Highly selective conversion of NO to NO3—through radical modulation over UiO-66–67-NH2 S-scheme heterojunction

Abstract

Semiconductor photocatalysis presents significant potential for reducing low concentrations of NO, yet achieving efficient and selective conversion of NO to NO₃^—while suppressing toxic NO₂ release remains challenging. Here, a UiO-66–67-NH₂ S-scheme heterojunction, synthesized by integrating UiO-66-NH₂ and UiO-67-NH₂, generate ·O₂^— as the sole active species for efficient NO to NO₃^—conversion under visible light. The photocatalytic performance evaluation indicates that the optimized UiO-66–67-NH₂ efficiently and selectively converts NO to NO₃⁻. The photocatalytic NO removal efficiency reaches 78 %, which is 2.2 times and 3.4 times higher than that of the individual UiO-66-NH₂ and UiO-67-NH₂, respectively. Experimental results and DFT calculations reveal that charge redistributions within the heterojunction creates an internal electric field, facilitating effective charge separation. The selective adsorption of O₂ and NO at the Zr sites facilitates of ·O₂^— generation and NO enrichment, while the -NH₂ sites suppress the formation of ·OH and ¹O₂, inhibiting NO₂ release. The rate-determining step, reaction between *NO₂ and *O is energetically favored in the heterojunction, accelerating NO₃^— formation. This study provides valuable insights into designing photocatalysts for environmental remediation by controlling reactive oxygen species and NO removal.