Step-by-Step Improving Photocatalytic Hydrogen Evolution Activity of NH₂–UiO-66 by Constructing Heterojunction and Encapsulating Carbon Nanodots

Abstract

Carbon nanodots (CDs) have attracted enormous attention in the photocatalytic area for their high light-harvesting and outstanding electron transfer abilities. In this work, NH2–UiO-66 was first composited with g-C3N4 to construct an NH2–UiO-66/g-C3N4 heterojunction. Then, CDs were incorporated into the pores of NH2–UiO-66 by the pore space of the framework serving as confined nanoreactors to construct a CD@NH2–UiO-66/g-C3N4 ternary composite. The ultrasmall CDs transformed from incapsulated glucose in the pores of NH2–UiO-66 were uniformally distributed in MOFs and extensively improve the photocatalytic hydrogen evolution activity of the composite under visible-light irradiation. The optimum photocatalytic H2 evolution rate of the CD@NH2–UiO-66/g-C3N4 composite with a CD content of 2.77 wt % is 2.930 mmol·h–1·g–1 under visible-light irradiation, which is 32.4, 38.6, and 17.5 times as high as that of bulk g-C3N4, NH2–UiO-66, and NH2–UiO-66/g-C3N4, respectively. The remarkable enhancement of the photocatalytic activity should be that CDs as cocatalysts effectively increase the transport properties of electrons and efficient charge separation. Moreover, CD@NH–UiO-66/g-C3N4 nanocomposites showed excellent stability during the photocatalytic process as determined by XRD and TEM analyses for the sample after reaction. The results of the mechanism investigation reveal that CDs in the ternary composite serve as electron transfer mediation to facilitate charge separation, enhancing light absorption and extending the lifetime of photoinduced carriers. The present work shows that encapsulating CDs into the pores of MOFs is an efficient strategy to improve the activity of an MOF-based photocatalyst.

Engineering a Rapid Charge Transfer Pathway for Enhanced Photocatalytic Removal Efficiency of Hexavalent Chromium over C3N4/NH2–UIO‐66 Compounds

“…The long‐tail absorption in the visible light region is probably due to the interaction between CU and NU, which balances the delocalized electron redistribution among the π conjugate network of CN and NU through the ZN bonding, thus affecting the electronic states of ZrO clusters and the amine groups on NU, improving the optical absorption. [ 39,41 ]…”

Heterostructured MOFs photocatalysts for water splitting to produce hydrogen

“…For example, the NH 2 -UiO-66 nanoparticles were grown on the outer surface of C 3 N 4 nanotubes forming g-C 3 N 4 /UiO-66-NH 2 heterostructure, which showed high hydrogen production activity and stability [69]. For the sake of improving the charge separation efficiency of the MOFs/g-C 3 N 4 heterostructure, coupling with co-catalyst such as CDs [70] and noble metals [71] into this system has been verified to be feasible and effective.…”

Carbon Dots in Porous Materials: Host–Guest Synergy for Enhanced Performance

“…Ty pical examples include CNDs@ZIF-8 with tunable luminescence and CD@NH 2 -UiO-66 with photocatalytic properties. [24] Particularly,t his method facilitated the production of CDs with tunable sizes of 1.5, 2.0, to 3.2 nm by choosing HKUST-1, ZIF-8, and MIL-101 with varied pore sizes as host, respectively.T he luminescence emission of as-prepared CDs are red-shifted with the increasing size ( Figure 2b). [10] ForM OFs with large mesopores,i mpregnation would be af acile method to load CDs into the channels of MOFs.F or instance,G QDs (av.3 .1 nm) could be impregnated into am esoporous porphyrinic zirconium-based MOF (PCN-22) resulting in excellent electrical conductivity ( Figure 2c).…”

“…As for electron transfer in CDs@PM composites (e.g., CDs@ meso ‐TiO 2 , CDs@MOFs, CDs@porous C), electrons and holes can transfer between the components with matched energy levels, thus enabling composites to serve as electrical transportation materials with excellent charge separation and enhanced photocatalysis performance . Compared with the bulk carriers, porous matrices possess the advantage of short electron transmission distance between acitve sites and confined CDs.…”

“…Compared with the bulk carriers, porous matrices possess the advantage of short electron transmission distance between acitve sites and confined CDs. For instance, CDs are immobilized in the void cages of MOFs, very close to the metal clusters and organic linkers, forming a highly‐efficient charger transfer path . As an excellent electron storage host, porous C can transfer electrons to CDs via covalence bonds, achieving efficient charge separation process .…”