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.