Today. Two scientific research progress of Zhejiang University.
The top international journals were launched again.
Science
Professor Bai Hao of the School of Chemical Engineering and Biological Engineering
and Associate Professor Weiwei Gao in the Department of Polymer Science and Engineering
A new strategy was learned.
They mimic the "core-shell" structure of polar bear hair.
An encapsulated aerogel was prepared.
Ultra-insulating man-made fibers.
It not only has the thermal insulation function of traditional insulation materials.
It can also "block" the infrared rays that the human body radiates outward.
Mechanical properties such as tensile resistance have also been greatly improved.
Can be directly woven.
It can really realize the aerogel "wearing" on the body.
Professor Xiao Fengshou of the School of Chemical Engineering and Biological Engineering
Team with researcher Liang Wang
A new catalyst design strategy was proposed.
They used dealuminized beta zeolite zeolite molecular sieves as a carrier.
Regulation of copper nanoparticles.
Dynamic evolutionary processes in catalytic reactions.
Eliminate sintering of copper particles
and control the already sintered copper nanoparticles.
Secondary dispersion is carried out.
This significantly extends the life of the catalyst.
This scheme is based on the regulation of the dynamic fireworks process.
It takes into account the stability and activity of the catalyst.
It is expected to be applied to the development of more durable catalysts.
Let's learn more about the two scientific achievements.
Aerogel weaves a "polar bear sweater".
Wear it light and super warm!
The perfect warm garment has yet to appear
When it comes to keeping warm, polar bears are a "textbook" for walking. A super warm "sweater" allows them to adapt to the environment of minus 40. The polar bear's fur is a hollow structure that encapsulates a large amount of "still" air to reduce heat loss by inhibiting heat conduction and heat convection. Warm clothing is designed with this principle in mind. For example, wool and down have the effect of inhibiting heat conduction and heat convection.
Pictured: Polar bear fur under a light microscope
In the quest to be thinner and lighter while keeping warm, it's natural to think of packing more air with less material. Aerogels with very high porosity and a density smaller than air (more than 90% of the total volume of air) are an ideal choice. In the past few decades, attempts have been made to "coat" aerogel on the surface of fabrics, or to "spin" fibers containing aerogel directly. However, due to the fact that the aerogel coating is easy to peel off;Or the aerogel content of the material is limited, and the mechanical properties such as wear resistance and tensile resistance are poor, and the performance of the next generation of thermal clothing seems to be difficult to improve.
Pictured: A polar bear sweater made in 2018 is knitted with tweezers
In 2018, Bai Hao's research group made the first generation of "polar bear sweater"., which has attracted wide attention from academic journals including Nature magazine and industry. The thin porous fiber has good thermal insulation performance, but its axial tensile resistance is not ideal, in order to wrap the experimental white rabbit in a "polar bear sweater", the graduate student carefully used tweezers to carefully weave a "blanket". "There are several solutions that do not solve the problem of warmth, thinness and durability at the same time. ”With new challenges, Bai Hao's research group opened their "textbook" - polar bear hair. Sure enough, they noticed an overlooked detail in the past:The fur of the polar bear is not only hollow, but it also has a shell!Under an electron microscope, the shell is about 20 microns thick, accounting for nearly a quarter of the diameter of a hair. It was this discovery that inspired the team's research on "Polar Bear Fur 2."0". A number of doctoral and master's students have participated in this work. Super Warmth: "Lock" Infrared Radiation
The picture on the left shows the microstructure of polar bear hairThe image on the right shows the microstructure of the bionic polar bear's hair.
Borrowing from the "core-shell" structure of polar bear hair, it took nearly 6 years for the team to make itA new type of fiber: the center of the fiber is a polymer aerogel, which is distributed with long pores with a diameter of about 10-30 microns, which are arranged in the same direction, like a "warehouse" for storing air;At the same time, a TPU (thermoplastic polyurethane elastomer) shell encapsulates the aerogel inside. One core and one shell, they each have their own functions.
Let's start with the "nuclear", which is responsible for achieving super warmth. "Keeping warm is, to a certain extent, preventing heat loss. *The first author, doctoral student Wu Mingrui, introduced that the main forms of human heat dissipation include thermal radiation, heat convection, heat conduction and sweat evaporation, among which thermal radiation has the greatest impact (accounting for 40-60%), and heat is lost in the form of infrared radiation. However, existing insulated clothing has limited contribution to regulating heat radiation. Some traditional materials with disordered nanopore structures, because the pore size is much smaller than the wavelength of infrared rays, they are almost "transparent" to infrared rays and cannot block infrared radiation.
Figure: The biomimetic gas gel fiber core layer can lock in a large amount of still air, thereby blocking heat conduction and limiting heat convection. What's more, the oriented lamellar pore structure provides a large number of gas-solid interfaces, which reflect the infrared radiation emitted by the human body in multiple stages to achieve more efficient warmth
The research team believes that by adjusting the direction and size of the pores inside the fibers, it is possible to "lock" infrared radiation. "Infrared rays are radiated outward from the surface of the body, so that the orientation of the small holes is perpendicular to the direction of radiation, and the size is adjusted at the same time, it is expected to match the wavelength of infrared rays, so as to achieve the purpose of locking infrared radiation. Wu Mingrui said.
Pictured: Warmth Challenge for various clothing fabrics
To test the warmth effect, the researchers turned the temperature-controlled cold storage in the school cafeteria at minus 20 degrees Celsius into a makeshift "fitting room" where a "warmth challenge" was held. *Co-author Zhang Zibei, a Ph.D. student, served as a model to try on a down jacket, a woolen sweater, a cotton sweater and a "polar bear sweater" with the same initial temperature, and recorded the rise in the surface temperature of the clothing. After a few minutes, the surface of the cotton sweater rises to 108. The surface temperature of the down jacket rises to 38℃。The thickness is close to that of a woolen sweater, and the surface of the "polar bear sweater", which is only about one-third to one-fifth of the down jacket, only rises to 35 – Less warming means less heat loss from the body," polar bear hair 20" defeated the other "opponents". "Since down has a poor effect on inhibiting infrared rays, it is necessary to increase the thickness several times to achieve the same warmth effect. Wu Mingrui said.
"The new aerogel fibers are able to respond to heat radiation, heat convection and heat conduction at the same time, which is a big step forward in thermal insulation. ”Gao Weiwei said. "All current insulation materials rely on encapsulating as much air or vacuum as possible to inhibit heat conduction and convection. Our fibers have an ordered pore structure while inhibiting thermal radiation. This is also the difference between polar bear hair and ordinary hollow fibers, and it is also an important inspiration we get from polar bears. ”
Stretch-resistant, washable, can be directly on the textile machine
Then there is the "shell", which is responsible for being strong and durable. "The shell is like a skeleton, providing good mechanical support for the fibers, making them resistant to wear, stretch and wash. ”Bai Hao said that this is the challenge that the team has paid the most attention to since the first generation of bionic polar bear fur was made, "Good comprehensive performance is the key to the application of bionic fibers." Compared with static insulation (such as fresh-keeping boxes), fiber fabrics have more stringent requirements, and they also need to solve a series of problems such as tensile and pressure resistance, washing resistance, and thinning. ”
Figure: Tensile test of bionic polar bear hair fibers.
The team designed a TPU shell for the fiber, a common elastic material. In the experiment, the new fiber can be stretched to twice its length without breaking, which well meets the anti-tensile needs of clothing fibers. Biomimetic fibers have been tested to be prepared in continuous macroquantities in the laboratory and can be woven directly into fabrics on commercial textile machines. "Of course, the stronger the shell, the better," Wu Mingrui said, adding that an excessively thick shell would affect the warmth of the fibers, so the team chose an optimal value that took into account the warmth and mechanical properties of the material.
Polar bear fur shows us how nature solves problems by 'decoupling' design. The nucleus and shell have their own roles and are indispensable, and together they make one of nature's most cold-resistant materials. Bai Hao said, "The design of the new type of braidable aerogel fiber follows this idea. In follow-up experiments, the team also tested other applications of bionic polar bear fur. For example, waterproof,The new fiber is washable and does not shrink after washing, nor does it affect its thermal properties。In addition, bionic polar bear fur can be easily colored.
Figure: The new fiber is washable, will not shrink after washing, and the warmth effect is still the same.
When discussing the wording of ** with the team, the reviewer suggested that "it may be said that artificial polar bear hair 'surpasses' natural polar bear hair", and Bai Hao believes that the term "transcendence" is not necessarily appropriate. “The essence of biomimicry is to learn how to solve problems from nature, and it does not mean that we have fully understood nature. Biomimicry is an endless learning process, and even a polar bear hair must have wisdom in it that we don't know, so it's too early to say 'transcendence'. When we encounter new problems, we will continue to learn from nature, and nature can always give us precious inspiration. It is the mission of biomimetic research to constantly reveal the secrets of nature, discover new knowledge, and create new materials to improve people's lives by seeing what is common and thinking about what people have never thought about, and it is also the pursuit we have insisted on for many years. Bai Hao said.
*Links:Reverse "maturation".
Let the catalyst live forever!
The vitality of the catalyst is "cursed".
More than 90% of the chemical industry processes rely on the involvement of catalystsThe catalyst is not static throughout the reactionIn fact, metal atoms, clusters, and particles on the surface of the catalyst undergo complex dynamic structural evolution, such as diffusion, migration, and agglomeration. A direct evidence of this is that many supported nano-metal catalysts sinter after a period of use, and extraordinarily large particles appear in the otherwise uniform nano-metal particles. The transformation process of metal particles from small to large mostly follows the mechanism of "migration and agglomeration" and "Ostwald maturation". Chemically induced effects in a reactive atmosphere lead to a greater likelihood of the latter. As early as 1896, the German physical chemist Wilhelm Ostwald pointed out that when a solute is precipitated from a supersaturated solution, the smaller particles will gradually dissolve and be deposited on the larger crystalline or sol particles. "Oswald maturation" is also one of the classic theories of crystal growth. “The catalyst typically works in high temperatures of hundreds of degrees Celsius, and the atoms on the surface of the metal particles on the support are very reactive, the induction of chemical molecules in the reaction atmosphere causes them to fall off and 'stand in line' again, and they are more inclined to 'run' towards the larger size of the particles, where the surface energy is lower and more stable. Over time, the large particles become larger and larger, and the smaller particles become smaller and gradually abled. Wang Liang said that this is determined by the "nature" of microscopic particles. For many years, "OswalThe "German ripening" effect is like an unbreakable "curse", causing irreversible damage to the performance of the catalyst. In order to cope with this "recession", the common method in industry is to increase the amount of catalyst by several times, or suspend production to regenerate or replace the catalyst, just like the vehicle needs regular maintenance and renewal parts, which requires high costs. Reverse "maturation".
Don't "grow up" – this has been the vision of supported metal catalysts for a long time. The existing scheme is to use oxides, carbon materials, etc. to encapsulate metal nanoparticles, which can inhibit metal sintering, but also mask part of the active sites. "This way of thinking is sacrificing some of the activity for stability. Wang Liang said that in order to achieve both stability and activity, new design ideas are needed.
Figure: Relatively strong sites were designed on the surface of the weakly interacting support to capture the reaction atmosphere-induced Ostwald ripening intermediates to form new nucleation centers and reverse the sintering process of traditional metal particles.
The research team designed nanometal particles that "do not grow up" by controlling the dynamic structural evolution pathways of metal species in the traditional sintering process. "Let's say a celebrity is going to have a concert, in order to avoid overcrowding, we should let the fans stay at home as much as possible and not go out?Or do you want to add other performances in the same city that are equally or even more exciting, and 'induce' everyone's choice?Xiao Fengshou said, "The essence of regulating 'maturation' is not to let the particles not 'run', but to 'run' in a different direction." "When the catalyst enters the high-temperature operating environment, the "agitation" of the atoms on the surface under the reaction atmosphere begins. Atoms that fall off particles naturally run to their biggest target, and the research team is trying to reverse that. "We have designed some 'grippers' along the path of atomic-level intermediate migration to capture these 'wild' atoms. Wang Liang introduced, theyA dealuminized zeolite zeolite carrier was designed for the copper nanoparticle catalyst, and a large number of "silicon hydroxyl nest" sites were embedded in the support structure, just like "pits" on the road surfaceBy grasping the migrating intermediates through chemical reactions and forming new nucleation sites, the growth of large particles is inhibited. These "pits" are not pits in the physical sense, but "pits" in the chemical sense, and the copper atomic-level intermediates in the pits and the hydroxyl nest of the zeolite zeolite have a chemical reaction and form a strong interaction with the carrier, which makes the thermodynamics of the whole process beneficialLater, the copper atoms on the large particles will continue to migrate towards these new nucleation sites and eventually reach dynamic equilibrium. This introduces a new force into the original catalytic system, which reverses the dynamic evolution process of catalyst particles. "Not only did we cut off the path for the particles to become larger, but we also created new nucleation sites along the way, ultimately reversing the process. ”Wang Liang said.
A magical scene: large particles become smaller, and small particles become more
Can the copper nanoparticle catalyst made by the new strategy really reverse the "maturation" and prolong the life cycle?The research team used the novel catalyst for the hydrogenation of dimethyl oxalate, which is an important reaction in the coal-to-ethylene glycol process. According to the "Oswald maturation" effect, the "big" copper particles on the fresh dealuminized zeolite zeolites have an overwhelming "attraction", and they continue to grow by attracting more copper atoms during the catalytic process. The results of the experiment show that:These "bulky" particles slowly become smaller in methanol vapor at 200 °C, from 56 nm shrunk to 2Around 4 nanometers. "This is consistent with what we envisioned, and this hydroxyl nest-rich zeolite zeolite successfully reversed the sintering, and methanol-induced copper intermediates nucleated at these nest sites, eventually forming new small nanoparticles. *First author, Dr. Lujie Liu, said. More interestingly, after the physically mixed copper powder and dealuminized zeolite zeolite zeolite were treated with methanol atmosphere, uniformly dispersed small copper particles were observed on the zeolite zeolite zeolite (see figure below). Through mass spectrometry experiments, they also detected intermediates that may be generated during the migration of copper atoms, and combined with theoretical calculations, further elucidated the mechanism of hydroxyl litters from the capture of copper atoms to the formation of stable copper nanoparticles. Studies have shown that the new catalyst retains high efficiency even after a long reaction period. It is worth pointing out that this copper-based zeolite catalyst can also catalyze the conversion of dimethyl oxalate to ethylene glycol stably and efficiently at atmospheric pressure.
Figure: The migration and dispersion of large copper surface atoms to the zeolite zeolite surface induced by methanol atmosphere.
"Not only did we achieve our goal of reverse maturation, but we also achieved a significant increase in the life cycle of our catalysts. ”Xiao Fengshou believes that this new design strategy has certain universality, and the research team will explore the design and preparation of more durable catalysts in the next step.
*The first unit is the School of Chemical Engineering and Biological Engineering, Zhejiang University. Professor Xiao Fengshou and researcher Wang Liang of Zhejiang University, Professor Cao Xiaoming of East China University of Science and Technology, and Professor Ma Jiabi of Beijing Institute of Technology are the corresponding authors, Dr. Liu Lujie of Zhejiang University is the first author, and Lu Jiaye of East China University of Science and Technology is the co-first author. Prof. Wang Zhandong from the University of Science and Technology of China, Prof. Lina Li from the Shanghai Advanced Research Institute of the Chinese Academy of Sciences, Prof. Yong Wang from the School of Materials Science and Technology of Zhejiang University, Dr. Yahui Yang and Dr. Wolfgangruettinger from BASF, and Associate Prof. Xinhua Gao from Ningxia University contributed to the structural and mechanistic research of this work. This work has been funded by the National Key R&D Program and the National Natural Science Project.
*Link: Content**: Zhejiang University Academic Committee "Seeking Truth Style" WeChat*** Wen Zhou Wei丨 Drawing Sun Shiyun Part *** in the research group).
Today's editor: Zhou Yiying.
Editor in charge: Zhou Yiying.
Recommended Reading:1.Like!Zhejiang University liberal arts good results 2Youth role model!They are among the top 10 college students of Zhejiang University.
3.Deepen the construction of basic disciplines!The Institute for Advanced Study of Physics of Zhejiang University was inaugurated!4.The main battlefield of youth is in the north and south of the motherland 5Decorate with love!The wall painting of Yuquan Yi Dining Hall comes from a group of innocent painters ......6.2024 National Master's Admission Examination Zhejiang University Test Center Candidates.
Like and watch, cheer for the scientists!