For decades, Environmental Hormones (EHs) have been extensively used to augment agricultural production for exponentially-growing population need. However, although these hormones provide some benefits, they inevitably pose a serious threat to human and wildlife health. In fact, some studies have suggested that EHs have a negative impact on the reproductive system, nervous system, and the immune system of organisms, leading to slow and malformed development, decreased sperm counts, poor sperm motility, and increased cancer risks [1, 2].
Regarding environmental hormones, 17ß-estradiol (E2) is a typical steroid estrogen, significantly the reproduction of aquatic organisms even at extremely low concentrations. Biegel et al.  reported, the stripes of male crocodiles transformed to that of female crocodiles, and they exhibited female-like reproductive behavior as well due to this estrogen. The study of Diamante  also observed that the zebrafish embryo underwent some changes including curved body axis, yolk-sac edema, and pericardial edema after treatment with E2. Angus et al.  reported that high dosage of E2 led to the death of juvenile fishes in water bodies. Consequently, considerable attention has been paid towards the development of techniques for removal of E2. Including biodegradation [6–8], ion exchange [9, 10] adsorption [11, 12], and photocatalysis [13, 14].
Although biodegradation could facilitate the decomposition of E2 into inorganic matter to some extent, the applications of the biodegradation were still limited due to the long the long time of degradation and the strict conditions for bacterial growth. On the contrary, ion exchange and adsorption technologies were also incapable to degrade E2.
Compared to these methods, photocatalysis is popularly regarded as most appropriate for E2 due to its high removal efficiency, shorter degradation period, and decomposable intermediates. In the photoreaction process, light irradiates the semiconductor, to cause the excitation of electrons from the Valence Band (VB) to the Conduction Band (CB), creating positively charged holes (h+) and negatively charged electrons (e−) available for photochemistry. This process also accelerated the photocatalysis process, where a catalyst promoted secondary photoreactions due to the formation of strong oxidizing capabilities of holes and reducing potentials of electrons .
Among the typical catalysts (e.g, TiO2, CeO2, ZnO, SnO2), TiO2 is widely used in the photocatalysis process as it is a chemically stable, low cost, and nontoxic material with promising reusability . Recently, significant attention has been paid towards heterogeneous doping of TiO2 to enhance adsorption under visible light irradiation by decreasing its band gap, and preventing the recombination of electrons and holes. However, several investigations utilized expensive heavy metals (e.g. Au, Ag, and Pt) as dopant [17, 18] to increase the overall cost and the pollution risk. Consequently, an environmentally friendly and biocompatible substitute, PN-TiO2, has been proposed for the photo decomposition of E2.
Regarding novel materials, Phosphorene (PN) is a novel Two-Dimensional (2D) material with a high current on/off ratio (~ 104 − 105) and high electron mobility (~ 200–1000 cm2 V− 1 s− 1) at room temperature [19–21]. Therefore, it can be used to dope TiO2, to enhance the excitation of electrons from VB to CB and inhibit electron-hole recombination, leading to the increased generation of hydroxyl radicals (•OH). Furthermore, Wang et al.  have reported that •OH and 1O2 could be generated when PN is irradiated with Ultraviolet (UV) and visible light, respectively. This strongly supported that PN is an electrochemically feasible photocatalyst. Therefore, photocatalytic performance of TiO2 may be improved if it is doped with PN. In addition, PN owns a large specific surface area  that aids the adsorption of contaminants onto the reactive sites at the surface of TiO2, significantly promoting the removal of E2.
In this study, PN was fabricated to mix with various amounts (0.5%, 1.0% and 3.0% weight) of PN and TiO2 using microwave heating to synthesize PN-TiO2 composites, (e.g, 0.5%PN-TiO2, 1.0%PN-TiO2, and 3.0%PN-TiO2). The degradation efficiencies of these composites are investigated to quantify the performance of E2 elimination. Although several studies [24–26] investigated the degradation efficiency of TiO2 or TiO2-based composites, the removal capacities were still low and the operation inevitably required strong illumination. In this study, only an 8 W UV light source was used to demonstrate treatability of effective photocatalysis with cost and energy-effectiveness. This study exhibited the most representative PN-based hybrid for elimination of hydrophobic and refractory pollutants in aqueous solutions.