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Structure–Activity Relationships of Er3+ and MWCNT-Modified TiO2: Enhancing the Textural and Optoelectronic Properties of TiO2

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journal contribution
posted on 2019-12-15, 16:03 authored by Diseko Boikanyo, Shivani B. Mishra, Sekhar Ray, Sabelo D. Mhlanga, Ajay K. Mishra
Photoactive erbium-modified titanium dioxide grafted onto multiwalled carbon nanotubes (Er:TiO2/MWCNT) nanopowders were synthesized via a facile sol–gel route. Studies showed that the photocatalysts were monophasic crystalline anatase TiO2, with crystallite sizes ranging from 13.93 nm for neat TiO2 and 5.6 nm for Er:TiO2/MWCNT. The incorporation of Er3+ and MWCNT into TiO2 enhanced the textural properties and formed a mesoporous nanocomposite, where Er:TiO2/MWCNT had the highest surface area (103.14m2/g) and pore volume (0.4464 cm3/g). The composite contained Er2O3 and Ti–O–C structural fragments coincident with Er2O3 on the nanocomposites’ surfaces forming Ti–O–Er and Ti–O–C bonds. Er3+ induced a blueshift in the TiO2 absorption edge. The Er:TiO2/MWCNT had the highest photoactivity for the decolorization of RR120 compared to Er:TiO2 and TiO2 with an apparent rate constant of 28.37 × 10–3 min–1, which was more than 3.5 times greater than that of the pure TiO2 (8.39 × 10–3 min–1) and a maximum color removal efficiency of 99.49% over 180 min of irradiation. The increased photocatalytic efficiency is due to a combination of adsorption of the dye by the composite and the enhanced optoelectronic properties where Er:TiO2/MWCNT exhibited a marked decrease in photoluminescence intensity compared to TiO2, evincing suppression of electron–hole recombination originating from the formation of Er 4f sub-band gap states beneath the TiO2 conduction band and thereby lowering the excitation energy (Eg) of TiO2, while the MWCNT acted as a porous coadsorbent and photosensitizer by transferring electrons to the TiO2 CB, thus broadening the spectral photoresponse for a high-potential solar active photocatalyst.

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