Environmental problems can potentially be solved by covalent organic frameworks (COFs) that contain predesigned porous architectures. Herein, we developed an amorphous tetrazine-triazine-functionalized covalent organic framework (TzTPT-COF) by performing one-pot polycondensations of 2,4,6-tris-(4-formylphenoxy)-1,3,5-triazine (TPT-CHO) and s-tetrazine-diamine (Tz). The TzTPT-COF possesses ordered-disordered accessible nano-channels with an experimental pore width of 8.5 nm and simulated pore width of 6.4 nm. We detail the characterization of two-dimensional TzTPT-COF with readily accessible 8.5 nm-sized pores, which was subsequently employed as a porous adsorbent for the static and dynamic adsorption of small dye molecules, especially methylene blue from dye-adulterated water. Additionally, the COF quickly attained up to 99% of its maximum adsorption capacity within 15 min. The thermal stability of the COF was maintained, with the onset of gradual weight loss observed at 280 °C. Furthermore, the COF exhibited no crystallinity and possesses a mesoporous structure. The experimental findings and in silico simulation revealed that to create COF-based adsorbents with effective dye adsorption capabilities, it is necessary to concurrently consider the inherent pore size of the COF material as well as the size of the organic dye molecules. The TzTPT-COF has a great deal of potential as an adsorbent material for eliminating cationic dyes and other organic pollutants from wastewater due to the high adsorption efficiencies, ultrafast kinetics, and outstanding reusability. Hence, the present findings suggest that COFs can also be proven to be highly versatile porous materials for various environmental remediation applications. © 2023 The Royal Society of Chemistry.