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Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO₂.

ABSTRACT: We report the experimental observation of and theoretical explanation for the reduction of dopant ions and enhancement of magnetic properties in Ce-doped TiO₂ diluted magnetic semiconductors from UV-light irradiation. Substantial increase in Ce³⁺ concentration and creation of oxygen vacancy defects in the sample due to UV-light irradiation was observed by X-ray and optical methods. Magnetic measurements demonstrate a combination of paramagnetism and ferromagnetism up to room temperatures in all samples. The magnetization of both paramagnetic and ferromagnetic components was observed to be dramatically enhanced in the irradiated sample. First-principle theoretical calculations show that valence holes created by UV irradiation can substantially lower the formation energy of oxygen vacancies. While the electron spin densities for defect states near oxygen vacancies in pure TiO₂ are in antiferromagnetic orientation, they are in ferromagnetic orientations in Ce-doped TiO₂. Therefore, the ferromagnetically-oriented spin densities near oxygen vacancies created by UV irradiation are the most probable cause for the experimentally observed enhancement of magnetism in the irradiated Ce-doped TiO₂.

SUBMITTER: Wu TS

PROVIDER: S-EPMC8027894 | biostudies-literature | 2021 Apr

REPOSITORIES: biostudies-literature

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Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO2.

Wu Tai-Sing TS Syu Leng-You LY Lin Bi-Hsuan BH Weng Shih-Chang SC Jeng Horng-Tay HT Huang Yu-Shan YS Soo Yun-Liang YL

Scientific reports 20210407 1

We report the experimental observation of and theoretical explanation for the reduction of dopant ions and enhancement of magnetic properties in Ce-doped TiO2 diluted magnetic semiconductors from UV-light irradiation. Substantial increase in Ce3+ concentration and creation of oxygen vacancy defects in the sample due to UV-light irradiation was observed by X-ray and optical methods. Magnetic measurements demonstrate a combination of paramagnetism and ferromagnetism up to roo ...[more]

PMID: 33828150

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Project description:In this work, various amounts of Ce were added to TiO2 to form a mixed oxide support; Ce x Ti1-x O2 (x = 0, 0.003, 0.05, 0.10 and 0.15) and then those synthesized supports were impregnated by 10 wt% Ni to produce a catalysts. The 10 wt% Ni-Ce x Ti1-x O2 (x = 0, 0.003, 0.05, 0.10 and 0.15) catalysts were tested for CO2 methanation reaction by using a fixed-bed reactor in the temperature range of 100-500 °C. The sample was pretreated at 450 °C under H2 and then a mixed feed gas of CO2 and H2 was switched into the reactor to start the reaction. The results showed that 10 wt% Ni-Ce0.003Ti0.997O2 catalyst (the lowest Ce content) exhibited the highest CO2 conversion and CH4 yield. Moreover, 10 wt% Ni-Ce0.003Ti0.997O2 showed highly stable during the stability test (50 h.). The results indicated that upon addition of small amount of Ce into TiO2-supported Ni, the surface, structural, electrical and redox properties of the catalyst were improved to the extent that these properties can promote the catalytic activities for CO2 methanation. The Ce addition can improve the CO2 methanation catalytic activity by several ways. First, higher dispersion of Ni on catalysts surface upon addition of Ce was observed which resulted in higher adsorption rate of H2 on this metal active site. Second, formation of a larger amounts of oxygen vacancies as well as basicity improvement upon addition of Ce were occurred which can increase the CO2 adsorption on catalyst surface. Third, incorporation of Ce resulted in improving of a starting reduction temperature of Ni2+ to Ni0 for TiO2-supported Ni catalyst which can indicate that the reducibility of Ce-doped TiO2-supported Ni catalyst was enhanced and then alter its catalytic activity. However, increasing of Ce content led to lowering of CO2 methanation activities which resulted from increasing of basicity by Ce addition. The excess amounts of adsorbed CO2 would lead to competitive adsorption to H2 and then lead to a decrease of catalytic activity. Therefore, an appropriate amount of H2 and CO2 adsorption ability on catalyst surface was a prominent factor to dominate the catalytic activity.

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Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO₂.

Publications

Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO<sub>2</sub>.

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