Harnessing ZnCr2O4/g-C3N4 nanosheet heterojunction for enhanced photocatalytic degradation of rhodamine B and ciprofloxacin

Utilizing semiconductors for photocatalytic processes in water bodies as an approach to environmental remediation has gained considerable attention. Theoretical band position calculations revealed a type-II step-scheme charge flow mechanism for ZnCr2O4/g-C3N4 (ZCr/gCN), emphasizing effective heterojunction formation due to synergies between the materials. A composite of agglomerated nanoparticle ZnCr2O4 (Zinc chromium oxide - ZCr)/g-C3N4 (graphitic carbon nitride - gCN) nanosheets was synthesized using the ultrasonication and leveraging the heterojunction to enhance degradation efficiency and active sites participation. The synthesized sample was characterized by XRD, XPS, FTIR, BET, HRSEM, EDX, HRTEM, EIS PL, and UV-visible spectroscopy. XRD analysis confirmed the successful formation of pure ZnCr2O4, g-C3N4 (gCN), and their composite without any secondary phases. Optical investigations demonstrated a red shift (444-470 nm) in UV-visible spectra as ZnCr2O4 content increased. Morphological assessment via HRSEM unveiled agglomerated nanoparticle and nanosheet structures. FTIR analysis indicated the presence of gCN with the tri-s-triazine breathing mode at 807 cm-1, and the identification of octahedral Zn-O (598.11 cm-1) and tetrahedral Cr-O (447.01 cm-1) metal bonds within the spinel structure of ZnCr2O4. A Surface area of 134.162 m2/g was noticed with a microporous structure of pore radius 1.484 nm. Notably, the 15% ZCr/gCN composite achieved a remarkable 93.94 % (Rhodamine B-RhB) and 74.36 % (Ciprofloxacin - CIP) within 100 and 120 min, surpassing the performance of pure gCN. Improved degradation was attributed to higher charge separation (photo-excited electrons and holes), reducing charge recombination, as supported by photoluminescence and photoelectrochemical analyses. The presence of active species like superoxide during degradation was confirmed through a scavenger test. The stability analysis confirms the sample's stable nature (without secondary phase formation) after degradation. This work underscores the potential of ZnCr2O4 based metal-free compounds intended for effective environmental remediation.