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 an 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.<br>

Influence of Ion Exchange on Photoresponsive Properties of Potassium Poly(heptazine imide)

“…The observed XRD patterns for K 2.88 H 0.12 PHI and HPHI (δ = 0.00) were consistent with those of KPHI and HPHI reported in previous studies. 18,28,30 Regarding the metal ion dependence of the crystal structure of MPHI, Kroger et al stated that the structure within the PHI layer does not change with the type of metal ion but the stacking structure does. 28 For example, LiPHI is considered to be more prone to possessing stacking faults than KPHI and others.…”

“…According to a recent study, NaPHI exhibited the highest ionic conductivity and photocatalytic activity in ambient environments. 28 However, in addition to the unresolved photocatalytic mechanism of MPHI, its optical and electrical properties have not been thoroughly investigated. In particular, the relationships among phenomena such as photochromism, photoconduction, and charge accumulation, as well as the specific role of encapsulated ions, remain unresolved.…”

Ultrasound waves at the service of photocatalysis: From sonochemical synthesis to ultrasound-assisted and piezo-enhanced photocatalysis

“…However, the sono-assisted approach showed lower photocatalytic performance than one-step exfoliation, which could be related to a higher degree of structural defects introduced by sonication in the g-C 3 N 4 nanosheets. Interestingly, Kröger et al [22] used ultrasonication to systematically modulate the particle size and the concentration of surface functional groups of 2D carbon nitride (Fig. 2c), demonstrating their role in H 2 evolution.…”

“…Zhang and coauthors [19] recently compared different exfoliation methods (thermal, chemical, ultrasonic, and one-step exfoliation) to prepare g-C 3 N 4 for water purification: ultrasonic exfoliation resulted in better performance compared to the chemical method. Exfoliation is beneficial to photocatalytic activity by increasing surface area, porosity, and surface functional groups for attaching co-catalyst [22]. However, the sono-assisted approach showed lower photocatalytic performance than one-step exfoliation, which could be related to a higher degree of structural defects introduced by sonication in the g-C 3 N 4 nanosheets.…”

Mixing Characteristic and High-Throughput Synthesis of Cadmium Sulfide Nanoparticles with Cubic Hexagonal Phase Junctions in a Chaotic Millireactor

“…9 Furthermore, the difference in the specific surface area caused by the variation in particle size could also affect the photocatalytic performance. 10 According to the LaMer model, the synthesis of NPs can be divided into three stages as illustrated by the LaMer diagram (Figure 1). (I) The degree of supersaturation (S) rises sharply with the monomer feed.…”