From Scrap to Functional Materials: Exploring Green and Sustainable

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

pubs.acs.org/jchemeduc

From Scrap to Functional Materials: Exploring Green and Sustainable Chemistry Approach in the Undergraduate Laboratory Damodaran Divya† and Kovummal Govind Raj*,‡ †

District Institute of Education and Training, Calicut, Kerala 673101, India Department of Chemistry, Malabar Christian College, Calicut, Kerala 673001, India

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S Supporting Information *

ABSTRACT: A practical approach for synthesizing functional material from waste material is described. The work was carried out by chemistry undergraduate students as a group project. The concepts used mainly in inorganic quantitative approaches were applied to transform an iron-containing material to magnetic iron oxide nanoparticles. The magnetic nanoparticles were applied for the removal of contaminants from water after making composite with activated carbon. Prior to this work, students had only theoretical knowledge about most of the concepts used. The experiment involving the synthesis of nanoparticles from waste material and its application to address a real-life problem helped the students to experience green and sustainable approach in the laboratory. KEYWORDS: Upper-Division Undergraduate, Graduate Education/Research, Environmental Chemistry, Inorganic Chemistry, Inquiry-Based/Discovery Learning, Materials Science, Nanotechnology

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INTRODUCTION Advances in educational research have emphasized the importance of student-centric approaches in the teachinglearning process. Since the past decade, there had been a paradigm shift in teaching methodologies, especially in higher education.1 There had been a conscious effort to nurture higher levels of critical thinking. A science classroom, where scientific principles and theories are learned, becomes effective with a combination of critical and creative thinking.2 The scientific knowledge acquired in classrooms need to be applied to become sustainable solutions to some real issues around us. Unfortunately, in most of the Indian universities, undergraduate laboratory courses consist of experiments that concentrate on the fundamental concepts only. Mostly a student fails to understand the broader perspective in which an experiment or a set of experiments can be organized to address a real problem. A subject like nanotechnology and its application, which occupies the center stage of current scientific research, hardly finds any place in the undergraduate practical courses and is generally considered as an elite branch that needs specialized instruments for practicing. However, from a global perspective, there are many reports in which laboratory experiments related to electrochemistry of nanomaterials, environmental nanotechnology, nanobiosensors, quantum dots, carbon-based nanomaterials, etc. were introduced to undergraduate students.3−9 The laboratory experiment described in this article introduces a green chemical approach for the synthesis and application of a nanocomposite for addressing environmental pollution. © XXXX American Chemical Society and Division of Chemical Education, Inc.

One of the most challenging issues faced by human race is the pollution of our water bodies with contaminants like dyes, heavy metal ions, oils, etc. Different chemical and physical approaches such as chemical precipitation, ion-exchange, adsorption, membrane filtration, electrochemical treatment technologies, etc. had been in use to remove these contaminants and make water clean.10,11 Among these approaches, the most commonly used method is adsorption.12 Functionalized mesoporous silica have been extensively used for the removal of both heavy metal ions and oil from water due to the advantages like high efficiency and selectivity.13 Adsorbents derived from bioresources like Rice husk, Coconut shell, Corn cobs, Cotton stalks, Barley straw, Rice straw, etc. have been preferred over systems containing mesoporous synthetic silica to their low-cost and ease of availability.14 With the advances in nanotechnology, new materials have emerged that can improve the existing technologies to a large extent.15 Both pristine and chemically modified carbon nanotubes were used as adsorbents for the removal of heavy metal ions from water.16 Comparative studies have shown that oxidized nanotubes can have higher adsorption capacity when compared to the pristine material.16 Experiments with carbon nanotube sponges have shown that they can remove oil from an area 800-times larger than the size of sponge.17 Another typical example is the use of magnetic nanoparticle-adsorbent Received: June 23, 2018 Revised: November 19, 2018

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DOI: 10.1021/acs.jchemed.8b00484 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

composite material for removing water contaminants.18,19 Nanodimensional magnetic iron oxide, a material used for different technological applications and various biomedical applications due to its biocompatibility, is one of the main components of the adsorbent composite.18,20 A composite of iron oxide nanoparticles and a suitable adsorbent combines the properties of adsorbent and the magnetic material, by which the removal of adsorbent to which the pollutant is adsorbed, from the water sample becomes a straightforward process.18,20 An external magnet with sufficient strength can pull the composite from the water instantaneously and the whole process becomes fast and effective.19 There are many examples for such composite systems in literature, in which iron oxide nanoparticle is essentially the magnetic part of the composite.18−20 This article deals with an inquiry-based approach adopted by undergraduate students for synthesizing and applying a carbonbased magnetic composite material for removing contaminants from water. The composite material was applied to two different systems, a methylene blue dye solution and an artificial oil spill, for removing the contaminants. The students were successful in developing a new strategy for the synthesis of iron oxide nanoparticles, which otherwise are the most expensive component of the adsorbent system. Generally, the nanoparticles are synthesized from water-soluble iron salts like chlorides.21 However, here iron oxide nanoparticles were synthesized from used razor blades, which is one of the readily available iron-containing material. Used razor blades have another advantage that they are discarded very soon, generally after its first use itself, and hence can be collected without any corrosion. Thus, in this experiment, using the chemical principles studied in the undergraduate curriculum, waste material was converted to a value-added product for the application in water treatment. The pedagogical goals of this experiment are four-fold:

Students Had Prior Knowledge about the Following Concepts

• Volumetric estimation of cations (both theoretical and practical). • Precipitation reactions (both theoretical and practical). • Nanomaterials: theory, synthesis, characterization, and applications (theoretical). • Principles of green chemistry (theoretical). • Adsorption and its application (theoretical). These concepts were once again reviewed before starting the experiment. Students had also learned the synthetic methods for the preparation and characterization of iron oxide nanomaterials, the importance of composite materials and their applications before conducting the experiment. The X-ray diffraction experiment was performed using PANalytical’s X’Pert PRO machine. The imaging of nanoparticles was carried out using an FEI, TECNAI G2TF20 transmission electron microscope (TEM). A detailed list of chemicals and apparatus used is included in the Supporting Information. Quantitative Estimation of Fe2+ Ion in Razor Blades

Quantitative estimation of Fe2+ ion in razor blades was carried out by permanganometry. This experiment was a part of the undergraduate curriculum and the students had an excellent understanding and technical expertise for performing the analysis. However, the sampling of razor blades by dissolving in Conc. HCl was a fresh experience. Zinc powder was used to convert ferric ion present in the solution, if any, to ferrous ion before the permanganometric estimation. From the titration result, the quantity of iron (w/w) in razor blade calculated by different student groups was around 74 ± 1% (see Table T3, Supporting Information). Therefore, it was concluded that the razor blades contain a high proportion of iron and hence can be used as a precursor for the synthesis of iron oxide. Synthesis of Iron Oxide-Activated Carbon Composite

• Understand that the chemical principles learned in inorganic quantitative analysis can be used for the synthesis of nanoparticles.

The iron oxide nanoparticles were synthesized by coprecipitation method. The theory of coprecipitation was explained to the students before the experiment. The razor blades were dissolved in Conc. HCl to obtain a green colored iron salt solution (Figure S1). From this solution, iron oxide was precipitated by adding 25% aqueous solution of ammonia from a buret until the solution pH rises above 10. The iron oxide nanoparticles were allowed to grow in size by Ostwald ripening process.21 The students were able to identify this method of preparation as an extension of the method used for the gravimetric estimation of Iron in undergraduate chemistry practical course.22 In the gravimetric estimation of Iron, the Fe2+ solution is precipitated as Iron hydroxide at pH 7−8 and then heated to convert it to iron oxide.23 However, here iron oxide was precipitated directly at pH above 10.23 Figure 1 shows the image of magnetic iron oxide nanoparticles synthesized using this method. The photograph was taken after keeping magnetic nanoparticles in the influence of an external magnetic field. The magnetic lines of flux emerging from the edges of the powder can be seen in the image. The nanoparticles were also observed to follow the rotation of a magnetic stirrer, and hence the students could visually confirm the magnetic property of iron oxide. A video of the same is included as Supporting Information Video V1. A composite of iron oxide and activated carbon (1:1 weight ratio) was prepared by stirring both the components for 1 h at

• Experience the green and sustainable chemical approach by using a waste material as a precursor for the synthesis of functional materials. • Understand that composite material can have better applicability than individual component. • Apply the magnetic iron oxide-activated carbon composite material for removal of spilled oil and methylene blue from the water.

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EXPERIMENTAL PROCEDURE The laboratory experiment described is suitable for an introductory course in inorganic chemistry, material sciences courses, nanotechnology, environmental chemistry and chemical engineering. The methodologies used include the synthesis and application of nanostructured materials or nanocomposites. The experiment was performed as a part of the course by 30 final year undergraduate students, with five students working in a group. Thus, the experiment was repeated six times. For convenience, the entire experiment is split in three lab periods, each of 3 h duration (see Student’s handout in the Supporting Information) B




Figure 1. Iron oxide nanoparticles synthesized from razor blades when kept on top of a magnetic stirrer. The magnetic lines of flux can be clearly seen at the edges and outer surface. Figure 2. XRD pattern of iron oxide nanoparticles synthesized from razor blades.

80 °C. At this condition, the individual components of the mixture get linked together through weak attractive forces. The composite was also observed to respond to the external magnetic field when placed on top of a magnetic stirrer (Supporting Information Video V2).

respond readily to an external magnetic field, as shown previously in Figure 1. The TEM image of the iron oxide nanoparticles shows that the nanoparticles are polydisperse in nature, as expected after the coprecipitation synthesis (Figure 3). TEM image shows that the nanoparticles are in the size range 50−20 nm, which is in line with the average crystallite size calculated using XRD.

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HAZARDS Standard protocols for general lab safety and safe handling of chemicals should be followed. Students must use goggles, lab coat, and gloves throughout the experiment. Special care must be taken while handling hazardous corrosives like concentrated acids and while cutting razor blades. Students are advised to take help from the laboratory staff for cutting used razor blades into small pieces. The dissolution of razor blade involves the use of hot concentrated acid and the evolution of pungent gas. Hence, students are advised to wear a mask and carry out this step using a gas trap to avoid the emission of toxic gases. If gas trap is not used, the students must carry out this step under a hood with proper exhaust. Ammonia solution can cause serious health issues if not used properly. Students must read MSDS before handling ammonia solution. Avoid release of zinc powder to the environment and must be disposed of as a hazardous waste. Activated carbon should be used only after wearing a mask. Methylene blue may cause skin/eye irritation and indigestion. Students should contact the laboratory incharge to clean up any spills immediately and wash their hands thoroughly with water and soap solution at the completion of the laboratory work. All waste generated during the lab experiment should be disposed properly with the help of laboratory staff.

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RESULTS AND DISCUSSION

Figure 3. TEM image of the nanoparticles synthesized from razor blades.

Characterization of Iron Oxide Nanoparticles

The iron oxide nanoparticles were characterized using X-ray diffraction (XRD). Even though students had prior knowledge about the theory of XRD experiment, the analysis of XRD pattern was carried out with the help of a teacher. The XRD pattern shown in Figure 2 matches well with the standard simulated pattern of Iron oxide (JCPDS Card # 39−1346, γFe2O3). The average crystallite size of nanoparticles calculated using the Scherrer equation (D = 0.9λ/β cos θ, λ of Cu Kα radiation = 1.5418 Å) was 27 nm. The iron oxide nanoparticles in this size regime are expected to have very low coercivity. Even though they have no spontaneous magnetization, they

Application of Nanocomposite

The activated carbon−iron oxide magnetic composite material was applied for the removal of oil and methylene blue from water. For oil removal application, a small amount of oil was added on top of water taken in a Petri dish.19 The composite material was then smeared on top of the oil and then pulled out with the help of a small laboratory magnet. The images of each step involved in the process are shown in Figure 4. The oil recovery process was quite instantaneous. Students could quickly identify that the removal of oil by this kind of C



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EVALUATION AND ASSESSMENT Out of the 30 students who participated in the experiment, a pretest (Supporting Information, Appendix I) clearly showed that the students had only a vague understanding about the possibility of converting waste material to useful ones. They were not aware of any of the practical approaches that could be used. The students had only theoretical understanding about nanomaterials and no one had ever synthesized a functional nanomaterial. Sixty percent of the students thought that it was impossible to synthesize a nanomaterial in their undergraduate laboratory. All students agreed upon the fact that they would not be able to synthesize a nanomaterial, even if provided with all experimental setup, since they were not aware of the synthetic steps involved. All of them were aware of the green chemistry approaches and had a good theoretical understanding regarding water contamination and its harmful effects. The student response was recorded after the experiment (Supporting Information, Appendix II). Eighty-five percent of the questions in appendix II (questions 1−10) were answered correctly by the students. They also identified some drawbacks in the experiment, that the composite material discharges a few submicron carbon particles in water while applying for removal of dye imparting a gray color to the solution after dye removal. They were able to interpret this observation satisfactorily, that some of the fine carbon particles are not tightly bound to iron oxide nanoparticles and hence cannot be pulled along the nanomagnet. Thus, the gray color of water after the removal of methylene blue is due to the fine carbon particles that came out from the composite during the process. After the lab, students agreed on the majority of (88.5%) the statements. There was also a significant improvement in the understanding of fundamental concepts involved in the synthesis and application of nanomaterials.

Figure 4. Different steps involved in oil removal application. (a) Water taken in Petri dish, (b) red colored oil spilled on water surface, (c) composite material is added on top of oil, and (d) composite material is pulled by an external magnet.

composite material is mainly due to hydrophobic interactions between oil and activated carbon along with the kinetic drag produced by the composite, which tends to pull the oil layer. The video of the whole process is given as Supporting Information Video V3. To remove methylene blue from water, a 50 ppm solution of the dye was prepared; 0.2 g of composite material was added to the dye solution. In this case, the decolourization of MB was not instantaneous. A small wait time of ∼5 min was required for the adsorption of dye on the composite material. The dye adsorbed material could be then separated from water by using the same laboratory magnet. Figure 5 shows the different steps involved in the process.

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CONCLUSION Iron oxide nanoparticles were successfully synthesized starting from used razor blades, which is a common waste material. A magnetic adsorbent was then produced by combining the adsorption properties of activated carbon and magnetic properties of iron oxide nanoparticles. This material was then used for the removal of contaminants from water. The whole process was straightforward and involved chemical principles that were familiar to the undergraduate students. With this laboratory experiment, the students could apply the theoretical concepts studied in the undergraduate curriculum to address a real problem. The experiment enhanced the understanding of different topics like green chemistry, quantitative analysis, nanomaterial synthesis, characterization, and application. From the student response, it was clear that the students were highly motivated by the experiment.

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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.8b00484. Detailed experimental procedure, sample copy of response sheets used for pretest and post-test (PDF, DOCX) Response of iron oxide to external magnetic field video (AVI) Composite material to external magnetic field video (AVI)

Figure 5. Methylene blue removal from water. (a) 50 ppm methylene blue solution and (b) decolorized solution from which adsorbent is removed by a magnet. D



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Oil adsorbed material to external magnetic field video (AVI)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kovummal Govind Raj: 0000-0002-2978-2822 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to acknowledge the administration, Malabar Christian College, Calicut for the laboratory facilities. The XRD spectra and TEM image was obtained with the help of Jithesh K., Assistant professor, Sree Narayana College, Kannur, India. Pranav M., Shabna K., Anushma K. K., and Sharfina Azeez are also duly acknowledged for their efforts in optimizing the experiment.

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From Scrap to Functional Materials: Exploring Green and Sustainable

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