Chemical Industry & Chemical Engineering Quarterly Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ Chem. Ind. Chem. Eng. Q. 24 (4) 303−307 (2018) CI&CEQ 303 PAULA DE FREITAS ROSA JAQUELINE COSTA MARTINS BRUNO DE ARAÚJO LIMA MARCOS VINÍCIUS CAMARGO OISHI MÔNICA LOPES AGUIAR ANDRÉ BERNARDO Chemical Engineering Department, Federal University of São Carlos, São Carlos, SP, Brazil SCIENTIFIC PAPER UDC 544.772:546.57:66 ATOMIZATION OF SILVER NANOPARTICLES SUSPENSION AS AN ALTERNATIVE FOR GENERATING NANOSILVER AEROSOL Article Highlights • Simple way to generate silver nanoparticles • Applications in matrices such as antimicrobial • Use of a simple, inexpensive and easily accessible apparatus to generate the aerosol Abstract Nanomaterials are highly attractive for use in many applications, primarily due to their greater contact surface area and enhanced effects compared to the corresponding bulk materials. However, nanomaterials present risks to human health, since they are able to penetrate deep into the respiratory tract. It is therefore important to know the particle sizes of these substances, although such measurements can present difficulties associated with the generation of this type of material. It is also important to investigate the mechanism of aero- sol generation, considering the properties of the starting material. Here, evalu- ation was performed of the generation of an aerosol of silver nanoparticles from a suspension, using an environmentally friendly and simple synthesis method. A reduction reaction was used to produce the silver nanoparticles. The aerosol was generated using a modified nebulizer inhaler, and particles were counted using an SMPS system. The measurements showed that the predominant particle sizes were 45.63±2.49 nm (determined by SMPS) and 50.7±0.7 nm (determined by DLS analysis). Keywords: silver nanoparticles, aerosol generation, micro-nebulizer. Despite the increasing interest and research concerning nanomaterials, there are potential health risks associated with the uses of nanoparticles in areas including the pharmaceutical industry [1,2], computing, engineering and medicine [3,4]. In the specific case of silver nanoparticles (AgNPs), it is important to understand how effectively the aerosol retains the properties of silver, as well as the degree of agglomeration of the original particles. Silver par- ticles have a biocidal effect and can be used sup- ported or in the composition of numerous materials and matrices. These materials and matrices can be used for decontamination or in inhibiting the growth of Correspondence: P.F. Rosa, Chemical Engineering Department, Federal University of São Carlos, São Carlos, SP, Brazil. E-mail: [email protected]Paper received: 26 August, 2017 Paper revised: 2 January, 2018 Paper accepted: 6 February, 2018 https://doi.org/10.2298/CICEQ170826002R microorganisms on surfaces [5,6]. AgNPs can be sus- pended in liquids to be aerosolized and used as anti- microbials, for example, in personal hygiene products (such as throat and anti-odor sprays) [7], catheters [8] and disinfectant sprays [7], among other applications. There are many methods available for gener- ating metal nanoparticles, including spark generation [9,10], electrospray pyrolysis [11], chemical vapor deposition and sputtering. Currently, many atomizat- ion methods are performed; however, the authors performed atomization using electricity or flame [12,13]. Thus, this work shows promise in not having the need to use these energy sources for aerosol generation. A useful and economical method to generate aerosols is by spraying a solution or suspension [14]. A cloud of droplets is generated during atomization of the solution, followed by evaporation of the liquid by heat exchange with the environment. In this part of the process, a solution containing nanoparticles is
Transcript
Chemical Industry & Chemical Engineering Quarterly
Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ
Chemical Engineering Department, Federal University of São Carlos,
São Carlos, SP, Brazil
SCIENTIFIC PAPER
UDC 544.772:546.57:66
ATOMIZATION OF SILVER NANOPARTICLES SUSPENSION AS AN ALTERNATIVE FOR GENERATING NANOSILVER AEROSOL
Article Highlights • Simple way to generate silver nanoparticles • Applications in matrices such as antimicrobial • Use of a simple, inexpensive and easily accessible apparatus to generate the aerosol Abstract
Nanomaterials are highly attractive for use in many applications, primarily due to their greater contact surface area and enhanced effects compared to the corresponding bulk materials. However, nanomaterials present risks to human health, since they are able to penetrate deep into the respiratory tract. It is therefore important to know the particle sizes of these substances, although such measurements can present difficulties associated with the generation of this type of material. It is also important to investigate the mechanism of aero-sol generation, considering the properties of the starting material. Here, evalu-ation was performed of the generation of an aerosol of silver nanoparticles from a suspension, using an environmentally friendly and simple synthesis method. A reduction reaction was used to produce the silver nanoparticles. The aerosol was generated using a modified nebulizer inhaler, and particles were counted using an SMPS system. The measurements showed that the predominant particle sizes were 45.63±2.49 nm (determined by SMPS) and 50.7±0.7 nm (determined by DLS analysis).
Despite the increasing interest and research concerning nanomaterials, there are potential health risks associated with the uses of nanoparticles in areas including the pharmaceutical industry [1,2], computing, engineering and medicine [3,4]. In the specific case of silver nanoparticles (AgNPs), it is important to understand how effectively the aerosol retains the properties of silver, as well as the degree of agglomeration of the original particles. Silver par-ticles have a biocidal effect and can be used sup-ported or in the composition of numerous materials and matrices. These materials and matrices can be used for decontamination or in inhibiting the growth of
Correspondence: P.F. Rosa, Chemical Engineering Department, Federal University of São Carlos, São Carlos, SP, Brazil. E-mail: [email protected] Paper received: 26 August, 2017 Paper revised: 2 January, 2018 Paper accepted: 6 February, 2018
https://doi.org/10.2298/CICEQ170826002R
microorganisms on surfaces [5,6]. AgNPs can be sus-pended in liquids to be aerosolized and used as anti-microbials, for example, in personal hygiene products (such as throat and anti-odor sprays) [7], catheters [8] and disinfectant sprays [7], among other applications.
There are many methods available for gener-ating metal nanoparticles, including spark generation [9,10], electrospray pyrolysis [11], chemical vapor deposition and sputtering. Currently, many atomizat-ion methods are performed; however, the authors performed atomization using electricity or flame [12,13]. Thus, this work shows promise in not having the need to use these energy sources for aerosol generation.
A useful and economical method to generate aerosols is by spraying a solution or suspension [14]. A cloud of droplets is generated during atomization of the solution, followed by evaporation of the liquid by heat exchange with the environment. In this part of the process, a solution containing nanoparticles is
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incorporated into a dry air stream, forming an aerosol. The sizes of the nanoparticles in the aerosol are a function of the characteristics of the atomized solution or suspension. This method is simple, environment-ally friendly (it does not generate toxic waste and does not release particles into the atmosphere as in the case of pyrolysis), and capable of reproducibly maintaining the characteristics of the particles gener-ated, such as size.
EXPERIMENTAL
Synthesis and characterization of silver nanoparticles suspension
The silver nanoparticles were prepared using the reduction method originally proposed by Turk-evich [15] and modified by Lee and Meisel [16], which was further studied by Rosa et al. [17], employing sodium citrate as a reducing agent.
A solution of silver nitrate was prepared by dis-solving 0.0339 g of AgNO3 (99% purity, Synth) in 200 mL of water. The reducing agent (sodium citrate, 99% purity, Qhemis) was prepared by mixing 0.50 g of the salt with 50 mL of water, resulting in an 1% solution. All these solutions were prepared with deionized water (18 MΩ cm) in glassware that had been pre-viously decontaminated with dilute nitric acid (HNO3). The habit, composition, and particle size distribution (PSD) of the synthesized materials were charac-terized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and dyn-amic light scattering (DLS), respectively. The SEM analyses were performed using a Philips XL-30 FEG SEM microscope. EDS detector was coupled to the SEM microscope. The DLS measurements employed a Malvern Zetasizer Nano ZS90 system.
Test rig
Figure 1 shows a schematic illustration of the test rig used to generate the silver nanoparticles aero-
sol, consisting of: 1) air purification filters, 2) aerosol generator, 3) diffusion dryer, 4) radioactive Kr-85 neutralizer, 5) filter medium support, 6) manometer, 7) radioactive Am-241 neutralizer, 8) flowmeter and 9) electrostatic classifier, condensation particle counter and computer for data acquisition. In the first section, the carrier gas was purified before proceeding to the aerosol generator. After generation, the aerosol passed (in sequence) through the diffusion dryer (for the removal of humidity), the first neutralizer, the filter support (in the present work, the filter medium was not used) and the second neutralizer. The aerosol then proceeded to the classifier and particle counter denominated scanning mobility particle sizer (SMPS).
Aerosol generator
The micro-nebulizer used (model I-205, NS) is simple, readily available, and widely used in hospital and home environments. This nebulizer is a double fluid type, with sections for the passage of compres-sed air and the nanoparticle suspensions. The device has a length of approximately 6.5 cm, with a 15 mL capacity reservoir coupled to an outlet nozzle. Com-pressed air is injected at the base through a 0.35 cm diameter hose, passing through the inside of the reservoir containing the suspension, which is forced to pass through a hole 1 mm in diameter, with the contact between the suspension and the high velocity air resulting in atomization. During this process, the larger droplets returned to the suspension. The dev-ice is illustrated in Figure 2.
Figure 2. Micro-nebulizer.
Figure 1. Layout of the test rig for generation of the silver nanoparticles aerosol.
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RESULTS AND DISCUSSION
Scanning electron microscopy was used to eva-luate the size of the nanoparticles. Figure 3a and b show images of the silver nanoparticles, acquired at different magnifications. It is possible to distinguish lumped agglomerates with submicrometric size, as well as individual particles. The greater magnification (Figure 3a) also allows distinguishing individual par-ticles smaller than 100 nm. It was possible to detect the presence of silver nanoparticles, which was con-firmed by means of transmission electron microscopy coupled with EDS detection. This analysis is shown in Figure 4.
The EDS scan from 0 to 10 keV showed clear peaks for aluminum (from the sample holder) and silver, confirming that the synthesized material cor-responded to silver.
Figures 5 and 6 show the size distributions of the generated nanoparticles, measured using two dif-ferent techniques. The analyses were performed in triplicate and the results are presented as the means of the measurements.
The particle size data provided by the particle counter (SMPS system) were summarized in terms of the median, mean, and mode values. The median is a
measure of central tendency that exactly indicates the central value of a data sample, and the value found was 51.36±0.47 nm. The mean value considers the entire data distribution, and the value obtained was 66.23±0.35 nm. The mode is a measure of central tendency, corresponding to the value observed most frequently in a data set, and here it was 45.65±2.49 nm. In the measurements made using the DLS tech-nique, values of 39±0.5 nm and 50.7±0.7 nm were obtained for the mean and the mode, respectively. DLS is a measure of the particles in the original liquid suspension, while SMPS is a measure of the particles in the gas. The proximity between the results of the two techniques indicates that the particles were car-ried from the liquid to the gas, without there being any significant change as classification or agglomeration. Thus, the results of this work suggest that nanopar-ticles can be designed in a liquid medium and carried to the gas by simple atomization, and this is a simpler and cheaper way to obtain gaseous suspensions of nanoparticles when compared to traditional methods aided by flame or electricity [12,13]. The measure-ments by the two techniques showed the importance of taking account of the particle size range consi-dered, as well as identifying the most appropriate descriptor of the data, depending on the aim of the
Figure 3. Silver nanoparticles images before being aerosolized – magnification of a) 80000× and b) 20000×.
Figure 4. EDS analysis of silver nanoparticles.
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Figure 5. Particle size distribution by SMPS.
Figure 6. Particle size distribution by DLS.
study. Kalimuthu et al. and Parashar et al. also syn-thesized in their work silver nanoparticles with sizes of 50 nm and confirmed the size of the particles syn-thesized using scanning electron microscopy (SEM) and transmission electronic microscopy (MET), res-pectively [18,19]. Thus, the technique used is shown to be in agreement with some presented in the lite-rature.
CONCLUSIONS
The results demonstrated that generation of sil-ver nanoparticles could be achieved in a simple and environmentally friendly way using a suspension syn-thesized by a reduction reaction, a simple commercial inhaler, and a controlled airflow. The results showed that the particle size distribution in the aerosol is quite similar to those dispersed in the liquid, which is con-firmed by the mode values measured by the two emp-loyed techniques, 45.63±2.49 nm (SMPS technique) and 50.75±0.75 nm (DLS technique).
Acknowledgments
The authors wish to thank FAPESP and CNPq for financial support.
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PAULA DE FREITAS ROSA JAQUELINE COSTA MARTINS
BRUNO DE ARAÚJO LIMA MARCOS VINÍCIUS CAMARGO
OISHI MÔNICA LOPES AGUIAR
ANDRÉ BERNARDO
Chemical Engineering Department, Federal University of São Carlos, São
Carlos, SP, Brazil
NAUČNI RAD
ATOMIZACIJA SUSPENZIJE NANOČESTICA SREBRA KAO ALTERNATIVA ZA DOBIJANJE AEROSOLA NANOSREBRA
Nanomaterijali su veoma atraktivni za mnoge primene, prvenstveno zbog njihove veće kontaktne površine i poboljšanih efekata u poređenju sa odgovarajućim materijalima u rasutom stanju. Međutim, nanomaterijali predstavljaju rizik za ljudsko zdravlje, jer mogu prodreti duboko u respiratorni trakt. Zbog toga je važno znati veličinu čestica ovih sup-stanci, iako takva merenja mogu biti praćena teškoćama vezanim za stvaranje ovog materijala. Takođe, važno je istražiti mehanizam dobijanje aerosola, s obzirom na oso-bine početnog materijala. U radu je izvršena evaluacija dobijanja aerosola nanočestica srebra iz suspenzije, korištenjem ekološki prihvatljive i jednostavne metode sinteze. Reakcija redukcije je korišćena za dobijanje nanočestica srebra. Aerosol je dobijen ko-rišćenjem modifikovanog inhalatora za raspršivanje, a broj čestica je meren pomoću SMPS sistema. Merenja su pokazala da je veličina čestica pretežno bila 45,63±2,49 nm (određene SMPS) i 50,7±0,7 nm (određene DLS analizom).
