The Great Step Backwards: Polymer to Monomer

By Hyungjun Cho, member-at-large for the GCI

There is a movement to develop a new type of product life system called ‘the circular economy’ [3]. Part of this movement aims to manufacture products from recycled or raw materials, and after its useful lifetime, re-introduce the product (now considered waste) as recycled material. The motivation for the introduction of the circular economy is to minimize the need for virgin raw material, especially when it originates from non-renewable resources. This effort is being spearheaded by the Ellen MacArthur Foundation with major industry partners like Google, Unilever, Solvay, and Philips, among others [3]. A critical component to the function of the circular economy is developing the capability to turn waste into a desirable product.

There are several methods of recycling all the different types of materials we use in every day life. This blog will discuss a niche in the ‘plastic to monomer’ field. Evidently, in April of 2019, IUPAC named ‘plastic to monomer’ as part of the 10 chemical innovations that could have high impact in society [6]. Before discussing ‘plastic to monomer’, I must clarify the term ‘plastic’. Generally, plastic is made up of many polymer chains that are physically entangled with one another. A macroscopic analogy is when many electrical wires (think of Christmas tree lights) become entangled: the wires are stuck to each other and the rigidity of the ball of wire is greater than the rigidity of a single wire.

Much like the type of wire influences the tangled ball it forms, the chemical structure of the polymer influences the material properties of the plastic. Examples of properties of plastics include rigidity, elasticity, malleability, gas permeability, friction to skin, transparency, and many others. The polymers that are used for commercial plastic products have been studied and developed for decades to be able perform a specific function. For example, polyvinyl chloride and polystyrene were initially discovered in the 1800s [2,8]. Thus, it would be ideal if the currently used polymers can be de-polymerized back into monomers for recycling purposes. This would be a major move by the plastics industry to become environmentally friendly.

The conventional method to turn polymers into monomer is thermal decomposition. Samples of polymer can be heated to high temperature (typically 220-500 °C) to break some of the bonds that hold the monomers together [10]. When this occurs, radicals can form at the site of the broken bond, which can lead to de-polymerization [10]. The required temperature and how much monomer is formed is dependent on the chemical structure of the monomers that are formed. Thermal decomposition to recover monomer is suitable only for a few types of polymers, such as poly(α-methylstyrene), which has ceiling temperature of 66 °C to propagate depolymerization; the monomer recovery after thermal decomposition of poly(α-methylstyrene) is excellent at 95% [11]. However, for polymers like polyethylene (PE, the most produced polymer) and polypropylene (PP, 2nd most produced polymer), the monomer recovery yield is poor (0.025-2%) [11]. In some cases such as polyvinylchloride (PVC, 3rd most produced polymer), thermal decomposition is even more problematic because PVC will release harmful hydrochloric acid and vinylenes upon heating [11]. Thus, the monomer recovery is poor (1 %) and the process is highly corrosive.

Therefore, one of the key challenges to address for ‘polymer to monomer’ is to perform de-polymerization at a low temperature. There are 4 recent publications that explore this challenge [5,7,9,12]. In general, the authors synthesized polymers using reversible-deactivation radical polymerization (RDRP) techniques and explored the de-polymerization reactions they encountered. Below is a brief highlight from the publications from the Haddleton group [9] and the Gramlich group [5].


Scheme 1: De-polymerization of RAFT polymers with trithioester end-group [5]. Reproduced from ref. [5] with permission from The Royal Society of Chemistry.

Flanders et al. polymerized methacrylate monomers, including methylmethacrylate (MMA), using reversible addition-fragmentation chain-transfer (RAFT) polymerization with a trithioester chain-transfer agent (CTA) [5]. This type of polymerization places trithioester end-group at end of the polymer chain (Scheme 1). Typically, this end-group is used to re-start the polymerization at the trithioester end of the polymer. However, as we will see, it may have another function. The authors isolated the polymer, then re-dissolved the polymer in 1,4-dioxane at 70 °C (Scheme 1). This caused monomers to be released from the polymer chains at a temperature much less than the ceiling temperature of MMA, which is 227 °C [13]. Analysis of the polymer after partial de-polymerization demonstrated that the trithioester end-group was still attached to the polymer and the size dispersity (range of polymer ‘molecular weight’) was low, which suggested that the de-polymerization was moderated by the trithioester end-group. The authors observed 10-35% de-polymerization after heating at 70 °C for 12-60 hrs.


Scheme 2: ATRP of NIPAM in carbonated water, followed by de-polymerization [9]. Reproduced from ref. [9] with permission from The Royal Society of Chemistry.

Lloyd et al. used an alkylbromide initiator, Cu-based catalyst system to polymerize N-isopropylacrylamide (NIPAM) in Highland Spring carbonated water at 0 °C (Scheme 2) [9]. This type of polymerization places a halide at the end of the polymer chain. The authors monitored the monomer conversion into polymer using 1H-NMR spectroscopy. They measured that ca. 99% of the monomer was converted into polymer chains within 10 min. Unexpectedly, in the next 50 min. the authors observed 50% de-polymerization. The authors attempted to optimize de-polymerization conditions by changing the pH, using dry ice in HPLC grade water instead of Highland Spring carbonated water, etc. which led to 34-71% de-polymerization after 0.5-24 hrs. Years later, the same group used a very similar polymerization condition to polymerize NIPAM [1]. This time, non-carbonated water was used as the solvent and they did not report any de-polymerization.

The reports on RDRP followed by de-polymerization highlighted here are not yet ready to make an impact to ‘plastic to monomer’. The authors admit that the mechanism of de-polymerization is unknown. However, these seem to be the first set of reports on de-polymerization occurring at low temperatures. Perhaps these publications could be the birth of the reversible-deactivation radical de-polymerization (RDRDe-P) field. This is especially intriguing because RDRP have already been studied for decades in academia and are being adopted by the polymer industry [4]. Companies like BASF, Solvay, DuPont, L’Oréal, Unilever, 3 M, Arkema, PPG Industries, etc. already claimed patents for technology and products based on RDRP [4]. Somewhat ironically, RDRP was also part of the IUPAC’s 10 chemical innovations for impact on society but not for its potential to recycle polymer [6].

The polymers of the future may not be made from monomers abundantly used today, but the polymers of the future may be degradable through a low energy process.


  1.  Alsubaie, F.; Liarou, E.; Nikolaou, V.; Wilson, P.; Haddleton, D. M. Thermoresponsive Viscosity of Polyacrylamide Block Copolymers Synthesised via Aqueous Cu-RDRP. European Polymer Journal 2019, 114, 326–331.
  2. Baumann, E. Ueber Einige Vinylverbindungen. Justus Liebigs Annalen der Chemie 1872, 163 (3), 308–322.
  3. Circular Economy – UK, USA, Europe, Asia & South America – The Ellen MacArthur Foundation (accessed Jan 5, 2020).
  4. Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over? Chem. 2018, 9 (40), 4947–4967.
  5. Flanders, M. J.; Gramlich, W. M. Reversible-Addition Fragmentation Chain Transfer (RAFT) Mediated Depolymerization of Brush Polymers. Chem. 2018, 9 (17), 2328–2335.
  6. Gomollón-Bel, F. Ten Chemical Innovations That Will Change Our World: IUPAC Identifies Emerging Technologies in Chemistry with Potential to Make Our Planet More Sustainable. Chemistry International 2019, 41 (2), 12–17.
  7. Li, L.; Shu, X.; Zhu, J. Low Temperature Depolymerization from a Copper-Based Aqueous Vinyl Polymerization System. Polymer 2012, 53 (22), 5010–5015.
  8. Liebig, J. Justus Liebig’s Annalen Der Chemie. Annalen der Chemie 1832, 1874-1978.
  9. Lloyd, D. J.; Nikolaou, V.; Collins, J.; Waldron, C.; Anastasaki, A.; Bassett, S. P.; Howdle, S. M.; Blanazs, A.; Wilson, P.; Kempe, K.; et al. Controlled Aqueous Polymerization of Acrylamides and Acrylates and “in Situ” Depolymerization in the Presence of Dissolved CO2. Commun. 2016, 52 (39), 6533–6536.
  10. Microwave-Assisted Polymer Synthesis. Springer eBooks 2016
  11. Moldoveanu, Șerban. Analytical Pyrolysis of Synthetic Organic Polymers; Techniques and instrumentation in analytical chemistry; Elsevier: Amsterdam ; Oxford, 2005.
  12. Sano, Y.; Konishi, T.; Sawamoto, M.; Ouchi, M. Controlled Radical Depolymerization of Chlorine-Capped PMMA via Reversible Activation of the Terminal Group by Ruthenium Catalyst. European Polymer Journal 2019, 120, 109181.
  13. SFPE Handbook of Fire Protection Engineering, 5th ed.; Hurley, M. J., Gottuk, D. T., Jr, J. R. H., Harada, K., Kuligowski, E. D., Puchovsky, M., Torero, J. L., Jr, J. M. W., Wieczorek, C. J., Eds.; Springer-Verlag: New York, 2016.
Boat Antifouling Technology: the problems and the green chemistry solutions!

Boat Antifouling Technology: the problems and the green chemistry solutions!

By Alana Rangaswamy (Vice-President, Dalhousie University Green Chemistry Initiative)


The iconic Halifax Ferry is one of many boats to traverse the Harbour every day.

One great part of attending Dalhousie University is living steps away from the ocean. Much of Halifax’s history and development is due to its access to water, both as a naval base and port of call. With the massive amount of boat traffic seen daily by the harbour, marine industries strive to maximize the efficiency of travel. And one major way to do that is preventing small creatures from hitching a ride on your boat, causing drag and lowering the efficiency of your vessel. Enter antifoulants: coatings that kill organisms or otherwise block their ability to stick onto your ship. Antifouling is a necessary technology, but introducing biocidal agents into a marine environment, unsurprisingly, poses many environmental challenges. Let’s take a look at two commonly used antifoulants, their issues, and how scientists have tried to fix them:


You may have heard of tributyltin (TBT) as a biocidal agent. TBT is an excellent poison – effectively nonpolar due to its alkyl groups, it’s able to accumulate in organisms, rapidly killing them due to the high toxicity of SnIII. This property makes TBT an extremely effective antifouling agent, however, it easily leaches from boat hull paint into the ocean where it persists due to its high stability. Fortunately, the dangers TBT have been recognized worldwide and use as a biocidal agent has been banned as of 20081. Canada jumped on the bandwagon slightly earlier, with the last TBT-containing paint product registered in 1999.2 With this restriction, the industry is searching for alternatives that are as effective as TBT, without the environmental drawbacks.


Copper as a bulk metal is naturally antiseptic, promoting the formation of reactive hydroxyl radical species which lead to cell death in living systems.3 Copper has been used on boat hulls since the 1700s, and now usually shows up in paints as its metal oxide4 or as a suspension of copper powder.5 Although copper is less bioavailable than TBT, it persists and continually forms unstable radical species (and can, therefore. wreak ecological havoc) in a marine environment. Since copper is widely considered the new “gold” standard in antifouling, the sheer amount of it present on (and leaching off of) boat hulls today points to a long-term impact.

New Antifouling Tech

Green chemistry and engineering are all about designing cleaner systems that work as well as, or better than, the existing standard. TBT and copper are high bars to clear, but scientists are up to the challenge. As early as 1996, the environmentally benign Sea-Nine antifouling compound had received the Designing Greener Chemistry Award as part of the US EPA’s Presidential Green Chemistry Challenge.6 Sea-Nine is a derivative of isothiazolinone, a 5-membered heterocycle containing nitrogen and sulfur atoms. The compound is acutely toxic to marine organisms at the surface of boats, but biodegrades rapidly in marine environments through a ring-opening mechanism to form non-toxic by-products. Sea-Nine (and its derivatives) is currently present in commercial boat hull paints,7 however, degradation times may vary based on geographical location and local environment8 so our job isn’t done yet.

There are many newer studies in the works. For instance, investigation has been done into using natural products as antifouling agents. Natural products are secondary metabolites produced by microorganisms as a defence mechanism in response to stress. As such, they often have antimicrobial properties, while being naturally biodegradable. For example, 1-hydroxymyristic acid, a simple alpha-hydroxy fatty acid, was isolated from the marine bacterium Shwanella oneidensis. When panels were coated with paint containing the fatty acid, and subsequently immersed in a marine environment, no growth of foulants was observed even after 1.5 years.9 Other studies have added hydrophobic coatings which disrupt the binding interactions between the microorganism and the vessel’s hull, and promote detachment due to the natural flow of the water over the hull.10 Some research has diverted away from chemical modifiers altogether, using microtextures, which remove the flat surfaces required for spores to settle,10 to deter growth. UV-LEDs11 which are mutagenic and cytotoxic at a small scale, have also been used to reduce growth of foulants.

The long history and many methods developed to prevent boat hull fouling demonstrates that this is an important and challenging problem. But many results are promising, and green chemists and engineers are well on their way to solving it.


  2. Health Canada – Consumer Product Safety Registrar

  1. Grass, G., Rensing, C., and Solioz, M. Metallic copper as an antimicrobial surface. Environ. Microbiol. 2011, 77, 1541-1547. DOI: 10.1128/AEM.02766-10.
  6. Chen, L. and Lam, J. C. W. SeaNine 211 as an antifouling biocide: a coastal pollutant of emerging concern. Environ. Sci., 2017, 61, 68-79. DOI: 10.1016/j.jes.2017.03.040.
  7. Qian, P-Y., Xu, Y. and Fusetani, N. Natural products as antifouling compounds: recent progress and future perspectives. Biofouling, 2009, 26, 223-234. DOI: 10.1080/08927010903470815.
  8. Salta, M. et al. Designing biomimetic antifouling surfaces. Trans. R. Soc. A, 2010, 368, 4729-4757. DOI:10.1098/rsta.2010.0195




The plastic problem – accumulation before alternatives

The plastic problem – accumulation before alternatives

By Karlee Bamford, Treasurer for the GCI

Plastics undoubtedly play a central role in our daily lives and played a pivotal role in the development of consumer societies across the globe for over a century. Concurrent with newfound materials and newfound possibilities, unprecedented environmental problems have emerged as a result of our reliance on plastics. The accumulation of plastics in allocated disposal sites (e.g. landfills) and in otherwise uninhabited spaces (e.g. beaches, open ocean) present threats to human health, water security, and food supply. These challenges now impact communities globally, irrespective of their actual contribution to the generation of plastic waste, and affect individuals of all economic backgrounds.

Figure 1. Examples of waste plastic accumulation in landfills and the environment. Images source: Pixabay.

Given the scale and significance of these challenges, is there anything that chemists can do to resolve this panhuman problem? A recent blog post from the Green Chemistry Initiative ( highlighted the advances that have been made in synthetic and materials chemistry towards plant-derived and biodegradable plastics as alternatives to traditional petroleum-derived plastics. While this is undoubtedly a crucial area of research as humanity has become permanently dependent on plastics, the design of next generation plastics that are inherently sustainable will not mitigate the overwhelming impacts of existing plastic waste. Arguably, attenuating the problem of plastic waste is more important than finding alternatives to traditional plastics. Indeed, the decomposition time for products made from the top four families of commodity plastics (PP, PE, PVC, PET), produced on a 224.6 million tonne-scale alone in 2017,1 is estimated at 1 to 600 years in marine environments2 and considerably longer in landfills due to lack of moisture.4

Figure 2. Examples of the top five most-produced commodity polymers and their production scale in 2017.1,3

Traditional plastic-recycling methods are not equipped to resolve the issue of waste plastic accumulation either. Recycling can be broken down into three distinct varieties: primary, secondary, and tertiary.5 Primary recycling, which is equivalent to repurposing or reusing, is used limitedly for products such as plastic bottles, typically made of PET, which be directly reused following the necessary sterilization. Secondary recycling involves mechanical processing of plastics into new materials and frequently results in reduction of the plastics overall quality or durability due to the thermal or chemical processes involved. Primary and secondary recycling account for the majority of recycling efforts, however, as a consequence of poor consumer compliance (e.g. <10 % in the US and 30-40 % in the EU)6 and the deteriorating value of plastics with repeated secondary recycling, all plastics eventually become waste. The last and most underutilized form of recycling is tertiary recycling, the degradation or depolymerization of plastics into useful chemicals or materials. In the last year alone, numerous high profile editorial and review articles have appeared in Science7,8,9 and Nature6,10 emphasizing the incredible potential of chemical (tertiary) recycling as means of reducing plastic waste and as a new, sustainable chemical feedstock for the polymer (plastics) industry.

The challenge of chemical recycling is immediately evident: plastics have been expertly designed to be highly durable and chemically resistant, and thus, plastics cannot be easily transformed chemically. Ideally, polymers used in plastics could be depolymerized to monomer for subsequent repolymerization. For condensation polymers, such as polyethylene terephthalate (PET), the reverse of the polymerization reaction is the addition of a small molecule to the polymer to reform monomer. While completely reversible on paper or in theory, such depolymerization strategies have had limited success for PET.

Reacting the polymeric PET material with protic reagents (e.g. amines, alcohols) followed by hydrolysis to give monomers that can be repolymerized, if of sufficient purity (Figure 3), requires high temperature (250-300 °C) and high pressure (0.1-4 MPa) conditions unless additives, such as strong acids and bases or metal salts, are used.11 The action of many additives is not well understood, thus precluding rational improvement of the system. Hydrolysis of PET itself, especially at neutral pH, is the most challenging approach to PET chemical recycling as water is a relatively poor nucleophile. Hence stronger nucleophiles, such as ethylene glycol, are preferred.

Figure 3. Depolymerization of PET by glycolysis.

One practical problem in the chemical recycling of any plastic is its insolubility. Phase transfer catalysts –  species capable of transferring from one phase to another – have been used to address the insolubility of PET12 and have permitted the direct hydrolysis of PET at operating temperatures as low as 80 °C, as in the work of Karayannidis and coworkers (Figure 4). The phases in these systems are the insoluble PET polymer (the organic phase) and the basic solution (the aqueous phase) surrounding it.13

Figure 4. Phase transfer catalyzed hydrolysis of PET (catalyst shown in blue).

Addition polymers, such as polypropylene (PP) or polyethylene (PE), cannot be depolymerized to monomer form using the above strategies as their polymerization does not involve the loss of small molecules. Until very recently, the best end-of-life purpose for the majority of plastics has been energy recovery through incineration. The work of Huang and coworkers on the chemical degradation of PE plastics is a break-through for the field of plastic recycling. While previous studies have reported that thermolysis of PE yields poorly defined mixtures of hydrocarbons, these authors have found a remarkable, highly targeted method for converting PE to a narrow distribution of fuels (3 to 30 carbons in length) using a dehydrogenative metathesis strategy (Figure 5).14 The homogeneous iridium catalysts employed were previously reported in the literature for alkane dehydrogenation (step 1) and hydrogenation (step 3), but no such polymer substrates had apparently been attempted for main-chain dehydrogenation. Similarly, the authors used a previously-established rhenium oxide/aluminium oxide catalyst for olefin metathesis (step 2).

Figure 5. The transition-metal catalyzed degradation of PE to liquid fuels reported by Huang and Guan (catalysts shown in blue).14

The chemical recycling of PET by phase transfer catalysis and of PE by dehydrogenative-metathesis have very little in common with one another on a technical level. What unites these two strategies is the desire to transform the problematic, highly abundant and inexpensive resource that is waste plastic into useful commodities. Perhaps more importantly, these two examples both take revolutionary approaches to old problems through inspiration from fundamental research and parallels found in small molecule catalysis. Rethinking the plastic problem into a challenge for catalysis, rather than solely a call for clever materials design, is critical if we wish to reduce the threats that waste plastics pose to our health and our environment.


  1. Tavazzi, L., et al., The Excellence of the Plastics Supply Chain in Relaunching Manufacturing in Italy and Europe, The European House, Ambrosetti, 2013 (as cited in Bühler‐Vidal, J. O. The Business of Polyethylene. In Handbook of Industrial Polyethylene and Technology; Spalding, M. A.; Chatterjee, A. M., Eds.; John Wiley & Sons: Hoboken, NJ, 2017; p. 1305).
  2. Mote Marine Laboratory Biodegradation Timeline; 1993. Available from: ; accessed July 10, 2018.
  3. Image sources: Image sources: (Plastic recycling symbols) ; (PP) ; (LLDPE) ; (HDPE) ; (PVC) ; (PET)
  4. Andrady, A. L. Journal of Macromolecular Science, Part C: Polymer Reviews, 1994, 34(1), 25-76.
  5. Hopewell, J.; Dvorak, R.; Kosior, E. Trans. R. Soc. B, 2009, 364, 2115–2126.
  6. Rahimi, A.; García, J. M. Nature Reviews Chemistry, 2017, 1, 0046.
  7. MacArthur, E. Science, 2017, 358 (6365), 843.
  8. García, J. M.; Robertson, M. L. Science, 2017, 358(6365), 870-872.
  9. Sardon, H.; Dove, A. P. Science, 2018, 360(6387), 380-381.
  10. The Future of Plastic. Nature Communications, 2018, 9, 2157.
  11. Venkatachalam, S.; Nayak, S. G.; Labde, J. V.; Gharal, P. R.; Rao, K.; Kelkar, A. K. Degradation and Recyclability of Poly (Ethylene Terephthalate). In Polyester; Saleh, H. E. M., Ed.; InTech: London, 2004; p. 78.
  12. Glatzer, H. J.; Doraiswamy, L. K. Eng. Sci. 2000, 55(21), 5149-5160.
  13. Kosmidis, V. A.; Achilias, D. S.; Karayannidis, G. P. Mater. Eng. 2001, 286(10), 640-647.
  14. Jia, X.; Qin, C.; Friedberger, T.; Guan, Z.; Huang, Z. Science Advances 2016, 2(6), e1501591.

Issues of Sustainability in Laboratories Outside the Field of Chemistry: Pipette Tips

Issues of Sustainability in Laboratories Outside the Field of Chemistry: Pipette Tips

By David Djenic, Member-at-Large for the GCI

As a biochemistry student in the Green Chemistry Initiative, I’m interested in looking at how to implement the principles of green chemistry in molecular biology and biochemistry labs. While molecular biology labs focus more on studying biological systems and molecules rather than synthesizing new molecules, like in synthetic chemistry, there are still problems when it comes to performing environmentally sustainable research.

Pipette tips and pipette tip racks are major contributors to non-chemical waste in biomedical labs because of the volume of tips thrown out and the lack of recycling programs to deal with tips and racks. Pipette tip racks are commonly used because they reduce the risk of contaminating pipette tips. Pipette tip racks are made of #5 plastic (polypropylene), the same material as yogurt cups, medicine bottles and David_blog 1microwavable containers, making them lightweight and very safe to use [1].
However, #5 plastics are rarely accepted by curbside recycling programs and are placed in landfills and incinerators instead [2]. The plastic from the empty polypropylene racks take hundreds, if not thousands, of years to degrade [3].

Biomedical companies have worked in the past 10 years to reduce the amount of waste from pipette tip racks. For example, Anachem, a pipette and pipette tip manufacturing company in the UK, has collaborated with a plastic recycling company to collect racks from qualifying laboratories, ground them down, melt them, and remould into new products [3]. A similar program is run at the Environment, Health and Safety (EHS) division of the National Cancer Institute at Frederick (NCI-Frederick), where, from 2003 to 2006, approximately 8,400 pounds of pipette tip boxes were recycled, saving approximately $7,400 in medical waste contract money [4].

David_blog 2

Pipette tip box waste to be recycled through the EHS program [4].

There aren’t many statistics on the waste produced by the pipette tips themselves. But whenever I’m in a biochemistry lab course, the orange bins where used tips are thrown are filled to the brim with pipette tips, microcentrifuge tubes, Falcon tubes, etc. It is more difficult to reduce and recycle tips rather than tip racks because they are heavily contaminated after use. GreenLabs at the University of Chicago offers some interesting suggestions on reducing pipette waste, such as using pipette tip refills, buying pipette tips made from sustainable material, and generally reducing pipette tip use when possible. However, more research on pipette tip waste is needed to quantifiably analyze the impact of tips and come up with solutions to reduce potential waste.

I think undergraduate biomedical teaching and research labs do apply basic green chemistry principles, even if they are not explicitly brought up. Many of the reactions are done in very small, precise quantities and waste is generally disposed of in the proper place. However, there does not seem to be much exposure, if at all when it comes to green chemistry issues; biochemistry and biomedical students aren’t aware of the environmental impact they generate in labs. Introducing green chemistry education in biomedical laboratories at U of T, especially when it comes to the issue of pipette tips and racks, would help U of T reduce its environmental impact even more.






[4] G. A. Ragan, J. Chem. Health Saf. 2007, 14, (6) 17-20.

Recycling Perovskite Solar Cells

Recycling Perovskite Solar Cells

By Judy Tsao, Member-at-Large for the GCI

Solar energy is arguably the most abundant and environmentally friendly source of energy that we have access to. In fact, crystalline silicon solar cells have been employed in parts of the world at a comparable cost to the price of electricity derived from fossil fuels.1 The large-scale employment of solar cells, however, remains challenging as the efficiency of existing solar cells still needs to be improved significantly.

An important recent breakthrough the field of solar cells is the use of perovskite solar cells (PSC), which includes a perovskite-structured compound as the light-harvesting layer in the device (Figure 1). Perovskite is a name given to describe the specific 3-D arrangement of atoms in such materials. Even though the first PSC was reported only in 2009, its power conversion efficiency (PCE) has already been reported to exceed 20%, a milestone in the development of any new solar cells which typically takes decades of optimization to achieve.2


Figure 1. Thin-film perovskite solar cell manufactured by vapour deposition (photo credit: Boshu Zhang, Wong Choon, Lim Glenn & Mingzhen Liu)

PSC has several advantages compared with traditional solar cells, including low weight, flexibility, and low cost.3 There are, however, several challenges that must be overcome before PSC can be brought to the market. The most common PSC to date includes CH3NH3PbI3 and related materials, which contain soluble lead (II) salts that are toxic and strictly regulated.

Interestingly, there has been a consensus in the literature that the lead content in the perovskite layer is not actually the main issue in the environmental impact of PSC production.4 Part of the reason for this conclusion is simply that the thickness of perovskite layer required would amount to less than 1000 mg of lead in one square meter of material. This value is only modest compared to lead pollution from other human sources such as lead paints or lead batteries.5

The main environmental concerns regarding PSCs appear to lie in the use of gold and high temperature processes during the manufacturing of the devices.6 It has thus been suggested that, in order to reduce the environmental impact of PSCs, recycling of raw materials is very important. In a recent study by Kadro et al., 7 a facile protocol for the recycling of perovskite solar cell was developed. The entire procedure takes place at room temperature and takes less than 10 minutes (Figure 2).


Figure 2. Schematic process for recycling PSC components [7].

As it turns out, components of a fully assembled PSC can be extracted by sequentially placing the device in different solvents. Step 1 of the procedure uses chlorobenzene to remove the gold layer, while step two uses ethanol to dissolve CH3NH3I. This then leaves PbI2 to be the only component remaining on the device, which can be removed by just a few drops of N,N-dimethylformamide. It is also worth noting that the recycled materials can be fabricated into a complete PSC again without significant drop in performance.

Even though the discovery of PSC has only been made less than a decade ago, its potential in applications in photovoltaics has been underlined by numerous studies. It is especially gratifying to see that the environmental impacts of such devices are already under active research before PSCs are introduced to the market. While these studies have demonstrated that PSCs have low environmental impacts when properly recycled, there are other challenges still facing researchers in this field. In particular, the short lifetime of such devices needs to be improved to match that of traditional silicon-based solar cells. Nevertheless, the facile method of recycling PSCs without compromising the performance will certainly make them even more competitive than traditional solar cells.


  1. Branker, K. et al. Renewable Sustainable Energy Rev. 2011, 15, 4470.
  2. Yang, W. S. et al. Science, 2015, 348, 1234.
  3. Snaith, H. J. Phys. Chem. Lett. 2013, 4, 3623.
  4. Serrano-Lujan, L. et al. Energy Mater. 2015, 5, 150119.
  5. Dabini, D. Phys., 2015, 6, 3546.
  6. Espinosa, N. et al. Adv. Energy Mater. 2015, 5, 1.
  7. Kadro, J. M. et al. Energy, Environ. Sci. 2016, 9, 3172.