Development of Photoactive g-C₃N₄/Poly(vinyl Alcohol) Composite Hydrogel Films with Antimicrobial and Antibiofilm Activity

Free-standing, composite hydrogels containing the visible-light responsive metal-free semiconductor graphitic carbon nitride (g-C₃N₄) as an integral component have been fabricated by direct casting techniques. At 0.67% g-C₃N₄ loading, intermolecular interactions between the semiconductor particles and the PVA polymer chains enhance both the mechanical and photophysical properties of the resulting hydrogels. In contrast, much higher g-C₃N₄ loadings of 3.3 or 6.7% g-C₃N₄ resulted in growth of the average semiconductor particle size and reduction in interactions between the incorporated photocatalyst and the PVA chains. The increased dimensions of the g-C₃N₄ semiconductor particles had the effect of compromising the mechanical properties of the composite system and reducing the lifetime of photogenerated charge carriers. However, the close proximity of g-C₃N₄ particles that is realized at increased semiconductor loading densities improves the absorption cross section of the material, resulting in an overall improvement in the photocatalytic activity of the material. Application of visible radiation caused all of the composite hydrogels to generate hydrogen peroxide (H₂O₂) at catalytic rates of 0.9-2.5 μM/min, while H₂O₂ decomposition rates remained similar across the different preparations. In studies to examine antimicrobial performance, irradiation of 6.7% g-C₃N₄/PVA hydrogel samples with visible radiation (400 ≤ λ ≤ 800 nm) generated sufficient H₂O₂ to significantly reduce both the viable planktonic cell population and biofilm formation in cultures of Pseudomonas aeruginosa.