Influence of Ion Exchange on Photoresponsive Properties of Potassium Poly(heptazine imide)
Influence of Ion Exchange on Photoresponsive Properties of Potassium Poly(heptazine imide)
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DOI：
10.1021/acs.chemmater.2c03325
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发表时间：
2023-01
影响因子：
8.6
通讯作者：
Mai Hattori;Miyu Nakamichi;Aika Yamaguchi;C. Miyazaki;G. Seo;Ryosuke Ohnuki;S. Yoshioka;
中科院分区：
文献类型：
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作者：
Mai Hattori;Miyu Nakamichi;Aika Yamaguchi;C. Miyazaki;G. Seo;Ryosuke Ohnuki;S. Yoshioka;
金属聚（七嗪酰亚胺）（MPHI）通过在其基于七嗪的类石墨二维层中容纳各种金属离子而表现出各种光电功能。尽管钾 PHI (KPHI) 是 MPHI 系列中研究最深入的，但关于其独特性能的机制，特别是其高光催化活性，仍存在未解决的问题。其他不同特性（例如光致变色和光电导）背后的机制也仍然未知。在此，我们重点阐明 KPHI 中的光致变色和光电导机制。我们开发了一种用 H+ 逐步取代 KPHI 中 K+ 的方法，并成功制备了 K+ 浓度可调的样品。通过各种实验和理论计算，对具有连续变化的 K+ 浓度的样品的结构、化学、光学、电子和电学性质进行了深入研究。首先，利用 X 射线光电子能谱、X 射线衍射 (XRD) 和傅里叶变换红外光谱研究了 KPHI 中 K+ 逐渐取代 H+ 的情况。 XRD分析表明KPHI中的K+并非随机被H+取代，但即使少量的K+取代也会导致HPHI长程有序区域的形成。吸光度测量显示，随着 K+ 的比率相对于 KPHI 的比率降低，吸收边缘发生连续蓝移。能带计算表明HPHI的能隙比KPHI的能隙大14%以上。 K+浓度测量对光致变色和光电导性能的依赖性表明，在富含K+的样品中，白光照射下从PHI层释放的K+对电导性能具有显着影响。在环境条件下，K+传导在 KPHI 的电传导（包括光电传导）中占主导地位。然而，HPHI 中 H+ 的迁移率非常低，这导致在光激发和最小电导率后昏昏欲睡地返回基态。
Metal poly(heptazine imide) (MPHI) exhibits various optoelectronic functions by accommodating various metal ions in its heptazine-based graphite-like two-dimensional layer. Although potassium PHI (KPHI) is the most well-studied in MPHI series, there are unresolved issues regarding the mechanism responsible for its unique properties, particularly its high photocatalytic activity. The mechanisms underlying other diverse properties, such as photochromism and photoconduction, also remain unknown. Herein, we focused on elucidating the mechanisms of photochromism and photoconduction in KPHI. We developed a method to gradually replace K+in KPHI with H+and successfully prepare samples with tunable K+concentrations. The structural, chemical, optical, electronic, and electrical properties of samples with continuously varying K+concentrations were thoroughly investigated through various experiments and theoretical calculations. First, the gradual substitution of K+for H+in KPHI was investigated using X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy. XRD analysis revealed that K+in KPHI was not randomly substituted with H+, but even small amounts of K+substitution led to the formation of the long-range ordered region of HPHI. Absorbance measurements revealed a continuous blue shift of the absorption edge as the ratio of K+decreased from that of KPHI. Energy band calculations revealed that the energy gap of HPHI was more than 14% larger than that of KPHI. The dependence of the K+concentration measurements on the photochromism and photoconductive properties showed that in the K+-rich samples, the K+released from the PHI layer upon white light irradiation had a significant effect on the electrical conduction properties. K+conduction was dominant in the electrical conduction of KPHI, including photoconduction, under ambient conditions. However, the mobility of H+in HPHI was very low, which was responsible for the lethargic return to the ground state after photoexcitation and minimal electrical conductivity.