原位低场核磁共振弛豫法定量监测光催化Cr(Ⅵ)还原反应

A Quantitative Study of Photocatalytic Reduction of Cr(Ⅵ) by Operando Low-Field NMR Relaxometry

本文利用原位低场核磁共振(LF-NMR)技术在真实固液反应环境中对光催化还原Cr(Ⅵ)反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂(Ag/g-C3N4)在可见光照射下催化Cr(Ⅵ)还原为Cr(Ⅲ)的性能进行了研究.研究发现,Ag纳米颗粒负载(负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%)可以有效提高g-C3N4的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C3N4的4倍.此外,本文还通过横向弛豫时间(T2)定量分析了反应体系中顺磁性Cr(Ⅲ)离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr(Ⅵ)还原反应性能的可行性.

In this work, operando low-field nuclear magnetic resonance(LF-NMR) technology was used to quantitatively study the photocatalytic reduction of Cr(Ⅵ) in a real solid-liquid reaction environment. The performance of Ag/g-C3N4 photocatalysts with different loadings of Ag for the photocatalytic reduction of aqueous Cr(Ⅵ) to Cr(Ⅲ) under visible-light irradiation was systematically investigated. The results showed that the addition of Ag cocatalysts(Ag loading amount: 1 wt.%, 2 wt.%, 5 wt.%, and 10 wt.%) significantly enhanced the photocatalytic performance of g-C3N4 photocatalysts, while the optimal content of Ag loading was 5 wt.%, which was greater than that of pristine g-C3N4 by a factor of 4.0. Furthermore, we carried out a quantitative analysis on the concentration of paramagnetic Cr(Ⅲ) ions in solution by using the transverse relaxation time(T2) values, and proved the viability of employing operando LF-NMR relaxometry for monitoring the photocatalytic Cr(Ⅵ) reduction performance.