Biomass photocatalytic reforming for hydrogen production over nanostructured catalysts

Photoreforming of biomass, as a promising strategy, has gradually become an emerging field to be investigated within the last decade to mitigate the ever-increasing exhaustion of fossil fuels because biomass is a sustainable, clean energy and renewable resource. Photocatalytic reforming initiating with semiconductors is an efficient approach towards the conversion of solar energy and biomass into value-added chemicals and green hydrogen in a relatively mild condition. However, the low conversion efficiency of solar energy on current photocatalysts and the recalcitrant structure of the biomass (lignocellulose composed by cellulose, hemicellulose and lignin) always hinder the performance of photoreforming. Notably, the investigation of photoreforming is primarily divided into two basic pathways, e,g., hydrogen generation and high value-added chemicals production, during the whole research history. Therefore, this PhD study will achieve deep understanding of these mechanisms in the process of photoreforming by a series of high performance photocatalysts. Initially, glucose solution, as the basic unit of cellulose, was reformed to release a great amount of hydrogen by solar energy over three heterostructured ZnS modified carbon nitride (g-C3N4) which were respectively prepared by doping ZnS nanoparticles (10-15 nm diameters) on three different precursors, e.g., melamine, dicyanamide and urea. It is worth noting that ZMCN can exhibit a robust hydrogen generation rate (69.8 mmol gcat-1 h-1) among three modified g-C3N4. Then, the basic mechanism regarding hydrogen evolution is discussed in Chapter 3. Considering the low efficiency of charge transfer and separation on the three pristine g-C3N4, ultra-thin g-C3N4 was synthesised and introduced into the glucose reforming reaction with a performance around 15 times higher than that of pristine g-C3N4. Meanwhile, Pt single-atom were also loaded on the surface of ultra-thin g-C3N4 (melamine) to improve the photoresponse capacity by surface plasmon resonance (SPR) effect (Chapter 4). Moreover, the more efficient Z-scheme Van der Waals heterojunction was fabricated from the synergy of ZnIn2S4 and ultra-thin g-C3N4 (dicyanamide) which provided a further understanding for the photoreforming process (Chapter 5). Additionally, the competition of proton transfer between the β-O-4 dissociation and hydrogen production was identified through the S vacancy engineering in ZnIn2S4 nanosheets. The concentration and position of S vacancies were tuned to optimize the performance to increase the possibility of the photoerforming at the industry scale (Chapter 6). This PhD work unveils the fascinating mechanism in photocatalytic reforming of biomass via a series of different modifications on efficient photocatalysts, which underpins the photoreforming toward the industrialization level