Nanocrystalline zeolites in supercritical water. Part B: Challenges of synthesis in organotemplate-free condition

[Display omitted] •Applying single and two-step procedure for the rapid synthesis of nanocrystalline zeolites in SCW.•Study on the effects of operational parameters in free-template condition.•Rapid synthesis of zeolite W in SCW as valuable product.•Study on the main reasons for the synthesis of analcime zeolite and other impurities. In the second part, fast synthesis of nanocrystalline zeolites in supercritical water (SCW) condition is studied in the absence of hazardous organic templates with a main product of analcime. The reason is attributed to the reduction in ion dissociation in SCW. In order to reach higher ion dissociation and therefore increase the chance to obtain other type of zeolites, first the alkalinity atmosphere of precursor batch composition changed from sodium hydroxide to potassium hydroxide in SCW followed by adding a long-chain alcohol (namely 2-decanol) in order to add the concentration of OH− in synthesis system. The addition of 2-decanol shows a noteworthy modification in the size and size distribution of nanocrystals as well as product yield. This method is green and promising for the rapid synthesis of zeolitic nanoparticles in uniform size with a high degree of purity and crystallinity as well.