Influence of Ion Exchange on Photoresponsive Properties of Potassium Poly(heptazine imide)

Abstract

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.

Stability and Crystallinity of Sodium Poly(Heptazine Imide) in Photocatalysis

“…The enhancement of crystallinity also leads to gradual decrease of Na + content (W Na ) in the samples (10.74-8.85 wt%, Table S1), measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Solid-state 13 C nuclear magnetic resonance (NMR) spectra of the samples show similar peaks, further indicating their similar bonding structures (Figure S9). According to elemental analysis results, N/C molar ratios of the three samples are 1.42 � 0.01, further indicating their similar framework structures, but the slightly greater N/C molar ratio of PHIÀ b (1.43) than those of PHIÀ e and PHIÀ be (1.41) maybe suggest a little lower polymerization degree of PHIÀ b, consistent with its lower crystallinity.…”

Spatial Position Regulation of Cu Single Atom Site Realizes Efficient Nanozyme Photocatalytic Bactericidal Activity

“…Four peaks were observed in the high‐resolution spectrum of N 1s, as shown in Figures S9,S9c (Supporting Information), the peak centered at 398.6 eV was assigned to the sp 2 ‐hybridized nitrogen atom (C─N═C) in the heptaazine ring, while the weak peak at 399.9 eV is usually attributed to the N atom in the N─(C) 3 bond. [ 41 ] The peak at 400.9 eV is assigned to the amino group (C─N─Hx). The peak at 404.1 eV can be attributed to the surface charging effect.…”

Defective Potassium Poly(Heptazine Imide) Preventing Spin Delocalization and Hole Transfer Deactivation for Efficient Solar Energy Conversion and Storage

“…The basic tectonic unit for KMACN had been determined in the previous work by examining the local chemical structure using SSNMR. [23] The basic unit of KMACN consists of two pores of 10 imide bridged heptazine rings linked by 7 imide bridges and 4 deprotonated imide bridges, in which three-quarters of terminal amino groups are substituted for the 13 C direct excitation SSNMR spectra of BKCN and BKM. Basic tectonic units of c) BKCN and d) BKM prior to optimization.…”

“…The 13 C cross-polarization/magic-angle spinning (CP/MAS) SSNMR spectra of BKCN and BKM are shown in Figure 3a. Two main chemical shifts at 156.7 ppm (C1) and 163.3 ppm (C2) appear in both 13 C CP/MAS SSNMR spectra.…”

“…The 13 C cross-polarization/magic-angle spinning (CP/MAS) SSNMR spectra of BKCN and BKM are shown in Figure 3a. Two main chemical shifts at 156.7 ppm (C1) and 163.3 ppm (C2) appear in both 13 C CP/MAS SSNMR spectra. C1 and C2 correspond to the central C atom (N c ─C═N) and the edge C atom next to the imide bridge (C-N 2 (NH)) of the heptazine unit, [1,3] respectively, as illustrated in Figure 3c.…”