Research On Preparation Of Bi₃O₄Br-based Materials By Mechanosynthesis And The Performance Of Photocatalytic Degradation For Organic Pollutants

Water is essential for the alternation of plant and animal life,human productive activity and life,and the ecological cycle of the planet.Maintaining the safety of the water environment is related to the vital interests of the people.The Party’s"14th Five-Year Plan"outlined the ultimate goal of winning the battle of the prevention and control of water pollution.Therefore,there is an urgent need to explore efficient treatments for water pollution.Antibiotics and dyes are the main sources of water pollution and their presence in water bodies poses a threat to environmental safety and human health and is difficult to remove effectively due to their chemical stability.Photocatalysis,an advanced sunlight-driven oxidation technology,has promising applications in environmental treatment,and its degradation capacity can be further enhanced through the design of catalyst structures.In this paper,a series of modification strategies for Bi₃O₄Br materials are proposed,which effectively enhance the separation and migration efficiency of photogenerated carriers and promote the generation of reactive oxygen species,ultimately achieving a significant improvement in the photocatalytic performance of the materials.The compositional structure,morphology,and optoelectronic properties of the materials have been investigated by various characteristic methods,the photocatalytic degradation performance of the prepared Bi₃O₄Br-based materials has been examined,and the possible reaction mechanism has been elucidated.The main research contents of this paper are as follows:（1）Bi₃O₄Br-M ultrathin nanosheets were synthesized by a rapid room-temperature mechanically assisted ionic liquid method.The presence of tensile strain in Bi₃O₄Br-M was confirmed by high-resolution transmission electron microscopy images and Raman spectroscopy.The stress effect modifies the atomic arrangement of Bi₃O₄Br-M,which is manifested by the optimization of the energy band structure and the significant enhancement of the photogenerated electron-hole separation and migration ability.Under visible light irradiation,the photodegradation efficiency of 20 mg of Bi₃O₄Br-M for rhodamine B(10 mg L^-1,100 m L)and tetracycline(20 mg L^-1,100 m L)was 90.21%（60 min）and 65.53%（120 min）,respectively,which were 3.02 and 6.10 times higher than those of calcined Bi₃O₄Br.The photocatalytic degradation mechanism of Bi₃O₄Br-M is that the tensile-strained Bi₃O₄Br-M enhances the photogenerated charge separation and promotes the large-scale generation of superoxide radicals,singlet oxygen,and holes for effective degradation of dyes and antibiotics.（2）Based on the above research work,a series of Mn-doped Bi₃O₄Br materials（Mn-BOB）were constructed by introducing the transition metal ion Mn²⁺through a rapid room-temperature mechanically assisted ionic liquid method.The doping of Mn²⁺enables the energy band modulation of Bi₃O₄Br materials and effectively enhances its visible light absorption.Meanwhile,Mn²⁺,as an effective hole-trapping agent,can inhibit the photogenerated charge recombination and enhance the separation of photogenerated carriers.Mn-BOB-3 exhibits the best tetracycline degradation performance,and the degradation rate of tetracycline(20 mg L^-1,100 m L)by 20 mg catalyst was 81.74%after 120 min of visible light irradiation,which was1.22 times higher than that of Bi₃O₄Br.The photocatalytic degradation mechanism of Mn-BOB was that the introduction of Mn²⁺leads to the formation of doping energy level,which contributes to the effective separation of photogenerated carriers and thus significantly enhances its performance in photocatalytic degradation of pollutants.The main active species are singlet oxygen,superoxide radicals,and holes.（3）Based on the property that Bi₃O₄Br can generate hydrogen peroxide（H₂O₂）under visible light irradiation,amorphous Fe OOH quantum dots were grown in situ on its surface to construct a semi-self-sufficient photo-Fenton system（Fe OOH/BOB）.Surface loading of amorphous Fe OOH quantum dots on Bi₃O₄Br nanosheets not only broadens the visible light absorption range of Bi₃O₄Br but also facilitates efficient charge transfer at the interface.Upon introduction of exogenous H₂O₂,Fe OOH/BOB exhibits enhanced photo-Fenton degradation of tetracycline compared with Bi₃O₄Br,Fe OOH,and mixtures of both,with 5 wt%Fe OOH/BOB being the best performance,and the degradation of tetracycline(20 mg L^-1,100 m L)by 20 mg catalyst under 60 min visible light irradiation reached 94.82%,which was 1.50 and 1.33 times higher than that of Bi₃O₄Br and Fe OOH,respectively.The photocatalytic degradation mechanism of Fe OOH/BOB was that the H₂O₂generated by Bi₃O₄Br effectively activates the photo-Fenton degradation function of Fe OOH/BOB,thus significantly improving the performance for photocatalytic degradation of organic pollutants.In the photo-Fenton reaction,singlet oxygen and superoxide radicals are the main reactive species,with holes and hydroxyl radicals playing some supporting roles.