Abstract
Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1−x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x(CuInS2)1−x/ZnS (core–shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose—quantum dot hybrid aerogels have apparent densities of 37.9–57.2 mg cm−3. Their BET surface areas range from 296 to 686 m2 g−1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)2 route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO2 drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.
Highlights
Aerogels are fascinating functional materials that consist of coherent open-porous networks of loosely packed, bonded particles or fibers and feature very low densities at high specific surface area (Liebner et al 2013)
Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1-x/ZnS quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels
Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x (CuInS2)1-x/ZnS QDs by 1-mercapto-3(trimethoxysilyl)-propyl ligands
Summary
Aerogels are fascinating functional materials that consist of coherent open-porous networks of loosely packed, bonded particles or fibers and feature very low densities at high specific surface area (Liebner et al 2013). To the best of our knowledge, the current paper describes for the first time the direct replacement of a considerable percentage of long-chain mercaptoalkyl groups introduced during thermolysis to prevent QDs from agglomeration by a-mercapto-x-trialkoxysilyl ligands at room temperature, the furnishing of alloyed (ZnS)x(CuInS2)1-x/ZnS (core/shell) QDs with ligands having terminal functionalities that can be used as anchor groups for covalent immobilization on cellulose, and eventually the preparation of highly openporous, lightweight, fluorescing cellulose aerogels with covalently immobilized QDs with high quantum yields of up to 30 % and emission colors within a wide range of the visible light
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