Fig. 1: Schematic of the “one-pot” processes to prepare transition metal oxides and nitrides with periodic structures on three different length scales.
From: Hierarchically ordered porous transition metal compounds from one-pot type 3D printing approaches
a The ink is composed of Pluronics-family block copolymers (BCPs) mixed with transition metal sols hydrolyzed from metal alkoxides in acidic ethanol solutions. The syringe pump-type print head extrudes the ink into a dish containing either hexane for periodic cubic woodpile structures or gel-like 25% Pluronic F127 by mass in water for periodic helical structures. After drying and annealing, b 3D printed Pluronics-sol hybrid woodpiles with self-assembled periodic hexagonal mesostructures and helices are calcined in air to yield c mesoporous transition metal oxides. After further heat treatments in ammonia and carburizing gas (mixture of methane, hydrogen, and nitrogen) at higher temperatures up to 950 °C, oxides are converted to d mesoporous crystalline transition metal nitride helices and hexagonally ordered woodpiles with cubic rocksalt atomic lattices.
