Longtian Kang

Controlled Morphogenesis of Organic Polyhedral Nanocrystals from Cubes, Cubooctahedrons, to Octahedrons by Manipulating the Growth Kinetics

Morphological control of organic nanocrystals (ONCs) is important in the fields ranging from specialty chemicals to molecular semiconductors. Although the thermodynamic shape can be readily predicted, most growth morphologies of ONCs are actually determined by kinetic factors and remain poorly understood. On the basis of the reduction of zinc tetraphenylporphyrin perchlorate (ZnTPP(+)ClO(4)(-)) with sodium nitrite (Na(+)NO(2)(-)), we synthesized two series of ONCs of aquozinc tetraphenylporphyrin (ZnTPP·H(2)O), in the presence of either cetyltrimethylammonium bromide (CTAB) or poly(vinyl pyrrolidone) (PVP) as the capping ligands. As the cationic precursors of ZnTPP(+) are separated in the solution phase, smoothly controlled release of ZnTPP·H(2)O building blocks via the reduction reaction facilitates the separation between the nucleation and growth stages during the formation of ONCs and provides a high and tunable supersaturation unavailable by employing conventional crystallization techniques. We found that CTAB mainly serve as the colloidal stabilizer, while selective adhesion of PVP on the {020}s facet alters the crystal habits significantly. In both cases, manipulation of the growth kinetics had been achieved by adjusting the concentration of ZnTPP·H(2)O growth units, and consequently, the supersaturation for the crystallization, thus yielding ONCs with well-controlled sizes and shapes. Remarkably, thermodynamically stable octahedrons have been obtained at high supersaturation in both CTAB and PVP cases.

A pure organic heterostructure of μ-oxo dimeric iron(III) porphyrin and graphitic-C3N4 for solar H2 roduction from water

Due to the two-dimensional flexible structure and abundant pendant amine, graphitic-C3N4 (g-C3N4) may be easily modified by organic molecules as a promising photocatalyst for solar H-2 production from water. Here, through a simple liquid chemical reaction between g-C3N4 and the precursor of m-oxo dimeric iron(III) porphyrin [(FeTPP)(2)O], we provide a novel route to construct a pure organic heterostructure of g-C3N4/(FeTPP)(2)O on the basis of the pi-pi and the Fe-amine interactions. The experimental results demonstrated that (FeTPP)(2)O acted not just as a photosensitizer, but also played the role of a charge promotor to prohibit the recombination of the excited electrons and holes of g-C3N4. As compared to pure or mixed g-C3N4 and/or (FeTPP)(2)O, the obtained pure organic g-C3N4/(FeTPP)(2)O heterostructure exhibited dramatic photocatalytic H-2 production under solar light without any cocatalysts.

Superhydrophobic pure silver surface with flower-like structures by a facile galvanic exchange reaction with [Ag(NH3)2]OH

Superhydrophobic pure silver film composed of flower-like microstructures built by interconnected silver nanoplates on a copper plate without any modification was prepared by a facile galvanic exchange reaction between the aqueous [Ag(NH3)2]OH and the copper plate, giving rise to a contact angle as high as 157 degrees .

Rapid room-temperature synthesis of silver nanoplates with tunable in-plane surface plasmon resonance from visible to near-IR

We report a rapid (within 15 minutes), simple, green, inexpensive, versatile, and reproducible method for the synthesis of Ag triangular and hexagonal nanoplates in aqueous phase under ambient atmosphere. The method involves reducing silver oxide (Ag2O) with hydrazine (N2H4) in the presence of trisodium citrate (TSC) and ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA) in aqueous phase. In our system, TSC molecules serve as colloidal stabilizers to prevent as-prepared colloids from aggregating, while EDTA molecules serve as a ligand to monomers. The complexation of EDTA to Ag+ not only significantly slows the reduction kinetics of Ag+ by N2H4, but also kinetically controls the formation and growth of nanoplates. By varying the amount of EDTA, the shape (triangular and hexagonal) and edge length of nanoplates have been readily controlled, providing a surface plasmon resonance (SPR) response tunable from visible to near infrared. Most importantly, the SPR response is almost a linear function of the quantity of EDTA. Silver nanocrystals with a required SPR response can be provided, even without considering the actual nature of the Ag colloids. Recent results suggest that this chelation-mediated kinetic control over the sizes and morphologies of nanostructures can also be applied for other metal nanostructures.

Chemical redox modulated fluorescence of nitrogen-doped graphene quantum dots for probing the activity of alkaline phosphatase

Alkaline phosphatase (ALP) as an essential enzyme plays an important role in clinical diagnoses and biomedical researches. Hence, the development of convenient and sensitivity assay for monitoring ALP is extremely important. In this work, on the basis of chemical redox strategy to modulate the fluorescence of nitrogen-doped graphene quantum dots (NGQDs), a novel label-free fluorescent sensing system for the detection of alkaline phosphatase (ALP) activity has been developed. The fluorescence of NGQDs is firstly quenched by ultrathin cobalt oxyhydroxide (CoOOH) nanosheets, and then restored by ascorbic acid (AA), which can reduce CoOOH to Co2+, thus the ALP can be monitored based on the enzymatic hydrolysis of L-ascorbic acid-2-phosphate (AAP) by ALP to generate AA. Quantitative evaluation of ALP activity in a range from 0.1 to 5U/L with the detection limit of 0.07U/L can be realized in this sensing system. Endowed with high sensitivity and selectivity, the proposed assay is capable of detecting ALP in biological system with satisfactory results. Meanwhile, this sensing system can be easily extended to the detection of various AA-involved analytes.

Graphene oxide derived graphene quantum dots with different photoluminescence properties and peroxidase-like catalytic activity

Graphene quantum dots (GQDs), as a new kind of carbon nanomaterial, have been widely prepared with graphene oxide (GO) as precursor via various methods. However, little work has been done to detail the structural relationship between GQDs and pristine GO. Herein, we synthesized GQDs through acidic oxidation of GO and separated blue-photoluminescent GQDs (b-GQDs) and green-photoluminescent GQDs (g-GQDs) by a simple dialysis technique. Although the transmission electron microscopy (TEM) and atomic force microscopy (AFM) images reveal their similar morphology, the results of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy and zeta potential measurements reveal their distinct structures with different origins from the GO. The b-GQDs may originate from the intact sp2 cluster of GO, while the g-GQDs are derived from the relaxed carbon backbone with numerous oxygen-containing functional groups. Besides photoluminescence (PL) properties, the peroxidase-like catalytic activity of the two GQDs was also compared. Interestingly, the g-GQDs exhibit higher peroxidase-like catalytic activity and can be used to detect H2O2 with a detection limit of 87 nM, which is lower than most other reported methods. We believe this work provides important insights into the structure, PL properties and potential applications of GO-derived GQDs.

Controllable Nanonet Assembly Utilizing a Pressure‐Difference Method Based on Anodic Aluminum Oxide Templates

Self-assembly of organic molecules from solution is one of the simplest methods to generate ordered nanostructures with potentially new properties. In particular, nanostructured architectures on the macroscopic scale have possible applications in the fields of electronics, catalysis, and medicine. However, controllable fabrication of nanostructured materials is still limited by the available processing methods. Template synthesis has been widely used as a controllable approach to achieve desirable nanostructured materials. Of the many different types of templates, anodic aluminum oxide (AAO) offers clear advantages in the making of onedimensional nanostructured materials and arrays; the AAO templates provide hexagonally packed, uniform pore arrays with a pore diameter that can be varied up to 200 nm. Amongst other applications, AAO has been used as a template for the syntheses of nanotubes for biomedicine and biotechnology, Bi1 xSbx nanowires as thermoelectric wires, SBA-15 nanorod arrays for protein separation and catalysis, and lipid nanotube arrays as a model of cellular membranes. Despite such progress, there have been few reports on the application of AAO as a substrate for the control of surface morphology on the macroscopic scale. Herein, we report for the first time the synthesis of the largearea (ca. 12 cm) nanonet architecture of 5,10,15,20-tetrakis(p-chlorophenyl)porphyrin (TClPP; C44H26Cl4N4) using the AAO template as a substrate. Figure 1 shows the 3D structure of the TClPP molecule and its stacking. Alkylated polycyclic discotic molecules, such as porphyrins, are frequently employed as building blocks because of their ability to stack and form architectures and liquidcrystalline phases. We were able to use the stacking property of TClPP to successfully cultivate nanonet network architectures on the AAO templates. The TClPP nanonets were fabricated as follows. A 2-cm-diameter AAO disk about 15 mm in thickness was laid on a Buchner funnel fitted with a fritted disk. The funnel was then placed on a filter flask connected to a vacuum pump, which was used to maintain a pressure differential across the AAO disk. A solution of TClPP (1 mL, 0.13m) in CH2Cl2 was added dropwise to the AAO template. TClPP nanonets of different meshes in accordance with the AAO pore sizes were thus grown on the rear of the AAO template, that is, the side opposite to that of TClPP deposition. This process was repeated several times to obtain nanoparticles of larger size. Experimental parameters, such as the pressure differential, concentration of the TClPP solution, and the number of times of solution deposition, affected the type and the quality of the nanostructures formed, which will be discussed below. The morphology and size of the nanostructures were examined by field-emission scanning electron microscopy (SEM; Hitachi S-4300). Figures 2a and b show the SEM images of the TClPP nanonet structures formed on the AAO templates. It is evident that the nanonet structures were created as a result of uniform self-assembly of interlocking TClPP nanoparticles. The SEM images also suggest that the knots of the nanonets were formed by a single larger nanoparticle or by several assembled nanoparticles. In Figure 2a, the inner pores of the AAO substrate can be seen behind the floating nanonet. An advantage of this synthesis method was that the fabricated nanonet structure could be easily removed from the AAO substrate. Figure 2b shows the SEM image of a nanonet after it was removed from the substrate. The weblike nanonets showed ordered network structures with meshes mimicking the pore sizes of the AAO templates. Apparently the orderly pores of the AAO template aided the formation of the periodic pattern of the nanonets on the back surface of the template. Three different pore sizes (50, 100, and 200 nm) of the AAO templates were tried in the making of nanonets. A small Figure 1. 3D structure of the TClPP molecule (left) and its stacking (right).

Thermal expansion of nano-sized BaTiO3

BaTiO3 (BTO) nanoparticles (NPs) with various sizes from 6 to 210 nm were synthesized by a one-step hydrothermal method. The powder X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) display the formation of highly crystalline BTO NPs with a narrow size distribution. The size effect of BTO NPs on crystal structures and thermal expansion was investigated according to refined high-temperature XRD data obtained through a full-profile Rietveld method. These results show that unit cell volume (UCV) drastically increases and tetragonality (the c/a ratio) decreases as the size of BTO NPs is reduced. The coefficients of thermal expansion (CTE) of different BTO NPs reveal that the size dependence of positive thermal expansion of BTO mainly results from the ferroelectrostriction of the tetragonal phase. Through further analysis, we find that the mixed phase of tetragonal and cubic BTO may be a core/diffused shell structure which changes with decreasing NP size. Furthermore, it is speculated that the core/shell structure or tetragonality disappears when the size of BTO NPs is reduced to about 12 nm. The value is in accordance with the obtained results through the study of the change of Raman spectra and the ratio of c/a with the size of BTO NPs as well as with the reported reasonable results in the range of 5–16 nm.

Direct photocatalytic hydrogen evolution from water splitting using nanostructures of hydrate organic small molecule as photocatalysts

Organic small molecules with a suitable energy level have usually been considered as photosensitizers rather than catalysts for photocatalytic hydrogen evolution (PHE). Herein, we achieved direct PHE using hydrate zinc tetraphenylporphyrin (ZnP, ZnTPP·H2O) nanostructures synthesized by a liquid-phase chemical reaction as photocatalysts. The shape-dependent photocatalysis revealed that the ZnP nanosheets (ZnP-NS) exhibit higher PHE activity (∼0.16 mmol g−1 h−1) than the ZnP octahedron nanoparticles (ZnP-NPs) (∼0.06 mmol g−1 h−1). After in situ construction of the rubrene/ZnP-NS heterostructure, more efficient PHE of this pure organic nanostructure was obtained due to the occurrence of photoinduced electron transfer and Forster resonance energy transfer (FRET). The optimal PHE rate is ∼0.56 mmol g−1 h−1. Furthermore, with the addition of 3.0 mM methyl viologen (MV) and 3.8 wt% platinum, a PHE rate of ∼9.3 mmol g−1 h−1 can be achieved at pH = 7. This study offers a new route to design organic small molecules as photocatalysts.

Organic core/diffuse-shell nanorods: fabrication, characterization and energy transfer

We successfully prepared organic core/diffuse-shell nanorods, which presents fluorescence resonance energy transfer from the core to shell components.