Highly efficient photocatalytic degradation of oil pollutants by oxygen deficient SnO2 quantum dots for water remediation

The oil spill pollution has become one of the most significant threats to the marine environment and coastal ecology. An efficient way is urgently expected to remove the oil pollutants at this last stage of the petroleum age. In this work, the oxygen vacancy-rich SnO2 quantum dots (QDs) are prepared in aqueous solution via a facile bottom-up self-assembly route. The QDs are applied to the photocatalytic degradation of oil pollutants in water. A high degradation efficiency of 91.9% for octane is obtained within 48 h under the ultraviolet-visible irradiation and the excellent performance is able to be maintained within a period of 90 days. The primary reactive radical is superoxide anion (O-2(center dot-)) in the degradation process, where the oxygen supply is essential to the photocatalytic removal of oil pollutants. The optical characterizations conclude that the QDs have 16.7% of oxygen vacancies and a band gap of 4.2 eV. Based on these characteristics, a computational model is established for the first principle-based simulation, which reveals the electrical properties and demonstrates a deep energy level of oxygen vacancies at 1.4 eV below the conduction band. The proficient photocatalytic degradation efficiency is ascribed to the inherent oxygen vacancies, which build an internal Z-scheme mechanism for the electron transition. A novel strategy is therefore proposed that the deep energy levels in low dimensional semiconductors are beneficial to the enhancement of photocatalytic activity. The present oxygen vacancy-rich SnO2 QDs are prospective candidates for mass degradation of organic oil pollutants in water and they are of great significance to the development of semiconductor photocatalysts as well as the remediation of marine environment.