内电场增强S型异质结N-C3N4/BiOClxI1-x的制备及其光催化性能

徐凯旋; 亢玉龙; 高晓明; 贺红斌; 袁中强; 胡亚楠

内电场增强S型异质结N-C₃N₄/BiOCl_xI_1-x的制备及其光催化性能

延安大学化学与化工学院, 陕北低阶煤清洁高效利用协同创新中心, 陕西延安 716000

基金项目: 陕西省自然科学基金项目(2022 QFY07-03)

详细信息

通讯作者:
高晓明，教授，主要从事光催化的研究联系方式：ydgaoxm@126.com

中图分类号: X75
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- 被引次数: 0
出版历程
- 收稿日期: 2022-10-17
- 修回日期: 2022-11-20
- 录用日期: 2022-11-26
- 网络出版日期: 2022-12-16

Preparation of S-type heterojunction N-C₃N₄/BiOCl_xI_1-x with internal electric field and enhanced photocatalytic properties

Department of Chemistry and Chemical Engineering, Clean Utilization of Low Rank Coal of Shaanxi Collaborative Innovation Center, Yan’an University, Yan’an, 716000, P. R. China

Funds: Natural Science Foundation of Shaanxi Province, China(2022 QFY07-03)

摘要

摘要: 目的随着人类社会的发展，环境污染问题愈发严重。苯酚作为一种工业用品，被广泛应用于生产树脂、杀菌剂、防腐剂以及药物等，但其不合理的排放导致水环境污染严重。同时Cr(Ⅵ)作为一种重要的工业化学品，被排放到水环境中很容易被水生物吸收，从而威胁人类健康和生态系统。近年来，光催化技术因其环境友好、成本低、毒性低和高效的优势，被广泛用于环境污染物治理。而在此领域，高效光催化剂的筛选与制备是光催化研究的核心课题。BiOCl光催化材料具有独特的晶体结构和多样的电子结构，为太阳能光催化技术提供了新的突破点。然而，然而，光吸收范围窄、载流子分离效率低、光生电荷迁移速率慢是现有BiOCl光催化材料存在的主要缺陷，严重限制了光催化活性的提高。近年来，人们采用大量的手段，如金属或非金属掺杂、固溶体的构建，提高其光催化效率。方法采用水热法制备BiOCl和BiOI，通过调节卤素的比例，制备固溶体BiOClI；以静电自组装的形式构建S-型异质结N-CN/BiOClI。以水中苯酚、Cr(VI)为污染模型，研究N-CN/BiOClI光催化氧化与还原性能。通过捕获实验、ESR、DFT计算研究N-CN/BiOClI的内电场及其对光催化性能增强的机理。结果 XRD的衍射角偏移、衍射峰强度变化表明BiOClI固溶体与N-CN/BiOClI异质结的结构。FTIR的表面官能团分析说明形成了N-CN/BiOClI异质结。Zeta电位分析证明N-CN与BiOClI是以静电自组装的形式结合。SEM和TEM分析表明N-CN与BiOClI充分接触。XPS表征表明电子N-CN转移BiOClI。光催化实验结果表明N-CN/BiOClI具有优异的光催化氧化有机污染物与还原Cr(VI)的活性。DFT计算表明形成了从N-CN到BiOClI的内部电场，抑制了电子-空穴对的复合，加速了界面载流子的分离和转移。电化学测试、UV-Vis DRS计算表明N-CN/BiOClI异质结具有合适的氧化还原电位。捕获实验、ESR测试表明苯酚的光催化氧化过程中可以产生活性物种·O、·OH。结论 (1)采用水热法，利用静电自组装的形式制备了N-CN/BiOClI S型异质结光催化剂。(2)在降解和还原的过程中20%N-BiOClI呈现出高的催化性能，可见光照射2.5 h，苯酚的降解率达到98.53%，是N-CN、BiOClI的3.22、2.33倍。在可见光照射1 h时，20%N-BiOClI的Cr(VI)的还原率达到99.11%，是N-CN、BiOClI的13.27、4.54倍。(3)通过ESR技术确定20%N-BiOClI光催化反应过程中主要产生·O和·OH，使用光电子能谱和样品的理论功函数验证了光生电子的流向，结合能带位置，推测光生载流子分离和转移的可能模式为S型。此结构可提升载流子的分离效率，有效抑制光生载流子的复合。(4)N-CN/BiOClI具有强的光吸收，在可见光照下，载流子从N-CN穿过界面转移到BiOClI，在二者的见面处形成强的界面电场，抑制了电子-空穴对的复合。界面电场形成、能带边缘弯曲以及N-CN和BiOClI界面处库仑力的存在，提高了N-CN/BiOClI的光催化性能。
- 光催化 /
- N-C₃N₄/BiOCl_xI_1-x /
- 静电自组装 /
- S型异质结 /
- 内电场
Abstract: N-C₃N₄/BiOCl_xI_1-x S-type heterojunctions were prepared by a facile one-step hydrothermal method. The crystal form, morphology, structure, elemental composition, surface functional groups and optical properties of the samples were characterized by XRD, XPS, SEM, TEM, FTIR and UV-Vis. The photocatalytic activity of N-C₃N₄/BiOCl_xI_1-x oxidation of organic pollutants and reduction of Cr(VI) was investigated. The results show that N-C₃N₄/BiOCl_xI_1-x sample exhibited the effective enhancement in light absorption. The charge carriers were generated by the transfer of the photoinduced electron from N-C₃N₄ to BiOCl_xI_1-x across the interface under irradiation, which inhibited the recombination of electron-hole pairs. Under visible light irradiation, 20%N-BiOCl_0.5I_0.5 exhibited high activity, the degradation rate of phenol reached 98.53% with 2.5 h of visible light irradiation. Meanwhile, the reduction rate of Cr(VI) of 20% N-BiOCl_0.5I_0.5 reached to 99.11% with 1 h of visible light irradiation. 20%N-BiOCl_0.5I_0.5 showed good stability after five cycles. The TOC removal rate of degradation phenol by 20%N-BiOCl_0.5I_0.5 within 3 hours was 80.21%. Combined with capture experiment, ESR and DFT calculation, the improvement activity of N-C₃N₄/BiOCl_xI_1-x was attributed to the formation of S-type heterojunction, the internal electric field based on different Fermi levels between N-C₃N₄ and BiOCl_xI_1-x, as well as band bending and Coulomb force, which together accelerated spatial separation of photogenerated carriers and orderly electron flow.
- photocatalytic /
- N-C₃N₄/BiOCl_xI_1-x /
- Electrostatic self-assembly /
- S-type heterojunction /
- Internal electric field

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图 1 (a) BiOCl_xI_1-x的XRD图谱，(b) BiOCl_xI_1-x在2θ=25-37 °的XRD图谱，(c) N-C₃N₄/BiOCl_xI_1-x的XRD图谱，(d)样品的FT-IR图谱，(e) N-C₃N₄的zeta谱图，(f) BiOCl_0.5I_0.5的zeta谱图

Figure 1. (a) XRD pattern of BiOCl_xI_1-x, (b) XRD pattern of BiOCl_xI_1-x at 2θ=25-37 °, (c) XRD pattern of N-C₃N₄/BiOCl_xI_1-x, (d) FTIR pattern of the as-prepared samples, (e) the zeta spectrum of N-C₃N₄ (f) the zeta spectrum of BiOCl_0.5I_0.5

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图 2 样品的HR-XPS:(a) Bi4f，(b) Cl2p，(c) O1s，(d) I3d，(e) N1s，(f) C1s

Figure 2. HR-XPS of the sample: (a) Bi4f, (b) Cl2p, (c) O1s, (d) I3d, (e) N1s, (f) C1s

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图 3 样品的SEM图像：(a) BiOI，(b) BiOCl_0.5I_0.5，(c) 20%N-BiOCl_0.5I_0.5局部放大图

Figure 3. SEM image: (a) BiOI (b) BiOCl_0.5I_0.5 (c) partial enlargement of 20%N-BiOCl_0.5I_0.5

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图 4 (a-c) 20%N-BiOCl_0.5I_0.5的TEM图，(d-j) 20%N-BiOCl_0.5I_0.5的EDS mapping，分别为Bi、Cl、O、I、C

Figure 4. (a-c) TEM image of 20%N-BiOCl_0.5I_0.5, (d-j) EDS mapping of 20%N-BiOCl_0.5I_0.5, corresponding to Bi, Cl, O, I, N and C respectively

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图 5 (a) N-BiOCl_xI_1-x的UV-Vis漫反射谱图，(b) BiOCl_xI_1-x的带隙

Figure 5. (a) The UV-Vis DRS of N-BiOCl_xI_1-x, (b) band gap of N-BiOCl_xI_1-x

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图 6 N-C₃N₄(a)和BiOCl_0.5I_0.5(b)的Mott-schottky曲线，(c)能带结构

Figure 6. (a) Mott schottky curve N-C₃N₄, (b) mott schottky curve BiOCl_0.5I_0.5, (c) band structure

C^-2—Interfacial capacitance; F^-2—Frequency

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图 7 (a)苯酚的光催化降解曲线，(b，c)光催化还原六价铬曲线和表观速率常数，(d) 20%N-BiOCl_0.5I_0.5循环降解苯酚稳定性测试，(e) 20%N-BiOCl_0.5I_0.5在五个循环前后的XRD图谱，(f) 20%N-BiOCl_0.5I_0.5可见光降解苯酚的TOC去除率

Figure 7. (a) Photocatalytic degradation curve of phenol, (b, c) photocatalytic reduction curve and apparent rate constant of Cr(Ⅵ), (d) recycling use of 20% N-BiOCl_0.5I_0.5 for phenol degradation, (e) XRD patters of before and after five cycles of 20% N-BiOCl_0.5I_0.5 for for phenol degradation, (f) removal rate of TOC of phenol over 20%N-BiOCl_0.5I_0.5

C₀—Initial solution concentration; C_t—the solution concentration at t; K—apparent rate constant; TOC₀—total organic carbon of initial solution; TOC—total organic carbon of solution at t

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图 8 20%N-BiOCl_0.5I_0.5: (a)·O₂⁻测试，(b)·OH测试，(c)h⁺测试

Figure 8. 20%N-BiOCl_0.5I_0.5: (a)ESR spectrum of DMPO -·O₂⁻, (b) ESR spectrum of DMPO - ·OH, (c) ESR spectrum of DMRO- h⁺

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图 9 (a) N-C₃N₄理论模型，(b) N-C₃N₄的功函数，(c) BiOCl_0.5I_0.5的功函数，(d，e) 20%N-BiOCl_0.5I_0.5三维电子密度差图(其中蓝色(椭圆形)和黄色(矩形框)区域代表电子耗尽和累积)

Figure 9. (a) N-C₃N₄ theoretical model, (b) N-C₃N₄ of work function calculation, (c) BiOCl_0.5I_0.5 of work function calculation, (d,e) three-dimensional charge density differences of 20% N-BiOCl_0.5I_0.5 (where the blue (oval) and yellow (rectangular) areas represent electron depletion and accumulation)

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图 10 光催化降解机制图:(a) II型异质结，(b) S型异质结

Figure 10. Photocatalytic degradation mechanism: (a) type II heterojunction, (b) S-scheme heterojunction

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