Channel: RESEARCH ARTICLE http://www.jim.org.cn EN-US http://www.jim.org.cn/EN/1000-324X/current.shtml http://www.jim.org.cn 1000-324X http://www.jim.org.cn/EN/10.15541/jim20200358 The inherent poor stability of CsPbBr₃ perovskite quantum dots (QDs) is the main impediment restricting their applications. In this work, a CsPbBr₃@TiO₂ core-shell structure nanocomposite with high water stability and efficient photocatalytic activity was fabricated through the hydrolysis of tetrabutyl titanate, followed by calcination. The as-prepared CsPbBr₃ QDs have a size of ca. 8 nm, encapsulated by incompletely crystallized TiO₂ protective layer with a thickness of ca. 20 nm. The photocatalytic performance of the CsPbBr₃@TiO₂ nanocomposite was investigated by degradation of Rhodamine B (RhB) in water under visible light irradiation. The result shows that the CsPbBr₃@TiO₂ nanocomposite exhibits much more enhanced photocatalytic activity than pure TiO₂ and CsPbBr₃ perovskite quantum dots. The photocurrent test results showed that the formation of the CsPbBr₃@TiO₂ heterostructure can promote the separation of photogenerated carriers, which led to the improvement of photocatalytic performance of the composite material. More importantly, TiO₂ can act as a protective layer to separate CsPbBr₃ from water, which brings about the high water stability of the CsPbBr₃@TiO₂ nanocomposite. After photocatalytic degradation of pollutants, the recovered CsPbBr₃@TiO₂ nanocomposite retained its original morphology, luminescent and photocatalytic properties.

]]> http://www.jim.org.cn/EN/10.15541/jim20200383 Exploration of pressure-resistant materials largely facilitates the operation under extreme conditions where the stable structure and properties are highly desirable. Magic-sized nanocrystals (MSNs) are of great interest due to their well-defined structure, ultra-small particle size, and precise atomic composition. Here, we reported the colloidal synthesis of CdSe MSNs with a sharp first exciton absorption peak at 463 nm. The corresponding photoluminescence (PL) spectrum exhibited a very narrow full width at half-maximum (FWHM) of about 13 nm. In situ high-pressure evolutions of PL and absorption unambiguously indicated that the peak position of as-prepared CdSe MSNs kept nearly unchanged with the pressure increasing. This behavior was completely different from conventional materials upon the stimulus of external pressure. Furthermore, the decompressed samples retained the original structure and morphology of CdSe MSNs. The properties of good pressure resistance of the CdSe MSNs are reflected in the process of pressurization, which improves the research of the magic-sized materials under extreme pressure.

]]> http://www.jim.org.cn/EN/10.15541/jim20200346 By employing density functional theory calculations, the mechanical, electronic and piezoelectric properties of graphene-like monolayers ZnO (g-ZnO) and GaN (g-GaN) were investigated. Elastic stiffness constants and piezoelectric tensors of monolayers g-ZnO and g-GaN using their Clamped-ion and Relaxed-ion components were mainly studied. Results indicate that these two graphene-like structures are semiconductors with excellent elasticity. The piezoelectric coefficient of monolayers g-ZnO and g-GaN are about 9.4 and 2.2 pm路V^-1, respectively, implying their piezoelectric effect in extremely thin film devices, especially the g-ZnO. The remarkable piezoelectricity of monolayer g-ZnO enables it a wide range of applications, such as mechanical stress sensors, actuators, transducer and energy harvesting devices.

]]> http://www.jim.org.cn/EN/10.15541/jim20200421 The dense ceramic oxygen-permeable membrane has attracted much attention due to its potential applications in production of oxygen from air and manipulation of oxygen-consuming industrial chemical processes. In the present study, Gd_0.1Ce_0.9O_2-未-La_0.6Sr_0.4FeO_3-未 (GDC-LSF) dual-phase composite membrane was prepared using the phase-inversion tape casting/lamination/sintering method. The as-prepared membrane consisted of an 80 渭m thick dense oxygen separation layer sandwiched between two 420 渭m thick finger-like porous support layers. The inner surface of the support layers was further modified with Nd₂NiO_4+未 (NNO) nanoparticles using the impregnation method. An oxygen permeation flux of 1.53 mL路cm^-2路min^-1 was measured at 900 鈩� by exposing one side of the membrane to a flowing air stream and the other side to a flowing He stream. When CO₂ was used as sweep gas, an oxygen permeation flux of 0.6 mL路cm^-2路min^-1 was obtained, and no decrease in the flux was observed during 90 h of testing. The membrane remained intact after experiencing over 70 thermal cycles between 800 and 900 鈩�. GDC-LSF dual-phase composite membrane with straight pores and sandwich structure has demonstrated satisfactory combination of oxygen permeability, chemical stability and thermal mechanical strength, promising for applications in separation of oxygen from air and oxy-fuel combustion with CO₂ capture.

]]> http://www.jim.org.cn/EN/10.15541/jim20200386 Mn⁴⁺ activated red phosphor is one of the current research hot-spots in the field of white light emitting diodes (wLEDs). The shortest emission of Mn^{4+ 2}E鈫�⁴A₂ transition in aluminate is 651 nm realized in MgAl₂O₄, but the doped manganese ions exists in multiple valence states (+2/+4/+3, etc.) due to the fact that there exist two cationic sites (Mg²⁺/Al³⁺) forming tetrahedron or octahedron coordination in the spinel structure. In this study, variation of the Al₂O₃ polymorphs (纬/伪 ratio) in the starting materials and post-annealing were used to control the doping sites and valence state of manganese ions in the MgAl₂O₄ structure. The results show that a high 伪/(伪+纬) ratio of starting Al₂O₃ favors the formation of Mn²⁺ while a low 伪/(伪+纬) ratio of starting Al₂O₃ favors the formation of Mn⁴⁺ dopant. By using highly active nano-纬-Al₂O₃ as the Al³⁺-bearing source, the occupancy of manganese ions in the Mg²⁺ site and the formation of Mn²⁺ valence state were effectively suppressed. Bright and pure MgAl₂O₄:Mn⁴⁺ phosphors in which only the red luminescence from Mn⁴⁺ was observed in the visible spectral region were successfully prepared via once heat treatment at 1550 鈩� for 5 h in air. The intrinsic reason for the dependence of manganese doping valence state on the Al₂O₃ polymorph lies in that the reactivity of Al₂O₃ determined the sequences of doping reactions and then the doping site/valence of manganese ions in MgAl₂O₄:Mn. All the above data demonstrated that the control of reaction sequences was a new method to regulate the valence state of manganese in aluminate phosphors.

]]> http://www.jim.org.cn/EN/10.15541/jim20200389 Photo-thermal-refractive (PTR) glass was irradiated with 纬-ray at the total dose of 0.35, 1, 10 and 100 kGy, respectively, and then annealed. Irradiation mechanism of the photo-thermal-refractive glass was studied by absorption spectroscope, luminescence spectroscope and electron paramagnetic resonance. The results showed that the absorption of the 纬-irradiated PTR glass in the visible light was mainly caused by the Ag⁰, silver molecular clusters Ag₂, Ag₃, silver nanoparticles Ag_m⁰, and non-bridge oxygen hole center HC₁ and HC₂. Under different doses of 纬-ray irradiation, valence state of the ions (Ag⁺, Ce³⁺) in the glass matrix changed. At the same time, non-bridged oxygen bonds in the glass matrix broke, generating non-bridged oxygen hole defects HC₁, HC₂ and Ag⁰. With the increase of the radiation dose, silver molecular clusters Ag₂ and Ag₃ generated, and the concentration of HC₂ center in the glass matrix increased, resulting in enhanced absorption near 639 nm. After being irradiated and annealed at 250 鈩�, HC₁ and HC₂ defect centers was bleached. Silver molecules appeared after annealing at 430 鈩�, of which absorption peak had a redshift and was broadened with the increase of annealing duration.

]]> http://www.jim.org.cn/EN/10.15541/jim20200396 Due to efficient performance and stability, nanozymes have recently attracted much attention in bioreaction. In this work, a facile approach for preparing N-doped hollow carbon sheres (N-HCSs) by using CaCO₃ spheres as green template and polydoamine as nitrogen and carbon sources was reported. Morphologies and structures of the samples were characterized. Using TMB (3,3,5,5掳 tetramethylbenzidine) as a substrate, UV spectra photometry was used to investigate its oxidase-like activity and catalytic mechanism. The results showed that N-HCSs displayed oxidase-like activity. The oxidase-like activity of N-HCSs increased by three times after activation by KOH. These enzymes conform to the Michaelis-Menten kinetic equation, and the K_m constant before and after activation were 0.105 and 0.083, respectively, indicating good affinity for substrates. The data demonstrate that it is superoxide anion (O₂? ^-) that plays a major role in catalytic reaction. This work data provides a theoretical basis for the design and preparation of high activity oxidase-mimicking enzymes.

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