Precious-metal free catalysts for photochemical organo-hydride donor regeneration and reduction of small molecules /

Open in iSearch

Student Theses

2023

Kwok, Chun Leung Eric

Hong Kong : The Education University of Hong Kong

Thesis

Solar fuels are an alternative energy source to replace non-renewable and environmentally not friendly fossil fuels. Artificial photosynthetic reactions have attracted chemists to study their applications in solar energy conversion to storable fuels and synthesizing valuable products from earth-abundant feedstocks, including water, oxygen, and carbon dioxide. In recent years, photocatalytic systems involving precious-metal catalysts have been widely studied. In contrast, precious-metal-free photocatalytic systems, which are more environmentally friendly and economical, were seldom reported. It is important to develop effective precious-metal-free catalytic systems for solar energy conversion.Chapter 2 discovered a NAD(P)H synthetic analogue, 1-benzyl-1,4-dihydronicotinamide (1,4- BNAH), was regenerated photocatalytically from its conjugated cation, 1-benzylnicotinamide triflate (BNA+) by cobalt diimine-dioxime complexes and the BF2-bridged derivatives as the catalysts, in both organic and aqueous conditions with metal and organic photosensitizers. The maximum TONs (vs. catalyst) were found at 31.1 and 14.8 in organic and aqueous conditions, respectively, under the irradiation of visible light (λ > 420 nm). 1H NMR analysis confirmed the production of 1,4-BNAH, and the proton was provided by water.In chapter 3, a series of cobalt tripodal iminopyridine complexes, bearing substitutions with different electronic properties at the pyridine moieties for photocatalytic water reduction to hydrogen in precious-metal-free condition, using an organic photosensitizer, tri(n-butyl)triazatriangulenium dye, and sacrificial electron donor, triethylamine, in aqueous acetonitrile (2.5% (v/v)) was discussed. Under visible light irradiation (λ > 420 nm), hydrogen was produced, and the yield was improved by increasing the proton activity. The highest TONs of 1430−2810 were recorded with the pyridine moieties substituted cobalt catalysts, and the hydrogen yield was highly dependent on the catalytic potential (Ecat) of the catalysts, which varied by the electronic properties of the substituents.In chapter 4, it discovered a series of triangulenium dyes as the photocatalysts for oxygen reduction to hydrogen peroxide in the presence of triethylamine as the sacrificial electron donor in aqueous acetonitrile (5% (v/v)). A TON up to 4070 was recorded using the tri(n-butyl)triazatriangulenium photocatalysts after 6 hours of irradiation (λ = 470 nm). The hydrogen peroxide yield was decreased when more aza groups in the trianguleniums were replaced with oxa groups, while the E(PC+/•) shifted cathodically with an increasing number of aza groups in the PC (PC = photocatalyst). Further studies on photocatalytic oxidative N−N coupling of aniline yielded azobenzene as the major product when the same trianguleniums were used as photocatalysts. A TON up to 410 was recorded using the tri(n-butyl)triazatriangulenium photocatalysts after 24 hours of irradiation (λ = 470 nm)

LG51.H43 Dr 2023eb Kwokcle

https://educoll.lib.eduhk.hk/records/rGFjNpkR