【作者】 孙鹏；

【导师】 张荻； 张旺；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2020， 博士

【摘要】 当今世界正面临严峻的化石燃料及水资源短缺危机。充分借助来源广泛、清洁高效的太阳能以及海水资源,通过太阳能光热海水淡化的方式提供净水,有望成为解决水资源匮乏和能源枯竭的有效途径。然而如何进一步提升光热转换材料的能量利用率以满足当前的实际需求,仍是能源、材料等领域公认的重要课题。近年来,新型功能材料的广泛应用极大地推动了科技与工业的进步。材料的性能取决于多方面因素,既受到材质、成分的影响,又深受微观构型的影响。因此,合理的微观构型设计,有助于提升材料的功能特性。目前采用人工方法已制得具有不同微观结构的光功能材料,在一定程度上满足了光热疗法、光学检测、光催化、光热/电转换等领域的需求。但受限于结构设计原理与材料制备技术,引入材料体系中的微纳构型仅限于一、二维或简单三维结构,这在一定程度上制约着精细微观构型与人工材质耦合效应与增强机制的研究。可见,精准地构筑具有三维精细分级构型的微观结构,对创制新型高效光功能材料具有重要意义。为此,我们虚心地向大自然寻找答案。经历亿万年的选择和进化,自然界中的生物为了更好地生存和繁衍,已进化出众多与功能相匹配的多尺度、高维度、多层次的精巧结构。基于这些精细微纳分级构型为模板制备的材料有效解决了功能材料结构单一化的问题,为多个学科领域的研究工作提供了灵感和借鉴。因此,本研究选取了具有不同微纳精细构型的蝴蝶（驳灰蝶、鹤顶粉蝶、裳凤蝶）以及向日葵为生物模板,结合光热转换机理不同的三种典型成分,创制了保留原始生物微纳精细构型的贵金属（Au）、贵金属-半导体（Au-Cu S）以及多孔碳等材质的光热材料,分别用于太阳能光热水蒸发,获得了有效的宽谱光吸收性能和优异的光热转换效率,并对三维精细分级结构与人工材质的耦合机制以及提升光热性能的有效途径进行了探讨,为今后光热材料的设计、开发提供借鉴。主要研究成果如下:（1）以gyroid构型的驳灰蝶和窗口构型的鹤顶粉蝶为生物模板,采用化学镀的制备方法获得了保留蝶翅原始三维微纳构型的金蝶翅材料,对其微观构型、亲水性、光学性质等进行表征,并分别将其用于表面增强拉曼散射检测以及光热水蒸发测试。结果表明,使用镀金驳灰蝶衬底获得的拉曼信号强度约为镀金鹤顶粉蝶的6.7倍(532nm激发,罗丹明1361 cm^-1特征峰),其超强等离激元共振效应得益于gyroid结构独特的三维周期性密集分布热点结构、高空间利用率及大散射截面。镀金驳灰蝶同时获得了有效的宽谱光吸收特性,一倍太阳光功率下光热水蒸发效率为74.0%;而窗口构型镀金鹤顶粉蝶的水蒸发效率相对较低,为65.4%。本研究表明gyroid结构在等离激元光吸收-热转换方面具有一定优势,为高效光热转换材料的设计、制备提供了参考。（2）对比研究了驳灰蝶、鹤顶粉蝶以及裳凤蝶前翅原始生物模板的形貌、结构及光学特性,分析各微观构型的特点与差异。采用化学还原及溶胶凝胶法合成了具有gyroid构型、减反射蜂窝状构型和窗口构型的三种Au-Cu S复合蝶翅,并探索不同微观构型对于光热水蒸发性能的增强机制。首先,通过调控Cu S颗粒沉积时间,制备了一系列不同填充率（29-80%）的gyroid结构Au-Cu S蝶翅材料,随着填充率逐渐增加,其光热性能先增加后减小。且沉积时间80 min时,gyroid结构具有适中的填充率（57%）与最大内表面积,实现了水输运-蒸发动态平衡的“局域水蒸发效应”,获得了最高的光热转换效率（88.8%）。有限时域差分法数值模拟表明gyroid结构可增加空间利用率及入射光散射截面,同时与Au-Cu S材质有效耦合实现等离激元响应增强,最终导致光吸收的显著增强。其次,减反射蜂窝状结构Au-Cu S蝶翅具有结构赋予的本征光吸收特性,因此可实现86.2%的较高水蒸发效率;而仅具有窗口构型的Au-Cu S蝶翅水蒸发效率最低,为72.2%。可见,微观构型的选取与精细调控对于光热性能影响显著,对未来光热材料的设计与优化具有一定的借鉴意义。（3）基于天然植物向日葵的生物构型,采用碳化的方法获得了保留生物模板分级多孔结构及三维构型的碳化向日葵,将其用于光热水蒸发测试。结果表明,不借助额外保温隔热材料,在一倍太阳光强度照射下蒸发效率可达93.7%。其优异的光热水蒸发性能一方面得益于碳化向日葵具备的分级微纳多孔结构,实现了高效的太阳光吸收和热转换、连续的水吸收和输送、良好的保温和隔热性能;另一方面则归功于碳化向日葵独特的的三维构型,可实现漫反射和热辐射损失的二次吸收,同时显著增加水-气界面,便于水蒸气逸出。本章为经常作为生物废料的向日葵拓展了应用领域,也为今后光热水蒸发领域新材料的设计研发提供了启发。受到自然的启迪,本文的研究充分利用自然界生物微纳精细构型,以蝴蝶、向日葵等生物模板成功获得了高效的光热转换材料,为相关领域的机理探索和性能优化提供了科学依据与研究方法。为具有微纳精细分级构型的光功能材料的设计与制备提供了借鉴,并为进一步获得高效等离激元响应性能、提高太阳光热转换效率及海水淡化能力起到促进作用。更多还原

【Abstract】 Nowadays,the world is facing with severe problems of fossil fuel crisis and water shortage.It is expected to be an effective way to solve the shortage of fresh water resource and energy crisis via making full use of the widely available,clean and efficient solar energy and sea water resources.However,how to promote the energy conversion efficiency of the photothermal materials to meet the needs in applications is still recognized as an important topic in the fields of energy and materials.During the past decades,novel functional materials are greatly promoting the progress of science,technology and engineering because of their widely-spread applications in various fields.The properties and performances of the materials depend on various factors,including the intrinsic properties of components,and the micro/nano architectures as well.Hence,the proper design of fine micro/nano architectures can further promote the performances of functional materials.Now,some micro/nano hierarchical structures developed via artificial methods,could meet various application requirements in many fields,e.g.photothermal therapy,biological sensing and detection,photocatalysis,photothermal and photoelectricity conversion.However,there are still some difficulties to break through the designs and technologies during artificial fabrication.Most of the architectures are restricted to 1D,2D or simple 3D structures,which seriously restrict the investigation and development of optical functional devices.Therefore,it holds a key role in achieving the preparation of optical functional devices for superior performances by precisely exploiting novel hierarchical micro/nano-structures and importing into material devices.Thus,we modestly seek answers from nature.For the purpose of survival and propagation,creatures of animals and plants have already developed various multiscale,multidimensional and multilevel excellent micro/nano hierarchical structures,as the results of the evolutionary selection for billions of years,providing tremendous inspirations for scientific researches.Therefore,this work selects the biotemplates of butterflies and sunflower heads with different fine hierarchical micro/nano architectures,combined with three kinds of typical photothermal materials of different mechanisms,fabricates photothermal materials of noble metal(Au),noble metal-semiconductor(Au-Cu S)and porous carbon materials inheriting the pristine 3D fine micro/nano bio-structures,achieves effective broadband solar absorption and outstanding photothermal conversion efficiency for solar steam generation.What’s more,the coupling effects of artificial textures with the fine hierarchical architectures and the mechanisms of promoting photothermal properties are also investigated.The main results are listed as follows:(1)The gold butterfly wings inheriting the pristine fine hierarchical bio-structures are fabricated by an electroless plating method by using C.rubi with gyroid structure and H.glaucippe with periodic lattice structure as bio-templates.Their microstructures,hydrophilicity and optical properties are investigated,and used in SERS detection and solar steam generation.The experiment results show that the SERS signal of Au gyroid is6.7-fold higher than Au lattice,demonstrating the excellent localized surface plasmon resonance(LSPR)enhancement owning to the 3D intensly distributed hotspots of gyroid structures and large scattering cross-section.The LSPR caused effective broadband light absorption enables Au gyroid a high evaporation efficiency of 74.0% under 1 sun.And the evaporation efficiency of Au lattice is 65.4%,lower than the former.The results demonstrate the superiority of gyroid structures over lattice structures in the field of plasmonic photothermal conversion.It is inspiring for the preparation of high performance photothermal materials with hierarchical architectures.(2)By templating from butterfly C.rubi with gyroid structures,T.helena with antireflection honeycomb structures and H.glaucippe with periodic lattice structures,Au-Cu S/GMs,Au-Cu S/TMs and Au-Cu S/LMs are fabricated and utilized for solar steam generation,respectively.Firstly,a series of Au-Cu S/GMs with different volume filling rate(FR～29-80%)are achieved by controlling Cu S NPs deposition time.Along with the FR increasing,the evaporation efficiency of Au-Cu S/GMs first increases and then decreases,Au-Cu S/GMs-80 with FR of 57% has the highest photothermal conversion efficiency(88.8%)under 1 sun,which realizes a dynamic balance of water absorption-evaporation of“localized evaporation effect”.FDTD simulation results demonstrates that gyroid structures possess full utilization of the space,large scattering cross-sections and effective couple with Au-Cu S plasmon components,leading to the significant enhancement of light absorption.Due to the synergistic LSPR caused by coupling effects of Au-Cu S NPs with gyroid structures,Au-Cu S/GMs possess superior light absorption capability.What’s more,Au-Cu S/TMs,owning intrinsic light absorption characteristic of antireflection honeycomb structures,possess a relatively high evaporation efficiency(86.2%);The evaporation efficiency of Au-Cu S/LMs with only periodic lattice structures is the lowest(72.2%).The results provide new paths to select and regulate 3D fine hierarchical structures for improving the properties of photothermal materials.(3)Carbonized sunflower heads inheriting the fine structures with interconnected porous networks and 3D macro structures are prepared via carbonization process by using natural sunflower heads as bio-templates and utilized for photothermal water evaporation.The experimental results show that carbonized sunflower heads exhibit high evaporation efficiency of 93.7% without additional insulation devices under 1 sun irradiation.The five aspects for steam output are summarized below: efficient solar absorption and heat generation ability;continuous water absorption and transport;resistance of heat loss and thermal insulation property;good capability for reabsorbing diffuse reflection and thermal radiation;and enlarged water/air interface for steam escape.This research work develops novel utilization methods and promising applications for sunflower heads as wastes,and provides inspirations for the future design and fabrication of high-performance photothermal devices.Inspired by nature,this work achieves efficient photothermal materials via utilizing unique hierarchical micro/nano architectures of bio-templates,including butterflies,and sunflower heads.It demonstrates research methods and scientific basis for mechanism exploration and performance optimization in related fields.It also provides a reference for the design and preparation of optical functional materials with micro/nano fine hierarchical configurations,and promotes the further acquisition of efficient LSPR performance,improvement of photothermal conversion efficiency and desalination capacity.更多还原