There are a plenty amount of topics because the sustainability concept refers to sustainable governance, civic culture, Mobility, Economy and so on. It really depends on your interests. My advice is that study the following book to choose your topics:
McKinnon, A., Cullinane, S., Browne, M., & Whiteing, A. (2015). Green Logistics: Improving the environmental sustainability of logistics.
You can analyze the impact on emissions generated, cost associated and resource efficiency through different models of supply chain regarding circular economy.
Now a days best topic for research is development of performance measurement system for sustainable supply chain management with environmental management.
I reccommend you all titles from EcoProduction Book Series (Environmental Issues in Logistics and Manufacturing) https://www.springer.com/series/10152?detailsPage=titles.