Polymethylacrylic acid-induced fabrication of hollow hZrO2/g-C3N4 composite photocatalysts: study on solar photocatalytic performance and mechanism insight

Herein, hollow hZrO2/g-C3N4 composite photocatalysts were successfully fabricated using polymethylacrylic acid (PMAA) nanospheres as sacrificial templates via reflux-precipitation polymerization and subsequent ZrO2 layer coating by sol–gel method over PMAA nanospheres, calcining process, and forming composites with g-C3N4 in sequence. The formation mechanism of the unique composites was proved by FESEM, TEM, XPS, XRD, and EDX mapping characterizations. The photodegradation tests of methylene blue (MB) and ciprofloxacin (CIP) were used to investigate the photocatalytic activity. The results revealed that hZrO2/g-C3N4 exhibited significantly boosted photocatalytic activity for degrading 99.7% methylene blue and 81.5% ciprofloxacin in 120 min under simulated sunlight irradiation (Xe lamp, 500 W), which was much better than that of hZrO2 (42.1% for MB and 19.1% for CIP). The enhanced performance is presumably attributed to the synergetic interaction of the two components and the efficient separation of the photoproduced electron–hole pairs between ZrO2 and g-C3N4, which was verified using photocurrent and EIS characterizations. On the basis of the scavenging studies of free radicals (e−, h+, ˙O2−, and ˙OH), the mechanism of the boosted photocatalytic activity was proposed. More significantly, the composites presented excellent reusability confirmed by cyclic photocatalytic degradation experiments, which is crucial for the sustainable and green applications of photocatalysts.