Hydrolysis-Induced CuO Networks and the Triggered Peroxidase-Mimic Activity by Cr under Neutral Conditions.

The current small-scale synthesis and relatively large size of CuO have limited its practical applications. Herein, we developed a hydrolysis strategy to prepare phase-pure CuO networks composed of small granules (ca. 25 nm) on a gram scale. The preparation involves in situ hydrolyzing the H[CuCl] complexes prereduced in ,'-dimethylformamide (DMF). The DMF-soluble H[CuCl] complexes are critical for the homogeneous nucleation of CuCl seeds and subsequent hydrolysis, allowing for separate control over the nucleation and growth stages to regulate the formation of CuO networks. The novel CuO networks possess numerous exposed active sites and hierarchical porosities, conferring high catalytic activity and fast mass transfer capability. The inherent peroxidase-mimic activity of CuO is severely inhibited under neutral conditions but can be triggered by Cr, enabling the colorimetric assay of Cr with the assistance of the oxidation-induced color change of 3,3',5,5'-tetramethylbenzidine. Through density functional theory calculation, we confirmed that the attachment of Cr on the CuO surface reduced the dissociation energy of HO, enhancing the enzyme-mimic activity. The colorimetric detection method demonstrated a sensitive and specific assay capability for Cr (LOD = 0.095 μM). Our work offers a straightforward protocol for novel design of metal or metal-based nanomaterials for nanozymes or other applications.