Structural Iridescent Tuned Colors from Self-Assembled Polymer Opal Surfaces

Structural colors are the object of a wide scientific interest, not only for the potential technical applications of their intriguing optical properties but also for the need of coloring agents to replace toxic and carcinogenic dyes. We present a simple methodology to obtain polymer opal surfaces of self-assembled core–shell nanoparticles with different degree of order for structural color applications. Polymer nanospheres prepared by surfactant-free emulsion radical copolymerization of an hydrophobic and an hydrophilic comonomer (styrene and methacrylic acid) spontaneously assemble into core–shell particles. Nanoparticles with identical composition and different diameters were prepared by modulating the degree of ionization of the weakly acidic comonomer. We report experimental results revealing how the synthesis parameters affect the properties of the core–shell particles and their influence on the optical properties of the final polymer opal surfaces, which depend on size, charge, and packing arrangement of the constituent nanoparticles

Hierarchical Hematite Nanoplatelets for Photoelectrochemical Water Splitting

A new nanostructured α-Fe₂O₃ photoelectrode synthesized through plasma-enhanced chemical vapor deposition (PE-CVD) is presented. The α-Fe₂O₃ films consist of nanoplatelets with (001) crystallographic planes strongly oriented perpendicular to the conductive glass surface. This hematite morphology was never obtained before and is strictly linked to the method being used for its production. Structural, electronic, and photocurrent measurements are employed to disclose the nanoscale features of the photoanodes and their relationships with the generated photocurrent. α-Fe₂O₃ films have a hierarchical morphology consisting of nanobranches (width ∼10 nm, length ∼50 nm) that self-organize in plume-like nanoplatelets (350–700 nm in length). The amount of precursor used in the PE-CVD process mainly affects the nanoplatelets dimension, the platelets density, the roughness, and the photoelectrochemical (PEC) activity. The highest photocurrent (<i>j</i> = 1.39 mA/cm² at 1.55 V_RHE) is shown by the photoanodes with the best balance between the platelets density and roughness. The so obtained hematite hierarchical morphology assures good photocurrent performance and appears to be an ideal platform for the construction of customized multilayer architecture for PEC water splitting