The interaction of iron and metal‐free meso‐tetra (4‐sulfonatophenyl) porphines with CVD graphene: a comparative Raman spectroscopy study

In this work, a non‐covalent interaction of iron and metal‐free meso‐tetra (4‐sulfonatophenyl) porphines (FeTPPS and TPPS, respectively) with high‐quality single‐layer graphene is studied by Raman spectroscopy. Such a kind of graphene functionalization is promising for a development of novel optoelectronic devices and sensors. Our results show that the central metal atom of porphyrin macrocycle, iron particularly, plays an important role in the integrity of FeTPPS on graphene surface; however, the predicted Raman enhancement is not significant. The interaction of metal‐free TPPS with graphene leads to the deprotonation of TPPS molecules and higher Raman enhancement values. Moreover, initially deprotonated TPPS solutions after the adsorption onto the graphene surface demonstrate the appearance of new Raman bands and significantly enhanced Raman signals. We propose that a strong interaction between deprotonated TPPS and graphene is realized through pyrrole and desulfonated phenyl rings of closely located planar TPPS molecules on the graphene surface. The results show that both the protonation of porphyrin macrocycle and the existence of central metal atom are crucial for a formation of nanocomposites with defined electronic properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Multifunctional human serum albumin in the surface‐enhanced Raman spectroscopy of porphyrin: demetalation promoter,molecular spacer and stabilizer

Human serum albumin (HSA), a model protein, was introduced to the surface‐enhanced Raman spectroscopy (SERS) of cationic porphyrin 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)‐21H,23H‐porphine (H₂TMPyP4). HSA was found to have a great influence not only on Ag nanoparticle aggregation state but also on the interaction between Ag nanoparticle and H₂TMPyP4 molecules. In the (H₂TMPyP4‐Ag colloid)/HSA system, addition of H₂TMPyP4 to Ag colloid led to a quick Ag colloid aggregation, and subsequent HSA addition could stabilize this system. The SERS spectrum was dominated by a combination of Ag(II)TMPyP4 and free base H₂TMPyP4. More interestingly, a photoinduced demetalation of Ag(II)TMPyP4 to free base H₂TMPyP4 was observed in the (H₂TMPyP4‐Ag colloid)/HSA system. This demetalation process was partially reversible when the laser was turned off or the laser power was reduced. In this case, HSA acts as both a stabilizer and a demetalation promoter. In the (HSA‐H₂TMPyP4)/Ag colloid system, when H₂TMPyP4 was premixed with HSA prior to the Ag colloid addition, no obvious Ag colloid aggregation appeared, and the SERS spectrum was just characteristic of free base H₂TMPyP4. In this case, HSA is proposed to function as both a stabilizer and a molecular spacer. Copyright © 2010 John Wiley & Sons, Ltd.     

SER(R)S of porphyrins on Ag nanoparticles immobilized by silane: a unique way to obtain free‐base porphyrin spectra

We measured the surface‐enhanced resonance Raman scattering (SER(R)S) spectra of 5,10,15,20‐tetrakis (1‐methyl‐4‐pyridyl)porphyrin (TMPyP) by using solid SERS‐active substrates: Ag nanoparticles immobilized by aminosilane on glass plates. We report the surprising result that by using such substrates it is possible to obtain SER(R)S spectra of porphyrins in the unperturbed free‐base form, although by using silver nanoparticles directly in solution, the porphyrin molecules are completely metalated. We suggest that silane used for nanoparticle immobilization modifies the surface properties and, therefore, makes porphyrin metalation impossible. Copyright © 2007 John Wiley & Sons, Ltd.     

SERS microRaman spectral probing of adsorbate‐containing,liquid‐overlayed nanosponge Ag aggregates assembled from fractal aggregates

Adsorbate‐containing, nanosponge Ag aggregates overlayed by a thin (~1.5 mm) liquid layer are reported as a new type of sample for Surface‐enhanced Raman scattering (SERS) microRaman spectral measurements and adsorbate (analyte) detection. Macroscopic Ag aggregates (of about 1.5 × 1.0 × 0.025 mm size) with the nanosponge internal morphology (revealed by Scanning electron microscopy (SEM)) were prepared by 3D assembling of fused fractal aggregates (D = 1.84 ± 0.04) formed in Ag nanoparticle hydrosol/HCl/adsorbate systems with 2,2’‐bipyridine (bpy) and/or a cationic free‐base tetrakis(2‐methyl‐4‐pyridiniumyl) porphine (H₂TMPyP) as the testing adsorbates. For SERS microRaman measurements, the macroscopic aggregate was overlayed by a thin (~1.5 mm) layer of the residual liquid. Preparation procedure, nanoscale imaging, and SERS spectral probing including the determination of the detection limits of the adsorbates revealed the following advantages of the adsorbate‐containing, liquid‐overlayed 3D nanosponge aggregate as a sample for SERS microRaman spectral measurements: (1) localization of adsorbate (analyte) into hot spots and, simultaneously, prevention of the analyte decomposition during the spectral measurement (carried out without an immersion objective), (2) fast and simple sample preparation, and (3) minimization of sample volume and an efficient concentration of hot spots into the focus of the laser beam. The advantages of the nanosponge Ag aggregates are further demonstrated by the 40 fmol limit of detection of bpy as Ag(0)‐bpy surface complex, as well as by preservation of the native structure of the cationic free‐base porphyrin H₂TMPyP. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced photocatalytic activity of Cu-doped ZnO nanorods

Cu-doped ZnO nanorods with different Cu concentrations were synthesized through the vapor transport method. The synthesized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–vis spectroscopy. The XRD results revealed that Cu was successfully doped into ZnO lattice. The FE-SEM images showed that the undoped ZnO has needle like morphology whereas Cu-doped ZnO samples have rod like morphology with an average diameter and length of 60–90 nm and 1.5–3 μm respectively. The red shift in band edge absorption peak in UV-vis absorbance spectrum with increasing Cu content also confirm the doping of Cu in ZnO nanorods. The photocatalytic activity of pure and Cu-doped ZnO samples was studied by the photodegradation of resazurin (Rz) dye. Both pure ZnO and the Cu-doped ZnO nanorods effectively removed the Rz in a short time. This photodegradation of Rz followed the pseudo-first-order reaction kinetics. ZnO nanorods with increasing Cu doping exhibit enhanced photocatalytic activity. The pseudo-first-order reaction rate constant for 15 % Cu-doped ZnO is equal to 10.17×10^?2min^?1 about double of that with pure ZnO. The increased photocatalytic activity of Cu-doped ZnO is attributed to intrinsic oxygen vacancies due to high surface to volume ratio in nanorods and extrinsic defect due to Cu doping.     

ZnO纳米棒的低温溶液法制备、光电特性研究及其在有机/无机复合电致发光中的应用

利用水热法制备了垂直于衬底的定向生长的ZnO纳米棒,利用扫描电子显微镜及光致发光的方法对其形貌及光学特性进行了表征,利用场发射性能测试装置对ZnO纳米棒的场发射性能进行了测试.结果表明:利用水热法在较低的温度(95 ℃) 下生长了具有较好形貌和结构的ZnO纳米棒,并表现出了较好的场发射特性,当电流密度为1 μA/cm²时,开启电场是2.8 V/μm,当电场为6.4 V/μm时,电流密度可以达到0.67 mA/cm²,场增强因子为3360.稳定性测试表明,在5 h内,4.5 V/μm的电场下,其波动不超过25%.将制备的ZnO纳米棒应用到有机/无机电致发光中,其中ZnO纳米棒为电子传输层,m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) 为空穴传输层,得到了ZnO的342 nm的紫外电致发光,此发光较ZnO纳米棒光致发光的紫外发射有约40 nm的蓝移. 关键词： ZnO纳米棒 场发射 水热法 有机/无机复合电致发光     

Surface morphology and growth mechanism of catalyst‐free ZnO and Mgx Zn1–x O nanorods

High‐resolution transmission electron microscopy was employed to investigate morphologies and catalyst‐free growth mechanism of ZnO/Mg_x Zn_1–x O ‘multi‐quantum well’ and ‘core‐shell’ nanorod heterostructures as well as ZnO nanorods. The one‐dimensional growth mechanism and the hexagonal faceting of ZnO nanorod were explained by the surface energy anisotropy. The morphology change by alloying with Mg was successfully explained by investigating the energy gain by adatom adsorption and the reduction in the surface energy anisotropy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Red/Near‐Infrared Emissive Metalloporphyrin‐Based Nanodots for Magnetic Resonance Imaging‐Guided Photodynamic Therapy In Vivo

Near‐infrared emissive (NIR) porphyrin‐implanted carbon nanodots (PCNDs or MPCNDs) are prepared by selectively carbonization of free base or metal complexes [M = Zn(II) or Mn(III)] of tetra‐(meso‐aminophenyl)porphyrin in the presence of citric acid. The as‐prepared nanodots exhibit spontaneously NIR emission, small size, good aqueous dispersibility, and favorable biocompatibility characteristic of both porphyrins and pristine carbon nanodots. The subcellular localization experiment of nanodots indicates a lysosome‐targeting feature. And the in vitro photodynamic therapy (PDT) results on HeLa cells indicate the nanodots alone have no adverse effect on tumor cells, but display remarkable photodynamic efficacy upon irradiation. Moreover, MnPCNDs containing paramagnetic Mn(III) ions, which possesses good biocompatibility, NIR luminescence, and magnetic resonance imaging and efficient singlet oxygen production, are further studied in magnetic resonance imaging‐guided photodynamic therapy in vivo.     

Fast piezoresistive sensor and UV photodetector based on Mn‐doped ZnO nanorods

A low cost hydrothermal synthesis method to synthesize Mn‐doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH^– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn‐doped ZnO NRs show that the Mn‐doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c‐axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn_0.85Mn_0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa^–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa^–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human‐friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small‐size, low‐cost and easy‐to‐customize application‐specific requirements. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

CdS/ZnO纳米复合结构的制备、表征及其光催化活性的改善

利用简单的水热法在ZnO纳米棒表面合成CdS纳米粒子.用扫描电镜(SEM)和X射线衍射(XRD)对CdS/ZnO异质结构进行表征.实验结果表明,在生长CdS的过程中ZnO被逐渐地腐蚀.选择CdS/ZnO纳米复合材料作为光催化剂在紫外光和绿光照射的条件下降解甲基橙(MO).CdS/ZnO纳米复合材料纳米棒作为光催化剂降解...     

Resistive switching characteristics of sol–gel based ZnO nanorods fabricated on flexible substrates

The authors report the resistive switching characteristics of sol–gel based ZnO nanorods (NRs) fabricated on flexible substrates. A resistance ratio of 10, endurance of over 100 cycles, and narrower dispersion in the ON/OFF voltages and resistances compared to ZnO thin‐film devices are demonstrated. Furthermore, the resistive switching characteristics on flexible substrates are maintained under severe substrate bending because of the ductile properties of the nanorods. Devices composed of the Au/sol–gel based NRs/Au structure have the potential for low‐temperature flexible nonvolatile memory applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Mn doping on the microstructures and photoluminescence properties of CBD derived ZnO nanorods

Mn-doped ZnO nanorods were synthesized from aqueous solutions of zinc nitrate hexahydrate, manganese nitrate and methenamine by the chemical solution deposition method (CBD). Their microstructures, morphologies and optical properties were studied in detail. X-ray diffraction (XRD) results illustrated that all the diffraction peaks can be indexed to ZnO with the hexagonal wurtzite structure. Scanning electron microscope (SEM) results showed that the average diameter of Mn-doped ZnO nanorods was larger than that of the undoped one. Photoluminescence (PL) spectra indicated that manganese doping suppressed the emission intensity and caused the blue shift of UV emission position compared with the undoped ZnO nanorods. In the Raman spectrum of Mn-doped ZnO nanorods, an additional mode at about 525 cm⁻¹ appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.     

Preparation and enhanced visible light-driven catalytic activity of ZnO microrods sensitized by porphyrin heteroaggregate

An inorganic-organic composite (ZnO/TAPPI-CoTPPS) composed of ZnO microrods and nano-heteroaggregates containing tetrakis(4-trimethylaminophenyl) porphyrin (TAPPI) and tetrakis(4-sulfonatophenyl) porphyrin cobalt(II) (CoTPPS), has been achieved by a simple mixing method. From the solid diffuse reflectance UV-vis spectrum of ZnO/TAPPI-CoTPPS, it can be observed that the Soret band of the porphyrin heteroaggregate of ZnO/TAPPI-CoTPPS is blue-shifted in comparison with that of the pure TAPPI-CoTPPS heteroaggregate while the Q bands are red-shifted, which demonstrates that there exists some interaction between the porphyrin heteroaggregate and ZnO. In addition, the photodegradation of rhodamine B (RhB) in water catalyzed by ZnO/TAPPI-CoTPPS was investigated at room temperature. Under visible light irradiation (λ ≥ 420 nm), the photocatalytic activity of the ZnO/TAPPI-CoTPPS composite was higher than those of the porphyrin monomers modified ZnO composite and pure ZnO.     

Effect of the layer charge on the interaction of porphyrin dyes in layered silicates dispersions

Interaction between tetracationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP), and layered silicates in aqueous dispersions was studied using absorption, steady-state and time-resolved fluorescence spectroscopies. The charge density of silicates increases in order synthetic laponite (LAP)<Kunipia F montmorillonite (KF)<synthetic fluorohectorite (FHT). Interpretations of the spectra of layered silicate-porphyrin (LSP) systems considered models of dye adsorption on clay mineral colloid particles, analyzing phenomena occurring in similar systems such as structural changes of TMPyP and the formation of dye molecular assemblies. Structural changes of TMPyP, including flattening of the porphyrin molecule, do not fully explain all the spectral observations. One should mention variations of the Q-bands and fluorescence spectra in dependence on the layer charge. The molecular association of the TMPyP molecules is expected to occur to a certain extent in dependence on the layer charge of a clay mineral template. H-aggregates were not observed in any system. Only FHT colloids induced the formation of at least two components with significantly different spectral properties.     

Plasmonic enhancement of blue emission from ZnO nanorods grown on the anodic aluminum oxide (AAO) template

Luminescent properties of ZnO nanorods covered with Ag nanoparticles are examined. Nanorods were synthesized on AAO templates using Atomic Layer Deposition (ALD) technique. Two types of the samples were prepared with different arrangement of ZnO nanorods and doping conditions. Nanorods of the second type were codoped with Al, to stimulate defect-related emissions. The ZnO material fills heterogeneously the interior of the AAO nanopores and has hexagonal, wurtzite structure. Both types of structures exhibit a broad defect-related emission at about 440 nm, most probably related to recombination at zinc interstitial (Zn_i) defects. This emission in samples with a random distribution of ZnO:Al nanorods and finer Ag nanoparticles is enhanced by factor of ～2.5 upon Ag deposition. The so-obtained material is interesting from the point of view of its application in blue range emitting diodes.     

Site‐specific deposition of Ag nanoparticles on ZnO nanorod arrays via galvanic reduction and their SERS applications

A controllable heterostructure consisting of ZnO nanorod arrays with attached Ag nanoparticles at only one end has been synthesized via a facile and convenient galvanic reduction method. Scanning electron microscopic images of these nanostructures showed good selectivity of Ag deposition on the tip of ZnO nanorod arrays. The formation of these regular Ag ZnO heterogeneous nanorod arrays can be explained by a localization of the electrons at the ends of the ZnO nanorods after the electron transfer step. By tuning the reaction time and the concentration of silver nitrate, the density of Ag nanoparticles on the tip of ZnO nanorods can be well controlled. Owing to the introduction of Ag nanoparticles with different densities, the resulting Ag ZnO heterogeneous nanorod arrays have been proved to be a versatile substrate for surface‐enhanced Raman scattering not only for common organic molecules but also for label‐free protein detection. Copyright © 2009 John Wiley & Sons, Ltd.     

Double‐layer channel structure based ZnO thin‐film transistor grown by atomic layer deposition

A double channel structure has been used by depositing a thin amorphous‐AlZnO (a‐AZO) layer grown by atomic layer deposition between a ZnO channel and a gate dielectric to enhance the electrical stability. The effect of the a‐AZO layer on the electrical stability of a‐AZO/ZnO thin‐film transistors (TFTs) has been investigated under positive gate bias and temperature stress test. The use of the a‐AZO layer with 5 nm thickness resulted in enhanced subthreshold swing and decreased V_th shift under positive gate bias/temperature stress. In addition, the falling rate of the oxide TFT using a‐AZO/ ZnO double channel had a larger value (0.35 eV/V) than that of pure ZnO TFT (0.24 eV/V). These results suggest that the interface trap density between dielectric and channel was reduced by inserting a‐AZO layer at the interface between the channel and the gate insulator, compared with pure ZnO channel. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CTAB对四-(4-N-甲基吡啶)卟啉SERS谱的影响

研究了阳离子表面活性剂十六烷基三甲基溴化铵 (CTAB)对四 ( 4 N 甲基吡啶 )卟啉 (H2 TMPyP)及其银配合物 (AgTMPyP)在Ag胶中的表面增强拉曼散射 (SERS)谱的影响 .SERS光谱表明 ,吸附于Ag胶粒的H2 TMPyP与衬底银原子结合形成AgTMPyP ,加入CTAB后 ,部分AgTMPyP表面络合物还原为H2 TMPyP .相似的去金属化反应也出现在AgTMPyP/Ag胶 /CTAB体系中 .CTAB的加入使SERS谱带强度明显增加 .AgTMPyP的去金属化被认为是由于CTAB的存在使Ag胶颗粒表面附近微环境发生改变     

Effect of ultrasonic treatment before and after hydrothermal process on the morphologies and formation mechanism of ZnO nanorods

ZnO nanorods were fabricated by ultrasonic treatment before and after a hydrothermal process. The morphology and structure of the nanorods were individually characterized by scanning electron microscopy and X-ray diffraction. The results show that before the hydrothermal process, fore-ultrasonic treatment can directly gain ZnO nanorods which mainly experienced four conversion stages from initial bulk Zn(OH)₂, a coexisting phase of bulk Zn(OH)₂ with ZnO nanoslices, ZnO nanoslices with flower-like ZnO nanorods and finally to purely flower-like ZnO nanorods. After the hydrothermal process, the post-ultrasonic treatment mainly influences the aggregation degree of the ZnO nanorods. The formation mechanism of ultrasonic treatment on ZnO nanorods is also discussed.     

Enormous enhancement of ZnO nanorod photoluminescence

ZnO nanorod arrays were grown on quartz slices in the aqueous solution of zinc acetate and hexamethylenetetramine at 90 °C. Then ZnO:Mg shells were epitaxially grown on the nanorods to form core/shell structures in the aqueous solution of zinc acetate, magnesium acetate and hexamethylenetetramine at the same temperature. Effects of the shells and UV laser beam irradiation on the crystal structure and photoluminescence properties of ZnO nanorods were studied. ZnO:Mg shells suppress the green emission and enhance the UV emission intensity of the nanorods by 38 times. Enhancement of the UV emission depends on the Mg content in the shells. Short time UV laser beam irradiation could improve ZnO nanorod emission efficiently. The UV emission intensity of ZnO nanorods is enhanced by 71 times by capping and subsequent UV laser beam irradiation.