Photocatalytic regulation of gas–liquid reactive species in a light-transmissive surface dielectric barrier discharge reactor

Air surface dielectric barrier discharge (SDBD) produces abundant reactive oxygen and nitrogen species, but the formation and conversion of these species are strongly coupled, making selective regulation of the product chemistry challenging. Here, we report a light-transmissive SDBD reactor integrated with UVC/TiO2 photocatalytic oxidation for directional regulation of plasma-generated reactive products. The reactor employs a transparent ITO electrode to provide optical access, allowing 254 nm UVC irradiation to pass through the discharge structure and activate a TiO2-coated ceramic filter placed close to the SDBD region. Electrical diagnostics showed that the introduction of UVC irradiation and the TiO2-coated filter caused negligible changes in the voltage–current characteristics, indicating that the observed product regulation mainly arose from photochemical and photocatalytic reactions rather than discharge modification. Time-resolved gas-phase measurements revealed that UVC/TiO2 coupling markedly suppressed O3 accumulation while promoting NO2 formation. At 18 W UVC input power, the O3 concentration in the low-voltage mode decreased from approximately 950 to 600 ppm, whereas NO2 increased from below the detection limit to nearly 50 ppm. In the high-voltage mode, UVC/TiO2 accelerated O3 depletion and increased NO2 accumulation from about 80 to 190 ppm. This regulated gas-phase chemistry was further reflected in the liquid phase, leading to reduced apparent dissolved O3, enhanced total NO2−/NO3− accumulation, and modified H2O2 evolution. Consequently, methyl orange decolorization was enhanced by more than 35% relative to SDBD alone in both voltage modes at 18 W UVC input power, together with improved decolorization energy yield. These results demonstrate an in situ plasma–photocatalytic strategy for directional regulation of SDBD reactive product chemistry.