Caebon Dots/polyer Composites For UV Blocking And Building Interior Temperatures Reducing

With global warming,energy saving has been an enduring topic and an important social awareness in today’s world.Growing energy demand increases carbon dioxide emissions and contributes to global warming.In addition,due to global warming,the Arctic polar vortex experiences frequent and extreme low temperatures in winter,and this change can contribute to the formation of clouds in the stratosphere,which can provide suitable reaction conditions for chemicals such as chlorofluorocarbons emitted by humans decades ago to react with ozone in the stratosphere and deplete it.When there is a hole in the ozone layer,the UV radiation reaching the surface is enhanced.To mitigate the global warming effect as well as to solve the UV radiation problem,carbon dots（CDs）/polymer composites for UV blocking and temperature reducing were prepared in this paper from three forms:liquid,film,and hydrogel.CDs with blue,green and red fluorescence were prepared by hydrothermal method and compounded with polymers to study the UV-blocking properties as well as the cooling performance of the composites,mainly as follows:（1）Thermo-responsive liquids（TRL）was synthesized with N-isopropylacrylamide（NIPAm）,and composited TRL with biomass-derived carbon dots（CDs）by a simple blending method to obtain CDs@TRL.CDs@TRL possesses high specific heat capacity(4.41 k J·kg^-1·K^-1)and thermal storage capacity(264.6 kg^-1·K^-1).The composite liquid has a low transmittance in the ultraviolet region,only 5%in the cold state,and completely shields the ultraviolet light in the hot state.In addition,the liquid has a shielding effect in the near-infrared region,and the 10 mm CDs@TRL in the hot state has a near-zero transmittance in the near-infrared region,which can effectively block infrared radiation.In addition,the liquid achieved a maximum temperature difference of8.8°C in the simulation experiment,and a maximum temperature of 3.9°C in the actual sunlight environment.The CDs@TRL exhibited excellent stability while showing reliable reversibility through multiple cyclic thermal response processes.（2）Green fluorescent CDs and acrylates were prepared using xylose and epoxidized soybean oil（ESO）as raw materials,respectively,and composite films were prepared by a self-assembly strategy.The composite films exhibited excellent UV-blocking ability and almost shielded UV light with a 99%shielding rate.In addition,the presence of barium sulfate（Ba SO₄）allowed the membranes to reflect infrared light and achieve a radiative cooling effect.The composite film achieved a cooling effect of 8.4°C and 4.4°C in indoor and outdoor tests,respectively.the first film composed of CDs and epoxy resin not only weakened UV but also reduced the absorption of UV by the second film,providing protection for the second film.the second film composed of Ba SO₄ and acrylate mainly provided a radiation cooling effect.In addition,the recovery rate of Ba SO₄/acrylate film is over 95%,which makes the second layer film sustainable.（3）Red fluorescent CDs were prepared using spinach as the biomass raw material,and the hydrogel was composed of polyacrylamide（PAM）and polyethylene glycol（PEG）.The 10 mm hydrogel can shield 99%of UV rays.PAM provides a mechanical framework with a compressive strength of 170 k Pa,and PEG imparts the ability of the hydrogel to reflect infrared light.Li Br can effectively retain water,and its morphology does not change after 84 hours at room temperature,and provides water regeneration ability for hydrogels,which can maintain long-term evaporative cooling work.The regeneration ability of the hydrogel increased with the increase of Li Br concentration,and the regeneration time was 4 h when the Li Br concentration was 55%.The cooling effect of the hydrogel was tested by simulation and actual testing,and the cooling effects were achieved at 9.5°C and 5.6°C,respectively.