Selective adsorption and photocatalysis of low-temperature base-modified anatase nanocrystals

Anatase titania photocatalysts with positive (TSC60) and negative (TAH60) surface charge were synthesized by extraction with Na ₂CO ₃ and NH ₄OH, respectively, from an acid stabilized sol at low temperature. XRD, TEM, N ₂ adsorption and ζ -potential were conducted and revealed that the low-temperature synthesized catalysts differ mainly in their surface charge. These catalysts exhibited opposing preferential adsorption and fully selective photocatalysis of methylene blue (MB) and methyl orange (MO) dyes from their aqueous mixture. The preferential adsorption behaviour toward MB and MO was attributed to the catalyst's surface charge whereas the selective photocatalysis was explained by a combined effect of surface charge and crystallinity. On the other hand, the calcined catalysts showed considerable reduction in their dye adsorption capacity and loss of their selective dye degradation. The reduction in surface charge and increase in crystallinity after calcination were found to be responsible for these observations. Degussa P25 was also tested and compared with synthesized catalysts with regard to dye adsorption and photocatalysis. A mechanism for the selective dye positioning on TSC60 and TAH60 coated FTO/ITO plate is also proposed. © 2012 The Royal Society of Chemistry.