Optimizing the Band Structure of Crystalline Potassium Poly(heptazine imide) for Enhanced Photocatalytic H₂O₂Production and Pollutant Degradation

Abstract

The photocatalytic selective oxygen reduction reaction on a polymeric carbon nitride framework is one of the most promising approaches toward sustainable H2O2 production. Potassium poly­(heptazine imide) (K-PHI) was highly active for photocatalytic H2O2 production. Most importantly, by introducing 1-methyl-1H-tetrazole-5-thiol (MTT) into the precursor for the K-PHI synthesis, the size of the layer stacking structure was reduced, the polymerization in the heptazine plane was improved, and the conduction band position was negatively shifted. The MTT-regulated K-PHI (K-PHI-2) showed remarkable H2O2 photoproduction performance, for example, a record high H2O2 photoproduction rate of 41.7 μmol h–1 mg–1 in an acidic environment. Meanwhile, K-PHI-2 showed a significantly enhanced performance in the photocatalytic degradation of the carbamazepine. Additionally, by introducing 5 ppm O3 in the reaction system, ciprofloxacin at a concentration of 100 ppm was eliminated rapidly on K-PHI-2 via a peroxone reaction.

Polymeric Carbon Nitride from Inorganic Precursor in Eutectic Salts: Enhanced Exciton Dissociation and Photocatalytic H2O2 Production

“…Additionally, a low pH could reduce the K + in the framework, which is critical for the photocatalytic performance. 22,30,41 We thus speculate that the photoresponse of the catalyst could be the key to the H 2 O 2 formation. Further increasing the pH to 11 significantly reduced the concentration of H 2 O 2 , which may be attributed to decreased stability of H 2 O 2 in such a basic environment.…”

“…On AT-CN, the photocatalytic production of H 2 O 2 was sensitively impacted by the pH of the suspension, and the basic environment with a pH of around 9.0–10.0 was the optimistic reaction condition, which indicated that the protonation step was not the rate-determining step for H 2 O 2 production. Additionally, a low pH could reduce the K + in the framework, which is critical for the photocatalytic performance. ,, We thus speculate that the photoresponse of the catalyst could be the key to the H 2 O 2 formation. Further increasing the pH to 11 significantly reduced the concentration of H 2 O 2 , which may be attributed to decreased stability of H 2 O 2 in such a basic environment.…”

“…Polymeric carbon nitride (PCN) frameworks have found wide applications in various solar-driven chemical conversion reactions, such as water splitting, CO 2 reduction, organic chemical conversion reactions, and so on. − Although PCN has unique advantages, such as earth abundance of the composition, chemical stability, nontoxicity, and the visible-light activity, limited exciton dissociation causes low photon-to-chemical conversion efficiency. , Various strategies have been developed for expanding the visible light absorption and boosting the exciton dissociation, such as morphology control, heteroatom doping, defect engineering, crystallinity improvement, and so on. − The polymeric carbon nitride frameworks have a low dielectric constant; the excitons are localized in the heptazine unit, and the polarons are hopping along the direction perpendicular to the heptazine unit via the overlapped molecular orbitals in Brownian motion . Much effort has been devoted to developing new routes toward the synthesis of PCN frameworks with highly ordered layer stacking structure, so as to the significantly improve the solar-to-chemical conversion efficiency. − Polymerization reaction in the ionothermal condition is a quite feasible approach for tailoring the structural features of PCN, as the mass and heat transfer are enhanced in the molten salt, favoring the formation of highly ordered structure. ,− For further maximizing the advantageous features of the ionothermal synthesis, in this work, we paid attention to further enhancing the mass transfer during polymerization in the molten salt. An inorganic salt, ammonium thiocyanate (NH 4 SCN), was employed as the precursor in the ionothermal synthesis of PCN with a eutectic salt mixture of KCl/LiCl.…”

Nanoarchitecture Manipulation by Polycondensation on KCl Crystals toward Crystalline Lamellar Carbon Nitride for Efficient H2O2 Photoproduction

“…The in-plane periodicity of ATC-CNK poses certain similarities to that in the potassium poly(heptazine imide) (K-PHI) nanocrystals due to the diffraction peaks at 8.1°for both ATC-CNK and K-PHI. 21,39,47 The shift of the (002) diffraction peak reveals that the spacing of the layer stacking is reduced by 0.01 nm after the incorporation of K + in the framework, indicating that the incorporation of K + could enhance the interaction between the layers. 4,48 Since the polymeric carbon nitride frameworks have low dielectric constant, and the excitons are localized in the heptazine unit and the polarons are hopping along the direction perpendicular to the heptazine unit via the overlapped molecular orbitals in Brownian motion.…”

Efficient Exciton Dissociation in Ionically Interacted Methyl Viologen and Polymeric Carbon Nitride for Superior H2O2 Photoproduction

“…It has been frequently observed that the formation of the N-metal coordination bond in the CN framework will lead to a partial charge transfer from nitrogen to metal, and this charge transfer will cause the enhancement of the π* resonance peaks in the N K-edge XANES profile. 59,60 The enhancement of the π* resonance peaks herein is thus indicative of the perturbation 22 of the electronic structure via partial electron transfer from CN to the surface-complexed MV unit (Figure 2c).…”