Carbon-based
sensors for the detection of ascorbic acid (AA) and
ferric ions have drawn a great deal of attention recently, owing to
their excellent optical properties and good biocompatibility for biological
applications. In this work, a series of nitrogen-doped carbon dots
(NCDs) were fabricated by a microwave-assistant approach with a combination
of dl-malic acid and urea as precursors. Under optimal experimental
conditions, NCDs with an average size of 4.52 ± 0.05 nm were
prepared, containing amino N and C–N functional groups on the
surface of carbon cores. Optical analysis showed that the NCDs exhibited
excitation-dependent and concentration-dependent emission properties.
A single emission at 450 nm was observed with two luminescent centers
at 280 and 370 nm for concentrations ranging from 0.02 to 0.08 mg/mL.
Moreover, the NCDs were further used as a fluorescence sensor to detect
AA and Fe3+ in solution. From the metal ion sensing research,
Fe3+ demonstrated significant quenching abilities on NCDs
with a detection limit of 1.9 μM. More importantly, the NCDs
also showed an excellent quenching response by AA through the static
quenching mechanism and inner filter effect with a detection limit
of 2.6 μM. Additionally, the low cell toxicity against MA104
and 293T cells from both monkeys and humans were affirmed, respectively.
Therefore, the NCDs developed in the present work provide a “turn-off”
strategy for the highly sensitive detection of AA and Fe3+ ions and can be potentially applied in both environmental and biological
systems.
A novel anionic surfactant-templated synthesis of ZnO/mesoporous silica nanocomposites has been carried out by using N-hexadecylethylenediamine triacetate (HED3A), a triprotic surfactant, as the structure-directing agent. The chelating template can capture zinc ions in solution and then direct the mesophase formation, enabling an amount of zinc oxide to be embedded in the porous silica matrix during calcination. With variation of the molar ratio of Zn(2+) to HED3A in the template, a series of composites with different doping amounts were obtained after the removal of organic components. The variation of the zinc ion concentration in the initial template solution induces an evolution of the silica mesophase, presumably due to the change in electronegativity of the HED3A headgroup caused by the chelating effect. Spectroscopic studies show a strong host-guest interaction between the silica pore walls and ultrafine ZnO nanoparticles. The photoluminescence properties of the resulting composites exhibit a size-dependent light emission and quantum-confinement effect of ZnO, accompanied by an infrequent violet emission originating from the ZnO-SiO(2) interface.
A facile in situ approach has been designed to synthesize zinc ferrite/mesoporous silica guest-host composites. Chelating surfactant, N-hexadecyl ethylenediamine triacetic acid, was employed as structure-directing agent to fabricate mesoporous silica skeleton and simultaneously as complexing agent to incorporate stoichiometric amounts of zinc and iron ions into silica cavities. On this basis, spinel zinc ferrite nanoparticles with grain sizes less than 3 nm were encapsulated in mesoporous channels after calcination. The silica mesostructure, meanwhile, displayed a successive transformation from hexagonal p6mm through bicontinuous cubic Ia3̅d to lamellar phase with increasing the dopant concentration in the initial template solution. In comparison with zinc ferrite nanopowder prepared without silica host, the composite with bicontinuous architecture exhibited higher sensitivity, lower detection limit, lower optimum working temperature, quicker response, and shorter recovery time in sensing performance toward hydrogen sulfide. The significant improvements are from the high surface-to-volume ratio of the guest oxides and the three-dimensional porous structure of the composite. We believe the encapsulation route presented here may pave the way for directly introducing complex metal oxide into mesoporous silica matrix with tailorable mesophases for applications in sensing or other fields.
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