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Influence of the Base Fluid and Surfactant Arrangement on the Enhancement of Heat Transfer in Metal–Nanofluids Used in Concentrating Solar Power Plants: A Molecular Level Perspective
Published in K.R.V. Subramanian, Tubati Nageswara Rao, Avinash Balakrishnan, Nanofluids and Their Engineering Applications, 2019
Elisa I. Martín, Antonio Sánchez-Coronilla, Javier Navas, Roberto Gómez-Villarejo, Rodrigo Alcántara, Concha Fernández-Lorenzo
The analysis of the RDFs for the Au nanofluid system with surfactant is shown below. The surfactant was tetraoctylammonium bromide, (C8H17)4NBr (TOAB). Thus, for this analysis, the N atom of the surfactant was taken as the reference atom of the interaction between the surfactant and the gold particles. The number of N atoms will indicate the number of surfactant molecules around the central atom. By analysing the RDFs corresponding to the Au-N pair at the three temperatures (100, 300, and 500 K), it is possible to understand the interaction between the Au and the surfactant molecule (Figure 18.10). The RDF for Au-N pair at 100 K shows two peaks centred around 7.3 and 7.9 Å that integer to one N atom each peak (Figure 18.10). With the increasing of the temperature up to 300 K, it is observed a shift of both peaks towards the Au, so, the RDF shows a wide peak centred around 6.7 Å that integrates two N atoms. Those atoms belong to two surfactant molecules at 300 K (Figure 18.10). However, it is of note that at higher temperature only a wide peak centred around 8.5 Å that integrates one N atom it is shown in Figure 18.10 for 500 K. Therefore, two surfactant molecules approach the gold cell occupying a first layer around the gold nanoparticle at low temperature (300 K), while these two surfactant molecules move away from gold unit cell at high temperature (500 K) with only one molecule remaining in the second layer.
Nanosensor Laboratory
Published in Vinod Kumar Khanna, Nanosensors, 2021
Rosso-Vasic et al. (2009) synthesized stable and brightly emitting amine (organic compounds of nitrogen, such as ethylamine, C2H5NH2, that may be considered ammonia derivatives, in which one or more hydrogen atoms have been replaced by a hydrocarbon radical)-terminated SiNPs with different alkyl chain lengths between the Si core and the amine end group. Their procedure was as follows: (i) 1.5 g of tetraoctylammonium bromide, TOAB or TOABr, [CH3(CH2)7]4NBr, molecular formula: C32H68BrN, were mixed with 100 mL of dry toluene (C7H8 or C6H5CH3). The mixture was sonicated (using ultrasound energy to agitate particles in a sample) for 30 minutes; this sonication was done under a flow of dry argon; (ii) 100 mL of Si(OCH3)4 (tetramethyl orthosilicate) was added through a gas-tight syringe and sonication was continued for 30 minutes allowing entry into the “micelles” (a submicroscopic aggregation of molecules, as in a droplet in a colloidal system); (iii) 2.3 mL of LiAlH4 [1 M in tetrahydrofuran (THF)] was added to the above for the formation of hydrogen-terminated SiNPs; (iv) After 30 minutes sonication, dry and de-aerated methanol (30 mL) was added to react with the surplus LiAlH4; (v) Alkylamine (a compound consisting of an alkyl group attached to the nitrogen of an amine; an example is ethylamine, C2H5NH2)-terminated NPs with three different alkyl chain lengths resulted in the reactions of degassed allyl-amine (2.7 g), hex-5-en-1-amine (2.4 g) and undec-10-en-1-amine (Cl11H23N) (4.4 g) to each flask with hydrogen-terminated SiNPs obtained under argon (Ar), in the presence of 40 μL of 0.05 M H2PtCl6 catalyst; (vi) after 30 minutes sonication, 3-aminopropyl, 6-aminohexyl, and 11-aminododecyl SiNPs were extracted with water; 3-aminopropyl = NH2CH2CH2CH2; 6-aminohexyl = C7H16N2O2, carbamic acid; dodecyl = CH3(CH2)10CH2. They were washed with ethyl acetate (EtOAc), CH3COOC2H5 or C4H8O2) and filtered thoroughly by passing through syringe membrane filters; and (vii) the resulting SiNPs were further purified by dialysis (the separation of smaller molecules from larger molecules or of dissolved substances from colloidal particles in a solution by diffusion through a selectively permeable membrane) against water to remove any remaining unreacted aminoalkene (amino = the radical -NH2; alkene = open chain hydrocarbons with one or more carbon–carbon double bonds, having the general formula CnH2n) and surfactant (a material that can greatly reduce the surface tension of a liquid when used in very low concentrations), that had remained with the NPs.
Nano-dimensional gold synthesis for biomedical applications: upscaling and challenges
Published in Particulate Science and Technology, 2023
Subhasis Chakraborty, Suvadeep Mal, Asim Halder, Suvadra Das, Kalyan Kumar Sen, Arup Mukherjee, Partha Roy
This method is a two-phase process developed in 1994 which involves AuNPs synthesis by altering the ratio of thiol to gold. This can produce a very small size apparently 2–5 nm in size. The principle of this method is to use a phase transfer agent e.g.,: tetraoctylammonium bromide (TOAB) and transfer gold salts into organic solvent from aqueous solution (Kemp et al. 2009) (Figure 1). Then the reduction of the gold is done by sodium borohydride along with an alkanethiol. A color change is visible in the solution from orange to deep brown due to the stabilization of AuNPs by alkanethiols (Venkatpurwar and Pokharkar 2010; Du et al. 2007) followed by purification of the nano dimensional gold.
Gold nanoparticles as radiosensitizer for radiotherapy and diagnosis of COVID-19: A review
Published in Nanoscale and Microscale Thermophysical Engineering, 2022
Abdul Khaliq Mokhtar, Norsyahidah Mohd Hidzir, Faizal Mohamed, Irman Abdul Rahman, Syazwani Mohd Fadzil, Afifah Mardhiah Mohamed Radzi, Nur Ain Mohd Radzali
Brust method involves two-phase process; first step is the move of gold salt to organic solvent such as toluene from aqueous solution using tetraoctylammonium bromide (TOAB) as phase transfer reagent and stabilizing agent, and second step involves the reduction of gold using sodium borohydride (NaBH4) in the presence of an alkanethiol [96]. This method produced low dispersity AuNPs in size between 1.5–5.2 nm by varying the thiol-to-gold ratio [97]. The alkanethiols stabilize the AuNPs thus resulting in color changes from orange to brown [97].