A novel ultraviolet light source of microwave discharge electrodeless ultraviolet lamp: Luminescence mechanisms, reactor structures, and environmental applications

Microwave discharge electrodeless ultraviolet (MWUV) lamp is a novel type of ultraviolet equipment that utilizes microwave excited plasma to emit ultraviolet light. It offers the advantages of stable light intensity and an extended lifespan. Currently, MWUV has been extensively investigated for pollutant degradation, adsorbent regeneration, and bacterial inactivation. Research has demonstrated that MWUV exhibits remarkable efficacy in degrading norfloxacin, ciprofloxacin, dimethoate, etc … Moreover, it enables adsorbent regeneration through microwave thermal release and stimulates electrodeless lamps to generate ultraviolet light, thereby reducing environmental pollution. By utilizing the non-thermal effect of microwaves on bacteria which disrupts their structure, MWUV enhances bacterial inactivation via ultraviolet light exposure. The MWUV can be integrated with various processes, such as photocatalytic systems, photo-Fenton, or photoelectric-Fenton systems, through different configurations including microwave oven reactor, exogenous microwave supply reactor, closed chamber reactor, and complete ultraviolet reactor. These systems have been found to produce abundant reactive oxygen species like ·OH, ·O, and ·OH2. The presence of microwaves promotes free radicals production while lowering the activation energy required for contaminants degradation. Notably, even without microwaves present in the MWUV system, MWUV still exhibit superior photocatalytic performance compared to low-pressure mercury lamps for pollutant degradation. This review provides a detailed introduction to the luminescence mechanisms and structures of MWUV reactors for producing ultraviolet light, as well as their current applications.