Novel p-ZnCo2O4/n-Bi2WO6 heterojunctions for efficient rhodamine B and tetracycline photodegradation, and Cr(VI) photoreduction under visible LED and sunlight irradiation

Abstract

Coupling of photocatalysts extends the photoresponse interval and improves the photogenerated pair migration. Herein, novel visible-light heterojunctions (HETs) of n-Bi₂WO₆ and p-ZnCo₂O₄ (weight ratios from 2:1 to 16:1) were prepared by two straightforward procedures, coprecipitation and hydrothermal, and applied to the photodegradation of rhodamine B (RhB) and tetracycline (TC), as well as photoreduction of chromium (VI) (Cr(VI)) under 100 W blue LED and sunlight irradiation. Several characterization techniques were used to analyze the physicochemical properties of the HETs, revealing an effect on the Bi₂WO₆ content in HETs. The 16Bi₂WO₆/ZnCo₂O₄ obtained by coprecipitation (16BWO/LDO-C) showed superior degradation of RhB compared to the other synthesized HETs, and the degradation percentage of RhB (%X_RhB) attained was 100 % (k₁ = 1.13 × 10⁻² 1/min) within 300 min using a catalysts dosage of 100/100 mg/mL, RhB initial concentration of 5 mg/L and pH 3. In addition, this HET achieved a %X_TC of 83 % (k₂ = 0.81 × 10⁻¹ L/mg min) in 90 min, and %X_Cr(VI) of 96 % (k₁ = 3.89 × 10⁻² 1/min) in 60 min. Sunlight boosted the rate of photocatalytic processes by 2.8, 1.3, and 1.6 times for RhB, TC, and Cr(VI), in that order, compared to LED irradiation. After three photocatalytic cycles, the 16BWO/LDO-C showed high performance (%X_RhB = 100 % and %X_TC = 78 %), confirming its high stability. At the same time, trapping assays revealed that holes and superoxides are the main species oxidizing RhB and TC molecules, consistent with the plausible charge transfer mechanism for 16BWO/LDO-C. This study provides new insights into designing innovative and high-performance BWO/LDO HETs to remove organic and inorganic pollutants from water.