Compared to traditional cooling systems, radiative cooling (RC) is a promising cooling strategy in terms of reducing energy consumption enormously and avoiding severe environmental issues. Radiative cooling materials (RCMs) reduce the temperature of objects without using an external energy supply by dissipating thermal energy via infrared (IR) radiation into the cold outer space through the atmospheric window. Therefore, RC has a great potential for various applications, such as energy-saving buildings, vehicles, water harvesting, solar cells, and personal thermal management. Herein, we review the recent progress in the applications of inorganic nanoparticles (NPs) and microparticles (MPs) as RCMs and provide insights for further development of RC technology. Particle-based RCMs have tremendous potential owing to the ease of engineering their optical and physical properties, as well as processibility for facile, inexpensive, and large area deposition. The optical and physical properties of inorganic NPs and MPs can be tuned easily by changing their size, shape, composition, and crystals structures. This feature allows particle-based RCMs to fulfill requirements pertaining to passive daytime radiative cooling (PDRC), which requires high reflectivity in the solar spectrum and high emissivity within the atmospheric window. By adjusting the structures and compositions of colloidal inorganic particles, they can be utilized to design a thermal radiator with a selective emission spectrum at wavelengths of 8–13 μm, which is preferable for PDRC. In addition, colloidal particles can exhibit high reflectivity in the solar spectrum through Mie-scattering, which can be further engineered by modifying the compositions and structures of colloidal particles. Recent advances in PDRC that utilize inorganic NPs and MPs are summarized and discussed together with various materials, structural designs, and optical properties. Subsequently, we discuss the integration of functional NPs to achieve functional RCMs. We describe various approaches to the design of colored RCMs including structural colors, plasmonics, and luminescent wavelength conversion. In addition, we further describe experimental approaches to realize self-adaptive RC by incorporating phase-change materials and to fabricate multifunctional RC devices by using a combination of functional NPs and MPs.

中文翻译：

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用于被动日间辐射冷却的胶体无机纳米颗粒和微粒

与传统冷却系统相比，辐射冷却（RC）在大幅降低能耗和避免严重环境问题方面是一种很有前景的冷却策略。辐射冷却材料（RCM）通过红外（IR）辐射通过大气窗口将热能消散到寒冷的外层空间，从而在不使用外部能源的情况下降低物体的温度。因此，RC在节能建筑、车辆、集水、太阳能电池和个人热管理等各种应用中具有巨大的潜力。在此，我们回顾了无机纳米粒子（NP）和微粒（MP）作为RCM应用的最新进展，并为RC技术的进一步发展提供见解。基于颗粒的 RCM 具有巨大的潜力，因为其光学和物理特性易于设计，并且易于加工、廉价和大面积沉积。无机纳米粒子和MP的光学和物理性质可以通过改变它们的尺寸、形状、组成和晶体结构来轻松调节。此功能使基于粒子的 RCM 能够满足与被动日间辐射冷却 (PDRC) 相关的要求，该要求需要太阳光谱中的高反射率和大气窗口内的高发射率。通过调整胶体无机颗粒的结构和组成，它们可以用来设计在8-13μm波长范围内具有选择性发射光谱的热辐射器，这对于PDRC来说是优选的。此外，胶体颗粒可以通过米氏散射在太阳光谱中表现出高反射率，这可以通过改变胶体颗粒的组成和结构来进一步设计。总结并讨论了利用无机纳米颗粒和MP的PDRC的最新进展，以及各种材料、结构设计和光学性能。随后，我们讨论了功能 NP 的集成以实现功能 RCM。我们描述了彩色 RCM 设计的各种方法，包括结构色、等离子体和发光波长转换。此外，我们进一步描述了通过结合相变材料实现自适应RC以及通过使用功能NP和MP的组合来制造多功能RC器件的实验方法。