ABSTRACT
Fluorescent carbon quantum dots (CQDs) rich in amine moieties that can be easily protonated under acidic conditions were electrostatically interacted with diblock copolymer poly[sodium(carboxylate sulfamate) isoprene]-b-poly(ethylene oxide) (CSS-IEO-3) possessing negatively charged sulfamate and carboxylate species on the CSS part of the diblock copolymer. The so-formed CQDs/CSS-IEO-3 material was found to be stable in a neutral and high salinity environment, which is critical when aiming for biological applications. Moreover, the photoluminescence of CQDs within CQDs/CSS-IEO-3, with emission at 420 nm upon excitation at 320 nm, was unaffected by pH and salinity changes, denoting the absence of significant aggregation phenomena and highlighting the potential of CQDs/CSS-IEO-3 for bioimaging. The photoluminescence of CQDs/CSS-IEO-3 was employed to develop a selective and sensitive method for the facile detection of Fe3+, in the presence of other metal salts, with a detection limit of 8.37 µM. Furthermore, integration of bovine serum albumin (BSA) furnished the three-component CQDs/CSS-IEO-3·BSA nanoensemble, without causing cytotoxicity when subjected to RKO human colon adenocarcinoma cell line. Evidently, confocal fluorescence microscopy allowed the imaging of CQDs/CSS-IEO-3·BSA within living cells, and illustrated its application potential for bioimaging and drug delivery.
ABSTRACT
The simultaneous polymer functionalization and exfoliation of graphene sheets by using mild bath sonication and heat treatment at low temperature is described. In particular, free-radical polymerization of three different vinyl monomers takes place in the presence of graphite flakes. The polymerization procedure leads to the exfoliation of graphene sheets and at the same time the growing polymer chains are attached onto the graphene lattice, which gives solubility and stability to the final graphene-based hybrid material. The polymer-functionalized graphene sheets possess fewer defects as compared with previously reported polymer-functionalized graphene. The success of the covalent functionalization and exfoliation of graphene was confirmed by using a variety of complementary spectroscopic, thermal, and microscopy techniques, including Raman, IR and UV/Vis spectroscopy, thermogravimetric analysis, and transmission electron microscopy.
ABSTRACT
Amphiphilic block copolymer poly(isoprene-b-acrylic acid) (PI-b-PAA) was used to stabilize exfoliated graphene in water, allowing the immobilization of semiconductor CdS nanoparticles forming CdS ⢠PI-b-PAA/graphene. Characterization using high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy proved the success of the preparation method and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS ⢠PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS ⢠PI-b-PAA/graphene, in the presence of ammonium formate as a quencher for the photogenerated holes, resulted in the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (>80 ± 4% at 20 min; 100% at 24 min), much faster and more efficient compared to when reference CdS ⢠PI-b-PAA was used as the photocatalyst (<30 ± 3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS ⢠PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS ⢠PI-b-PAA/graphene was rationalized in terms of effective separation of holes and electrons, contrary to reference CdS ⢠PI-b-PAA, in which rapid recombination of the hole-electron pair is inevitable due to the absence of exfoliated graphene as a suitable electron acceptor.
