Highly fluorescent C-dots obtained by pyrolysis of quaternary ammonium ions trapped in all-silica ITQ-29 zeolite

Abstract

Abstract.C-dots obtained in homogeneous phase may exhibit a broad particle size distribution. Formation of C-dots within nanometric reaction cavities could be a methodology to gain control on their size distribution. Among the various possibilities, in the present work, the cavities of small pore size zeolites have been used to confine C-dots generated by pyrolysis of the organic structure directing agent present in the synthesis of these crystalline aluminosilicates. To explore this methodology, ITQ-29 zeolite having a Linde type A (LTA) structure was prepared as pure silica with 4-methyl-2,3,6,7-tetrahydro-1H,5H-pyrido[3.2.1-ij]quinolinium as organic structure directing agent. Pyrolysis under inert atmosphere at 550 ºC of a pure-silica ITQ-29 sample (cubic particles of 4 m edge) renders a highly fluorescent zeolite containing about 15 wt.% of carbonised residue. While other small pore zeolite, ITQ-12 (ITW), also renders photoluminescence C-dots under similar conditions, medium or large pore zeolites, such as silicalite (MFI) or pure silica Beta (BEA), failed to produce fluorescent powders under analogous thermal treatment and only decomposition and complete removal of the corresponding quaternary ammonium ion templates was observed for these zeolites. Dissolution of the pyrolysed ITQ-29 zeolite framework and extraction of the carbon residue with ethyl acetate has allowed characterisation of C-dots with particle size between 5-12 nm and a photoluminescence quantum yield of 0.4 upon excitation at 350 nm that is among the highest reported for non surface functionalized C-dots. The photoluminescence varies with the excitation wavelength and is quenched by oxygen. Pyrolysed ITQ-29 powders can act as fluorescent oxygen sensor.

Carbon Dots‐in‐Matrix Boosting Intriguing Luminescence Properties and Applications

“…Note that the selection of a suitable zeolite host is a key for pyrolysis of organo‐templated zeolites to generate CDs. Baldovi et al revealed that small pore zeolites ITQ‐29 (LTA) and ITQ‐12 (ITW) might facilitate the generation of CDs in zeolites during heating treatment, whereas medium or large pore zeolites silicalite (MFI) or pure silica Beta (*BEA) led the complete removal of occluded organic templates . Due to their high thermal stability, zeolite structures are almost retained in the reported CDs@zeolite composites, but CDs should be embedded in the interrupted nanospaces or reside on the external surface of zeolite matrices due to the larger size of CDs (≈2–6 nm) compared to the diameter of micropores (less than 2 nm).…”

Amino acid functionalized blue and phosphorous-doped green fluorescent carbon dots as bioimaging probe

“…5 In top-down approach, graphite and its derivatives are used to synthesize CDs through laser ablation, arc discharge and electrochemical oxidation. [21][22][23][24][25][26] In general, due to their simple and cost effective approach, bottom-up is more favourable than that of top-down techniques. [21][22][23][24][25][26] In general, due to their simple and cost effective approach, bottom-up is more favourable than that of top-down techniques.…”

Revival of Zeolite‐Templated Nanocarbon Materials: Recent Advances in Energy Storage and Conversion

“…Baldovi et al employed small pore zeolites, ITQ-29 (LTA structure), and ITQ-12 (ITW structure) as rigid templates, tetramethylammonium hydroxide (TMAOH), 4-methyl-2,3,6,7tetrahydro-1H,5H-pyrido[3.2.1-ij]quinolinium hydroxide, and 1,3,4-trimethylimidazolium as the organic structure directing agent respectively. [159] After compressing to high pressure of 3 Ton cm −2 , these pelletized zeolite samples were calcined in inert atmosphere at required temperature. Carbon dots with particle size from 5 to 12 nm were obtained after etching the matrix of ITQ-29 and ITQ-12.…”