A highly active perovskite is needed to activate peroxymonosulfate (PMS) into reactive oxygen species (ROS) to degrade organic pollutants in wastewater. High surface area LaCoO3 was fabricated via nano-casting employing mesoporous silica KIT-6 (a 3D material, first fabricated in Korea Advanced Institute of Science and Technology number 6) as the hard template. The NC-LaCoO3 showed a higher surface area (81.33 m2·g−1), pore volume (0.21 cm3·g−1) and pore diameter (7.78 nm), abundant acidic/basic sites, rich oxygen vacancies (OVs), and easily accessible active sites, as well as higher catalytic efficiency to degrade atrazine than uncast/citric acid-assisted perovskite (CA-LaCoO3), CA-La2O3 and Co3O4. Under the specific experimental condition (PMS concentration: 4.30 mM; catalyst dosage: 0.60 g·L−1; pH: 8.20; atrazine concentration: 10 mg·L−1; and room temperature), in 6.0 min, approximately 19.02 %, 56 %, 29.38 %, and 39.21 % of atrazine were degraded by sole PMS, CA-LaCoO3/PMS, CA-La2O3/PMS and Co3O4/PMS respectively, while it was completely degraded in 4.0 min in NC-LaCoO3/PMS. Moreover, 0.06 mg/L leaching of cobalt was detected during oxidation in the NC-LaCoO3 /PMS process. The NC-LaCoO3 depicted stable catalytic efficiency after six recycling terms. Radical scavengers depicted that SO4•− and •OH were produced as the main reactive species at the initial phase of the catalytic reaction, and subsequently, O2•− and 1O2 were generated as the secondary oxidative species. A comparatively dominant inhibitory effect of methanol compared to TBA suggested that SO4•− was mainly involved in atrazine degradation. XPS, EPR, in-situ ATR-FTIR, EIS, LSV, and chronoamperometric measurements were employed to explore the catalytic reaction mechanism. High catalytic efficiency was ascribed to better textural properties, diffusion-friendly structure, rich oxygen vacancies, and radical species. This research suggests that perovskites with a range of A and B metals can be synthesized by nanocasting using high surface area templates for advanced oxidation processes, especially PMS activation, to remediate organic wastewater.