Dependence of Hydrocarbon Sensitivity on the Distance of Linked Phenyl Group to CdSe Quantum Dots Surfaces

Abstract

The hydrocarbon sensing properties of CdSe semiconductor quantum dots (QDs) tailored with benzoic, phenylacetic, 4-phenylbutanoic, or 6-phenylhexanoic acids as a surface enhancement agent have been studied to determine their dependence on the phenyl group distance from the QD surface. QDs of roughly the same size were used to attach each of the mentioned surface agents with similar surface coverages, as determined by nuclear magnetic resonance technique, followed by drop-coating and drying of the QD solutions onto porous anodic aluminum oxide substrates for sensing tests. Results indicated that normalized photoluminescence (PL) enhancement did not vary noticeably for QDs with longer chained phenyl groups compared to those with shorter length groups upon film exposure to xylenes vapors over the range of 15 to 9400 ppm in a balance of air. The quantum yield of CdSe QDs with the 6-phenylhexanoic acid surface ligand has a higher value, 29.4%, compared to those with benzoic acid, 4.5%. Moreover, the PL sensitivity toward xylenes exposure for QDs with 6-phenylhexanoic acid versus those with the surface-bound benzoic acid was about 8 times and 16 times greater at xylenes concentrations below 2500 ppm and above 4500 ppm, respectively. These results suggest that the QDs with longer length surface-enhancing ligands are more promising for this type of hydrocarbon sensing applications.

Surface functionalized manganese ferrite nanocrystals for enhanced uranium sorption and separation in water

“…Magnetic metal oxide nanocrystals, including iron-and manganese oxides, have shown considerable potential for application in radionuclide sorption, separation, sensing, and stabilization, all of which remain critical challenges for a number of disciplines. [1][2][3][4][5][6][7][8] For uranium in particular, such nanoscale oxide materials have demonstrated high sorption capacities due to both high surface to volume ratios, thermodynamically favorable surface chemistries (for chemisorption), and enhanced (surface) redox potentials. Varied oxidation states of surface transition metal ions (iron(II and III) and manganese(II, III, and IV)) underpin such processes including facile reduction and thus immobilization of soluble uranyl(VI) as uranium(IV) precipitates.…”

Semiconductor quantum dots for photoluminescence-based gas sensing

“…10,27,44 For example, it has been proposed to surface-modify CdSe core dots for sensitive and selective detection of aromatic hydrocarbon vapors by utilizing a combination of stabilizing ligands (TOPO and stearic acid (SA)) and interaction-enhancing functional agents. 10,28,38 As for the latter, the surface-modifying group such as benzoic acid (BA) is expected to enhance the QD interaction with the aromatic hydrocarbons through electrostatic π -π interactions between the grafted group and the target analyte.…”

“…Thus, it is of interest to study the dependence of hydrocarbon sensitivity on the distance of the linked phenyl group to the QD surfaces. 28 CdSe QDs of roughly the same size were synthesized with in situ attachment of BA, phenylacetic (PA), 4-phenylbutanoic (PBA), or 6-phenylhexanoic acids (PHA) surface agents with similar surface coverage, as determined by nuclear magnetic resonance techniques. This is important to confi rm since, as noted above, different surface coverage will likely affect the degree of ligand to QD charge transfer effects.…”

“…10,[12][13][14][15][16] A prominent characteristic of these nanoparticles is that their photoluminescent (PL) properties have shown strong sensitivity to surface-bound ligands, as well as to changes in their surrounding chemical environment, [17][18][19][20][21][22][23][24] rendering them promising candidates for chemical sensing applications. [25][26][27][28][29] Depending on the nature of these interactions, possible causes for environmental sensitivity include changes in the surface/interface trap states, charge trapping/untrapping (surface passivation) at these states, and charge or energy transfer with the surroundings, as well as charge relaxation dynamics such as trapping duration. It has been already shown that the PL intermittency of CdSe/zinc sulfi de (ZnS) core/shell QDs is correlated with the dielectric environment surrounding the QDs.…”

Multisize CdSe Nanocrystal/Polymer Nanocomposites for Selective Vapor Detection Identified from High-Throughput Screening Experimentation

“…We incorporated CdSe nanocrystals of different diameters into a poly­(methyl methacrylate) (PMMA) film and have found that each size of CdSe nanocrystals in this polymeric nanocomposite unexpectedly demonstrated its own photoluminescence (PL) response pattern upon exposure to polar and nonpolar vapors in air. Single-size/single-color CdSe quantum dots with different surface modifying groups were also encapsulated into PMMA films − and porous anodic aluminum oxide substrates , to study their response to organic vapors.…”