Hydrothermally activated TiO2 nanoparticles with a C-dot/g-C3N4 heterostructure for photocatalytic enhancement

Abstract

Dye degradation via photocatalysis technology has been investigated intensively to tackle environmental issues and energy crisis concerns. In this study, a newly designed ternary photocatalyst was facilely prepared by a simple one-pot hydrothermal process by directly mixing TiO₂ nanoparticles with carbon dots (C-dots) and graphitic carbon nitride (g-C₃N₄). The optimized precursor treatments and heterostructure components show significantly enhanced photodegradation activity towards organic dyes Rhodamine B (RhB) and methylene blue (MB). Excellent photocatalytic activities were achieved owing to the better attachment of anatase-type TiO₂ nanoparticle-aggregations to the C-dots/g-C₃N₄ (CC) nanocomposite, which impressively displays superhydrophilicity by employing the hydrothermal activation process. FT-IR spectra revealed that the hydrothermal treatment could remarkably increase the coupling interactions between TiO₂ nanoparticles and the CC nanosheets within the ternary catalyst, enhancing the photocatalytic activity. Thus, it was concluded that this ternary photocatalyst is highly suitable for the remediation of dye-contaminated wastewater.

Fig. 1. Schematic of the preparation processes of the ternary composites TiO₂/C-dots/g-C₃N₄. (A) “One-pot” hydrothermal process; (B) “two-step” hydrothermal process.

Fig. 2. (A) TEM images of the one-pot hydrothermally treated TCC-1 hybrids. (B) HRTEM micrograph of TCC-1 (the red arrow points to the c-dots attached on TiO₂ particles).

Fig. 3. XRD patterns of (A) each precursor (CC, g-C₃N₄ and C-dots) and (B) as-prepared photocatalyst (A: anatase; R: rutile; CN: g-C₃N₄).

Fig. 4. FT-IR spectra of TCC-1, TCC-2 and TCC-3 (inset is the FT-IR spectra of C-dots, CC and g-C₃N₄).

Fig. 5. (A) XPS spectrum of TCC-1 and high-resolution XPS spectra of (B) C 1s, (C) N 1s and (D) Ti 2p for TCC-1.

Fig. 6. Photodegradation activities of RhB (A) and MB (B) aqueous solution with original concentration of 1.0 × 10⁻⁵ M with different photocatalysts under 15 W mercury-light irradiation. The variation curves of ln(C₀/C_t) with the reaction time for the photocatalytic degradation of RhB (C) and MB (D). The kinetic constants of RhB (E) and MB (F) degradation by various photocatalysts.

Fig. 7. (A) Electrochemical impedance spectroscopy (EIS) and (B) the transient photocurrent responses of samples TCC-1, TCC-2, and TCC-3.

Fig. 8. The PL emission spectra of “one-pot” hydrothermally treated CC and TCC-1.

Fig. 9. Photocatalytic degradation of RhB (A) and MB (B) by TCC-1 with different scavengers under UV irradiation. The kinetic constants of RhB (C) and MB (D) degradation with different radical scavengers.

Fig. 10. Proposed mechanisms of RhB photodegradation by the TCC-1 hybrid under UV irradiation.