Electronic Supplementary Information Monodisperse Anatase Titania Microspheres with High-thermal Stability and Large Pore Size ( ~ 80 nm ) as Efficient Photocatalysts

To fabricate an effective antibacterial coating on the surfaces of diverse sanitary ceramic utensils, efficient titania photocatalysts with integrated features including high temperature anatase phase stability (>800 °C), excellent particle mobility for the formation of uniform thin coatings, high crystallinity and narrow particle size distribution are desirable. In this study, monodisperse dopant-free titania microspheres were synthesized with large pore size (∼80 nm) that remain anatase even after calcination at 900 °C. These titania microspheres were fabricated via a facile solvothermal treatment of amorphous spheres in the presence of 4.5 wt% ammonia solution and consisted of well-crystallized and faceted anatase nanocrystals with a uniform size of 24 nm. The anatase nanocrystals with high crystallinity and narrow crystal size distribution are responsible for their high temperature stability. The resulting anatase titania microspheres exhibited enhanced photocatalytic performance even after calcination at high temperature due to the retention of the anatase phase and the enhanced crystallinity. Such monodisperse anatase microspheres have potential to be applied as smart coating materials for antibacterial and self-cleaning applications.

The X-ray photoelectron spectrometer (XPS) data were recorded on a VG ESCALAB 220i-XL spectrometer (UK) equipped with a twin crystal monochromated Al K  X-ray source, which emitted a photon energy of 1486.6 eV at 10 kV and 22 mA.Samples were secured onto Al holders and were measured in the analysis chamber at a typical operating pressure of ~7×10 −9 mbar.An electron flood gun was used to compensate the charging effect of non-conductive materials.Spectra were obtained at a step size of either 1.0 eV (survey scans) or 0.05 eV (regional scans).Quantification and curve fitting of XPS spectra were performed using CasaXPS software.The C1s peak at 285.0 eV was used as a reference for the calibration of the binding energy scale.The reported surface energy values of the {101} and {001} facets are 0.44 J m -2 and 0.90 J m -2 , respectively. 5To reduce the surface energy during the crystal growth, the resulting anatase nanocrystals will grow in size gradually minimising the exposure of high energy {001} facets and therefore leading to the final anatase crystals showing a truncated bipyramid crystal habit.This result is in good agreement with previous papers. 6,7   This sample retains its spherical morphology, the nanoparticles on the outer surfaces come from partial damage to the surface layer of the titania microspheres as a result of the continuous stirring during the photocatalytic reaction.These results suggest that the sample has good mechanical stability due to the sintering at high temperature (> 800 C).Both the MTS-0 wt.% -900 C and MTS-17.4wt.% -900 C sample had a mixed phase titania composition and they had lower specific surface area and porosity than the MTS-4.5 wt.% -900 C sample.The photocatalytic activities of the MTS-0 wt.% -900 C and MTS-17.4wt.% -900 C samples were inferior to that of MTS-4.5 wt.% calcined at same temperature due to their much reduced specific surface area and porosity, and relatively larger crystal sizes (Shown in Fig. S13 a4, b4 and c4).

Fig 3 Fig
Fig. S1 Experimental set-up for evaluating photocatalytic performance of the titania materials investigated in this study.A dichroic mirror (66226, Oriel) was installed above the jacked beaker to vertically deliver UV light (280<λ<400 nm) onto the reaction mixture.The UV radiation intensity at the surface of the suspension was 16.7 ± 0.2 mW cm -2 .

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Fig. S3 High magnification SEM image of the monodisperse titania microspheres solvothermally treated at 220 °C in the presence of 4.5 wt.% ammonia solution and calcined at 1000 °C in air.SEM image was taken without metal sputter coating of the sample.

Fig. S4
Fig. S4 Histogram of the size distribution of the monodisperse titania spheres solvothermally treated at 220 °C in the presence of 4.5 wt.% ammonia solution (a) and then calcined at 800 °C (b), 900 °C (c), and 1000 °C (d) in air.

Fig. S5
Fig. S5 Raman spectrum of the monodisperse titania spheres solvothermally treated at 220 °C in the presence of 4.5 wt.% ammonia solution then calcined at 900 °C for 2 h in air.

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Fig. S6 XRD patterns of the Degussa (Evonik) P25 nanoparticles as obtained and after calcination at temperatures ranging from 500 to 900 °C for 2 h in air.A = Anatase and R = Rutile phase titania.

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Fig. S7 XRD patterns of the amorphous precursor spheres (APS) and after calcination (without solvothermal treatment) at temperatures ranging from 500 to 800 °C for 2 h in air.A = Anatase and R = Rutile phase titania.

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Fig. S8 UV-vis diffuse reflectance spectra of MTS (a) and P25 (c) calcined at varying temperatures for 2 h in air, and the relationship between the transformed Kubelka-Munk function versus the photon energy (b and d) for each material.In (b) and (d), a straight line tangential tothe slope was extended to cut the horizontal axis to obtain the band gap energy of the titania samples.[1][2][3]

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Fig. S10 (a) Arrenhius plot of ln(A R /A 0 ) νs 1/T for activation energy calculations according to a previously reported method. 4(b) XRD patterns of the MTS calcined at varied temperatures for 2 h (as indicated) in air.

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Fig. S14 XRD patterns of the titania microspheres solvothermally treated at 220 °C in the presence of 17.4 wt.% ammonia solution and calcined at diverse temperatures ranging from 800 to 1000 °C for 2 h in air.A = Anatase and R = Rutile phase titania.

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Fig. S15 (a) Time profile of methylene blue (MB) absorbance spectrum and (b) corresponding photodegradation of MB (rate constant: k=0.001 min -1 ) observed in the absence of photocatalyst under UV light irradiation.The amount of MB photodegraded was obtained by calculating the change of concentration (C/C 0 ) from the variation of absorbance (A/A 0 ) at 665 nm.C 0 and A 0 denote initial concentration and absorbance of MB, respectively.

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Fig. S16 SEM image of the MTS-4.5 wt%-800 C sample after the photocatalytic test.

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Fig. S17 Comparison of the apparent rate constants for the photocatalytic reactions employing the MTS samples prepared in the presence of different ammonia concentrations and subsequently calcined at 900 C in air.

Table S1 .
Phase content and physical properties of the MTS samples calcined at 900 C in air.Specific surface area obtained from adsorption data in the P/P 0 range from 0.05 to 0.20.Pore volume calculated from the adsorption branch at P/P 0 =0.98.