ORIGINAL PAPER Waste-free synthesis of silica nanospheres and silica nanocoatings from recycled ethanol–ammonium solution Krzysztof Cendrowski 1 • Pawel Sikora 2,3 • Elzbieta Horszczaruk 2 • Ewa Mijowska 1 Received: 20 May 2016 / Accepted: 6 September 2016 Ó Institute of Chemistry, Slovak Academy of Sciences 2016 Abstract In this study, ethanol–ammonium recovery using a distillation system was evaluated. The experimental design was used to evaluate the possibility of solvent re-use and the influence of distillation on the recovery yield, ethanol–am- monium ratio (catalyst concentration) and size of the obtained nanostructures. The synthesised silica nanospheres from distilled ethanol–ammonium were compared in terms of size and shape (ammonium concentration) to the nanos- tructures obtained from filtrated and centrifuged solvents. The results showed that the process for ethanol–ammonium recovery proposed in this work, provides a large potential for reducing the amount of waste from the synthesis. Keywords Sol–gel Á Sto ¨ber method Á Nanosilica Á Recycling Á Waste-free synthesis Introduction Nanotechnology is a field of science which, in recent dec- ades, has undoubtedly contributed to the accelerated devel- opment of technology. There are various methods for the preparation of nanoparticles, i.e., plasma synthesis, chemical vapour deposition, micro-emulsion processing, combustion synthesis, sol–gel processing or hydrothermal techniques. Most silica synthesis methods are based on hydrothermal and sol–gel reactions. Due to certain properties, the sol–gel method has gathered particular attention. There are several advantages in employing this method; first of all is the ease of controlling the process parameters (i.e. temperature, pH, consistent relations, their concentrations etc.) making it possible to provide definite particle sizes in accordance with the required composition. As such, it becomes possible to achieve optimal particle packing (Shakhmenko et al. 2013). Moreover, synthesis can be carried out at low temperature and it is relatively simple and cost-effective compared to other methods (Singh et al. 2015). Finally, this method provides material of high purity (Singh et al. 2001; Sto ¨ber et al. 1968). One of the most popular and often employed sol– gel methods for silica synthesis is the Sto ¨ber method (Shakhmenko et al. 2013; Oertel et al. 2014a, b; Land and Stephan 2015). It allows obtaining nanoparticles with the desired size and surface area. The preparation of monodispersed silica particles according to the Sto ¨ber method proceeds with the hydrol- ysis and condensation of alkoxysilanes (often tetraethyl orthosilicate (TEOS)) in an alcohol solution and ammonia as a catalyst. In general, the hydrolysis reaction gives a monomer to monosilicic acid that is very prone to inter- molecular condensations. The catalyst, ammonium hydroxide, ensures that the concentration of silicic acid is above its solubility and that the nucleation concentration is consequently exceeded (Yao et al. 2006; Wang et al. 2006). Subsequently, this intermediate product condenses to dis- ilicic acid, followed by a trimer acid, to eventually form silica. The reaction of synthesis has been described in detail elsewhere (Sto ¨ber et al. 1968). The so-called Sto ¨ber & Krzysztof Cendrowski kcendrowski@zut.edu.pl 1 Faculty of Chemical Engineering, Institute of Chemical and Environment Engineering, West Pomeranian University of Technology in Szczecin, Al. Piastow 45, 71-311 Szczecin, Poland 2 Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology in Szczecin, Al. Piastow 50, 71-311 Szczecin, Poland 3 Department of Building Materials Engineering, Faculty of Building Engineering, Warsaw University of Technology, Al. Armii Ludowej 16, 00-637 Warsaw, Poland 123 Chem. Pap. DOI 10.1007/s11696-016-0099-y