A review of quartz crystal microbalance as a tool to monitor photocatalytic properties.

Quartz crystal microbalance (QCM) is a versatile and sensitive technique for monitoring small interfacial mass changes through variations in the resonance frequency of a piezoelectric quartz crystal. Photocatalytic processes, particularly interfacial degradation and photoreduction, can therefore be monitored in situ and in real-time using QCM. This review summarizes QCM-based photocatalytic studies reported over the past two decades, covering both fundamental and application-oriented investigations involving a range of photocatalytic materials and organic or inorganic species. A structured literature search and selection strategy was used to identify and categorize reported QCM-based photocatalytic studies and to critically evaluate their experimental approaches and findings. Particular attention is given to quantitative comparison, experimental reproducibility, methodological limitations, and factors that can complicate the interpretation of QCM responses during photocatalysis. Emerging opportunities involving QCM-D, operando measurements, multimodal characterization, microfluidic platforms, and advanced acoustic resonators are also discussed.