Precipitation of Inorganic Phases through a Photoinduced pH Jump: From Vaterite Spheroids and Shells to ZnO Flakes and Hexagonal Plates

Abstract

This report demonstrates a new way to precipitate inorganic phases through pH jumps driven by optical excitation of a photobase. The level of the pH jumps is manipulated by either the wavelength range or illumination time used. The method is demonstrated by precipitation of CaCO3 and ZnO. Vaterite spheroids and shells for CaCO3 as well as flakes and hexagonal plates for ZnO are formed under various controllable conditions. Notably, ZnO films could be formed and patterned directly on quartz substrates using a photomask. The film thickness was easily controlled by illumination time. This method is an important step toward self-organized crystallization with spatiotemporal control fully in the hands of the experimenter.

Light‐Controlled Nucleation and Shaping of Self‐Assembling Nanocomposites

“…Already shape‐preserving ion‐exchange reactions have been developed toward a wide pallet of chemical compositions including perovskites, metals, and metal chalcogenides. [ 16–23 ] Therefore, the here‐demonstrated light‐controlled assembly strategies give unique independent control over shape and composition which directly impacts our access to user‐defined chemical compositions with desirable optic, catalytic, electronic, magnetic, and photovoltaic functionalities. The power of our strategy is that it enables full leveraging of the precision and control of photolithography techniques with the versatility and simplicity of bioinspired self‐assembly.…”

“…Already, post‐synthesis functionalization and ion‐exchange reactions of such architectures have enabled shape‐preserving conversion into chemical compositions with photovoltaic, magnetic, and catalytic performance. [ 16–23 ] Moreover, rudimental patterning and shaping of these composites has been demonstrated by modulating the reaction conditions either dynamically and globally, or statically and locally, leading to similar shapes, but not yet following exact user‐defined designs. Unlocking the full potential of this self‐assembly approach will require the ability to control chemical gradients both dynamically and locally—instead of statically and globally—for precisely guiding both nucleation and growth to guide assembly according to user‐defined designs.…”

“…From this perspective, photochemical reactions offer attractive possibilities for modulating local gradients. [ 7,23,24 ] Specifically, the photochemical generation of carbonate via photodecarboxylation of ketoprofen (KP) can onset precipitation of BaCO 3 /SiO 2 composites, [ 24 ] but precise control over nucleation and growth, let alone assembly according to user‐defined designs, is not possible yet. In particular, it remains unclear how the intricate interplay between photogenerated precursors, crystallization, reaction, and diffusion processes affect self‐assembly.…”

Formation of Iron (Hydr)Oxide Nanoparticles with a pH-Clock

“…The first approach needs external control and it can lead to unwanted high local concentrations of the precipitating agent, which in turn affects the size distribution and morphology of the resulting particles [ 2 ]. The use of light-triggered systems, such as photo-acids/-bases [ 3 ], or performing reactions under hydrothermal conditions (that is, at high temperature and pressure in specially designed vessels) [ 4 ] are common approaches for changing pH in situ. Nevertheless, they still rely on external stimuli and do not allow the programming of particle synthesis in the time domain.…”

Mesoscale Transformation of Amorphous Calcium Carbonate to Porous Vaterite Microparticles with Morphology Control

“…By influencing the crystallization process using different additives, various morphologies of CaCO 3 have been reported. CaCO 3 with shapes that can be described as “large micropatterned single crystals”, , “fibers”, “flower-like”, , “microrings”, and “spherical particles” − have been synthesized by researchers. The mechanisms behind the crystallization and the formation of different superstructures of CaCO 3 have also been widely discussed.…”