Structural and optical advances in Cu/Sr Co-doped ZnO nanomaterials for accelerated photocatalytic degradation of organic pollutant

Abstract

Rational co-doping of ZnO with electronically active and lattice-modifying elements has proven to be an effective strategy to enhance photocatalytic efficiency through simultaneous band-structure tuning and defect engineering. Herein, Cu/Sr co-doped ZnO nanomaterials (Zn_1−(x+y)Cu_xSr_yO, with x = 0.03, 0.06, 0.09 and y = 0.04) were synthesized via a one-step chemical precipitation method under controlled pH and thermal treatment. X-ray diffraction (XRD) confirmed the retention of the wurtzite ZnO structure with systematic lattice expansion, indicating successful substitutional incorporation of Cu²⁺ and Sr²⁺ ions. Optical absorption measurements showed a red-shift of the absorption edge and reduced band-gap energy (∼2.98 eV) compared with pristine ZnO (∼3.20 eV). Under simulated solar irradiation (678.32 W m⁻²), the co-doped ZnO exhibited markedly enhanced photocatalytic degradation of Congo red (∼97% removal within 90 min at a catalyst dose of 15 mg), following pseudo-first-order kinetics (k = 0.040 min⁻¹, R² = 0.992). Photoluminescence (PL) quenching, radical scavenger experiments, and reduced charge transfer resistance from electrochemical impedance spectroscopy (EIS) collectively indicate improved charge separation and suppressed recombination in the co-doped system. Furthermore, the photocatalyst retained its structural integrity and photocatalytic efficiency over five consecutive cycles, as confirmed by post-reaction XRD analysis. These findings demonstrate that synergistic Cu/Sr co-doping effectively tuned the structure–property–performance relationship in ZnO, leading to enhanced and stable photocatalytic activity.