Utilization of Carbon Nanospheres in Photocatalyst Production: From Composites to Highly Active Hollow Structures

Abstract

Titanium dioxide–carbon sphere (TiO2–CS) composites were constructed via using prefabricated carbon spheres as templates. By the removal of template from the TiO2–CS, TiO2 hollow structures (HS) were synthesized. The CS templates were prepared by the hydrothermal treatment of ordinary table sugar (sucrose). TiO2–HSs were obtained by removing CSs with calcination. Our own sensitized TiO2 was used for coating the CSs. The structure of the CSs, TiO2–CS composites, and TiO2–HSs were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The effect of various synthesis parameters (purification method of CSs, precursor quantity, and applied furnace) on the morphology was investigated. The photocatalytic activity was investigated by phenol model pollutant degradation under visible light irradiation (λ > 400 nm). It was established that the composite samples possess lower crystallinity and photocatalytic activity compared to TiO2 hollow structures. Based on XPS measurements, the carbon content on the surface of the TiO2–HS exerts an adverse effect on the photocatalytic performance. The synthesis parameters were optimized and the TiO2–HS specimen having the best absolute and surface normalized photocatalytic efficiency was identified. The superior properties were explained in terms of its unique morphology and surface properties. The stability of this TiO2–HS was investigated via XRD and SEM measurements after three consecutive phenol degradation tests, and it was found to be highly stable as it entirely retained its crystal phase composition, morphology and photocatalytic activity.

Unexpected Link between the Template Purification Solvent and the Structure of Titanium Dioxide Hollow Spheres

“…In our previous publication, we demonstrated that not only the synthesis conditions of TiO2 coating but also that the parameters applied during the preparation of CSs can significantly affect the properties of the resulting titania [21]. In this paper, we present the importance of the purification solvent by using either acetone or ethanol to eliminate the residual organic contaminants formed during the synthesis of CSs, since it was observed that this parameter might be the most crucial of all in our system.…”

Carbon Sphere Template Derived Hollow Nanostructure for Photocatalysis and Gas Sensing

“…Carbon spheres have been widely researched and applied to various fields-including batteries, photocatalysis, capacitors, and fuel cells-due to their easily available sources and facile synthesis. The last few decades have witnessed a rapid growth in sustainable energy field and this has led to the research of various application and approaches of carbon spheres, including carbonization routes [29], chemical vapor deposition (CVD) [30], ultrasonic-spray [31], and hydrothermal carbonization (HTC) [6,32,33]. Among these methods, hydrothermal carbonization is the one that aroused the greatest interest due to its facile procedure and mild experimental condition.…”

“…This is the critical superiority when carbon spheres are applied as templates. Moreover, many researchers are focusing on a wide range of source to obtain carbon spheres by hydrothermal reaction, including general monosaccharide (xylose [38], glucose [38]), disaccharides (sucrose [6,38], lactose [39]), polysaccharides (starch [40,41], cellulose [42]), and some biomasses [39]. The possible formation procedure is shown schematically in Figure 2.…”

“…In 2001, Zou et al [3] first discovered In 1-x Ni x TaO 4 photocatalyst with visible light activity for photolytic water splitting. The past two decades, various kinds of semiconductor photocatalysts have been widely studied, such as oxides [4][5][6][7][8][9], sulfides [10][11][12][13][14], nitrides [15][16][17][18], carbides [15,[19][20][21], etc. Domen's recent studies based on particulate photocatalyst sheets provide a possible way for the large-scale and practical photocatalytic water splitting [22][23][24].…”

Enhancement of photocatalytic activity of titanium dioxide-based photocatalysts

“…not crystalline) carbon was used [220][221][222]. Conversely, the hollow spherical morphology can enhance the photocatalytic activity via enhancing the light trapping properties of the photocatalyst [21,73,99,146,155,160,161].…”