Photocatalysis on pristine g-C 3 N 4 (CN) often suffers from fast recombination of photogenerated electrons and holes. Herein, we demonstrate the superior photocatalytic performance of free base tetrakis(4-carboxyphenyl) porphyrin (TCPP) -g-C 3 N 4 (CN/TCPP) hybrids synthesised by a facile ultrasound aided impregnation. Structural and morphological characterisation confirmed the successful formation of the hybrid via noncovalent π-π stacking. Optical/electrochemical characterisation, as well as DFT study, designates the shifting of the optical absorption edge to visible range along with inhibition of carrier recombination through enhanced charge transfer. The CN/ TCPP hybrids exhibited superior performance towards the degradation of persistent antibiotic ciprofloxacin under visible irradiation signifying its enhanced visible light sensitivity. The enhanced photocatalytic activity of CN/TCPP is ascribed to the charge transfer by through-space conjugation by migration of electrons and holes in opposite directions, which minimises the possibility of electron-hole recombination. From the LCMS data, scavenging studies, and first principles DFT analysis, the photodegradation of CIP is proposed to proceed via the destruction of the piperazine ring initiated mainly through the electrophilic attack by the holes.
Elemental doping engineering has proven to be a powerful method for tailoring the physical and chemical properties of two-dimensional materials. However, we still lack an understanding of how to control it for our desired purpose. Graphitic carbon nitride (g-CN) is an exciting material that has received much attention for enhanced optical and photo-physical properties due to elemental doping. Sulfur-doped g-S-CN is an interesting example of elemental doping that exhibits both enlarged and narrowed band gaps. Hence, it is necessary to understand the electronic origin of band gap variation with respect to the structure of the doped material. Herein, we aim to provide a systematic theoretical understanding of the enhanced optical properties of electron-rich sulfur-doped g-S-CN and the electron-precise carbon sulfur dual-doped g-CS-CN. In our theoretical investigation, we have successfully shown that a mere change of dopant site alters the electronic structure owing to the geometrical changes at the atomic level in order to maintain proper π-electron delocalization in the system. The prominent effect observed in the replacement of di-coordinated aromatic N-atom by the C-atom is the destabilization of the σ-valence band, while the substitution of tri-coordinated terminal and central N-atom by C-atom destabilizes the π-conduction band as compared to g-S-CN. Considering the suitable position of the bands, band gap, and low substitution energy, the dual-doped pristine g-CN (band gap = 2.80 eV) formed by the substitution of aromatic N-atom with S-atom and terminal/central N-atom with C-atom leads to rather stable systems with ΔE sub(g‑CS‑CNx) of 0.68 and 0.90 eV, as well as higher photocatalytic reactivity, where the former shows a redshift (2.37 eV) and the latter shows a blueshift (3.09 eV) within the visible region. Thus, promising theoretical understanding about the tuning of band edge levels of these novel C,S-dual doped g-CN can attract more experiments for potential applications to be developed, especially for photocatalysis.
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