Photocatalytic selective oxidation of alcohols over triazine-based organic polymers

Liao, Longfei; Palkovits, Regina (Thesis advisor); Liauw, Marcel (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

The catalytic selective oxidation of aromatic alcohols to the corresponding aldehydes or ketones is a critical reaction for fine chemicals and intermediates in the chemical industry. Photocatalytic oxidation using metal-free photocatalysts presents a simple and environmentally benign alternative overcoming some limitations like harsh conditions used in the traditional methods. Therefore, different metal-free organic catalysts: black phosphorus-doped g-C3N4, thiophene-based CTFs, and sulfur-containing CTF-M@SBA-15 were prepared and used to evaluate the photocatalytic performance in photocatalytic oxidation of aromatic alcohols in this thesis.In Chapter 3, a novel efficient metal-free heterostructure catalyst of black phosphorus/g-C3N4 was successfully fabricated via a simple ball-milling synthetic method, and morphological structure analysis indicated that black phosphorus was homogeneously distributed on g-C3N4. Photocatalytic selective oxidation of various alcohols was applied to evaluate the photocatalytic performance of the prepared black phosphorus/g-C3N4 nanocomposites, and the results indicated that phosphorus-doped g-C3N4 possessed a higher conversion and selectivity than pure g-C3N4. Black phosphorus heteroatoms doping into graphitic carbon nitride changed the structure of g-C3N4, and the charge injection from g-C3N4 into black phosphorus leads to an efficient carriers’ separation by reducing the probability of recombination of photo-generated electron-hole pairs, which will also improve the catalytic performance. In Chapter 4, several sulfur-containing metal-free CTFs were successfully prepared via a new amidine-aldehyde polymerization method, and a variety of characterizations was used to study their physical and chemical properties. Photocatalytic selective oxidation of various alcohols was used to evaluate the photocatalytic performance of the prepared CTFs, and the results indicated that full conversion and a selectivity as high as 90% to benzaldehyde were obtained over thiophene-based CTFs in photocatalysis due to their narrowed band gap, and the fast photo-generated electron/hole separation and transfer. In Chapter 5, sulfur-containing monomers and molecular sieve SBA-15 were used to prepare CTF-M@SBA-15 via a solvent-free cyclization polymerization procedure under trifluoromethanesulfonic acid vapor. A variety of characterization methods were used to characterize the structure, morphology, physical and chemical properties, and photoelectric properties of the prepared CTFs. Besides, a sulfur-free CTF and carrier-free CTFs were used to make a comparison with those sulfur-containing CTF-M@SBA-15 in terms of photocatalytic performance and characteristics. The results indicated that the conversion of sulfur-containing CTF-BT@SBA-15 is almost 4 times higher than that of sulfur-free CTFs and 10 times that of carrier-free CTF-M, respectively, indicating that sulfur element and support materials play an important role in affecting the photocatalytic performance.In summary, black phosphorus-doped g-C3N4, thiophene-based CTFs, and sulfur-containing CTF-M@SBA-15 were prepared by facile and scalable methods. By tailoring the structure of g-C3N4 and CTFs with proper promotions, the materials can be activated for photocatalytic selective oxidation of various alcohols.