Photothermal Hydrogen Production Using Noble-Metal-Free Ti@TiO₂ Core–Shell Nanoparticles under Visible–NIR Light Irradiation

Abstract

Limiting resources of fossil fuels and environmental issues inevitably require more efficient utilization of solar energy. Photocatalytic production of hydrogen is identified as one of the most promising routes for developing clean and sustainable energy. However, engineering of low-cost materials exhibiting high catalytic activity in the entire range of solar spectrum is still a challenge. Here we report, for the first time, simple, easily scalable and environmentally friendly synthesis of stable Ti@TiO 2 core-shell nanoparticles exhibiting photocatalytic activity in hydrogen production under Vis/NIR light irradiation without any noble metals. Stable to oxidation core-shell Ti@TiO 2 nanoparticles have been obtained by the simultaneous actions of ultrasound and hydrothermal treatment on air-passivated titanium metal nanoparticles in pure water. The obtained material is composed of quasi-spherical Ti particles (20-80 nm) coated by 5-15 nm crystals of defect-free anatase with small amounts of rutile. In contrast to pristine TiO 2 , the Ti@TiO 2 nanoparticles extend the photo response from UV to NIR light region due to the light absorption by nonplasmonic Ti core. In MeOH-H 2 O solutions, the Ti@TiO 2 nanoparticles exhibit the strongest catalytic activity in H 2 formation under joint effect of Vis/NIR light and heat. Isotopic study using MeOH-D 2 O solutions suggested the reaction mechanism involving electron holes accumulation in semiconducting TiO 2 shell via charge separation and multiple charge-transfer steps that follow Ti interband transition. The electron transport from Ti core presumably occurs through the junctions between TiO 2 crystals at the surface of core-shell nanoparticles.

Insights into the Photothermal Hydrogen Production from Glycerol Aqueous Solutions over Noble Metal‐Free Ti@TiO2 Core–Shell Nanoparticles

“…The details are presented in the Experimental Section. Powder X‐ray diffraction data (XRD) analysis (Figure S1, Supporting Information) of air‐passivated Ti NPs are consisted with α‐phase of metallic titanium with admixtures of tetragonal titanium hydride TiH x in agreement with our previous results . The X‐ray patterns of treated Ti NPs clearly indicate the presence of crystallized anatase phase of TiO 2 in addition to metallic titanium.…”

“…290 °C) allowed to investigate the photothermal effect in larger temperature range compared to quite volatile methanol (b.p. 65 °C) studied in our previous work . Platinized titania was shown to exhibit a high photocatalytic activity in hydrogen production from GL solutions .…”

“…In this view, preparation of stable and nontoxic photocatalysts from earth‐abundant elements active at vis/NIR light is of great importance for sustainable energetics. In previous study, we found that Ti@TiO 2 core–shell nanoparticles (NPs) exhibit strong photocatalytic activity under joint effect of vis/NIR light and heat . More recently, photothermal effect also was reported for catalytic formic acid reforming in the presence of platinized titania .…”

Black Magic in Gray Titania: Noble‐Metal‐Free Photocatalytic H2 Evolution from Hydrogenated Anatase

“…[13] This finding triggered al arge amount of follow-up work and ac onsiderable number of beneficial effects of 'blackening' TiO 2 were reported,i ncluding photoelectrochemical H 2 production,p hotocatalytic pollution degradation, and use in supercapacitor electrodes. [21] In other words, as uitable hydrogenation treatment not only leads to av isible light absorption as reported by Chen, Mao, and co-workers,b ut also creates an intrinsic cocatalytic active center in TiO 2 ,s imilart ot he cocatalytic effect obtained by noble metal decoration. [21] In other words, as uitable hydrogenation treatment not only leads to av isible light absorption as reported by Chen, Mao, and co-workers,b ut also creates an intrinsic cocatalytic active center in TiO 2 ,s imilart ot he cocatalytic effect obtained by noble metal decoration.…”

A new strategy for utilization of NIR from solar energy—Promotion effect generated from photothermal effect of Fe3O4@SiO2 for photocatalytic oxidation of NO

“…Also, a stable core-shell Ti@TiO 2 with NIR response was reported. The photocatalyst could response from UV to NIR light region and exhibited photothermal effect as a result of Ti core [27]. These works pointed out a new path for the utilization of NIR light energy, but currently there was very few studies focused on Fe 3 O 4 and gas-solid phase photocatalytic reaction.…”