Noble Metal Free, Visible Light Driven Photocatalysis Using TiO₂ Nanotube Arrays Sensitized by P‐Doped C₃N₄ Quantum Dots

Abstract

Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light‐driven transformation of 4‐nitrobenzenethiol (4‐NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.

TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Driven Water-Splitting

“…The secondary electron cut-off energy of this material is 18.4 eV (Figure 3c). According to the expression given before, the work function with respect to the vacuum level is 2.8 eV, which is up shifted by 1.5 eV from the normal WF value of 4.3 eV for anatase TiO2 [24]. Additionally, the valence band maximum was calculated to be 5.21 eV (Figure 3d).…”

“…One strategy consists of forming core@shell heterojunctions wherein WBG nanotubes or nanorods ("core") are coated with a thin absorbing layer of a lower bandgap semiconductor ("shell") [20,21]. While core-shell heterojunctions have shown considerable promise in improving the performance of photoelectrochemical water splitting [22][23][24], photoanodes constituted exclusively of semiconductors suffer thermodynamic losses for supra-bandgap photons. On the other hand, photoanodes consisting of plasmonic metal-semiconductor heterojunctions can reduce thermalization losses by efficiently harvesting hot carriers while simultaneously sensitizing WBG semiconductors to visible photons [25,26].…”

A Review and Recent Developments in Full‐Spectrum Photocatalysis using ZnIn2S4‐Based Photocatalysts

“…[7] TiO 2 , a typical semiconductor photocatalytic material, has gained particular interest in past decades owing to its superiority that it is low cost, nontoxic, and chemically stable. [8][9][10] However, the practical application of TiO 2 is highly restricted due to the fact that it can only absorb ultraviolett (UV) light, which is caused by its wide bandgap (3.2 eV). As we all know, UV light occupies only 3-5% of the total solar spectrum, and the visible (Vis)-near infrared (NIR) light accounts for 95% of the total solar spectrum.…”

Photoelectrochemical performance of tubewall‐separated titanium dioxide nanotube array photoelectrode

“…Attractive TiO 2 NTA conducts the photoinduced electron–hole generation, separation, and feasible electron transfer which can be well applied for photocatalysis and electrochemical energy storage 24,25 . Specifically, TiO 2 NTA becomes highly suitable photocatalyst and photoelectrocatalyst for full degradation and decomposition of various organic pollutants, showing the effective environmental purification 21,26,27 . In general, anodic TiO 2 NTA keeps a nanotube wall connecting structure.…”