Effect Law And Formation Mechanism On The Enhanced Photocatalytic Activity Of BiOX Solid Solutions By Natural Schorl

The issue on energy shortage and environmental pollution is one of the most important challenges in the global scope. Photocatalysis technology is regarded as an innovative and high technology with great development potential, because it can directly use solar light as reaction source to produce hydrogen and degrade organic pollutant. As a new photocatalyst in numerous photocatalysts, Bi OX?X=Cl, Br, I?shows the excellent photocatalytic performance because of its special layer structure. On basic of the discussions of photocatalytic activity of Bi OX solid solutions, this study mainly focused on the effect law and formation mechanism of the enhanced photocatalytic activity of Bi OX solid solutions by natural schorl.Firstly, Bi OX solid solutions were synthesized by alcoholysis method at room temperature, including Bi OCl_x Br_1-x, Bi OBr_x I_1-x, and Bi OCl_x I_1-x?0?x?1?. The XRD results indicated that the as-prepared solid solutions had high purity and single phase. The observation from SEM and TEM images showed that all Bi OX solid solutions had loose layered structure. The UV-vis DRS analysis revealed that, with the decrease of x value, the absorption of visible light by the photocatalyst increased, and the band gap of the photocatalyst decreased. Rhodamine B?Rh B? was employed as the target pollutant to evaluate the photocatalytic property of Bi OX solid solutions. The experimental results indicated that, in the photocatalytic system of Bi OCl_x Br_1-x solid solutions, Bi OCl_0.5Br_0.5 exhibited the highest photocatalytic activity for the discoloration of 20 mg/L Rh B, and Rh B discoloration ratio could reach 100 % after 1.5 h with the catalyst dosage of 1 g/L; in the photocatalytic system of Bi OBr_x I_1-x solid solutions, Bi OBr_0.75I_0.25 exhibited the highest catalytic activity for the discoloration of 20 mg/L Rh B, and discoloration ratio could reach 100 % after 2.5 h with the catalyst dosage of 1 g/L; in the photocatalytic system of Bi OCl_x I_1-x solid solutions, Bi OCl_0.75I_0.25 exhibited the highest catalytic activity for the discoloration of 20 mg/L Rh B, and discoloration ratio could reach 100 % after 1.5 h with the catalyst dosage of 1 g/L.Then, the composite photocatalysts composed of natural schorl and Bi OX solid solutions with the best stoichiometric ratio were synthesized by alcoholysis method with the assistance of ultrasound, marked as Bi OCl_0.5Br_0.5/schorl, Bi OBr_0.75I_0.25/ schorl and Bi OCl_0.75I_0.25/schorl. The XRD results indicated that the addition of small amount of schorl could not change the crystal structure of Bi OX solid solutions; SEM and TEM observation showed that Bi OX solid solutions still exhibited the loose layered structure and were successfully compound onto the surface of schorl. The experimental results indicated that Bi OCl_0.5Br_0.5/schorl had the best photocatalytic efficiency when the synthesis temperature was 50 ?, the synthesis time was 8 h and the schorl content in the composite was 5 %. Furthermore, it should be noted that the photocatalytic activity of Bi OCl_0.5Br_0.5 could be effectively enhanced by schorl. UV-vis DRS analysis showed that the addition of schorl could reduce the band gap of Bi OCl_0.5Br_0.5. In addition, there existed permanent spontaneous polarization electric field on the surface of schorl particles, which could reduce the recombination rate of electron-hole and thereby enhance the photocatalytic activity of Bi OCl_0.5Br_0.5. However, for Bi OBr_0.75I_0.25/schorl and Bi OCl_0.75I_0.25/schorl, the addition of schorl could not have a positive improvement for their photocatalytic activity. UV-vis DRS results manifested that the addition of schorl could increase the band gap of both Bi OBr_0.75I_0.25 and Bi OCl_0.75I_0.25. Therefore, schorl exhibited different photocatalytic effects for Bi OX solid solutions with different bang gaps, On the whole, the spontaneous polarization of schorl could make it easy to reduce the band gap for the broad-band semiconductor and increase the band gap for the narrow-band semiconductor, which provided an important theoretical and practical reference for schorl to modulate the band gap of a semiconductor.