Green Chemistry and Green Engineering: A Framework for Sustainable Technology Development

EG36CH11-Mulvihill-NEW ARI 29 October 2011 13:14

Green Chemistry andGreen Engineering: AFramework for SustainableTechnology DevelopmentMartin J. Mulvihill,1 Evan S. Beach,2

Julie B. Zimmerman,2 and Paul T. Anastas2

1Berkeley Center for Green Chemistry, University of California, Berkeley,California 94720-7360; email: marty_m@berkeley.edu2Center for Green Chemistry and Green Engineering, Yale University, New Haven,Connecticut 06520; email: evan.beach@yale.edu, julie.zimmerman@yale.edu,paul.anastas@yale.edu

Annu. Rev. Environ. Resour. 2011. 36:271–93

First published online as a Review in Advance onAugust 19, 2011

The Annual Review of Environment and Resourcesis online at environ.annualreviews.org

This article’s doi:10.1146/annurev-environ-032009-095500

1543-5938/11/1121-0271$20.00

Keywords

toxicity, efficiency, interdisciplinary, design, safer chemicals,nanotechnology

Abstract

Green chemistry and engineering seek to maximize efficiency and min-imize health and environmental hazards throughout the chemical pro-duction process. This review demonstrates how green chemistry prin-ciples and metrics can influence the entire life cycle of a chemical fromdesign through disposal. After reviewing essential metrics and recent ad-vances in the field within this context, we consider the case of nanotech-nology. As an emerging field, nanotechnology provides an instructiveframework to consider the influence and application of green chem-istry. Interdisciplinary innovation guides both fields, and both seek totransform the nature of technology. The applications and implicationsof emerging green technology are discussed, and future opportunitiesfor interdisciplinary collaborations are highlighted.

Contents

1. INTRODUCTION . . . . . . . . . . . . . . . . 2721.1. Historical Context . . . . . . . . . . . . . 2731.2. Drivers for Green

Chemistry Adoption . . . . . . . . . . . . 2742. APPLYING GREEN

CHEMISTRY. . . . . . . . . . . . . . . . . . . . . 2752.1. Design Tools for

Green Chemistry . . . . . . . . . . . . . . . 2762.2. Raw Materials

for Green Chemisry. . . . . . . . . . . . . 2802.3. Manufacturing with

Green Chemistry . . . . . . . . . . . . . . . 2812.4. Chemical Use . . . . . . . . . . . . . . . . . 2832.5. End of Life for Chemicals

and Products . . . . . . . . . . . . . . . . . . . 2842.6. Need for Collaboration . . . . . . . . 284

3. CASE STUDY: GREENNANOTECHNOLOGYDEVELOPMENT . . . . . . . . . . . . . . . . 2853.1. Design of Nanotechnology . . . . . 2853.2. Raw Materials for

Nanotechnology . . . . . . . . . . . . . . . . 2863.3. Production of

Nanomaterials . . . . . . . . . . . . . . . . . . 2863.4. Use of Nanotechnology . . . . . . . . 2883.5. End of Life of

Nanomaterials . . . . . . . . . . . . . . . . . . 2883.6. Lessons from Green

Nanotechnology . . . . . . . . . . . . . . . . 2894. FUTURE OF GREEN

CHEMISTRY. . . . . . . . . . . . . . . . . . . . . 2894.1. Educational Efforts . . . . . . . . . . . . 2894.2. Concluding Comments . . . . . . . . 289

1. INTRODUCTION

“Green chemistry” is defined as “the design ofchemical products and processes that reduce oreliminate the use and generation of hazardoussubstances” (1, p. 11). Green chemistry seeks toreinvent the production and use of chemicals inour society so that they are inherently safer andmore efficient (2, 3). This focus aligns with thebroader sustainability movement and the terms

sustainable/green chemistry are often used in-terchangeably.1

It has been widely recognized that atransition to a sustainable society necessitatessignificant changes in resource and energy con-sumption. To efficiently use limited resources,both transmaterialization and dematerializa-tion must occur. Transmaterialization is theprocess of shifting away from hazardous andnonrenewable resources toward safer and/orrenewable or reusable materials. Demateri-alization seeks to minimize the material andenergy inputs to society while maintaining itsprosperity. These broad shifts seek to avoid theenvironmental and human health hazards asso-ciated with resource and energy consumption.Future chemicals and processes should havephysical, chemical, and toxicological propertiesthat allow safe handling and disposal. Greenchemistry aims to accomplish this through therational design of chemicals and processes ac-cording to a set of principles and metrics identi-fied during the past few decades. To achieve thefull potential of green chemistry, a coordinatedtransformation of many social, political, eco-nomic, and technological factors must occur.

Green chemistry provides an intellectualand technological framework that advancesboth transmaterialization and dematerializa-tion strategies within the chemical enterprise.The principles of green chemistry alongwith other sustainability metrics help identifyopportunities for innovation. Green chemistryensures that new technologies minimizeunintended hazards and provides insights intothe implications that new technologies have.By considering both the applications and im-plications for new technology, green chemistrystands apart from other technological trendsthat focus almost exclusively on application.This perspective promotes interdisciplinary

1The term green chemistry is used commonly by academicsbecause of the historical development of the field. The termsustainable chemistry is often preferred by industry as a wayto distinguish technological innovation from the potentialpolitical overtones of the word green.

272 Mulvihill et al.

design and development of new technologiesthat embody principles of sustainability.

1.1. Historical Context

The green chemistry movement startedover two decades ago. Initial motivation forredesigning chemicals and chemical processcame from the pollution prevention legislationin the early 1990s authored by the Environ-mental Protection Agency (EPA) (4). Thislegislation clearly articulated a shift towardinherently safer and sustainable chemicals asbeing the best pollution prevention strategy.

EPA: EnvironmentalProtection Agency

Key early support of green chemistry camefrom the U.S. Presidential Green ChemistryChallenge Awards established in 1995 (5), theGreen Chemistry Institute founded in 1997(6), and the publication of the inaugural issueof the Royal Society of Chemistry journal,Green Chemistry, in 1999 (7). The publicationof Green Chemistry: Theory and Practice (1) in1998 clearly explained the 12 principles (seeTable 1) of green chemistry and helped pro-vide a coherent vision for the emerging greenchemistry movement. Although seeminglyintuitive, the formulation of these principleshelped chemists and chemical engineers

Table 1 The 12 principles of green chemistrya

Number Principle1 Prevention: It is better to prevent waste than to treat or clean up waste after it has been created2 Atom economy: Synthetic methods should be designed to maximize the incorporation of all

materials used in the process into the final product3 Less hazardous chemical syntheses: Wherever practicable, synthetic methods should be

designed to use and generate substances that possess little or no toxicity to human health andthe environment

4 Designing safer chemicals: Chemical products should be designed to effect their desiredfunction while minimizing their toxicity

5 Safer solvents and auxiliaries: The use of auxiliary substances (e.g., solvents, separation agents,and others) should be made unnecessary wherever possible and innocuous when used

6 Design for energy efficiency: Energy requirements of chemical processes should berecognized for their environmental and economic impacts and should be minimized. Ifpossible, synthetic methods should be conducted at ambient temperature and pressure

7 Use of renewable feedstocks: A raw material or feedstock should be renewable rather thandepleting whenever technically and economically practicable

8 Reduce derivatives: Unnecessary derivatization (use of blocking groups,protection/deprotection, temporary modification of physical/chemical processes) should beminimized or avoided if possible because such steps require additional reagents and cangenerate waste

9 Catalysis: Catalytic reagents (as selective as possible) are superior to stoichiometric reagents10 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 theenvironment

11 Real-time analysis for pollution prevention: Analytical methodologies need to be furtherdeveloped to allow for real-time, in-process monitoring and control prior to the formation ofhazardous substances

12 Inherently safer chemistry for accident prevention: Substances and the form of a substanceused in a chemical process should be chosen to minimize the potential for chemicalaccidents, including releases, explosions, and fires

aReprinted and adapted from Reference 1 with permission.

www.annualreviews.org • Green Chemistry 273

understand how principles of sustainabilitycould be applied to their research.

1.2. Drivers for GreenChemistry Adoption

The adoption and development of green chem-istry has been catalyzed by the formulation ofprinciples and metrics that guide the designof sustainable chemicals. Key examples includethe following: atom economy (8, 9), environ-mental factor (E-factor) (10), the 12 principlesof green chemistry (1), principles of sustain-able chemistry (11, 12), and 12 more princi-ples of green chemistry (13). Other design andengineering metrics were also developed in-cluding the 12 principles of green engineering(14), cradle to cradle design (15, 16), naturalcapitalism (17, 18), and design for the environ-ment (19). These metrics share a common vi-sion that chemistry should be developed in amanner that seeks to maximize efficiency andminimize health and environmental hazardsthroughout every stage of a chemical’s life cycle.

The proliferation of metrics allows re-searchers, business people, and politicians toeach characterize progress toward meetingsustainability goals. The various stakeholdersoften prioritize aspects of green chemistryaccording to their own needs and choosemetrics accordingly. Although enabling thespread of green chemistry ideas, the diversityof metrics can confuse the interpretation ofgreenness claims. Recent press and marketingcampaigns extolling promises of green jobsand the green economy complicate matters,bringing a new wave of greenness claims thatwill need to be examined carefully.

Two things should be remembered whenevaluating a greenness claim: (a) There is alwaysroom for improvement, and (b) every metricneeds a baseline. Creating safer, more efficienttechnologies is an iterative process, wherebyeach innovation improves on previous technol-ogy. As a result, there can be greener chemi-cals, but the claims of a green product shouldbe carefully scrutinized. To lend credibility toimprovement claims, such claims should always

be referenced to a baseline and should be quan-tifiable. Specific examples of greenness metricsare discussed in more detail below as they relateto the design of chemicals.

1.2.1. Economic drivers. Green chemistrytools and metrics have allowed businesses tostart evaluating their products and processeswithin the context of a “triple bottom line,”which incorporates economic, environmental,and social factors into the decision makingprocess (20). Green chemistry provides metricsto evaluate the efficiency, environmental, andhealth impacts of new technology. Under con-ditions of good protection rules for health andenvironment, green chemistry clearly makeseconomic sense. In spite of the capital barrierto changes, there are a growing number ofacademic and business studies that demonstratethe profitability of green chemistry initiatives(21, 22). The cost savings generated by theseinitiatives can be explained by decreasingcosts associated with waste removal, protectiveequipment, regulatory compliance, decreasedliability, and manufacturing security (3).

The U.S. government recently reportedthat the cost associated with safety and en-vironmental regulation compliance is as highas 4% of gross domestic product across allmanufacturing sectors (23). Green chemistryguides the creation of inherently safer chem-icals that will necessitate fewer manufacturingsafety controls. Further cost savings could berealized if regulations provided an advantage togreen chemistry solutions used to meet regula-tory compliance. For example, inherently saferchemical alternatives could have a fast-track ap-proval process, making them more attractiveto chemical companies and formulators. Thedevelopment of green chemistry and sustain-able business practices in industry have begunto challenge the myth that investing in greentechnologies is too costly to be competitive.

1.2.2. Health and safety drivers. Greenchemistry has been hailed by politicians andpublic interest groups as a solution to chem-ical hazards in consumer products and the

environment. These groups see the promise of“benign by design” as the solution for elimi-nating the toxic chemicals that are sometimesfound in consumer products. As both thefederal and state governments in the UnitedStates consider chemical policy reform, greenchemistry has been identified as a key tool forcomprehensively addressing the current weak-nesses in chemical regulation (24). By placinggreen chemistry and safe chemical design atthe center of policy reform, advocates hope toavoid chemical-by-chemical regulation, whichhas led to regrettable substitutions of onehazardous chemical for another.

1.2.3. Research drivers. Green chemical–based innovation has produced numerous suc-cesses for research and development opera-tions. The rate of patent applications and thenumber of new green technologies emerginghave been increasing (25–27). The growth ingreen chemistry patents over the past 15 yearshas largely been driven by industry, which capi-talized on the cost savings brought by increasedefficiency and the minimization of hazardouswaste. Green chemistry patents have been filedby a wide array of both chemical producersand chemical users, demonstrating the need forinnovation throughout the supply chain. Thebroad appeal of new cleaner technologies hasspurred academic research as well, and aca-demic literature describing green chemistry hasseen similar growth.

Many technological breakthroughs guidedby green chemistry have occurred in the past15 years, and there are a number of literature re-views that highlight this work (2, 3, 14, 28). Thepurpose of this review is to put these technicalbreakthroughs in the broader context of inter-disciplinary work concerning the environment,energy, and resources. To do so, this review isorganized along the chemical production lifecycle: design, raw materials, manufacturing,use, and end of life. At each point, significantadvances and opportunities are discussed. Theapplication of green chemistry to the con-comitantly emerging field of nanotechnology

is used to highlight how green chemistry caninfluence technology development.

2. APPLYING GREEN CHEMISTRY

Green chemistry is a design philosophy. Thedesign stage of a new chemical or process isthe most appropriate and critical stage to en-gage in green chemistry. During the designphase of a new chemical or product, the scopeof possible innovation ranges from incremen-tal or superficial design improvements to com-pletely redesigning the system of production—a much deeper form of innovation. Consider thefollowing design problem: The electronics in-dustry wants to remove a toxic flame retardantfrom circuit boards without sacrificing perfor-mance or function (29). See Figure 1.

Drop-in replacements like tetrabromo-bisphenol-A (TBBA) meet the stated goal butintroduce other safety concerns. The safetyprofile could be improved by polymerizingthe TBBA, immobilizing the chemical. Thisdecreases the exposure potential while contin-uing to use chemicals of concern during themanufacturing process.

Deeper innovation, requiring significanttechnological redesign, could design away the

Substance

Material

Product

Circuit board example

Reduce voltage

Separate high and low voltage

Change board material

Mineral-based retardants

Phosphorus-based retardants

Polymerized TBBA

TBBA to replace PBDE/PBBs

Figure 1The innovation possibilities for replacement of toxic brominated flameretardants in circuit boards. This figure shows the range of possible solutionsavailable to the electronics industry as they remove pentabromodiphenyl ether(PBDE) and related polybrominated biphenyls (PBBs) from circuit boards.There are many potential solutions ranging in complexity, cost, and potentialimpact. Reprinted and adapted from Reference 29 with permission.

LCA: life-cycleanalysis

flammability potential in circuit boards. Forexample, inherently safer mineral-based flame-retardant chemicals could have been used.Unlike the drop-in replacements discussedin Figure 1, these new materials would haverequired significant changes in the manufactur-ing process. Decreasing the operating voltageof the circuits on the board creates the poten-tial to remove the source of the flammabilityhazard and eliminates the need for an addedflame retardant. It also requires redesigning thecircuits rather than the circuit board. Althoughthis solution requires the largest investment, italso has the largest potential payoff. Reducingthe operating voltage of the circuits potentiallyremoves the flammability hazard, decreases theenergy consumption, and increases the productdurability.

All possible innovation, from superficialto deep, should be considered during thedesign process. There are advantages to eachapproach. Often, simple innovations can bereadily adopted on a short timescale, meetingimmediate goals without significant researchand development investment. Deeper innova-tion takes more resources but has potentiallygreater economic and sustainability benefits.The immediate appeal of innovation by simplematerial substitution is also complicated bypotential unintended consequences associatedwith drop-in replacements. These includechanges in product performance or shifting thetoxicity burden from one pathway to another,resulting in a different harmful outcome.

Sustainable innovation is catalyzed byinterdisciplinary collaboration during thedesign process. If you ask a chemical engineerhow to solve the flame-retardant problem, thesolutions may all be related to chemical sub-stance substitutions. Electrical and mechanicalengineers might adopt a heat dissipation tech-nology, and materials scientists may considermodifying the resins in the circuit board.Each idea should be thoroughly consideredbefore resources are allocated. This is onlypossible in multidisciplinary design teams.The advantage of interdisciplinary teams goesbeyond manufacturing design to the design and

implementation of technology in the academicsetting. A recent study quantified the productiv-ity of interdisciplinary research collaboration.This study demonstrated that interdisciplinaryteams publish more than research teamswithout interdisciplinary collaboration (30).

The circuit board example demonstratesthe importance of design. The design phasedetermines much of a product’s final cost andenvironmental impacts (Figure 2). In fact,over 70% of costs are committed during theinitial design of a product (31). These socialand environmental costs are not incurreduntil much later in the chemical life cycle.The majority of costs are incurred during themanufacture, use, and disposal stages. Figure 2underscores the importance of consideringenvironmental and health effects during theinitial design period, despite the fact that theseimpacts are associated with the later stages ofcommercialization.

2.1. Design Tools forGreen Chemistry

During the design phase, innovators must beable to rapidly compare competing ideas on thebasis of their sustainability profiles. A number oftools have been introduced to aid the evaluationof chemicals, processes, and product life cycles.Many of the early adopters of green chemistrycreated metrics that focused on particular as-pects of the design process. These metrics canbe grouped into three categories: materials ef-ficiency, energy efficiency, and toxicity. Suchmetrics are most useful for evaluating individ-ual chemicals, chemical reactions, or single-stepchemical processes. To evaluate product life cy-cles, systems thinking approaches are needed.Although many tools exist, two of the mostcommonly used frameworks in green chemistryare the 12 principles of green chemistry (1) andlife-cycle analysis (LCA) (32, 33).

2.1.1. Materials efficiency. Chemists aremost familiar with materials efficiency metrics(see Figure 3). The first metric they learn is re-action yield, which is calculated by dividing the

Figure 3The four most common materials efficiency metrics, described in Section 2. � refers to the summation ofthe components.

amount of the product obtained by the maxi-mum amount that could have been obtained ifthere were complete conversion of the startingmaterial into product. This metric neglects toaccount for any of the excess reagents, solvents,or auxiliary inputs to the chemical reaction. Theconcept of atom economy (8) partially addressesthis issue by considering the total amount ofall reagents (not just the starting material) thatcontributes to the product. Atom economy iscalculated by dividing the molecular weight ofthe desired product by the summed molecu-lar weights of all of the reagents. A calculationof atom economy assumes complete conver-sions of the reactants into products (i.e., 100%yield) and neglects to include the contributionof solvents and auxiliaries. The reaction massefficiency is a more holistic metric that incor-porates both atom economy and reaction yieldby dividing the mass of the desired product bythe sum of the masses of all of the reactants.By using the actual masses of reactants ratherthan their molecular weights, this metric cap-tures the atom efficiency as well as the reactionefficiency. Even though the reaction mass effi-ciency still neglects contributions by solvent or

auxiliaries, it has become widely used by indus-trial chemists as a quick evaluation for chemicalprocedures (34).

The first metric to account for the con-tributions of solvents and auxiliaries was theE-factor (35). The E-factor is derived by di-viding the total mass of waste by the mass ofproduct. The E-factor was first used to quan-tify the large amount of waste being generatedby various sectors of the chemical industry. Un-like yield and atom economy, the E-factor canbe calculated for an industrial process as a wholeas well as for individual chemical reactions. Thebroad scope and simplicity of the E-factor havemade it an oft-cited metric. A similar metric,mass productivity, expresses the same conceptas a percentage, making it easier to comparewith the other materials efficiency metrics.

The utility of the various materials efficiencymetrics was evaluated within the context of drugsynthesis (34). Constable et al. (34) concludedthat the reaction mass efficiency and massproductivity were the most valuable metrics fordriving business adoption of greener processesbecause they made sense to both scientists andbusiness leaders.

Erratum

2.1.2. Energy efficiency. Energy efficiencyis a central theme in the sustainability move-ment as well as one of the central tenets ofgreen chemical design. The overall energyconsumption in the chemical industry wasrecently quantified. Chemical manufacturingtypically consumes 25%–30% of the totalenergy used by the manufacturing sector inthe United States. This represents significantenergy consumption, about 5% of all U.S.energy use. For example, in 1994, chemicalsproduction consumed 5.1 EJ (Exa joules) ofenergy and produced the equivalent of 282 Mt(megatons) of CO2 emissions (36).

Opportunities for reducing energy use andCO2 emissions exist in most chemical man-ufacturing processes. For example, processesthat operate at or near room temperatureand atmospheric pressure require much lessenergy. Materials with lower-embodied energy(i.e., recycled or reclaimed material) and/orhigh biological content could be used to reduceoverall energy consumption throughout theirlife cycle. This is particularly true whenproducts are designed so that their embodiedenergy can be partially recovered at the end oflife, either through reuse or efficient, nontoxicincineration coupled with energy generation.

Green chemists have also developed alter-natives to conventional heating methods forchemical reactions; these include microwaveirradiation and sonochemical methods. Thesemethods have the potential to reduce theamount of energy consumed. They have alsoenabled the discovery of new reaction pathwaysand processes (37, 38).

Traditionally, the energy efficiency of pro-cesses is optimized after a chemical process hasalready been developed. If energy is only con-sidered after the development phase has beencomplete, many of these potential efficiency-improving technologies discussed cannot beapplied. The authors of this review believethat energy consumption should be consideredduring the research and development phase,and more techniques to improve the energyuse profile of chemical manufacturing areneeded.

2.1.3. Toxicity. Understanding the potentialhazard associated with a chemical or product isessential for successful green chemical design.Ideally, chemicals would be comprehensivelyscreened for potential toxicity using structure-function relationships before being produced.The current state of the art is not this advanced,but recent developments in predictive toxicol-ogy and quantitative structure activity relation-ships are making predictive tools more availableto molecular designers (39).

Traditional toxicology relies on a “kill andcount” methodology to assess acute toxicity,where increasing doses of a signal chemical areadministered to model animals (rat, mouse,rabbit, and others) until the animals die. Thedose at which 50% of a test population dies isconsidered the median lethal dose. Althoughthe lethal dose may be a useful measure of achemical’s acute toxicity, many of the currentconcerns in chemical production arise fromother toxicity end points. Current producersand consumers are concerned with chemicals’carcinogenic, mutagenic, endocrine disrupting,persistence, and bioaccumulation potentials.These end points are species and environ-ment specific and require a much greaterunderstanding of the chemical and biologicalprocesses occurring at the molecular level.

Many of the chemical toxicity resources cur-rently available to scientists and engineers wererecently reviewed by Voutchkova et al. (40).The emerging technologies in toxicology arerapidly producing a large amount of pathway-specific toxicological information. The abilityfor toxicologists to collect and interpret in-formation about gene- and protein-level inter-actions with toxic substances (toxicogenomics)provides detailed information about many hu-man and environmental health end points.Some of this information is freely available on-line in a variety of public databases includingPubChem (40a) and the EPA’s ACToR (40b).This information is also being used to developmore robust predictive tools (41).

In addition to detailed toxicological infor-mation, there are a number of easily measuredor modeled chemical properties, which can be

used to help predict a chemical’s fate in theenvironment. Programs like the EPA’s PBTprofiler (42), ToxCast (42a), and CalTOX (43)use calculated partition coefficients, vapor pres-sures, solubility, and others to estimate the per-sistence, bioaccumulation, and toxicity profilesof many organic chemicals. These programs areeasy to use and provide a good starting point toevaluate and compare hazard profiles for relatedorganic compounds. Another more recent anal-ysis correlates molecular properties, includingsize, shape, flexibility, solubility, and electron-ics, to molecular toxicity (41). By starting withreadily quantifiable molecular attributes, thesemethods make it easier for chemists to considerthe hazard potential of a new chemical muchearlier in the design process.

2.1.4. Comprehensive design metrics.Consumer, regulatory, and business interestsgenerate a demand to define particular chem-icals or products as green or not green. Giventhe diversity of metrics available, this is nota straightforward process. Binary green/notgreen categorizations can be misleading be-cause (a) they discount the necessity of contin-uous improvement and (b) assume that all endusers value various green criteria in the sameway. A number of comprehensive metrics havebeen developed that seek to quantify and/orcompare chemicals using an array of sustain-ability factors. These include the 12 principlesof green chemistry, LCA, cradle to cradle,and design for environment. The two mostcommonly used by academic researchers arethe 12 principles of green chemistry and LCA.

The 12 principles of green chemistry werefirst developed by Anastas & Warner (1). Bothwere trained as organic chemists, and the12 principles sought to translate the broad con-cepts of sustainability into practical advice thatchemists could use while developing new chem-icals or processes. The 12 principles (Table 1)address all aspects of chemical reactions fromchemical feedstocks (principle 7) to end-of-lifeconsiderations (principle 10). They give practi-cal advice concerning the selection of reactants(principle 9), solvents (principle 5), and reaction

conditions (principle 6), as well as ways to plan(principles 2, 4, and 8) and monitor (principle11) chemical reactions. In general, the princi-pals promote a safer (principles 3, 4, and 12)and more efficient (principles 1 and 2) approachto chemistry. Rather than a set of quantifiablemetrics, the 12 principles of green chemistryembody a design philosophy for chemical syn-thesis most useful to chemists and engineerscreating new products and processes.

In contrast LCA is a well-defined set ofquantifiable metrics used to evaluate the en-vironmental impact of a product. The LCAmethodology is outlined in the InternationalStandards Organization (ISO) protocol 14040(44). A LCA consists of four activities: (a) defi-nition of goals and scope; (b) inventory analysis;(c) impact assessment; and (d ) interpretation. Byevaluating production processes against manymetrics, LCA helps prevent unintended burdenshifting. LCAs rely on data that are often onlyavailable for high production volume chemi-cals or for products of concern that have beenthoroughly studied (32). LCA is well suitedfor rigorously comparing existing alternatives,whereas the 12 principals are better applied tothe development of new technologies.

Both of these comprehensive design met-rics incorporate materials efficiency, energyefficiency, and toxicity considerations. Theyalso address product degradation and variousenvironmental impacts. To fully evaluate achemical or process using either LCA or the 12principles of green chemistry, large amountsof data are needed. For many chemicals, someof the required data are missing, necessitatingassumptions that reduce the accuracy of themetrics. Although a complete evaluation ofchemicals helps designers to make choices,each method gives different results.

A recent article compares the results ofLCA to the 12 principles of green chemistryfor 12 different polymers (45). As seen inTable 2, the ranking of the polymers undereach design metric is strikingly different. Bothdesign metrics consider a wide range of safetyand efficiency metrics. The analysis showsthat LCA favors overall materials efficiency,

Table 2 Rankings for each of the polymers based on the 12 principles green design and thenormalized life-cycle assessment resultsa

Polymer (production process)bRank by green chemistry

principles Rank by life-cycle analysisPLA (NatureWorks) 1 6PHA (Utilizing Stover) 2 4PHA (General) 3 8PLA (General) 4 9High-density polyethylene 5 2Polyethylene terephthalate 6 10Low-density polyethylene 7 3Biopolyethylene terephthalate 8 12Polypropylene 9 1General purpose polystyrene 10 5Polyvinyl chloride 11 7Polycarbonate 12 11

aReprinted and adapted from Reference (43) with permission.bAbbreviations: PLA, polylactic acid; PHA, polyhydroxyalkonate.

whereas the 12 principles favor biobased ma-terials. Similar valuation of particular designtraits is present in all comprehensive designmetrics. There are many ways to measure theimpacts of a chemical, and researchers andcompanies will often favor particular metrics.If the various weights and biases in the metricare made clear and transparent, then end userscan make use of the information intelligently.

2.2. Raw Materialsfor Green Chemisry

Traditionally, chemicals have been made frompetroleum feedstocks. Although chemical pro-duction only accounts for 3%–5% of petroleumconsumption, petroleum sources representover 98% of chemical feedstocks (46, 47).Chemists, chemical companies and consumersall envision advantages for moving to renewablefeedstocks. The chemists see an opportunity fornew innovation and a chance to take advantageof nature’s ability to perform exquisitely selec-tive chemistry. Chemical companies envisionrenewable feedstocks providing a financiallystable source of starting material. With sucha large portion of starting materials coming

from oil, chemical companies are particularlyvulnerable to fluctuations in crude oil prices.Finally, consumers are increasingly choosingnaturally derived products because of theirperceived safety and environmental benefits.

Petrochemical feedstocks provide very sim-ple hydrocarbons, which chemists have learnedto make more complex. Natural feedstocksare inherently different. They are complexmolecules, and chemists are still developing el-egant ways to efficiently transform them intouseful products (48). The idea of a biorefinery,which could take biomass and postconsumerwaste and turn it into fuels (49) and other chem-ical products (46, 50), has been suggested bymany researchers as an important path towardchemical sustainability. Figure 4 outlines thepotential materials flow through a biorefinery.Like a traditional petroleum refinery, a biore-finery maximizes materials utilization throughmany parallel processes. An ideal biorefineryuses all input mass to produce biofuel or chem-ical feedstock material.

Future biorefineries are envisioned to inte-grate the conversion of biomass into both fu-els and fine chemical products in one facility(51). The conversion of biomass to products

Figure 4The materials flow from biomass material to final products or chemical feedstocks. Reprinted and adaptedfrom Reference 51 with permission.

usually proceeds either through a biologicalpathway or a thermochemical pathway. Biolog-ical pathways use fermentation or other naturalforms of biomass conversion to turn raw ma-terials into simpler chemicals (see Figure 4).Then, these molecules can be used directly asfuels or feedstock, or they can undergo furtherchemical modification to make materials or finechemicals (51).

Thermochemical pathways use heat andcontrolled amounts of oxygen or steam to pro-duce syngas. This mixture of carbon monoxideand hydrogen can be converted into petroleum-like feedstocks. The gasification of biomass canbe accomplished on a wide range of both virginand waste streams, making the process attrac-tive. Because the products are similar to petro-chemicals, many researchers see this as a viableoption in the short term. Unfortunately, thismethod uses a significant amount of energy toproduce the syngas, and it also destroys the po-tential chemical complexity of the feedstock,two aspects of the process that do not complywith the 12 principles of green engineering (52).

2.3. Manufacturing withGreen Chemistry

Although green chemistry encourages innova-tion throughout the chemical supply chain, thegreatest advances in the past 15 years havebeen related to chemical production. This isnatural, given that the training of chemistsfocuses on techniques for molecular manipula-tion. The scope, precision, and sustainability ofthese transformations continue to rapidly im-prove. For the sake of this review, we focus ona few classes of chemicals and processes whererecent research has been influenced by greenchemistry.

2.3.1. Catalysis. The Nobel Prize in chem-istry has been awarded three times in thepast 10 years for advances in catalysis. In2001, it was awarded for chiral hydrogenationand oxidation reactions. The 2005 awardrecognized the discovery metathesis reactionsin organic synthesis and highlighted theirimportance for green chemistry. In 2010, the

Nobel committee recognized the importanceof palladium-catalyzed cross-coupling reac-tions in chemical synthesis. This recognitionunderscores the importance of catalysis. Recenttrends in green catalysis include catalysts thatare recyclable, catalysts made using abundantnontoxic metals, and biocatalysis.

Catalysts by their very nature improve ef-ficiency, and waste can be further reduced ifthe catalysts are immobilized on a solid sup-port. In addition to reducing waste, these re-cyclable catalysts present significant reductionsin cost and hazard by removing the expensiveand potentially toxic metals from the chemicalwaste stream. Catalysts have been successfullysupported on inorganic surfaces (53, 54) as wellas on polymer surfaces (55). Inorganic meso-porous and nanomaterials have also been shownto be effective on their own as catalysts for manyreactions (56).

Biological systems rely on catalysts, in theform of enzymes, for the majority of chemicaltransformations. Recent advances in our under-standing of proteomics have allowed chemiststo harness and tailor many of these enzymes toperform desired chemical reactions (57). Theuse of enzyme-based catalysts in chemical pro-cesses has been termed biocatalysis. Biocatal-ysis encompasses whole-organism processes,such as fermentation, isolated enzymes used inchemical reactions, and chemically or geneti-cally modified enzymes. Computer modeling(58) and directed evolution (59) are two of themany techniques that have been used to rapidlydevelop efficient enzymes for chemical reac-tions (57). Biocatalysis is becoming a vibrantarea for the research and development of newcatalysts because of the dual advantages of sus-tainability and increased selectivity. Biocatal-ysis exemplifies interdisciplinary collaborationleading to important developments in greenchemistry, and it is expected to grow substan-tially in coming years (57).

2.3.2. Solvents. Solvents often contribute thegreatest adverse impact to the LCA of chemicalreactions and processes (60). When possible,the elimination of solvent is the greenest

alternative. The removal of solvents fromreactions can be aided using alternative typesof heating. For example, microwave irradiationhas effectively promoted a number of reactionswithout the addition of solvent (37). Solventlessreactions have also been enabled using eutecticmixtures and ball milling technologies (61).

For reactions requiring solvent, a number ofalternative green solvents have been developed(61). The major classes of alternative solventsinclude ionic liquids, supercritical CO2/gas-expanded liquids, switchable solvents, and re-newably sourced solvents. Green solvents aredesigned to minimize or eliminate exposures tovolatile organic compounds, which contributeto air pollution, flammability hazards, and ad-verse human health effects. To promote theadoption of alternative solvents in industry,tools have been developed to aid in the solventselection process (62) see Table 3. These toolshelp chemists quickly identify safer alternativesfor many of the common hazardous solvents.

Some green solvents have the added benefitof being optimized for product isolation.Supercritical CO2 can be removed by changingthe pressure of the reactor, leaving only theproducts of the reaction (63). Similarly, the useof switchable solvent has been shown to aid inthe precipitation of products at the completionof the reaction (64). By designing a solventthat functions well for both the reaction andthe separation steps, there is a potential to saveboth waste and energy, making these moreexotic solvents more attractive.

2.3.3. Separations. The isolation of a pureproduct is paramount for the production offine chemical products. Many techniques forthe isolation and purification of chemicals uselarge quantities of solvent and energy. Devel-opments in pervaporation membranes haveyielded high-purity chemicals with low energyconsumption (65). Micro- or nanostructuredmembranes have also been developed toimprove the isolation of catalysis, metals, poly-mers, and other by-products from reactions(66). Improvements in membrane technologywill enable greater product isolation, decreased

Table 3 Solvent replacement optionsa

Undesirable solvents Alternativeb

Pentane HeptaneHexane(s) HeptaneDiisopropyl ether or diethyl ether 2-MeTHF or tert-butyl methyl etherDioxane or dimethoxyethane 2-MeTHF or tert-butyl methyl etherChloroform, dichloroethane, or carbon tetrachloride DichloromethaneDimethyl formamide, dimethyl acetamide, orN-methylpyrrolidinone

Acetonitrile

Pyridine Triethylamine (if pyridine used as base)Dichloromethane (extractions) EtOAc, MTBE, toluene, 2-MeTHFDichloromethane (chromatography) EtOAc/heptaneBenzene Toluene

aReprinted from Reference 62 with permission.bAbbreviations: EtOAc, ethyl acetate; MTBE, methyl tert-butyl ether; 2-MeTHF, 2-methyltetrahydrofuran.

energy use, and cleaner waste streams, as wellas improve water treatment.

2.4. Chemical Use

Chemical users have a tremendous potentialto drive change in the chemical industry. Mostchemicals are not sold directly to the public;rather chemicals are essential componentsof business supply chains. A single consumerproduct often contains or was made using manydifferent solvents and chemicals. Traditionally,information about chemical identities andhazards associated with chemicals are noteffectively shared through the supply chain.Recent consumer demand for safer and moresustainable products, coupled with increasedregulatory scrutiny, has caused businesses toseek greener chemicals and processes through-out their supply chains. Some of the key driversof this shift include decreasing liability, in-creasing market share, responding to chemicalregulations, responding to voluntary initiativesor incentive programs, and responding topublic awareness (67).

Because most chemical users do not developtheir own chemicals, their approach to greenchemistry naturally involves assessing alterna-tives. Like the comprehensive design metricsdiscussed above, alternatives assessment meth-

ods evaluate chemicals or design options againstmultiple factors. Chemicals need to meet prod-uct performance and price constraints as wellas perform well against greenness metrics. Anumber of tools have been developed to helpbusinesses and other chemical users evaluatechemicals and their alternatives (67).

The prerequisite for using any of these toolsis obtaining full ingredient disclosure from allchemical and product suppliers. Some pro-grams like the EPA’s Design for the Environ-ment (67) and CleanGredients (67) have tried tostreamline this process by acting as third-partyaccrediting agencies, which evaluate chemicalsunder nondisclosure agreements and then makea summary of the results publicly available.Although third-party evaluation is valuablewhen available, it cannot currently be relied onto supply all of the information necessary toevaluate materials throughout a business supplychain. Changes to regulations regarding confi-dential business information or greater supportfor third-party evaluation are necessary beforemany products can be evaluated.

In the face of these constraints, businesseshave adopted two complementary strategies.The first begins by using publically available au-thoritative lists of hazardous chemicals and bymaking a restricted substance list. A restrictedsubstance list can be distributed to suppliers,

allowing companies to dictate what chemicalsare not included in their supply streams. Com-panies can also distribute solicitations for the in-clusion of preferred substances. The restrictedand preferred substance lists can influence sus-tainability choices throughout the supply chain(67).

When information is available for a partic-ular class of chemicals, alternative assessmentscan be accomplished. Through a partnershipbetween the EPA Design for the Environment,CleanGredients, and the National ScienceFoundation, the surfactants and cleaningproducts used by janitors in King County,Washington, underwent an alternatives analy-sis. This process resulted in the identificationof safer alternatives, which reduced bothhealth and environmental hazards associatedwith cleaning products (68). Although thisevaluation took a significant investment intime and resources, it can now be easily appliedto other municipalities or janitorial companieswith relatively little additional effort.

2.5. End of Life for Chemicalsand Products

Chemicals and products should be created sothat they degrade or can be reused at the endof their useful life. For most organic chemi-cals, this means that, at the end of life, naturallyoccurring processes, including hydrolysis, pho-tolysis, and enzymatic degradation, should beable to break the chemical down. The designof biodegradable small molecules has been re-viewed by Boethling and coworkers at the EPA(69). The review includes rules of thumb thatcan qualitatively guide chemical evaluation. Ingeneral, water-soluble compounds break downfaster, especially those containing hydroxyl, es-ter, carboxylic acid, aldehyde, or ketone groups.For hydrophobic compounds, it is preferableto have linear structures, especially >4 carbonchains, rather than aromatic or branched struc-tures. Finally, quaternary carbons and halogensubstituents should be avoided because they areassociated with slow biodegradation.

For some inorganic or highly engineeredmaterials, natural degradation is either imprac-tical or undesirable. Products with these mate-rials should be designed so that the materialscan be easily reclaimed and recycled (15, 52).The proliferation of electronic devices has ledto a significant waste disposal issue. The knowntoxic materials in electronics have resulted in e-waste being classified as hazardous under theBasel Convention. A closer look at this wastestream reveals a great opportunity for recycling.Over half of the material in e-waste is metal,which has the potential to be recycled. How-ever, about 2.5% of the material in the wastestream consists of known toxins, including lead,cadmium, and brominated flame retardants(70). Unfortunately, these materials are not eas-ily separated, and the conditions found in cur-rent recycling facilities produce unacceptablyhigh exposures to these toxic compounds. Manyof these residual toxic chemicals are then re-leased into the air and water, adversely effectingthe surrounding population and environment.

New initiatives and regulations promotingextended producer responsibility have beendriving innovation in product design to stream-line the reuse, recycling, and safe disposal ofconsumer goods. The European Union di-rective 2000/53/EC (71) stipulated minimumreuse and recovery rates for vehicles. This pro-gram will eventually mandate a 95% reuse andrecovery rate by mass in 2015. Even though ad-vances in shredding technology have allowedthe current standards to be met without signif-icant redesign, the 95% standard has spurredEuropean car companies to design cars forgreater ease of disassembly (71). By designingproducts that are more easily disassembled, ex-posure to toxic chemicals during the recyclingprocess can be reduced.

2.6. Need for Collaboration

There are many drivers of green chemistry. Thepromotion of greener chemicals and processesnecessitates collaboration and communicationbetween scientists, engineers, business leaders,politicians, and the public. Designing across

the life cycle of a chemical product requiresmany types of technical knowledge. Enablinggreen chemical policies and markets necessi-tates the inclusion of nontechnical experts andadvocates. Effective communication betweenthese stakeholders can be challenging becausethey use different technical terms and maintaindifferent vested interests, but the design andproduction of greener products depend on theability of these groups to communicate.

Collaboration can be promoted with thecreation of interdisciplinary research centers.Interdisciplinary research centers promotecollaboration by including all of the stake-holders (industry, government, academic, andadvocacy groups) in discussions concerning thefuture of chemical development. By identifyingkey issues and then supporting innovation, ap-plicable technological solutions can be rapidlydeveloped. The American Chemical Societypharmaceutical and formulator roundtablesare good examples of innovation hubs whereindustry leaders collectively identify challengesand help fund research that advances greenchemistry solutions. The new technology isthen made available to all of the roundtablemembers and eventually to the public throughpeer-reviewed publications (72).

Another example of recent success in mul-tistakeholder collaboration is Green CenterCanada (72a), an interdisciplinary academiccenter that evaluates both the technologicaland business potential of university inventions.When promising technologies are identified ithelps academic researchers partner with indus-try to pursue the commercialization of greenproducts and services. The authors believe thata collaborative model will bolster the marketfor green chemistry solutions in the future.

3. CASE STUDY: GREENNANOTECHNOLOGYDEVELOPMENT

Both nanotechnology and green chemistry havepromised to do more with less, which willadvance the dematerialization of technology.The development of nanotechnology occurred

concurrently with the development of greenchemistry. Innovation and practical techno-logical applications have been hallmarks ofboth fields. Proponents of both technologieshave promised to help address the challengescurrently facing society. Nanotechnology haspromised advances in catalysis, energy pro-duction, and human health by harnessing thenovel properties of materials that occur at thenanoscale. Green chemistry has promised to ad-dress many of the same challenges by minimiz-ing the adverse health effects of chemicals whilemaximizing the efficiency of their production.

From inception, nanotechnology has beendriven by application, whereas green chemistryhas sought to balance the benefits from appli-cations of new technologies with the adverseimplications that they may have for human andenvironmental health. Although nanotechnol-ogy has garnered significantly more govern-ment and industry support, advances in greenchemistry are now well situated to help en-sure that nanotechnology realizes its promisewithout regrettable implications owing to un-intended hazards or negative public perception(73).

It is instructive to consider the current statusof nanotechnology from a life-cycle perspec-tive. We have highlighted areas where greenchemistry has been integrated into nanotech-nology as well as areas where the developmentof nanotechnology could benefit from a greenerapproach.

3.1. Design of Nanotechnology

Research groups and companies around theworld are designing new products and processesthat incorporate nanotechnology. This is theoptimal time to consider how these processescan be made safe and efficient. Many of thesame metrics that were discussed above can beapplied to processes involving nanotechnology.Application of even simple design metrics canbe very helpful as nanomaterials are consideredfor commercialization. For example, one studycalculated E-factors for five different syntheticpathways to make gold nanoparticles. These

pathways had E-factors ranging from 200 to96,400 kg waste/kg product (74), highlightingthe need for efficient nanomaterials syntheses,and the significant differences between currentsynthetic strategies.

The E-factor does not include any consid-eration of the potential toxicity of the reagentsused in the synthesis. In the above exam-ple, the synthesis that used the most benignreagents, starch and glucose, had one of thehighest E-factors (29,600 kg waste/kg prod-uct). The most mass-efficient synthesis usedreagents with more significant health concerns.These trade-offs should be carefully consid-ered through the application of comprehensivedesign metrics like the 12 principles. The 12principles have be adapted for nanosynthesis byDahl et al. in their recent review of greener nan-otechnology (75); see Figure 5.

Although many of the inputs for nanomate-rial production are evaluated using the metricsalready discussed, the nanomaterials themselvespresent new challenges. In particular, concernssurrounding human and environmental toxicityare beginning to draw attention from scientists,lawmakers, and consumers (73, 74). The sameproperties that impart novel reactivity couldpotentially also result in new hazards.

Evidence has shown that the toxicity ofnanomaterials is dependent on a wide range offactors that cannot be easily generalized (76).Toxicity pathways that rely on the productionof reactive oxygen species are often materialdependent, and bioavailability is often dictatedby surface coating and/or surfaces charges (76).New assays (77) and risk management models(78) for assessing nanoparticle hazards are beingdeveloped. Further support for research in thisarea is needed to guarantee the safety and so-cial acceptance of nanotechnology in consumerproducts.

3.2. Raw Materialsfor Nanotechnology

Nanotechnology researchers have alreadybegun incorporating some alternative chemical

feedstocks into their synthetic strategies. Sci-entists have used natural products as reducingagents and nanoparticle coatings during thesynthesis of nanomaterials. Starch, agar, pro-teins, sugars, tea extract, coffee extract, ascorbicacid, and even whole organisms have been usedas reducing agents and nanoparticle coatings tosynthesize nanomaterials (75). The diversity ofelements from which nanomaterials have beenfashioned spans most of the periodic table.The next step in greening nanomaterial feed-stocks needs to focus on the metal precursors.The metals used should, when practicable,be earth abundant and nontoxic. Addition-ally, care should be taken to use precursorsthat minimize hazard and embedded energycontent.

3.3. Production of Nanomaterials

Greening the production of many of thecommon nanomaterials (Au, Ag, CdSe, ZnO,FexOy, TiO2, and carbon nanotubes) has al-ready occurred. Many of the most acutely toxicreagents and hazardous solvents have alreadybeen replaced for more benign alternatives (75).For example, initial reports for the produc-tion of gold nanoparticles used borane or di-borane as the reducing agent in benzene asa solvent (74). With a focus on commercial-ization, it was clear that less hazardous ma-terials and methods were needed. A 2011ISIWeb of Science R© search for “gold nanoparti-cle synthesis” yields over 1,200 hits for the past15 years. Many of these methods use much saferchemicals.

A number of synthetic strategies have beendeveloped to improve nanoparticle production.These include using molten salt and hydrother-mal, templated, sonochemical, and microreac-tor methods (75, 79). Like other green chem-istry methodologies, the application of thesetechniques enables safer, more efficient, andoften novel chemistry.

The purification of nanomaterials re-mains a significant challenge in nanoscience.The chemical and physical properties of

nanoparticles prohibit many traditionalmethods for chemical purification. In general,nanomaterials cannot be distilled, recrystal-lized, or purified by chromatography. Some ofthe more common methods for purification,including dialysis, centrifugation, and filtering,are time and resource intensive. In an effort toimprove purification, reduce solvent waste, andspeed the dialysis purification, researchers haveused a continuously flowing diafiltration in-strument to improve selectivity and yield (80).A similar flow technique designed specificallyfor colloidal separations, field flow fractiona-tion, uses centrifugal force to separate varioussized particles. Field flow fractionation hasbeen used as both an analytical and preparatorytechnique for the separation of biological andinorganic nanoscale materials (81). Given thesimilar size scales of proteins and nanoparticles,techniques for biological separation includingelectrophoretic (82) methods have also beenadapted to nanoparticle purification. Unfor-tunately, these separation techniques are noteasily scaled to the volumes needed for produc-tion. Additional practical and scalable methodsare needed to minimize solvent and energyuse.

The advances in green synthetic techniqueshave given scientists many tools. Now the chal-lenge becomes applying these tools throughoutthe discovery and synthesis of the next gen-eration of nanomaterials. The most efficientsynthesis will be accomplished when the needfor auxiliaries, purification, and multiple surfacefunctionalization steps are eliminated.

3.4. Use of Nanotechnology

The market for nanotechnology continues togrow, with an average annual growth rategreater than 30%. Some researchers projecta $1 trillion market for nanotechnology bythe year 2015 (74). As the market contin-ues to grow, consumers and regulators willdemand a greater understanding of the po-tential hazards associated with nanomaterials.Manufacturers also demand high degrees of

product uniformity and reliability. To meetthese demands, new technologies for rapidcharacterization and screening of nanoparti-cles are needed (83). The technology currentlyused to characterize nanomaterials relies onadvanced microscopy techniques, which aretime-consuming and often only characterize afew representative nanostructures. These tech-niques are expensive, time-consuming, and noteasily adapted to the high-throughput require-ments of the manufacturing setting. Addition-ally, microscopy is not suited for the iden-tification of residual molecules or ions thatmay actually have a significant effect on thefunction and hazards associated with the mix-ture (83). Changes from batch to batch canaffect both product performance and healthhazards. This bottleneck highlights the im-portance of analytical chemistry in promotingthe adoption of new greener technologies andwill continue to inspire innovation in comingyears.

3.5. End of Life of Nanomaterials

Like their toxicity, the fate of nanoparticlesin the environment is hard to predict. It isinfluenced by material composition and thenature of the nanomaterial surfaces (84).The relationships between nanoparticles’physical properties and features (composition,shape, size, and coating) and their fate anddegradation in the environment are still poorlyunderstood. If these relationships could beunderstood, then the principles of green chem-istry could be applied toward the design of safernanomaterials.

To design around the current uncertainty,researchers have targeted biologically inspiredbionanocomposite materials similar to abaloneshells (85). Even though this approach is notuniversally applicable, both application and im-plication benefit from using biology for de-sign inspiration. The benefits of biological andbiologically inspired materials have influencedboth green chemistry and nanotechnology overthe past two decades.

3.6. Lessons from GreenNanotechnology

Nanotechnology has focused on the develop-ment of new applications. In our opinion, theattention to rapid development of technologyby researchers and funding agencies has some-what overshadowed the need for understandingthe implications of these new technologies.Application-based research has attractedsignificantly more funding, with only recentappropriations being made to understand theimplications of these technologies (73, 74).By taking a green chemistry approach, someresearchers have proactively demonstrated thepotential for the acceptance and success ofnanotechnology in the market place (75, 86).The green chemistry framework helps providean advantage to emerging technologies thatpromote both performance and safety.

Both nanoscience and green chemistry callfor an interdisciplinary approach to researchand development. The far-reaching appli-cations for both technologies are clear. Thepotential synergy can be supported throughthe integration of green chemistry into thealready existing interdisciplinary collaborationsin nanoscience. This allows comprehensivedesign and analysis of nanomaterials to occurin collaborative atmospheres and includes ananalysis of the environmental impacts of nano-technology. The interdisciplinary Center forEnvironmental Implications of Nanotechnol-ogy has begun making this vision a reality (87).

4. FUTURE OF GREENCHEMISTRY

Green chemistry and green engineeringcontinue to grow, influencing scientists andengineers worldwide. The growing interna-tional community now includes educationaland/or research initiatives in more than 25countries. New technical journals, numerousinternational conferences, and emerging socialnetworking sites for green chemistry havehelped practitioners collaborate. Many ofthese collaborations are built around educating

chemists about the potential benefits of greenchemistry. In order for green chemistry toimpact the way materials are produced, sus-tainability concepts need to be incorporatedthroughout the educational process.

4.1. Educational Efforts

Educational programs in green chemistry arebeing promoted by open-access models forcurriculum dissemination, including many re-sources that are available on the Web. This isparticularly important for the global dissemi-nation of green chemistry curricula. The Be-yond Benign Foundation (89), the AmericanChemical Society Green Chemistry Institute(90), and the Greener Education Materials (91)Web sites all contain curricular material thathas been developed and tested in classrooms.Although most of the available resources focuson chemistry education, new interdisciplinaryprograms are being enabled by campus-widesustainability efforts. Interdisciplinary collab-orations and learning opportunities can exciteand engage even more people about the poten-tial for green chemistry to meet the needs ofsociety’s pressing resource challenges.

4.2. Concluding Comments

Green chemistry is an iterative process. Apply-ing the various metrics and principles of greenchemistry helps identify better products, butthere will always be room for improvement.This means that there are no green chemi-cals, only greener alternatives. This notion ofcontinual improvement is natural and appeal-ing to most scientists and academics but cancause some confusion among politicians, busi-ness leaders, and consumers, who often preferdefinite answers. To avoid flawed policies, poorinvestments, and greenwashing campaigns, it isimportant for scientists and engineers to reachout to the public. They must explain both theapplications and implications of emerging tech-nologies.

Green chemistry takes the first step by get-ting scientists to consider both application- and

implication-driven questions. The interdisci-plinary interactions that arise from this holis-tic approach to technology development shouldencourage more effective communication with

the public. We must take this opportunity toengage all of the public stakeholders becausethe success of any new technology ultimatelyrests with the public.

SUMMARY POINTS

1. Green chemistry is a design strategy.

2. Green chemistry and engineering seek to maximize efficiency and minimize health andenvironmental hazards throughout every stage of a chemical’s life cycle.

3. Green chemistry evaluates and designs for both the applications and implications of newtechnology.

4. Green chemistry and engineering have the potential to improve the performance andpublic acceptance of new technologies.

FUTURE ISSUES

1. Interdisciplinary collaboration and cooperation are needed to realize the full potentialof green chemistry and engineering.

2. Continued development of predictive toxicology models and high-throughput screeningwill speed the design of safer chemicals.

3. Education initiatives aimed at the public will help curtail greenwashing and inform con-sumer activity.

4. Chemical policy reform should make chemical safety data publicly available.

5. Transparency throughout supply chains is needed to improve chemical manufacturingand product formulation.

DISCLOSURE STATEMENT

The authors are not aware of any biases that might be perceived as affecting the objectivity of thisreview.

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Figure 2Plotting the trends in cost over time with respect to design and use. Typically 70% of costs andenvironmental impacts are determined in the design phases, even if they are not incurred until themanufacturing and use phases. Reprinted with permission of John Wiley & Sons, Inc., c© 2009,Environmental Engineering: Fundamentals, Sustability, Design, by J.R. Mihelcic and J.B. Zimmerman (31).

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