Restricted by the limited exciton diffusion and unproductive exciton recombination, the efficiency of photon-to-chemical conversion on polymeric carbon nitride (CN) photocatalyst is generally unsatisfactory. The rational design of an efficient polymeric photocatalyst is challenging due to the ambiguous understanding of the structure–property–photocatalytic activity relationship. The study herein demonstrates an unprecedently efficient photocatalyst for the photoproduction of hydrogen peroxide (H2O2), as well as the mechanistic rationale behind the remarkable catalytic performance. Anchoring cationic methyl viologen (MV) on the CN with an anionic moiety generates an ionic link and elicits an internal local electric field in the organic photocatalyst framework, which significantly enhances the exciton dissociation. Femtosecond transient absorption spectroscopy analysis demonstrates that the MV surface complex-induced internal local electric field favors the generation of long-lived trapped electron, especially under the high photon-flux irradiation of >450 mW cm–2. CN–MV thus exhibits superior photocatalytic performance in H2O2 production, for example, 114.2 mM H2O2 in a 53 min reaction in a continuous microbatch photoreactor. The apparent quantum yield reaches a high value of 51.1%. The present study highlights the significant impact of the surface complex on the electronic energy landscape of the photocatalyst toward enhanced exciton dissociation and hence improved photon-to-chemical conversion efficiency in various photocatalytic applications.

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.

Efficient approaches toward selective removal of the emerging organic pollutants are of critical importance to the well-being of the human health and the eco-system. Peroxymonosulfate-involved advanced oxidation process is promising in water treatment due to a couple of intrinsic advantages of the reaction system, and the development of an efficient catalyst is essential to the real application of this technique. In this work, a series of single-atom Fe catalysts were fabricated via a facile method, and the single-atom center was identified to be in a Fe–N4 configuration by Fe K-edge X-ray absorption spectroscopy. On the optimum catalyst with 4.8 wt % Fe single atom, 22 ppm BPA could be eliminated within 40 s under mild reaction conditions, affording a remarkable pseudo-first-order reaction rate constant of 8.4 min–1. The durability of the catalyst was tested with a fixed-bed flow reactor, and 55.2 L of polluted water with 10 ppm BPA could be treated with a removal rate of >95% by 1 g of catalyst. Through a series of probe reactions and spectroscopic analysis, the mediated electron-transfer mechanism was identified to be dominant during the pollutant degradation process.

A lamellar carbon nitride (CN) framework is one of the most promising materials for solar-driven hydrogen peroxide production. The low dielectric constant of the organic CN framework leads to severe recombination of the excitons, and the photon-to-chemical conversion efficiency is thus unsatisfactory. In this work, by polycondensation of the small molecules on the KCl crystal surface, K + -incorporated crystalline CN (CNK) frameworks show significantly extended periodicity of the stacking layers and in-plane orderly organized heptazine/triazine units. The crystalline CNK frameworks exhibit a series of favorable photophysical properties, such as enhanced photon absorption, negatively shifted LUMO potentials, and attenuated emissive decay of the excitons. The CNK frameworks thus present remarkable performance in the photocatalytic selective oxygen reduction reaction for hydrogen peroxide production, e.g., CNK framework from the polycondensation of NH 4 SCN on the KCl surface could produce hydrogen peroxide at a remarkable reaction rate of 26.7 mmol h −1 g −1 with a high apparent quantum yield of 25.0%, which is 23.5 times that on its counterpart synthesized in the absence of KCl. This method is generally applicable to all of the precursors for CN synthesis.

Catalytic activation of peroxymonosulfate is one of the most promising advanced oxidation processes for water treatment. The development of advanced functional catalysts is essential to efficient and selective elimination of the emerging organic pollutants in water. Via a facile one-step method using the naturally abundant tannic acid and low-cost melamine as precursors, the atomically dispersed Fe was anchored on a nitrogen-doped carbon matrix, and the configuration of Fe-N 4 was confirmed by synchrotron X-ray absorption spectroscopy. The singleatom Fe catalyst was efficient in catalytic degradation of various organic pollutants, e.g., removal of 100 μM BPA within 40 s under mild reaction conditions. The essential role of high-valent iron-oxo species in selective degradation of pollutants was identified by systematic mechanistic investigations. This work demonstrates the unique advantages of high-valent Fe IV =O in selective elimination of emerging organic pollutants and sheds light on the design of an efficient and durable single-atom catalyst for a variety of applications.