纳米金刚石基于功能材料应用的研究现状

Review on the Development of Nanodiamonds Used as Functional Materials

由于天然金刚石非常稀少名贵,满足不了日益增长的工业需求,经过人们不断努力通过成熟的合成技术制备人造金刚石的年产量已经远远超过天然金刚石。目前在工业上,主要利用金刚石的高硬度特性将其作为磨料和超硬材料使用,最多的是用于磨具、刀具、钻进、切割、抛光等工具材料。但是,金刚石除了硬度高之外,光、电、催化、润滑、生物相容性等其他性能也非常优异,非常适合用于功能材料。人造金刚石的合成主要有三种方法:一是静态触媒法超高压高温合成金刚石单晶;二是采用化学气相沉积法制备大尺寸金刚石块(片)体材料;三是利用爆轰法合成纳米级粒度超细金刚石微粉。大颗粒单晶、大尺寸块(片)体、纳米级超细微粉等是金刚石作为功能材料应用中最被看好的材料形态,代表了当前的发展趋势。但是,对金刚石及其复合材料的功能性研究和应用开发还很不够。特别是纳米金刚石的多种优异特性,如高模量、高硬度、高热导率、良好的绝缘性、独特的光电特性、低摩擦系数及耐磨损特性、良好的化学稳定性和生物相容性,使其呈现出功能多样性。纳米金刚石作为功能材料的应用,最初主要用作光电材料,现在已经在生物医疗、药物递释、催化、热管理、润滑等领域获得了初步的应用,研究和开发处于快速发展阶段,应用前景广阔。纳米金刚石具有纳米材料的性质,容易发生团聚,采用搅拌球磨法、超声法、静电纺丝法等手段能够解决纳米金刚石的团聚问题。针对特定的应用目的,还需要对纳米金刚石进行化学改性。研究者采用羧化、氢化、氨化、酰胺化、酰氯化和羟化等化学改性方法,在纳米金刚石表面形成一些化学官能团,通过改变、调整和设计纳米金刚石表面的化学活性,降低纳米金刚石的凝聚,改进其在溶剂(或其他基体)中的溶解度和分散能力。改性后的纳米金刚石在生物成像、生物印记、生物传感、靶向特定细胞药物传输和组织工程等领域的应用研究获得了快速的发展。纳米金刚石经化学改性后表面官能团增多,能与聚合物通过共价键结合,其在聚合物中的分散得以改善,能明显提高聚合物的导热性能,非常适合作为复合材料的增强相。此外,改性后的纳米金刚石还被广泛用作光催化材料、摩擦材料、光电材料、自清洁材料等,展现出很大的研究价值。本文归纳了纳米金刚石用作功能材料的研究进展,在介绍纳米金刚石的改性方法、团聚与分散的基础上,重点介绍了纳米金刚石及其复合材料在前述诸多领域的应用情况,以期为拓展和深入纳米金刚石基于功能材料的应用研究提供参考。

Natural diamonds are too rare and precious to satisfy the growing industrial demand.Annual output of artificial diamonds made by industrial synthesis technology has exceeded remarkably that of natural diamonds.Now,because of their extreme hardness,diamonds are mainly used as abrasive materials and super-hard materials in industry,mostly for grinding tools,blades and for drilling,cutting,polishing,etc.In addition to the high hardness,diamonds also display other excellent properties,such as optical properties,electrical properties,catalytic properties,lubrication properties,biocompatibility,etc.,and thus are especially suitable for functional materials.Synthetic diamonds have been successfully prepared through three different strategies：Ⅰ.Ultrahigh-pressure and high-temperature process,i.e.the so-called static catalyst approach,which results in single crystal diamonds;Ⅱ.Chemical vapor deposition efficient for producing bulk（or sheet）diamond with large size;Ⅲ.The detonation method that can synthesize ultrafine（usually nanosized）diamond powders.Large single crystal,large-size bulk（sheet）and nanosized powders are currently the most promising,exemplary and state-of-the-art forms for functionalized artificial diamonds.However,the research and innovation for the functionalization of diamond and its composites are inadequate,especially for nanodiamond that shows a variety of excellent properties,such as high modulus,high hardness,high thermal conductivity,good insulation,unique photoelectric characteristics,low friction coefficient and excellent wear resistance,satisfactory chemical stability and biocompatibility.The original application of nanodiamonds and their composites is to serve as photoelectric materials,and have now been extended to the fields of biological medicine,drug delivery,catalysis,thermal management,lubrication,etc.,indicating a rapid,hopeful and high-potential development prospect.Nanosized diamonds generally tend to agglomerate,which is similar to other nanomaterials.This can be solved or alleviated by stirring-assisted ball milling,ultrasonic treatment,electrospinning,and so on.Moreover,for certain application purpose,chemical modification is also indispensable.For the sake of grafting ideal chemical functional groups onto the surface of nanodiamond,changing,adjusting and designing the chemical activity of their surfaces,and in consequence,further mitigating agglomeration and improving solubility and dispersibility in solvents（or solid matrices）,researchers have tentatively adopted various chemical modification approaches including carboxylation,hydrogenation,ammoniation,amidation,acylation and hydroxylation.And the modified nanodiamonds have successfully and swiftly found biomedical application,e.g.biological imaging,molecular imprinting,bio-sensing,cell-targeted drug delivery,tissue engineering and so on.The surface functionalization of the nanodiamonds facilitates the combination of them with polymer matrices by forming covalent bonds,which can promote dispersion and thermal conductivity of the nanodiamond-reinforced composites.Furthermore,functionalized nanodiamonds have also been applied in the fields of photocatalytic materials,friction materials,photoelectric materials,self-cleaning materials,etc.In this paper,the recent advances of nanodiamonds serving as functional materials is summarized.The modification methods,agglomeration and dispersion of nanodiamonds are introduced,focusing on the above-mentioned application situation.It is expected to provide a reference for the further research.