Bi/Bi2O2CO3 等离子体复合材料的合成及其光催化性能

图1 BOC and Bi/Bi₂O₂CO₃样品的XRD谱

Fig.1 XRD patterns of BOC and Bi/Bi₂O₂CO₃ composites

2.2 样品的形貌

如图2所示，BOC和Bi/BOC-1样品具有不规则的片状结构，其中BOC的片层厚度为30~60 nm，而Bi/BOC-1的片层更薄、尺寸更小，厚度为10~20 nm。图3a表明，Bi/BOC-1样品呈现不规则纳米片状结构，放大后可见分散在表面的Bi纳米颗粒(图3b)。在图3c给出的典型HRTEM图像中可见两组清晰的晶格条纹，其中间距为0.27 nm的条纹对应正交晶系Bi₂O₂CO₃的(002)晶面，而间距为0.33 nm的条纹则对应三方晶系Bi的(012)晶面。两套晶格条纹在界面处相连，表明Bi与Bi₂O₂CO₃形成了紧密的异质结界面。选区电子衍射(SAED)花样(图3d)进一步证实了两相共存：内环强点对应基体相Bi₂O₂CO₃的(002)晶面(d ≈ 0.27 nm)，外环弱点对应Bi的(110)晶面(d ≈0.23 nm)。由于Bi/BOC-1中金属Bi含量极低，Bi(012)晶面(d ≈ 0.33 nm)的衍射信号极弱且更靠近中心，未在图中单独标出。上述结果和XRD数据都证明已经成功构建了Bi/Bi₂O₂CO₃复合材料。

图2

图2 BOC和Bi/BOC-1样品的SEM照片

Fig.2 SEM images of BOC (a, b) and Bi/BOC-1 (c, d)

图3

图3 Bi/BOC-1的TEM、HRTEM图和SAED衍射花样

Fig.3 TEM images (a, b), HRTEM image (c), and SAED pattern (d) of Bi/BOC-1

2.3 样品的光吸收性能

用紫外-可见漫反射光谱(UV-Vis DRS)表征样品的光吸收性能，结果如图4所示。纯相BOC的吸收边位于368 nm，对应带隙约为3.37 eV，只响应紫外光。引入金属Bi的复合材料在可见光区(400~800 nm)均出现吸收增强，且随着Bi负载量的增加呈规律性变化：Bi/BOC-1和Bi/BOC-2呈现微弱吸收尾，表明少量Bi纳米颗粒产生初步的SPR效应；Bi/BOC-3和Bi/BOC-4形成宽化吸收肩峰，为局域等离子体共振效应(LSPR)典型特征；Bi/BOC-5因过量Bi形成连续金属相，表现了全谱段强背景吸收。样品的颜色由白色依次变为浅灰、灰、深灰直至黑色，与可见光吸收增强的趋势一致，证实已引入金属Bi和产生了SPR效应。

图4

图4 不同样品的紫外可见分光光度谱

Fig.4 UV-Vis diffuse-reflectance spectra of the as-synthesized samples

2.4 化学组成和表面元素电子状态

图5a中的XPS全谱表明，样品中主要有Bi、C和O三种元素。Bi元素来源于制备出的复合材料，而C和O元素来源于仪器本底及表面吸附羟基的较小贡献。在高分辨率Bi 4f XPS谱(图5b)中156.42 eV和161.70 eV处的两个强峰分别归属于Bi 4f_7/2和Bi 4f_5/2跃迁，表明Bi以Bi³⁺的形式存在。在154.98 eV和160.37 eV处的两个较弱的峰，归属于金属单质Bi的特征信号。O 1s高分辨谱(图5c)可拟合成三个峰：位于527.63 eV的峰归属于层状Bi₂O₂CO₃中[Bi₂O₂]²⁺层内的Bi-O键；528.44 eV和528.76 eV处的峰则分别对应复合材料表面吸附的羟基和碳酸根物种。在C 1s谱(图5d)中位于286.30 eV的峰来源于Bi/Bi₂O₂CO₃中的O=C-O结构单元，而282.28 eV与283.49 eV处的峰则归属于外来碳污染。XPS结果进一步证实，所制备的复合材料表面存在单质Bi。为了确定Bi₂O₂CO₃表面单质Bi的相对含量，对Bi/BOC-1至Bi/BOC-4的XPS高分辨Bi 4f谱进行分峰拟合和半定量分析。结果表明，4个样品中单质Bi的相对含量(原子比)依次为2.01%、3.12%、3.24%和3.78%，即随着多聚甲醛用量的增加呈单调递增趋势。Bi/BOC-5的XRD谱已证实其为纯Bi相，表明碳酸盐基体完全分解，单质Bi的比例接近100%。

图5

图5 Bi/BOC-1样品的XPS总谱以及Bi 4f、O 1s和C 1s的高分辨谱

Fig. 5 XPS survey spectrum of Bi/BOC-1 (a), and high-resolution spectra of Bi 4f (b), O 1s (c), and C 1s (d)

2.5 样品的光催化性能

以MG和CIP作为模拟污染物，表征了样品的光催化性能。图6给出了在模拟太阳光照射下不同光催化剂对MG和CIP的降解效果。结果表明，Bi/BOC-1对两种污染物的降解效率最高，可见光照射1 h后分别降解约96%的MG和94%的CIP。相比之下，纯相BOC对MG和CIP的降解率仅为46%和64%。Bi/BOC-2的光催化性能与BOC相近，而Bi/BOC-3、Bi/BOC-4和Bi/BOC-5的性能则明显低于BOC。

图6

图6 所制备样品对MG和CIP的降解活性和-ln(C/C₀)与时间的关系

Fig.6 Activities of as-prepared samples for the degradation of MG (a) and CIP (c), and plots of -ln(C/C₀) vs. time (b, d)

根据图6b、d中的数据，降解动力学符合准一级反应模型。以CIP降解为例，BOC、Bi/BOC-1和Bi/BOC-5的表观速率常数(k)分别为0.019、0.046和0.0044 min^-1。其中Bi/BOC-1的降解速率约为BOC的2.4倍，表明在BOC纳米片上负载适量的Bi纳米颗粒可显著提高其光催化性能。但是，负载量增加的Bi/BOC-5，其光催化降解速率反而低于BOC的1/4。这表明，过量负载的Bi纳米颗粒在BOC纳米片表面聚集，阻碍了对光的吸收。因此，需精确控制Bi的负载量。

为了表征Bi/BOC-1复合材料的结构稳定性，进行了5次循环降解实验，结果如图7所示。在相同反应条件下，Bi/BOC-1的循环稳定性良好：第1次循环60 min内CIP的降解率达95.6%，第5次循环后仍保持88.4%的降解效率。催化剂的循环寿命实验结果表明，这种复合材料具备良好的结构稳定性和重复使用性能。

图7

图7 Bi/BOC-1对CIP光催化降解的循环图

Fig.7 Cycling runs of photocatalytic degradation of CIP over Bi/BOC-1

表1对比了近5年文献报道的同类Bi基等离子体光催化材料。与传统方法相比，即采用溶剂热法、室温组装或两步法合成并以NaBH₄、乙二醇或甲酰胺等为还原剂，采用一步水热法并以廉价的多聚甲醛兼作碳源与还原剂，可见合成流程显著简化。Bi/BOC-1对MG的降解速率常数(0.085 min^-1)比文献报道的Bi/Bi₂O₂CO₃体系(0.045 min^-1)提高了近90%，表明其具有显著增强的光催化活性。

表1 不同合成策略下Bi/Bi₂O₂CO₃基光催化材料的性能对比

Table 1 Comparison of photocatalytic performance of Bi/Bi₂O₂CO₃-based materials prepared via different synthesis strategies

Catalysts	Synthesis method	Reducing agent	Target pollutant	Rate constantk / min⁻¹	Source
Bi/BOC-1	Hydrothermal method	Polyoxymethylene (Bifunctional)	MG	0.085	This work
Bi/BOC-1	Hydrothermal method	Polyoxymethylene (Bifunctional)	CIP	0.046	This work
Bi/Bi₂O₂CO₃	Solvothermal method	Formamide	RhB	0.090	[27]
Bi/Bi₂O₂CO₃	Hydrothermal method	DMF	BPA	0.028	[28]
Bi/BiOI/Bi₂O₂CO₃	Room temperature assembly	NaBH₄	NO(gaseous phase)	-	[29]
Bi/Bi₂O₂CO₃	Hydrothermal method	Thiourea	NO(gaseous phase)	0.045	[30]
Bi/Bi₂O₂CO₃	Solvothermal method	Methanol	Hydrogen production	81.5 μmol/(g·h)	[31]
Bi/BiOF/Bi₂O₂CO₃	Hdydrothermal method	Ethylene glycol	CIP	0.062	[32]

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2.6 光电化学性能

为了揭示Bi纳米颗粒对Bi₂O₂CO₃半导体光催化的影响，测试了光生载流子在材料中的转移与分离。图8a给出了在一定偏压下每间隔40 s光照和不光照条件下的电流变化曲线；图8b给出了暗态下三种材料的Nyquist曲线。可以看出，Nyquist曲线是接近半圆的弧线，对应高频范围下电荷转移的特征，弧线半圆的直径对应电子转移的阻力。与纯相BOC相比，Bi/BOC-1样品具有比纯BOC更高的光电流强度和更低的电化学阻抗，表明Bi/Bi₂O₂CO₃复合材料中电子与空穴的分离效率显著提高。金属Bi作为导电组分，降低了材料的界面电荷转移阻力。因此，在相同测试条件下，Bi/BOC-5表现出最低的电化学阻抗与最强的光电流响应。尽管Bi/BOC-5具有最优的载流子分离与传输能力，其在污染物降解实验中却表现出最低的光催化活性。这表明，Bi纳米颗粒的导电性虽然有利于促进光生载流子在半导体材料中的分离与迁移，但是过量的Bi纳米颗粒团聚覆盖了材料表面的活性位点，从而降低了光催化效率。

图8

图8 样品的瞬态光电流响应和Nyquist图

Fig.8 Transient photocurrent response (a) and Nyquist plots (b) of the as-prepared samples

图9给出了固体荧光(PL)光谱。可以看出，在365 nm激发下纯相BOC在~625 nm处出现较强的本征荧光发射峰，归属于光生电子-空穴的带间辐射复合。Bi/BOC-1的荧光强度比BOC显著降低，表明适量的Bi纳米颗粒能抑制载流子复合，与其增强的光电流响应和降低的电化学阻抗结果一致，解释了其光催化活性最优。但是，Bi/BOC-5的荧光强度反而高于纯BOC，呈现出“荧光增强-活性骤降”的反常现象。过量Bi纳米颗粒虽因其高导电性降低了界面电荷转移阻力(表现为最低EIS弧径和最强光电流)，但是其在BOC表面严重团聚成为光生载流子的复合中心，导致电子-空穴在金属Bi表面即发生湮灭，不能参与表面的氧化还原反应。这一结果揭示：Bi/Bi₂O₂CO₃复合材料的光催化活性并非单纯取决于载流子分离效率，而是光吸收、电荷分离以及表面活性位点三者协同作用的结果。适度的Bi负载(如Bi/BOC-1)，可在拓宽可见光响应的同时通过肖特基结驱动的界面电荷转移促进载流子空间分离。

图9

图9 固体荧光(PL)光谱

Fig.9 Solid-state photoluminescence (PL) spectra of the as-synthesized samples

2.7 活性物种的确定

进行Bi/BOC-1的捕获实验以确定光催化过程中的活性物种。在光催化反应体系中分别引入抗坏血酸(AA)、乙二胺四乙酸(EDTA)和甲醇(CH₃OH)作为超氧自由基( $\cdot$ O $_{2}^{-}$ )、空穴(h⁺)和羟基自由基( $\cdot$ OH)的清除剂，分析其对MG降解的影响。结果如图10所示，可见加入1 mmol/L EDTA对MG的降解效率影响甚微，表明h⁺在该光催化过程中没有显著的作用。相比之下，加入1 mmol/L AA或CH₃OH，MG的降解效率显著下降，说明 $\cdot$ O $_{2}^{-}$ 和 $\cdot$ OH是Bi/BOC-1体系中的主要活性物种。因此，光催化过程主要由 $\cdot$ O $_{2}^{-}$ 和 $\cdot$ OH驱动。

图10

图10 Bi/BOC-1样品在添加不同捕获剂条件下对MG的降解

Fig.10 Degradation of MG by Bi/BOC-1 sample under different capturing agent conditions

为了确认催化体系中存在羟基自由基与超氧自由基，采用DMPO作为捕获剂进行电子顺磁共振(EPR)检测Bi/Bi₂O₂CO₃复合光催化剂。DMPO可与超氧自由基反应生成加合物DMPO- $\cdot$ O $_{2}^{-}$ ，用EPR谱仪进行测定其顺磁信号，从而定性分析超氧自由基。实验结果如图11所示。可以看出，用紫外光照射5 min后Bi/Bi₂O₂CO₃复合光催化体系的EPR谱中出现了六重特征峰，对应DMPO- $\cdot$ O $_{2}^{-}$ 加合物的信号。这表明，在紫外光催化反应过程中生成了超氧自由基。同时，谱中还出现了DMPO- $\cdot$ OH加合物的特征信号峰，其强度比为1∶2∶2∶1，进一步证实生成了羟基自由基。

图11

图11 样品中DMPO- $\cdot$ O $_{2}^{-}$ 和DMPO-·OH的电子自旋捕获共振光谱

Fig.11 Electron spin trapping resonance spectra of DMPO- $\cdot$ O $_{2}^{-}$ (a) and DMPO-·OH (b) in the sample

2.8 复合材料的光催化机理

根据结合自由基捕获实验结果和能带结构分析，提出了Bi/Bi₂O₂CO₃复合光催化剂在紫外-可见光照射下的反应机理，如图12所示。在太阳光辐照下金属Bi的Fermi能级(约-0.17  eV)高于Bi₂O₂CO₃的导带位置(约-0.68 eV)^[33]，表明Bi表面SPR效应激发的光生电子可注入至Bi₂O₂CO₃的导带。由于O₂/ $\cdot$ O $_{2}^{-}$ 的氧化还原电位(-0.33 eV)较Bi₂O₂CO₃导带更正，导带电子可将O₂还原成 $\cdot$ O $_{2}^{-}$ 自由基；同时，Bi₂O₂CO₃的光生电子与来自Bi的电子也可将O₂还原为H₂O₂，(O₂/H₂O₂电位约为0.695 eV)^[34]。生成的H₂O₂进一步捕获电子转化为体系中主要的 $\cdot$ OH自由基，与活性物种捕获实验结果一致。同时，Bi与Bi₂O₂CO₃上的光生空穴也能将表面吸附的OH^-氧化成 $\cdot$ OH自由基，因为Bi₂O₂CO₃价带电势高于OH^-/ $\cdot$ OH的氧化还原电位(约1.99 eV)^[35]。体系中的 $\cdot$ O $_{2}^{-}$ 自由基，主要来源于光照射下Bi纳米粒子表面SPR效应激发的高能电子与O₂之间的反应^[35]。

图12

图12 Bi/Bi₂O₂CO₃复合材料在可见光照射下的电子-空穴分离示意图

Fig.12 Schematic diagram of separation of electron-hole pairs over Bi/Bi₂O₂CO₃ composites under visible light

3 结论

(1) 以多聚甲醛作为碳源和还原剂的双功能前驱体，用一步水热法可使Bi³⁺还原和原位构筑Bi/Bi₂O₂CO₃异质结。

(2) 调控多聚甲醛用量(0.8 g为优化条件)，可精确调节单质Bi负载量，制备出的催化剂对环丙沙星和孔雀石绿的光催化活性最优。

(3) 金属Bi的等离子体共振效应与Bi/Bi₂O₂CO₃肖特基异质结的协同作用，可增强可见光吸收和促进光生载流子的分离与传输，使光催化效率显著提高。

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[J]. ACS Mater. Lett., 2021, 3(5): 574

[22]

Shoueir

, Kandil

, El-Hosainy

, et al.

Tailoring the surface reactivity of plasmonic Au@TiO₂ photocatalyst bio-based chitosan fiber towards cleaner of harmful water pollutants under visible-light irradiation

[J]. J. Clean. Prod., 2019, 230: 383

DOI [本文引用: 1]

A plasmonic fiber was rationally designed as an efficient visible-light photocatalyst for the breakdown of organic and inorganic pollutants. The nanostructured Au@TiO2 with tuneable size was fabricated via a photodeposition method and then soaked in chitosan fiber to produce the photoactive plasmonic fiber. Based on the X-ray photoelectron spectroscopy results, some of Ti4+ was reduced in situ to Ti3+ when Au was added, which enhanced the stability and degradation performance. Different water pollutants, including methylene blue, carbofuran, and metronidazole, were completely attacked and degraded by the plasmonic fiber but not the Au@TiO2 photocatalyst. Moreover, the active plasmonic fiber could convert toxic chromium, Cr(VI), to biocompatible Cr(III) (similar to 98.9%) in the presence of citric acid within 21 min. In some cases, the catalytic performance remained almost unchanged, even after being recycled 8 times, with little loss (similar to 4.1%). The plasmonic fiber exhibited enhanced degradation activity, consistent kinetic behavior, catalytic reduction, and stability. This fabric photocatalyst should contribute to possible energy saving and environmental applications. (C) 2019 Elsevier Ltd.

[23]

, Wang

X F

, Chen

Non-noble metal and nonmetallic plasmonic nanomaterials with located surface plasmon resonance effects: photocatalytic performance and applications

[J]. Catalysts, 2023, 13(6): 940

Photocatalysts with located surface plasmon resonance effects (LSPRs) have been studied in recent years due to their superior light harvesting capacity and photocatalytic performance in solving environmental problems and energy shortages. Plasmonic-noble-based photocatalysts are limited in terms of their practical application on account of their high cost, fixed plasma frequency, and low abundance. In order to solve these shortcomings, non-noble metal and nonmetallic plasmonic photocatalysts with LSPRs and advantages such as a lower cost and wider light adsorption range from the UV to NIR region have been developed. This paper reviews the recent development of non-noble metal and nonmetallic plasmonic photocatalysts and advances the research direction of plasmonic photocatalysts to achieve high photocatalytic activity and stability, providing guidance for photocatalysis to solve environmental problems and energy shortages.

[24]

Humayun

, Ullah

, Shu

, et al.

Plasmon assisted highly efficient visible light catalytic CO₂ reduction over the noble metal decorated Sr-incorporated g-C₃N₄

[J]. Nano-Micro Lett., 2021, 13(1): 209

DOI [本文引用: 1]

The photocatalytic performance of g-C3N4 for CO2 conversion is still inadequate by several shortfalls including the instability, insufficient solar light absorption and rapid charge carrier’s recombination rate. To solve these problems, herein, noble metals (Pt and Au) decorated Sr-incorporated g-C3N4 photocatalysts are fabricated via the simple calcination and photo-deposition methods. The Sr-incorporation remarkably reduced the g-C3N4 band gap from 2.7 to 2.54 eV, as evidenced by the UV–visible absorption spectra and the density functional theory results. The CO2 conversion performance of the catalysts was evaluated under visible light irradiation. The Pt/0.15Sr-CN sample produced 48.55 and 74.54 µmol h−1 g−1 of CH4 and CO, respectively. These amounts are far greater than that produced by the Au/0.15Sr-CN, 0.15Sr-CN, and CN samples. A high quantum efficiency of 2.92% is predicted for the Pt/0.15Sr-CN sample. Further, the stability of the photocatalyst is confirmed via the photocatalytic recyclable test. The improved CO2 conversion performance of the catalyst is accredited to the promoted light absorption and remarkably enhanced charge separation via the Sr-incorporated mid gap states and the localized surface plasmon resonance effect induced by noble metal nanoparticles. This work will provide a new approach for promoting the catalytic efficiency of g-C3N4 for efficient solar fuel production.

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Z A

, Xie

Y X

, Yang

X M

, et al.

Semimetal bismuth-enhanced light absorption, charge transfer and photocatalytic activity

[J]. J. Photoch. Photobiol., 2025, 459A: 116030

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Wei

, Xiao

, Niu

R R

, et al.

Dual plasmonic coupling effect in Bi/vacancy-rich Bi₂WO₆ heterojunction for selective CO₂ photoreduction to CH₄

[J]. Chem. Eng. Sci., 2024, 292: 120012

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Zhou

, Zhong

S T

, Shen

, et al.

Formamide-assisted one-pot synthesis of a Bi/Bi₂O₂CO₃ heterojunction photocatalyst with enhanced photocatalytic activity

[J]. J. Alloy. Compd., 2018, 769: 301

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Gong

S Q

, Zhang

R Y

, Sui

C J

, et al.

One-pot hydrothermal preparation of Bi/Bi₂O₂CO₃ with improved photocatalytic activity for bisphenol A degradation

[J]. J. Environ. Chem. Eng., 2025, 13(1): 115062

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Sun

Y J

, Liao

J Z

, Dong

, et al.

A Bi/BiOI/(BiO)₂CO₃ heterostructure for enhanced photocatalytic NO removal under visible light

[J]. Chin. J. Catal., 2019, 40(3): 362

[30]

Dong

, Li

Q Y

, Sun

Y J

, et al.

Noble metal-like behavior of plasmonic Bi particles as a cocatalyst deposited on (BiO)₂CO₃ microspheres for efficient visible light photocatalysis

[J]. ACS Catal., 2014, 4(12): 4341

[31]

Sun

D F

, Huang

, Li

, et al.

Plasma enhanced Bi/Bi₂O₂CO₃ heterojunction photocatalyst via a novel in-situ method

[J]. J. Colloid Interface Sci., 2020, 571: 80

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L C

, Yin

H S

, Wang

, et al.

One-pot preparation of Bi/BiOF/Bi₂O₂CO₃ Z-scheme heterojunction with enhanced photocatalysis activity for ciprofloxacin degradation under simulated sunlight

[J]. Mater. Today Nano, 2024, 25: 100446

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W J

, Sun

Y J

, Jiang

G M

, et al.

Defective Bi₄MoO₉/Bi metal core/shell heterostructure: enhanced visible light photocatalysis and reaction mechanism

[J]. Appl. Catal., 2018, 239B: 619

[34]

Xiang

Q J

, Yu

J G

, Cheng

, et al.

Microwave-hydrothermal preparation and visible-light photoactivity of plasmonic photocatalyst Ag-TiO₂ nanocomposite hollow spheres

[J]. Chem. Asian J., 2010, 5(6): 1466