Valorisation of recycled glass: novel catalytic routes for water purification

This research made an extensive use of Catalytic Wet Peroxide Oxidation (CWPO) techniques by using recycling glass as a catalyst for the abatement of organic pollutants namely phenol, ibuprofen, benzyl alcohol and 1-phenylethanol to CO2 and water or by selectively oxidizing them.
Based on the composition of recycled glass, other than main compositions, it also contains metal compounds such as MnO2 or Cr2O3 and Fe2O3 about 1 wt.%, which fall in the range of other metal-doped catalysts. Experiments showed that Fe3+ has the largest activity in triggering the generation of ·OH in comparing to Cr3+ and Mn2+. ICP showed negligible fluctuations between samples made it a robust catalyst system, and the glass colour and feedstock variability will not influence the catalyst performance. XPS results revealed that more Fe is distributed at the surface (0.5 at.%) rather than the bulk (0.1 at.%), this reflects the iron propensity to readily oxidize facilitates migration of Fe from the bulk to the surface as Fe2O3 over time.
This study successfully demonstrated the concept of using of recycled glass (green and brown) containing Fe3+ centres as a heterogeneous catalyst for phenol and ibuprofen oxidation by CWPO. The results have indicated that decreasing the size of the glass particles leads to increased phenol conversion and carbon dioxide production with the size range of 0.1 - 0.5 mm showing the best catalytic activity. It enables the possibility of a scale-up application in the industry. As a result, the performance of recycled glass can be comparable and promising (i.e., 100% phenol and ibuprofen conversion and 20% CMB, low metal leaching (less than 0.2 wt.%)) to industrial catalyst, namely Fe/ZSM-5 under appropriate reaction conditions (increased mass and longer reaction time) for an overall much lower (about 3000 times) cost. This approach closes the material loop through high-value recycling, further extending the life cycle of these resources and as such reduces the need of new input of energy demanding raw materials.
Although the selective oxidation of benzyl alcohol and 1-phenylethanol was not fully achieved, these results represent a valuable fundamental investigation, providing key insights to guide future optimisation of reaction conditions and improvements in selectivity.
This research marks a significant step forward in sustainable water treatment technologies by using waste materials in innovative ways. This approach not only addresses critical environmental issues but also aligns with the global shift towards a circular economy. The findings have promising implications for both water management and chemical manufacturing industries, offering a cost-effective, sustainable, and scalable solution to some of the most pressing environmental challenges of our time.