Dendritic Fibrous Nanosilica Coated with a Graphitic Carbon Nitride Shell as a Selective Catalyst for N-Dealkylation

KCC-1@g-C3N4 composites, synthesized via thermal condensation of the melamine–cyanuric acid (MCA) complex on mesoporous KCC-1 silica nanoparticles, were developed with g-C3N4 content ranging from 7 to 45 wt %. Characterization by SEM, STEM, FTIR, XPS, and UV–vis DRS revealed a core–shell structure with band gaps of 2.82 and 2.86 eV and specific surface areas of 167.5–526.8 m2/g. These composites were evaluated as photocatalysts for the transformation of rhodamine B under visible light. At low g-C3N4 content (7–33 wt %), the composites selectively promote N-dealkylation, converting rhodamine B to rhodamine-110, as confirmed by UV–vis spectroscopy and mass spectrometry MALDI-TOF. Higher g-C3N4 content (38–45 wt %) leads to chromophore destruction, resembling pure g-C3N4 behavior. The enhanced N-dealkylation selectivity at lower g-C3N4 ratios is attributed to efficient charge separation facilitated by KCC-1 impurity electronic levels and the defects in the g-C3N4 shell. These findings highlight the potential of KCC-1@g-C3N4 composites for selective photocatalytic transformations, offering applications in environmental remediation and organic synthesis.