Enhanced photocatalytic reduction of Cr(vi) to Cr(iii) over g-C₃N₄catalysts with Ag nanoclusters in conjunction with Cr(iii) quantification based onoperandolow-field NMR relaxometry

The design of efficient semiconductor photocatalysts to promote solar-to-chemical conversion remains a tremendous challenge. The present study addresses this issue by loading Ag₉(H₂MSA)₇and Ag₃₂(MPG)₁₉nanoclusters (NCs) onto graphitic carbon nitride (g-CN) using a simple impregnation method to form Ag₉NCs/g-CN and Ag₃₂NCs/g-CN hybrid nanocomposites. The performance of the prepared photocatalyst samples investigated for the photocatalytic reduction of aqueous Cr(vi) to Cr(iii) under visible-light irradiation is systematically investigated. The proposed nanocomposites exhibit excellent optical absorption properties and efficient separation and migration of photogenerated electron-hole pairs. As a result, the Ag₉NCs/g-CN and Ag₃₂NCs/g-CN nanocomposites provide improved photocatalytic performances relative to that of pristine g-CN photocatalysts with reduction rate constants that are greater than that of pristine g-CN by factors of 2.3 and 2.0, respectively. Furthermore, we for the first time demonstrate the viability of employingoperandolow-field NMR relaxometry for monitoring the photocatalytic Cr(vi) reduction performance by quantifying the concentration of paramagnetic Cr(iii) ions in solution using the transverse relaxation times determined from the Carr-Purcell-Meiboom-Gill pulse sequence. Our study provides new insights for the rational design of high efficiency visible-light photocatalysts, and develops a more efficient method for quantifying the photocatalytic performance of catalysts for transforming heavy metal ions.