Enhancement of Ce/Cr Codopant Solubility and Chemical Homogeneity in TiO₂ Nanoparticles through Sol–Gel versus Pechini Syntheses

Abstract

Ce/Cr codoped TiO nanoparticles were synthesized using sol-gel and Pechini methods with heat treatment at 400 °C for 4 h. A conventional sol-gel process produced well-crystallized anatase, while Pechini synthesis yielded less-ordered mixed-phase anatase + rutile; this suggests that the latter method enhances Ce solubility and increases chemical homogeneity but destabilizes the TiO lattice. Greater structural disruption from the decomposition of the Pechini precursor formed more open agglomerated morphologies, while the lower levels of structural disruption from pyrolysis of the dried sol-gel precursor resulted in denser agglomerates of lower surface areas. Codoping and associated destabilization of the lattice reduced the binding energies in both powders. Cr formation in sol-gel powders and Cr formation in Pechini powders suggest that these valence changes derive from synergistic electron exchange from intervalence and/or multivalence charge transfer. Since Ce is too large to allow either substitutional or interstitial solid solubility, the concept of integrated solubility is introduced, in which the Ti site and an adjacent interstice are occupied by the large Ce ion. The photocatalytic performance data show that codoping was detrimental owing to the effects of reduced crystallinity from lattice destabilization and surface area. Two regimes of mechanistic behavior are seen, which are attributed to the unsaturated solid solutions at lower codopant levels and supersaturated solid solutions at higher levels. The present work demonstrates that the Pechini method offers a processing technique that is superior to sol-gel because the former facilitates solid solubility and consequent chemical homogeneity.

Design strategies for ceria nanomaterials: untangling key mechanistic concepts

“…7,55 Intervalence charge transfer (IVCT), involving electron exchange between dopant and matrix ions or between codopant ions, and multivalence charge transfer (MVCT), involving electron exchange between multiple-dopant ions and matrix ions, both without defect formation otherwise, represent underappreciated means of explaining valence changes. [56][57][58][59][60][61][62][63][64][65][66][67][68][69] Three types of colour centres (F 0 , F + , F ++ ) have been suggested by modelling 70 and validated experimentally for pure CeO 2Àx . 71 While, the latter were generated at room temperature, high-energy irradiation often is required to create the Schottky pairs that are involved in the generation of such F-centres.…”

Synthesis and Photocatalytic Activity of Cerium‐Modified CdS‐TiO2 Photocatalyst for the Formaldehyde Degradation at Room Temperature

“…The intensity of the crystalline peaks of CdS slightly enhanced when the Ce(NO 3 ) 3 · 6H 2 O/butyl titanate mass ratio was 1.5 wt % , . However, when the Ce(NO 3 ) 3 · 6H 2 O/butyl titanate mass ratio was 2.1 wt %, the pattern of Ce‐CdS‐TiO 2 showed a weak diffraction peak at 2 θ = 25.28, and the results of the performance test showed that the photocatalytic performance of the catalyst was adversely affected by reduced crystallinity …”

A comparison of syntheses approaches towards functional polycrystalline silicate ceramics

“…A type of sol-gel approach, named after its inventor Maggio Pechini (P) [24], was chosen as a soft chemistry route to achieve a homogenous powder product on a molecular level. This type of sol-gel synthesis was chosen as the steric entrapment afforded by the chelation-polymerisation pathway is known to facilitate homogeneity in oxide systems with multiple cation sites [25,26]. A total metal ions: citric acid: ethylene glycol molar ratio of 1:6:6 was used in this work.…”