Organic load removal and microbial disinfection of raw domestic sewage using SrSnO3/g-C3N4 with sunlight.

Sewage treatment and water reuse are, undoubtedly, one of the main points on scientific agenda of the 21st century. Many technologies for sewage treatment are available; however, it is still as an open issue that deserves much attention in order to facilitate their application, develop more effective methods and propose alternative treatment for unusual situations. Developing high performance materials for sewage treatment fits the idea of the development of efficient and alternative methods for microorganism removal and the high organic load of wastewater and is of fundamental importance. In this paper, a heterojunction with perovskite-type strontium stannate (SrSnO3) and graphitic carbon nitride (g-C3N4) - SrSnO3/g-C3N4 - was synthesized and used for photocatalytic treatment of domestic sewage using only sunlight. Results were accompanied by assessing the total organic carbon decrease and removal of pathogenic microorganisms. X-ray diffraction and X-ray excited photoelectron spectroscopy demonstrated that a heterostructure was successfully formed and photocatalytic tests showed an important activity in the visible range, i.e., under sunlight. Exposing raw sewage to 240 min (from 11 a.m. until 3 p.m.) in the presence of SrSnO3/g-C3N4, led to a 56.1% mineralization. This process was 2.5 more efficient than photolysis under sunlight. Moreover, the treated sewage showed no coliform growth (either fecal or total) or heterotrophic bacteria. This simple treatment makes sewage suitable and safe for reuse, for example, for agriculture purposes according to Brazilian regulations criteria and could be an alternative for isolated areas in which sewage treatment plants are not available.

Toxicological study of the degradation products of antineoplastic agent etoposide in commercial formulation treated by heterogeneous photocatalysis using SrSnO3.

Etoposide is an antineoplastic agent used for treating lung cancer, testicular cancer, breast cancer, pediatric cancers, and lymphomas. It is a pollutant due to its mutagenic and carcinogenic potential. Disposal of waste from this drug is still insufficiently safe, and there is no appropriate waste treatment. Therefore, it is important to use advanced oxidative processes (AOPs) for the treatment and disposal of medicines like this. The use of strontium stannate (SrSnO3) as a catalyst in heterogeneous photocatalysis reactions has emerged as an alternative for the removal of organic pollutants. In our study, SrSnO3 was synthesized by the combustion method and characterized by X-ray diffraction (XRD), Raman, UV-Vis, and scanning electron microscopy (SEM) techniques, obtaining a surface area of 3.28 m2 g-1 with cubic and well-organized crystallinity and a band gap of 4.06 eV. The experimental conditions optimized for degradation of an etoposide solution (0.4 mg L-1) were pH 5 and catalyst concentration of 1 g L-1. The results showed that the degradation processes using SrSnO3 combined with H2O2 (0.338 mol L-1) obtained total organic carbon removal from the etoposide solution, 97.98% (± 4.03 × 10-3), compared with TiO2, which obtained a mineralization rate of 72.41% (± 6.95 × 10-3). After photodegradation, the degraded solution showed no toxicity to zebrafish embryos through embryotoxicity test (OECD, 236), and no genotoxicity using comet assay and micronucleus test.