Nitrogen-Rich Carbon Nanodot-Sensitized TiO2 with MWCNT Composites for Efficient Visible Light Photocatalysis

TiO₂-based composite photocatalysts are currently being explored to address concerns intrinsic to TiO₂, specifically high charge carrier recombination and UV light activation. Among various materials utilized for composite formation, carbon nanomaterials stand out due to their high electron conductivity, charge storage, photosensitization, and surface properties. However, high carbon content in composites has been shown to reduce performance with potential toxicity concerns. To harness the diverse properties of carbon nanomaterials in a single composite while optimizing the carbon content below 1% by weight, multi-walled carbon nanotubes (MWCNT)/TiO₂ sensitized by carbon nanodots (CND) are synthesized. The heterojunction formed between MWCNTs and TiO₂ in the binary composite reduced the charge carrier recombination rate compared to TiO₂. The addition of CNDs to MWCNT/TiO₂ induced visible light absorbance of the resulting ternary composite, due to the forbidden electron transitions undergone in CND aggregates. CND/MWCNT/TiO₂ exhibited a fivefold and 1.6-fold increase in photocatalytic degradation of acid orange 7 and tetracycline under visible light compared to TiO₂. This enhancement is attributed to the photosensitizing property of CNDs working in synergy with the charge storage ability of MWCNTs. A plausible charge transfer pathway for the activity of CND/MWCNT/TiO₂ is proposed.