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

Abstract

Photocatalytic production of hydrogen from renewable sources with platinum group metal‐free catalysts is of great importance for environmentally friendly energetics. Herein, Ti@TiO2 core–shell nanoparticles prepared by sonohydrothermal treatment of titanium metal nanoparticles are examined for hydrogen generation from aqueous glycerol solutions under vis/NIR light irradiation. It is shown that photocatalytic reforming of glycerol in the presence of Ti@TiO2 exhibits strong photothermal effect allowing more efficient use of solar energy. Apparent activation energy equal to E act = 27 ± 2 kJ mol−1 indicates that the thermal effect is related to the diffusion of reaction intermediates at catalyst surface rather than to the activation of chemical bonds. The photoexcitation mechanism of Ti@TiO2 particles involves interband transitions in nonplasmonic Ti metal core followed by nonradiative Landau damping. Effective electron–hole separation between Ti core and nanocrystalline TiO2 anatase shell in Ti@TiO2 nanoparticles is confirmed by photoluminescence spectroscopy. In studied system, photothermal hydrogen production is not accompanied by CO2 emission indicating that glycerol is oxidized to glyceric acid without further decarboxylation.

Tailoring Noble Metal-Free Ti@TiO2 Photocatalyst for Boosting Photothermal Hydrogen Production

“…Among Ti@TiO 2 NPs, the sample obtained at 214 • C displays the lowest R 2 value indicating the fastest charge transfer rate for this material. This conclusion is in an agreement with an effective charge separation in Ti@TiO 2 NPs recently demonstrated using photoluminescence spectroscopy (Nikitenko et al, 2018).…”

“…Stable Ti@TiO 2 NPs were prepared by SHT treatment of Ti nanopowder in pure water (Milli-Q 18.2 M •cm at 25 • C). The SHT reactor is shown in Supplementary Figure 1 and described previously (Cau et al, 2013;Nikitenko et al, 2015Nikitenko et al, , 2018. In a typical experiment, 2 g of air passivated Ti nanopowder was dispersed in 50 mL of water using ultrasonic bath, placed in SHT reactor and heated at selected temperatures in the range of T = 100-214 • C (autogenic pressure P = 1.0-19.0 bar) under simultaneous ultrasonic treatment (f = 20 kHz, P ac = 17 W) for 3 h. After cooling, the treated NPs were recovered by centrifugation, washed with pure water and dried at room temperature under reduced pressure.…”

“…Core-shell nanoparticles have attracted a great deal of attention as promising photocatalysts for hydrogen production due to the synergism between the cores and shells and/or new properties providing by the interactions between the cores and shells (Gawande et al, 2015). Recently, we reported strong photothermal effect in the process of photocatalytic hydrogen production from the aqueous solutions of methanol and glycerol in the presence of noble metal-free Ti@TiO 2 core-shell nanoparticles (NPs) (Nikitenko et al, 2015, Nikitenko et al, 2018. It is noteworthy that the combination of photonic and thermal energy could be very beneficial for efficient solar energy harvesting (Ma et al, 2020).…”

“…In this work, we applied simultaneous ultrasonic and hydrothermal treatment, called sonohydrothermal treatment (SHT), for the preparation of Ti@TiO 2 NPs with controlled Ti/TiO 2 ratio. SHT is an emerging environmentally benign technique effective for the synthesis of nanocrystalline materials with enhanced properties (Nikitenko et al, 2015, Nikitenko et al, 2018, Cau et al, 2013. Glycerol reforming was used to evaluate the photothermal performance of prepared Ti@TiO 2 NPs.…”

Sonocatalytic degradation of EDTA in the presence of Ti and Ti@TiO2 nanoparticles

“…Herein, we report, for the first time, sonocatalytic AOP of EDTA using nanoparticles (NPs) of metallic titanium, Ti 0 , and core-shell Ti@TiO 2 NPs. It has been recently shown that Ti@TiO 2 NPs exhibit strong photothermal effect in the process of photocatalytic hydrogen production from aqueous solutions of methanol [8] and glycerol [9] . Photocatalytic activity of core-shell Ti@TiO 2 NPs has been attributed to the effective charge separation [(TiO 2 h+ )(Ti e− )], where h + in photoexcited core-shell particles.…”