构筑Z型MnO_(2)/BiOBr异质结用于光催化环丙沙星去除和CO_(2)还原

Construction of Z-Scheme MnO_(2)/BiOBr Heterojunction for Photocatalytic Ciprofloxacin Removal and CO_(2) Reduction

日益严峻的能源短缺以及生态环境污染问题已成为引发全球持续关注的焦点问题,这严重影响了人类自身健康和社会可持续发展。多种技术被开发出来用于实现新能源开发和污染物控制,其中,光催化因其具有低耗能、无二次污染、操作流程简单、温和的反应条件等优点成为环境治理与能源催化领域的研究重点。不过值得注意的是,光催化技术尽管在抗生素的高效去除和CO_(2)还原领域的应用方兴未艾,但其工业化应用和大规模推广始终受限于光催化剂的光吸收效率、氧化还原能力和光生电子分离或迁移效率等诸多因素。基于当前光催化剂的组成/结构调控及其催化性能研究,探索高效实用的改性策略构筑性能更加优化的复合结构光催化剂,使光催化剂发挥出更高的光吸收/利用以及光催化表/界面反应性能是亟待解决的关键问题。在常见的改性策略中,Z型异质结构构筑不仅明显可以提高光吸收能力和显著降低光生电子空穴复合率,更重要的是,还可以保持光生电子/空穴的强还原/氧化能力来实现环境污染物去除和清洁能源转化。在本文中,采用机械辅助球磨法构建了MnO_(2)/BiOBr (MO/BiOBr) Z型异质结复合材料。在黑暗和光照条件下进行的原位X射线光电子能谱(XPS)测试可以证实MnO_(2)中的光生电子可以通过Mn3+/Mn4+氧化还原电对实现向BiOBr的定向迁移,以构建Z型载流子转移路径。通过电子自旋共振谱(ESR)和能带结构分析也可以推导出类似的结论。基于MnO_(2)中存在的Mn^(3+)/Mn^(4+)氧化还原电对以及MnO_(2)与BiOBr材料交错的能带位置,MnO_(2)和BiOBr材料可以构筑Z型异质结以实现氧化中心和还原中心的空间分离。此外,通过紫外可见光吸收光谱(UV-Vis DRS)和稳态荧光光谱(PL)分析相比较于BiOBr,MO/BiOBr复合材料具有增强的光吸收和显著降低的光生电子-空穴复合率。因此,MO/BiOBr复合材料表现出优异的光催化环丙沙星(CIP)氧化和CO释放性能。MO/BiOBr复合材料的CIP去除率在60min时可达77.3%,是BiOBr(60.2%)的1.28倍。同时,MO/BiOBr复合材料(20.02μmol·g^(-1)·h^(-1))的光催化CO生成性能是BiOBr (9.08μmol·g^(-1)·h^(-1))的2.2倍。光电流和电化学阻抗分析表明,相比于MnO_(2)和BiOBr单体,构筑的MnO_(2)/BiOBr Z型异质结具有更高的界面电子转移效率。此外,选用液相质谱联用光谱(LC-MS)和原位傅里叶变换红外光谱(in situ FTIR)对光催化CIP去除和CO_(2)还原过程的中间体生成路径进行分析。并通过毒性评估软件(T.E.S.T.)计算CIP和在MO/BiOBr复合材料光催化降解CIP过程中产生的中间体对应的大型溞的48 h半数致死浓度、黑头软口鲦的96 h半数致死量、致突变性和生物累积因子来评估CIP和相应中间体的实际生理毒性。因此,本研究提供了一种简便方法来构筑Z型异质结以实现太阳能驱动的高效抗生素去除和燃料合成。

Rapid increase in energy shortage and ecological environmental pollution has become a major issue that has been continuously drawing global attention,because it severely affects human health and limits sustainable social development.Various technologies have been developed and used to rationalize the utilization of new energy sources and pollution control.Among these technologies,photocatalysis has become a research priority in the field of environmental governance and energy development.Advantages such as low energy consumption,no secondary pollution,simple operation methods,and mild reaction conditions make photocatalysis an attractive choice.Notably,although photocatalysis is a promising approach for enhancing antibiotic removal and CO_(2) reduction efficiency,the industrialization and large-scale application of photocatalysts is limited because of issues such as low photo-absorption efficiency,redox capacity,and photogenerated electron separation or migration efficiency.The progress of current research on the regulation of composition/structure and performance of photocatalysts has promoted the exploration of efficient and practical modification strategies to construct photocatalyst composites with improved performance by facilitating light absorption/utilization and enhancing photocatalytic surface/interface reaction performance.Among the many common modification strategies,the construction of a Z-scheme heterojunction can enhance the light absorption ability and significantly reduce the recombination rate of photogenerated electron-hole pairs.Additionally,this strategy maintains the strong reduction/oxidation ability of photogenerated electrons/holes to facilitate the oxidation of environmental pollutants and conversion to clean energy.In this study,Z-scheme MnO_(2)/BiOBr(MO/BiOBr)composites were effectively constructed using a mechanically assisted ball-milling process.In situ X-ray photoelectron spectroscopy under dark and light conditions confirmed that photoexcited electrons in MnO_(2) can migrate directionally to BiOBr through Mn^(3+)/Mn^(4+)redox couple to create a Z-scheme transfer path.A similar conclusion can also be deduced from the results of electron spin-resonance spectroscopy and band structure analysis.The formation of a Z-scheme heterojunction between MnO_(2) and BiOBr,attributed to the Mn^(3+)/Mn^(4+)redox couple from MnO_(2) and staggered energy band,enabled the space separation of oxidation and reduction centers.Furthermore,compared with BiOBr,MO/BiOBr composites exhibited enhanced light absorption and a markedly reduced photoinduced electron-hole pair recombination rate,as confirmed by ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence spectroscopy.Thus,the MO/BiOBr composites exhibited exceptional photocatalytic performance toward ciprofloxacin(CIP)oxidation and CO evolution.The CIP removal efficiency of the MO/BiOBr composites reached 77.3%in just 60 min,which is 1.28 times higher than that of BiOBr(60.2%).Simultaneously,the photocatalytic CO_(2)-to-CO performance of the MO/BiOBr composites(20.02μmol·g^(−1)·h^(−1))was found to be 2.20-fold higher than that of BiOBr(9.08μmol·g^(−1)·h^(−1)).Photocurrent measurement and electrochemical impedance spectroscopy indicated that the MnO_(2)/BiOBr Z-scheme heterojunction has higher interfacial electron transfer efficiency than pure MnO_(2) and BiOBr.Additionally,liquid chromatograph mass spectrometry and in situ Fourier transform infrared spectroscopy is conducted to study the generation of intermediates during the photocatalytic CIP removal and CO_(2) reduction process.The toxicity of CIP and corresponding intermediates after the photocatalytic degradation of the MO/BiOBr composites was evaluated using toxicity estimation software(T.E.S.T.)to analyze the actual physiological toxicity,based on indexes such as Daphnia Magna lethal concentration 50%(LC_(50),48 h),Fathead Minnow lethal dose 50%(LD_(50),96 h),mutagenicity,and bioaccumulation factor.Thus,this study proposed a novel and simplified approach for constructing a Z-scheme heterojunction to facilitate solar-derived antibiotic removal and fuel synthesis.