Penggang Yin

Three Dimensional Design of Large-Scale TiO2 Nanorods Scaffold Decorated by Silver Nanoparticles as SERS Sensor for Ultrasensitive Malachite Green Detection

We have designed a large-scale three-dimensional (3D) hybrid nanostructure as surface-enhanced Raman scattering (SERS) sensor by decorating silver nanoparticles on TiO2 nanorods scaffold (Ag/TiO2). Taking p-mercaptobenzoic acid (PMBA) as the probe molecule, the SERS signals collected by point-to-point and time mapping modes show that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1079, 1586 cm(-1)) is less than 10%, demonstrating good spatial uniformity and time stability. This hybrid substrate also exhibits excellent SERS enhancement effect due to the formation of high-density hot spots among the AgNPs, which was proved by finite-difference time-domain (FDTD) simulations. The application of the new nanostructures as SERS sensors was demonstrated with the detection of malachite green (MG). The quantification of MG can be accomplished with the detection limit of 1 × 10(-12) M based on the Raman intensity. The results show that the Ag/TiO2 nanostructure can be a promising candidate for SERS sensor.

Photocatalytic hydrogen generation enhanced by band gap narrowing and improved charge carrier mobility in AgTaO3 by compensated co-doping

The correlation of the electronic band structure with the photocatalytic activity of AgTaO3 has been studied by simulation and experiments. Doping wide band gap oxide semiconductors usually introduces discrete mid-gap states, which extends the light absorption but has limited benefit for photocatalytic activity. Density functional theory (DFT) calculations show that compensated co-doping in AgTaO3 can overcome this problem by increasing the light absorption and simultaneously improving the charge carrier mobility. N/H and N/F co-doping can delocalize the discrete mid-gap states created by sole N doping in AgTaO3, which increases the band curvature and the electron-to-hole effective mass ratio. In particular, N/F co-doping creates a continuum of states that extend the valence band of AgTaO3. N/F co-doping thus improves the light absorption without creating the mid-gap states, maintaining the necessary redox potentials for water splitting and preventing from charge carrier trapping. The experimental results have confirmed that the N/F-codoped AgTaO3 exhibits a red-shift of the absorption edge in comparison with the undoped AgTaO3, leading to remarkable enhancement of photocatalytic activity toward hydrogen generation from water.

A novel surface-enhanced Raman scattering nanosensor for detecting multiple heavy metal ions based on 2-mercaptoisonicotinic acid functionalized gold nanoparticles

A novel, effective and simple surface-enhanced Raman scattering (SERS) nanosensor for selectively and sensitively detecting heavy metal ions in aqueous solution has been developed in the form of 2-mercaptoisonicotinic acid (2 MNA)-modified gold nanoparticles (AuNPs). Multiple heavy metal ions can be identified and quantified by using relative peak intensity ratios of selected vibrational bands in the SERS spectra of 2 MNA. Especially, concentration of Hg(2+) and Pb(2+) ions are determined by comparing the intensity ratios of the bands 1160/1230 cm(-1) for Hg(2+) and 861/815 cm(-1) (or 815/1392 cm(-1)) for Pb(2+), with detection limits of 3.4×10(-8) and 1.0×10(-7)M, respectively. 2 MNA-AuNPs sensors show a high selectivity for Hg(2+) without masking reagent, and they can also be highly selective for Pb(2+) when using sodium thiosulphate and l-cysteine as masking reagents. These results demonstrate that these 2 MNA-AuNPs nanosensors are promising candidates for in situ heavy metal ions detection and quantification, maybe even inside living cells.

Bioinspired Design and Assembly of Layered Double Hydroxide/Poly(vinyl alcohol) Film with High Mechanical Performance

Inspired by the hierarchical structure and excellent mechanical performance of nacre, LDH nanosheets with an appropriate aspect ratio to withstand significant loads and at the same time allow for rupture under the pull-out mode were synthesized as artificial building blocks for the fabrication of nacre-like films. Multilayered PVA/LDH films with a high tensile strength and ductility were prepared for the first time by bottom-up layer-by-layer assembly of pretreated LDH nanosheets and spin-coating of PVA. The weight fraction of inorganic LDH platelets in the hybrid PVA/LDH films (wp) was controlled by changing the concentration of PVA solution applied in the spin-coating process. The resulting films revealed that the PVA/LDH hybrid films were piled close together to form a well-defined stratified structure resembling the brick-and-mortar structure of natural nacre. In the hybrid films, the content of inorganic LDH platelets was comparable to the value in nacre, up to 96.9 wt %. It could be clearly seen that the mechanical performance of the as-prepared PVA/LDH films was greatly improved by increasing the rigid building-block LDHs. The tensile strength of the 2 wt % PVA/LDH hybrid film reached a value of 169.36 MPa, thus exceeding the strength of natural nacre and reaching 4 times that of a pure PVA film. Meanwhile, its elastic modulus was comparable to that of lamellar bone.

Highly Reproducible Surface-Enhanced Raman Spectra on Semiconductor SnO2 Octahedral Nanoparticles

Highly reproducible surface-enhanced Raman scattering (SERS) spectra are obtained on the surface of SnO(2) octahedral nanoparticles. The spot-to-spot SERS signals show a relative standard deviation (RSD) consistently below 20 % in the intensity of the main Raman peaks of 4-mercaptobenzoic acid (4-MBA) and 4-nitrobenzenethiol (4-NBT), indicating good spatial uniformity and reproducibility. The SERS signals are believed to mainly originate from a charge-transfer (CT) mechanism. Time-dependent density functional theory (TD-DFT) is used to simulate the SERS spectrum and interpret the chemical enhancement mechanism in the experiment. The research extends the application of SERS and also establishes a new uniform SERS substrate.

High-performance microwave absorption of flexible nanocomposites based on flower-like Co superstructures and polyvinylidene fluoride

Flower-like Co superstructures were synthesized via a facile hydrothermal process at low temperature; then the flexible Co/PVDF nanocomposites were prepared by combining the Co nanocrystal with a polyvinylidene fluoride (PVDF) matrix. The Co/PVDF hybrids exhibit distinct microwave absorption properties in the range of 2–18 GHz. With filler loading of 25 wt%, the minimum reflection loss reaches −38.9 dB at 6.4 GHz as the thickness is 2.5 mm. The frequency bandwidth less than −10 dB covers from 4.64 to 10.56 GHz by adjusting the weight content from 15 wt% to 40 wt%. The possible microwave absorbing mechanism has been also discussed in detail.

Tuning plasmonic and chemical enhancement for SERS detection on graphene-based Au hybrids

Various graphene-based Au nanocomposites have been developed as surface-enhanced Raman scattering (SERS) substrates recently. However, efficient use of SERS has been impeded by the difficulty of tuning SERS enhancement effects induced from chemical and plasmonic enhancement by different preparation methods of graphene. Herein, we developed graphene-based Au hybrids through physical sputtering gold NPs on monolayer graphene prepared by chemical vapor deposition (CVD) as a CVD-G/Au hybrid, as well as graphene oxide-gold (GO/Au) and reduced-graphene oxide (rGO/Au) hybrids prepared using the chemical in situ crystallization growth method. Plasmonic and chemical enhancements were tuned effectively by simple methods in these as-prepared graphene-based Au systems. SERS performances of CVD-G/Au, rGO/Au and GO/Au showed a gradually monotonic increasing tendency of enhancement factors (EFs) for adsorbed Rhodamine 6G (R6G) molecules, which show clear dependence on chemical bonds between graphene and Au, indicating that the chemical enhancement can be steadily controlled by chemical groups in a graphene-based Au hybrid system. Most notably, we demonstrate that the optimized GO/Au was able to detect biomolecules of adenine, which displayed high sensitivity with a detection limit of 10(-7) M as well as good reproducibility and uniformity.

Controlled Dispersion of Silver Nanoparticles into the Bulk of Thermosensitive Polymer Microspheres: Tunable Plasmonic Coupling by Temperature Detected by Surface Enhanced Raman Scattering

By in situ reduction of Ag(+) ions pre-dispersed inside thermosensitive microspheres of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)), a 3D copolymer-supported network of silver nanoparticles is created and extensively characterized by surface-enhanced Raman scattering (SERS). The effective dispersion and the suitable density of the silver nanoparticles in the composite microspheres are demonstrated by the thermal-induced SERS signal and its high reproducibility during thermocycling. When the temperature of the system increases above 32 °C, spatial separation of the silver nanoparticles decreases and the numbers of Ag nanoparticles and P(NIPAM-co-MAA) microspheres under illumination spot increase as a result of the shrinkage of the P(NIPAM-co-MAA) chains, leading to the ramp of the SERS effect. By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM-co-MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal-induced variation of special separation.

Ca2+ Enhanced Nacre-Inspired Montmorillonite–Alginate Film with Superior Mechanical, Transparent, Fire Retardancy, and Shape Memory Properties

Inspired by nacre, this is the first time that using the cross-linking of alginate with Ca ions to fabricate organic-inorganic nacre-inspired films we have successfully prepared a new class of Ca2+ ion enhanced montmorillonite (MMT)-alginate (ALG) composites, realizing an optimum combination of high strength (∼280 MPa) and high toughness (∼7.2 MJ m-3) compared with other MMT based artificial nacre. Furthermore, high temperature performance of the composites (with a maximum strength of ∼170 MPa at 100 °C) along with excellent transmittance, fire retardancy, and unique shape memory response to alcohols could greatly expand the application of the mutilfunctional composites, which are believed to show competitive advantages in transportion, construction, and insulations, protection of a flammable biological material, etc.

One-pot assembly of Cu2O chain-like hollow structures.

Novel Cu2O chain-like network was assembled via a facile one-pot solution process with the assistance of poly(vinylpyrrolidone) (PVP). TEM observations showed that the chain-like structures were aggregated by hollow spheres approximately 70 nm in diameter. To be worth mentioning, HRTEM image recorded from the coherent interfacial region demonstrated that the lattice fringes penetrate from one sphere into the adjacent one smoothly without apparent diffraction contrast, which indicated that the hollow spheres experienced lattice fusion and grew into each other. Based on the systematic studies, an oriented aggregation mechanism was proposed, i.e., Cu2O nanoparticles into hollow spheres and subsequently the hollow spheres into the chain-like structures. The Raman spectra of the Cu2O chain-like hollow nanostructures were also investigated. It was found that the Raman peak intensity is different from that in the previous reports, which might be originated from the structure defect resulted from the oriented attachment.