Evaluation of Fe3O4-MnO2@RGO magnetic nanocomposite as an effective persulfate activator and metal adsorbent in aqueous solution.

A reduced graphene oxide (RGO) supported Fe3O4-MnO2 nanocomposite (Fe3O4-MnO2@RGO) was successfully prepared for catalytic degradation of oxytetracycline (20 mg/L) by potassium persulfate (PS) and adsorption removal of mixture of Pb2+, Cu2+, and Cd2+ ions (each 0.2 mM) in the synchronous scenario. The removal efficiencies of oxytetracycline, Pb2+, Cu2+, and Cd2+ ions were observed as high as 100%, 99.9%, 99.8%, and 99.8%, respectively, under the conditions of [PS]0 = 4 mM, pH0 = 7.0, Fe3O4-MnO2@RGO dosage = 0.8 g/L, reaction time = 90 min. The ternary composite exhibited higher oxytetracycline degradation/mineralization efficiency, greater metal adsorption capacity (Cd2+ 104.1 mg/g, Pb2+ 206.8 mg/g, Cu2+ 70.2 mg/g), and better PS utilization (62.6%) than its unary and binary counterparts including RGO, Fe3O4, Fe3O4@RGO, and Fe3O4-MnO2. More importantly, the ternary composite had good magnetic recoverability and excellent reusability. Notably, Fe, Mn, and RGO could play a synergistic role in the improvement of pollutant removal. Quenching results indicate that surface bounded SO4•- was the major contributor to oxytetracycline decomposition, and the -OH groups on the composite surface shouldered a significant role in PS activation. The results indicate that the magnetic Fe3O4-MnO2@RGO nanocomposite has a good potential for removing organic-metal co-contaminants in waterbody.

The tunable bandgap effect of SnS films.

Two-dimensional (2D) SnS has attracted much attention as a phosphorene analogue due to the promising applications in next-generation nanoelectronic and photovoltaic devices. It has a bandgap of 1.3 eV, which is matched very well with incident solar radiation. To improve the switching character of devices, it is significant to modulate the bandgap of 2D SnS. In this work, potassium ion (K+) or calcium ion (Ca2+) is absorbed on the top surface of SnS films to produce an electric field, by which the bandgap can be tuned effectively. By first-principles method we studied the electronic properties and the modulation mechanism of bandgap in detail. The calculated ionization energy and formation energy are 0.41 eV and 0.26 eV for K (1.33 eV and 1.07 eV for Ca). Such little values indicate that it is feasible for ion absorbed on the surface to be used to modulate the bandgap of SnS films. Our calculations also show that the carrier mobility in plane of SnS films has a character of strong anisotropy and the electron mobility is very high in y direction (25.22 × 103 cm2 V-1 s-1 for SnS trilayer). Therefore 2D SnS has potential application in nanoelectronic and photovoltaic devices in the future. We hope our results will motivate experimental efforts of 2D SnS.