Photocatalytic decomposition of organic materials-contained aqueous solution is assessed using a plasma discharged into the liquid directly. The correlation of H-2 generation and optical emission spectroscopy is discussed in terms of photocatalytic H-2 production using plasma and photocatalysts. Variations of the active species are evaluated according to the conditions of the plasma in the liquid phase. The optical emission spectra vary according to the plasma discharging conditions in the liquid phase. The intensities of the OH center dot peaks at 309 nm increase with the addition of ethanol or acetaldehyde in water. The highest intensities and rate of H2 evolution are observed at a 10% acetaldehyde concentration in the aqueous solution. The rates of H-2 evolution in the ethanol or acetaldehyde solution correspond to the concentration of OH center dot in the solution. The photocatalytic reaction using liquid plasma generates hydrogen at the same time as the decomposition of the organic chemicals. The rate of hydrogen evolution in aqueous solutions containing the organic chemicals is higher than that in pure water. This is because hydrogen is further generated due to hydrogen generation by photolysis of the organic chemicals. CaTiO3 perovskite photocatalyst shows better photocatalytic activity than TiO2. Ni loading on the photocatalyst lead to an increase in H-2 production. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.