Transformation of Silver Nanoparticles in Phosphate Anions: An

Laboratory Experiment pubs.acs.org/jchemeduc

Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

Transformation of Silver Nanoparticles in Phosphate Anions: An Experiment for High School Students Peter N. Njoki* Department of Chemistry and Biochemistry, Hampton University, Hampton, Virginia 23668, United States

J. Chem. Educ. Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/23/19. For personal use only.

S Supporting Information *

ABSTRACT: A laboratory experiment has been developed to illustrate the transformation of silver nanoparticles (Ag NPs) in water containing phosphate anions. The experiment, conducted by high school students, involved hands-on learning to synthesize and characterize Ag NPs via ultraviolet−visible (UV−vis) spectroscopy. This was followed by a UV−vis probe of the interaction of Ag NPs with phosphate anions. The observations of the color and shift in the absorption spectrum of NPs were explored to help students understand the transformation of NPs in water containing anions.

KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Hands-On Learning/Manipulatives, Laboratory Equipment/Apparatus, Minorities in Chemistry, Nanotechnology, Synthesis, UV−Vis Spectroscopy

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anions.19 Citrate anions physisorb (physically adsorb) on the surface of the Ag NPs and provide a negative charged Coulombic barrier to agglomeration. Coulombic barrier is the energy barrier due to the electrostatic interaction that two charged nanoparticles have to overcome before they can react. If this barrier is disrupted by cations and/or anions, the NPs tend to combine and aggregate.20 In this work, we describe 2 h hands-on laboratory experiments which were performed by two high school students (rising 10th and 11th graders) in a six-week summer research project.21 The students synthesized aqueous solution of citrate-stabilized Ag NPs by reducing a solution of silver nitrate (AgNO3) with sodium citrate (reducing agent/capping agent) and tannic acid solutions at refluxing temperature (100 °C) using a conventional heating mantle22,23 and at hydrothermal temperature of 100 °C using a laboratory microwave synthesizer.24 The NPs were characterized with UV−vis before and after reactions with phosphate anions. If accessible, transmission electron microscopy (TEM) analysis can be done to provide size and morphology of the NPs. Samples of Ag NPs were deposited on carbon-coated copper grids25 and sent to a local TEM user facility for analysis. Prior to performing laboratory experiments, the students attended a 2 h safety training. This was followed by a tour of the chemistry laboratory where the faculty mentor reinforced the lab and fire safety rules and showed the students the locations of eyewash, safety shower, fire extinguishers, and

INTRODUCTION Nanomaterials have become ubiquitous in our daily lives with about 2000 nanomaterial-based products in the market.1 According to data from the Woodrow Wilson Center’s Project on Emerging Nanotechnologies, ∼24% of nanomaterial-based consumer products contain nanosilver.1 Ag NPs are preferred due to their antimicrobial properties,2−4 and this has led to applications in dietary supplements, clothing, household, as well as baby products.1,5,6 While the promise of nanotechnology to enhance our quality of life appears boundless, it is inevitable that these nanomaterials will eventually get into the aquatic environment.7,8 Nanomaterials are released into the aquatic environment through domestic sewage (washing nanocontaining textiles, cosmetics or cleaning agents), industrial waste, urban runoffs, and agricultural application (fertilizer and pesticides).6,9−11 Ag NPs have distinct physicochemical properties, such as surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and catalytic activity, making them valuable in many applications.12,13 The functional application of Ag NPs requires understanding of how they react in the environment. The potential liberation of these NPs into the aquatic environment has raised concerns about their potential effect on the ecosystem and human health.14 Indeed, several studies have shown that Ag NPs can produce toxic effects on marine life. For example, the presence of Ag NPs in the water system leads to the poisoning of microorganisms,15 zebra fish,15 aquatic plants,16 and human cells (skin keratinocytes and lung fibroblast cells).17,18 Herein, we explore the transformation of citrate-stabilized Ag NPs in the presence of water containing phosphate © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: July 27, 2018 Revised: January 7, 2019

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DOI: 10.1021/acs.jchemed.8b00602 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education chemical storage.21 The students were then issued personal protective equipment (lab coats, goggles, and gloves) and notebooks. Students received an additional 2 h instruction on nanoscience, introductory chemistry, nanotechnology applications, and nanomaterial safety. The second day, we reviewed two journal articles22,23 on the synthesis of Ag NPs and YouTube videos26 on the transformation of nanomaterials in the environment. During the first lab activity, the students undertook handson learning and skill development of micropipette manipulation (10−100 μL, 100−1000 μL, 1000−5000 μL), the use of the analytical balance to weigh salts, and the operation of the UV−vis to measure absorbance of presynthesized NPs. Later, the students synthesized Ag NPs using the conventional heating mantle and microwave methods and characterized the optical properties of NPs utilizing UV−vis. Finally, they prepared a 0.5 M potassium phosphate monobasic (0.5 M KH2PO4) solution. This solution was used to investigate the transformation of Ag NPs over a period of 7 days. The transformation was monitored by change in color, absorbance, and shift in the SPR peak.

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HAZARDS

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EXPERIMENTAL PROCEDURES

Laboratory Experiment

Silver nitrate is a corrosive chemical that will stain and burn the skin and eyes; students and instructors working with solid silver nitrate should take appropriate precautions that include wearing appropriate personal protective equipment (chemical safety goggles, nitrile gloves, and lab coat.) In addition, proper attire including closed shoes, long pants, and long sleeves should be worn in the lab. The instructor should prepare the silver nitrate solution beforehand in order to reduce the students’ exposure. Furthermore, the students should be required to read the Safety Data Sheets (SDS) for the chemicals used in the experiment. To avoid burns, the students should handle hot glassware using heat resistant gloves. Additionally, a safety culture in the lab that calls for recognition of hazards, assessment and minimization of the risks of hazards, and preparation for emergencies should be adopted.27 Finally, silver waste should be treated as hazardous waste and disposed off per the hazardous waste guidelines.

EQUIPMENT AND REAGENTS

Reagents

Synthesis of Silver Nanoparticles Using Conventional Heating Mantle

Sodium citrate tribasic dihydrate (C6H5Na3O7·2H2O, 99%) was purchased from Acros Organics. Tannic acid (C76H52O46, ACS reagent) was from Sigma-Aldrich, and silver nitrate (AgNO3, 99.9+ %) and potassium phosphate monobasic (KH2PO4, 99%) were from Fisher Scientific. All reagents were used as received. Water was purified to 18 MΩ cm with a Barnstead water purification system. The following laboratory equipment and apparatus were employed: an analytical balance, a hot plate with magnetic stirrer (Figure S1), a heating mantle, a three-neck roundbottom flask equipped with a Liebig condenser, 0−110 °C thermometer, micropipettes, a microwave synthesizer (Figure 1),24 pressure rated glass reaction vials, and conventional laboratory glassware.

The faculty mentor premade the following stock solutions: sodium citrate tribasic dihydrate solution (sodium citrate), tannic acid, and silver nitrate. The synthesis of aqueous solution of Ag NPs was based on a modified method.22 Briefly, 10.0 mL of 3.88 × 10−2 M sodium citrate, 13.0 mL deionized water, and 1.0 mL of 2.70 × 10−4 M tannic acid solution were transferred into a clean 50 mL threeneck round-bottom flask and heated on a heating mantle while stirring. A Liebig condenser was used to prevent water loss during reflux. Once the mixture started boiling, 0.25 mL of 3.32 × 10−2 M silver nitrate solution was added. An immediate change in color from colorless solution to a yellow solution was noted. Heating was continued for 10 min. The reaction took 35 min to cool from 100 °C to room temperature. Synthesis of Silver Nanoparticles Using Microwave Method

A pipet was used to add 9.65 mL of deionized water and 7.42 mL of 3.88 × 10−2 M sodium citrate to a clean 35 mL pressure rated glass reaction vial that had a magnetic stirring bar. This was followed by addition of 0.742 mL of 2.70 × 10−4 M tannic acid using a micropipette, and finally 0.185 mL of 3.32 × 10−2 M silver nitrate was added (using a different pipet tip). The mixture was hermetically sealed and placed in the microwave. The sample was rapidly heated to the hydrothermal temperature of 100 °C, with pressure of 250 psi, and then held at this temperature for 10 min. The reaction took ∼2 min to reach 100 °C, with 10 min at a set point of 100 °C and 5 min to cool to below 50 °C. Fast cooling was facilitated by the influx of compressed air into the microwave cavity.

Figure 1. (Left) Microwave synthesizer and (right) a 35 mL pressure rated glass reaction vial used for synthesis of silver nanoparticles.

Optical Characterization of Silver Nanoparticles via UV−Vis Spectroscopy

The microwave synthesizer (Figure 1) operates at predetermined power, temperature, and pressure as reported in our previous work.25 The synthesis was done in 35 mL pressure rated glass vials that are specially made for this instrument (Figure 1). After the reaction, an influx of compressed air into the microwave reaction chamber was used to cool the product in a controlled manner.

Six new plastic cuvettes were rinsed with deionized water and air-dried. A measured amount of Ag NPs and deionized water were added to each of the five cuvettes for a total volume of 3.0 mL. In the sixth cuvette, 3.0 mL of deionized water was added as the blank (Table 1). B


Journal of Chemical Education

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Table 1. Comparison of Silver Nanoparticle Samples Used for UV−Vis Characterization Water

Total Volume of Solution

0 0.1 0.2 0.4 0.5 1.0

3.0 2.9 2.8 2.6 2.5 2.0

3.0 3.0 3.0 3.0 3.0 3.0

RESULTS AND DISCUSSION

Synthesis and Optical Characterization of Silver Nanoparticles

Sample Volume in mL Ag NPs


The synthesis and characterization were performed by high school students under the guidance of the faculty mentor. The

Characterization of Silver Nanoparticles Using Transmission Electron Microscopy

A volume of ∼10 μL of Ag NPs was deposited on a carboncoated copper grid (400 mesh) and dried in air. The dried sample was analyzed using a TEM operating at 120 kV accelerating voltage with a LaB6 filament. This was done at the Virginia Commonwealth University Nanomaterials Core Characterization facility (VCU NCC).

Figure 3. UV−vis spectra of different concentrations of Ag NPs in deionized water with the SPR at 394 nm which indicates nanoparticles of ∼10.0 nm as determined by TEM.

Probing the Transformation of Silver Nanoparticles in Phosphate Anions

Nine new cuvettes were rinsed with deionized water and airdried. A 0.2 mL portion of Ag NPs was added to each cuvette followed by deionized water and 0.5 M KH2PO4 solution for a total volume of 3.0 mL (Table 2). We noted the change in the color of the mixture and ran UV−vis to monitor the transformation of the Ag NPs in KH2PO4 over a period of 7 days. Table 2. Comparative Volume of Water, Silver Nanoparticles, and Potassium Phosphate Monobasic for the Transformation Study Figure 4. Schematic illustration of formation of citrate-stabilized Ag NPs in deionized water.

Sample Volume in mL Ag NPs

0.5 M KH2PO4

Deionized Water

Total Volume of Solution

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

0.0 0.1 0.2 0.4 0.5 0.6 0.7 0.8 1.0

2.8 2.7 2.6 2.4 2.3 2.2 2.1 2.0 1.8

3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0

NPs synthesized using the conventional heating mantle took ∼60 min from start to cooling to room temperature while those made via the microwave were ready within 17 min. The use of microwave technology shortens reaction time, making it possible to perform the reactions within the normal laboratory session.28 Furthermore, the microwave irradiation approach allows for the use of less solvent in the synthesis, which translates to less waste in accordance to the principles of green chemistry.29 Figure 2 shows pictures of diluted samples of Ag NPs after synthesis. The NPs were yellow in color and were

Figure 2. Pictures of different volumes of Ag NPs in deionized water with the amounts of Ag increasing from left to right. The NPs were yellow in color. C




Figure 5. (A) TEM image of microwave synthesized Ag NPs and (B) the corresponding histogram showing an average size of 10.0 ± 3.5 nm.

Figure 7. UV−vis spectra at 10 min showing the transformation of 0.2 mL of Ag NPs in different amounts of 0.5 M KH2PO4 (inset). The absorbance at 396 nm decreased, and a new peak emerged at ∼560 nm. This shows that the NPs aggregated to large NPs.

consistent for both methods. Sodium citrate was used as a reducing agent as it has a dual function of reducing and stabilizing the NPs while tannic acid controlled the size.22,30 Ag NPs have a distinct yellow color (Figure 2) which originates from a phenomenon known as surface plasmon resonance (SPR).22,23 The SPR absorption occurs in the UV− vis region of the electromagnetic spectrum and is dependent on size, shape, and surrounding medium.22,23 It emanates from the coherent excitation and collective oscillations of the free electron in the conduction band at the surface of NPs that is correlated with the electromagnetic field of the incoming light. The optical properties of NPs were characterized by a UV− vis spectrometer (Figure S5) between 300 and 800 nm. As shown in Figure 3, an SPR peak was obtained at 394 nm which is consistent with Ag NPs with a diameter of ∼10.0 nm.22 The reaction of AgNO3 and C6H5Na3O7·2H2O could be expressed as follows:

Characterization of Silver Nanoparticles Using Transmission Electron Microscopy

A representative TEM microgram of our Ag NPs is shown in Figure 5. The TEM image confirms the formation of spherical NPs with an average size of 10.0 nm as reported for similar syntheses.22 Transformation of Silver Nanoparticles in Phosphate Anions

The transformation19,33 of Ag NPs in various concentrations of aqueous solutions of 0.5 M KH2PO4 was studied over a period of 7 days. Shown in Figures 6 and 7 are the transformation results at 5 and 10 min. Our monitoring of the transformation of Ag NPs in the presence of the phosphate anions shows that the NPs were unstable as demonstrated by a change in color from yellow to pink in Figure 6. As the amount of 0.5 M KH2PO4 increased from 0.1 to 1.0 mL, Ag NPs aggregated into large particles. Figure 7 shows the UV−vis spectra after 10 min of adding 0.5 M KH2PO4. The results show a decrease in absorbance and a shift in the absorption peak at 394 nm to a longer wavelength band (∼560−580 nm) as the amount of 0.5 M KH2PO4 increased. This evolution reflects a decrease of free Ag NPs and the formation of Ag aggregates or Ag complexes34 such as AgPO3, Ag3PO4, and Ag2HPO4. The broad peak at ∼560−580 nm is consistent with particle aggregation which indicates scattered light from large aggregates. The aggregates are formed when added KH2PO4 displaces citrate from the surface of Ag NPs, thus lowering the repulsive

4Ag + + C6H5O7 Na3 + 2H 2O → 4Ag 0 + C6H5O7 H3 + 3Na + + H+ + O2 ↑

(1)

In this reaction, some of the sodium citrate reduced silver ions (Ag+) to Ag NPs, and the rest physisorbed on Ag NPs. The adsorption of citrate plays a prominent role in stabilizing growing Ag NPs by providing a particle surface charge20,32 as shown in the schematic illustration in Figure 4. The use of excess sodium citrate ensures that enough citrate molecules are available to stabilize the NPs by providing a negatively charged surface that prevents aggregation.

Figure 6. Picture at 5 min showing the change in color when 0.2 mL of Ag NPs was mixed with different amounts of 0.5 M KH2PO4. The color changed from yellow to pinkish as the amount of 0.5 M KH2PO4 increased (left to right). This demonstrates that the NPs aggregated to form larger sizes of Ag particles. D




Figure 8. Idealized illustration of interactions of Ag NPs with phosphate anions and shielding of charge that leads to particles aggregation.

the creation of Ag+ ions36 which react with phosphate ions causing aggregation and removal of Ag NPs from solution. In addition, the presence of oxygen can lead to oxidation of Ag NPs to Ag2O and subsequent reaction with protons in water to form Ag+ ions.36 After 148 h had elapsed (Figure 10), the absorbance at 398 nm continued to decrease and the absorption peak at ∼560 nm flattens, indicating instability of Ag NPs in KH2PO4 solution within the period of study. This trend was observed from 10 min (Figure 7) to 167 h (Figure S7). Electrostatic repulsive forces between NPs prevent nanoparticle aggregation, but this charge screening was removed by the presence of phosphates that induce aggregation of NPs.37 The color of the solutions at >0.4 mL of KH2PO4 changed to colorless, which is consistent with dissolution of Ag NPs to Ag+ ions and precipitation of NPs aggregates, thus removing Ag NPs from solution. The phosphate anions affect the aggregation rate of citrate-capped Ag NPs by increasing the ionic strength, which reduces the thickness of the electrical double layer around the NPs and lowers the barrier to aggregation. Furthermore, they replace physisorbed citrate anions with a chemisorbed layer of phosphate anions, which tends to reduce the surface charge, further lowering the repulsive barrier.20,31,38 As a final remark, the students were provided with hands-on training in conventional heating and microwave methods used in the synthesis of Ag NPs. They learned to operate the UV− vis spectrometer to characterize the optical property of Ag NPs, use micropipettes to measure small volumes, and use the analytical balance to weigh reagents. This activity engaged the students in basic nanotechnology research and introduced them to the transformation of nanomaterials in an aquatic environment. In addition, they acquired skills in laboratory safety, team work, data acquisition and processing, and communication of science to the community. The acquisition of these skills was demonstrated during a poster session, at the end of the six-week research program, where the students presented their work to the parents and Hampton University (HU) community.21 Two of the high school students were later invited to present posters at the annual HU School of Science research symposium. The two students have since transitioned to college where they are pursuing Science, Technology, Engineering, and Mathematics (STEM) studies and coursework.

Figure 9. UV−vis spectra after 76 h showing the transformation of 0.2 mL of Ag NPs in different amounts of 0.5 M KH2PO4 (inset). The absorbance at 394 nm decreased with more anions, and the absorption peak shifted from 394 to 398 nm. The intensity of peaks at ∼560 nm decreases and flattens. The Ag NPs aggregates at ∼560 nm ionized or precipitated from the solution.

Figure 10. UV−vis spectra after 148 h showing the transformation of 0.2 mL of Ag NPs in different amounts of 0.5 M KH2PO4 (inset). The absorbance at 398 nm decreased with time while the peaks at ∼560 nm flatten (Figures 7 and 9 and Figure S7). The Ag NP aggregates at ∼560 nm ionized or precipitated from the solution.

electrostatic forces between the particles, Figure 8. The negative charges from citrate (Figure 4) keep the particles suspended in solution. Salts like KH2PO4 and NaCl shield the charges, allowing the particles to interact through electrostatic forces to form aggregates.19,32 As time progressed, the absorption peak at ∼560 nm decreased as the large aggregates precipitated from solution. Figure 9 shows the UV−vis after the elapse of 76 h since the addition of 0.5 M KH2PO4. The results show a decrease in absorbance and a shift in the absorption peak from 394 to 398 nm consistent with a slight size increase. In addition, the absorption peak at ∼560 nm decreased and flattened, indicating instability of the Ag NPs in KH2PO4 solution within the period of study. This is consistent with oxidative dissolution of Ag NPs to Ag+ ions35 in the presence of light. Light causes the ejection of electrons from Ag NPs leading to

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CONCLUSION The experiments provide a simple approach to introduce nanomaterials’ transformation in an aquatic environment containing phosphate anions. Ag NPs, which are ubiquitous in our lives, were used to illustrate transformation of nanomaterials in water containing phosphate anions. Work from this study can be applied in teaching upper high school students and first-year undergraduate students the chemistry of E




(7) Benn, T. M.; Westerhoff, P. Nanoparticle Silver Released into Water from Commercially Available Sock Fabrics. Environ. Sci. Technol. 2008, 42 (11), 4133−4139. (8) Panácě k, A.; Kvítek, L.; Prucek, R.; Kolár,̌ M.; Večeřová, R.; Pizúrová, N.; Sharma, V. K.; Nevěcň á, T.; Zbořil, R. Silver Colloid Nanoparticles: Synthesis, Characterization, and Their Antibacterial Activity. J. Phys. Chem. B 2006, 110 (33), 16248−16253. (9) Wiesner, M. R.; Lowry, G. V.; Alvarez, P.; Dionysiou, D.; Biswas, P. Assessing the Risks of Manufactured Nanomaterials. Environ. Sci. Technol. 2006, 40 (14), 4336−4345. (10) Luoma, S. N. Silver Nanotechnologies and The Environment: Old Problems or New Challenges; Woodrow Wilson International Center for Scholar Project on Emerging Nanotechnologies: Washington, DC, 2008. (11) Servin, A. D.; White, J. C. Nanotechnology in Agriculture: Next Steps for Understanding Engineered Nanoparticle Exposure and Risk. NanoImpact 2016, 1, 9−12. (12) McFarland, A. D.; Van Duyne, R. P. Single Silver Nanoparticles as Real-Time Optical Sensors with Zeptomole Sensitivity. Nano Lett. 2003, 3 (8), 1057−1062. (13) Panacek, A.; Kvítek, L.; Prucek, R.; Kolar, M.; Vecerova, R.; Pizurova, N.; Sharma, V. K.; Nevecna, T. J.; Zboril, R. Silver Colloid Nanoparticles: Synthesis, Characterization, and Their Antibacterial Activity. J. Phys. Chem. B 2006, 110 (33), 16248−16253. (14) Albrecht, M. A.; Evans, C. W.; Raston, C. L. Green Chemistry and the Health Implications of Nanoparticles. Green Chem. 2006, 8 (5), 417−432. (15) Levard, C.; Hotze, E. M.; Lowry, G. V.; Brown, G. E. Environmental Transformations of Silver Nanoparticles: Impact on Stability and Toxicity. Environ. Sci. Technol. 2012, 46 (13), 6900− 6914. (16) Metz, K. M.; Sanders, S. E.; Miller, A. K.; French, K. R. Uptake and Impact of Silver Nanoparticles on Brassica Rapa: An Environmental Nanoscience Laboratory Sequence for a Nonmajors Course. J. Chem. Educ. 2014, 91 (2), 264−268. (17) Nel, A.; Xia, T.; Madler, L.; Li, N. Toxic Potential of Materials at the Nanolevel. Science 2006, 311 (5761), 622−627. (18) Asharani, P. V.; Mun, G. L. K.; Hande, M. P.; Valiyaveettil, S. Cytotoxicity and Genotoxicity of Silver Nanoparticles in Human Cells. ACS Nano 2009, 3 (2), 279−290. (19) Baalousha, M.; Nur, Y.; Römer, I.; Tejamaya, M.; Lead, J. R. Effect of Monovalent and Divalent Cations, Anions and Fulvic Acid on Aggregation of Citrate-Coated Silver Nanoparticles. Sci. Total Environ. 2013, 454−455, 119−131. (20) Peterson, K. I.; Lipnick, M. E.; Mejia, L. A.; Pullman, D. Temperature Dependence and Mechanism of Chloride-Induced Aggregation of Silver Nanoparticles. J. Phys. Chem. C 2016, 120 (40), 23268−23275. (21) Claville, M. O. F.; Babu, S.; Parker, B. C. NanoHU: A Model of Community Mentoring for STEM Excellence at Hampton University. In Mentoring at Minority Serving Institutions (MSIs): Theory, Design, Practice and Impact; McClinton, J., Mitchell, D. S. B., Carr, T., Melton, M. A., Hughes, G. B., Eds.; Perspective on Mentoring Series; Information Age Publishing Inc.: Charlotte, NC, 2018; pp 225−238. (22) Bastús, N. G.; Merkoçi, F.; Piella, J.; Puntes, V. Synthesis of Highly Monodisperse Citrate-Stabilized Silver Nanoparticles of up to 200 nm: Kinetic Control and Catalytic Properties. Chem. Mater. 2014, 26 (9), 2836−2846. (23) Cooke, J.; Hebert, D.; Kelly, J. A. Sweet Nanochemistry: A Fast, Reliable Alternative Synthesis of Yellow Colloidal Silver Nanoparticles Using Benign Reagents. J. Chem. Educ. 2015, 92 (2), 345−349. (24) Zovinka, E. P.; Stock, A. E. Microwave Instruments: Green Machines for Green Chemistry? J. Chem. Educ. 2010, 87 (4), 350− 352. (25) Njoki, P. N.; Wu, W.; Lutz, P.; Maye, M. M. Growth Characteristics and Optical Properties of Core/Alloy Nanoparticles Fabricated via the Layer-by-Layer Hydrothermal Route. Chem. Mater. 2013, 25 (15), 3105−3113.

nanotechnology, transformation of nanomaterials, and aggregation and disposal of metallic nanoparticles in the environment.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00602.

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Notes for instructors, safety information, detailed experimental procedure, and characterization of Ag NPs before and after reaction with KH2PO4 (PDF, DOCX)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Peter N. Njoki: 0000-0001-5085-1178 Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS The high school students who participated in this work were supported through Nanoscience Transforming STEM Education at Hampton University (NanoHU) program, funded by the National Science Foundation through Historically Black Colleges and Universities Undergraduate Program (HBCUUP), Achieving Competitive Excellence (ACE) Implementation Award HRD-1238838. NanoHU provided opportunities for high school students (minorities in chemistry) to participate in a 6-week nonresidential summer research program. I would like to thank the high school students who participated in this laboratory activity and the Department of Chemistry & Biochemistry at Hampton University for the use of equipment, reagents, and instrumentation needed for this work. We also thank the VCU Nanomaterials Core Characterization facility for TEM access.

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REFERENCES

(1) Vance, M. E.; Kuiken, T.; Vejerano, E. P.; McGinnis, S. P.; Hochella, M. F., Jr.; Rejeski, D.; Hull, M. S. Nanotechnology in the Real World: Redeveloping the Nanomaterial Consumer Products Inventory. Beilstein J. Nanotechnol. 2015, 6, 1769−1780. (2) Kim, J. S.; Kuk, E.; Yu, K. N.; Kim, J. H.; Park, S. J.; Lee, H. J.; Kim, S. H.; Park, Y. K.; Park, Y. H.; Hwang, C. Y.; Kim, Y. K.; Lee, Y. S.; Jeong, D. H.; Cho, M. H. Antimicrobial Effects of Silver Nanoparticles. Nanomedicine 2007, 3 (1), 95−101. (3) Sondi, I.; Salopek-Sondi, B. Silver Nanoparticles as Antimicrobial Agent: A Case Study on E. coli as a Model for Gram-Negative Bacteria. J. Colloid Interface Sci. 2004, 275 (1), 177−182. (4) Balogh, L.; Swanson, D. R.; Tomalia, D. A.; Hagnauer, G. L.; McManus, A. T. Dendrimer-Silver Complexes and Nanocomposites as Antimicrobial Agents. Nano Lett. 2001, 1 (1), 18−21. (5) Marambio-Jones, C.; Hoek, E. M. V. A Review of the Antibacterial Effects of Silver Nanomaterials and Potential Implications for Human Health and the Environment. J. Nanopart. Res. 2010, 12 (5), 1531−1551. (6) Gunawan, C.; Marquis, C. P.; Amal, R.; Sotiriou, G. A.; Rice, S. A.; Harry, E. J. Widespread and Indiscriminate Nanosilver Use: Genuine Potential for Microbial Resistance. ACS Nano 2017, 11 (4), 3438−3445. F




(26) Center for the Environmental Implications of NanoTechnology. Does Every Silver Lining Have a Cloud?. https://ceint.duke.edu/ education-outreach/programs (accessed Jan 2019). (27) Hill, R. H.; Finster, D. C. Laboratory Safety for Chemistry Students, 2nd ed.; John Wiley & Sons: Hoboken, NJ, 2016; pp 1−31. (28) Katritzky, A. R.; Cai, C.; Collins, M. D.; Scriven, E. F. V.; Singh, S. K.; Barnhardt, E. K. Incorporation of Microwave Synthesis into the Undergraduate Organic Laboratory. J. Chem. Educ. 2006, 83 (4), 634−636. (29) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: New York, 1998; p 30. (30) Ranoszek-Soliwoda, K.; Tomaszewska, E.; Socha, E.; Krzyczmonik, P.; Ignaczak, A.; Orlowski, P.; Krzyzowska, M.; Celichowski, G.; Grobelny, J. The Role of Tannic Acid and Sodium Citrate in the Synthesis of Silver Nanoparticles. J. Nanopart. Res. 2017, 19, 273. (31) Xu, H.; Suslick, K. S. Water-Soluble Fluorescent Silver Nanoclusters. Adv. Mater. 2010, 22 (10), 1078−1082. (32) Mulfinger, L.; Bahadory, M.; Jeyarajasingam, A. V.; Rutkowsky, S. A.; Boritz, C.; Solomon, S. D. Synthesis and Study of Silver Nanoparticles. J. Chem. Educ. 2007, 84 (2), 322−325. (33) Lowry, G. V.; Gregory, K. B.; Apte, S. C.; Lead, J. R. Transformations of Nanomaterials in the Environment. Environ. Sci. Technol. 2012, 46 (13), 6893−6899. (34) Li, X.; Lenhart, J. J.; Walker, H. W. Dissolution-Accompanied Aggregation Kinetics of Silver Nanoparticles. Langmuir 2010, 26 (22), 16690−16698. (35) Amaris, Z. N.; Freitas, D. N.; Mac, K.; Gerner, K. T.; Nameth, C.; Wheeler, K. E. Nanoparticle Synthesis, Characterization, and Ecotoxicity: A Research-Based Set of Laboratory Experiments for a General Chemistry Course. J. Chem. Educ. 2017, 94 (12), 1939−1945. (36) Zhou, W.; Liu, Y. L.; Stallworth, A. M.; Ye, C.; Lenhart, J. J. Effects of pH, Electrolyte, Humic Acid, and Light Exposure on the Long-Term Fate of Silver Nanoparticles. Environ. Sci. Technol. 2016, 50 (22), 12214−12224. (37) Ortega-Vinuesa, J. L.; Martín-Rodríguez, A.; Hidalgo-Á lvarez, R. Colloidal Stability of Polymer Colloids with Different Interfacial Properties: Mechanisms. J. Colloid Interface Sci. 1996, 184 (1), 259− 267. (38) Afshinnia, K.; Baalousha, M. Effect of Phosphate Buffer on Aggregation Kinetics of Citrate-Coated Silver Nanoparticles Induced by Monovalent and Divalent Electrolytes. Sci. Total Environ. 2017, 581−582, 268−276.

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Transformation of Silver Nanoparticles in Phosphate Anions: An

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