Lingbo Zong

Hierarchical nanoscale multi-shell Au/CeO2 hollow spheres

Multi-shell ceria hollow spheres (MSCHSs) with a uniform size of ∼300 nm and controlled shell number up to quadruple were synthesized using carbonaceous spheres as the template in a process combining hydrothermally enhanced metal cation adsorption and tunable calcination. The featured sizes of these MSCHSs are in the hierarchical nanoscale region, including the diameters of the interior and exterior hollow spheres (80–300 nm), the thickness of the shells (∼30 nm), the distance between shells (<100 nm), and the pore size in the shells (∼4 nm), which meant that the as-synthesized MSCHSs possess not only a large specific surface area (∼90 m2 g−1) and narrow mesopore distribution, but also nanosized interconnected chambers. With these structural characteristics, the MSCHSs show fascinating capacities as good hosts for noble metals. Gold nanoparticles with sizes below 5 nm could be loaded on these MSCHSs with a high content and good dispersity to construct effective catalysts, which demonstrated a much improved catalytic performance in the reduction of p-nitrophenol. The optimal values of the reaction rate constant (k) reached up to 0.96 min−1. Moreover, this approach opens up a new way to form nanosized multi-shell structures, especially for those with large cation radii.

Precursor-induced fabrication of β-Bi2O3 microspheres and their performance as visible-light-driven photocatalysts

Flower-like β-Bi2O3 microspheres with high specific surface area and excellent visible-light-driven photocatalytic activity (for degradation of Rhodamine B) were successfully synthesized via a facile hydrothermal process and subsequent calcination. By precisely adjusting the hydrothermal conditions, the composition and morphology of the microspherical precursors could be well controlled, so that upon further optimized calcination of the precursors, the selective formation of the monoclinic α-Bi2O3 and tetragonal β-Bi2O3 with three dimensional (3D) hierarchical architectures could be achieved. These tetragonal β-Bi2O3 microspheres with an average diameter of 3 μm were constructed by nanoflakes with an average thickness of 50 nm, which, as far as we know, is the first reported result on the 3D hierarchical architectures of tetragonal β-Bi2O3. Its flower-like microspherical architecture made the tetragonal β-Bi2O3 possess not only much improved specific surface area but also a narrower band gap, which significantly enhanced its visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB). To further optimize the synthetic conditions and realize the controllable synthesis, the formation mechanism for the morphologies and polymorphs of the Bi2O3 microspheres was discussed in detail.

Multiple Au cores in CeO2 hollow spheres for the superior catalytic reduction of p-nitrophenol

In many catalytic systems the structure of the catalyst plays a crucial role in the reaction especially for catalytic reduction, organic pollutant oxidation and other organic transformations. Herein, we report a template-free approach to the synthesis of multiple Au cores in CeO2 hollow spheres (MACCHS). This material was fabricated by impregnating CeO2 hollow spheres with a HAuCl4 aqueous solution. NaBH4 was then used to reduce HAuCl4 to Au nanoparticles to form multiple Au cores in the CeO2 hollow spheres. We used MACCHS as a catalyst for p-nitrophenol reduction and achieved excellent activity. The catalyst showed enhanced stability toward p-nitrophenol reduction compared with bare Au nanoparticles and CeO2 hollow spheres. This simple method to achieve multi-core-in-shell hollow structures will likely have applications in various biological, medical and energy related fields.

Y2O3:Yb3+/Er3+ Hollow Spheres with Controlled Inner Structures and Enhanced Upconverted Photoluminescence

Multishell Y2 O3 :Yb(3+) /Er(3+) hollow spheres with uniform morphologies and controllable inner structures are prepared successfully by using a glucose-template hydrothermal process followed by temperature-programmed calcination. Much enhanced upconverted photoluminescence of these Y2 O3 :Yb(3+) /Er(3+) are observed, which are due to the multiple reflections and the enhanced light-harvesting efficiency of the NIR light resulting from the special features of the multishell structures.

Composite Yttrium-Carbonaceous Spheres Templated Multi-Shell YVO4 Hollow Spheres with Superior Upconversion Photoluminescence

Complex oxide YVO4 multi-shell hollow spheres with uniform morphologies and controllable shell numbers are successfully prepared by using a newly developed and general composite yttrium-carbonaceous sphere templated approach. The prominent upconversion luminous intensity of the YVO4 :Yb3+ /Er3+ hollow spheres might be attributed to the enhanced near-infrared excitation light harvesting efficiency originated from the multiple reflections.

Highly active CeO 2 hollow-shell spheres with Al doping

Metal oxide hollow structures are of great interest in many current and emerging areas of technology. This paper presents a facile and controlled protocol for the synthesis of Al-doped CeO2 hollow-shell spheres (CHS), where the dopant confers enhanced stability and activity to the material. These Al-doped CeO2 hollow-shell spheres (ACHS) possess a controllable shell number of up to three, where the sizes of the exterior, middle, and interior spheres were about 250‒100 nm,150‒50 nm, and 40‒10 nm, respectively, and the average shell thickness was ~15 nm. The thermal stability of the ACHS structure was enhanced by the homogeneous incorporation of Al atoms, andmore active oxygen species were present compared with those in the non-doped congener. Au NPs supported on ACHS (Au/ACHS) showed superior catalytic performance for the reduction of p-nitrophenol. For the same Au NP content, the reaction rate constant (k) of the Au/ACHS was nearly twice that of the non-doped Au/CHS, indicating that Al doping is promising for improving the performance of inert or unstable oxides as catalyst supports.摘要本文利用多孔碳球为模板, 通过竞争吸附控制煅烧法制备了铝掺杂的氧化铈多壳层空心球材料. 通过XRD、SEM、TEM对所得材料的结构、表面形貌以及热稳定性能进行了表征, 结果表明该方法制备的不同掺杂比例的多壳层空心球均一分散, 铝原子被均匀地分布到氧化铈的晶格中, 使其热稳定性得到提高. XPS结果表明铝的掺杂大大提高了材料中三价铈和表面氧空位的比例, 所以当其被作为催化剂载体时, 负载的金纳米粒子更加分散且与载体结合作用更强. 将该催化剂应用于硝基苯酚加氢反应, 其催化活性比未掺杂铝的样品提高了一倍.本文研究结果表明铝掺杂可以有效提高氧化铈催化剂的稳定性和活性; 竞争吸附控制煅烧法是制备空心掺杂材料的一种简单实用的方法.

Controlled synthesis of highly active Au/CeO2 nanotubes for CO oxidation

Uniform CeO2 nanotubes with smooth thin walls and high porosity were controllably synthesized using a simple well-controlled solvothermal technique. The growth of CeO2 nanotubes was explored and it was found that it followed the oriented attachment-Ostwald ripening mechanism. Furthermore, through an auto-redox process, gold nanoparticles of ∼5 nm size could be homogeneously generated on these CeO2 nanotubes. These novel nanocomposites exhibited outstanding performance in terms of both activity and stability for catalytic CO oxidation.

Low temperature molten salt synthesis of perovskite-type ACeO3(A=Sr, Ba) in eutectic NaCl-KCl

A molten salt method was developed for the synthesis of ACeO3(A=Sr, Ba) with perovskite structure at 750 °C(SrCeO3) and 850 °C(BaCeO3) in the eutectic NaCl-KCl. The synthetic temperature was much lower than that of the conventional method(generally>1000 °C). The structure and morphology of the product were characterized by means of X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM) and transmission electron microscopy(TEM). The results show that the synthesized octahedral SrCeO3 crystallizes in the orthorhombic system with the unit cell parameters of a=0.85855 nm, b=0.61523 nm, c=0.60059 nm, and the synthesized cuboid BaCeO3 crystallizes in the cubic system with the unit cell parameter of a=0.43962 nm. The result of X-ray photoelectron spectroscopy(XPS) analysis indicates that both Ce4+ and Ce3+ exist in the two structures, and the Ce4+/Ce3+ peak area ratios for SrCeO3 and BaCeO3 are 1.93 and 2.12, respectively. Meanwhile, the adsorbed/lattice oxygen ratios(1.87 for SrCeO3 and 3.04 for BaCeO3) indicate the existence of a lot of oxygen vacancies in the structures of SrCeO3 and BaCeO3, which indicates a far-reaching significance to study the corresponding physicochemistry performance.

Phase evolution and photoluminescence enhancement of CePO4 nanowires from a low phosphate concentration system

Uniform CePO4 nanowires have been successfully synthesized in a low phosphate concentration system through a single-step hydrothermal process. The low phosphate concentration might decrease the surface PO43− adsorption of the as-synthesized CePO4 nanowires efficiently and benefit their photoluminescence. The CePO4 nanowires were identified to go through phase evolution from pure monoclinic to mixed hexagonal and monoclinic phase by only increasing the initial molar ratio of cerium and phosphate source (denoted as Ce/P). Interestingly, the strongest photoluminescence was observed in the CePO4 nanowires synthesized with the initial Ce/P of 4:1, which proved to be the critical phase evolution point between the hexagonal and monoclinic CePO4. Therefore, the strong photoluminescence could be explained by the existence of the structure-sensitive energy level in the CePO4. This kind of photoluminescence enhancement would be a meaningful reference for design of other photoluminescent materials, in which the photoluminescent emission might be related to the structure-sensitive energy level. Additionally, the growth processes of CePO4 nanowires based on related well-designed experiments were proposed.