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Subject: search.filters.subject.Sono-assisted exfoliation

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    Ultrasonically-assisted surface modified TiO2/rGO/CeO2 heterojunction photocatalysts for conversion of CO2 to methanol and ethanol
    (2019-11-01)
    Seeharaj, Panpailin
    ;
    Kongmun, Panyata
    ;
    Paiplod, Piyalak
    ;
    Prakobmit, Saowanee
    ;
    Sriwong, Chaval
    Converting CO<inf>2</inf> to usable fuel may contribute to lowering of global warming, thus this study developed effective heterojunction photocatalysts for the photoreduction of CO<inf>2</inf> with water into methanol and ethanol fuels. The photocatalysts were prepared from combining surface modified titanium dioxide (TiO<inf>2</inf>) nanoparticles with reduced graphene oxide (rGO) and cerium oxide (CeO<inf>2</inf>). The TiO<inf>2</inf> surfaces were firstly modified via the sono-assisted exfoliation, with high intensity ultrasonic waves (ultrasonic horn, 20 kHz, 150 W/cm<sup>2</sup>) in 10 M NaOH for 1 h. Highly reactive nanosheets delaminated from outer surfaces of the primary TiO<inf>2</inf> crystals leading to an increase in specific surface active area, light absorption and decrease in electron-hole recombination rate, which enhanced photocatalytic activity. Then, 0.75 wt% rGO and 1 wt% CeO<inf>2</inf> were incorporated into the surface modified TiO<inf>2</inf> to promote photogenerated charge separation, electron mobility and CO<inf>2</inf> absorptivity. The modified TiO<inf>2</inf>/rGO/CeO<inf>2</inf> photocatalysts exhibited superior photocatalytic performance by producing methanol at 641 μmol/g<inf>cat</inf>h and ethanol at 271 μmol/g<inf>cat</inf>h, almost 7 times higher than rates from pure TiO<inf>2</inf>. The significant improvement in CO<inf>2</inf> photoconversion activity was mainly attributed to the high interfacial contact area and strong connection between the reactive delaminated TiO<inf>2</inf> nanosheets, rGO and CeO<inf>2</inf>, which, in turn, facilitated the flow of large number of photogenerated charge carriers to react with the absorbed species, and the multi-step charge transportation due to the heterojunction effect that effectively retarded electron-hole recombination.
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    Surface modification of TiO2 particles with the sono-assisted exfoliation method
    (2017-11-01)
    Thasirisap, Eakkasit
    ;
    Vittayakorn, Naratip
    ;
    Seeharaj, Panpailin
    This study reported a novel approach to optimize the photocatalytic property of anatase TiO<inf>2</inf> particles by delaminating their outer surface into highly reactive nanosheets via the sono-assisted exfoliation method. To modify the surface, TiO<inf>2</inf> particles were dispersed in aqueous solution of 10 M sodium hydroxide (NaOH) and tetrabutylammonium hydroxide (TBAOH), followed by irradiation with high intensity ultrasonic wave (20 kHz, 150 W/cm<sup>2</sup>) for 60 min. The intercalation and exfoliation processes were accelerated with the driving force of the extreme acoustic cavitation leading to the delamination of TiO<inf>2</inf> nanosheets with highly reactive exposed {0 0 1} facets from the mother TiO<inf>2</inf> crystals. The presence of TBAOH increased yield of nanosheets formation and stabilized the nanosheet structure. The unique morphology of the surface modified TiO<inf>2</inf> particles provided benefits in increasing the specific surface area and lowering the optical band gap energy (E<inf>g</inf>) and electron-hole recombination rate resulting in an enhancement of methylene blue dye degradation efficiency. The surface modification of TiO<inf>2</inf> particles by the sono-assisted exfoliation method can optimize the photocatalytic activity by yielding synergetic effects of the high surface reactive sites of the nanosheets and the high degree of crystallinity of the bulk structure.