A team of researchers from theUniversity of Hamburghas developed a novel 3D printing process for nanoparticle-based aerogels that could result in a new generation of photothermal devices.
基于直接墨水写作（DIW）3D打印，该技术为制造太阳能蒸汽产生或基于二氧化钛（TIO2）纳米颗粒的Aerogels的设计自由度提供了新的设计自由。
While TiO2 was used as the basis for the study, the researchers say their technique can also be generalized for a “broad material library” and allow nanoparticle inks to be designed with specific functionalities that can be adapted to their target applications.
基于纳米颗粒的气凝胶的挑战
气凝胶是高度多孔的固体，可在宏观尺度上保持单个纳米材料的特性。虽然可以创建各种尺寸，形状，成分和表面化学的纳米材料具有显着性能，但基于宏观纳米材料的设备的大量生产仍然是一个挑战。
纳米材料加工的主要困难之一是在多个长度尺度上保存纳米镜的特性。尽管凝胶铸造为将纳米材料加工到气凝胶中提供了有吸引力的方法，但可用的模具几何形状范围有限，以及以这种方式创建的气凝胶具有有限的形状可调节性，防止复杂的微结构几何形状产生。
研究人员将基于挤出的DIW 3D打印确定为克服这些挑战的一种有前途的技术，因为该技术是从陶瓷加工进化而来的，可以从预制的颗粒中制造材料和设备。然而，由于粒度和孔隙率的差异，陶瓷和纳米颗粒的气凝胶具有根本不同的特性。
As such, the researchers needed to formulate additive-free 3D printable inks, similar to conventionally cast aerogels, that were compatible with the DIW process in order to fully capture the nanomaterials’ properties within the 3D printed aerogel.
3D printing nanoparticle-based aerogels
During the study, the researchers focused on developing a DIW 3D printing process capable of processing TIO2-based aerogels. Instead of using rheologic additives to ensure printability, which can be detrimental to the nanomaterial’s properties, the printing process took place in a liquid alkaline bath. This allowed the researchers to maintain the ink’s nanoscopic characteristics while also creating macroscopic translucent aerogel geometries.
The process started with forming an ink via nanoparticle gelation which was then 3D printed in the liquid bath before undergoing post-processing via supercritical drying. The researchers identified that inks loaded with a particle concentration of 4% volume were best suited for 3D printing. Leveraging an发动机人力资源3D printer fromHyrel 3D，在液体浴中进行了3D打印过程，以克服在空气中打印基于纳米颗粒的气凝胶时观察到的蒸发引起的凝胶损伤。
Additionally, the researchers found that they could easily process multicomponent inks by mixing TIO2 with additional nanoparticles such as gold (AU) nanoparticles (AuNP) or Au nanorods (AuNR) prior to the gelation process.
The team demonstrated the design flexibility of their method by printing geometries with high shape fidelity and precision, including void-free cubes, 3D grids, boats with large overhangs, and other multi-material geometries. The 3D printed aerogels contained a randomly organized interconnected mesoporous network with pore sizes in the range of 20nm, and large relative surface areas and low densities typical of conventionally cast metal oxide aerogels.
The researchers also showcased the design freedom of their method by successfully combining the superior thermal insulating capabilities of metal-oxide aerogels with the photothermic properties of plasmonic AuNRs. Their DIW 3D printing process defined not only the dimension of the printed material but also its composition and photothermal properties at any desired point.
不过，最重要的突破是能够设计其制造的光热气凝胶的微观结构，以提供改进的光穿透性，并在3D中提供更均匀的加热。根据该团队的说法，这可以使新一代的光热设备用于太阳蒸汽生成或热化学热量存储。
To achieve this, the team used two print heads loaded with different nanomaterials. On its own, TiO2 ink absorbs UV radiation and appears translucent, however when loaded with AuNRs features strong extinction in the visible and near-infrared (NIR) range due to plasmonic excitations. The researchers leveraged the free-form capabilities of their DIW technique to locally define the aerogel’s photothermal properties and improve its heat generation and light distribution properties.
In addition to TiO2, the approach can be applied to SiO2, Al2O3, or ZrO2 nanoparticle-based aerogels commonly used in photothermal devices. Photothermal heating of plasmonic nanoparticles has been leveraged in the past for prototype devices for clean water regeneration, energy generation, and photothermal catalysis, however until now has been limited to thin films due to the inability to structure nanoscopic properties on a 3D macroscopic scale.
通过在宏观物体中启用更多同质的热量产生，研究人员认为他们的diw 3D打印技术为制造大型3D结构化光热设备提供了一种全新的方法。
Further information on the study can be found in the paper titled:“Additive-free, gelled nanoinks as a 3D printing toolbox for hierarchically structured bulk aerogels,”published in the Advanced Functional Materials journal. The article was co-authored by M. Rebber, M. Trommler, I. Lokteva, S. Ehteram, A. Schropp, S. Konig, M. Froba, and D. Koziej.
Fabricating aerogels via DIW
DIW 3D printing has been previously explored for producing aerogels with optimized properties, with some notable developments occurring over the past year.
2021年3月，UC Santa Cruzand the默塞德纳米材料的能量和传感中心（MACES）使用DIW到fabricate porous carbon aerogelsfor electrodes in ultra-low temperature supercapacitors, which could power future missions both on Earth and in space. Funded byNASA, the research sought to reduce heating needs for vehicles and devices used in future missions within extremely cold environments.
Elsewhere, scientists from the布法罗大学developed a novelwater-purifying graphene aerogelusing DIW that could be scaled for use in large wastewater treatment plants, while researchers at劳伦斯利弗莫尔国家实验室使用DIW生产由石墨烯气凝胶制成的电化学反应器的流动电极，据报道反应堆性能提高高达100倍.
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Featured image shows3D打印Tio2气凝胶的分层体系结构。通过高级功能材料图像。
