Authors: T.V.L Thejaswini, Deivasigamani Prabhakaran*, M. Akhila Maheswari

Manuscript Title: Soft Synthesis of Potassium Co-doped Al-ZnO Nanocomposites: A Comprehensive Study on their Visible Light Driven Photocatalytic Activity on Dye Degradation

Authors: T.V.L Thejaswini, Deivasigamani Prabhakaran*, M. Akhila Maheswari

Supplementary Information (JMSC-D-16-00870-R1):

XRD Analysis:

Fig. S1 XRD spectra for Al doped, (1%)K-Al and (3%)K-Al co-doped ZnO NPs

Fig. S1 the XRD spectra for Al doped and (1% & 3%) K co-doped Al-ZnO NPs, with all the samples exhibitingthecrystallite single-phase hexagonal wurtzite ZnO structure. This has been confirmed by the 2θ peaks at 31.7°, 34.4°, 36.2° and 56.7° that corresponds to the planes (100), (002), (101) and (110), respectively. As mentioned in the manuscript for the bare, doped and co-doped ZnO, the variation in thedoping/co-doping stoichiometry’s of K-Al-ZnO NPs didnot reveal anyXRD peaks relating to Al and K. The peak broadening effect is clearly noticed with (3%)K-Al-ZnO NPs, apart from a significant decrease in the peak intensity when compared to that of 1%(K)-Al-ZnO and Al-ZnO NPs. This denotes the decreasing ZnO NPs size with co-dopantconcentration and this phenomenon is found to beara significant improvement in the surface area due to the increase in the surface-to-volume ratio. The increasing surface area with decreasing particle size is also found to improve the photocatalytic activity of K-Al-ZnO NPs, due to the greater availability of active sites for dye adsorption followed by light induced dissipation through reactive radial species formation.

SEM Imaging:

Fig. S2 SEM images of undoped and 2% Al doped ZnO

Fig. S2a and S2bshowthe SEMimages of bare ZnO NPssurface morphology at different resolutions and it can be seen that the particlesreveal micro-porous structure with irregular spherical shape design, with an average particle size of 40 nm. Similarly, the SEM imagesof 2% Al doped ZnO NPs, are shown in the Fig. S2c and S2d, which reveals that the morphology of Al doped almost exhibit similar resemblance to that of bare ZnO NPs, however with the slight variations in their particle size. It is found that the Al doped ZnO NPs shows a marginal decrease in its average particle size (34 nm) in comparison to the undoped ZnO NPs (40 nm).

Fig. S3 SEM images of 3%(K)-Al co-doped ZnO NPs

Fig.S3 shows the SEM images of 3 mole % doping of K on 2% Al doped ZnOat different resolutions. Fig.S3a and S3b, reveals irregular patterns of near spherically shaped micro-porous structurednanoparticle agglomerate surface morphology design, with an average particle size of 23nm at higher magnifications. This phenomenon of decreasing particle size with increasing co-dopant content is in agreement with the observed XRD data, which can be substantiated by the peak broadening effect.