Photocatalytic removal of estrogenic compounds (ECs), specifically 17-estradiol (E2) and 17-ethinylestradiol (EE2), was investigated using a mixed-phase TiO2-ZnO nanocomposite (NC) across a range of initial concentrations (Co: 10 mg/L to 0.05 mg/L). The photocatalytic efficiency was evaluated under both UV and visible light irradiation with a fixed catalyst dosage of 10 mg/L over a 240-minute duration. After 240 minutes, GC×GC TOF MS analysis revealed complete transformation of E2 at Co ≤ 1 mg/L under visible light, while only 25% transformation was observed at Co = 10 mg/L. Degradation involved cleavage of the fused ring structure of E2, yielding lower molecular weight by-products that were subsequently mineralized, as confirmed by total organic carbon (TOC) removal. Under UV irradiation, approximately 30% and 20% mineralization were achieved for E2 and EE2, respectively, at Co = 10 mg/L. Under visible light, mineralization reached about 25% for E2 and 10% for EE2. Estrogenicity changes were assessed using the E-screen assay with estrogen receptor-positive MCF-7 breast cancer cells. Complete elimination of estrogenic activity was confirmed after 240 minutes of photocatalysis under both UV and visible light. FTIR spectroscopy of the NC post-E2 photocatalysis identified sorbed organic residues. Desorption followed by GC×GC TOF MS analysis revealed these as photocatalytic by-products. Subsequent desorption and calcination at 600°C for one hour restored active sites on the NC, enabling efficient reuse for three cycles under visible light without loss in performance.
Natural and synthetic steroid hormones such as E2 and EE2 are frequently detected in global water bodies. Chronic exposure—even at low ng/L to μg/L levels—can disrupt endocrine systems due to high affinity for estrogen receptors (ER). These compounds mimic natural estrogens, leading to abnormal physiological responses including infertility, reduced sperm count, male feminization, increased vitellogenin induction, and elevated risks of testicular, ovarian, and breast cancers. Inadequate removal during secondary wastewater treatment is common, particularly because conjugated forms can deconjugate and reactivate during treatment, increasing active EC concentration in effluent. Ozonation may generate by-products with similar or enhanced estrogenic or androgenic activity. Chlorination combined with UV can produce more toxic transformation products and hinder complete mineralization. Thus, conventional tertiary treatments often fail to eliminate ECs entirely or may generate hazardous by-products.
Heterogeneous photocatalysis has emerged as a promising strategy for removing emerging pollutants like E2 and EE2. Its key advantage lies in potential near-complete mineralization, reducing both toxicity and estrogenic effects. Titanium dioxide (TiO2) and zinc oxide (ZnO) are widely used photocatalysts, but both operate primarily under UV light and suffer from poor charge carrier separation.FUK Antibody medchemexpress Semiconductor heterojunctions or hybrid structures can overcome these limitations by facilitating efficient charge separation through interfacial electron transfer between phases. TiO2-ZnO hybrids have demonstrated enhanced performance in degrading dyes, herbicides, and other contaminants. Although TiO2 and ZnO possess similar bandgaps (~3.22 eV for anatase TiO2, ~3.37 eV for wurtzite ZnO), their conduction and valence band positions allow for effective charge transfer. However, their wide bandgaps limit visible light activity unless modified via doping or composite formation. This study utilized a sol-gel-synthesized TiO2-ZnO NC with a Ti:Zn molar ratio of 1:0.AGTPBP1 Antibody Purity 3, calcined at 600°C for one hour, resulting in a mixed-phase material containing crystalline TiO2, ZnO, and zinc titanates. This composition enabled visible light activity due to defect-induced mid-gap states promoting sub-bandgap absorption.
The study focused on degradation kinetics, mineralization extent, intermediate identification, estrogenic activity reduction, and reusability—all critical aspects often overlooked in prior research. Experiments were conducted at environmentally relevant EC concentrations ranging from 50 μg/L to 10 mg/L, unlike many studies that use much higher doses. Photocatalytic reactions were carried out in a quartz reactor equipped with either UV or visible lamps. Initial contact in the dark allowed sorption equilibrium before irradiation. Samples were collected periodically and analyzed via SPE-GC×GC-TOF MS. Sorption behavior was modeled using the Langmuir-Hinshelwood (L-H) model. Post-catalysis, the NC was analyzed by FTIR to identify sorbed organics, which were then desorbed and analyzed again by GC×GC-TOF MS. Regeneration involved washing and calcination at 600°C for one hour, allowing reuse over three cycles.
Characterization confirmed the presence of multiple phases: anatase and rutile TiO2, wurtzite ZnO, and zinc titanates (ZnTiO3, Zn2TiO4). XRD and SAED patterns indicated polycrystallinity and preferred orientation of the anatase phase. FTIR showed characteristic Ti–O and Zn–O vibrations, along with evidence of Ti–O–Zn linkages. The NC exhibited a bandgap of ~2.5 eV, corresponding to a threshold wavelength of 496 nm, confirming visible light responsiveness. The presence of oxygen vacancies and Ti³⁺ states, confirmed by Raman and XPS, contributed to enhanced sub-bandgap absorption and improved photocatalytic activity.
Under UV and visible light, E2 and EE2 degradation followed pseudo-first-order kinetics. Complete transformation of E2 occurred at Co ≤ 1 mg/L under both light sources, whereas EE2 showed incomplete removal even at low concentrations. Mineralization was significantly higher under photocatalysis than photolysis—up to sevenfold for EE2 under UV. At lower Co values (0.1 mg/L), mineralization exceeded 70%. The L-H model parameters revealed that EE2 had higher reactivity at maximum surface coverage (kr) but lower sorption energetics (β), indicating that its removal was limited by adsorption rather than reaction rate. In contrast, E2 removal was constrained by photocatalytic kinetics despite favorable sorption.
GC×GC-TOF MS identified intermediates during E2 degradation under visible light: testosterone, estrone, and DEA (10,17-dihydroxyestra-1,4-diene-3-one). These indicated oxidation of phenolic groups. Ring-opening products resembling dehydroabeitic acid and pimaric/isopimaric acids appeared between 120 and 180 minutes, followed by smaller molecules such as malic acid derivatives beyond 180 minutes. A proposed degradation pathway involves sequential oxidation, ring cleavage, and fragmentation into low-molecular-weight compounds.PMID:35089224 For EE2, only a few intermediates were identifiable, suggesting complex or unstable degradation pathways.
Estrogenic potency was monitored via E-screen assay. Photolysis resulted in less than 50% reduction in estrogenicity due to accumulation of highly hydroxylated intermediates with strong ER binding. In contrast, photocatalysis led to rapid decline in estrogenic activity. Complete removal was observed for E2 at all tested concentrations. For EE2, removal reached 85% and 78% under UV and visible light, respectively, at Co = 5 mg/L. At lower concentrations (0.05 mg/L), no estrogenicity remained beyond 150 minutes. Undiluted samples beyond 120 minutes still showed mild agonistic activity (RPE < 10%), indicating residual intermediates. However, this activity vanished after 210 minutes for E2 and 240 minutes for EE2. Visible light activity was attributed to three key features: preferred orientation of anatase planes enhancing surface reactivity; a narrow bandgap (~2.5 eV) due to Urbach tailing and mid-gap states; and high density of oxygen vacancies and Ti³⁺ defects. These features were absent in control samples (TiO2 alone and Ti:Zn = 1:0.4), confirming their role in enabling visible light response. Recalcination at 600°C effectively regenerated the NC by removing sorbed organics, restoring FTIR signals and maintaining catalytic performance over three reuse cycles. BET surface area decreased slightly (from 21.29 to 19.66 m²/g), but no significant structural degradation occurred. In conclusion, the mixed-phase TiO2-ZnO nanocomposite demonstrates high efficacy in removing E2 and EE2 under both UV and visible light. It achieves substantial mineralization and complete elimination of estrogenic activity. The ability to regenerate via calcination enables sustainable reuse for up to three cycles without performance loss. This makes the material a promising candidate for practical water treatment applications targeting endocrine-disrupting compounds.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
