Photodegradation of odorous 2-mercaptobenzoxazole through zinc oxide/hydroxyapatite nanocomposite

Abstract

In this study, ZnO/HAP nanocomposite with excellent photocatalytic activities was successfully synthesized by sol–gel method and used for degradation of 2-mercaptobenzoxazole (MBO) as model of odorous mercaptan compound in water. To optimize the performance of ZnO/HAP photocatalytic capabilities, ZnO/HAP loading (0.05–0.3 g/L), irradiation time (15–180 min), pH (3–11) and initial concentration of MBO (10–100 ppm) were investigated. At neutral pH of 7, the highest amount of the MBO (99.45 %) was degraded by ZnO/HAP nanocomposite through photocatalytic oxidation process within 2 h of irradiation time. A maximum adsorption capacity of 197.64 mg g−1 was obtained for ZnO/HAP under optimized conditions. BET results indicated that ZnO/HAP had a surface area of 182.36 mg2g−1 which was much greater than pure ZnO nanoparticles (31.2 mg2g−1). TEM image demonstrated a spherical shape structure of ZnO/HAP with average particle size of 25 nm in diameter. The XRD patterns revealed the principal components of ZnO/HAP including HAP and ZnO. FTIR spectrum results supported formation ZnO and HAP by their stretching mode in composite. Comparison of photocatalytic activity of ZnO/HAP with pure ZnO and HAP nanoparticles had clearly recognized that latter is the most active photocatalyst in the degradation of MBO using UV light as source energy. The reason for greater activity of ZnO/HAP was due to its larger specific surface area (182.36 m2g−1) and high generation of active $${\text{HO}}^{\cdot}$$ and $${\text{O}}_{2}^{- 2 \cdot}$$ species.