Preparation Of Novel Ceria Hollow Spheres And Their Application In Dye Adsorption And Photodegradation

Efficient visible-light-driven photocatalysts promote the industrial photocatalytic application. Therefore, they are focus area of photocatlytic material research. In recent years, inorganic hollow spheres are of burgeoning interest, principally because such hollow sphere can display novel and enhanced properties, such as well-defined morphology, uniform size, low density, large surface area and wide range of potential applications in visible-light-driven catalysis. In this study, with the soap free polymerization, monodisperse PSAA spheres were synthesized which are negatively charged by –COO- groups on the surface and they were further utilized as template to fabricate ceria hollow spheres and Ti O2@Ce O2 hollow spheres. Ceria hollow spheres have enhanced acid dye adsorption capacity. In addition, 3 dimensional macroporous ceria materials were fabricated. The as-obtained ceria samples have improved visible-light-driven photocatalytic activity. The research contents and results are as follows:(1) The preparation and characterization of ceria hollow spheres. PSAA spheres were used to synthesize ceria hollow spheres with yield improvement to 95%. The accumulation of inorganic solgel particles largely depends on the sol-gel system. The initiator of sol-gel system is the first important factor to control such accumulation. The feed of caustic soda with peristaltic pump provided uniform sol-gel system with satisfying results, which was proposed for scale up production of ceria hollow spheres. The amount of ceria precursor decided the thickness of sol particles accumulation. The temperature of sol-gel system has mild effect on the morphology of hollow spheres. The diameter and shell thickness are the result of diameter of polymeric template and the shell shrinkage during calcination of composite spheres. The BET area and shell porous structure are the function of the size of sol-gel particles, diameter and shell thickness of hollow spheres.(2) The application of ceria hollow spheres on dye adsorption and photodegradation. The as-obtained ceria hollow spheres has excellent dye adsorption capacity. In our investigation, ceria hollow spheres have superior acid dye adsorption capacity to activated carbon and ceria nanoparticles. For the adsorption of acid black, both pseudo-second-order model and Langmuir models fit well with the adsorption data. It is attributed to a good dispersion of ceria crystalline on the shell and the uniform distribution of active sites for dye molecule adsorption. Based on the Langmuir equation, the value of qm is calculated to be 140.2 mg g-1, which is greater than that in the literature of ceria materials with different morphologies. Additionally, ceria hollow spheres have good reusability for more than 6 times with limited dysfunction.The photodegradation of ceria hollow spheres was investigated under visible light. Ceria hollow spheres showed enhanced photocatalytic activity to Rhodamine B. Within 180 min, the ratio of photodegradation are 93%. The photocatalytic degradations performed under visible light do not follow pseudo-first-order reaction kinetics, in particular with auto-accelerated effect. The photodegradation efficiency of Rhodamine B is higher than ceria with different morphologies in the literature. The mechanism of ceria hollow spheres for dye degradation is that the exited electronhole pair under visible light generated oxygen radicals instead of hydrogen radicals under UV light. The movement of oxygen vacancies generated from exited holes inside ceria related to the temperature. The enhancement of photocatalytic activity of ceria hollow spheres is also attributed to the hollow sphere morphology, which provides the space for dye adsorption, degradation and release.(3) Double shelled Ti O2@Ce O2 hollow spheres fabrication and enhanced photocatalytic activity. The morphology of hollow spheres were controlled with well-defined shape of 290 nm in diameter and 18.8 nm for shell thickness. The as-obtained hollow spheres had strawberry like surface. Ti O2@Ce O2 hollow spheres with band gap of 2.7 e V exhibited a markedly enhanced photocatalytic activity under visible light irradiation. The maximum degradation of Rhodamine B is 0.738 mg g-1 min-1, much bigger than ceria in other morphologies. The enhanced photocatalytic performance was attributed to hollow sphere morphologies with a novel capture-photodegradationrelease and Ti O2@Ce O2 heterostructures with broad light wavelength absorption and energy band matching.(4) Fabrication of ceria macroporous materials and the photodegradation of Rhodamine B. The as-obtained 3 dimensional array of ceria hollow spheres had porous structure with macro holes and interconnected windows. It is a potential candidate for industrial catalyst. The attractiveness is that this method is simple, direct and suitable for industrial scale production. With PSAA spheres, colloidal crystal template was first prepared by vertical deposition. Afterwards, it was impregnated in ceria precursor sol-gel solution, and finally ceria inverse opal was fabricated with 3 dimensional ordered microporous structure. The as-obtained ceria inverse opal has band gap of 2.63 e V, corresponding to 471 nm, with enhance light adsorption. The performance of the dye degradation were superior to ceria hollow spheres. The ceria inverse opal had better enhanced photocatalytic activity due to the 3D ordered structure, which moved adsorption edge to visible light region and offered big space and surface area to mass transportation during catalytic reaction. The slow photon effect of inverse opal structure contributed to band gap movement towards visible light region, which cannot be achieved by nano-size effect of ceria crystallite.