Morphology Control in 2D Carbon Nitrides: Impact of Particle Size on Optoelectronic Properties and Photocatalysis

Abstract

The carbon nitride poly(heptazine imide), PHI, has recently emerged as a powerful 2D carbon nitride photocatalyst with intriguing charge storing ability. Yet, insights into how morphology, particle size, and defects influence its photophysical properties are virtually absent. Here, ultrasonication is used to systematically tune the particle size as well as concentration of surface functional groups and study their impact. Enhanced photocatalytic activity correlates with an optimal amount of those defects that create shallow trap states in the optical band gap, promoting charge percolation, as evidenced by time‐resolved photoluminescence spectroscopy, charge transport studies, and quantum‐chemical calculations. Excessive amounts of terminal defects can act as recombination centers and hence, decrease the photocatalytic activity for hydrogen evolution. Re‐agglomeration of small particles can, however, partially restore the photocatalytic activity. The type and amount of trap states at the surface can also influence the deposition of the co‐catalyst Pt, which is used in hydrogen evolution experiments. Optimized conditions entail improved Pt distribution, as well as enhanced wettability and colloidal stability. A description of the interplay between these effects is provided to obtain a holistic picture of the size–property–activity relationship in nanoparticulate PHI‐type carbon nitrides that can likely be generalized to related photocatalytic systems.

Conductivity Mechanism in Ionic 2D Carbon Nitrides: From Hydrated Ion Motion to Enhanced Photocatalysis

“…Hence, conductivity can be an additional important parameter in tuning photocatalysts besides other, often intertwined properties, affecting the efficiency of the process. [ 12 ]…”

Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO3 and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting

“…A further aspect to be considered in semiconductor photocatalysis is the catalyst particle size. Many studies have investigated particle size effects for different photocatalysts and found that the interplay of factors such as specific surface area [61,62], charge-carrier dynamics [63,64] and light absorption [63,65] is crucial. Especially, if photocatalysts of similar composition are compared, the explanation of observed differences in catalytic activity needs to consider particle size effects, which are hardly covered by existing FOMs [66].…”

Exfoliation-induced O-doped g-C3N4 nanosheets with improved photoreactivity towards RhB degradation and H2 evolution

“…1–4 As a “rising star” in photocatalysis, g-C 3 N 4 has attracted great interest because of its moderate bandgap (2.7 eV), nontoxicity and wide material sources. 5–9 Generally, g-C 3 N 4 is obtained by thermal condensation of C/N-rich precursors (urea, cyanoguanidine, etc. ).…”

“…[1][2][3][4] As a "rising star" in photocatalysis, g-C 3 N 4 has attracted great interest because of its moderate bandgap (2.7 eV), nontoxicity and wide material sources. [5][6][7][8][9] Generally, g-C 3 N 4 is obtained by thermal condensation of C/N-rich precursors (urea, cyanoguanidine, etc.). Due to the incomplete thermal polymerization, the product obtained is bulk g-C 3 N 4 with a specific surface area of less than 10 m 2 g −1 and limited solar-light absorption, resulting in its intermediate photocatalytic performance.…”