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    Ferroelectric-assisted enhancement of the photocatalytic activity of g-C 3 N 4 / TiO 2 nanotubes heterojunctions through the addition of strontium
    (Elsevier Science Sa, 2024) Alsubaie, Modi Nasser; Alabbad, Sanaa Saad; Alrashidi, Wadha; Alomair, Nuhad Abdullah; Kochkar, Hafedh; Berhault, Gilles; Jomni, Fathi
    The effect of adding strontium to nanocomposites formed of g-C 3 N 4 /TiO 2 nanotubes (TiNT) (g-C 3 N 4 : 4.0 wt%) on the photocatalytic activity was herein investigated using formic acid as a model target pollutant. g-C 3 N 4 material was prepared by a solvothermal method using a mixture of urea and cyanuric chloride as precursors and acetonitrile as a solvent at 220 degrees C for 15 h, while TiNT material was obtained by the alkaline hydrothermal method of P25 at 130 degrees C for 20 h. A series of xSr-gC 3 N 4 /TiNT nanocomposites were then synthesized through progressive incorporation of strontium (from 0.2 to 1.0 wt%) at the surface of the composites. Samples were then characterized mainly using N 2 adsorption - desorption measurements, X-ray diffraction, UV - vis diffuse reflectance, Raman and photoluminescence (PL) spectroscopies, and scanning and transmission electron microscopy (with energy -dispersive X-ray spectroscopy and Z -mapping). The Sr -containing g-C 3 N 4 /TiNT composites were then also fully characterized by electrochemical impedance spectroscopy (EIS) for their dielectric properties, while a deep kinetics analysis was also performed. Such an approach allowed us to establish a correlation between photocatalytic performance and the material ' s propensity to be polarized. Results emphasize the beneficial role of ferroelectricity induced by adding strontium. Indeed, enhancement of the photocatalytic activity by 2.3 times compared to a Sr -free counterpart was related to the material ' s ability to be polarized for Sr loadings <= 0.6 wt%. At higher Sr loadings, supplementary factors (decrease of the anatase crystallinity, formation of TiO 2 (B), disruption of the g-C 3 N 4 /TiO 2 interaction, or lower mobility of photogenerated charges) negatively impact the activity, counterbalancing partly the beneficial ferroelectric effect. In this way, this study emphasizes the role played by ferroelectric effects in enhancing the photocatalytic ability of a given semiconductor.
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    The Role of the Ferroelectric Polarization in the Enhancement of the Photocatalytic Response of Copper-Doped Graphene Oxide-TiO2 Nanotubes through the Addition of Strontium
    (Amer Chemical Soc, 2023) Alomair, Nuhad Abdullah; Al-Aqeel, Nouf Saleh; Alabbad, Sanaa Saad; Kochkar, Hafedh; Berhault, Gilles; Younas, Muhammad; Jomni, Fathi
    To evaluate the potential role of in situ formed Sr-Ti-O species as a ferroelectric component able to enhance the photocatalytic properties of an adjacent TiO2 semiconductor, Cu-doped/graphene oxide (GO)/TiO2 nanotubes (TiNTs) composites (with 0.5 wt % Cu and 1.0 wt % GO) have been synthesized while progressive amounts of strontium (up to 1.0 wt %) were incorporated at the surface of the composite through incipient wetness impregnation followed by post-thermal treatment at 400 degrees C. The different resulting photocatalytic systems were then first deeply characterized by means of N2 adsorption-desorption measurements, X-ray diffraction (XRD), UV-vis diffuse reflectance (UV-vis DR), Raman and photoluminescence (PL) spectroscopies, and scanning electron microscopy (SEM) (with energy-dispersive X-ray (EDX) spectroscopy and Z-mapping). In a second step, optimization of the kinetic response of the Sr-containing composites was performed for the formic acid photodegradation under UV irradiation. The Sr-containing Cu/GO/TiNT composites were then fully characterized by electrochemical impedance spectroscopy (EIS) for their dielectric properties showing clearly the implication of polarization induced by the Sr addition onto the stabilization of photogenerated charges. Finally, a perfect correlation between the photocatalytic kinetic evaluation and dielectric properties undoubtedly emphasizes the role of ferroelectric polarization as a very valuable approach to enhance the photocatalytic properties in an adjacent semiconductor.
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    Strontium-Modified TiO2 Nanotubes for Efficient Photodegradation of Formic Acid
    (Springer Heidelberg, 2025) Al Hajri, Eman; Alrashedi, Wadha; Alomair, Nuhad Abdullah; Alabbad, Sanaa Saad; Younas, Muhammad; al Malih, Rasha Jubran; Alzahrani, Asala
    This study explores the enhancement of photocatalytic activity in one-dimensional TiO2 nanotubes (TiNT) through strontium (Sr) doping, using the incipient impregnation method to introduce Sr concentrations ranging from 0.2 to 1.0 wt%. The photocatalytic performance of the resulting xSr-TiNT composites was evaluated by examining the degradation of formic acid under UV irradiation. The materials were characterized using N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis, Raman spectroscopy, photoluminescence (PL), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effective surface area was determined by XPS, revealing a significant increase in surface area with Sr loading, which correlates with enhanced photocatalytic performance. This enhancement in surface area is in agreement with the observed expansion of the unit cell volume in presence of Sr. Results show that a small amount of Sr (0.2 wt%) enhances the generation of oxygen vacancies and Ti3+ species, leading to increased photocatalytic activity. The degradation followed the Langmuir-Hinshelwood model, with the highest degradation rate observed at 0.8 wt% Sr, showing a 3.36-fold increase compared to pristine TiNT. At higher Sr concentrations, the proportion of oxygen vacancies and Ti3+ defects decreased due to the formation of Ti-O-Sr moieties. Additionally, the polarization effect induced by Sr doping improved charge separation, reducing electron-hole recombination and further enhancing photocatalytic efficiency. These findings emphasize the critical role of Sr concentration, effective surface area, and unit cell volume expansion in tuning the photocatalytic properties of TiO2 nanotubes, with an optimum Sr loading of 0.8 wt% leading to improved photocatalytic activity.