Assessment of Photocatalytic Hydrogen Production from Biomass or Wastewaters Depending on the Metal Co-Catalyst and Its Deposition Method on TiO2

Abstract

A systematic study on the solar photocatalytic hydrogen production (photoreforming) performance of M/TiO2 (M = Au, Ag, Cu or Pt) using glucose as a model substrate, and further extended to lignocellulose hydrolysates and wastewaters, is herein presented. Three metal (M) co-catalyst loading methods were tested. Variation of the type of metal results in significantly dissimilar H2 production rates, albeit the loading method exerts an even greater effect in most cases. Deposition-precipitation (followed by hydrogenation) or photodeposition provided better results than classical impregnation (followed by calcination). Interestingly, copper as a co-catalyst performed satisfactorily as compared to Au, and slightly below Pt, thus representing a realistic inexpensive alternative to noble metals. Hydrolysates of either α-cellulose or rice husks, obtained under mild conditions (short thermal cycles at 160 °C), were rich in saccharides and thus suitable as feedstocks. Nonetheless, the presence of inhibiting byproducts hindered H2 production. A novel photocatalytic UV pre-treatment method was successful to initially remove the most recalcitrant portion of these minor products along with H2 production (17 µmol gcat−1 h−1 on Cu/TiO2). After a short UV step, simulated sunlight photoreforming was orders of magnitude more efficient than without the pre-treatment. Hydrogen production was also directly tested on two different wastewater streams, that is, a municipal influent and samples from operations in a fruit juice producing plant, with remarkable results obtained for the latter (up to 115 µmol gcat−1 h−1 using Au/TiO2).

Hydrogen photogeneration using ternary CuGaS2-TiO2-Pt nanocomposites

“…This may indicate a core-shell structure for the noble metal component, with an inner metallic layer and an outer oxidized layer. Such a structure has been shown to be beneficial for photo-activity [53]. holes and valence band free holes with trapped electron.…”

Simultaneous H2 Production and Bleaching via Solar Photoreforming of Model Dye‐polluted Wastewaters on Metal/Titania

“…Experimental metal loadings and average particle sizes, as preliminarily published, [39] are given for convenience in Table S2 for all M /TiO 2 materials. Whilst loadings are close to the expected 1 % value (despite occasional divergence), large differences in particles sizes are observed, depending on the metal and its deposition method, as hinted above according to XRD data.…”

“…The M /TiO 2 ( M =Au, Ag, Cu or Pt; 1 % w / w nominal loading) photocatalysts were prepared by either deposition‐precipitation followed by hydrogenation ( H,DP M /TiO 2 ), photodeposition ( PD M /TiO 2 ) or impregnation followed by calcination ( IM M /TiO 2 ), as previously reported [39] . The procedures are briefly described herein as follows.…”

“…This is consistent with previous results obtained in our laboratories using glucose as the substrate. [39] A recent report by Idriss and co-workers suggested that photocatalytic H 2 production from ethanol/water mixtures is enhanced on relatively large (> 5 nm) Au particles as compared to Pd or Pt. [91] The same research team proved that activities per Au surface atom did not vary noticeably across a wide particle size range (3-30 nm).…”

“…[17,36] Despite the considerable amount of fundamental knowledge on photoreforming using M/TiO 2 , most of the related research has been performed using the aforementioned and highly reactive hydroxyl-functionalised model substances (e. g. methanol, ethanol, glycerol or glucose), but less is known for resistant substrates such as biomass waste streams or noxious water pollutants. [22,[37][38][39] Transition to these more realistic substrates is expected to require additional insight on photocatalyst features, especially regarding the composition and morphology of metal co-catalysts.…”