Chromium-Mediated and Ligand-Dependent Activity Engineering of Boron-Doped g-C 3 N 4 Photo-oxidative Nanozymes for Breaking the pH Limitation.

How to overcome the intrinsic low activity of most oxidase and peroxidase mimics at neutral pH has been extremely challenging. Herein, we represent a chromium-mediated and ligand-dependent strategy to activate the oxidase-like activity of boron-doped g-C 3 N 4 (B-g-C 3 N 4 , denoted as BG), aiming at breaking the pH limitation. Cr (III) can be in situ oxidized to Cr (IV) by generated • O 2 - upon UV light irradiation, which then works as a catalysis mediator to oxidize TMB under a neutral environment. Excitingly, the TMB oxidation can be rationally modulated by ligands on the BG coordinating with chromium. We verify that the PEI-Cr 3+ coordination outperformed Cit-PEI-Cr 3+ on the oxidase-like activity through a more accelerated electron transfer, unveiled by the Gauss theoretical calculations. This study highlights a paradigm of tuning the coordination environment on nanozyme surface via the ligand engineering strategy for boosting the oxidase-mimicking activity and breaking the pH limitation. Meanwhile, the catalysis-based colorimetric assay for accurate and selective identification of Cr 3+ was achieved.