用

提出了通过TiO₂表面修饰纳米Au的方法来提高纳米TiO₂光催化杀伤癌细胞的效率. 采用化学还原法合成了Au改性的TiO₂ (Au/TiO₂)纳米复合物, 并研究了不同掺杂量(1 wt%, 2 wt%, 4 wt%)的Au/TiO₂对人结肠癌LoVo细胞的光催化杀伤效应. 结果显示, Au的掺杂大大地提高了TiO₂纳米粒子光催化杀伤结肠癌LoVo细胞的效率, 而且Au掺杂量的高低影响Au/TiO₂光催化杀伤癌细胞的效率, 掺金量为2%的Au/TiO₂对结肠癌LoVo细胞具有最高的光催化杀伤效率. 在光强为1.8 mW/cm²的紫外灯(λ_max＝365 nm)下光照110 min, 50 μg/mL掺金量为2%的Au/TiO₂能够杀死所有的癌细胞, 而同样浓度的TiO₂只能杀死70%的癌细胞.     

Electron‐Transfer Mediator Microbiosensor Fabrication Based on Immobilizing HRP‐Labeled Au Colloids on Gold Electrode Surface by 11‐Mercaptoundecanoic Acid Monolayer

In this paper, a new strategy for constructing a mediator‐type amperometric hydrogen peroxide (H₂O₂) microbiosensor was described. An electropolymerized thionine film (PTH) was deposited directly onto a gold electrode surface. The resulting redox film was extremely thin, adhered well onto a substrate (electrode), and had a highly cross‐linked network structure. Consequently, horseradish peroxidase (HRP) was successfully immobilized on nanometer‐sized Au colloids, which were supported by thiol‐tailed groups of 11‐mercaptoundecanoic acid (11‐MUA) monolayer covalently bound onto PTH film. With the aid of the PTH mediator, HRP‐labeled Au colloids microbiosensor displayed excellent electrocatalytical response to the reduction of H₂O₂. This matrix showed a biocompatible microenvironment for retaining the native activity of the covalent HRP and a very low mass transport barrier to the substrate, which provided a fast amperometric response to H₂O₂. The proposed H₂O₂ microbiosensor exhibited linear range of 3.5 μM–0.7 mM with a detection limit of 0.05 μM (S/N=3). The response showed a Michaelis‐Menten behavior at larger H₂O₂ concentrations. The K_M^app value for the biosensors based on 24 nm Au colloids was found to be 47 μM, which demonstrated that HRP immobilized on Au colloids exhibited a high affinity to H₂O₂ with no loss of enzymatic activity. This microbiosensor possessed good analytical performance and storage stability.     

Hydrophilicity Control of Visible‐Light Hydrogen Evolution and Dynamics of the Charge‐Separated State in Dye/TiO2/Pt Hybrid Systems

Visible‐light‐driven H₂ evolution based on Dye/TiO₂/Pt hybrid photocatalysts was investigated for a series of (E)‐3‐(5′‐{4‐[bis(4‐R¹‐phenyl)amino]phenyl}‐4,4′‐(R²)₂‐2,2′‐bithiophen‐5‐yl)‐2‐cyanoacrylic acid dyes. Efficiencies of hydrogen evolution from aqueous suspensions in the presence of ethylenediaminetetraacetic acid as electron donor under illumination at λ>420 nm were found to considerably depend on the hydrophilic character of R¹, varying in the order MOD (R¹=CH₃OCH₂, R²=H)≈ MO4D (R¹=R²=CH₃OCH₂)> HD (R¹=R²=H)> PD (R¹=C₃H₇, R²=H). In the case of MOD /TiO₂/Pt, the apparent quantum yield for photocatalyzed H₂ generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD ‐ or PD ‐grafted transparent films of TiO₂ nanoparticles dipped into water at pH 3 commonly revealed ultrafast formation (<100 fs) of the dye radical cation (Dye^.+) followed by multicomponent decays, which involve minor fast decays (<5 ps) almost independent of R¹ and major slower decays with significant differences between the two samples: 1) the early decay of the major components for MOD is about 2.5 times slower than that for PD and 2) a redshift of the spectrum occurred for MOD with a time constant of 17 ps, but not for PD . The substituent effects on H₂ generation as well as on transient behavior have been discussed in terms substituent‐dependent charge recombination (CR) of Dye^.+ with electrons in bulk, inner‐trap, and/or interstitial‐trap states, arising from different solvent reorganization.     

Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

A novel dopant‐free TiO₂ photocatalyst (V_o^.‐TiO₂), which is self‐modified by a large number of paramagnetic (single‐electron‐trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO₂ precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO₂ precursor, imidazole, and hydrochloric acid are all necessary for the formation of V_o^.‐TiO₂. Although the synthesis of V_o^.‐TiO₂ originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X‐ray diffraction, XPS, and EPR spectroscopy reveal that the V_o^.‐TiO₂ material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse‐reflectance spectroscopy and photoelectrochemical measurement demonstrate that V_o^.‐TiO₂ is a stable visible‐light‐responsive material with photogenerated charge separation efficiency higher than N‐TiO₂ and P25 under visible‐light irradiation. The V_o^.‐TiO₂ material exhibits not only satisfactory thermal‐ and photostability, but also superior photocatalytic activity for H₂ evolution (115 μmol h^?1 g^?1) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO₂ precursor) and calcination time on the photocatalytic activity and the microstructure of V_o^.‐TiO₂ were elucidated.     

Long‐Lived Room‐Temperature Deep‐Red‐Emissive Intraligand Triplet Excited State of Naphthalimide in Cyclometalated IrIII Complexes and its Application in Triplet‐Triplet Annihilation‐Based Upconversion

Cyclometalated Ir^III complexes with acetylide ppy and bpy ligands were prepared (ppy=2‐phenylpyridine, bpy=2,2′‐bipyridine) in which naphthal ( Ir‐2 ) and naphthalimide (NI) were attached onto the ppy ( Ir‐3 ) and bpy ligands ( Ir‐4 ) through acetylide bonds. [Ir(ppy)₃] ( Ir‐1 ) was also prepared as a model complex. Room‐temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir‐3 and Ir‐4 showed strong absorption in the visible range (ε=39600 M ^?1 cm^?1 at 402 nm and ε=25100 M ^?1 cm^?1 at 404 nm, respectively), long‐lived triplet excited states (τ_T=9.30 μs and 16.45 μs) and room‐temperature red emission (λ_em=640 nm, Φ_p=1.4 % and λ_em=627 nm, Φ_p=0.3 %; cf. Ir‐1 : ε=16600 M ^?1 cm^?1 at 382 nm, τ_em=1.16 μs, Φ_p=72.6 %). Ir‐3 was strongly phosphorescent in non‐polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir‐4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non‐polar solvents. Emission of Ir‐1 and Ir‐2 was not solvent‐polarity‐dependent. The T₁ excited states of Ir‐2 , Ir‐3 , and Ir‐4 were identified as mainly intraligand triplet excited states (³IL) by their small thermally induced Stokes shifts (ΔE_s), nanosecond time‐resolved transient difference absorption spectroscopy, and spin‐density analysis. The complexes were used as triplet photosensitizers for triplet‐triplet annihilation (TTA) upconversion and quantum yields of 7.1 % and 14.4 % were observed for Ir‐2 and Ir‐3 , respectively, whereas the upconversion was negligible for Ir‐1 and Ir‐4 . These results will be useful for designing visible‐light‐harvesting transition‐metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc.     

Carbon‐Dot‐Sensitized,Nitrogen‐Doped TiO2 in Mesoporous Silica for Water Decontamination through Nonhydrophobic Enrichment–Degradation Mode

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO₂ through an impregnation–hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO₂ nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6mm symmetry, a high specific surface area (446.27 m² g^?1), large pore volume (0.57 cm³ g^?1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO₂ nanocrystals are anchored to the carbon dot through Ti?O?N and Ti?O?C bonds, as revealed by X‐ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO₂ is also verified by the formation of the Ti?N bond. This composite shows excellent adsorption capabilities for 2,4‐dichlorophenol and acid orange 7, with an electron‐deficient aromatic ring, through electron donor–acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible‐light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible‐light activity of TiO₂. The adsorption capacity does not suffer any clear losses after being recycled three times.     

Synthesis and Crystal Structure of Di-n-butyltin（Ⅳ） Complex with 2-Oxo-propionic Acid （4-Pyridinecarbonyl） Hydrazone

The novel complex di‐n‐butyltin(IV) 2‐oxo‐propionic acid (4‐pyridinecarbonyl) hydrazone, (n‐C₄H₉)₂Sn‐[O₂CC(CH₃)=N‐N=C(‐O)C₅N‐4] (H₂O) has been synthesized and its structure has been determined by X‐ray diffraction analysis. The complex crystallizes in orthorhombic system with space group Pca2₁. Crystal data: a=2.7540(9) nm, b=0.9676(3) nm, c= 1.5750(5) nm, V=4.197(2) nm³, D_c= 1.444 g/cm³, Z=8. μ= 1.241 mm^?1. F(000)= 1856, R₁=0.0462 and wR₂=0.1001. In the crystals of the title complex, the tin atom is in six‐coordination with a distorted octahedral geometry, three oxygen atoms [O(1), O(3) and O(4)] and one nitrogen atom N(1) forming the equatorial plane and C(10)‐Sn(1)‐C(14) being the axis. Two molecules form a dimer with weak interactions of Sn‐O bonding and hydrogen bonds.     

K2Au(IO3)5 and β‐KAu(IO3)4: Polar Materials with Strong SHG Responses Originating from Synergistic Effect of AuO4 and IO3 Units

Two new polar potassium gold iodates, namely, K₂Au(IO₃)₅ (Cmc2₁) and β‐KAu(IO₃)₄ (C2), have been synthesized and structurally characterized. Both compounds feature zero‐dimensional polar [Au(IO₃)₄]^? units composed of an AuO₄ square‐planar unit coordinated by four IO₃^? ions in a monodentate fashion. In β‐KAu(IO₃)₄, isolated [Au(IO₃)₄]^? ions are separated by K⁺ ions, whereas in K₂Au(IO₃)₅, isolated [Au(IO₃)₄]^? ions and non‐coordinated IO₃^? units are separated by K⁺ ions. Both compounds are thermally stable up to 400 °C and exhibit high transmittance in the NIR region (λ=800–2500 nm) with measured optical band gaps of 2.65 eV for K₂Au(IO₃)₅ and 2.75 eV for β‐KAu(IO₃)₄. Powder second‐harmonic generation measurements by using λ=2.05 μm laser radiation indicate that K₂Au(IO₃)₅ and β‐KAu(IO₃)₄ are both phase‐matchable materials with strong SHG responses of approximately 1.0 and 1.3 times that of KTiOPO₄, respectively. Theoretical calculations based on DFT methods confirm that such strong SHG responses originate from a synergistic effect of the AuO₄ and IO₃ units.     

Magnetic Nanohybrids Loaded with Bimetal Core–Shell–Shell Nanorods for Bacteria Capture,Separation, and Near‐Infrared Photothermal Treatment

A novel antimicrobial nanohybrid based on near‐infrared (NIR) photothermal conversion is designed for bacteria capture, separation, and sterilization (killing). Positively charged magnetic reduced graphene oxide with modification by polyethylenimine (rGO–Fe₃O₄–PEI) is prepared and then loaded with core–shell–shell Au–Ag–Au nanorods to construct the nanohybrid rGO–Fe₃O₄–Au–Ag–Au. NIR laser irradiation melts the outer Au shell and exposes the inner Ag shell, which facilitates controlled release of the silver shell. The nanohybrids combine physical photothermal sterilization as a result of the outer Au shell with the antibacterial effect of the inner Ag shell. In addition, the nanohybrid exhibits high heat conductivity because of the rGO and rapid magnetic‐separation capability that is attributable to Fe₃O₄. The nanohybrid provides a significant improvement of bactericidal efficiency with respect to bare Au–Ag–Au nanorods and facilitates the isolation of bacteria from sample matrixes. A concentration of 25 μg mL^?1 of nanohybrid causes 100 % capture and separation of Escherichia coli O157:H7 (1×10⁸ cfu mL^?1) from an aqueous medium in 10 min. In addition, it causes a 22 °C temperature rise for the surrounding solution under NIR irradiation (785 nm, 50 mW cm^?2) for 10 min. With magnetic separation, 30 μg mL^?1 of nanohybrid results in a 100 % killing rate for E. coli O157:H7 cells. The facile bacteria separation and photothermal sterilization is potentially feasible for environmental and/or clinical treatment.     

Thermotropic Liquid Crystals Based on Extended 2,5‐Disubstituted‐1,3,4‐Oxadiazoles: Structure–Property Relationships,Variable‐Temperature Powder X‐ray Diffraction,and Small‐Angle X‐ray Scattering Studies

A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R¹‐C₆H₄‐{OC₂N₂}‐C₆H₄‐R² (R¹=R²=C₁₀H₂₁O 1 a , p‐C₁₀H₂₁O‐C₆H₄‐C?C 3 a , p‐CH₃O‐C₆H₄‐C?C 3 b ; R¹=C₁₀H₂₁O, R²=CH₃O 1 b , (CH₃)₂N 1 c ; F 1 d ; R¹=C₁₀H₂₁O‐C₆H₄‐C?C, R²=C₁₀H₂₁O 2 a , CH₃O 2 b , (CH₃)₂N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH₂Cl₂ solution, these compounds displayed a room‐temperature emission with λ_max at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions.