Glass recycling is far less straightforward than it appears. Using a cullet as a feedstock to fabricate original articles by remelting cannot always be applied. Some glasses are ‘unrecyclable' for several reasons, including the risks of degradation of their properties or the loss of chemical purity. The main obstacle to reusing glass waste is that it should pass through various expensive and time-consuming steps. Technological progress is necessary to improve production efficiency, environmental quality, and economic competitiveness. Moreover, the development of new applications is required due to the non-biodegradable nature and increasing quantities of waste. Achieving certain goals can be accomplished by producing glass microspheres of various forms (solid, hollow, and porous) through innovative flame synthesis techniques for diverse applications.

Pharmaceutical glasses in a borosilicate system were used to fabricate novel transparent and porous 3D glass structures. Fiberglass waste was subjected to alkali activation in an aqueous solution with different sodium/potassium hydroxide concentrations. The activated materials were fed into a methane–oxygen flame with a temperature of around 1600 °C to produce porous glass microspheres. The highest homogeneity and yield of porous glass microspheres (PGMs) corresponded to the activation with 9 M KOH aqueous solution. The obtained PGMs were used to prepare highly porous pellets with a specific surface area of nearly 20 m2/g, which is applicable for removing methylene blue as a model organic dye from wastewater. Moreover, 3D photocatalysts containing PGMs doped with TiO2 nanoparticles have been fabricated using the masked stereolithography technique.

Acknowledgement

This work is a part of the dissemination activities of the project FunGlass. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 739566. The authors also gratefully acknowledge the financial support from the Slovak Grant Agency of the Ministry of Education, Science, Research and Sport, VEGA 1/0456/20.