Separation and quantification of quantum dots and dissolved metal cations by size exclusion chromatography–ICP-MS

The prevalence of engineered metallic nanoparticles within electronic products has evoked a need to assess their occurrence and fate within environmental systems upon potential release of these nanoparticles. Quantum dots (QDs) are mixed-metal nanocrystals with the smallest of particle sizes (2–10 nm) that readily leach heavy metal cations in water, potentially creating a co-occurrence of nanoparticulate and dissolved metal pollutants. In this report, we develop a size exclusion chromatography–inductively coupled plasma–mass spectrometry method (SEC-ICP-MS) for the rapid separation and quantification of ~5-nm-sized CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations in water. The SEC-ICP-MS method provided a wide chromatographic separation of CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations only when using the smallest SEC column pore size available and an eluent composition that prevented loss of metals to column polymer surfaces by using a surfactant to ensure elution of QDs (ammonium lauryl sulfate) and a complexing ligand to ensure elution of metal cations (ethylenediaminetetraacetate). Detection limits were between 0.2 and 2 µg L^–1 for Cd²⁺ and Zn²⁺ among dissolved cation and QD phases, and ranges of linearity covered two to three orders of magnitude. Gold nanoparticles of sizes 5, 10, 20 and 50 nm were also effectively separated from dissolved Au³⁺ cations, illustrating the method applicability to a wide range of nanoparticle sizes and compositions. QD and dissolved metal concentrations measured by SEC-ICP-MS were comparable to those measured using the more conventional method of centrifuge ultrafiltration on split samples for dissolved and total metals. The applicability of the SEC-ICP-MS method to environmental systems was verified by measuring QDs and dissolved metals added to samples of natural waters. The method was also applied to monitoring CdSe/ZnS dissolution kinetics in an urban river water. The SEC-ICP-MS developed here may offer improved automation for characterising heterogeneous suspensions containing >1 µg L^–1 heavy metals.     

Role of entropy generation on thermal management of a porous solar collector using Al2O3–Cu/water nanofluid and magnetic field

Journal of Thermal Analysis and Calorimetry - The purpose of this study is a presentation of the thermal management of a flat plate solar collector via employing entropy generation analysis. The...     

A multi-period inventory model with multi-dimensional procurement bidding

We consider a multi-period inventory model with raw material procurements carried out via a reverse auction. Bids are multi-dimensional, and they consist of supplier information of price, shortage quantity and lead time. This work is an extension of our earlier work that has focused on multi-dimensional procurement auctions in single-period inventory models, to multi-period settings. The new model is based on a hybrid approach combining stochastic dynamic programming and simulation.     

Thermal performance assessment of a flat-plate solar collector considering porous media,hybrid nanofluid and magnetic field effects

Journal of Thermal Analysis and Calorimetry - In this work, a numerical study of thermal performance enhancement of a flat plate solar collector has been presented. The collector channel is...     

A lower bound for the length of a partial transversal in a Latin square

It is proved that every n×n Latin square has a partial transversal of length at least n−O(log²n). The previous papers proving these results (including one by the second author) not only contained an error, but were sloppily written and quite difficult to understand. We have corrected the error and improved the clarity.     

An investigation of intelligent tires using multiscale modeling of cord-rubber composites

A computational model based on the multiscale progressive failure analysis is employed to provide the theoretical predictions for damage development in the cord-rubber composites in tires. Vulcanized rubber, reinforcing belts, and carcass used in tire structures cause the anisotropic behavior under different loading conditions. Steel reinforcement layers made of steel wires combined with rubber complicate the macro-scale finite element modeling of tires. This paper presents a new three-dimensional model of the cord-rubber composite used in tires in order to predict the different types of damage including matrix cracking, delamination, and fiber failure based on the micro-scale analysis. Additionally, intelligent tires have the potential to be widely used to enhance the safety of road transportation systems, and this paper provides an estimation of the effects of void volume fraction, fiber volume fraction, and stacking sequence of the cord-rubber composites on the acceleration profile of the tire measured at the inner-liner.     

Synthesis of new functionalized reduced graphene oxide quantum dot composite for high-performance NO2 gas sensor

Research on Chemical Intermediates - In this research, synthesis of a novel magnetic 2-naphthalenesulfonic acid-grafted reduced graphene oxide quantum dot (Fe3O4-rGOQD-naphthalene-2-SO3H) via a...     

On a cooperative advertising model for a supply chain with one manufacturer and one retailer

, , ,  and  recently studied a game-theoretic model for cooperative advertising in a supply chain consisting of one manufacturer and one retailer. However, the sales-volume (demand) function considered in this model can become negative for some values of the decision variables, and in fact, this does happen for the proposed Stackelberg and Nash equilibrium solutions. Yue et al. (2006) acknowledge the negativity problem and suggest two constraints to fix it; however, they do not incorporate these constraints into their mathematical analysis. In this paper, we show that the results obtained by analyzing the advertising model under the constraints suggested by Yue et al. can differ significantly from those obtained in the previous papers.     

Synthesis and characterization of ZnO-functionalized multiwall carbon nanotubes nanocomposite as NOx gas sensor

Research on Chemical Intermediates - Synthesis of nano-zinc oxide-oxidized multiwall carbon nanotubes (ZnO-OMWCNTs) nanocomposite with different weight percentages of OMWCNTs via a multistep...