Du-Jeon Jang

Highly branched gold nanoshells (BAuNSs) having hollow and porous morphologies have been fabricated via a seed-assembly-mediated strategy. Gold seed assemblies can be prepared by removal of SiO ₂ nanotemplates with help of polyvinylpyrrolidone (PVP) molecules, which weakly link gold nanoparticles together even after SiO ₂ etching. L-3,4-dihydroxy phenylalanine (L-DOPA) and AgNO ₃ are employed as shape-directing agents to induce the anisotropic growth of gold. BAuNSs exhibit 7.4 and 4.4 times stronger activities than SiO ₂ @Au nanoparticles in catalysis and surface-enhanced Raman scattering (SERS) applications, respectively, due to their large surface areas and numerous hot spots. It is necessary to find the optimal amount of gold deposition in fabrication to effectively utilize the hollow and porous morpologies of BAuNSs for catalysis and SERS applications. Overgrown nanobranches can fill the nanopores and nanogaps of BAuNSs, resulting in decrease of activities in applications. Overall, the seed-assembly-mediated fabrciation can be employed to produce plasmonic nanostructures having unique morphologies and high application activities.

Pulsed lasers are promising candidates for fabricating plasmonic nanoparticles having unique structures, and there is a strong need for studies on the detailed effects of various experimental conditions on laser-induced fabrications. In this work, we demonstrate the effects of laser wavelengths and nanoparticle surface conditions, as well as laser fluences, in the structural modification of porous gold nanoshells induced by picosecond pulse irradiation. Laser wavelengths play a critical role in the modification because irradiating laser pulses excite not only porous gold nanoshells but also gold nanospheres, which have been produced via the melting of irradiated porous gold nanoshells. Significantly different localized surface plasmon resonances of gold nanospheres and porous gold nanoshells make the effect of laser wavelengths noticeable. The polyvinylpyrrolidone (PVP) concentration of colloid containing porous gold nanoshells also modifies the deformation of the structures. Gold nanostructures become positively charged by the irradiation, strengthening gold–PVP attraction. The stronger binding affinity of PVP is considered to reduce the deformation of irradiated porous gold nanoshells.

In this work, environmentally friendly photocatalysts with attractive catalytic properties are reported that have been prepared by introducing SnO₂ quantum dots (QDs) directly onto ZnSe(N₂H₄)_0.5 substrates to induce advantageous charge separation. The SnO₂/ZnSe(N₂H₄)_0.5 nanocomposites could be easily synthesized through a one‐pot hydrothermal process. Owing to the absence of capping ligands, the attached SnO₂ QDs displayed superior photocatalytic properties, generating many exposed reactive surfaces. Moreover, the addition of a specified amount of SnO₂ boosted the visible‐light photocatalytic activity; however, the presence of excess SnO₂ QDs in the substrate resulted in aggregation and deteriorated the performance. The spectroscopic data revealed that the SnO₂ QDs act as a photocatalytic mediator and enhance the charge separation within the type II band alignment system of the SnO₂/ZnSe(N₂H₄)_0.5 heterojunction photocatalysts. The separated charges in the heterojunction nanocomposites promote radical generation and react with pollutants, resulting in enhanced photocatalytic performance.

Plasmonic nanoparticles can produce an enhanced electromagnetic field in their vicinity due to their localized surface plasmon resonance (LSPR). In particular, gold nanoshells (NSs) are of great interest due to their tunable LSPR absorption band ranging from the visible to the infrared region with superior bio-compatibility. We have fabricated hollow and bumpy Au (HBA) NSs with rough surfaces using expanded silica mesopores as templates. Because some Au seeds were located at the inner surfaces of silica mesopores, the produced Au NSs have inherent inward-grown nanobumps. During seven successive reduction steps, the LSPR peak of Au nanostructures shifted progressively toward a longer wavelength as the sizes of Au seeds increased gradually. Measuring the cross-sections of HBA NSs milled by a focused ion beam, we have found that hollow and bumpy nanostructures arose from the pore structures of mSiO₂ nanotemplates. HBA NSs confine Raman-probe molecules well owing to their hollow structures and have ragged surfaces due to their inward-bumpy morphologies, exhibiting highly efficient surface-enhanced Raman scattering activity.

Pulse-laser irradiation is a promising approach to fabricate gold nanostructures with unique morphologies. Hollow and porous gold nanoshells with high surface-enhanced Raman scattering efficiency have been produced via irradiating SiO₂@Au@SiO₂ nanoparticles with nanosecond laser pulses; the synthetic strategy mainly relies on the laser-induced surface melting of gold nanoparticles.

Gold nanoparticles have been photodeposited directly on SiO₂ nanospheres by using carbon dots as excellent electron donors.