Construction of K⁺ Ion Gradient in Crystalline Carbon Nitride to Accelerate Exciton Dissociation and Charge Separation for Visible Light H₂ Production

Abstract

The sluggish exciton dissociation and charge transfer and separation due to weak driving force still restrict the further improvement of photocatalytic performance in crystalline carbon nitride (CCN). Here, a series of heptazine-based K+-implanted CCNs (KCCNs) were successfully prepared, while the K+ ion concentration was gradiently inserted by controlling its diffusion from the surface to the bulk in carbon nitride (CN). The built-in electric field (BIEF) induced by the K+ ion concentration gradient and cyano groups has powerful driving force to promote the dissociation of excitons into electrons and holes and accelerate the separation of photogenerated carriers and their transport from the bulk to the surface. Consequently, the KCCN with an optimized BIEF has increased 34 times compared with the original CN for visible light H2 evolution. Our proposed strategy to induce BIEF by constructing concentration gradients through a thermodynamically feasible diffusion-controlled solid-state reaction can be adopted to design other photocatalytic systems.

Cyanamide-defect-induced built-in electric field in crystalline carbon nitride for enhanced visible to near-infrared light photocatalytic activity

“…2f, the peaks located at 398.4, 400.0 and 400.9 eV corresponded to the structures of C-NvC, N-(C) 3 and NH x of the heptazine ring, respectively. 34,35 It is noted that the peak ratio of NH x in KSCN 1.0 and KOCN 0.5 decreased compared to that of KCCN (from 10.21% for KCCN to 8.33% for KSCN 1.0 or to 9.65% for KOCN 0.5), which supported the substitution of cyanamide groups and was in-line with the NMR results. The successfully grafted cyano (-CuN) groups within KCCN have electron-accepting properties.…”

“…As shown in Fig.2a, characteristic peaks located at 28.3°, 8.0°and 9.9°are observed in KCCN, KSCN x and KOCN x (x represents the content of potassium salts) samples, indicating that the crystalline structure is retained. These peaks can be assigned to the (002) crystal plane in the c-axis accumulation direction, and the (100) and (110) crystal planes related to the in-plane heptazine chain, respectively 34. With increasing potassium salt content, the intensity of the main peak at 28.3°decreases slightly and the peak shifts toward lower angle, indicating wider layer spacing due to the salt treatment.…”

Unraveling the dual defect sites in graphite carbon nitride for ultra-high photocatalytic H2O2 evolution

“…23 Notably, previous studies clearly indicated that alkali metal atoms (K or Na) doped in g-C 3 N 4 affect its structure and catalytic activity. [43][44][45] Through a series of precise characterizations, Shen et al proved that the use of NaBH 4 introduced N defects, as well as B doping in g-C 3 N 4 . 38 Detailed evidence has shown that B doping, N vacancies, and -CRN groups together optimize the electronic structure of g-C 3 N 4 and significantly enhance the oxygen evolution rate.…”

Edge- and bridge-engineering-mediated exciton dissociation and charge separation in carbon nitride to boost photocatalytic H2 evolution integrated with selective amine oxidation

“…4b, EBCN-2 possessed faster PL decay, with an average lifetime of 6.41 ns, compared to that of CN (7.70 ns), ECN (6.95 ns) and BCN (7.02 ns), suggesting that the embedded linker and edge sites destroyed the framework of carbon nitride to enhance the exciton dissociation. The exciton binding energy (E b ) can be obtained from the Arrhenius equation [ 53 As presented in Fig. 4c and S19 (ESI), † the E b of EBCN-2, C 3 N 4 , ECN and BCN were calculated to be 0.33, 0.39, 0.35 and 0.37 eV, respectively.…”