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138 results on '"Chen, Wen-Fan"'

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

Author

Chen, Wen-Fan, Mofarah, Sajjad S., Hanaor, Dorian Amir Henry, Koshy, Pramod, Chen, Hsin-Kai, Jiang, Yue, and Sorrell, Charles Christopher

Subjects
Condensed Matter - Materials Science
Abstract

Ce/Cr codoped TiO2 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 and rutile; this suggests that the latter method enhances Ce solubility and increases chemical homogeneity but destabilizes the TiO2 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. Cr4+ formation in sol gel powders and Cr6+ 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.

Published
2022
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20. Bioceramics in the CaMgSi2O6–Li2O System: A Glass-Ceramic Strategy for Excellent Mechanical Strength and Enhanced Bioactivity by Spontaneous Elemental Redistribution

Author

Tseng, Yu‐Sheng, Su, Yun‐Han, Chen, Chia‐Lin, Zhang, Ji, Wang, Chih‐Kuang, Hanaor, Dorian Amir Henry, and Chen, Wen‐Fan

Subjects
bioactivities, lithium oxides, diopside, mechanical properties, 500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften
Abstract

A novel glass-ceramic strategy for synthesizing mixed phase diopside (CaMgSi2O6)–lithium oxide (Li2O) bioceramics with excellent mechanical strength, superior biodegradation resistance, low environmental pH impact, enhanced bioactivity, and reasonable biocompatibility is developed for biomedical applications. The substitution of Li2O for MgO in CaMgSi2O6 stimulates the formation of secondary phases: CaSiO3, Li2Si2O5, SiO2, Li2SiO3, and Li2Ca2Si5O13. The evolution of CaSiO3 improves the surface hydroxyapatite (HAp) formation but lowers the mechanical strength and biological resistance, while the amorphous Li2Si2O5 phase tremendously reinforces the bioceramics by densifying the microstructure, indicating the simultaneous enhancement of bioactivity, mechanical strength, and durability. The promoted HAp formation is induced by the elemental redistribution where Mg elements are concentrated in large CaMgSi2O6 grains embedded in Li2Si2O5 amorphous matrix, which hinders the Mg2+ release and its readsorption by HAp. The cell viability is affected by Li2O substitution because of the high-dose Li+. In the current work, Li0.25 (25 mol% Li2O) has the highest hardness (700 Hv as sintered and 197 Hv after simulated body fluid soaking), lowest weight loss (≈0.6 wt%), lowest pH variation (≈8.1), efficient HAp formation, and reasonable cell viability (70.5%), demonstrating its remarkable potential for bone implant applications due to the synergistic structural densification and biological improvement.

Published
2023
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24. Bioceramics in the CaMgSi2O6–Li2O System: A Glass‐Ceramic Strategy for Excellent Mechanical Strength and Enhanced Bioactivity by Spontaneous Elemental Redistribution.

Author

Tseng, Yu‐Sheng, Su, Yun‐Han, Chen, Chia‐Lin, Zhang, Ji, Wang, Chih‐Kuang, Hanaor, Dorian Amir Henry, and Chen, Wen‐Fan

Subjects
BIOCERAMICS, BODY fluids, WEIGHT loss, CELL survival, DIOPSIDE, CERAMICS, HYDROXYAPATITE
Abstract

A novel glass‐ceramic strategy for synthesizing mixed phase diopside (CaMgSi2O6)–lithium oxide (Li2O) bioceramics with excellent mechanical strength, superior biodegradation resistance, low environmental pH impact, enhanced bioactivity, and reasonable biocompatibility is developed for biomedical applications. The substitution of Li2O for MgO in CaMgSi2O6 stimulates the formation of secondary phases: CaSiO3, Li2Si2O5, SiO2, Li2SiO3, and Li2Ca2Si5O13. The evolution of CaSiO3 improves the surface hydroxyapatite (HAp) formation but lowers the mechanical strength and biological resistance, while the amorphous Li2Si2O5 phase tremendously reinforces the bioceramics by densifying the microstructure, indicating the simultaneous enhancement of bioactivity, mechanical strength, and durability. The promoted HAp formation is induced by the elemental redistribution where Mg elements are concentrated in large CaMgSi2O6 grains embedded in Li2Si2O5 amorphous matrix, which hinders the Mg2+ release and its readsorption by HAp. The cell viability is affected by Li2O substitution because of the high‐dose Li+. In the current work, Li0.25 (25 mol% Li2O) has the highest hardness (700 Hv as sintered and 197 Hv after simulated body fluid soaking), lowest weight loss (≈0.6 wt%), lowest pH variation (≈8.1), efficient HAp formation, and reasonable cell viability (70.5%), demonstrating its remarkable potential for bone implant applications due to the synergistic structural densification and biological improvement. [ABSTRACT FROM AUTHOR]

Published
2023
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35. Assembly of cerium-based coordination polymer into variant polycrystalline 2D–3D CeO2−x nanostructures

Author

S. Mofarah, Sajjad, primary, Adabifiroozjaei, Esmaeil, additional, Wang, Yuan, additional, Arandiyan, Hamidreza, additional, Pardehkhorram, Raheleh, additional, Yao, Yin, additional, Assadi, M. Hussein N., additional, Mehmood, Rashid, additional, Chen, Wen-Fan, additional, Tsounis, Constantine, additional, Scott, Jason, additional, Lim, Sean, additional, Webster, Richard, additional, Zhong, Vicki, additional, Xu, Yuwen, additional, Koshy, Pramod, additional, and Sorrell, Charles C., additional

Published
2020
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43. Assembly of cerium-based coordination polymer into variant polycrystalline 2D–3D CeO2−x nanostructures.

Author

S. Mofarah, Sajjad, Adabifiroozjaei, Esmaeil, Wang, Yuan, Arandiyan, Hamidreza, Pardehkhorram, Raheleh, Yao, Yin, Assadi, M. Hussein N., Mehmood, Rashid, Chen, Wen-Fan, Tsounis, Constantine, Scott, Jason, Lim, Sean, Webster, Richard, Zhong, Vicki, Xu, Yuwen, Koshy, Pramod, and Sorrell, Charles C.

Abstract

Precise control over the morphology of nanomaterials is critical yet challenging. The present work reports an efficient approach to tailor the architecture of nanostructures. The process involves rapid disassembly/reassembly of an unstable metal-based coordination polymer (MCP) by controlling the kinetics of the reassembly process. The synthesis procedure delivers unprecedented polycrystalline nanostructures, e.g., holey 2D CeO2−x nanosheets, with precisely tailored thicknesses in the range of 10–100 nm, and hollow 3D pseudo-octahedra and spheres. The consequent high surface areas and pore volumes, short diffusion distances, and high defect densities of the holey 2D CeO2−x indicate significant densities of active sites. This holey architecture exhibits rapid CO conversion and outstanding solar light photocatalytic performance. This approach of directed assembly offers a template-free, controllable, and cost-effective approach to achieve engineered CeO2−x architectures, which are nearly impossible through existing approaches. [ABSTRACT FROM AUTHOR]

Published
2020
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47. Photocatalytic Performance of Undoped and Transition-Metal-Doped/Codoped TiO2 Thin Films

Author

Chen, Wen-Fan

Subjects
TiO2, Photocatalysis, Thin Film
Abstract

Undoped, single doped and codoped TiO2 thin films were fabricated by spin coating of sol-gel solutions on soda-lime-silica glass substrates followed by annealing at 450°C for 2 h. The mineralogical (GAXRD, Raman spectroscopy), microstructural (SEM, AFM), optical (UV-vis spectroscopy), hydrophilic (wetting angles), crystallographic (TEM) and photocatalytic (dye degradation) properties were determined. Undoped TiO2 thin films with thicknesses of~50-540 nm were fabricated. The films were discontinuous (1 cycle), continuous (4-11 cycles), and damaged (13-15 cycles), with the highest quality films being the continuous ones. The discontinuous and damaged films showed high wetting angles while the continuous films showed low angles. The free energies were the driving force for oxide bond formation and thus the highest contaminant levels were found for Na+ ions that freely diffused through the microstructure until it achieved saturation solubility. Co and V single-doped TiO2 thin films were fabricated with dopant levels of 0.05 to 1.00 mol%. All the films were highly transparent and contained anatase as the sole crystalline phase. At the lowest level (0.05 mol%), the dopant ions were distributed irregularly in the film microstructure and this contributed to defect formation and hindrance of nucleation of the TiO2 crystallites. With increasing dopant levels, the dopants distribution became more homogeneous and this favoured anatase recrystallisation and grain growth. Co formed substitutional solid solutions while V formed interstitial solid solutions in the anatase lattice. The changes in grain and microstructural characteristics of the films were owing to variations in dopant solubilites in the lattice. The data showed that Co has low solubility in TiO2 with the saturation limit being ~0.05 mol%. In contrast, for V doping, the solubility limit was higher, approaching 1.00 mol%. For Co + V codoped TiO2 thin films, substitutional solid solution caused increased anatase recrystallisation at the lowest dopant level. Macroscopic roughening at the highest dopant levels occurred owing to oversaturation, precipitation, and grain boundary pinning. The photocatalytic performance was related to the grain size owing to the associated changes in surface area, number of active sites and partial amorphisation. Intervalence charge transfer effects lowered photoactivity at higher dopant concentrations. Codoping was seen to have a synergistic effect on the photocatalytic performance. Low dopants levels were seen to be ideal for enhancing the photocatalytic performance through modification of the semiconducting properties.

Published
2016
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