g-C 3 N 4 usually acts as the oxidation counterpart for overall water splitting reactions in semiconductor heterojunctions. Due to the poor water oxidation ability of g-C 3 N 4 , it is difficult to achieve efficient photocatalytic overall water splitting over g-C 3 N 4 -based heterojunctions. In this work, one-dimensional (1D) LaNbON 2 with strong water oxidation ability is prepared for the first time, and combined with two-dimensional (2D) g-C 3 N 4 to form semiconductor heterojunction by electrostatic self-assembly. The results of surface states, theoretical calculations, band structures and chemical probes indicate that the 2D g-C 3 N 4 and the 1D LaNbON 2 are tightly bonded through the electrostatic attraction and form a S-scheme type semiconductor heterojunction. In the heterojunction, the 1D LaNbON 2 and the 2D g-C 3 N 4 work as oxidation and reduction counterpart, respectively. The built-in electric field at their heterointerfaces effectively accelerates carrier separation. Thereby the solar-driven photocatalytic overall water splitting rate of the optimal 2D g-C 3 N 4 /1D LaNbON 2 heterojunction is ∼ 3.3 times as much as that of the 2D g-C 3 N 4 .
Yanmei Xing,Liying Yin,Yingnan Zhao,Zhilu Du,Hua-Qiao Tan,Xing Qin,Wingkei Ho,Tianyu Qiu,Yang-Guang Li
The reasonable construction of heterojunction photocatalysts with clear nanostructures and a good interface contact especially the one-dimensional/two-dimensional (1D/2D) composite heterojunction with unique morphology is considered one of the most effective strategies for designing highly efficient photocatalysts. Herein, a series of the 1D β-keto-enamine-based covalent organic framework (COF)/2D g-C3N4 composite materials COF–CN (1:x; where 1:x represents the mass ratio of COF and g-C3N4, x = 2.5, 5, 10, 15, 20) is prepared through the in situ reaction of 2,4,6-triformylphloroglucinol (Tp) and benzidine (BD) in stripped g-C3N4 suspension. A series of characterizations, such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), have verified their 1D/2D heterojunction structure. With the introduction of 1D COF nanobelts, the absorption of the composite is largely extended to 560 nm. Photocatalytic experiments reveal that the composite COF/CN shows evidently superior photocatalytic performance than individual COF and g-C3N4. The optimized COF–CN (1:10) exhibits a H2 production rate of 12.8 mmol g–1·h–1 under visible-light (λ ≥ 420 nm) irradiation, which is about 62 and 284 times higher than those of COF and g-C3N4, respectively. The apparent quantum efficiency (AQE) of COF–CN (1:10) is about 15.09% under 500 nm light irradiation, which is one of the highest among previous COF- or g-C3N4-based materials. This work provides important strategies for designing and constructing high-efficiency heterojunction photocatalysts with multidimensional features.
Zhou Liu,Shuzhen Wu,Xiaojie Yang,Yijun Zhou,Jiaren Jin,Junmei Sun,Li Zhao,Shimin Wang
Carrier recombination and charge loss at the interfaces of perovskite layers have a significant influence on high-performance planar perovskite solar cells (PSCs). We employed two-dimensional graphitic carbon nitride (g-C3N4), which is a heat-resistant n-type semiconductor, to modify the electron-transport layer/perovskite and perovskite/hole-transport layer interfaces, respectively. g-C3N4 could passivate the surface trap states of the methylammonium lead iodide light absorber through the formation of a Lewis adduct between N and the under-coordinated Pb, and it could also remarkably reduce the grain boundaries between perovskite crystal particles. A maximum power conversion efficiency (PCE) of 19.67% (Voc = 1.14 V, Jsc = 21.45 mA cm−2, FF = 0.807) could be obtained from planar PSCs with long-term stability using dual-positioned g-C3N4. Therefore, we consider that ultrathin semiconductor films with a Lewis base nature are suitable as dual-functional transport materials for devices. This work provides new guidance for dual-interfacial modification to improve the PCE and stability of devices.
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