Future prospects of luminescent nanomaterial based security inks: from synthesis to anti-counterfeiting applications

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.

Formation of Rh frame nanorods using Au nanorods as sacrificial templates

Formation of Rh frame nanorods was studied using Au nanorods having high-index facets as sacrificial templates.

Facile synthesis of Au–Pt bimetallic nanocomplexes for direct oxidation of methanol and formic acid

Au–Pt bimetallic nanocomplexes were synthesized and the composition and morphology of the nanocomplexes could be easily controlled by a facile synthesis method.

Gold nanorod-templated synthesis of polymetallic hollow nanostructures with enhanced electrocatalytic performance

Anisotropic polymetallic hollow nanostructures are highly desired for many applications because of their unique morphology, large specific surface areas and attractive electronic effects. Here, a simple method using gold nanorods as a self-sacrificed template has been developed for the fabrication of hollow dumbbell-like nanorods of Au@PtAg. The formation of the hollow structures involves the growth of another metallic shell first, and then the etching of gold nanorods, which is induced by oxygen and ascorbic acid. The lattice mismatch and cohesive energy of the shell, along with its surface passivation, greatly affect the subsequent etching and the resulting products, as has been demonstrated by a positive control in the case of Rh and a negative control in the case of Pd. Hollow dumbbell-like nanorods of Au@PtAg show great enhancement for the dehydrogenation pathway in the oxidation of formic acid, as compared to solid Au@PtAg nanorods, PtAu nanotubes and commercial Pt/C.

Selective etching induces selective growth and controlled formation of various platinum nanostructures by modifying seed surface free energy

We present a strategy to achieve heterogeneous seeded growth on nanoparticle (NP) surfaces and construct various Pt nanostructures (cage- and ring-like) by using selective etching as surface-free-energy-distribution modifier. Preprepared Au polyhedron NPs (octahedron, decahedron, nanorod, and nanoplate) are mixed with KI, H(2)PtCl(6), and surfactant. Under heating, KI is first oxidized to I(2), which then selectively etches the edges of Au polyhedrons. Consequently, the partial removal of surface Au atoms creates highly active sites (exposed high-index facets, atom steps, and kinks) on the etched edges. Then the reduced Pt(0) atoms deposit on the etched edges preferentially and grow further, generating bimetallic nanostructures, Au octahedrons, or decahedrons with edges coated by Pt. The Pt layer protects the Au on the etched edges against further etching, changing the etching route and causing the Au on {111} facets without a Pt layer to be etched. After the Au is removed completely from the bimetallic nanostructures, ring-like, frame-like, and octahedral cage-like Pt nanostructures form. The evolution from Au polyhedrons to Pt ring or octahedron cage is investigated systematically by high-resolution transmission electron microscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, scanning transmission electron microscopy, and high-angle annular dark field.