Recent advances in photocatalytic membranes modified by quantum dots-based heterostructures: a comprehensive review

The challenges of environmental pollution, especially pollution of aquatic environments, are accelerating human research on methods to reduce or eliminate these pollutants from water resources. The weakness of purification processes has led to the development of more efficient strategies in the field of water purification. One of the emerging strategies that is effective in water and wastewater purification applications is the photocatalytic membrane. The photocatalytic membrane is the result of the synergy between the photocatalytic degradation process and membrane technology. In addition to the weaknesses of each technique that have been overcome in the photocatalytic membrane, unfortunately, the reduction of photocatalytic power has emerged as a weakness in the photocatalytic membrane. In this regard, a group of emerging photocatalysts possessing distinctive physicochemical characteristics such as a large specific surface area, nanoscale dimensions, adjustable optical behavior, modifiable surface composition, and favorable wettability has been introduced into membranes as quantum dots (QDs) with a size below 10 nm. This review offers an overview of QDs, including their classification, preparation methods, and designs of quantum dot-based heterostructures. It also summarizes membrane classification and fabrication methods for photocatalytic membranes, along with a comparative table of studies on these membranes that incorporate carbon quantum dot (CQDs) and non-carbon quantum dot (NCQDs)-based heterostructures for water purification and wastewater remediation. The present review addresses the limitations of low light harvesting and high rates of electron-hole recombination observed in photocatalytic membranes that have been modified solely with nanoparticles, carbon, or quantum dot structures, as documented in previous studies. It suggests that quantum dot-based photocatalytic heterostructures may effectively overcome these challenges, thanks to their distinctive properties. The incorporation of quantum dot-based heterostructures can significantly enhance the efficiency of photocatalytic membranes, achieving up to 99% removal of pollutants. Finally, this review analyzes the constraints affecting the evolution of photocatalytic membranes and suggests prospective directions for continued research.