Fabrication of BiOBr-based broad-spectrum photocatalysts for environmental remediation

Broad-spectrum absorption photocatalysts incorporating up-converting phosphors and visible light catalysts have recently received significant attention due to high efficiency of sunlight utilization. This study designs and fabricates novel broad-spectrum absorption photocatalysts comprising up-converting phosphor of NaYF₄: Yb³⁺, Er³⁺ and visible light catalyst of BiOBr. Structural and morphological analyses show that heterojunctions between BiOBr and NaYF₄: Yb³⁺, Er³⁺ do form in the composites. Moreover, all the broad-spectrum absorption catalysts exhibit extremely excellent photocatalytic performance as comparison to pure BiOBr. For instance, the kinetic k values of broad-spectrum absorption catalysts reflecting photocatalytic activity can reach up to 0.104 min^-1, which is twice that of pure BiOBr (k = 0.053 min^-1). An underlying mechanism proposed in the paper implies that this great enhancement in the photocatalytic performance of broad-spectrum absorption photocatalysts could be attributed two factors: (1) BiOBr can additionally absorb the NIR energy (mainly at 980 nm) upconverted by NaYF₄:Yb³⁺, Er³⁺ for participating in the photocatalytic reaction, (2) heterojunctions between BiOBr and NaYF₄: Yb³⁺, Er³⁺ significantly reduce the oxygen vacancy concentration in the composite catalyst by over 22% and thus contribute to the inhibition of photogenerated carrier recombination. It is commendable that BiOBr and NaYF₄: Yb³⁺, Er³⁺ can form such broad-spectrum absorption photocatalysts over a wide range of component ratios, which is highly beneficial for their application in environmental remediation.