Enhanced Sunlight‐Driven Photocatalytic Degradation of Binary Organic Dyes Using Bi‐ and Cr‐Doped ZnO Nanoparticles for Environmental Remediation

ABSTRACT

Pure ZnO, 0.5 wt.% Bi‐doped ZnO, and 0.5 wt.% Cr‐doped ZnO nanoparticles were synthesized using a simple co‐precipitation method and evaluated for sunlight‐driven photocatalytic degradation of a binary dye system containing methylene blue (MB) and rhodamine B (RhB). PXRD confirmed the single‐phase hexagonal wurtzite structure without detectable impurities. Dopant incorporation induced lattice distortion, reduced crystallite size from 36.4 to 33.8 nm, and increased lattice strain and dislocation density. FTIR confirmed characteristic Zn─O vibrational bands. TEM revealed a particle‐size reduction from 42 ± 5 nm for pure ZnO to 35 ± 4 nm for Cr‐doped ZnO, while HRTEM and SAED confirmed crystallinity and polycrystalline characteristics. Cr‐doped ZnO exhibited the highest degradation efficiencies, reaching 98.4% for MB and 94.0% for RhB, compared with 93.0% and 89.0% for Bi‐doped ZnO and 88.0% and 82.0% for pure ZnO, respectively. Kinetic analysis indicated pseudo‐first‐order behaviour. Scavenger experiments identified hydroxyl radicals (•OH) as the predominant reactive species. The enhanced photocatalytic activity of Cr‐doped ZnO is attributed to its smaller particle size, increased defect density, and improved charge separation. These findings highlight its potential for sunlight‐driven treatment of dye‐contaminated wastewater.