Haibin Tang

Ag nanoparticle decorated nanoporous ZnO microrods and their enhanced photocatalytic activities.

Nanostructured Ag nanoparticles (Ag-NPs)/nanoporous ZnO micrometer-rods (n-ZnO MRs) have been synthesized by a two-step method. The n-ZnO MRs was initially prepared by solvothermal-assisted heat treatment. The rods had the diameter ranged from 90 to 150 nm and length between 0.5 and 3 μm. They were found to be porous and were composited of ZnO nanopartiles with size of about 20 nm. In the second stage, Ag-NPs with a diameter of 20-50 nm were anchored onto the surface of the as-prepared n-ZnO MRs by a photoreduction method. The Ag-NPs/n-ZnO MRs were evaluated for their ability to degrade methylene blue (MB) solution under visible to ultraviolet (UV) light irradiation. The rate of degradation of the as-prepared Ag-NPs/n-ZnO MRs was more than twice and nearly 5.6 times faster than that of using bare n-ZnO MRs under the UV and solar light irradiation, respectively. The formation of Schottky barriers in the regions between the Ag-NPs and n-ZnO MRs had improved the charge separation and consequently enhanced the efficiency of the degradation process. Moreover, the as-prepared hybrid structure exhibited high photostability, and 98% of degradation efficiency could be maintained even after being used five times. This endurance was attributed to the retardation of photocorrosion of ZnO as a result of the low concentration of surface defects in the as-prepared n-ZnO MRs. It also minimized the surface defects of the as-prepared n-ZnO MRs and consequently further inhibited the photocorrosion of ZnO when the deposited Ag-NPs were much more inclined to combine with the chemisorbed oxygen.

Ag Nanoparticle-Grafted PAN-Nanohump Array Films with 3D High-Density Hot Spots as Flexible and Reliable SERS Substrates.

A facile fabrication approach of large-scale flexible films is reported, with one surface side consisting of Ag-nanoparticle (Ag-NP) decorated polyacrylonitrile (PAN) nanohump (denoted as Ag-NPs@PAN-nanohump) arrays. This is achieved via molding PAN films with ordered nanohump arrays on one side and then sputtering much smaller Ag-NPs onto each of the PAN-nanohumps. Surface-enhanced Raman scattering (SERS) activity of the Ag-NPs@PAN-nanohump array films can be improved by curving the flexible PAN film with ordered nanohump arrays during the Ag-sputtering process to increase the density of the Ag-NPs on the sidewalls of the PAN-nanohumps. More 3D hot spots are thus achieved on a large-scale. The Ag-NPs@PAN-nanohump array films show high SERS activity with good Raman signal reproducibility for Rhodamine 6G probe molecules. To trial their practical application, the Ag-NPs@PAN-nanohump array films are employed as SERS substrates for trace detection of trinitrotoluene and a congener of polychlorinated biphenyls. A lower detection limit of 10(-12) m and 10(-5) m can be achieved, respectively. Furthermore, the flexible Ag-NPs@PAN-nanohump array films can also be utilized as swabs to probe traces of methyl parathion on the surface of fruits such as apples. The as-fabricated SERS substrates therefore have promising potential for applications in rapid safety inspection and environmental protection.

ZnO-nanotaper array sacrificial templated synthesis of noble-metal building-block assembled nanotube arrays as 3D SERS-substrates

This paper describes a ZnO-nanotaper array sacrificial templated synthetic approach for the fabrication of the arrays of nanotubes with tube-walls assembled by building-blocks of Ag-nanoplates, Au-nanorods, Pt-nanothorns or Pd-nanopyramids, thus possessing high-density 3D “hot spots” in sub-10-nm gaps of neighboring building blocks with nano-tips, -corners or -edges. Additionally, these hierarchical nanostructure arrays possess high surface area with rich surface chemistry, being beneficial to capturing the analyte. The Ag-nanoplateassembled nanotube arrays can be used as sensitive surface-enhanced Raman scattering (SERS) substrates with good signal uniformity and reproducibility. Using such Ag hierarchical nanostructure arrays as SERS-substrates, not only has 10−14 M rhodamine 6G been identified, but also 10−7 M polychlorinated biphenyls (PCBs, a notorious class of persistent organic pollutants) are recognized, and even two congeners of PCBs can be identified in a mixture, showing the potential applications of the materials in SERS-based rapid detection of environmental organic pollutants.

Polyacrylic acid sodium salt film entrapped Ag-nanocubes as molecule traps for SERS detection

AbstractSurface-enhanced Raman spectroscopy (SERS) is a fast analytical technique for trace chemicals; however, it requires the active SERS-substrates to adsorb analytes, thus limiting target species to those with the desired affinity for substrates. Here we present networked polyacrylic acid sodium salt (PAAS) film entrapped Ag-nanocubes (denoted as Ag-nanocubes@PAAS) as an effective SERS-substrate for analytes with and without high affinity. Once the analyte aqueous solution is cast on the dry Ag-nanocubes@PAAS substrate, the bibulous PAAS becomes swollen forcing the Ag-nanocubes loose, while the analytes diffuse in the interstices among the Ag-nanocubes. When dried, the PAAS shrinks and pulls the Ag-nanocubes back to their previous aggregated state, while the PAAS network “detains” the analytes in the small gaps between the Ag-nanocubes for SERS detection. The strategy has been proven effective for not only singleanalytes but also multi-analytes without strong affinity for Ag, showing its potential in SERS-based simultaneous multi-analyte detection of both adsorbable and non-adsorbable pollutants in the environment.

Ag-nanoparticles-decorated NiO-nanoflakes grafted Ni-nanorod arrays stuck out of porous AAO as effective SERS substrates

NiO-nanoflakes (NiO-NFs) grafted Ni-nanorod (Ni-NR) arrays stuck out of the porous anodic aluminum oxide (AAO) template are achieved by a combinatorial process of AAO-confined electrodeposition of Ni-NRs, selectively etching part of the AAO template to expose the Ni-NRs, wet-etching the exposed Ni-NRs in ammonia to obtain Ni(OH)2-NFs grafted onto the cone-shaped Ni-NRs, and annealing to transform Ni(OH)2-NFs in situ into NiO-NFs. By top-view sputtering, Ag-nanoparticles (Ag-NPs) are decorated on each NiO-NFs grafted Ni-NR (denoted as NiO-NFs@Ni-NR). The resultant Ag-NPs-decorated NiO-NFs@Ni-NR (denoted as Ag-NPs@NiO-NFs@Ni-NR) arrays exhibit not only strong surface-enhanced Raman scattering (SERS) activity but also reproducible SERS-signals over the whole array. It is demonstrated that the strong SERS-activity is mainly ascribed to the high density of sub-10 nm gaps (hot spots) between the neighboring Ag-NPs, the semiconducting NiO-NFs induced chemical enhancement effect, and the lightning rod effect of the cone-shaped Ni-NRs. The three-level hierarchical nanostructure arrays stuck out of the AAO template can be utilized to probe polychlorinated biphenyls (PCBs, a kind of global environmental hazard) with a concentration as low as 5 × 10(-6) M, showing promising potential in SERS-based rapid detection of organic environmental pollutants.

Hexagonally arranged arrays of urchin-like Ag hemispheres decorated with Ag nanoparticles for surface-enhanced Raman scattering substrates

The surface topography of noble metal particles is a significant factor in tailoring surface-enhanced Raman scattering (SERS) properties. Here, we present a simple fabrication route to hexagonally arranged arrays of surface-roughened urchinlike Ag hemispheres (Ag-HSs) decorated with Ag nanoparticles (Ag-NPs) for highly active and reproducible SERS substrates. The urchin-like Ag-HS arrays are achieved by sputtering Ag onto the top surface of a highly ordered porous anodic aluminum oxide (AAO) template to form ordered arrays of smooth Ag-HSs and then by electrodepositing Ag-NPs onto the surface of each Ag-HS. Owing to the ordered arrangement of the Ag-HSs and the improved surface roughness, the urchin-like hierarchical Ag-HS arrays can provide sufficient and uniform “hot spots” for reproducible and highly active SERS effects. Using the urchin-like Ag-HS arrays as SERS substrates, 10−7 M dibutyl phthalate (a member of plasticizers family) and 1.5 × 10−5 M PCB-77 (one congener of polychlorinated biphenyl, a notorious class of pollutants) are identified, showing promising potential for these substrates in the rapid recognition of organic pollutants.

Ostwald‐Ripening‐Induced Growth of Parallel Face‐Exposed Ag Nanoplates on Micro‐Hemispheres for High SERS Activity

Ag nanoplates, as two-dimensional plasmonic nanostructures, have attracted intensive attention due to their strong shape-dependent optical properties and related applications. Here parallel face-exposed Ag nanoplates vertically grown on micro-hemisphere surfaces have been achieved by firstly electrodepositing the micro-hemispheres assembled by Ag nanoplates, whose planar surfaces are stuck together, on indium tin oxide substrates, and then Ostwald ripening the as-electrodeposited micro-hemispheres in water. The sizes of the nanoplates and the gaps between the neighboring nanoplates have been tailored by tuning the Ostwald-ripening duration, so that the SERS activity of the micro-hemispheres has been remarkably improved. The improved SERS activity can be well explained by our systematic finite-element simulation. Therefore, Ostwald ripening offers a route to the synthesis of Ag nanoplates, and the optimization of plasmon coupling and SERS activity of nanostructure-assembled systems.

Urchin-like Au-nanoparticles@Ag-nanohemisphere arrays as active SERS-substrates for recognition of PCBs

A simple fabrication route is developed for ordered urchin-like Au-nanoparticles decorated Ag-nanohemisphere nanodot arrays with a highly active and reproducible surface-enhanced Raman scattering effect for rapid recognition of 4-chlorinated biphenyl.

CNTs-anchored egg shell membrane decorated with Ag-NPs as cheap but effective SERS substrates

We report a simple approach for the fabrication of cheap but effective surface-enhanced Raman scattering (SERS) active substrates consisting of natural egg shell membrane (ESM) grafted with Ag-nanoparticles (Ag-NPs) decorated carbon nanotubes (CNTs) (denoted as Ag-NPs@CNTs@ESM), via ultrasonic adsorption of CNTs on the ESM and the subsequent Ag-sputtering. As high density Ag-NPs were sputtered onto each CNT anchored on the ESM nanofiber, homogeneous nanoscaled gaps between the neighboring Ag-NPs were achieved, leading to high SERS activity with excellent SERS signal homogeneity over the whole membrane. Using the Ag-NPs@CNTs@ESM membranes as SERS-substrates, methyl parathion (one of the most hazardous insecticides), PCB-3 (one congener of polychlorinated biphenyls belonging to persistent organic pollutants) and bovine serum albumin (BSA, biomolecules) with a concentration down to 10−11 M, 10−6 M and 0.1 ppb were detected respectively, showing promising potentials in rapid trace detection of environmental pollutants and biochemicals.摘要本文报道了一种利用具有均匀纤维网络结构的鸡蛋膜作为三维骨架, 制备碳纳米管/鸡蛋膜复合表面增强Raman散射SERS)衬底的简单廉价的方法. 首先, 借助超声吸附, 将碳纳米管组装到经过前处理的鸡蛋膜纤维的表面, 得到均匀的碳纳米管/鸡蛋膜复合膜; 后, 借助溅射方法, 将银纳米颗粒组装到碳纳米管和鸡蛋膜纤维的表面, 得到银纳米颗粒修饰的碳纳米管/鸡蛋膜复合膜. 这种方法制备的复合膜表面的碳纳米管对小分子目标分析物有很好的吸附和富集作用; 同时, 由于高密度银纳米颗粒的存在, 衬底表面有大量的SERS活性位点, 因此这种复合膜是一种有效的SERS衬底. 研究表明, 采用这种银纳米颗粒修饰的碳纳米管/鸡蛋膜复合SERS衬底, 可实现对农药甲基对硫磷、 多氯联苯以及生物分子牛血清蛋白等的快速痕量识别. 由于该衬底的制备方法简单、 原材料环保且来源广泛、 衬底的活性高, 所以该衬底在基于SERS技术对环境污染物和生物分子的快速痕量检测方面具有广泛的应用前景.

Origin of strong and narrow localized surface plasmon resonance of copper nanocubes

Inexpensive copper nanoparticles are generally thought to possess weak and broad localized surface plasmon resonance (LSPR). The present experimental and theoretical studies show that tailoring the Cu nanoparticle to a cubic shape results in a single intense, narrow, and asymmetric LSPR line shape, which is even superior to round-shaped gold nanoparticles. In this study, the dielectric function of copper is decomposed into an interband transition component and a free-electron component. This allows interband transition-induced plasmon damping to be visualized both spectrally and by surface polarization charges. The results reveal that the LSPR of Cu nanocubes originates from the corner mode as it is spectrally separated from the interband transitions. In addition, the interband transitions lead to severe damping of the local electromagnetic field but the cubic corner LSPR mode survives. Cu nanocubes display an extinction coefficient comparable to the dipole mode of a gold nanosphere with the same volume and show a larger local electromagnetic field enhancement. These results will guide development of inexpensive plasmonic copper-based nanomaterials.