构筑Bi纳米粒子负载BiOCl纳米片欧姆结用于光催化CO_(2)还原

煤炭、石油和天然气等能源的不断增长消耗,不仅导致不可再生能源逐渐枯竭,还使大气中的CO_(2)浓度显著上升,引发严重的能源危机和气候问题。因此,我们必须开发清洁、可持续的能源转换技术,以应对不断增长的能源需求和日益严重的环境危机。受到自然界光合作用的启发,光催化CO_(2)转化利用太阳能驱动,可以将CO_(2)和水转化为高附加值的化学品。经过多年的发展,人工光合作用已被认为是一种绿色、经济、可持续的方法,有望助力实现国家的碳中和发展目标。然而,现有的光催化剂存在着载流子分离效率低和活性位点不足的问题,从而导致CO_(2)光还原效率较低。为了应对这些科学问题,研究人员发现将金属纳米粒子负载到半导体材料上形成欧姆结,可以产生内建电场,有助于光生电子和空穴的分离。因此,本研究通过溶剂热法在BiOCl纳米片表面负载Bi纳米粒子,构建了Bi/BiOCl欧姆结光催化剂。通过X射线衍射(XRD)、X射线光电子能谱(XPS)和透射电子显微镜(TEM)分析了光催化剂的成分和微观结构。利用紫外-可见漫反射光谱(UV-Vis DRS)研究了催化剂的光吸收性能。通过瞬态光电流响应测试、电化学阻抗谱(EIS)和电子自旋共振谱(ESR)研究了光生电子和空穴的分离能力。由于Bi纳米粒子与BiOCl的功函数不同,二者形成的欧姆结具有优异的电荷转移特性,可以显著提高光生载流子的利用效率。此外,Bi纳米粒子还可以作为助催化剂,促进惰性CO_(2)分子的活化。光催化测试结果显示,经过300 W氙灯照射4 h后,具有最佳活性的复合材料(Bi/BiOCl-2)将CO_(2)还原为CO(34.31μmol·g^(-1))和CH_(4)(1.57μmol·g^(-1))的速率分别是BiOCl纳米片的2.55倍和4.76倍。同位素示踪实验证实,产物是CO_(2)和水分子经过光催化反应得到的。此外,根据原位傅里叶变换红外光谱(in situ FTIR)结果,发现在CO_(2)还原过程中形成了^(*)CHO、^(*)CH_(3)O、b-CO_(3)^(2-)、m-CO_(3)^(2-)、HCO_(3)^(-)、HCOOH、^(*)COOH和HCOO^(-)等中间体,并进一步提出了可能的光催化CO_(2)还原机制。经过25 h的CO_(2)光还,原反应后,CO和CH_(4)产量持续增加,同时结合XRD、XPS和TEM结果表明,制备的Bi/BiOCl-2材料具有良好的结构稳定性。这项研究为高效CO_(2)光还原催化剂的构建提供了有益的参考。

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

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。

Construction of nitrogen and phosphorus co-doped graphene quantum dots/Bi5O7I composites for accelerated charge separation and enhanced photocatalytic degradation performance

Nitrogen and phosphorus co-doped graphene quantum dot-modified Bi5O7 I(NPG/Bi5O7 I)nanorods were fabricated via a simple solvothermal method.The morphology,structure,and optical properties of the as-prepared samples were investigated by X-ray diffraction,scanning electron microscopy,high-resolution transmission electron microscopy,X-ray photoelectron spectroscopy(XPS),and diffused reflectance spectroscopy.The photocatalytic performance was estimated by degrading the broad-spectrum antibiotics tetracycline and enrofloxacin under visible light irradiation.The photodegradation activity of Bi5O7 I improved after its surface was modified with NPGs,which was attributed to an increase in the photogenerated charge transport rate and a decrease in the electron-hole pair recombination efficiency.From the electron spin resonance spectra,XPS valence band data,and free radical trapping experiment results,the main active substances involved in the photocatalytic degradation process were determined to be photogenerated holes and superoxide radicals.A possible photocatalytic degradation mechanism for NPG/Bi5O7 I nanorods was proposed.

Facile microwave-assisted ionic liquid synthesis of sphere-like BiOBr hollow and porous nanostructures with enhanced photocatalytic performance

In this work, two kinds of self-assembled hierarchical BiOBr microcrystals were rapidly synthesized through a simple microwave-assisted route in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide([C_(16)mim]Br). These porous and hollow BiOBr microspheres were obtained via a facile solvothermal method with or without polyvinyl pyrrolidone(PVP), respectively. During the synthetic process, ionic liquid [C_(16)mim]Br played as solvent, reactant and template at the same time. Moreover, the BiOBr hollow and porous microspheres exhibited outstanding photocatalytic activities for the degradation of rhodamine B(RhB) under visible light irradiation. A possible photocatalytic mechanism was also discussed in detail. It can be assumed that the higher photocatalytic activities of BiOBr porous microspheres materials could be ascribed to the novel structure, larger specific surface area, narrower band gap structure and smaller particle size.

Improved visible light photocatalytic activity of mesoporous FeVO_4 nanorods synthesized using a reactable ionic liquid

Mesoporous FeVO4 nanorods were successfully synthesized by calcining the precursor Fe- VO4·1.1H2O nanorods, which were obtained via a simple hydrothermal method in the presence of a reactable metal-ion-containing ionic liquid, 1-octyl-3-methylimidazolium tetrachloride ferrate(III)([Omim]FeCl4). The structure and morphology of the prepared samples were examined using various characterization techniques. During the synthetic process,[Omim]FeCl4 acted as the solvent, reactant, and capping agent simultaneously. Moreover, the porous FeVO4 nanorods as the heterogeneous photo-Fenton-like semiconductor catalyst for the degradation of tetracycline and rhodamine B under visible light irradiation exhibited excellent photocatalytic activity. This excellent photocatalytic activity of the porous FeVO4 nanorods can be attributed to the synergistic effect of their high electron-hole pair separation rate, suitable band gap structure, and large specific surface area. The possible photocatalytic degradation mechanism of FeVO4/H2O2 photocatalytic systems was also discussed in detail.

Oxygen defect modulating the charge behavior in titanium dioxide for boosting photocatalytic nitrogen fixation performance

Extremely high-temperature and high-pressure requirement of Haber-Bosch process motivates the search for a sustainable ammonia synthesis approach under mild conditions.Photocatalytic technology is a potential solution to convert N2 to ammonia.However,the poor light absorption and low charge carrier separation efficiency in conventional semiconductors are bottlenecks for the application of this technology.Herein,a facile synthesis of anatase TiO_(2)nanosheets with an abundance of surface oxygen vacancies(TiO_(2)-OV)via the calcination treatment was reported.Photocatalytic experiments of the prepared anatase TiO_(2)samples showed that TiO_(2)-OV nanosheets exhibited remarkably increased ammonia yield for solar-driven N2 fixation in pure water,without adding any sacrificial agents.EPR,XPS,XRD,UV-Vis DRS,TEM,Raman,and PL techniques were employed to systematically explore the possible enhanced mechanism.Studies revealed that the introduced surface oxygen vacancies significantly extended the light absorption capability in the visible region,decreased the adsorption and activation barriers of inert N2,and improved the separation and transfer efficiency of the photogenerated electronhole pairs.Thus,a high rate of ammonia evolution in TiO_(2)-OV was realized.This work offers a promising and sustainable approach for the efficient artificial photosynthesis of ammonia.

“Electron collector”Bi_(19)S_(27)Br_(3)nanorod‐enclosed BiOBr nanosheet for efficient CO_(2) photoconversion

Although CO_(2)photoreduction is a promising method for solar‐to‐fuel conversion,it suffers from low charge transfer efficiency of the photocatalysts.To improve the CO_(2)photoreduction performance,introduction of electron‐accumulated materials on the photocatalyst surface is considered an effective method.In this study,the Bi_(19)S_(27)Br_(3)/BiOBr composites were designed and synthesized.The Bi19S27Br3 nanorod in this photocatalytic system acts as an electron‐accumulated active site for extracting the photogenerated electrons on the BiOBr surface and for effectively activating the CO2 molecules.As a result,Bi_(19)S_(27)Br_(3)/BiOBr composites exhibit the higher charge carrier transfer efficiency and further improves the CO_(2)photoreduction performance relative to that of pure Bi_(19)S_(27)Br_(3)and BiOBr.The rate of CO formation using Bi_(19)S_(27)Br_(3)/BiOBr‐5 is about 8.74 and 2.40 times that using Bi_(19)S_(27)Br_(3)and BiOBr,respectively.This work provides new insights for the application of Bi_(19)S_(27)Br_(3)as an electron‐accumulating site for achieving high photocatalytic CO2 reduction performance in the future.

In-situ embedded ultrafine Bi_(12)O_(17)Br_(2)nanotubes in MOF-derived hierarchical porous carbon for enhanced photocatalytic CO_(2)conversion to CO

Increasing the utilization efficiency of photogenerated electrons is highly recognized as one of the ef-ficient approaches to boost the photocatalytic CO_(2)conversion efficiency.Herein,ZIF-67-derived porous carbon(PC)material was employed for the construction of PC@ultrafine Bi_(12)O_(17)Br_(2)nanotubes(PC@BOB NTs)composites through a facile solvothermal synthesis in order to optimize the use of excited elec-trons in the BOB NTs.Photoelectrochemical characterization results revealed that the introduction of PC material achieved a faster charge separation rate in the PC@BOB composites,ensuring more photogener-ated electrons participate in the CO_(2)adsorption and activation process.Moreover,the pore structures of ZIF-67-derived PC material provided abundant confined spaces for the enrichment of CO_(2)molecules.Af-ter 5 h of Xenon lamp irradiation,PC@BOB composites exhibited obviously increased photocatalytic CO_(2)reduction activity in the pure water.When the addition amount of PC was 5 wt%,the PC@BOB-2 com-posite showed the highest CO evolution rate of 359.70μmol/g,which was 2.95 times higher than that of the pure BOB NTs.This work provides some independent insights into the applications of Metal-Organic Framework(MOF)-derived hierarchical porous structures to strengthen the CO_(2)enrichment,as well as the excited charge utilization efficiency,thus achieving a high solar-to-fuel conversion efficiency.

CoTCPP integrates with BiOBr microspheres for improved solar-driven CO_(2)reduction performance

CO_(2) photoreduction into carbon-based chemicals has been considered as an appropriate way to alleviate the energy issue and greenhouse effect.Herein,the 5,10,15,20-tetra(4-carboxyphenyl)porphyrin cobalt(II)(CoTCPP)has been integrated with BiOBr microspheres and formed the CoTCPP/BiOBr composite.The as-prepared CoTCPP/BiOBr-2 composite shows optimized photocatalytic performance for CO_(2) conversion into CO and CH_(4) upon irradiation with 300 W Xe lamp,which is 2.03 and 2.58 times compared to that of BiOBr,respectively.The introduced CoTCPP significantly enhanced light absorption properties,promoted rapid separation of photogenerated carriers and boosted the chemisorption of CO_(2) molecules.The metal Co^(2+) at the center of the porphyrin molecules also acts as adsorption center for CO_(2) molecules,accelerating the CO_(2) conversion into CO and CH_(4).The possible mechanism of CO_(2) photoreduction was explored by in-situ FT-IR spectra.This work offers a new possibility for the preparation of advanced photocatalysts.

Enhanced photocatalytic performance of carbon quantum dots/Bi OBr composite and mechanism investigation

Novel carbon quantum dots（CQDs）/Bi OBr composite photocatalysts have been constructed through a facile hydrothermal synthesis in the presence of ionic liquid 1-hexadecyl-3-methylimidazolium bromide（[C16 mim]Br）. Series of characterizations have been performed to confirm the uniform distribution of CQDs in Bi OBr nanosheets and the synergistic effect for photocatalytic degradation organic pollutants between CQDs and Bi OBr. The results show that 3.1 wt% CQDs/Bi OBr photocatalyst possesses the best photocatalytic activity for the degradation of colorless antibiotic tetracycline（TC）, endocrine disrupter bisphenol A（BPA） and dye rhodamine B（Rh B）, under visible light irradiation, which exhibited the highest photocatalytic performance. The enhanced photocatalytic performance for CQDs/Bi OBr composites could be attributed to the wider optical absorption range and fast separation of photogenerated charge carriers after the introduction of CQDs. The key roles of CQDs for the enhanced photocatalytic activity of Bi OBr have been discussed. A possible mechanism of CQDs/Bi OBr on the enhancement of visible light performance was proposed.

In-Situ Synthesis of CQDs/BiOBr Material via Mechanical Ball Milling with Enhanced Photocatalytic Performances

Designing simple, efficient, and environmentally friendly methods to construct high-efficient photocatalysts is an important strategy to promote the further development of the field of photocatalysis. Herein, flower-like carbon quantum dots(CQDs)/Bi OBr composite photocatalysts have been prepared via in-situ synthesis by mechanical ball milling in the existence of ionic liquid. The CQDs/Bi OBr composites exhibit higher photo-degradation performance for tetracycline(TC) than Bi OBr monomer and the commercial Bi_(2)O_(3) under visible light irradiation. For comparison, the different Br sources and synthetic methods are chosen to prepare Bi OBr and CQDs/Bi OBr composites. Photocatalysts prepared by ball milling and ionic liquid present significantly enhanced photocatalytic performance for removing TC. In addition, the introduction of CQDs could distinctly enhance the photocatalytic performances of pure Bi OBr. The reason is that CQDs as electron acceptor effectively separate electrons and holes and inhibit their recombination. The intermediates during photocatalytic degradation were tested using liquid chromatography-mass spectrometry(LC-MS) and possible degradation pathways were given. During degradation, ·OH, O_(2)^(·-)and h^(+) were identified to be the main active species based on electron spin resonance(ESR) spectra and free radical trapping experiments. A possible mechanism of CQDs/Bi OBr with enhanced photocatalytic performances was further proposed.