Interfacing Plasmonic Nanoparticles with Ferroelectrics for Hot-Carrier-Driven Photocatalysis: Impact of Schottky Barrier Height

Abstract

Emergent strategies for efficient solar energy conversion have focused on ways to harness photons in the lower-energy range of sunlight that cannot be utilized by conventional semiconductor photocatalyst systems. Recent research has demonstrated that interfaced plasmonic−ferroelectric particles represent a promising strategy for the utilization of near-infrared (NIR) light owing to the possibility of the more efficient injection of hot charge carriers from noble metal nanoparticles. Described herein, platinumend-capped gold nanorods (AuNRs) function as antennae to absorb lowenergy NIR photons to generate hot electrons that can be injected into ferroelectric PbZr x Ti 1−x O 3 (PZT; x = 0.48, 0.50, 0.52, 0.54, 0.56, and 0.60) and drive the reduction of water to molecular hydrogen at its surfaces. As an aqueous suspension, the interfaced AuNR-PZT particles exhibited maximal photocatalytic rates for hydrogen formation under a 976 nm diode laser (powder density = 2.0 W cm −2 ) for the 52% Zr (x = 0.52) composition at a photon conversion efficiency of ∼0.28%. This efficiency is significantly higher than in previously reported metal−semiconductor combinations, i.e., of ∼0.01% to 0.1%, owing to the large ferroelectric polarization of PZT at its morphotropic phase boundary that yields the smallest Schottky barrier height. Reduction of the Schottky barrier height at the AuNR-PZT interface results from the effect of the surface electric polarization on interfacial band bending, and helps to drive charge injection and the photocatalytic activity for molecular hydrogen production. Photocatalytic rates were also measured as a function of the irradiant power density, ranging from ∼0.1 to 2.0 W cm −2 , and exhibited an increasing, nonlinear dependence that is consistent with the production rate of hot electrons above the Schottky barrier. Thus, this study reveals original insights into the critical parameters needed to design integrated plasmonic−ferroelectric photocatalyst systems for utilizing hot electrons produced from NIR light and achieving higher solar conversion efficiencies.

Study on Simultaneous Removal of Dye and Heavy Metal Ions by NiAl-Layered Double Hydroxide Films

“… 22 , 48 In our experiments, reduced heavy metal ions contacted with NiAl-LDHs (n-type semiconductor) to form a Schottky barrier ( Figure 11 ), which could act as electron traps, separate photogenerated electron–hole pairs, and thus improve the photocatalytic activity of NiAl-LDHs on MO. 15 , 22 , 27 Metals with high E F , which showed a low work function and Schottky barrier, had a more active surface, facilitated the transfer of electrons from NiAl-LDHs to metals, 49 − 51 and then increased their photocatalytic efficiency. Therefore, with the increase in the E F of the coexisting metals, the removal rate of MO by NiAl-LDHs increased.…”

“… 26 The surface polarization on the interface affected the band bending and thus decreased the Schottky barrier height at the interface between noble metals (such as Au) and PbZr x Ti 1– x O 3 , which improved their photocatalytic activity. 27 Heavy metal ions such as Ag, Au, and Pb ions can be reduced by photogenerated electrons and reduction sites of LDHs 28 − 30 and deposited on the surface of LDHs, which could improve the photocatalytic performance of LDHs. When treating mixed wastewater containing heavy metal ions and organic pollutants, the simultaneous treatment of heavy metal ions and organic pollutants in mixed wastewater with a single photocatalyst would be achieved.…”

Photoactivated materials and sensors for NO2 monitoring

“…The backward flow of hot electrons is feasible for ohmic contact due to the absence of a barrier, so the electron-hole separation cannot be promoted. Therefore, the tuning of the potential barrier height plays a key role in the photoactivation of plasmonic metal-semiconductor systems (it should not be too high or too small to enable the hot electron injection in the semiconductor and avoid the back-flow of hot electrons) [81][82][83]. Figure 3 depicts a schematic view of the metal-n-type semiconductor system with Schottky junctions and their photoactivation for both cases discussed above.…”

Morphology-Governed Performance of Plasmonic Photocatalysts

“…Summarizing, as pointed by Kumar et al it is important to realize that the integration of plasmonic metals with ferroelectrics might be beneficial for two aspects: (1) The injected charge carriers are effectively driven to spatially separate over the ferroelectric particles; and (2) tuning the Schottky barrier height, e.g., by changing the chemical composition of noble-metal/semiconductor, thus providing an interfacial contact that favors the hot charge injection [139]. Both effects can prolong the lifetimes of both the excited electrons and holes.…”