ACS AMI: a cellulose paper with self-cleaning surface and radiant cooling function

With the rapid economic and social development, air-conditioning and refrigeration has become an indispensable method for keeping the internal temperature comfortable in buildings.
However, the air-compression refrigeration technology commonly used in air-conditioning not only consumes a lot of electricity, generates a lot of greenhouse gases, but also causes a "net" warming Effect
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In addition, the leakage of compressor refrigerant during use will destroy the atmospheric ozone layer and exacerbate other environmental problems
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In contrast, passive daytime radiant refrigeration (PDRC) technology with net cooling capacity has extremely high reflectivity to sunlight, and at the same time can dissipate its own heat to outer space through atmospheric transparent windows with a wavelength of 8-13 μm.
It is possible to realize spontaneous cooling of the surface of the building without power consumption, which is expected to replace the air compression refrigeration system, which is of positive significance to the world energy pattern and the mitigation of global climate warming
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However, the practical application of PDRC materials still faces the problems of complicated and expensive manufacturing methods and continuous degradation of refrigeration performance caused by surface contamination
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?? In response to the above problems, Professor Zheng Yi from Northeastern University in the United States and researcher Tang Changyu from Chengdu Science and Technology Development Center designed a self-cleaning surface, radiant cooling, and renewable cellulose paper
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In this work, cellulose paper with high infrared emissivity and high sunlight reflectivity was selected as the substrate, and PTFE micro-nano particles were uniformly embedded in the micropores on the surface of the cellulose paper to form a lotus-like effect.
Super-hydrophobic coating (Figure 1); the introduction of this coating can not only enhance the solar reflectance on the surface of the cellulose paper (the reflectivity from 0.
89 to 0.
93) and increase the cooling power (Figure 2), but also protect the cellulose paper from Due to rainwater and dust pollution, this waterproof and self-cleaning ability helps to solve the problem of the radiant cooling performance of PDRC materials attenuating in the outdoor environment
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Under the solar radiation intensity of 834 W/m2 and 671 W/m2, the radiant cooling power of the superhydrophobic paper can reach 104 W/m2, which can achieve a cooling effect of 5°C lower than the atmospheric temperature
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In addition, the cellulose paper can be recycled and pulped into radiant refrigeration paper again, which is environmentally friendly and low-cost
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? Figure 1.
(a) Original paper, (b) Surface wetting state and microstructure of PTFE-coated cellulose paper
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? Figure 2.
Hemispherical reflectance spectra of original paper and radiant paper
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? The research further advances the application and exploration of radiant refrigeration materials in outdoor building models
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In the experiment, the cellulose composite sheet was dyed red and yellow and pasted on the surface of the wooden house model (Figure 3).
The outdoor cooling effect was compared with the wooden house model dyed in the same color.
It was found that the house model was pasted with red and yellow paper.
The indoor temperature is 2.
2°C and 2.
6°C lower than the same stained house model, respectively (Figure 3)
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The results further show that the dyed cellulose composite paper can absorb the appropriate visible light wavelength to display a specific color, and at the same time effectively reflect near-infrared light to reduce the solar heating effect, thereby taking into account the needs of building radiant cooling and beautiful decoration
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? Figure 3.
Wooden house model covered by dyed radiant refrigeration paper
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? The research progress was published on ACS Applied Materials and Interfaces under the title "Superhydrophobic and Recyclable Cellulose-Fiber-Based Composites for High-Efficiency Passive Radiative Cooling"
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The co-authors of the paper are Tian Yanpei and Shao Hong, and the corresponding authors are Professor Zheng Yi and Researcher Tang Changyu
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