Surface amination modification of g-C3N4 and enhancement mechanism study
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摘要: 以g-C3N4为光催化剂进行分解水制氢和污染物降解的研究受到广泛关注，但如何采用简单易行的方法制备出高效、稳定且具有良好光热稳定性的催化剂是本领域的研究热点和难点。本文采用一种简单的水热法在g-C3N4表面引入更多的氨基，通过SEM、TEM等研究表面氨基化对g-C3N4表面形貌的影响，发现氨基化对其边缘位置的形貌影响较大；XRD、FTIR、UV-vis、XPS等分析表明表面氨基化反应对g-C3N4的主体结构没有破坏；光催化分解水制氢和罗丹明B降解性能表明，当采用浓度为15wt%的氨水处理时，g-C3N4对RhB的光催化降解性能也达到最优，90 min的降解率为98.12%，是g-C3N4 的1.55倍(63.28%)，过高或过低的氨水浓度均不能使光催化性能达到最优；同时其分解水制氢速率性能最优(180.24 μmol·g−1·h−1)，为g-C3N4的1.46倍(123.04 μmol·g−1·h−1)；光电性能测试结果发现表面氨基化后光催化性能的增强机制可归结为，氨基是供电子基团，氨基含量的增加有利于光催化反应的发生，过度的氨基化导致离域三嗪环结构的破坏，光催化性能大幅降低。Abstract: The research of hydrogen production from water decomposition and pollutant degradation using g-C3N4 as photocatalyst has been widely concerned, but how to prepare efficient, stable and good photothermal stability catalyst by a simple and easy method is the research hotspot and difficulty. A simple hydrothermal method was used to introduce more amino groups on the surface of g-C3N4. The influence of surface amination on the surface morphology of g-C3N4 was studied by SEM and TEM, and find that amination has a great influence on the morphology of edge position. XRD, FTIR, UV-vis, XPS analysis show that the surface amination reaction dose not damage the main structure of g-C3N4. Studies on photocatalytic water hydrogen production and Rhodamine B (RhB) degradation performance show that the highest hydrogen production rate of g-C3N4 when treated with 15wt% ammonia (180.24 μmol·g−1·h−1), which is 1.46 times higher than that of g-C3N4 (123.04 μmol·g−1·h−1). At the same time, the photocatalytic degradation performance of RhB also reaches the optimum. The degradation rate of RhB is 98.12% in 90 min duration irradiation, which is 1.55 times higher than that of g-C3N4 (63.28%). Neither too high nor too low ammonia concentration can make the photocatalytic performance reach the optimum. The photoelectric performance test results show that the mechanism of the enhancement of photocatalytic performance after surface amination can be attributed to the fact that the amino group is an electron donor group. After excitation, the increase of amino content is conducive to the occurrence of photocatalytic reaction, and excessive amination leads to the destruction of the delocalized triazine ring structure, and the photocatalytic performance is greatly reduced.
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Key words:
- g-C3N4 /
- photocatalysis /
- hydrogen production /
- pollutants degradation /
- catalysis mechanism
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图 1 g-C3N4的SEM(a)和TEM图像(b); 采用浓度15wt%氨水处理的不同放大倍数g-C3N4的SEM图像((c)~(e))和TEM图像((f)~(h)); 采用浓度5wt% (i)、10wt% (j)、20wt% (k)和25wt% (l)氨水处理g-C3N4的SEM图像
Figure 1. SEM (a) and TEM (b) image of g-C3N4; (c)-(e) SEM images of g-C3N4 treated with 15wt% ammonium hydroxide; (f)-(h) TEM images of g-C3N4 treated with 15% ammonium hydroxide; SEM images of g-C3N4 treated with 5wt% (i), 10wt% (j), 20wt% (k) and 25wt% (l) ammoniumhydroxide
图 2 g-C3N4和不同浓度氨水处理g-C3N4的FTIR图谱(a)、XRD图谱(b)、UV-vis图谱(c)、光致发光图谱(d)、N2吸附-脱附平衡曲线图(e)和孔径分布曲线图(f)
Figure 2. FTIR spectra (a), XRD patterns (b), UV-vis spectra (c), PL spectra (d), N2 adsorption-desorption equilibrium (e) and pore size distribution (f) curves of g-C3N4 and g-C3N4 treated with different concentration of ammonium hydroxide
图 3 g-C3N4和g-C3N4(15%)的XPS的全图谱(a)、C1s图谱(b)、N1s图谱(c)和g-C3N4的结构示意图(d)
Figure 3. XPS spectra of full survey (a), C1s spectra (b), N1s spectra (c) and structure diagram (d) of g-C3N4 and g-C3N4(15%)
图 4 g-C3N4和不同浓度氨水处理g-C3N4的降解RhB曲线(a)、三次循环降解RhB曲线(b)、分解水制氢性能曲线(c)和三次循环分解水制氢性能曲线(d)
Figure 4. RhB degradation curves (a), three times RhB degradation curves (b), hydrogen production curves (c) and three times hydrogen production curves (d) of g-C3N4 and g-C3N4 treated with different concentration of ammonium hydroxide
η—Degradation rate of RhB
图 5 g-C3N4和不同浓度氨水处理g-C3N4的光电流曲线(a)和瞬态荧光图谱(b)
Figure 5. Photocurrent curves (a) and transient fluorescence spectra (b) of g-C3N4 and g-C3N4 treated with different concentration of ammonium hydroxide
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