Enhanced Photodegradation of Antibiotics and Antimicrobial Activity by a g-C₃N₄/g-C₃N₅ Nanosheet Heterojunction Photocatalyst

An organic C-N polymeric nanocomposite, g-C₃N₄/g-C₃N₅ sheet (ECN45), was designed through thermal polymerization, followed by KBr-assisted exfoliation, to investigate its potential as a photocatalyst for the photodegradation of organic antibiotic pollutants and antimicrobial activities. Graphitic carbon nitride (g-C₃N₄) is a 2D material recognized as a highly promising photocatalyst; however, it possesses an elevated frequency of photogenerated electron-hole pair recombination and a constricted absorption range for visible light of up to 450 nm. Therefore, the formation of a heterojunction of 1D g-C₃N₅ upon g-C₃N₄ can minimize the charge recombination of g-C₃N₄. Furthermore, due to a lack of sufficient surface activation, the bulk composite (BCN45) was exposed to KBr exfoliation, resulting in a g-C₃N₄/g-C₃N₅ sheet (ECN45). The 1D/2D hybrid catalyst exhibits a reduction in band gap of up to 1.81 eV due to the presence of azo linkages and π-conjugated bonds compared to its pristine elements. The nanocomposite shows a red shift toward the visible light spectrum compared to its pristine forms. The morphological, spectroscopic, and physicochemical investigations of the nanocomposite are confirmed by TEM, SEM-EDX, BET, XRD, UVDRS, FTIR, XPS, PL, and electrochemical analysis techniques. The photocatalytic application is shown by the composite for degrading the antibiotic CIP (ciprofloxacin) for about 93.1% at an acidic environment of pH 3 at its lowest concentration of 10 mg L^-1 in 120 min. Further, the catalyst is examined to show antimicrobial action against Gram-negative bacteria <i>Escherichia coli</i> (<i>E. coli</i>) and Gram-positive bacteria <i>Staphylococcus aureus</i> (<i>S. aureus</i>) with the help of the inhibition zone test, MIC (minimum inhibition concentration), and photocatalytic cellular leakage of the microbial body. Also, the plausible Z-scheme mechanisms exhibited by the formed 2D/1D heterostructure for CIP degradation and antimicrobial activity are explained. The enhanced photoactivity is attributed to the synergistic effects of 1D/2D hybrid nanostructure, extended conjugation leading to enriched light harvesting, and Z-scheme heterojunction for better photogenerated charge separation. This approach makes grounds to establish an effective metal-free composite showing efficient photocatalytic activity.