Oxygenated Triazine-Heptazine Heterostructure Creates an Enormous Ascension to the Visible Light Photocatalytic Hydrogen Evolution Performance of Porous C3 N4 Nanosheets

Axial O Atom-Modulated Fe(III)-N4 Sites for Enhanced Cascade Catalytic 1O2-Induced Tumor Therapy

The rational construction of efficient hypoxia-tolerant nanocatalysts capable of generating singlet oxygen (1O2) without external stimuli is of great importance for tumor therapy. Herein, uniformly dispersed and favorable biosafety profile graphitic carbon nitride quantum dots immobilized with Fe-N4 moieties modulated by axial O atom (denoted as O-Fe-N4) are developed for converting H2O2 into 1O2 via Russell reaction, without introducing external energy. Notably, O-Fe-N4 performs two interconnected catalytic properties: glutathione oxidase-mimic activity to provide substrate for subsequent 1O2 generation, avoiding the blunting anticancer efficacy by glutathione. The O-Fe-N4 catalyst demonstrates a specific activity of 79.58 U mg-1 at pH 6.2, outperforming the most reported Fe-N4 catalysts. Density functional theory calculations demonstrate that the axial O atom can effectively modulate the relative position and electron affinity between Fe and N, lowering the activation energy, strengthening the selectivity, and thus facilitating the Russell-type reaction. The gratifying enzymatic activity stemming from the well-defined Fe-N/O structure can inhibit tumor proliferation by efficiently downregulating glutathione peroxidase 4 activity and inducing lipid peroxidation. Altogether, the O-Fe-N4 catalyst not only represents an efficient platform for self-cascaded catalysis to address the limitations of 1O2-involved cancer treatment but also provides a paradigm to enhance the performance of the Fe-N4 catalyst.

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.

Enhancing the Activity of a Carbon Nitride Photocatalyst by Constructing a Triazine-Heptazine Homojunction

Establishing homojunctions at the molecular level between different but physicochemically similar phases belonging to the same family of materials is an effective approach to promoting the photocatalytic activity of polymeric carbon nitride (CN) materials. Here, we prepared a CN material with a uniform distribution of homojunctions by combining two synthetic strategies: supramolecular assemblies as the precursor and molten salt as the medium. We designed porous CN rods with triazine-heptazine homojunctions (THCNs) using a melem supramolecular aggregate (Me) and melamine as the precursors and a KCl/LiBr salt mixture as the liquid reaction medium. The triazine/heptazine ratio is controlled by varying the relative amounts of the chosen precursors, and the molten salt treatment enhances the structural order of the interplanar packing units for the THCN skeleton, leading to rapid charge migration. The resulting built-in electric field induced by the triazine-heptazine homojunction enhances photogenerated charge separation; the optimal THCN catalyst exhibits an excellent H2 evolution rate via photocatalytic water splitting, which is ∼24 times as high as that of reference bulk CN, with long-term stability.

Photoreduction of Aqueous Protons Coupling with Alcohol Oxidation on a S-Scheme Heterojunction Photocatalyst MnO/Carbon Nitride

Crystalline carbon nitride (CCN), derived from amorphous polymeric CN, is considered as a new generation of metal-free photocatalyst because of its high crystallinity. In order to further promote the photocatalytic performance of CCN, p-type MnO nanoparticles are in situ synthesized and merged with n-type CCN through a one-pot process to form p-n heterojunction. The formed interfacial electric field between the semiconductors with different work functions efficiently breaks the coulomb interaction between MnO and CCN. The prepared catalysts exhibit drastically increased photocatalytic hydrogen evolution (PHE) activity integrated with oxidation of alkyl and aryl alcohols under irradiation of visible light. In the aqueous solution of benzyl alcohol (BzOH), the hydrogen generation rate over MnO/CCN (39.58 µmol h-1) is nearly 7 times and 37 times that of pure CCN (5.76 µmol h-1) and CN (1.06 µmol h-1), respectively, combining with oxidation of BzOH to benzaldehyde. This work proposes an avenue for in situ construction of a novel 2D material-based S-scheme heterojunction and extends its application in solar energy conservation and utilization.

Progress of charge carrier dynamics and regulation strategies in 2D CxNy-based heterojunctions

Two-dimensional carbon nitrides (CxNy) have gained significant attention in various fields including hydrogen energy development, environmental remediation, optoelectronic devices, and energy storage owing to their extensive surface area, abundant raw materials, high chemical stability, and distinctive physical and chemical characteristics. One effective approach to address the challenges of limited visible light utilization and elevated carrier recombination rates is to establish heterojunctions for CxNy-based single materials (e.g. C2N3, g-C3N4, C3N4, C4N3, C2N, and C3N). The carrier generation, migration, and recombination of heterojunctions with different band alignments have been analyzed starting from the application of CxNy with metal oxides, transition metal sulfides (selenides), conductive carbon, and Cx'Ny' heterojunctions. Additionally, we have explored diverse strategies to enhance heterojunction performance from the perspective of carrier dynamics. In conclusion, we present some overarching observations and insights into the challenges and opportunities associated with the development of advanced CxNy-based heterojunctions.