Two-dimensional hexagonal boron nitride (h-BN) as an emerging nanomaterial exhibits unique physicochemical properties, making it suitable candidate for a wide spectrum of applications. However, due to its poor functionality, the processability of this nanomaterial is low. In this work, we report on a straightforward and scalable approach for the functionalization of h-BN by nitrene [2 + 1] cycloaddition at room temperature. The triazine-functionalized h-BN (Trz-BNs) showed a high reactivity toward nucleophiles, through which post-modifications are performable. The post-modification of Trz-BNs by L-cysteine was studied using cyclic voltammetry and differential pulse voltammetry. Taking advantage of the scalable and straightforward functionalization as well as ability of triazine functional groups for the controlled post-modifications, Trz-BNs is a promising nanoplatform for a wide range of future applications.