Xuebing Xing

Tunable high-performance microwave absorption for manganese dioxides by one-step Co doping modification

The frequencies of microwave absorption can be affected by the permanent electric dipole moment which could be adjusted by modifying the crystal symmetry of the microwave absorbing materials. Herein, we corroborate this strategy experimentally and computationally to the microwave absorption of manganese dioxides. Nanosized Co-doped cryptomelane (Co-Cryp) was successfully synthesized by a one-step reaction. The introduction of Co(III) induced a change of crystal symmetry from tetragonal to monlclinic, which could lead to an increase of its permanent electric dipole moment. As a result, the frequencies of maximum microwave absorption were regulated in the range of 7.4 to 13.9 GHz with a broadened bandwidths. The results suggested that microwave absorption of manganese dioxides can be tailored with Co doping to expand their potential uses for abatement of various microwave pollutions.

Removal of Chlorpheniramine from Water by Birnessite

With more and more emerging organic contaminants (EOCs) detected in the soil and groundwater, researches on interactions between these pollutants and soils or aquifer materials have attracted greater concerns. In this study, the removal of chlorpheniramine maleate (CP), an antihistamine drug used to treat rhinitis and urticaria, by birnessite, which is a common layered manganese oxide, in aqueous solution was investigated by batch studies, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses, and molecular simulations. The quantum mechanics simulation showed that the final energy of the interaction between CP and the (010) edge surfaces under a strong alkaline condition was much smaller than that under a neutral to slightly alkaline condition. A higher CP adsorption were achieved from neutral to weak alkaline solution, as the broken bond effect of birnessite was strongly influenced by solution pH by protonation and deprotonation of birnessite edges.

Synthesis of Cu and Ni chalcogenides and evaluation of their properties for electromagnetic wave absorption

Cu and Ni chalcogenides were synthesized by hydrothermal methods and characterized by XRD and SEM. Their properties on electromagnetic (EM) wave absorption were evaluated by a vector network analyzer with a coaxial measurement. For the Cu7.2S4 and Cu2Se–paraffin systems, the peak for minimum reflection loss (RL) shifted from high frequency to low frequency as the thickness increases. At a thickness of 1.6 mm, the Cu7.2S4–paraffin composite could achieve a RL value of −36.60 dB at the absorption peak frequency (APF) of 17.2 GHz with a bandwidth of 6 GHz for RL < −10 dB. For the Cu2Se–paraffin composite, the RL value, APF, and bandwidth were −27.5 dB, 11.76 GHz, and 3 GHz, respectively, at a thickness of 1.5 mm. For the NiO, NiS, and NiSe–paraffin composite systems, the APF for minimal RL moved from high to low frequency as the thickness increases, too. The NiO–paraffin had a RL of −12.68 dB at the APF of 12.8 GHz when the thickness of the sample was 2 mm. For the NiS–paraffin composite, the RL value, APF, and bandwidth were −31.93 dB, 7.52 GHz, and 2 GHz, respectively, with a thickness of 3 mm, while the NiSe–paraffin composite had a RL value, APF, and bandwidth of −41.22 dB, 8.24 GHz, and 1.6 GHz, respectively, with a thickness of 2.2 mm. All Cu and Ni chalcogenides had excellent EM reflection loss, enabling them to be excellent microwave absorbing materials. And most importantly, our results were the first to report superior EM absorption properties for selenides.

Adsorption of Atenolol on Kaolinite

In this study the adsorption of atenolol (AT), a -blocker, on kaolinite, a clay mineral of low surface charge, was investigated under varying initial AT concentration, equilibrium time, solution pH, ionic strength, and temperature conditions. The results showed that the amounts of AT uptake by kaolinite were close to its cation exchange capacity value and the AT adsorption was almost instantaneous, suggesting a surface adsorption. The adsorption was exothermic and the free energy of adsorption was small negative, indicating physical adsorption. The increase in ionic strength of the solution drastically reduced AT uptake on kaolinite. A significant reduction in AT uptake was found at solution pH below 5 or above 10. The FTIR results showed band shifting and disappearance for NH bending vibration and benzene ring skeletal vibration at 3360 and 1515 cm−1 and band splitting at 1412 and 1240 cm−1 attributed to C–N valence vibration coupled with NH bending vibrations and alkyl aryl ether linkage, suggesting the participation of NH, –O–, and benzene ring for AT adsorption on kaolinite.

Controllable adjustment of the crystal symmetry of K–MnO2 and its influence on the frequency of microwave absorption

Microwave (MW) is becoming an important polluter. Because of its wide frequency range in electromagnetic radiation, finding or developing materials with high efficiencies to absorb and attenuate MW is one of the most urgent research areas in material science. In developing this type of material, the ability to efficiently absorb MW in a wide frequency range is critical. In this study, Fe(III) was doped in nanosized cryptomelane (K–MnO2) to achieve MW absorption in an adjustable frequency range. Rietveld refinement of powder X-ray diffraction patterns and X-ray photoelectron spectroscopic results confirmed the presence of Fe(III) as partial substitute for Mn(III) and Mn(II) in the [MnO6] octahedra of K–MnO2. Electron microscopic observations showed a progressive change of morphology from nanofibrous into micrometer-sized prismatic crystals as Fe(III) doping increased. The lattice images of high-resolution transmission electron microscopy (HRTEM) showed a d-spacing of 0.71 nm for (110) of tetragonal Fe–K–MnO2, while a d-spacing of 0.56 nm corresponded to (200) of monoclinic Fe–K–MnO2. The frequency band of MW attenuation expanded and displayed a blue shift as the Fe(III) doping increased. Such a tunable property suggests that K–MnO2 and possibly other manganese dioxides could be customized to reduce potential hazards from a wider range of MW sources.

Adsorption Mechanism of Ciprofloxacin from Water by Synthesized Birnessite

The efficiency of ciprofloxacin (CIP) adsorption on synthesized birnessite was systematically studied under varying physicochemical conditions, such as solution pH, contact time, initial CIP concentration, and different average oxidation states (AOS) of Mn in birnessite. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and molecular simulations were employed to investigate the adsorption mechanism of CIP on birnessite. Experimental results showed that surface adsorption instead of cation exchange was responsible for the uptake of CIP on birnessite. The quantum mechanics simulation showed that the final energy of the interaction between CIP and birnessite was smaller under the condition when the AOS of Mn was lower, in comparison to the case when the AOS of Mn was high. The highest CIP adsorption occurred under a weak alkaline condition.

Degradation of Tetracycline by Birnessite under Microwave Irradiation

The efficiency and factors affecting tetracycline (TC) degradation by birnessite under microwave irradiation (MI) were investigated under different initial TC concentrations, solution pH, MI time, and MI power. The crystal structure, degradation efficiency, and reaction mechanism were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-Vis). The results showed that birnessite was an excellent microwave catalyst. The maximum TC removal efficiency by birnessite was 99% under MI at 400 W for 30 min in strongly acidic media. Under MI, the surface activity of birnessite increased, resulting in the ability to accelerate TC removal in high temperature.