The Copper Chemical Garden as a Low Cost and Efficient Material for Breaking Down Air Pollution by Gaseous Ammonia

Chemical garden (CG) from copper(II) sulfate, nitrate and chloride (CG CuSO, CG Cu(NO), CG CuCl) were grown, and characterized from the structural and compositional point of view by using scanning electron microscopy, X-ray powder diffraction, elemental analysis, thermogravimetric analysis coupled with mass spectrometry, and DR (diffuse reflectance) UV-Vis-NIR spectroscopy. The main crystalline phases, controlled by the anion of the starting salt, were brochantite and kobyashevite for CG CuSO, gerhardtite, rouaite and anthonyite for CG Cu(NO), and atacamite for CG CuCl. The materials were then exposed to ammonia vapors to test the effectiveness of their entrapping property. All materials proved to be very efficient and rapid in the uptake of ammonia, which invariably results in the formation of a Cu(II)/NH complex. However, after a few tens of minutes, CG Cu(NO) and CG CuCl release water and get wet, thereby resulting unsuitable for applications. Only CG CuSO remains dry for at least 25 hours. This makes it a valid candidate for building devices for trapping ammonia, and possibly other gases capable of interacting with Cu(II). The entrapment of ammonia by this material was also characterized by H and Si MAS-NMR XAS spectroscopies.