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

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.

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Polymeric Carbon Nitride Coupled with a Molecular Thiomolybdate Catalyst: Exciton and Charge Dynamics in Light-Driven Hydrogen Evolution

10.26434/chemrxiv.12941741 ◽

2020 ◽

Author(s):

Ashwene Rajagopal ◽

Elham Akbarzadeh ◽

Chunyu Li ◽

Dariusz Mitoraj ◽

Igor Krivtsov ◽

...

Keyword(s):

Hydrogen Evolution ◽

Energy Demand ◽

Soft Matter ◽

Carbon Nitride ◽

Molybdenum Sulfide ◽

Open Circuit ◽

Trap States ◽

Time Resolved ◽

Light Absorbers ◽

Polymeric Carbon

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled to highly efficient molecular catalysts might represent an attractive platform to address this issue. However, to-date, our mechanistic knowledge of these systems is still largely underdeveloped. In this study, a molecular molybdenum sulfide hydrogen evolving catalyst, [Mo3S13]2–, is loaded onto polymeric carbon nitride (CNx) photoabsorber by impregnation. The resulting composite shows enhanced photocatalytic activity for hydrogen evolution compared to pristine CNx under monochromatic visible light (l = 420 nm) irradiation in the presence of sacrificial reducing agents. The light-driven dynamics of excitons and charges involved in hydrogen evolution catalysis were studied by a combination of spectroscopic (steady-state and time-resolved photoluminescence, femtosecond time-resolved transient absorption) and photoelectrochemical (open-circuit photopotential transients) methods. We demonstrate that the molecular molybdenum sulfide catalyst, at optimum loading (10 wt% nominal), improves the charge separation in the CNx absorber by facilitating the depopulation of emissive (band-edge) or non-emissive (shallow trap) states, followed by an effectively catalyzed transfer of electrons from the charge-separated state (deep trap) to protons in the solution. The results provide important insights into the complex interplay between polymeric light absorbers and molecular redox catalysts, indicating that the electron transfer to the catalyst occurs on relatively longer (nanosecond – seconds) time scale, as the catalyst had no impact on the ultrafast (sub-nanosecond) photoinduced kinetics in the CNx. These findings are of crucial importance for further development of soft-matter based architectures for solar fuels production.

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A Comparative Study on the Role of Precursors of Graphitic Carbon Nitrides for the Photocatalytic Degradation of Direct Red 81

Materials Science Forum ◽

10.4028/www.scientific.net/msf.807.101 ◽

2014 ◽

Vol 807 ◽

pp. 101-113 ◽

Cited By ~ 5

Author(s):

J. Theerthagiri ◽

R.A. Senthil ◽

J. Madhavan ◽

B. Neppolian

Keyword(s):

Particle Size ◽

Photocatalytic Activity ◽

Visible Light ◽

Photocatalytic Degradation ◽

Visible Light Irradiation ◽

Carbon Nitride ◽

Light Irradiation ◽

X Ray Diffraction ◽

X Ray ◽

Carbon Nitrides

The graphitic carbon nitride (g-C3N4) materials have been synthesized from nitrogen rich precursors such as urea and thiourea by directly heating at 520 °C for 2 h. The as-synthesized carbon nitride samples were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) and particle size analysis. The photoelectrochemical measurements were performed using several on-off cycles under visible-light irradiation. The x-ray diffraction peak is broader which indicates the fine powder nature of the synthesized materials. The estimated crystallite size of carbon nitrides synthesized from urea (U-CN) and thiourea (T-CN) are 4.0 and 4.4 nm respectively. The particle size of U-CN and T-CN were analysed by particle size analyser and were found to be 57.3 and 273.3 nm respectively. The photocatalytic activity for the degradation of the textile dye namely, direct red-81 (DR81) using these carbon nitrides were carried out under visible light irradiation. In the present investigation, a comparison study on the carbon nitrides synthesized from cheap precursors such as urea and thiourea for the degradation of DR81 has been carried out. The results inferred that U-CN exhibited higher photocatalytic activity than T-CN. The photoelectrochemical studies confirmed that the (e--h+) charge carrier separation is more efficient in U-CN than that of T-CN and therefore showed high photocatalytic degradation. Further, the smaller particle size of U-CN is also responsible for the observed degradation trend.

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Polymeric Carbon Nitride Coupled with a Molecular Thiomolybdate Catalyst: Exciton and Charge Dynamics in Light-Driven Hydrogen Evolution

10.26434/chemrxiv.12941741.v1 ◽

2020 ◽

Author(s):

Ashwene Rajagopal ◽

Elham Akbarzadeh ◽

Chunyu Li ◽

Dariusz Mitoraj ◽

Igor Krivtsov ◽

...

Keyword(s):

Hydrogen Evolution ◽

Energy Demand ◽

Soft Matter ◽

Carbon Nitride ◽

Molybdenum Sulfide ◽

Open Circuit ◽

Trap States ◽

Time Resolved ◽

Light Absorbers ◽

Polymeric Carbon

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled to highly efficient molecular catalysts might represent an attractive platform to address this issue. However, to-date, our mechanistic knowledge of these systems is still largely underdeveloped. In this study, a molecular molybdenum sulfide hydrogen evolving catalyst, [Mo3S13]2–, is loaded onto polymeric carbon nitride (CNx) photoabsorber by impregnation. The resulting composite shows enhanced photocatalytic activity for hydrogen evolution compared to pristine CNx under monochromatic visible light (l = 420 nm) irradiation in the presence of sacrificial reducing agents. The light-driven dynamics of excitons and charges involved in hydrogen evolution catalysis were studied by a combination of spectroscopic (steady-state and time-resolved photoluminescence, femtosecond time-resolved transient absorption) and photoelectrochemical (open-circuit photopotential transients) methods. We demonstrate that the molecular molybdenum sulfide catalyst, at optimum loading (10 wt% nominal), improves the charge separation in the CNx absorber by facilitating the depopulation of emissive (band-edge) or non-emissive (shallow trap) states, followed by an effectively catalyzed transfer of electrons from the charge-separated state (deep trap) to protons in the solution. The results provide important insights into the complex interplay between polymeric light absorbers and molecular redox catalysts, indicating that the electron transfer to the catalyst occurs on relatively longer (nanosecond – seconds) time scale, as the catalyst had no impact on the ultrafast (sub-nanosecond) photoinduced kinetics in the CNx. These findings are of crucial importance for further development of soft-matter based architectures for solar fuels production.

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Shallow trap state-enhanced photocatalytic hydrogen evolution over thermal-decomposed polymeric carbon nitride

Chemical Communications ◽

10.1039/d0cc01870h ◽

2020 ◽

Vol 56 (44) ◽

pp. 5921-5924

Author(s):

Jiawei Xue ◽

Mamoru Fujitsuka ◽

Tetsuro Majima

Keyword(s):

Photocatalytic Activity ◽

Hydrogen Evolution ◽

Carbon Nitride ◽

Functional Group ◽

Electron Trap ◽

Trap States ◽

Shallow Trap ◽

Trap State ◽

Oxygen Functional Group ◽

Polymeric Carbon

Oxygen functional group-introduced shallow electron trap states enhance the photocatalytic activity of the thermal-decomposed polymeric carbon nitride for hydrogen evolution.

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Polymeric Carbon Nitride Coupled with a Molecular Thiomolybdate Catalyst: Exciton and Charge Dynamics in Light-Driven Hydrogen Evolution

10.26434/chemrxiv.12941741.v2 ◽

2020 ◽

Author(s):

Ashwene Rajagopal ◽

Elham Akbarzadeh ◽

Chunyu Li ◽

Dariusz Mitoraj ◽

Igor Krivtsov ◽

...

Keyword(s):

Hydrogen Evolution ◽

Energy Demand ◽

Soft Matter ◽

Carbon Nitride ◽

Molybdenum Sulfide ◽

Open Circuit ◽

Trap States ◽

Time Resolved ◽

Light Absorbers ◽

Polymeric Carbon

Solar hydrogen evolution from water is a necessary step to overcome the challenges of rising energy demand and associated environmental concerns. Low-cost photocatalytic architectures based on polymeric light absorbers coupled to highly efficient molecular catalysts might represent an attractive platform to address this issue. However, to-date, our mechanistic knowledge of these systems is still largely underdeveloped. In this study, a molecular molybdenum sulfide hydrogen evolving catalyst, [Mo3S13]2–, is loaded onto polymeric carbon nitride (CNx) photoabsorber by impregnation. The resulting composite shows enhanced photocatalytic activity for hydrogen evolution compared to pristine CNx under monochromatic visible light (l = 420 nm) irradiation in the presence of sacrificial reducing agents. The light-driven dynamics of excitons and charges involved in hydrogen evolution catalysis were studied by a combination of spectroscopic (steady-state and time-resolved photoluminescence, femtosecond time-resolved transient absorption) and photoelectrochemical (open-circuit photopotential transients) methods. We demonstrate that the molecular molybdenum sulfide catalyst, at optimum loading (10 wt% nominal), improves the charge separation in the CNx absorber by facilitating the depopulation of emissive (band-edge) or non-emissive (shallow trap) states, followed by an effectively catalyzed transfer of electrons from the charge-separated state (deep trap) to protons in the solution. The results provide important insights into the complex interplay between polymeric light absorbers and molecular redox catalysts, indicating that the electron transfer to the catalyst occurs on relatively longer (nanosecond – seconds) time scale, as the catalyst had no impact on the ultrafast (sub-nanosecond) photoinduced kinetics in the CNx. These findings are of crucial importance for further development of soft-matter based architectures for solar fuels production.

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Cobalt ion redox and conductive polymers boosted the photocatalytic activity of the graphite carbon nitride–Co3O4 Z-scheme heterostructure

New Journal of Chemistry ◽

10.1039/d0nj04322b ◽

2021 ◽

Vol 45 (1) ◽

pp. 162-168

Author(s):

Tao Li ◽

Jiandong Cui ◽

Yezhan Lin ◽

Kecheng Liu ◽

Rui Li ◽

...

Keyword(s):

Photocatalytic Activity ◽

Synergistic Effect ◽

Hydrogen Evolution ◽

Carbon Nitride ◽

Conductive Polymers ◽

Cobalt Ion ◽

Photocatalytic Hydrogen Evolution ◽

Conductive Polyaniline

The enhanced photocatalytic hydrogen evolution performance of g-C3N4–Co3O4 2D–1D Z-scheme heterojunctions was achieved through the synergistic effect of the cobalt ion redox, conductive polyaniline, and a Co3O4 nanobelt.

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Oxygen-doped and nitrogen vacancy co-modified carbon nitride for the efficient visible light photocatalytic hydrogen evolution

New Journal of Chemistry ◽

10.1039/d0nj03695a ◽

2020 ◽

Vol 44 (38) ◽

pp. 16320-16328 ◽

Cited By ~ 1

Author(s):

Yuanyuan Yang ◽

Wenting Guo ◽

Yunpu Zhai ◽

Qianwei Jin ◽

Hao Zhao ◽

...

Keyword(s):

Visible Light ◽

Hydrogen Evolution ◽

Carbon Nitride ◽

Nitrogen Vacancy ◽

Photocatalytic Hydrogen Evolution ◽

Practical Applications ◽

Carbon Nitrides ◽

Visible Light Photocatalytic

Typical non-metallic semiconductor carbon nitrides (CNs) have enormous potential in the field of photocatalysis, but the easy recombination of the photo-generated charges severely limits their practical applications.

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