Bactericidal allophanic materials prepared from allophane soil: I. Preparation and characterization of silver/phosphorus–silver loaded allophanic specimens

We prepared two kinds of silver-loaded sterilizing allophanic specimens for the development of natural allophane usage. One of them was synthesized by ion exchange of silver onto allophane soil carrier (silver loaded allophanic specimen (SLA)) and the other one by co-loading phosphorus and silver onto the same carrier using both ligand- and ion-exchange methodologies (phosphorus–silver loaded allophanic specimen (PSLA)). Chemical and mineralogical compositions of these specimens were estimated by X-Ray Powder Diffraction (XRD), X-Ray Fluorescence analysis (XRF), and chemical analysis. Also, chemical forms of loaded silver in these specimens were determined by Transmission/High-Resolution Electron Microscopy (TEM/HREM) and X-Ray Photoelectron Spectroscopy (XPS). ount of silver loading (ca. 0.18%) in SLA was about 1/5 of silver loading in zeolite specimens when prepared under similar conditions. On the other hand, the amount of silver loading in PSLA enhanced to 6–7 times than that of SLA. Silver elution speed from SLA to water was rapid and the elution rates of silver (percentage of the amount of silver eluting to the amount of silver loading) after 2 h of stirring were about 30%. In contrast to this, the elution rates of PSLA fell off to about 1/10 from that of SLA. While increasing the amount of silver loading, phosphorus co-loading influenced elution speed of silver loading remarkably. In both the allophanic specimens, the loaded silver contains Ag+ ion, metallic silver and silver oxide as chemical species. Metallic silver was confirmed to exist as ultra-fine particles of several ∼40 nm size. For PSLA specimens, the existence of silver diphosphate (Ag4P2O7) was emphasized along with the other three kinds of chemical species.