Impact of the annealing temperature on Pt/g-C 3 N 4 structure, activity and selectivity between photodegradation and water splitting

Abstract

This work presents a systematic study of the effect of fabrication temperature (450 to 650 o C) on the structure and electronic properties of g-C3N4 prepared from melamine. The work is conducted by X-ray diffraction, elemental analysis, BET nitrogen adsorption, UV-vis absorption, and electron paramagnetic resonance (EPR). The photocatalytic activity is tested for hydrogen production in the presence of oxalic acid (OA) as well as triethanolamine (TEOA). A considerable change in the morphology is observed with increasing the synthesis temperature resulting in an increase of the surface area, likely due to thermal etching at elevated temperatures. The decrease of charge carriers' concentration, per unit area, with annealing temperatures may be due to the decrease of the conjugation of the polymer. Probing the activity of g-C3N4 for hydrogen evolution reinforced this conclusion, the rate of hydrogen evolution per unit area for OA as well as TEOA decreased with annealing temperatures. An interesting finding is the correlation between CO2:H2 ratio and the increase in the band gap of g-C3N4 prepared at different temperatures when using oxalic acid as an electron donor. This suggests that water oxidation becomes easier with increasing band gap energy, probably due to a lowering of the valence band edge.

Mechanism of visible photon absorption: unveiling of the C3N4–ZnO photoactive interface by means of EPR spectroscopy

“…The presence of unpaired electrons in the localized excited state prior to illumination can be attributed to defects in the nanostructured material caused by melamine polymerization. 99,102,103 Upon visible light irradiation, performed with several band pass filters at different visible wavelengths of irradiation, the rising up of the Lorentzian line, due to the electron photoexcitation from the valence band (2p nitrogen orbitals) to the conduction band (2p carbon orbitals), dominates the EPR spectra (b-d) of Fig. 5, increasing the number of unpaired electrons in the localized p-conjugated system.…”

Photo-catalytic hydrogen production over Au/g-C3N4: effect of gold particle dispersion and morphology

“…This result is ascribed to the photo-degradation of oxalic acid. 6 Both gases follow very similar trends, therefore only hydrogen evolution is presented here. Bare g-C 3 N 4 is marginally active for hydrogen evolution.…”

“…5 Pristine g-C 3 N 4 allows hydrogen production in the presence of an electron donor compound. 5,6 Using a noble metal such as platinum increases g-C 3 N 4 performance which is commonly rationalized by the formation of a Schottky barrier at the metal/ semiconductor interface, thus poised to reduce charge recombination rates. 7,8 Other metals such as gold, in addition to their high work function, have localized surface plasmon resonance (LSPR) properties.…”

Mechanical, Structural and Electronic Properties of CO2 Adsorbed Graphitic Carbon Nitride (g-C3N4) under Biaxial Tensile Strain

“…In addition, Caux et al [ 18 ] have studied Pt-g-C 3 N 4 for CO 2 photoreduction to improve the catalytic performance ascribed to the charge-separation efficiency. Different from these composite photocatalysts prepared by expensive metal salts, the preparation of pristine g-C 3 N 4 photocatalyst can be made facilely by thermally polycondensing the cheap N-rich precursors, such as cyanamide, dicyanamide, urea and melamine [ 19 , 20 ].…”