Enhanced visible light photocatalytic degradation of eriochrome black T and eosin blue shade in water using tridoped titania decorated on SWCNTs and MWCNTs: Effect of the type of carbon nanotube incorporated

• SWCNT/Nd,N,S–TiO2 and MWCNT/Nd,N,S–TiO2 were prepared via sol–gel method.
• EBS and EBT degradation was studied in single and mixed dye solution.
• SWCNT/Nd,N,S–TiO2 displayed higher photocatalytic activity than MWCNT/Nd,N,S–TiO2.
• Relatively high TOC removal for EBS and EBT by SWCNT/Nd,N,S–TiO2.
• SWCNT/Nd,N,S–TiO2 displayed good stability for reuse.

Oxidised single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were each incorporated into a neodymium, nitrogen and sulphur tridoped TiO2 (Nd,N,S–TiO2) to form composite photocatalysts: SWCNT/Nd,N,S–TiO2 and MWCNT/Nd,N,S–TiO2. The fabricated composite photocatalysts were exploited for the photocatalytic degradation of eriochrome black T (EBT) and eosin blue shade (EBS) from single and mixed dye solutions. Incorporation of the carbon nanotubes significantly improved visible light response and the photocatalytic activity of the composites compared to MWCNT/TiO2, SWCNT/TiO2 and tridoped TiO2. The SWCNTs incorporating photocatalyst displayed superior photocatalytic activity over its MWCNTs incorporating counterpart. From single dye solutions degradation studies, the SWCNT/Nd,N,S–TiO2 reached maximum degradation efficiencies of 96.9% and 89.2% for EBS and EBT, respectively. Similarly, maximum degradation efficiencies of 61.4% and 54.1% were recorded from mixed dye solutions using SWCNT/Nd,N,S–TiO2, for EBS and EBT, respectively. First order kinetics studies revealed that EBS is degraded faster than EBT both from single and mixed dye solutions. Total organic carbon (TOC) analyses suggest a relatively high degree of complete mineralisation of both EBS (73.6% TOC removal) and EBT (66.2% TOC removal). The SWCNT/Nd,N,S–TiO2 composite photocatalyst displayed sufficient stability (88.8% EBS removal) after being reused for five times.