Embodied Energy and Solar Cells

Embodied Energy and Solar Cells

By Devon Holst, Member-at-Large for the GCI

Embodied energy is the sum of all energy consumed in the production of goods and services. Knowing the amount of energy something ‘embodies’ is useful when assessing the environmental impact of comparable goods and services as well as assessing the utility of technologies that produce or save energy. If a device intended to save energy embodies more energy than it will save over the entirety of its use, the product is considered to be unfavourable. A net energy loss would be the result of its application.

It is important to consider the embodied energy of renewable energy technologies to ensure there is a net energy gain. I am going to follow the production process of silicon solar cells as an example of how energy can be embodied into a product. To be effective, the embodied energy of a solar cell must be less than the total energy it produces. There are many processing steps needed to assemble a solar cell where the embodied energy should be kept to a minimum. Some of the largest sources of embodied energy in silicon solar cells are described below.

Devon_blog 1

Silicon Processing (Additional embodied energy: 460 kWh/kg)

Carbothermic reduction of quartz sand (silicon dioxide) is used to produce metallurgical grade silicon. This process consumes 20 kWh/kg of metallurgical grade silicon produced. Metallurgical grade silicon must then be further refined to electronic grade silicon through a reaction with hydrochloric acid at 300 oC followed by treatment with hydrogen gas at 1100 oC. This process consumes 100 kWh/kg of electronic grade silicon. This silicon is then melted at 1400 oC and crystallized, consuming 290 kWh/kg of silicon single crystal. This form of silicon is suitable for use in a solar cell. After accounting for losses of material during each step, these processes embody 460 kWh of energy into each kg of silicon single crystal.1

Solar Cell Production (Additional embodied energy: 120 kWh/m2)

The single crystal of silicon is sliced into wafers with a multiwire saw resulting in a 40% to 50% loss as dust. Following this, a sequence of high temperature diffusion, oxidation, deposition, and annealing steps are performed. This adds 120 kWh/m2 ­­­of embodied energy to the solar cell.1

Module Assembly (Additional embodied energy: 190 kWh/m2)

A module consisting of a glass front panel, an encapsulant, the solar cell, copper ribbon, a foil back cover, and an aluminum channel is then assembled. 190 kWh/m2 of embodied energy is added during assembly.1

Support Structure (Additional embodied energy: 200 – 500 kWh/m2)

The module is then typically installed in a field or on a rooftop. In a field, the module needs to be supported by concrete, cement, and steel. Construction and materials add 500 kWh/m2 of embodied energy. Rooftops have an existing support structure reducing the embodied energy of this aspect to 200 kWh/m2.1

Miscellaneous Components

Beyond the former sources of embodied energy there are many other components in an operational solar cell. An inverter, wiring, and a battery are a few examples of these components. Depending on the components needed, this will add a variable amount of embodied energy.1

Devon_blog2Emerging technologies such as perovskites and organic solar cells often have much lower embodied energies than their silicon counterparts. Material processing methods and the amount of material necessary to produce a solar cell are a couple of the major factors that account for the difference in embodied energy of these technologies.1,2 There are, however, many other factors that make a solar cell viable for large scale energy production which when considered in aggregate currently favour silicon solar cells. It is likely that multiple solar energy technologies will thrive in the future as each has unique characteristics making one more applicable to a given situation than another.1,3

The energy payback time of a given solar cell is calculated by dividing embodied energy by energy output per unit time. This is the amount of time a solar cell must operate before it generates the same amount of energy as its embodied energy. Silicon solar cells have a 1.65 to 4.12 year energy payback time, while some organic solar cells and perovskites have energy payback times of less than half a year.4,5

Embodied energy is part of an even broader picture. A picture that captures the energy used to recycle or dispose of something and the energy associated with environmental impacts incurred through goods and services in any way. The picture is complex, but a deep understanding of it is necessary in order to make decisions that are conscious of the future.

I wonder how much energy I embody…

References:

1) Nawaz, I.; Tiwari, G. N., Embodied energy analysis of photovoltaic (PV) system based on macro- and micro-level. Energy Policy 2006, 34 (17), 3144-3152.

2) Anctil, A.; Babbitt, C. W.; Raffaelle, R. P.; Landi, B. J., Cumulative energy demand for small molecule and polymer photovoltaics. Progress in Photovoltaics: Research and Applications 2013, 21 (7), 1541-1554.

3) Snaith, H. J., Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells. The Journal of Physical Chemistry Letters 2013, 4 (21), 3623-3630.

4) Espinosa, N.; Hosel, M.; Angmo, D.; Krebs, F. C., Solar cells with one-day energy payback for the factories of the future. Energy & Environmental Science 2012, 5 (1), 5117-5132.

5) Gong, J.; Darling, S. B.; You, F., Perovskite photovoltaics: life-cycle assessment of energy and environmental impacts. Energy & Environmental Science 2015, 8 (7), 1953-1968.

Image Sources:

  1. Solar panels (https://commons.wikimedia.org/wiki/File:SolarparkTh%C3%BCngen-020.jpg)
  2. Embodied energy (http://www.paveshare.org/library/embodied-energy)
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Green Chemistry Principle #10: Design for Degradation

By Shira Joudan, Chair of the Education Subcommittee for the GCI

10. Design for degradation: Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.

In video #10, Matt and I discuss designing chemicals that break down once their desired function is completed. Essentially, we want chemicals to degrade to molecules that are not harmful to humans, animals or the environment.

A lot of the chemicals we use in our day-to-day lives need to be stable to perform their function. For example, if your coffee mug dissolved when you poured your coffee into it, it wouldn’t be very helpful! Similarly, if lubricants degraded under high temperature and pressure, they may not work well in the engines of our cars or planes.

Once chemicals are done providing their main function, they might end up in a landfill or wastewater treatment plant where they can enter the waters, soil and air of our environment, or be taken up by animals or humans. The biggest challenge is making chemicals that are stable during usage, but don’t persist in the environment – or in other words, chemicals that can be degraded. Another important thing – we want the breakdown products to also be non-toxic and not persistent! It’s important to remember that there are different reasons a chemical can break down. It can be due to reactions with light (photodegradation), water (hydrolysis) or biological species, often with enzymes (biodegradation).

A common example that we hear about is biodegradation, especially with the well-known “biodegradable soaps.” We can use this as a good example about how we can design soaps, or detergents, to break down more easily in the environment.

Sodium dodecylbenzenesulfonate

Figure 1 Sodium dodecylbenzenesulfonate, an example of a linear alkylbenzene sulfonate (LAS) which is biodegradable.

Sodium dodecylbenzenesulfonate (Figure 1) is a common detergent, and is often referred to as LAS, for linear alkylbenzene sulfonates. Looking at its structure, you can see that it has a linear alkyl chain with a benzylsulfonate attached to it. It is useful as a detergent because it has a polar headgroup (sulfonate) and a non-polar alkyl group, making it a surfactant.

LAS is used in many things, especially laundry detergent. It degrades quickly in the environment under aerobic conditions, or when oxygen is present, because microbes are able to use to the linear alkyl chain as energy, via a process called β-oxidation, a process which breaks down the carbon chain. Once the long chain is degraded, the rest of the molecule can be degraded as well.

Branched alkylbenzene sulfonate.

Figure 2 A branched alkylbenezene sulfonate (does not biodegrade).

If you compare LAS to a branched version (Figure 2), you can immediately see that the alkyl chain looks very different. This molecule was also used as a detergent just like the linear version, but because of the location of the branches, microbes cannot perform β-oxidation since there are no good sites for that reaction to be initiated. Therefore, these branched detergents have been phased out in most developed countries because they are too persistent – they do not biodegrade.

The main way these molecules are degraded is through microbes, when oxygen is present. So if these soaps end up directly in water, like straight into a lake, they will not be broken down very quickly (even the linear version!). This is because there are fewer microbes in water as compared to in soil. Interestingly, the branched version is 4 times less toxic than the linear version, but can cause more damage because of its persistence. This is one of the reasons that it is very important to consider persistence, or a molecule’s resistance against degradation, and not only its toxicity.

You can see how designing chemicals to break down can be very challenging, but many researchers around the world are working on this right now. Some examples are biodegradable polymers that are used in plastics, like compostable cutlery.

Principle 10 is currently one of the largest challenges in green chemistry. If scientist designing new chemicals understand more about the mechanisms that can degrade them, we may be able to make chemicals that are reliable and stable during their intended use, but break down in the environment!

Celebrating the 5-Year Anniversary of the GCI

Celebrating the 5-Year Anniversary of the GCI

By Alex Waked, Co-Chair for the GCI

The Green Chemistry Initiative (GCI) at the University of Toronto was founded back in 2012 – it’s crazy to think that we’ve already reached the 5-year milestone. Before you know it, it’ll be 10 years, then perhaps even 20 years! But before we talk about the future, it’s always a good idea to take a step back and reflect on how we’ve gotten here in the first place. This organization wouldn’t even exist had it not been for the vision of co-founders Laura Hoch and Melanie Mastronardi, with help from many graduate students keen on educating themselves and their peers about sustainable practices. With the help of all the other dedicated GCI members over the years, they helped the GCI grow to the point at which we’re now standing. Being the 5-year anniversary of the GCI, I reached out to all the previous co-chairs and asked them to reflect on their time spent here.

GCI2013

GCI group photo from 2013

Laura Hoch (Co-Chair from 2012-2015):

I’m so excited to help celebrate the GCI’s 5-year anniversary by sharing some reflections and favorite memories from my time with the group. When I look at all the GCI has done over the past 5 years, I am so happy to see how much impact we’ve had. Within our own department, all the events and initiatives – trivia, seminars, workshops, the waste awareness campaign, and many more – have really raised awareness about green chemistry and made it more tangible. Through our work, we have also helped to inspire other students in Canada and around the world to get active, start their own student groups, and promote green chemistry in their own communities.

It’s really hard for me to pick a favorite event or project that I am most proud of – in my extremely biased opinion, we’ve done way too many awesome things! – but for me one of the moments when it really hit home how much of an impact we were having was at a networking session at the ACS Green Chemistry & Engineering Conference in Washington D.C. Waiting in the food line, I randomly ended up talking to a researcher at DuPont. When I mentioned that I was from U of T, he said “Oh! Are you one of those intrepid students from Toronto?!” and proceeded to describe in detail many of our activities and initiatives. It blew my mind that here was a complete stranger from Delaware, who wasn’t even an academic, who had heard of us and thought what we were doing was great.

I can honestly say that helping to start the GCI was by far the BEST thing I did in grad school. I’ve learned so much and have met so many amazing people through our work. I am so proud of what the GCI has accomplished and I really look forward to seeing what the GCI will do in the years to come!

Melanie Mastronardi (Co-Chair from 2012-2014):

It seems like just yesterday that we started the GCI, I can’t believe it’s been 5 years already! Thinking back to where we started (just a handful of grad students who wanted to learn how to conduct our research more sustainably), I’m so proud of all the GCI has been able to accomplish. From weekly trivia challenges to department seminars to hosting students and speakers from all over at our annual symposium, the GCI has created so many opportunities for students and researchers to learn about green chemistry and how to implement it. It’s also absolutely amazing to hear stories of how we inspired students at other universities to start similar organizations! One of my personal favourite projects was launching the 12 Principles of Green Chemistry video campaign. We’ve come a long way from the first one we filmed in Jes’ kitchen and last time I checked we are only 3 away from completing the full set!

Laura Reyes (Co-Chair from 2014-2016):

I am so grateful and proud to have been a founding member and co-chair for the GCI, and continue to be impressed by everything that the group does. It feels surreal to look back on everything that we have accomplished in only 5 years. The GCI started from the curiosity of a few grad students wanting to know how green chemistry could be applied to our own research, and now the group is well-known and respected throughout the green chemistry community as an example of a student-driven education effort. In that time, the GCI has managed to change the conversation around green chemistry in the UofT chemistry department. Subtle changes have compounded into a larger cultural shift, including anything from curriculum development for undergrad courses and labs (and signing Beyond Benign’s Green Chemistry Commitment!), to faculty members self-identifying as using green chemistry in their work. There is still much progress to be made, of course, but looking back on the accomplishments of the GCI and the professional experience that we all gained in being a part of this, it is hard to not feel proud of every project and event that we organized, starting with our very first seminar on the basics of green chemistry to recently teaching that seminar ourselves at the 100th CSC conference!

GCI group photo 2017

GCI group photo from 2017

Erika Daley (Co-Chair from 2015-2016):

Congratulations to all previous and current members of the Green Chemistry Initiative on its 5th anniversary! I was incredibly proud of all the accomplishments and activities that took place during my time as co-chair, and continue to be delighted by the success of the group. I think the value is especially put into perspective in my career when researchers, faculty, students, and industry employees know of or recognize the GCI and the impact it has had all over North America. While it is impossible for me to pick one particular initiative to highlight here, I think the collective outreach, education, data collection, and subsequent actions of the entire GCI team – from the departmental waste awareness campaign, to the community outreach events, to the undergraduate curriculum development – are all so important and speak volumes to what a group of dedicated student volunteers can accomplish.

Ian Mallov (Co-Chair from 2016-2017):

The 5-year anniversary of the GCI is an opportunity to reflect on our mission and goals. What did we want to accomplish, and what have we accomplished? Personally, I’m most proud of the fact that we have successfully ingrained green chemistry education into the fabric of our department through establishing regular events like symposia, seminars, and trivia, and that we helped encourage the department to sign the Green Chemistry Commitment. Green chemistry education should be fundamental to chemical education – it is our job as chemists to understand matter at the molecular and nano levels. I view the primary mission of green chemistry as a mission to impart a sense of responsibility to chemists to manage matter safely. I would hope the GCI has brought more chemists at U of T and beyond to consider this responsibility, and I’m really encouraged by the bright, dedicated people who continue to lead the GCI forward.

Greener Alternatives in Organic Synthesis Involving Carbonyl Groups: Dethioacetalization and Iron-Catalyzed Transfer Hydrogenation

By Diya Zhu, Member-at-Large for the GCI

A carbonyl functionality is a functional group composed of a carbon atom double-bonded to an oxygen atom (C=O). It is ubiquitous in nature as well as widely employed and studied in all areas of chemistry. In this blog, we will explore two common synthetic processes involving carbonyl groups with greener alternative reagents.

Dethioacetalization with NH4I

Carbonyl-containing compounds are abundant in nature, expressing a wide range of functionality. As targeted in many natural and non-natural product syntheses, the protection and deprotection of the carbonyl functional groups are critical and often require multiple steps. Common carbonyl protecting groups are dithianes and dithiolanes due to their easy accessibility and high stability under acidic/basic conditions. The traditional dethioacetalization is generally performed utilizing heavy-metal salts such as mercury(II) chloride, silver(II) nitrite, ceric ammonium nitrate, and selenium dioxide, of which the resulting waste is very toxic to the environment.1

From 1989 to 2005, serval hypervalent iodine compounds such as bis(trifluoroacetoxy)-iodobenzene (BTI), Dess-Martin periodinane (DMP), and o-iodoxybenzoic acid (IBX) have been employed as dethioacetalization reagents due to their low toxicity, high selectivity, and metal-ion free nature. While these reagents have a smaller environmental impact, they are still required in excess amount, which is economically wasteful.2, 3

Finally, in 2011, Ganguly and Mondal reported a mild, efficient, and greener dethioacetalization protocol using a catalytic amount of ammonium iodide with hydrogen peroxide.3 In this work, the deprotection was carried out with 10 mol% of nontoxic ammonium iodide and 30% hydrogen peroxide as the terminal oxidizer in an aqueous medium in the presence of sodium dodecylsulfate (SDS). This protocol (Figure 1) shows a high yield (>90%) deprotection of 1,3–dithianes and dithiolanes of activated aromatics and even deactivated and sterically encumbered substrates. The high tolerance, low environmental impact, mildness, operational simplicity, high throughput, and generality of the protocol make it an intriguing alternative.

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The greener dethioacetalization protocol by Ganguly and Mondal. [3]

Iron-catalyzed transfer hydrogenation with formic acid

Various catalyst systems for the reduction of carbonyl compounds have been established, such as Meerwein–Ponndorf–Verley (MPV) reduction.4 However, only a handful of protocols were reported for the transfer hydrogenation of aldehydes due to the difficulty in controlling the chemoselectivity in the process.

In these conversional protocols of transfer hydrogenation, many side-reactions (for example, aldol condensations) take place after deprotection by the base. The heavy-metal catalysts (such as rhodium, iridium, and ruthenium complexes) are expensive and often poisoned by the substrates, resulting in non-recyclable catalysts and many side-products. In addition, the hydrogenation of carbon-carbon double bonds (C=C) and aldehydes compete, resulting in poor chemoselectivity.5,6 Due to these drawbacks, there was a significant desire for more efficient and environmentally benign catalytic systems.

In the last decade, iron catalysts have received much attention due to their nontoxic, abundant, and inexpensive qualities. In 2013, Beller and his colleagues published an efficient iron-based catalyst system for the highly selective transfer hydrogenation of aldehydes under mild conditions.6 In this system, they suggested that iron-tetraphos complexes [(Fe(BF4)•6H2O and P(CH2CH2PPh2)3) are able to catalyze a wide range of substrates such as aromatic, aliphatic, and α,β-unsaturated aldehydes to the corresponding alcohols in excellent yields (>99%). Without the presence of a base, formic acid is used as a cheap, environmental friendly, and easy to handle hydrogen source. In addition, no significant amounts of side products were observed.

Diya_blog2

The iron-catalyzed transfer hydrogenation with formic acid. [6]

In addition to these two examples, many chemical companies promote the idea of green chemistry and offer more green choices to reduce environmental impact without compromising the quality and efficacy of research.7

 

References:

  1. J. Corey, B. W. Erickson, Journal of Organic Chemistry 36 (1971), 3553; E. Vedejs, P. L. Fuches, Journal of Organic Chemistry 36 (1971), 366.
  2. S. Kirshnaveni, K. Surendra, Y. V. D. Nageswar, K. R. Rao, Synthesis 15 (2003), 2295. DOI: 10.1055/s-2003-41055
  3. C. Ganguly, P. Mondal, Synthetic Communications 41 (2011), 2374. DOI: 10.1080/00397911.2010.502995
  4. Gladiali, E. Alberico, Chemistry Society Reviews 35 (2006) 226. DOI: 10.1039/B513396C
  5. S. M. Samec, J.-E. Bäckvall, P. G. Andersson, P. Brandt, Chemistry Society Reviews 35 (2006), 237. DOI: 10.1039/b515269k
  6. Wienhöfer, F. A. Westerhaus, K. Junge, M. Beller, Journal of Organometallic Chemistry 744 (2013) 156. DOI: 10.1016/j.jorganchem.2013.06.010
  7. Sigma Aldrich Alternative Product Page. http://www.sigmaaldrich.com/chemistry/chemistry-products.html?TablePage=119262253 (accessed Oct 15, 2017).

GCI gets behind-the-scenes look at GreenCentre Canada

by Dan Haves, Communications Officer, Department of Chemistry at U of T

This summer, the Green Chemistry Initiative (GCI) at U of T’s Department of Chemistry made a visit to GreenCentre Canada. The group of nine graduate students were in Kingston for a crash course on the transition from academia to industry in green chemistry. They learned from experts in the field on everything from product development to patents and intellectual property. We spoke with PhD student and GCI member Julia Bayne about the day.

What was the rationale behind organizing this career day?

Most graduate students are unfamiliar with green chemistry and tend to be unaware of potential careers for chemists other than academia or research positions in industry. Additionally, most students find it difficult to make the connection between academia and industry and this transition tends to cause a lot of people anxiety given their unfamiliarity with the latter. With this in mind, we, the Green Chemistry Initiative at U of T, wanted to plan a career day that would give students the opportunity to learn about other possible career options and to see the inner-workings of a successful company, whose mandate is built around green chemistry principles and sustainability.

Can you share a little bit of what you learned about GreenCentre and the work they do?

GreenCentre Canada is a one-stop shop for the commercialization of green chemistry technologies. They have a very hands-on approach to technology development and support the creation and development of green chemistry-based companies. They work with academics and entrepreneurs to commercialize their discoveries. As well, they provide support for established companies and help further develop research and development. They have a very diverse group of employees: experienced chemists, commercial experts and business professionals. Their unique skill set and talent has allowed them to develop new green chemistry-based technologies, support existing ones and create small businesses.

GCI Visit group photo

Were there any take-aways from the day in terms of potential career paths you may not have known about or some that you learned more about?

I think most people believe that in order to pursue a career outside of your field of study that you need to go back to school, which for graduate students who have been in school for at least ten years, can be intimidating. However, one thing that stood out to me from the visit was that you don’t necessarily have to have a degree or years of experience in a field outside of chemistry to hold a position that requires less chemistry. For instance, with a chemistry background, starting in a research position will definitely help develop your skills as a scientist, but this does not mean you can only be a research scientist. We learned that if you apply yourself, if you ask for additional responsibilities, if you teach yourself about another field you’re interested in, you can prepare yourself to change positions/careers and move away from a laboratory position – if you want. We learned that our chemistry degrees are valuable, not only for researcher positions, but also for leadership roles and business development roles. For most chemistry graduate students, these positions may seem unattainable with only research experience in your niche field. However, I found it interesting and encouraging to learn that the main separator is on-the-job-training and the passion and willingness to learn. Moreover, I learned that careers outside of the laboratory – like management or business development roles – are not outside of our reach as chemists!

What excites you the most about where you see green chemistry going?

Green chemistry has been receiving an increasing amount of attention in the recent years and most people now understand and appreciate that green chemistry has the potential to change our world for the better by developing sustainable, prosperous and healthy communities. With an overwhelming increase in population and decrease in resources predicted for our future, we need everyone to be thinking about green chemistry and sustainability. We’ve seen green chemistry practices used throughout U of T and we have seen first-hand the benefits associated with these changes, including energy and cost savings and a smaller environmental footprint. And I hope this continues!

I am looking forward to seeing these practices being implemented more at the university level throughout Canada and then at the federal level. Being the first school in Canada to sign the Green Chemistry Commitment, U of T has taken a pledge to implement green chemistry principles and practices into the undergraduate and graduate curriculum, and I hope this becomes the standard for all universities. I’m excited to see all levels of academia, industry and government working together to implement more green chemistry into our society, I’m excited to see how green chemistry will impact our lives and I am looking forward to what the future will look like!

Julia is a 4th-year PhD student working in the Stephan Research Group. Her research is focused on the design of new phosphorous-based compounds for Lewis-acid catalysis and frustrated Lewis pair reactivity.

 

This article was reproduced from the Department of Chemistry in the University of Toronto, see the original article here.

Ecocatalysis: Harnessing Phytoextraction for Chemical Transformations

Ecocatalysis: Harnessing Phytoextraction for Chemical Transformations

By Karlee Bamford, Treasurer for the GCI

What is ecocatalysis? I had never heard this term before until reading a recent publication from Grison and coworkers in the RSC journal Green Chemistry entitled “Ecocatalyzed Suzuki cross coupling of heteroaryl compounds”.1 In this work, the authors perform the familiar Suzuki cross-coupling of arylboronic acids (Figure 1) with heteroaryl halides. However, they use a thoroughly unfamiliar palladium catalyst: the common water hyacinth (Figure 2).

Karlee_blog1

Figure 1. The general reaction for Suzuki cross-coupling  (Ar = substituted phenyl, thiophene, or indole groups).

Karlee_blog2

Figure 2. The common water hyacinth (Eichhornia crassipes). Credit: Richard A. Howard, provided by Smithsonian Institution, Richard A. Howard Photograph Collection (Montréal, Canada). [2]

In broad terms, ecocatalysis is the use of plant-derived, metal-based catalysts in chemical reactions. If it were not for the author’s graphical abstract illustrating the plant body performing catalysis, I would have assumed that this was a more standard bioinorganic paper featuring a plant extract as catalyst. While the propensity of certain plants and microbiota to uptake (“phytoextract”) particular contaminants has long been used in waste water purification, for example in the uptake of inorganic phosphates (e.g. [PO4]3-),3 ecocatalysis represents a clever progression from plants being used in chemical sequestration to chemical transformation.

Plants currently used in phytoremediation, that is, the removal of contaminants such as heavy metals from anthropogenically polluted environments, could clearly be used in the production of ecocatalysts.4 One current use for such metal-laden plants is in phytomining as so-called bio-ore.5 This metal extraction process ultimately results in the majority of the plant bio-mass being wasted through the energy-consumptive process of incineration, whereas an ecocatalyst such as EcoPd requires that same bio-mass as a kind of ligand support.

Grison and colleagues report reaction times, conditions, and yields (typically >90 %) for their “EcoPd” catalyst that are competitive with typical Suzuki cross coupling experiments and catalysts, both homogenous and heterogeneous. Remarkably, the primarily root-based EcoPd catalyst can be reclaimed and reused without loss of activity, as the authors demonstrated in a control study that involved recycling the catalyst four times over. Finally, the palladium content of the used catalyst can be quantitatively recovered by rhizofiltration, that is, by returning the elemental palladium obtained in post-synthesis work-up to a new plant specimen for metal uptake. In practical terms, this involves filtering the post-synthesis solution, dissolving the isolated solids with aqua regia, and diluting the resultant palladium-containing solution with water before reintroducing it to the roots of E. crassipes.

Ecocatalysis is an entirely new and emerging field of chemistry (circa 2013) being pioneered by Grison and coworkers at The Laboratory of Bio-inspired Chemistry and Ecological Innovations (University of Monpellier) in France. Their research has furnished several other noteworthy ecocatalysts (EcoM’s) featuring nickel (EcoNi),6 zinc (EcoZn),7 manganese (EcoMn),8 copper (EcoCu),9 which have proven effective in Biginelli, Diels-Alder, reductive amination, and Ullmann reactions, respectively.

This new approach to catalysis is not only charmingly novel – at least to a non-bioinorganically-minded chemist such as myself – but it also offers a real solution to the problematic dependence of catalysis on pure precious metals. The plants themselves provide a means for both harvesting and using low-abundance metals in a format that does not require complicated ligand design and is consistent with homogenous catalysis. Clearly, EcoPd and other such EcoM may not be suitable replacements in every metal-catalyzed transformation, but they nonetheless provide a new avenue for recycling precious metals and realising catalyst sustainability.

The range of possible ecocatalysts is, in my mind, astounding. Plant species that are known to preferentially accumulate heavy metals, known as accumulators and hyperaccumulators, are greater than 500 in number and sequester metals from across the p- and d-block of the periodic table, each to varying extents.10 As the tolerance and preference for certain transition metals is in part gene-regulated,11 it is conceivable that genetic modification and controlled environmental conditions could in the future yield heavy metal-specific plant species for sequestration and, perhaps, subsequent ecocatalysis.

 

References:

  1. G. Clavé, F. Pelissier, S. Campidelli and C. Grison, Green Chemistry, 2017, DOI: 10.1039/c7gc01672g.
  2. Used with permission from Larry Allain, hosted by the USDA-NRCS PLANTS Database.
  3. J. Lv, J. Feng, Q. Liu and S. Xie, Int. J. Mol. Sci., 2017, 18.
  4. C. Grison, Environmental Science and Pollution Research, 2015, 22, 5589-5591.
  5. R. R. Brooks, M. F. Chambers, L. J. Nicks and B. H. Robinson, Trends in Plant Science, 1998, 3, 359-362.
  6. C. Grison, V. Escande, E. Petit, L. Garoux, C. Boulanger and C. Grison, RSC Adv., 2013, 3, 22340.
  7. V. Escande, T. K. Olszewski and C. Grison, Comptes Rendus Chimie, 2014, 17, 731-737.
  8. V. Escande, A. Velati, C. Garel, B.-L. Renard, E. Petit and C. Grison, Green Chemistry, 2015, 17, 2188-2199.
  9. G. Clavé, C. Garel, C. Poullain, B.-L. Renard, T. K. Olszewski, B. Lange, M. Shutcha, M.-P. Faucon and C. Grison, RSC Adv., 2016, 6, 59550-59564.
  10. H. Sarma, Journal of Environmental Science and Technology, 2011, 4 118-138.
  11. S. Jan and J. A. Parray, Approaches to Heavy Metal Tolerance in Plants, Springer Singapore, Singapore, 2016.
ACS Summer School on Green Chemistry and Sustainable Energy 2017

ACS Summer School on Green Chemistry and Sustainable Energy 2017

By Samantha Smith, Yuchan Dong, and Shira Joudan

Yuchan Dong, who previously studied in China, had begun to miss life with roommates while in Canada. She reminisced about how you could talk about your lives late into the night, and spend meals chatting with friends in the cafeteria. “Luckily, at the ACS summer school, [she] got the chance to experience such life again and got to know a lot people who share same interests.” The summer school brought us back to the more carefree times of our undergraduate lives. Living in dormitories, sharing a floor with fifty-two other highly educated students, sharing every meal with our newly-formed friends, and even tackling homework assignments were just like the “good old days”. The level of diversity strengthened the value of peer-networking and real friendships were made throughout the week.

ACS Summer School blog1

The week wasn’t just filled with relaxing chats in the Colorado sun; that was merely how we spent our free time. The days were jam-packed with riveting lectures during the day, assignments in the evening, and getting to know the local Golden beers at night (which was obviously a duty of ours as tourists). We also had the chance to take in the local scenery with hikes and whitewater rafting.

The ACS summer school on green chemistry is a competitive program offered to graduate students, post-doctoral fellows, and industry members every year in Golden, Colorado. Hosted by the Colorado School of Mines, the program consists of five days of lectures from green chemistry and sustainable energy experts, two poster sessions, a whitewater rafting trip, and lots of opportunity for networking. This program teaches global sustainability challenges with a focus on sustainable energy. The ACS Summer School is free of charge for successful attendees, including travel, accommodation on campus, and meals.

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Samantha, Yuchan, and Shira at the ACS Summer School

Jim Hutchison, a professor at the University of Oregon, spoke about how his department has completely reformatted their undergraduate chemistry curriculum to contain green and sustainable chemistry, something that particularly sparked Shira’s interest as lead of GCI’s Education Subcommittee. Bill Tolman, Chair of the University of Minnesota Chemistry Department, shared how students successfully cultivated the safety culture within his department. This had inspired Samantha to create new initiatives within our chemistry department. Queens University’s Professor Philip Jessop taught us about Life-Cycle Analysis (LCA) and assigned us multiple processes for which we calculated the gate-to-gate LCA. Mary Kirchhoff and David Constable from ACS gave talks on green chemistry and ACS resources, many of which would be useful to other departments. The format of the summer school allowed plenty of time to chat with the guest lecturers during coffee breaks, lunches, and poster sessions.

Many real-world issues were discussed. The worldwide energy usage and sources of energy were a main topic of discussion, as was the use of alternative sources. We were blown away by how multi-disciplinary green chemistry is, and we were enlightened on how we need experts in all fields to successfully create sustainable chemistry. We learned that to be able to effectively tackle environmental issues we need great synthetic chemists, whether they specialize in organic, materials or catalysis, as well as analytical chemists, engineers, environmental chemists, and toxicologists. We also need effective entrepreneurs and lobbyists.

Nearing the end of the summer school, a large group of us hiked up Tabletop mountain to get the most amazing view of the valley. A warm feeling of appreciation towards the summer school for bringing us out of the isolation of individual research in the busy city life was shared. We would like to thank ACS for giving us the chance to attend this amazing week. This experience has truly been beneficial to us, and we plan to use the knowledge gained during the week in our own studies as well as pass this knowledge on to our coworkers at the University of Toronto.

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Tabletop mountain in Golden, CO

We highly encourage anyone interested in green chemistry and sustainability to attend this beneficial program. Application deadlines are early in the year and submitted online. The application consists of the applicant’s CV, unofficial transcript, letter of nomination from faculty advisor or another faculty member, and a one-page essay describing your interest in green chemistry and sustainability as well as how it will benefit the applicant.