Interfacial Engineering of a Carbon Nitride–Graphene Oxide–Molecular Ni Catalyst Hybrid for Enhanced Photocatalytic Activity

Abstract

Carbon nitrides (CNx) are a promising class of photocatalyst for fuel and chemical synthesis as they are non-toxic and readily synthesized at a low cost. This study reports the enhanced photocatalytic activity for simultaneous alcohol oxidation and proton reduction when graphene oxide (GO) or reduced graphene oxide (RGO) is employed as an interlayer between a cyanamide-functionalized melon-type carbon nitride (NCN CNx) and a phosphonated Ni-bis(diphosphine) H2-evolution catalyst (NiP). Introduction of the GO/RGO enhanced the activity three times, reaching a specific activity of 4655 ± 448 µmol H2 (g NCN CNx) −1 h −1 with a NiP-based turnover frequency of 116 ± 3 h −1. Mechanistic studies into this closed photo-redox system revealed that the rate of electron extraction from NCN CNx is rate limiting. GO/RGO is commonly employed to improve the electron transfer dynamics on nanosecond timescales, but time-resolved photoluminescence and transient absorption spectroscopy reveal that these properties are not significantly affected in our NCN CNx-GO hybrid on fast timescales (< 0.1 s). However, long lived "trapped-electrons" generated upon photoexcitation of NCN CNx in the presence of organic substrates are shown by photoinduced absorption spectroscopy to be quenched faster with GO/RGO, supporting that GO/RGO improves electron transfer from NCN CNx to NiP on timescales > 0.1 s. The absorption profile of NiP in the presence of different GO loadings reveals that GO acts as a conductive interfacial 'binder' between NiP and NCN CNx. The enhancement in activity therefore does not primarily arise from changes in the photophysics of the NCN CNx, but rather from GO/RGO enabling better electronic communication between NCN CNx and NiP.

Polymeric carbon nitride coupled with a molecular thiomolybdate catalyst: exciton and charge dynamics in light-driven hydrogen evolution

“…The electron accumulation in polymeric carbon nitride photocatalysts is known to be one of the major bottlenecks in light-driven hydrogen evolution, 47,48 and has been typically addressed by deposition of Pt, [48][49][50] Ni-based molecular catalysts, [51][52][53] or enzymes. 11,54 We investigated polymeric carbon nitride Figure S10.…”

Solar Reforming of Biomass with Homogeneous Carbon Dots

“…The a-cel-CD/NiP system provides a benchmark activity of 13 450 mmol H 2 (g CDs ) À1 h À1 ( Figure S3, Table S5). [10,11,14] The a-cel-CDs display a maximum internal quantum efficiency (IQE at l = 360 nm, I = 4.05 mW cm À2 ) of 11.4 %, which compares favorably with g-N-CDs (5.3 %) and a-CDs (1.4 %). [10b] Future improvements in the development of the CDs should focus on high IQEs in the visible region.…”

Engineering Surface N‐Vacancy Defects of Ultrathin Mesoporous Carbon Nitride Nanosheets as Efficient Visible‐Light‐Driven Photocatalysts

“…The DUMCN and UMCN samples both have two diffraction peaks, %12.9 and 27.6 corresponding to the (100) and (002) peaks of GCN, respectively, which indicate that the introduction of N-vacancy did not alter the crystal structure of GCN. [39] The two peaks can be assigned to the in-plane repeat trigonal nitrogen linkage of tri-s-triazine units and interlayer stacking of the conjugated aromatic C─N heterocycles system. [28,37,40] It is shown that the peaks of DUMCN sample have a much-reduced intensity and become broad, which may attribute to the reduced length of interlayer periodicity and a larger spacing between the DUMCN layers result from the CN triple bond and N-vacancy.…”