A liquid scintillator containing a tetrakis (isopropyl acetoacetato)zirconium has been developed for ZICOS experiment. In order to reach the sensitivity $T_{1/2}^{0\nu} \geq 10^{27}$ years, we have to use tone scale of $^{96}$Zr and have to reduce 95 \% of $^{208}$Tl decay background. Using Monte Carlo simulation, we could demonstrate new method using the topological information of Cherenkov light, and could reduce 93 \% of $^{208}$Tl background with 78 \% efficiency for 0$\nu \beta \beta$ signal. For the discrimination of Cherenkov light, the precise spectral pulse shape from Cherenkov lights was directly measured by using sub-MeV electrons from $^{90}$Sr/$^{90}$Y beta source. The observed shape was clearly different from the shape of scintillation light. The pulse rise and fall (decay) time for Cherenkov light were 0.8 ns and 2.5 ns, respectively. They were actually shorter than those times of scintillation light which were also measured by 1.6 ns and 6.5 ns, respectively. This clear difference of rise time will be used for the pulse shape discrimination in order to select PMT which receive Cherenkov lights, and the topological information due to Cherenkov light will be used for the reduction of backgrounds from $^{208}$Tl decay which should be major backgrounds observed around Q-value (3.35MeV) of $^{96}$Zr neutrinoless double beta decay.