This
critical review analyzes and compares the efficiency of select
technologies that harness solar energy for point-of-use water disinfection,
including photocatalysts, photosensitizing chromophores, UVC light-emitting
diodes, and visible-to-UVC upconversion phosphors. The volume rate
of water that each material can treat to achieve 99% inactivation
of model microorganisms, given the same sunlight exposure, was estimated
on the basis of literature data and theoretical predictions, in the
context of both currently reported efficiencies and theoretical thermodynamic
maximum efficiencies. Each material is further critiqued in terms
of the spectral match with sunlight, quantum efficiency, and the relative
strength of the resulting disinfecting agent such as hydroxyl radicals,
singlet oxygen, and UVC radiation. This review emphasizes critical
needs for disinfection strategies that can efficiently inactivate
more than one type of microorganism. In addition, the approach described
herein can guide future research in efforts to identify more efficient
materials and technologies for capturing sunlight for water disinfection.