Photocatalytic Activity Of BiOX(X=Cl,Br) Prepared By Different Precipitants

Semiconductor photocatalytic technology is one of the efficient means fordecomposing organic pollutants. Bismuth oxyhalides compounds (BiOX, X=Cl,Br and I) compounds have a layer structure characterized by [Bi2O2]2+slabsinterleaved by double slabs of halogen atoms. The self-built electric fieldbetween [Bi2O2]2+and double slabs of halogen atoms could effectively separatethe photoinduced electron-hole pairs. BiOX has become a research focus due totheir unique layered structure, superior optical properties and excellentphotocatalytic activity. This paper aims to explore the applicability of hydrolysismethod to prepare BiOX (X=Cl, Br) BiOCl nano-photocatalyst with low energyconsumption. The effects of precipitants on the structure, crystallite size andmorphology distribution of BiOX were investigated systematically.·A facile andeffencient method and precipitant for synthesizing BiOX has been developed.The structure, crystallite size and morphology distribution of BiOX can becontrolled under appropriate conditions using different precipitants. Applicationsof BiOX in the removal of methyl orange(MO) have also been investigated.Furthermore, we first demonstrated the superior photocatalytic activity of BiOBrfor carbamazepine(CBZ) degradation. The obtained results broaden the application of BiOBr in the treatment of the recalcitrant pharmaceutical andpersonal care products(PPCPs).The main results are as follows:(1) A series of BiOCl photocatalysts with high purity were prepared byhydrolysis method under different precipitation conditions. Among of them, theas-synthesized BiOCl using urea as precipitant (BiOCl-3) exhibited highercrystallinity, narrower energy band and higher separation efficiency ofelectron-hole pairs.(2) The as-synthesized BiOCl-3exhibited high photocatalytic efficiencytowards the degradation of MO under simulated solar irradiation. MO waseliminated with a photocatalytic degradation rate of97%after60min irradiation.Additionally, BiOCl-3showed good stability with a photocatalytic degradationrate of89%for MO after four cycles. Radicals and holes trapping experimentsshowed that h+was involved in the photocatalytic process.(3) BiOBr photocatalysts were synthesised by different precipitants usinghydrolysis method and hydrothermal method. The BiOBr hierarchicalmicrospheres with diameter of1μm was synthesized using urea as precipitantby hydrolysis method, and walnut shaped structure with7.9μm was synthesizedby hydrothermal method. The obtained BiOBr samples were characterized bypowder X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy(DRS), and scanning electron microscopy (SEM). Results showed that theBiOBr possessed higher crystallinity and narrower band gap using urea as a precipitant.(4) The as-synthesized BiOBr using urea as precipitant with hydrolysismethod exhibited high photocatalytic activity towards the degradation of MOand CBZ under simulated solar irradiation. MO was nearly completelyeliminated after60min irradiation. The photocatalytic degradation efficiency ofCBZ was78%under120min. The photocatalytic stability was evaluated byusing MO as the research model, Results showed that BiOBr samples preparedby hydrolysis method displayed more superior stability than those prepared byhydrothermal method. The former possessed a degradation efficiency of94%after four cycles, while the degradation efficiency decreased to88%in the latter.Trapping experiments showed that h+and O2-were the main active species inthe photocatalytic process.