Effects of the Atmosphere in a Hydrothermal Process on the Morphology and Photocatalytic Activity of Cerium Oxide

Abstract

The hydrothermal method is widely applied in nanomaterials synthesis, and most of the influencing factors have already been taken into account. However, the effect of atmosphere in solution on the performance of nanomaterials has been underestimated for a long time. In this article, reaction solvents were saturated with three classical gases (argon, oxygen, and carbon dioxide), and then heated at 180 8C for 24 h to obtain the cerium dioxide (CeO 2 ) nanoparticles. The properties of the three types of CeO 2 are significantly different from that of the normal CeO 2 (without gas saturation). The morphologies of the prepared CeO 2 particles are different, even appear the hollow structure in CeO 2 ÀCO 2 (synthesized in CO 2 saturated condition). The more absorbing and meaningful thing is that the photocatalytic activity of CeO 2 ÀCO 2 has been greatly improved. The concordance of the CO 2 atmosphere (acid gas) and CeO 2 (owning substantial content of basic sites) is the key point for the excellent photocatalytic performance.Cerium oxide (CeO 2 ) is one of the most important earth metal oxides. Due to the unique optical, electrical, magnetic properties and the oxygen storage capacity (OSC) of CeO 2 nanomaterials, [1] they have been used in various applications, in industrial and commercial fields, including solid oxide fuel cells (SOFCs), [2] purification of automobile exhaust, [3] abrasives for chemical mechanical polishing (CMP), [4] and photocatalysis. [5,6] In order to obtain nanoscale CeO 2 materials, researchers have explored a lot of synthesis strategies, including ball milling, electrochemical, templates assisted, sol-gel, hydrothermal, chemical vapor, and other methods. [1] A hydrothermal method is also suitable for the growth of good-quality crystals because this method over other types of crystal growth is the ability to create crystalline phases which are not stable at the melting point. A hydrothermal reaction is governed by various chemical and thermodynamic parameters, involving chemical composition of the precursor, [7] kind of solvent, [5] pH value of the reaction medium, [8] reaction temperature, duration of reaction, and pressure. Moreover, other associated technologies, such as microwaves, electrochemistry, external magnetic field, and ultrasound, have been employed However, an important factor in a hydrothermal process, the atmosphere of the solution, may be ignored by people. For a long time, the effect of the atmosphere on the hydrothermal process has been underestimated due to its extremely little content in the solution. Nevertheless, the solution in a hydrothermal process is boiling or gas phase. The atmosphere will have a significant effect on the final products. If the precursors and solvent are matched with the selected gas (Gas can be strongly absorbed on the precursors or solvent.), the crystal growth process would be altered and further affect their morphologies and performances.Herein, we selected three typical gases, argon, oxygen and carbon dioxide, to determine the relationship betwe...

Design and Synthesis of Sm, Y, La and Nd‐doped CeO2 with a broom‐like hierarchical structure: a photocatalyst with enhanced oxidation performance

“…The SC photocatalyst as‐fabricated in this paper shows much higher activity for CH 3 CHO (340 ppm) oxidation than the activities of commercial metal oxide photocatalysts such as TiO 2 (21 ppm), S‐doped TiO 2 (150 ppm) and WO 3 (200 ppm) . It also shows much higher activity than the other CeO 2 photocatalysts with different morphologies including nanoparticles (200 ppm), hedgehog‐like (140 ppm), confeito‐like (100 ppm) and octahedral structures (80 ppm) …”

“…It may due to the substitution process can compensate for the charge generated by doping and promote the formation of oxygen vacancies in defective structured CeO 2 . And these vivacious O v , acting as a trapping center for photo‐generated electrons, formed a doping transition state between the conduction band (CB) and valence band (VB), and limited the recombination rate of electrons and holes significantly, leading to an outstanding improvement of photooxidation performance effectively . Therefore, it provides a forceful evidence to speculate that RE‐doped CeO 2 should have higher photocatalytic activity …”

“…Previous studies have shown that morphology and size control, doping of various metal ions, and heterojunction coupling are three common strategies for enhancing the photocatalytic performance of CeO 2 ‐based materials . The morphology of CeO 2 plays a major role in its photocatalytic performance, and our research group has successfully fabricated a series of high‐performance CeO 2 photocatalysts with different morphologies and superior performances including porous broom‐like, hedgehog‐like, confeito‐like and hollow octahedral structures . Difference in morphology and size can determine the specific surface area, active sites and separation of redox crystal facets, which are related to improvement of photocatalytic performance.…”

Nitrogen and sulfur co-doped CeO2 nanorods for efficient photocatalytic VOCs degradation

“…[1][2][3][4] Photocatalysis technology has been well recognized as a promising solution and the use of photocatalysis technology is expected to increase. [5][6][7][8] Previous investigations of photocatalysts have mainly focused on traditional titanium dioxide (TiO 2 ), but its practical application has been seriously hindered by its wide band gap and low visible light absorption. Cerium oxide (CeO 2 ) belongs to traditional n-type semiconductors with a relatively flexible conversion ability between trivalent and tetravalent cerium oxidation states.…”

Synthesis and Characterization of the Orthorhombic Sn3O4 Polymorph

“…As reported in studies of ZnO and CeO 2 , altering the gas composition resulted in differences in the oxygen vacancies and catalytic activity. [12,13] Therefore, we assumed that these parameters would also influence the synthesis of metastable tin oxide. By tuning the degree of filling of the precursor solution and the gas composition of the reaction system, we successfully synthesize an unreported phase of tin oxide, which is similar to the orthorhombic SnPb 2 O 4 phase.…”