Although SrNbO2N has a promising band gap of ∼1.8 eV for solar water splitting, its photocatalytic activity is generally very poor under ordinary conditions, primarily due to high defect levels caused by synthetic procedures. In this work, we managed to control defect levels inside SrNbO2N by incorporating Mg into the structure, i.e. SrMgx/3Nb1−x/3O2+yN1−y (0 ≤ x ≤ 1). Strikingly, a number of important properties such as band gap value, defect level, nitrogen content and particle size can be tuned by varying the amounts of Mg in the structure. More importantly, efficient photocatalytic water oxidation into oxygen was realized using these Mg modified SrNbO2N. An apparent quantum efficiency (AQE) as high as 5.13% was reached at 420 ± 20 nm for SrMg0.2Nb0.8O2+yN1−y (x = 0.6), which stands as the highest AQE reported to date for SrNbO2N. Mott–Schottky and X-ray photoelectron spectroscopy analyses revealed the shift of valence band maximum of SrNbO2N in response to Mg uptake. Moreover, open-circuit voltage decay measurements confirmed a much prolonged charge lifetime in Mg modified SrNbO2N. Thus, Mg serves not only to tailor band edge positions but also to ameliorate charge separation conditions in SrNbO2N, both of which contribute to the superior photocatalytic activities.
BaTaO 2 N owns a promising band gap of 1.8 eV and suitable band edge positions but generally exhibits poor photocatalytic activity for water splitting reactions. In this work, we have modified BaTaO 2 N by introducing Mg to the B site of perovskite lattice to form a new compound, i.e. BaTa 0.95 Mg 0.05 O 2+x N 1−y . This modification results in an alteration to a number of important parameters such as unit cell size, nitrogen content, optical absorption and microstructures etc. More importantly, Mg modifications are responsible for stronger Ta-O/N bonds, lower Ta 4+ defects concentration and positively shift of band edge positions, which in turn contribute to high photocatalytic activities for water oxidation reactions. Apparent quantum efficiency as high as 2.59% has been realized at 420 ± 20 nm, being the highest for BaTaO 2 N reported to date under similar conditions. Further photoelectrochemical analysis confirms better charge utilizations in Mg modified BaTaO 2 N.
Jinze Wang,Haiqi Zhang,Hongtao Hu,Sentao Hu,Lie Ma
Matrix metalloproteinase 9 (MMP-9) plays an important role in wound healing. However, overexpression of MMP-9 leads to the degradation of the newly formed extracellular matrix, which delays wound healing, ultimately leading to chronic wounds. Therefore, timely monitoring of the MMP-9 activity using simple, cost-effective methods is important to prevent the formation of chronic wounds. In this work, ferrocene-modified MMP-9 cleavage peptide (Fc-MG) modified carboxymethyl chitosan hydrogels were prepared as electrochemical biosensors. In the presence of MMP-9, the peptide chain is sheared, and the electrochemically active ferrocene segment is released. Therefore, analyzing the electrochemical activity of hydrogels using differential pulse voltammetry (DPV) can be used to determine MMP-9 activity. The results showed that the DPV peaks were correlated with the MMP-9 concentration in phosphate-buffered saline (PBS, pH 7.4) and Dulbecco's modified Eagle's medium (DMEM). Specifically, the corresponding coefficient of determination (R 2 ) were 0.918 and 0.993. The limit of detections were 73.08 ng/mL and 131.71 ng/mL, respectively. Compared with the enzyme-linked immunosorbent assay, the hydrogel biosensor determined the concentration of MMP-9 in solution with simpler steps. This study demonstrates a novel strategy based on Fc-MG-modified hydrogels to monitor MMP-9 activity in cell secretion samples and shows the potential application in chronic wounds.
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