With increased aviation travel and limited substitutes in this area, jet fuel demand has increased significantly. The traditional jet fuel consumes huge fossil energy and leads to serious environmental pollution. With the global warming effect, biomass, as a renewable resource to produce jet fuel, has attracted progressively more attention at the global scale. In recent years, the conversion routes of jet fuel derived from biomass mainly include catalytic cracking-olefin oligomerization, hydroprocessed esters, and fatty acids, Fischer–Tropsch (FT) synthesis, hydrothermal liquefaction, and fermentation alcohol synthesis.(1?10) However, the environment, resource, and economic performances of biomass-based jet fuel need to be evaluated and compared for seeking beneficial technical pathways.

The life cycle assessment (LCA) is a method for evaluating the environmental impact of a product throughout its life cycle. In order to compare the influence of different processes of biomass-based jet fuel on the environment and resources, some literature studies carried out a variety of life cycle evaluations of the abovementioned conversion processes. These studies mainly focused on the contribution of biomass-based liquid fuel to mitigate the greenhouse effect. Moreover, some comprehensive evaluations were based on the fuzzy mathematics method, such as the analytic hierarchy process (AHP).
Several researchers(7?9) performed the LCA of biomass-based jet fuel derived from hydrothermal liquefaction (HTL) of microalgae. Two HTL processes of algal jet fuel based on the different circumstances were analyzed, and Monte Carlo simulation and sensitivity analysis were completed. The results showed that the transportation of microalgae led to the increase in the life cycle climate change impacts, and compared to the process of petroleum-based jet fuel, greenhouse gas emissions could be reduced by 76.0% based on the optimized process of algal jet fuel.

Klein et al.(3,4) compared different routes for renewable jet fuel (RJF) production integrated with sugarcane biorefineries in Brazil based on the technoeconomic and environmental assessments. They concluded that hydroprocessed esters and fatty acids exhibited the highest production potential and FT synthesis showed the best economic performance among the studied scenarios of RJF. Moreover, all conversion technologies of RJF could reduce greenhouse gas emissions by more than 70% compared to the process of petroleum-based jet fuel...(10)

...Moreover, many researchers have integrated the AHP into LCA to evaluate the comprehensive performance of products.(14?16) Tao et al.(6) obtained a resource-environment-economic comprehensive performance evaluation model of biomass-based jet fuel from biomass gasification and FT synthesis based on AHP. They showed that the case of biomass-based jet fuel combined with waste heat for power generation exhibited a lower environmental impact than that combined with heat supply directly and the reduction of environmental impact indicators was in the range of 11.7–40.8%. Compared to petroleum-based jet fuel, the global warming potential (GWP) of biomass-based jet fuel reduced by 52.6–71.9% and the nonrenewable resource consumption reduced by 84.4–93.6%. Different environmental impact distribution methods, such as based on economic value distribution, energy distribution, and mass distribution, used in the biomass growth stage led to significant changes in the environmental evaluation, in particular, for GWP and eutrophication potential (EP). It could also be found that the comprehensive performance of biomass-based jet fuel is the most sensitive to feedstock consumption...

...The method of monetization is more objective and rational, which has the same criteria for weighting economic performance, resource performance, and environmental performance. Therefore, the comprehensive evaluation obtained is fairer to the entire society, and its decision-making meaning is more perfect. This study not only employed the monetization method to reflect economic benefits but also completed the comprehensive analysis through the monetization method on resource and environment, to avoid the subjective factors in comprehensive evaluation.

Figure 1. Process of jet fuel from biomass gasification and Fischer–Tropsch synthesis

Considering petroleum-based jet fuel as a reference, the performances of economy, resource, and environment were reflected by relative economic benefits (REBs), nonrenewable resources saving benefits (NRSBs), and pollution mitigation benefits (PMBs). These indicators are defined in the subsequent sections. Each alkane mixture is separated by distillation, and then the final product jet fuel (C8?C16), gasoline (C5?C7), and diesel (C17?C20) are obtained, in addition to by-product wax. The steam generated by the waste Figure 1. Process of jet fuel from biomass gasification and Fischer?Tropsch synthesis. heat is supplied for two cases, that is, heat directly (Bio-FTJ-1) and power generation (Bio-FTJ-2) cases.

Figure 2. Scope of LCA of Bio-FTJ systems.

Considering petroleum-based jet fuel as a reference, the performances of economy, resource, and environment were reflected by relative economic benefits (REBs), nonrenewable resources saving benefits (NRSBs), and pollution mitigation benefits (PMBs). These indicators are defined in the subsequent sections.

?, ?, and ? represent the weighting coefficients of REB, NRSB, and PMB, respectively.

Figure 3. ICP with different weighting coefficients.

Figure 4. Sensitivity of ICP to different prices.

Figure 5. Sensitivity of ICP to resource consumption and pollutant emission.

Figure 6. Influence of into-factory price of stalks on performance.

Figure 7. Influence of stalk consumption on performance.

Figure 8. Influence of the price of crude oil on REB.

Compared to Bio-FTJ-1, Bio-FTJ-2 can achieve greater benefits in saving nonrenewable resource and can emit less CO2 and other pollutants because it significantly reduces the consumption of external power input. However, owing to the high production cost of Bio-FTJ-2, its economic benefit is very low. Therefore, ICP of Bio-FTJ-2 is lower than that of Bio- FTJ-1.

According to the sensitivity analysis, the comprehensive performance of the two processes is highly sensitive to the price of crude oil and stalk consumption and the Bio-FTJ-1 is highly sensitive to electricity consumption. The higher the price of crude oil is, the better the comprehensive performance of the Bio-FTJ is. The results of this study indicate that the comprehensive performance of Bio-FTJ can be improved significantly by the reduction of the consumption of stalks and external power input in the production.

Technetium-99 (99Tc), a ?-emitting isotope (?–max = 293.7 keV), is generated from thermal-neutron-induced fission of uranium-235 (235U) and spontaneous fission of 238U in the earth’s crust.(1,2)99Tc is also formed from the decay of the medical radioisotope 99mTc with a half-life of only 6.0 h.(3) The most common chemical form is pertechnetate 99TcO4–, which is of particular environmental concern due to the long half-life of 99Tc (2.13 × 105 years)(1) and the resistance to adsorption on mineral surfaces and sediments that results in migration with potential ecosystem risks.(4?7)

Because all technetium isotopes species are radioactive, research progress is challenging. As a result, rhenium (Re) is often used as a nonradioactive chemical analogue of 99Tc.(8?11) One of the various methods used for removal of 99TcO4–/ReO4– from aqueous solution is conventional solvent extraction.(12,13) Nevertheless, there remain shortcomings, such as utilization of large amounts of toxic and volatile organic reagents, resulting in production of secondary wastes. Alternative ion exchange methods(14?16) require high quality of raw liquid to avoid column blockage. Despite a recent breakthrough toward TcO4– elimination via molecular recognition,(17) long-term storage stability of Tc-containing materials requires further attention, and large-scale practical applications have not been demonstrated.(18) Solid waste forms for 99Tc immobilization include metals such as Tc-Zr alloys(19) and borosilicate glasses.(20) Disadvantages of the latter are oxidation and release of volatile Tc molecules during high-temperature vitrification.(1)

An appealing method to immobilize 99Tc is reduction of soluble Tc(VII) to sparingly soluble Tc(IV) with removal from aqueous solution as 99TcO2·nH2O species,(8,21) which can be separated by physical filtration and then converted to metal or other waste forms for long-term disposal.(19,20)

Common reducing agents such as SO32–, Sn2+, Fe2+,(9,22,23) and biomass(24,25) are exhausted in one cycle and not readily reused. Using Fe(0)/Fe(II) as the reductant couple, 99Tc/Re was sequestrated using a simultaneous adsorption–reduction strategy.(21,26?28) Electrochemical methods(29?31) involve toxic chemicals, and furthermore, the presence of SO42– suppressed Re(VII) reduction in aqueous solution. Although ?-radiation-induced reduction(32) via hydrated electrons might efficiently reduce and separate Re(VII), the conditions are impractical. Photochemical-induced reduction(31,32) of Re(VII) using broadband UV or laser irradiation over 6 h afforded 94.7% recovery of Re; unfortunately, the high molar absorptivity of Re(VII) limits the practical concentration of Re(VII).

Heterogeneous semiconductor-based photocatalytic reduction of heavy metal ions such as Cu2+, Hg2+, Ag+, U(VI), and Cr(VI)(33?37) has been proposed. Many photocatalysts are regarded as environmentally friendly materials because of their chemical inertness and biological compatibility in natural systems. For example, titanium dioxide (TiO2) is a good prospect for photocatalytic reduction and removal of metal ions due to its high resistance to photocorrosion, nontoxicity,(38) low environmental pollution, regeneration ability, low cost, and convenient operations.(38,39) Evans et al.(40) reported selective removal (98%) of uranium from waste liquid containing strong complexing agents using TiO2 as a photocatalyst. Wang et al.(41) prepared a TiO2/g-C3N4 heterojunction composite that facilitated rapid separation and transfer of photogenerated electrons, thus achieving efficient reduction and fixation of uranium...

...The objective of this study was to provide fundamental understanding of photocatalytic 99Tc/Re reduction and removal using TiO2 nanoparticles in the presence of HCOOH. Most of this work was still conducted using nonradioactive ReO4– as a surrogate for 99TcO4–.(8,42) Anyway, the reported 99Tc(VII/IV) redox potential (E0 = +0.74 V) is somewhat more positive than that for Re(VII/IV) (E0 = +0.51 V), which means that photocatalytic reduction of Tc(VII) should be more energetically favorable. In addition, the reduction/removal mechanism was elucidated by photoelectrochemical measurements, electron paramagnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. These results suggest an environmentally friendly photocatalytic approach for 99TcO4–/ReO4– removal and sequestration from aqueous solution.

Tc Removal

99Tc was obtained as a 2% HNO3 stock solution of potassium pertechnetate (KTcO4) from China Institute of Atomic Energy. The 99Tc experiments were performed in a special radiological laboratory. In accordance with the above experimental protocol for Re, the corresponding 99TcO4– solution was illuminated for 150 min under the identified optimal Re(VII) reduction/removal conditions. Residual concentration of 99Tc was analyzed by a liquid scintillation counter (Tri-Carb, PerkinElmer). Aliquots of 0.5 mL were periodically collected during light irradiation and filtered through 0.2 ?m Millipore membranes before analysis. 0.2 mL of the filtrate was then mixed with 5 mL of liquid scintillation cocktail (ULTIMA Gold, PerkinElmer) and held in a 6 mL plastic scintillation vial for measurements. The reacted suspension was stirred in air to observe the reoxidation and release of reduced Tc.

Figure 1. (A) Removal of Re(VII), for no TiO2 and 0.4 g L–1 TiO2 in different conditions; pH = 3, [HCOOH] = 1%, [Re(VII)] = 5 mg L–1. Removal of Re(VII) for different concentrations of HCOOH, for (B) no light and (C) UV–visible irradiation; pH = 2, [Re(VII)] = 10 mg L–1. (D) Removal of Re(VII) with different organic additives under light irradiation; pH = 3, [organic additive] = 1%, [Re(VII)] = 5 mg L–1. V = 50 mL, T = 298 K throughout.

Figure 2. (A) First-derivative EPR spectra of DMPO spin adducts. In the dark: TiO2, HCOOH, and TiO2/HCOOH/Re(VII); under light: TiO2, HCOOH, TiO2/HCOOH, and TiO2/HCOOH/Re(VII). (B) TiO2 current–potential measurements: (black ■ Idark with 0.1 mol L–1 Na2SO4 + 0.1% HCOOH + 5 mg L–1 Re(VII); (blue ● Iphoto with 0.1 mol L–1 Na2SO4; (red ▲ Iphoto with 0.1 mol L–1 Na2SO4 + 0.1% HCOOH; (green ▼ Idark with 0.1 mol L–1 Na2SO4 + 0.1% HCOOH + 5 mg L–1 Re(VII).

Figure 3. Time profiles of Re(VII) reduction during the irradiation of TiO2 suspensions with N2 bubbling, V = 50 mL, T = 298 K. (A) Various dosages of TiO2, [HCOOH] = 1%, [Re(VII)] = 10 mg L–1, pH = 2. (B) Effects of initial Re(VII) concentration, [HCOOH] = 1%, 0.2 g L–1 TiO2, pH = 2. (C) Influence of NO3– concentration, [HCOOH] = 1%, [Re(VII)] = 10 mg L–1, 0.2 g L–1 TiO2, pH = 2. (D) Solution pH values, [HCOOH] = 0.2%, [Re(VII)] = 10 mg L–1, 0.4 g L–1 TiO2.

Figure 4. (A) Cycling runs of TiO2 for photocatalytic reduction of Re(VII). Time profiles of Re(VII) reduction during the irradiation of 0.4 g L–1 TiO2 suspensions at pH = 3, with N2 bubbling, [HCOOH] = 1%, [Re(VII)] = 5 mg L–1, V = 50 mL, T = 298 K. (B) Color change of both solid and solution before and after photocatalysis.

Figure 5. Time profiles of 99Tc(VII) and Re(VII) reduction during the irradiation of 0.4 g L–1 aqueous TiO2 suspensions at pH = 3, with N2 bubbling, [HCOOH] = 1%, [99Tc(VII)] or [Re(VII)] = 0.05 mmol L–1, [NO3–] = 20 mmol L–1, V = 50 mL, T = 298 K.

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5-inch Arctic cod in hollows of ice floes in the Arctic Ocean
Some cod species have a newly minted gene involved in preventing freezing.Credit: Paul Nicklen/NG Image Collection

In the depths of winter, water temperatures in the ice-covered Arctic Ocean can sink below zero. That’s cold enough to freeze many fish, but the conditions don’t trouble the cod. A protein in its blood and tissues binds to tiny ice crystals and stops them from growing.

Where codfish got this talent was a puzzle that evolutionary biologist Helle Tessand Baalsrud wanted to solve. She and her team at the University of Oslo searched the genomes of the Atlantic cod (Gadus morhua) and several of its closest relatives, thinking they would track down the cousins of the antifreeze gene. None showed up. Baalsrud, who at the time was a new parent, worried that her lack of sleep was causing her to miss something obvious.

But then she stumbled on studies suggesting that genes do not always evolve from existing ones, as biologists long supposed. Instead, some are fashioned from desolate stretches of the genome that do not code for any functional molecules. When she looked back at the fish genomes, she saw hints this might be the case: the antifreeze protein — essential to the cod’s survival — had seemingly been built from scratch1.

The cod is in good company. In the past five years, researchers have found numerous signs of these newly minted ‘de novo’ genes in every lineage they have surveyed. These include model organisms such as fruit flies and mice, important crop plants and humans; some of the genes are expressed in brain and testicular tissue, others in various cancers...

...Back in the 1970s, geneticists saw evolution as a rather conservative process. When Susumu Ohno laid out the hypothesis that most genes evolved through duplication2, he wrote that “In a strict sense, nothing in evolution is created de novo. Each new gene must have arisen from an already existing gene.”

Gene duplication occurs when errors in the DNA-replication process produce multiple instances of a gene. Over generations, the versions accrue mutations and diverge, so that they eventually encode different molecules, each with their own function. Since the 1970s, researchers have found a raft of other examples of how evolution tinkers with genes — existing genes can be broken up or ‘laterally transferred’ between species. All these processes have something in common: their main ingredient is existing code from a well-oiled molecular machine...

...But genomes contain much more than just genes: in fact, only a few per cent of the human genome, for example, actually encodes genes. Alongside are substantial stretches of DNA — often labelled ‘junk DNA’ — that seem to lack any function. Some of these stretches share features with protein-coding genes without actually being genes themselves: for instance, they are littered with three-letter codons that could, in theory, tell the cell to translate the code into a protein.

It wasn’t until the twenty-first century that scientists began to see hints that non-coding sections of DNA could lead to new functional codes for proteins. As genetic sequencing advanced to the point that researchers could compare entire genomes of close relatives, they began to find evidence that genes could disappear rather quickly during evolution...

...Some of these genes-in-waiting, or what Carvunis and her colleagues called proto-genes, were more gene-like than others, with longer sequences and more of the instructions necessary for turning the DNA into proteins. The proto-genes could provide a fertile testing ground for evolution to convert non-coding material into true genes. “It’s like a beta launch,” suggests Aoife McLysaght, who works on molecular evolution at Trinity College Dublin...

The Life and Science of Harold C. Urey Matthew Shindell University of Chicago Press (2019)

After witnessing the 1945 Trinity atomic-bomb test, the theoretical physicist J. Robert Oppenheimer recalled Hindu scripture: “Now I am become Death, the destroyer of worlds.” Although this is often interpreted as admitting moral culpability on the part of the Manhattan Project’s scientific director, Oppenheimer remained a central player in the nuclear-weapons establishment until he lost his security clearance in the mid-1950s.

Harold Urey also worked for the Manhattan Project. But by contrast, the Nobel-prizewinning chemist distanced himself from nuclear weapons development after the war. His search for science beyond defence work prompted a shift into studying the origins of life and lunar geology. Now, the absorbing biography The Life and Science of Harold C. Urey by science historian Matthew Shindell uses the researcher’s life to show how a conscientious chemist navigated the cold war.


Shindell argues that Urey’s pious upbringing underpinned his convictions about the dangers of a nuclear arms race, and his commitment to research integrity. Urey grew up a minister’s son in a poor Indiana farming family belonging to a plain-living Protestant sect, the Church of the Brethren. Progressing through increasingly diverse educational environments, culminating in a PhD at the University of California, Berkeley, Urey became self-conscious about the zealousness of his family’s faith. He also found the path to a cosmopolitan, middle-class life.

In the 1920s, Urey was among a small group of chemists who collaborated closely with physicists. Working at Niels Bohr’s Institute for Theoretical Physics at the University of Copenhagen, he kept abreast of developments in quantum mechanics. There, and on travels in Germany, he met the likes of Werner Heisenberg, Wolfgang Pauli and Albert Einstein. But Urey decided he lacked the mathematical skills to make theoretical advances in quantum chemistry. Moving back to the United States, he started both a family and an academic career.

At Johns Hopkins University in Baltimore, Maryland, and later at Columbia University in New York City, Urey taught quantum mechanics to chemists, while setting out on the trail that led him to deuterium. In 1931, he discovered this isotope of hydrogen. Predicted on the basis of work by Bohr, Frederick Soddy, and J. J. Thomson, its existence had been doubted by many chemists and physicists. Urey’s identification won him the Nobel three years later. By this time, he had also co-authored one of the first texts in English on quantum mechanics as applied to molecular systems, the 1930 Atoms, Quanta and Molecules.

Urey’s continuing work on stable isotopes of other chemical elements, such as nitrogen and oxygen, led to important applications in biochemistry and geochemistry, including the pioneering use of isotopic labels to study metabolic pathways. Living in New York also led Urey to political liberalism. He became aware of the anti-Semitism affecting Jewish scientists, and the lack of opportunities for women scientists. A generous mentor, he shared his Nobel prize money with two collaborators, and split a grant he had been awarded with the young Isidor Rabi (who later discovered nuclear magnetic resonance)...

...The Second World War changed Urey’s life, as it did those of most physical scientists and researchers in many countries. His expertise in isotopes made him valuable to the Manhattan Project. Here, he eventually headed a massive team of scientists and engineers working on the separation of uranium isotopes using gaseous diffusion methods. However, he was ill-suited to the pressure of managing this technologically complex and cumbersome project, and Leslie Groves — the project’s overall director — regarded him with suspicion. Even before the war’s end, Urey became deeply disenchanted with working for the military...

...After the war, Urey used his laureate status to voice alarm about the prospect of nuclear warfare. He backed international control through world government as a way to control the military future of atomic energy. This was not a radical view in 1946...

...Over this harrowing period, Urey lost faith in the ability of modern secular society to manage the new threats of the atomic age. Although he had long abandoned his parents’ religion, he began to argue that Judaeo-Christianity was key to democracy. He attributed the success of science itself, with its commitments to honesty and credit, to religious ethics...

...In the late 1940s, Urey used his expertise in mass spectrometry to begin work in geochemistry, and then in planetary science. It was a way to escape the orbit of the nuclear weapons establishment (although he still advised the US Atomic Energy Commission). With chemistry graduate Stanley Miller, he tested hypotheses on the origins of life by Soviet biochemist Alexander Oparin and biologist J. B. S. Haldane, and successfully produced amino acids by sparking a solution of water, methane, ammonia and hydrogen. In 1952, Urey published The Planets, a chemical treatise on the formation of the Solar System...

...Urey became influential during the early days of NASA, formed after the 1957 launch of the Soviet satellite Sputnik, offering the agency persuasive reasons to prioritize exploration of the Moon over other bodies. In 1969, he analysed lunar rocks collected during the Apollo 11 mission, which supported his theory of the Moon’s common origin with Earth. He wanted the well-funded agency to test theories about the origins of the Solar System — experimentation beyond the reach of individual university scientists. Despite his influence, he was disappointed in this: NASA focused on crewed space exploration over questions of cosmogony.

Following Campbell's death, Parker returned to New York City and the Volney Residential hotel. In her later years, she denigrated the Algonquin Round Table, although it had brought her such early notoriety:

These were no giants. Think who was writing in those days—Lardner, Fitzgerald, Faulkner and Hemingway. Those were the real giants. The Round Table was just a lot of people telling jokes and telling each other how good they were. Just a bunch of loudmouths showing off, saving their gags for days, waiting for a chance to spring them... There was no truth in anything they said. It was the terrible day of the wisecrack, so there didn't have to be any truth...[61]

Article 25.

(1) Everyone has the right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services, and the right to security in the event of unemployment, sickness, disability, widowhood, old age or other lack of livelihood in circumstances beyond his control.

ince 2000, many countries have achieved considerable success in improving child survival, but localized progress remains unclear. To inform efforts towards United Nations Sustainable Development Goal 3.2—to end preventable child deaths by 2030—we need consistently estimated data at the subnational level regarding child mortality rates and trends. Here we quantified, for the period 2000–2017, the subnational variation in mortality rates and number of deaths of neonates, infants and children under 5 years of age within 99 low- and middle-income countries using a geostatistical survival model. We estimated that 32% of children under 5 in these countries lived in districts that had attained rates of 25 or fewer child deaths per 1,000 live births by 2017, and that 58% of child deaths between 2000 and 2017 in these countries could have been averted in the absence of geographical inequality. This study enables the identification of high-mortality clusters, patterns of progress and geographical inequalities to inform appropriate investments and implementations that will help to improve the health of all populations.

Gains in child survival have long served as an important proxy measure for improvements in overall population health and development1,2. Global progress in reducing child deaths has been heralded as one of the greatest success stories of global health3. The annual global number of deaths of children under 5 years of age (under 5)4 has declined from 19.6 million in 1950 to 5.4 million in 2017. Nevertheless, these advances in child survival have been far from universally achieved, particularly in low- and middle-income countries (LMICs)4. Previous subnational child mortality assessments at the first (that is, states or provinces) or second (that is, districts or counties) administrative level indicate that extensive geographical inequalities persist5,6,7.

Progress in child survival also diverges across age groups4. Global reductions in mortality rates of children under 5—that is, the under-5 mortality rate (U5MR)—among post-neonatal age groups are greater than those for mortality of neonates (0–28 days)4,8. It is relatively unclear how these age patterns are shifting at a more local scale, posing challenges to ensuring child survival. To pursue the ambitious Sustainable Development Goal (SDG) of the United Nations9 to “end preventable deaths of newborns and children under 5” by 2030, it is vital for decision-makers at all levels to better understand where, and at what ages, child survival remains most tenuous.

a, U5MR at the second administrative level in 2000. b, U5MR at the second administrative level in 2017. c, Modelled posterior exceedance probability that a given second administrative unit had achieved the SDG 3.2 target of 25 deaths per 1,000 live births for children under 5 in 2017. d, Proportion of mortality of children under 5 occurring in the neonatal (0–28 days) group at the second administrative level in 2017.

Inorganic materials have essential roles in society, including in building construction, optical devices, mechanical engineering and as biomaterials1,2,3,4. However, the manufacture of inorganic materials is limited by classical crystallization5, which often produces powders rather than monoliths with continuous structures. Several precursors that enable non-classical crystallization—such as pre-nucleation clusters6,7,8, dense liquid droplets9,10, polymer-induced liquid precursor phases11,12,13 and nanoparticles14—have been proposed to improve the construction of inorganic materials, but the large-scale application of these precursors in monolith preparations is limited by availability and by practical considerations. Inspired by the processability of polymeric materials that can be manufactured by crosslinking monomers or oligomers15, here we demonstrate the construction of continuously structured inorganic materials by crosslinking ionic oligomers. Using calcium carbonate as a model, we obtain a large quantity of its oligomers (CaCO3)n with controllable molecular weights, in which triethylamine acts as a capping agent to stabilize the oligomers. The removal of triethylamine initiates crosslinking of the (CaCO3)n oligomers, and thus the rapid construction of pure monolithic calcium carbonate and even single crystals with a continuous internal structure. The fluid-like behaviour of the oligomer precursor enables it to be readily processed or moulded into shapes, even for materials with structural complexity and variable morphologies. The material construction strategy that we introduce here arises from a fusion of classic inorganic and polymer chemistry, and uses the same cross-linking process for the manufacture the materials.

Letter
Published: 16 October 2019
Crosslinking ionic oligomers as conformable precursors to calcium carbonate
Zhaoming Liu, Changyu Shao, Biao Jin, Zhisen Zhang, Yueqi Zhao, Xurong Xu & Ruikang Tang
Nature volume 574, pages394–398 (2019) | Download Citation

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Abstract
Inorganic materials have essential roles in society, including in building construction, optical devices, mechanical engineering and as biomaterials1,2,3,4. However, the manufacture of inorganic materials is limited by classical crystallization5, which often produces powders rather than monoliths with continuous structures. Several precursors that enable non-classical crystallization—such as pre-nucleation clusters6,7,8, dense liquid droplets9,10, polymer-induced liquid precursor phases11,12,13 and nanoparticles14—have been proposed to improve the construction of inorganic materials, but the large-scale application of these precursors in monolith preparations is limited by availability and by practical considerations. Inspired by the processability of polymeric materials that can be manufactured by crosslinking monomers or oligomers15, here we demonstrate the construction of continuously structured inorganic materials by crosslinking ionic oligomers. Using calcium carbonate as a model, we obtain a large quantity of its oligomers (CaCO3)n with controllable molecular weights, in which triethylamine acts as a capping agent to stabilize the oligomers. The removal of triethylamine initiates crosslinking of the (CaCO3)n oligomers, and thus the rapid construction of pure monolithic calcium carbonate and even single crystals with a continuous internal structure. The fluid-like behaviour of the oligomer precursor enables it to be readily processed or moulded into shapes, even for materials with structural complexity and variable morphologies. The material construction strategy that we introduce here arises from a fusion of classic inorganic and polymer chemistry, and uses the same cross-linking process for the manufacture the materials.

Main
Many materials are consolidated from their crystallized powders16, but their resulting discontinuous internal structures render them brittle with a poor ability to resist fracture17,18. By contrast, polymeric materials are ubiquitous in modern society, due not only to their varied properties but also to their ease of fabrication15,19. The polymerization strategy is superior to crystallization because of its efficiency and controllability. In polymer chemistry, covalent bonds have an important role in ensuring the linkage of small units. Although a few covalent-bond-based inorganic materials (for example silicone and silica)20,21 can be obtained as polymers, there is no general method for the preparation of such materials by crosslinking owing to the lack of investigation into ionic monomers or oligomers for this purpose. In the control of polymerization reactions, a capping agent is key22: capping can stabilize precursors, whereas de-capping can initiate polymerization. Analogously, we proposed that ionic oligomers could be stabilized by an appropriate capping agent. Capping based on hydrogen bonding was thought to be suitable, because most inorganic complexes contain oxygen. For example, triethylamine (TEA) can form a hydrogen bond with a protonated carbonate through its tertiary amine group. More importantly, TEA is a small molecule that can be volatilized at room temperature, and it was expected that this could initiate an expected crosslinking reaction.

a, Left, scheme of the capping strategy and reaction conditions for producing (CaCO3)n oligomers; right, a photograph of gel-like (CaCO3)n oligomers. b, Mass spectra of (CaCO3)n oligomers with different Ca:TEA molar ratios. c, Liquid-state 13C NMR spectra of CO2 or the carbonates of (CaCO3)n oligomers with different Ca:TEA molar ratios in ethanol. d, Scattering plots of (CaCO3)n measured by SAXS. The red curve is the fitting result obtained using DAMMIF. I, scattering intensity; q, scattering vector. The error bar represents the standard deviation of twenty measurements. e, Pair–distance distribution function (P(r)) of the (CaCO3)n oligomers. The inset shows the shape simulation of the oligomer. Error bars represent one standard deviation, n = 20.

a, b, Molecular dynamics simulation of the evolution of the Ca–O (from carbonate) coordination number (a) and the average cluster size (b) from ions (Ca2+ and CO32? in the absence (black) or presence (blue) of TEA. c, A typical simulated CaCO3 cluster capped with TEA (an oligomer). d, In situ FTIR spectra during the drying of (CaCO3)n oligomers. e, The change in the coordination number of Ca–O during crosslinking. Owing to the uncertainty in the exact density during measurements, the blue and red lines are shown to represent the maximum and minimum coordination number of Ca–O, respectively. The black line shows the average coordination number. f, High-resolution TEM images of (CaCO3)n oligomers grown at different Ca:TEA ratios from 1:100 to 1:2. g, TEM images depicting the transformation of (CaCO3)n oligomers to larger structures during condensation.

Centimetre-sized monolithic CaCO3 materials were obtained by the crosslinking of oligomers. The resulting bulk maintained the original morphology of the compact gel precursor (Fig. 3a). FTIR spectroscopy and thermal gravimetric analysis indicated the formation of pure ACC without organic residue (Extended Data Fig. 7a, b). Scanning electron microscopy (SEM) and TEM showed the structural continuity in the bulk (Fig. 3b–e), and the internal continuous and integral textures were confirmed by artificially creating a crack (Fig. 3c). At scales from nano- to micrometres, the fabricated material was fully dense and smooth with no porosity or cracks (Fig. 3d, e). A nanoindentation test revealed that the ACC sample (Fig. 3l, blue circle in Fig. 3m) had a Young’s modulus of 8.0 ± 1.6 GPa and a hardness of 0.33 ± 0.07 GPa; these values are greater than those of most plastic materials28.

a, Photograph of monolithic ACC prepared from (CaCO3)n oligomers. b–e, SEM (b, c) and TEM (d, e) images indicating the continuous solid phase of the prepared monolithic ACC. The inset of e is the fast-Fourier-transform image of the sample. Typically, the image of a crack in monolithic ACC exhibits continuity from the surface to the bulk (c). f, Snapshot of monolithic calcite prepared from monolithic ACC. g, Polarized-light optical microscopy (POM) image of the prepared monolithic calcite. h, SEM image of a surface on crystallized monolithic CaCO3. i, j, TEM images of the inner bulk of crystallized monolithic CaCO3. The inset of j is the fast-Fourier-transform image of the sample. k, XRD pattern of calcite powder, geological single-crystalline calcite and the calcite sample produced from (CaCO3)n oligomers. l, Load–displacement curves of the ACC sample, calcite sample and geological single-crystalline calcite sample measured by nanoindentation. m, Ashby plot of hardness (H) against Young’s modulus (E) for the prepared CaCO3 (including ACC and calcite) and other materials. The upper left inset is an exemplary residual indent of the Berkovich diamond tip on the crystallized CaCO3. Ē, plane strain modulus.

A considerable advantage of the crosslinking of ionic oligomers is that the oligomeric precursors can be moulded into shapes to enable continuously structured construction (Fig. 4a–c). This in turn enables the engineering of single-crystalline materials, including additive manufacturing. The construction of calcite rod arrays by oligomer crosslinking demonstrates the practicality of the preparation of single-crystal materials with structural complexity (Fig. 4d, e). This method can even be extended to repair damaged single crystals. Calcite single-crystal surfaces in optical devices30 can be damaged by mechanical crashing, scratching or corrosion, which reduces their functional performance—in particular transmittance. However, (CaCO3)n oligomers can generate oriented calcite within nano- and micro-sized pits or ditches of the damaged calcites in order to recover their smooth surface (inset of Fig. 4d, f, g). The repaired region (Fig. 4h, i) had exactly the same crystalline phase and orientation as the bulk beneath (Fig. 4j). The images of the high-resolution lattice fringes from the calcite bulk to the repaired front (Fig. 4k) demonstrate continuous (104) facets without any break, confirming that the same crystalline structure was reproduced exactly

a, Moulded CaCO3 with different dimensions and morphologies. b, c, Moulded CaCO3 with different patterns. The inset of c shows a single CaCO3 rod. d, Schemes for pattern construction on single-crystalline calcite (top path), and the repair of rough single-crystalline calcite to smooth calcite (bottom path). The insets show optical microscopy images of the calcite surface at different stages: native, corroded, and repaired. e, POM images of the patterned calcite rotated at different angles. f, g, SEM images of the repaired calcite (surface and cross-section, respectively). h, TEM image of a cross-sectional view of the repaired calcite. The different layers labelled 1, 2, 3 and 4 were characterized by selected area electron diffraction and high-resolution lattice fringes in j and k. i, EDS mapping of the repaired calcite in h, showing the repaired CaCO3 as well as gold nanolabels. j, Selected area electron diffraction patterns of different layers (1–3) of h with an aperture of around 170 nm in diameter, showing the same patterns from the bulk to the repaired surface. The red dots in 1 are the simulated diffraction pattern viewed along the <?4, 4, 1> zone axis. k, High-resolution lattice fringes at the different layers (1–4) of h, exhibiting the facets of (104) with exactly the same orientation from the bulk to the repaired surface.

The study of childhood diet, including breastfeeding and weaning, has important implications for our understanding of infant mortality and fertility in past societies1. Stable isotope analyses of nitrogen from bone collagen and dentine samples of infants have provided information on the timing of weaning2; however, little is known about which foods were consumed by infants in prehistory. The earliest known clay vessels that were possibly used for feeding infants appear in Neolithic Europe, and become more common throughout the Bronze and Iron Ages. However, these vessels—which include a spout through which liquid could be poured—have also been suggested to be feeding vessels for the sick or infirm3,4. Here we report evidence for the foods that were contained in such vessels, based on analyses of the lipid ‘fingerprints’ and the compound-specific ?13C and ?13C values of the major fatty acids of residues from three small, spouted vessels that were found in Bronze and Iron Age graves of infants in Bavaria. The results suggest that the vessels were used to feed infants with milk products derived from ruminants. This evidence of the foodstuffs that were used to either feed or wean prehistoric infants confirms the importance of milk from domesticated animals for these early communities, and provides information on the infant-feeding behaviours that were practised by prehistoric human groups.

The study of past infancy—including infant care, breastfeeding and weaning practices—provides valuable information on population demographics and health, reproduction rates, mortality patterns and fertility of individuals of past societies. Today, feeding practices for babies can be attributed to various ecological and socioeconomic constraints and cultural factors, such as health beliefs and food taboos1,5,6. Prehistoric humans probably practised a range of infant-feeding behaviours2,3,4,6,7, which had profound consequences for the biological and social wellbeing of the infants. Ethnographic, historical and social studies have shown differences across the breastfeeding phase, the nature of the addition of supplementary foods (during weaning) and the timing of cessation of breastfeeding1,5,6,8.

Breastfeeding is integral to infant care in all human groups and fundamental to the mother–infant relationship4. Breast milk provides an infant with all of the macro- and micronutrients that are required to sustain growth for the first six months of life9, together with bioactive components, which protect the infant from pathogenic organisms and facilitate the development and maturation of the immune system10. The introduction of energy and nutrient-rich, easily digestible, supplementary foods in infant feeding (that is, during weaning) is unique to humans11,12. Supplementary foods are generally introduced at around six months of age, when the metabolic requirements of an infant exceed the energy yield that the mother can provide through milk, contributing to the infant diet as chewing, tasting and digestive competencies develop1,12,13.

he widespread use of animal milk, either to feed babies or as a supplementary weaning food source, became possible with the domestication of dairy animals during the European Neolithic14, during which time generally improved nutrition contributed to an increased birth rate, with shorter inter-birth intervals, that resulted in considerable growth of the human population: the so-called Neolithic demographic transition15. Broad trends identified from the Neolithic to Iron Age in Central Europe suggest that supplementary foods were given to babies at around six months of age and weaning was complete by two to three years of age3.

Possible infant-feeding vessels that are made from clay first appear in Neolithic Europe. One of the earliest of such finds is a Linear Pottery Culture feeding vessel from Steigra, Germany, that has been dated16 to around 5500–4800 BC. These unique vessels, which have a small spout through which liquid could be poured or suckled, come in many forms and sizes and occasionally have a zoomorphic design (Extended Data Fig. 1). They become more common in Central Europe during the late Bronze and early Iron Age4 and are found in settlements, as stray finds, and in graves (particularly those of children), which strongly suggests that they were feeding or weaning vessels for infants.

The precious nature and often small openings of these vessels makes their sampling for organic residue analysis extremely challenging. However, infant-feeding vessels that have an open, bowl form, found in graves from cemeteries of Dietfurt-Tankstelle and Dietfurt-Tennisplatz in Germany, have recently become available for chemical analysis. The graves are part of a large early Iron Age cemetery complex (dating to approximately 800–450 BC) found in the lower Altmühl valley in Bavaria, Germany, with Dietfurt-Tankstelle encompassing 99 burials in 72 graves17 and Dietfurt-Tennisplatz containing 126 burials18. Child grave 80 at Dietfurt-Tennisplatz contained an east–west-oriented inhumation of a young child (0–6 years old), who had a bronze bracelet on the left arm, and in which feeding vessel 1 (Fig. 1a) was placed at the child’s feet18.

a, b, Drawings of child graves from Dietfurt (left) and images of the feeding vessels found in each grave (right). Photographs of vessels were taken by A.F. (a) and K.R.-S. (b). Drawings of the graves were reproduced from a previously published plan17 (a) and drawing18 (b).

n = 3 vessels. a–c, Partial gas chromatograms of transmethylated trimethylsilylated extracts from infant-feeding vessels 1–3. Red circles, n-alkanoic acids (fatty acids); blue triangles, n-alkanes; IS, internal standard, C34 n-tetratriacontane. d, ?13C values for the C16:0 and C18:0 fatty acids for archaeological fats extracted from infant-feeding vessels 1–3. The three fields correspond to the P = 0.684 confidence ellipses for animals raised on a strict C3 diet in Britain20. Each data point represents an individual vessel. e, The ?13C (?13C18:0 – ?13C16:0) values are from the same vessels as in d. The ranges shown here represent the mean ± 1 s.d. of the ?13C values from a global database comprising modern reference animal fats, which have been published previously24. f, Partial high-temperature gas chromatogram of trimethylsilylated total lipid extract of infant-feeding vessel 2, showing degraded animal fat. Red circles indicate short- and long-chain n-alkanoic acids with the indicated number of carbon atoms; monoacylglycerols (M) containing 16 and 18 acyl carbon atoms; diacylglycerols (D) containing 28, 30, 32 and 34 acyl carbon atoms; triacylglycerols (T), containing 40, 42, 44, 46, 48, 50, 52 and 54 acyl carbon atoms; the plasticizer is indicated by an asterisk. IS, internal standard n-tetratriacontane (n-C34). Replication was not possible owing to the unique and irreplaceable nature of the archaeological artefacts sampled, although the objects were analysed using two different extraction methods.

As the ?13C values are found to be at the top of the range for dairy fats, the vessels were also analysed by solvent extraction20 using high-temperature gas chromatography and high-temperature gas chromatography–mass spectrometry for diagnostic intact acyl lipids22. Figure 2f shows that triacylglycerols (TAGs) and their degradation products, di- and monoacylglycerols, were present in vessel 2, with TAGs comprising C40–C54 acyl carbon atoms with C48 being the most abundant homologue. The latter TAGs were not detectable in vessels 1 and 3, indicating complete diagenetic hydrolysis of the acyl lipids in these vessels. Fresh adipose fats are characterized by TAGs that contain 48–54 acyl carbon atoms, whereas dairy fats are distinguished by TAGs that contain 24–54 acyl carbon atoms23. Whereas shorter-chain TAGs (24–38 acyl carbon atoms) are rarely seen in degraded archaeological fats, owing to diagenetic loss (which has been demonstrated experimentally20), C40–C46 TAGs are highly diagnostic of dairy fats20,22. In summary, our findings provide unequivocal evidence that all three vessels were predominantly used to process dairy fats.

Milks are species-specific and there are key differences in the composition of human and ruminant milk. Animal milk could have been used as a supplementary food, but it would not have been a full replacement for human milk, which contains similar amounts of lipid but more carbohydrates (in the form of lactose) and considerably less protein. These differences might affect an infant in various ways. For instance, cow’s milk is more difficult for an infant to absorb as it contains higher quantities of saturated fatty acids and much larger fat globules than human milk25, causing a reduced energetic input for the infant. The processing of animal milk and the possible incorporation of meat-based gruel may have served to balance out nutritional deficiencies. However, the introduction of inappropriate supplementary foods would have provided an opportunity for infectious agents and pathogens, causing diarrhoea and other diseases, and putting the infant at greater risk of iron-deficiency anaemia14. These supplementary foods may also have been nutritionally inadequate, leading to malnutrition, which is detrimental to future development.

Joan Brennecke, the first female professor of chemical engineering at the University of Texas, has charted her own career course.

As a chemical-engineering student at the University of Texas in the 1980s, Joan Brennecke learned more than formulas and chemical processes; she learned how to stick up for herself. Some professors supported Brennecke in her engineering ambitions, helping her become more assertive and self-assured. Meanwhile, others represented the challenges she would face throughout her career in a male-dominated field.

Brennecke remembers casually chatting with a UT chemical-engineering professor about her career ambitions at a party in 1984, when he surprised her with a mocking laugh.

“A female faculty member in chemical engineering at the University of Texas? Over my dead body!” he declared.

After a $2.5 million governor’s grant returned the world-class researcher to her alma mater three decades later, Brennecke can’t help but laugh at the story’s irony.

“I try never to whine about others’ behavior,” says Brennecke, now UT’s first female full professor in chemical engineering. “I tend to ignore it and do my thing.”

Engineered to Succeed
Brennecke knew chemical engineering was her thing since early high school. She recalls hours spent in the garage with her father, a chemical engineer with a Ph.D., taking apart anything the two could find. When she was 12, they disassembled a massive mechanical calculator he brought home from his job at Alcoa.

Engineering runs in the family: Brennecke’s uncle works as a mechanical engineer, her mother is a secretary for an engineering company and three cousins ended up in engineering-related positions. Brennecke entered the family hall of fame as its first female engineer.

Today, women earn about 20 percent of all engineering degrees. When Brennecke hit high school in the mid-1970s, women earned just 3.4 percent of those degrees...

...Gabriela Avelar Bonilla, one of Brennecke’s Ph.D. students at Notre Dame, says Brennecke serves as a valuable resource for women in engineering.

“In a field that [is]usually dominated by men, it’s important to have role models that you can relate to,” Avelar Bonilla says, “[especially]someone like her because her career is very impressive and she is a good mentor.”

When paired with a female mentor, female engineering undergrads feel more confident, motivated and less anxiety, according to a study published earlier this year.

The first piece of advice Brennecke offers female engineering students is to focus on doing their best.
“There’s no substitute for competence,” she says.

“And for goodness’ sakes, don’t ever be dissuaded or even irritated by somebody’s stupid comments or what somebody does. Don’t waste your brain cells on them. Spend your brain cells on doing what you’re doing well.”