Room-temperature molecular oxygen (O2) dissociation is challenging toward chemical reactions due to its triplet ground-state and spin-forbidden characteristic. Herein, we demonstrate that BiOCl of oxygen and chlorine dual vacancies can photocatalytically dissociate O2 into monatomic reactive oxygen (•O–) for the ring opening of aromatic refractory pollutants toward deep oxidation. The electron-rich and geometry-flexible dual vacancies of oxygen and chlorine remarkably lengthen the O–O bond of adsorbed O2 from 1.21 to 2.74 Å, resulting in the rapid O2 dissociation and the subsequent •O– formation. During the photocatalytic degradation of sulfamethazine, the in situ-formed •O– plays an indispensable role in breaking the critical intermediate of pyrimidine containing a stubborn aromatic heterocyclic ring, thus facilitating the overall mineralization. More importantly, BiOCl of oxygen and chlorine dual vacancies is also superior to its monovacancy counterparts on the degradation of other refractory pollutants containing conjugated six-membered rings, including p-chlorophenol, p-chloronitrobenzene, p-hydroxybenzoic acid, and p-nitrobenzoic acid. This study sheds light on the importance of sophisticated defects for regulating the O2 activation manner and deliveries a novel O2 activation approach for environmental remediation with solar energy.

Two-dimensional semiconductors have attracted considerable attention in recent years because of their ability to utilize solar energy to mitigate environmental pollution through reactive oxygen species (ROSs) and synthesize solar fuels using superfluous CO2 as a raw material. However, low-dimensional materials usually display robust Coulomb interaction between electron and hole pairs because of their strong structure confinement ability, thus leading to the formation of electroneutral excitons. In light of this, excitonic effects overwhelmingly influence the photocatalytic properties of two-dimensional semiconductors, which should be comprehensively explored. Bismuth oxyhalides (BiOX, X = Cl, Br, I) of giant exciton binding energies are usually recognized as an excellent platform for excitonic effect investigation because their flexible geometric and electronic structures allow us to rationally manipulate the excitonic effects. This review first summarizes the recent progress in accelerating exciton dissociation for enhancing charge-carrier-dominated photocatalytic reactions and then demonstrates that harnessing the excitonic effects allows for the generation of singlet oxygen (1O2) for green chemical synthesis through a unique energy-transfer-dominated O2 activation route. We believe that a critical understanding of the excitonic effects in two-dimensional semiconductors can offer new perspectives and guidelines for the rational fabrication of advanced materials for photocatalytic applications.

The ultimate goal of photocatalytic CO2 reduction is to achieve high selectivity for a single product with high efficiency. One of the most significant challenges is that expensive catalysts prepared through complex processes are usually used. Herein, gram-scale cubic silicon carbide (3C-SiC) nanoparticles are prepared through a top-down ball-milling approach from low-priced 3C-SiC powders. This facile mechanical milling strategy ensures large-scale production of 3C-SiC nanoparticles with an amorphous silicon oxide (SiO x ) shell and simultaneously induces abundant surface states. The surface states are demonstrated to trap the photogenerated carriers, thus remarkably enhancing the charge separation, while the thin SiO x shell prevents 3C-SiC from corrosion under visible light. The unique electronic structure of 3C-SiC tackles the challenge associated with low selectivity of photocatalytic CO2 reduction to C1 compounds. In conjugation with efficient water oxidation, 3C-SiC nanoparticles can reduce CO2 into CH4 with selectivity over 90%.