Metal-organic framework coated titanium dioxide nanorod array p-n heterojunction photoanode for solar water-splitting

This paper presents a p-n heterojunction photoanode based on a p-type porphyrin metal-organic framework (MOF) thin film and an n-type rutile titanium dioxide nanorod array for photoelectrochemical water splitting. The TiO2@MOF core-shell n anorod array is formed by coati ng an 8 nm thick MOF layer on a vertically aligned TiO2 nanorod array scaffold via a layer-by-layer self-assembly method. This vertically aligned core-shell nanorod array enables a long optical path length but a short path length for extraction of photogenerated minority charge carriers (holes) from TiO2 to the electrolyte. A p-n junction is formed between TiO2 and MOF, which improves the extraction of photogenerated electr ons and holes out of the TiO2 nano rods. In additi on, the MOF coati ng sign ificantly improves the efficie ncy of charge in jecti on at the photoanode/electrolyte interface. Introduction of Co(lll) into the MOF layer further enhances the charge extraction in the photoanode and improves the charge injection efficiency. As a result, the photoelectrochemical cell with the TiO2@Co-MOF nanorod array photoanode exhibits a photocurrent density of 2.93 mA/cm^2 at 1.23 V (vs. RHE), which is ~ 2.7 times the photocurrent achieved with bare T1O2 nanorod array under irradiation of an unfiltered 300 W Xe lamp with an output power density of 100 mW/cm^2.

Origin of strong and narrow localized surface plasmon resonance of copper nanocubes

Inexpe nsive copper nano particles are generally thought to possess weak and broad localized surface plasm on resonance(LSPR).The,present experimental and theoretical studies show that tailoring the Cu nanoparticle to a cubic shape results in a single intense,narrow,and asymmetric LSPR line shape,which is even superior to round-shaped gold nanoparticles.In this study,the dielectric function of copper is decomposed into an interband transition component and a free-electron component.This allows interband transition-induced plasmon damping to be visualized both spectrally and by surface polarization charges.The results reveal that the LSPR of Cu nanocubes originates from the comer mode as it is spectrally separated from the interb and transitions.In additi on,the interband tran sitions lead to severe damping of the local electromagnetic field but the cubic corner LSPR mode survives.Cu nanocubes display an extinction coefficient comparable to the dipole mode of a gold nanosphere with the same volume and show a larger local electromagnetic field enhancement These results will guider-development of in expensive plasmonic copper-based nano materials.

Effects of Bi-dopant and co-catalysts upon hole surface trapping on La_(2)Ti_(2)O_(7) nanosheet photocatalysts in overall solar water splitting

Pristine and Bi-doped lanthanum titanium oxide(La_(2)Ti_(2)O_(7))nanosheets have been synthesized as photocatalysts for overall solar water splitting.The surface hole trap is a critical factor that limits the photocatalytic activity of pristine La_(2)Ti_(2)O_(7)-Deposition of cobalt phosphate(Co-Pi)and platinum(Pt)nanoparticles on La_(2)Ti_(2)O_(7) cannot remove the surface traps although they are essential for enabling the oxygen and hydrogen evolution reactions.It is interesting that doping bismuth(Bi)into La_(2)Ti_(2)O_(7) nanosheets has eliminated the surface traps due to surface enrichment of Bi.The Co-Pi/Bi-La_(2)Ti_(2)O_(7)/Pt nanosheets exhibit increasing photocatalytic activity toward overall water splitting with increasing the Bi-dopant level up to 5 at.%.Further increasing the Bi-dopant level leads to the formation of localized states above the valence band,leading to the lifetime reduction of photogenerated charge-carriers,and jeopardizing the photocatalytic activity.This work proposes an effective strategy to address the surface trapping and surface catalysis issues in the nanostructured metal oxide photocatalysts.