Rational Design of Mesoporous ZnFe₂O₄@g-C₃N₄ Heterojunctions for Environmental Remediation and Hydrogen Evolution

Mesoporous catalysts with a high specific surface area, accessible pore structures, and appropriate band edges are desirable for optimal charge transfer across the interfaces, suppress electron-hole recombination, and promote redox reactions at the active sites. The present study demonstrates the rational design of mesoporous ZnFe₂O₄@g-C₃N₄ magnetic nanocomposites (MNCs) with different pore sizes and pore volumes following a combination of facile thermal itching and thermal impregnation methods. The MNCs preserve the structural, morphological, and physical attributes of their counterparts while ensuring their effectiveness and superior catalytic capabilities. The morphological analysis confirms the successful grafting and confinement of ZnFe₂O₄ nanoparticles with the polymeric g-C₃N₄ nanosheets to form heterojunctions with numerous interfaces. The MNCs possess uniformly distributed small mesopores (pore size <4 nm), ample active sites, and a high specific surface area of 62.50 m²/g. The mesoporous ZnFe₂O₄@g-C₃N₄ notably improve hydrogen evolution rate and methylene blue dye degradation. The optimal loading weight of ZnFe₂O₄ is 20 %, in which the MNCs display the highest hydrogen evolution rate of 1752 μmol g^-1 h^-1 and photo-Fenton dye degradation rate constants of 0.147 min^-1, upon solar-light illumination. Furthermore, the photocatalysts demonstrate recyclability over five consecutive cycles, confirming their stability, while easy separation using a simple magnet underscores practical utility.