pH对低温燃烧法合成钨酸铋光催化降解罗丹明B的影响

以低温燃烧法制备钨酸铋(LCM-Bi2WO6), 并表征了其晶体结构、形貌特征、等电点及紫外漫反射谱, 同时以染料罗丹明B(RhB)为目标污染物(25 mg/L, pH=4), 考察了所制备Bi₂WO₆的吸附性能和光催化性能, 并探讨了RhB溶液pH(1、4、7、10)及酸度调节剂成分(盐酸和硫酸)的影响。结果表明, 所制备Bi₂WO₆为正交相, 吸收极限波长为455 nm, 禁带宽度为2.72 eV, 晶格粒径为14.7 nm, 等电点为3.43; 其对RhB的吸附和光催化效果强于水热法制备Bi₂WO₆和二氧化钛(TiO₂)。不同pH溶液中, LCM-Bi₂WO₆对RhB的吸附过程和光催化过程分别符合准二级动力学方程和一级动力学方程式, 且吸附平衡量(7.48~21.93 mg/g)和光催化速率常数(0.0197~0.1181 min^-1)均随pH降低而增大。LCM-Bi₂WO₆对RhB的光催化降解主要由·OH所致。光催化过程中, RhB紫外可见光谱的蓝移现象揭示LCM-Bi2WO6可通过脱乙基-共轭显色基团断裂途径降解RhB。以H₂SO₄调节酸度时, SO₄^2-离子可被Bi₂WO₆强吸附, 从而使得LCM-Bi₂WO₆对RhB的平衡吸附量(qe为6.03 mg/g)和光催化速率(kv为0.115 min-1)远小于HCl调节(qe为21.93 mg/g, kv为0.1181 min-1)时对RhB的平衡吸附量和光催化速率。

Effects of Solution pH on Photocatalytic Degradation of Rhodamine B Using Bismuth Tungstate Prepared by Low-temperature Combustion Method

Bismuth tungstate (Bi₂WO₆) was synthesized by low-temperature combustion method (LCM) and characterized by diffuse reflectance spectroscope (DRS), X-ray diffraction (XRD), scanning electron microscope (SEM) and Zeta potential. The effects of solution pH and acidity regulator types on the photocatalytic degradation of RhB by LCM-Bi₂WO₆ were investigated. Results showed that LCM-Bi₂WO₆ was an orthorhombic crystal and its wavelength of maximum absorption, forbid bandwidth, lattice size and isoelectric point were 455 nm, 2.72 eV, 14.7 nm and 3.43, respectively. Stronger adsorption and photodegradation of RhB (25 mg/L, pH=4) using LCM-Bi₂WO₆ as photocatalyst was observed, compared with using TiO₂ or Bi₂WO₆ prepared by hydrothermal method as photocatalyst. Adsorption and photodegradation of RhB by LCM-Bi₂WO₆ satisfied the pseudo-second-order kinetic equations and first order kinetic equations, respectively. Equilibrated adsorption capacity (7.48-21.93 mg/g) and photodegradation rate constants (0.0197-0.1181 min^-1) of RhB by LCM-Bi₂WO₆ were positively related to solution pH. Photocatalytic degradation of RhB by LCM-Bi₂WO₆ was mainly triggered by free hydroxyl groups (·OH). Blue shifts of RhB ultraviolet-visible spectrum indicated its degradation through ethyl removal and conjugated groups break pathway. Weaker adsorption (qe=6.03 mg/g) and photodegradation (kv=0.115 min^-1) of RhB by LCM-Bi₂WO₆ using H₂SO₄ as acidity regulator were observed compared with using HCl (qe=21.93 mg/g, kv=0.115 min^-1) as acidity regulator, because of SO₄^2- strong adsorption to LCM-Bi₂WO₆.