Photo-induced in-situ synthesis of Cu2O@C nanocomposite for efficient photocatalytic evolution of hydrogen
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摘要: Cu2O具有禁带窄、环境友好和储量丰富等优点，是一种理想的可见光催化剂，然而其光生载流子复合率高和稳定性差等问题限制了Cu2O在光催化领域的实际应用。为此，本文采用光诱导原位技术，以甲醇为碳源、硫酸铜为铜源，一步成功制备了超薄碳壳层包覆的Cu2O复合纳米材料（Cu2O@C）。结果显示，与常规碳包覆方法相比，光诱导原位技术避免了苛刻的反应条件及繁琐的合成步骤对Cu2O半导体结构的破坏，有效保留了Cu2O本征电子结构，使其具有优异的光催化活性及稳定性。同时，Cu2O@C的核壳结构不仅可以钝化半导体表面缺陷和促进光生载流子的分离，而且碳壳层的包覆还可以避免Cu2O纳米颗粒与溶液的直接接触，有效抑制高活性反应中间体对催化剂结构的破坏。与单独的Cu2O纳米颗粒相比，Cu2O@C复合纳米材料在可见光下的光解水产氢活性和稳定性得到显著提高，产氢速率可达1.28 mmol/(g·h)，且在连续五次循环稳定性测试中，氢气生成速率无明显变化。Abstract: Cuprous oxide (Cu2O) is an ideal visible light catalyst owing to its narrow band gap, environmental benignity and abundant storage; however, the fast recombination of photogenerated charge carriers and poor stability of Cu2O has impeded its application in photocatalysis. Herein, we demonstrate that Cu2O@C nanocomposite can spontaneously evolve from a methanol aqueous solution containing cupric ions under the induction of irradiation. Compared with the traditional carbon coating method, the Cu2O@C nanocomposite obtained by the photo-induced in-situ synthesis can reserve superior original characteristics of the semiconductor under mild reaction conditions, promote the charge transfer and enhance the separation efficiency of charge carriers; in addition, the carbon shells can also effectively prevent Cu2O from photo-corrosion. As a result, the Cu2O@C nanocomposite exhibits excellent photocatalytic activity in the hydrogen evolution in comparison with the Cu2O particles; the H2 evolution rate over the Cu2O@C nanocomposite reaches 1.28 mmol/(g·h) under visible light, compared with the value of 0.065 mmol/(g·h) over Cu2O. Moreover, the Cu2O@C nanocomposite displays good cycle stability, viz., without any deactivation in the catalytic activity after five cycles.
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图 1 Cu2O@C复合纳米材料的（a）TEM图，（b）HRTEM 图，（c）SEM图，（d）EDS mapping图
Figure 1 (a) TEM, (b) HRTEM, (c) SEM, (d) EDS mapping images of the Cu2O@C nanocomposite
图 3 Cu2O@C复合纳米材料的（a）XRD谱图；（b）Cu 2p XPS光谱谱图；（c）C 1s XPS光谱谱图；（d）O 1s XPS光谱谱图
Figure 3 (a) XRD pattern; (b) Cu 2p XPS spectrum; (c) C 1s XPS spectrum; (d) O 1s XPS spectrum of the Cu2O@C nanocomposite
图 4 不同光催化体系所得样品的XRD谱图
Figure 4 XRD patterns of the solid products prepared in different photocatalytic systems
图 5 甲醇浓度对碳壳层厚度的影响
Figure 5 Effect of methanol concentration on the thickness of carbon shell (a): 1.8 mol/L; (b): 3.1 mol/L; (c): 4.3 mol/L.
图 6 Cu2O和Cu2O@C的 (a)紫外-可见吸收光谱；(b) 荧光光谱
Figure 6 (a) UV-vis absorption spectra and (b) Fluorescence spectra of Cu2O and Cu2O@C
图 7 (a) 不同半导体光催化剂可见光下的光解水产氢性能；(b) Cu2O@C光解水产氢循环稳定性测试；(c) Cu2O@C稳定性测试前后的XRD谱图和 (d) 稳定性测试后的TEM图像
Figure 7 (a) Photocatalytic H2 evolution rate of as-prepared photocatalysts under visible light illumination; (b) Cycling stability test of photocatalytic hydrogen evolution over Cu2O@C nanocomposite; (c) XRD images of the Cu2O@C nanocomposite before and after cycling stability test; (d) TEM images after cycling stability test
图 8 (a) CD3OD-H2O 和 (b) CH3OH-D2O体系的气体产物质谱图
Figure 8 MS spectra of the obtained gas in (a) CD3OD-H2O and (b) CH3OH-D2O reaction system
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