Modulating Local Charge Distribution of Carbon Nitride for Promoting Exciton Dissociation and Charge-Induced Reactions

Design of a Single-Atom In-N3-S site to Modulate Exciton Behavior in Carbon Nitride for Enhanced Photocatalytic Performance

Rational tailoring of the local coordination environment of single atoms has demonstrated a significant impact on the electronic state and catalytic performance, but the development of catalysts beyond noble/transition metals is profoundly significant and highly desired. Herein, the main-group metal indium (In) single atom is immobilized on sulfur-doped porous carbon nitride nanosheets (In@CNS) in the form of three nitrogen atoms coordinated with one sulfur atom (In-N3-S). Both theoretical calculations and advanced characterization investigations clearly elucidated that the single-atomic In-N3-S structures on In@CNS are powerful in promoting the dissociation of excitons into more free carriers as well as the charge separation, synergistically elevating electron concentration by 2.19 times with respect to pristine CNS. Meanwhile, the loading of In single atoms on CNS is responsible for altering electronic structure and lowering the Gibbs free energy for hydrogen adsorption. Consequently, the optimized In@CNS-5.0 exhibited remarkable photocatalytic performance, remarkable water-splitting and tetracycline hydrochloride degradation. The H2 production achieved to 10.11 mmol h-1g-1 with a notable apparent quantum yield of 19.70% at 400 nm and remained at 10.40% at 420 nm. These findings open a new perspective for in-depth comprehending the effect of the main-group metal single-atom coordination environment on promoting photocatalytic performance.

Defect Engineering Simultaneously Regulating Exciton Dissociation in Carbon Nitride and Local Electron Density in Pt Single Atoms Toward Highly Efficient Photocatalytic Hydrogen Production

The high exciton binding energy (Eb) and sluggish surface reaction kinetics have severely limited the photocatalytic hydrogen production activity of carbon nitride (CN). Herein, a hybrid system consisting of nitrogen defects and Pt single atoms is constructed through a facile self-assembly and photodeposition strategy. Due to the acceleration of exciton dissociation and regulation of local electron density of Pt single atoms along with the introduction of nitrogen defects, the optimized Pt-MCT-3 exhibits a hydrogen production rate of 172.0 µmol h-1 (λ ≥ 420 nm), ≈41 times higher than pristine CN. The apparent quantum yield for the hydrogen production is determined to be 27.1% at 420 nm. The experimental characterizations and theoretical calculations demonstrate that the nitrogen defects act as the electron traps for the exciton dissociation, resulting in a decrease of Eb from 86.92 to 43.20 meV. Simultaneously, the stronger interaction between neighboring nitrogen defects and Pt single atoms directionally drives free electrons to aggregate around Pt single atoms, and tailors the d-band electrons of Pt, forming a moderate binding strength between Pt atoms and H* intermediates.

Flexo-/Piezoelectric Polarization Boosting Exciton Dissociation in Curved Two-Dimensional Carbon Nitride Photocatalyst

Two-dimensional (2D) carbon nitride (CN) materials have received tremendous attention as photocatalysts for clean energy and environmental treatment. However, the photocatalytic efficiency of CN is constrained by the high exciton binding energy and sluggish charge kinetics due to weak dielectric screening, impeding the overall process. Herein, localized flexo-/piezoelectric polarization is introduced via strain engineering, boosting exciton dissociation and promoting charge separation to enhance the multielectron photocatalytic process. Consequently, the exciton binding energy of polarized CN is reduced from 52 to 34 meV, and the hydrogen evolution yield increased by 2.9 times compared to that of the pristine CN. For other photocatalytic reactions (e.g., H2O2 production), the polarized CN also maintained a 2.1-fold increase compared to the pristine CN. This strategy of inducing localized polarization via strain engineering provides new insights for boosting photocatalytic reactions involving electrons.

Three-Component Donor-π-Acceptor Covalent-Organic Frameworks for Boosting Photocatalytic Hydrogen Evolution

Two-dimensional covalent-organic frameworks (2D COFs) have recently emerged as great prospects for their applications as new photocatalytic platforms in solar-to-hydrogen conversion; nevertheless, their inefficient solar energy capture and fast charge recombination hinder the improvement of photocatalytic hydrogen production performance. Herein, two photoactive three-component donor-π-acceptor (TCDA) materials were constructed using a multicomponent synthesis strategy by introducing electron-deficient triazine and electron-rich benzotrithiophene moieties into frameworks through sp² carbon and imine linkages, respectively. Compared with two-component COFs, the novel TCDA-COFs are more convenient in regulating the inherent photophysical properties, thereby realizing outstanding photocatalytic activity for hydrogen evolution from water. Remarkably, the first sp² carbon-linked TCDA-COF displays an impressive hydrogen evolution rate of 70.8 ± 1.9 mmol g^-1 h^-1 with excellent reusability in the presence of 1 wt % Pt under visible-light illumination (420-780 nm). Utilizing the combination of diversified spectroscopy and theoretical prediction, we show that the full π-conjugated linkage not only effectively broadens the visible-light harvesting of COFs but also enhances charge transfer and separation efficiency.

Expanding the Conjugate Structure of Polymeric Carbon Nitride for Enhanced Light Absorption and Photothermal Conversion

The development of efficient and inexpensive materials for light energy conversion is very important for achieving sustainable energy supply and carbon neutrality. Polymeric carbon nitride has become a promising material for light energy conversion due to its advantages of simple preparation and high physical and chemical stability. However, the pristine polymeric carbon nitride only absorbs light with a wavelength of less than 450 nm, and the energy conversion for low-energy photons is very limited. Here, by introducing the pyromellitic dianhydride component to construct an in-plane heterostructure, the conjugated structure of polymeric carbon nitride is successfully expanded. This in-plane carbon nitride-carbon nanoribbon (C₃ N₄ -C) heterostructure has an ultrawide absorption range from 200 to 2000 nm. Compared with the original material, the photothermal conversion performance of C₃ N₄ -C is significantly improved under the irradiation of Xe lamp or infrared laser. Furthermore, C₃ N₄ -C exhibits good potential for synergistic photothermal and chemotherapy. This work provides a simple strategy to construct expanded conjugate structure for improved light absorption and energy conversion materials based on polymeric carbon nitride.

DMAP molecule grafting on a carbon nitride heptazine ring for the better degradation of pollutants – the synergy of electron withdrawing and steric hindrance effects

Graphitic carbon nitride (CN) is a promising candidate for use in photocatalytic pollutant degradation, but it only shows moderate activity because of its sluggish photocarrier transfer and insufficient light absorption.