Modification And Its Visible Light Photocatalytic Degradation On Reactive Deep Blue K-R Of A Novel Bismuth-based Photocatalysts

With the development of industry, a number of dyes are extensively used andproduced in textile, printing and food industry. Since the dyeing and printing processesare always insufficient, about10¹5%of unused dyes are discharged into water bodydirectly. It is reported that60%⁷0%among all these dyes produced in the world are azodyes. However those azo dyes, which containing one or more azo groups in dyemolecules, in textile effluents are on environmental concern because of their potentialproducing of toxic, carcinogenic and mutagenic aromatic amines intermediates throughits reduction reaction processes. Reactive Deep Blue K-R is a most widely usedcommercial azo dye. Hence, it has important theoretical and realistic significance toinvestigate a efficient treatment to remove such highly toxic dye. But most of the dyesused in the textile industry are highly stable、soluble in water, resistant to reactions withchemical agents and low biodegradable, so they are very difficult to removed efficientlyby traditional wastewater treatments. In recent years, heterogeneous photocatalysis as anovel environmentally friendly treatment exhibits broad application prospects in theenvironment purification and the development of highly efficient visible light responsivephotocatalysts has aroused intense interests all over the world. Especially, bismuthoxyhalide photocatalysts exhibit excellent photocatalytic properties due to their speciallayered crystal structure and suitble band gap. Moreover, BiOI can be excited by visiblelight and make the best of the solar enegy, so investigating the modification of pure BiOIcatalyst is very meaningful. In this work, researches for the modifacations of BiOI werecarried out in three aspects. Firstly, BiOCl_0.2Br_0.1I_0.7ternary solid solution wassuccessfully prepared to modify the band structure and increase the specific surface areato promote its photocatalytic activity. Secondly, iodine self-doped BiOI1.5powders weresynthesized through a solvothermal method to suppress the recombination of photo-induced electron/hole pairs and increase visible-light absorption to enhance itsphotovatalytic activity. Thirdly, WO₃/BiOI composite photocatalysts were prepared byball milling method to effectively promote the separation of photo-induced electron/holepairs to gain superior photocatalytic activity.（1） Pure BiOI and BiOCl_0.2Br_0.1I_0.7ternary solid solution powders were bothprepared by liquid-phase precipitation method. According to the characterization results,all these as-prepared samples showed nanoplate morphology. The BET specific surfacearea of BiOCl_0.2Br_0.1I_0.7is much larger than that of BiOI, which can reach13.34m²/g. Onthe basis of the calculated band structures, the valance band potential of BiOCl_0.2Br_0.1I_0.7is2.50eV, while pure BiOI only have2.35eV. The deeper valance band potential ofBiOCl_0.2Br_0.1I_0.7indicates stronger oxidation ability. Moreover, BiOCl_0.2Br_0.1I_0.7exhibitedhigher photocatalytic activity than pure BiOI in photodegradation of Reactive deep blueK-R under visible-light irradiation. After the reaction for2h, the degradation rate for K-Rcould reach98%when using BiOCl_0.2Br_0.1I_0.7as catalysts, while pure BiOI could reach88%. Such superior photocatalytic performance of BiOCl_0.2Br_0.1I_0.7has a closerelationship with its larger BET specific surface area, lower photo-induced electron/holepairs recombination rate and stronger oxidation ability.（2） Pure BiOI and iodine self-doped BiOI1.5powders were synthesized through asolvothermal method. BiOI1.5exhibited higher photocatalytic activity than pure BiOI inphotodegradation of Reactive deep blue K-R under visible-light irradiation. After thereaction for2h, the degradation rate for K-R could reach97.8%when using BiOI1.5ascatalysts, while pure BiOI could reach70%. Furthermore, the BET specific surface areaof BiOI1.5is much larger than that of BiOI, which can reach43.72m²/g and BiOI1.5presents stronger visible-light absorption ability than pure BiOI, according to thecharacterization results. Meanwhile, the modified CB and VB band structures of iodineself-doped BiOI1.5is more beneficial for the separation of photo-induced electron/hole pairs, which results in higher photon efficiency.（3）WO₃/BiOI composite photocatalysts with different WO₃contents weresuccessfully prepared through a ball milling method. All the WO₃/BiOI compositephotocatalysts samples exhibited higher photocatalytic activity than pure BiOI inphotodegradation of Reactive deep blue K-R under visible-light irradiation. Especially,3%WO₃/BiOI composite showed the best photocatalytic activity and the degradationrate for K-R could reach92.8%after irradiation of2h, while pure BiOI could only reach70%. Moreover, the possible charge separation precesses between WO₃and BiOI wasproposed to illustrate the coupling effects which can effectively suppress therecombination of photo-induced electron/hole pairs and enhance the photon efficiency,on the basis of resulting calculated band sructures. However, with the content of WO₃inWO₃/BiOI composite being excess, numerous photo-induced electrons and holes wouldrecombine on the surface of WO₃.