Solvothermal synthesis of various C3N4 films on FTO substrates and their photocatalytic and sensing applications

This paper reports solvothermal syntheses of pristine and KOH–NaCl‐modified melon and melon–rGO composite films without post annealing and their applications in photocatalysis and Cu2+ sensing. Melon seed‐layer coating enhanced film adhesion to fluorine‐doped tin oxide substrates. X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy were used to verify melon film structures. Assorted complex agents were studied to tailor film morphologies. (001)‐Oriented nanorods were observed in KOH–NaCl‐modified melon films. Constituent elements were determined based on their binding energies using X‐ray photoelectron spectroscopy. Ultraviolet–visible and ultraviolet photoelectron spectroscopy were employed to confirm band gaps and valence band positions, respectively, of melon films. Associated energy‐band diagrams were then constructed. The melon–rGO composite films exhibited superior photodegradation of methylene blue (degradation rate constant [k] ≅ 6.4 × 10−3/min) and rhodamine B (k ≅ 2.5 × 10−3/min) under visible‐light irradiation. The performance was confirmed by nanorod structures, low photoluminescence emission, and high electrochemical surface areas. Furthermore, a reliable photoelectrochemical current density (~0.5 mA/cm2) at a 0.6‐V bias was obtained for KOH–NaCl‐modified melon and melon–rGO composite films. The KOH–NaCl‐modified melon films demonstrated excellent selectivity between Cu2+ and Cr6+, indicating promising applications in Cu2+ sensing.