Salt ions can control supraparticle structure during spray-drying of colloids, but they affect functionality–Volatile ammonium carbonate offers a smart workaround

Salts were found to be useful in order to manipulate the structure formation and shaping of supraparticles during spray-drying. However, commonly utilized salts such as calcium chloride (CaCl2) remain in the framework of the supraparticles and thus, potentially interfere with the properties of the supraparticles. In this study, ammonium carbonate ((NH4)2CO3) is introduced as a structure-directing agent and compared to CaCl2. Due to its thermal decomposability into gaseous species, (NH4)2CO3 can be completely post-synthetically removed by a simple heat treatment. Thus, undesired washing steps of the supraparticle products are avoided and interferences of the salt with the functional properties of supraparticles are eliminated. These advantages are highlighted for the example of hydrogen-indicating gasochromic supraparticles. In summary, (NH4)2CO3 acts as a structure-directing agent without affecting the intrinsic properties of the supraparticles, making it suitable for applications in systems where residual salt is undesired.