Search

• Single-atom Co loaded on silver birch leaf-like COF framework (COF-Co X) was obtained. • The formation of Co-N sites boost exciton dissociation and charge transfer. • COF-Co10 shows impressive peroxymonosulfate activation to degrade tetracycline. Covalent organic framework (COF) materials have received extensive attention in the field of photocatalysis in recent years, but the strong exciton effect in COF has seriously affected the separation of electron-hole pairs so that limiting the enhancement of the photocatalytic performance. It is of great significance to explore suitable ways to regulate the exciton behavior in COF materials and enhance their electron-hole's separation efficiency. By anchoring Co single-atoms within a silver birch leaf-like COF framework (COF-Cox), the exciton in COF is effectively dissociated by forming Co-N sites, producing massive free electrons and holes. Co-N sites also facilitate photogenerated holes aggregation toward Co single-atoms, which effectively drives the carriers' separation in COF framework. The carrier concentration of COF-Co10 is 2.81 times higher compared with the original COF. The reduced exciton binding energy (E b) further proves that the the formation of Co-N sites promote the exciton dissociation. Consequently, COF-Cox can well activate peroxymonosulfate (PMS) to degrade tetracycline (TC) pollutants, the reaction rate constant of COF-Co10 (3.65 × 10-2 min−1) is 5.27 times higher than COF (6.93 × 10-3 min−1). The possible activation routes and degradation products of TC are also discussed. This study provides a more comprehensive understanding of the exciton behavior for the design of more efficient COF-based catalysts. [ABSTRACT FROM AUTHOR]

The ground state, the fundamental transition, and the binding energies of heavy hole and light hole excitons confined in GaNAsBi/GaAs strained spherical quantum dots (QDs) are calculated. Computing is based on the variational method within the effective mass approximation, combined with the band anti-crossing model. Moreover, the exciton effective Bohr radius a B * is determined using two methods: (i) the radial probability density and (ii) the reciprocal variational parameter, and the limits of these methods are discussed. Theoretical computations of exciton diamagnetic coefficients σ are also presented and compared to the literature. Both excitons optoelectronic and diamagnetic parameters dependence on QD radii R in the range 2–14 nm, and nitrogen and bismuth contents (up to 12%) is obtained with respect to confinement conditions of electric charge carriers, tensile and compressive strain effects, and Coulomb's interaction. We find that the increase of a B * (R) is nearly linear and a B * < R for the pair (x N , y B i ) = (4 , 5) % , but a B * can exceed R for high concentrations of N and Bi. Besides, for a typical sphere radius of 4 nm, GaN x As 1-x-y Bi y /GaAs QDs exhibit broadband emission in the infrared wavelength range of about 1.03–2.55 μm which covers particularly the telecommunication wavelengths of 1.3 and 1.55 μm. By adjusting the adequate dot size and alloy contents, the operating spectral domain can be enlarged, and the emission wavelength can be controlled for several infrared applications. [ABSTRACT FROM AUTHOR]