Furthermore, in order to investigating the influence of hydroxyl radicals into the photocatalytic property of l-acid by ZnCr–LDHs and Ti/ZnO–Cr2O3 composite, isopropanol (2.0 g/L) was used as a trapping agent for hydroxyl radicals (CH3 CH OH CH3 + OH → CH3C (OH) CH3 + H2O). The l-acid photodegradation KW-6002 between inhibitor and no inhibitor are shown in Fig. 9A. It can be seen that the l-acid removal amount decreased from 90.2% to 51.5% for Ti/ZnO–Cr2O3 calcined at 800 °C, from 73.5% to 40.1% for Ti/ZnO–Cr2O3 calcined at 500 °C, from 48.9% to 30.6% for ZnCr–LDHs, when isopropanol was added. It is obviously synapse the concentration of hydroxyl radicals would greatly influenced the photocatalytic property of three photocatalysts. Thus, the amount of hydroxide radicals produced by photocatalytic systems was further determined using salicylaldehyde spectrophotometry . The result showed that the Ti/ZnO–Cr2O3 composite derived from organic–inorganic hybrid material (expecially for Ti/ZnO–Cr2O3 calcined at 800 °C) would produce much more hydroxide radicals than ZnCr–LDHs (see Fig. 9B).