Upconversion boosting pollutants degradation efficiency in wide-spectrum responsive photocatalysts

Recently, the composite photocatalysts coupled with upconversion materials have received widespread attention due to higher utilization efficiency of solar energy in a wide-spectrum range. Novel heterojunction photocatalysts of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ were designed and developed herein. The structural characterization, morphology and elemental composition analysis demonstrated that heterojunctions between CoWO₄ and NaYF₄:Yb³⁺,Er³⁺ were indeed formed in the composite photocatalysts. Moreover, CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts exhibited higher pollutants degradation efficiency. Especially, a great enhancement of +87% on the photocatalytic activity was achieved in the heterojunction photocatalyst of 60CoWO₄–NaYF₄:Yb³⁺,Er³⁺ compared with pure CoWO₄. The dominant radicals generated from the heterojunction photocatalysts were confirmed as the photo-generated holes (h⁺) and hydroxyl radicals (⋅OH) through the radical species trapping experiments and fluorescence detection, which is fully in line with the expected band structure characteristics of CoWO₄. Eventually, an underlying mechanism was proposed that the enhanced photocatalytic activity should be attributed to the wide-spectrum responsive features of CoWO₄@NaYF₄:Yb³⁺,Er³⁺ heterojunction photocatalysts. Within the heterostructures, CoWO₄ photocatalyst can absorb both the UV–Vis light due to its narrow bandgap and the Near-Infrared energy through the upconversion NaYF₄:Yb³⁺,Er³⁺, thereby utilizing solar energy more efficiently in a wide-spectrum range for photocatalytic reactions.