Carbon quantum dots (CQDs) were synthesized by an electrochemical etching method. The CQDs are well-dispersed with uniform size about 5 nm. FT-IR spectra suggest the presence of many hydroxyl groups on the surface of CQDs. Here, CQDs with diameter approximately 5 nm, directly used as effective heterogeneous nanocatalysts for H-bond catalysis in aldol condensations, show excellent photoenhanced catalytic ability (89% yields when 4-cyanobenzaldehyde is used). It demonstrated that aldol condensation between acetone and aromatic aldehydes resulted in higher yields with visible light irradiation than in the dark, confirming visible light is necessary for good conversion. The H-bond catalytic activities of CQDs can be significantly enhanced with visible light irradiation. The high catalytic activities of CQDs are due to highly efficient electron-accepting capabilities. Repeated catalytic experiments suggest that the CQD catalyst can be easily recycled as a heterogeneous catalyst with a long catalyst life.

Carbon Quantum Dots with Photoenhanced Hydrogen-Bond Catalytic Activity in Aldol Condensations

Cooperative interactions between aminoalkylsilanes and silanols on a silica surface can be controlled by varying the length of the alkyl linker attaching the amine to the silica surface from C1 (methyl) to C5 (pentyl). The linker length strongly affects the catalytic cooperativity of amines and silanols in aldol condensations as well as the adsorptive cooperativity for CO2 capture. The catalytic cooperativity increases with the linker length up to propyl (C3), with longer, more flexible linkers (up to C5) providing no additional benefit or hindrance. Short linkers (C1 and C2) limit the beneficial amine–silanol cooperativity in aldol condensations, resulting in lower catalytic rates than with the C3+ linkers. For the same materials, the adsorptive cooperativity exhibits similar trends for CO2 capture efficiency.

Tuning Cooperativity by Controlling the Linker Length of Silica-Supported Amines in Catalysis and CO2 Capture

The structural and cooperative catalytic characteristics of acid and base co-functionalized mesoporous silica synthesized through grafting and co-condensation methods are investigated. It is shown that incorporation of the mutually reactive amine and carboxylic acid functional groups is aided by a protecting group in the grafting method. Using a thermally cleavable protecting group on the carboxylic acid organosilane, the differential effect of silanol removal and acid group functionalization on catalytic activity is studied. For samples prepared here by both the co-condensation and grafting procedures, the removal of silanols and the introduction of the carboxylic acid has a negative impact on activity of the catalyst in aldol condensations under the conditions used here. These results demonstrate that a weaker Bronsted acid silanol is more effective in cooperatively catalyzing the aldol condensation in combination with an amine base than the stronger carboxylic acid for all the materials prepared in thi...

Cooperative Catalysis with Acid–Base Bifunctional Mesoporous Silica: Impact of Grafting and Co-condensation Synthesis Methods on Material Structure and Catalytic Properties

Recyclable organocatalysts based on hybrid silicas

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1938&context=chem_pubs

Schunai Che

Papers

An amphoteric mesoporous silica catalyzed aldol reaction