Carbon_nanotubes_supercharge
石墨相氮化碳光催化还原CO2研究进展
第 42 卷第 6 期2023年 11 月Vol.42 No.6Nov. 2023中南民族大学学报（自然科学版）Journal of South-Central Minzu University（Natural Science Edition）石墨相氮化碳光催化还原CO2研究进展常世鑫1，虞梦雪1，俞迨2，严翼1*，王之1，吕康乐1（1 中南民族大学资源与环境学院& 资源转化与污染控制国家民委重点实验室，武汉430074；2 杭州市质量技术监督检测院，杭州310019）摘要半导体光催化可以利用太阳能驱动CO2光催化还原制备碳氢燃料，成为研究热点.石墨相氮化碳（g-C3N4）具有制备简便和可见光响应性能的优点，是CO2还原的热门光催化材料。
但是它具有缺陷多、比表面积小和光生载流子易复合等缺点，光催化CO2还原性能不高.为此，介绍了高CO2还原活性的g-C3N4研究进展，内容包括：（1）g-C3N4研究基础（分子结构、制备方法与电子能带结构）；（2）高活性g-C3N4的分子设计策略（缺陷调控、元素掺杂、表面等离子体处理、单原子催化和异质结构建等），重点讨论了改性方式对g-C3N4的光吸收、光电性能和CO2还原产物选择性的影响.最后建议未来聚焦结晶氮化碳的修饰改性研究，强调利用原位和瞬态表征技术指导高CO2还原活性的g-C3N4的开发，并关注具有高能量密度的长链碳氢燃料产物的选择性.关键词氮化碳；光催化；CO2还原；选择性中图分类号O625.67；O643.3 文献标志码 A 文章编号1672-4321（2023）06-0721-12doi：10.20056/ki.ZNMDZK.20230601Research progress of photocatalytic CO2 reduction ongraphitic carbon nitrideCHANG Shixin1，YU Mengxue1，YU Dai2，YAN Yi1*，WANG Zhi1，LYU Kangle1（1 College of Resources and Environment & Key Laboratory of Resources Conversion and PollutionControl of the State Ethnic Affairs Commission， South-Central Minzu University， Wuhan 430074， China；2 Hangzhou Inspection Institute of Quality and Technical Supervision， Hangzhou 310019， China）Abstract Semiconductor photocatalysis can use solar energy to drive the photocatalytic reduction of CO2，producing hydrocarbon fuel，which becomes a research hotspot. Graphitic carbon nitride （g-C3N4）is a popular photocatalytic material for CO2reduction，which has the merits of facile synthesis and visible-light-response property. However，the photocatalytic activity of g-C3N4 is not high enough for CO2 reduction due to its drawbacks including many defects， small specific surface area， and easy recombination of photogenerated charge carriers. Herein， the recent progress of high active g-C3N4 for CO2 reduction was introduced， which included （1） the research fundamental of g-C3N4： molecular structure，synthesis method，and electronic band structures；（2）the strategies of g-C3N4 molecular design for high efficient CO2 reduction：defects engineering，elements doping，surface plasma treatment，single-atom catalysis，and heterojunction construction. Detailed discussions were focused on theeffects of different modification methods on light absorption，photoelectric property，and selectivity of CO2reduction of g-C3N4. Finally，it is suggested to focus on the study of crystalline g-C3N4modification in the future，emphasizing the use of in situ and transient characterization techniques in exploration of g-C3N4with high CO2reduction activity and selectivity of long-chain hydrocarbon fuel products with high energy density.Keywords carbon nitride； photocatalysis； CO2 reduction； selectivity收稿日期2023-04-12* 通信作者严翼（1986-），女，讲师，博士，研究方向：环境生态，E-mail：****************基金项目国家自然科学基金资助项目（41901235）第 42 卷中南民族大学学报（自然科学版）工业革命以来，人类活动不断的增加和工业的迅速发展促使了化石燃料的大量使用，导致CO2温室气体的大量排放［1-4］.伴随国家的“双碳”目标和绿色发展战略的提出，如何合理解决CO2气体造成的环境问题将影响社会和经济的可持续发展. CO2是一种比较稳定的分子，使C=O键断裂需要大约750 kJ‧mol-1的能量，常规的物理化学方法处理CO2较困难.但是分子中的O周围存在孤对电子，可以为路易斯酸中心提供电子，而其中C可以接受来自路易斯碱中心的电子［5］；此外，CO2可以吸附在绝大多数催化剂材料表面上，这为催化还原CO2分子提供可能性［5-6］.受光激发的半导体材料可以诱导CO2转化为高价值的碳氢燃料产物，在缓解温室效应的同时，还生产了高附加值工业化学品.因此，CO2的光催化还原具有节能和环保的优点，符合可持续发展的理念［7-8］.随着研究的不断深入，高活性CO2还原的半导体光催化材料的开发也从初始的TiO2逐渐拓展到硫化物、金属氧化物和非金属氮碳化物等［9-10］，这些催化剂的光吸收范围从紫外光逐渐向可见光拓展，CO2还原产物日渐丰富，从C1产物（如CO、CH4、CH3OH和HCOOH）过渡到C2产物（如C2H5OH 等）［5-6］.在这些半导体材料中，氮化碳由于具有较好的物理化学稳定性、优异的光响应范围、合适的带隙结构、便捷的制备方式和易于改性等优点而受到广泛关注［3-4， 7］.同时，由于氮化碳的能带结构满足光催化CO2还原的热力学条件，被迅速应用于CO2还原领域.但是，体相氮化碳仍然存在可见光吸收范围窄、载流子复合率高和比表面积小等缺点.针对这些问题，近年来研究人员致力于对氮化碳进行改性从而提升其光催化性能，特别是CO2还原产物的选择性，以产生更高价值的多碳产物.基于以上研究结果，本文主要针对氮化碳改性调节CO2还原产物的选择性进行总结，分别从缺陷调控、元素掺杂和构建异质结三个角度进行详细阐述，重点探讨了改性方法对于氮化碳光吸收、光电特性及还原产物选择性的影响，最后对氮化碳光催化材料未来发展提出展望.1 氮化碳的结构和性质氮化碳是一种热门的聚合型材料，拥有着较高的化学稳定性和热稳定性，耐酸碱腐蚀，最高可在700 ℃下保持热稳定性［4， 11］.氮化碳前驱体在高温环境中，可以一步一步缩合成环状结构，这种环状结构的雏形最早由BERZELIUS发现，并在1834年由LIEBIG命名为“melon”［11-14］.这种雏形材料继续进行缩合最终可得到两种氮化碳的主要结构——三嗪环（C3N3）［图1（a）］和七嗪环（C6N7）［图1（b）］.这两种聚合型的结构由于缩合不完全，使少量杂质氢在结构边缘上产生伯胺基团或者仲胺基团，产生大量无序的体相缺陷.这些体相缺陷的存在，不利于光生载流子的快速迁移扩散，而成为了载流子复合中心，抑制光催化活性.所以，需要对氮化碳进行结构修饰与改性，提升其光催化性能［11， 15-16］.氮化碳是一种典型的N型半导体材料，其能带结构如图1（c）所示，带隙约为2.7 eV，它的导带电位比大多数的CO2还原产物的电位更负，理论上可以生成诸多的还原产物.但在实际应用过程中，受到热力学和动力学因素的限制，氮化碳光催化CO2还原产物主要为CO和CH4［8］.在CO2还原反应过程中，氮化碳价带上的空穴分解H2O为导带产物的生成提供H+［16］；而导带上的电子还原CO2时，生成CH4比生成相同量的CO需要更多的电子和H+［公式（1）和公式（2）］，所以生成CH4受到动力学因素的影响程度更大.此外，氮化碳材料的导带电位也满足生成H2的条件，这也制约了氮化碳还原CO2生成CH4［16-17］.CO2 + 2H++ 2e-→ CO + H2OE0redox=-0.53 V (vs. NHE，PH = 7)，（1）CO2 + 8H++ 8e-→ CH4+ 2H2OE0redox=- 0.21 V (vs. NHE，PH = 7).（2）氮化碳可以通过尿素、氰胺、双氰胺、三聚氰胺、硫脲等前驱体［图1（d）］通过热聚合（包括水热合成法、模板法、熔融盐法等）得到，方法便捷、易于批量制备［12-13， 18-20］.其中，氰胺热缩合生成双氰胺，再由双氰胺热缩合生成三聚氰胺，最后通过三聚氰胺的逐渐缩合制备出氮化碳，这种途径被公认为是产生相对较少缺陷的聚合物的一种高效方法［4， 11］.但是制备出的氮化碳存在较多缺陷，为了改善氮化碳缺陷多和载流子易复合的问题以提高光催化剂的活性和调节产物的选择性，可以从制备方式出发，通过缺陷调控、元素掺杂或修饰改性、构造异质结等途径实现氮化碳的高效应用和产物选择性的调控［21-23］.对氮化碳进行改性处理后的CO2还原产物及选择性的结果详见表1.722第 6 期常世鑫，等：石墨相氮化碳光催化还原CO 2研究进展2 改性氮化碳调控CO 2光催化还原选择性CO 2的光催化还原，要经历多电子逐步还原的反应过程.CO 2在氮化碳表面的光催化还原产物主要有C 1产物和C 2产物，而生成更长链的多碳产物至今仍然面临着很大的挑战［5］.C 1产物的生成过程， 首先是H +与电子转移到CO 2表面，生成羧基中间体（COOH*），然后进一步生成CO 、CH 4等产物［6］.CO 由C =O*或C ≡O*生成，而其他C 1还原产物如HCHO 、CH 3OH 和CH 4的生成途径则由中间体CO*经过一系列反应生成［5］.其中CH 4的生成方式有两种：一种通过CO*加氢生成CH 3O*，再转化成CH 4和H 2O ；另一种由CO*生成COH*，然后脱水形成C*，最后逐步加氢生成CH 4［5-6， 50］.C 2产物由生成的CO*加氢生成*CHO ，然后碳碳键偶联产生COCHO*，继而生成乙醇和乙醛等产物［5， 24， 39］.改性后的氮化碳因为性能发生改变会导致CO 2还原过程中热力学性能和动力学性能发生改变，使得生成的中间体的种类和相应的生成速率发生变化，最终影响到产物的选择性［5， 16］.基于氮化碳的改性方式进行分类，本文将从多种氮化碳的改性方法对于产物选择性影响角度进行详细阐述.2.1 缺陷调控由于石墨相氮化碳的热聚合不完全，导致大量无序体相缺陷的生成，这些缺陷很容易成为光生载流子的复合中心，抑制石墨相氮化碳的光催化活性.但是，对于结晶度比较好在石墨相氮化碳，可以通过特定缺陷（如碳缺陷位点和氮缺陷位点）的引入来调控其半导体能带结构和表面化学环境，增强光吸收和载流子分离效率，实现CO 2还原的活性的增强和产物选择性的调控［1-2］.氮空位的引入可以增强CO 2的吸附性能，同时可以作为陷阱诱捕光生电子，通过延长载流子的寿命和抑制载流子复合，来提升石墨相氮化碳的光催化还原CO 2性能［17］.此外，捕获电子后的氮空位由于周围电子分布的改变更有利于CO 2吸附和活化［17］.通过制备出的三聚氰胺-三聚氰酸超分子进行自组装制备出氮化碳（表1序号1），将氮化碳置于550 ℃下，使用氩气和氢气的混合气体氛围进行氢热处理制备出有氮空位缺陷的管状氮化碳［17］.通过原位红外测试［图2（a ）］可知：在反应图1 氮化碳结构、性质和制备方法Fig.1 Structure ， properties and preparation method of carbon nitride723第 42 卷中南民族大学学报（自然科学版）表1 氮化碳改性策略与光催化还原CO2性能Tab.1 Modification strategies and photocatalytic CO2 reduction performances of carbon nitride序号1 234 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33催化剂名称TCN-1NVs-PCNg-CN-650g-CN-750HCN-AP-g-C3N4S-CN1% B/g-C3N42Au-CNCN/Aug-C3N4/Bi/CDsNi25/g-CNCN/PDA10Def-CNPt@Def-CNCo-MOF/g-C3N4Ni5-CNCu-CCNCCNBsK-CNMn1Co1/CNPtCu-crCNInCu/PCNPd1+NPs/C3N4P/Cu SAs@CNC3N4/rGO/NiAl-LDHsCo3O4/CNSg-C3N4/Cu2Og-C3N4/Ti3C2TxCN/ZnO/GAg-C3N4/FeWO4PN-g-C3N4CeCo-PTI改性方法氮空位氮空位氮空位氮空位局部结晶P改性S掺杂B掺杂纳米Au纳米Au纳米Bi纳米Ni2，6吡啶二羧酸掺杂缺陷氮化碳单原子PtCo-MOFNi单原子Cu单原子Cu修饰K掺杂双单原子双单原子双单原子单原子与纳米粒子金属单原子与非金属Ⅱ型半导体Z型异质结Z型异质结异质结Z型异质结Z型异质结多孔纳米带S型异质结光源300 W氙灯LED灯300 W氙灯300 W氙灯LED灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯氙灯300 W氙灯300 W氙灯500 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯氙灯300 W氙灯氙灯300 W氙灯300 W氙灯300 W氙灯250 mW cm-2氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯300 W氙灯活性/（µmol‧g-1‧h-1）CO： 7.1CO： 55.95CO： 5.3CH4： 34.4CH4： 52.8CH3COH： 1815CO： 2.4CH4： 1.8CO： 3.20CO： 0.45CH4： 0.16CH4： 1.55CO： 28.3CO： 9.08―CO： 284.7H2： 71CH4： 2.1CH4： 6.3CO： 6.75CH4： 5.47CO： 8.6CO： 3.1CO： 9.9H2： 0.94CO： 8.7CO： 47CH4： 2.8C2H5OH： 28.5CH4： 20.3C2H6： 616.6CO： 2.6CH4： 20.0CO： 13.3CH4： 3.2CH3OH： 0.71CO： 3.98CH4： 2.1CO： 33.9CO： 6.0CO： 29.8CH4： 45.4选择性100% CO85% CO86.6% CH496.4% CH498.3% CH3COH43.3% CH4100% CO26.2% CH419.1% CH495.6% CO98% CO28% CH4100% CO78% CH499% CH444.8% CH481.1% CO100% CO91.4% CO―100% CO19.4% CH492% C2H5OH97.8% CH433.0% C2H688.5% CH480.8% CO94.9% CH3OH34.7% CH492% CO91% CO100% CO88.3% CH4参考文献［17］［22］［16］［16］［24］［25］［26］［27］［28］［29］［30］［31］［32］［33］［33］［3］［34］［35］［36］［23］［37］［38］［39］［40］［41］［42］［43］［44］［45］［46］［47］［48］［49］724第 6 期常世鑫，等：石墨相氮化碳光催化还原CO 2研究进展过程中的产生了大量生成CO 的中间体——CH 3O*、HCOO -和COOH*，并未发现大量生成CH 4中间体，使CO 2还原更倾向于生成CO.除了改变煅烧热处理的气体氛围可以制造氮空位，利用甲酸辅助刻蚀也可以产生氮空位缺陷.杨朋举教授课题组［22］用三聚氰胺作为前驱体煅烧出氮化碳，利用氩气将甲酸带入管式炉对氮化碳进行热处理从而产生氮空位.通过表征发现氮空位主要集中在氮化碳的表面，形成氮空位后也极大地提高了CO 的产率，CO 选择性大约在85%（表1序号2）.通过吉布斯自由能的理论计算［图2（b ）］可以发现：这种方式引入的氮空位降低了生成COOH*的活化能，使得产物中CO 的选择性更高.氮空位的形成会影响材料能带结构，带隙的位置可以受到氮空位的电子密度的影响［16， 51］.张金龙教授课题组［16］报道三聚氰胺在空气氛围下通过改变温度进行高温煅烧可以制备出氮空位的氮化碳.根据CO 2还原的活性测试结果发现：随着催化剂煅烧温度的提高，CH 4的选择性大幅提高，750 ℃煅烧出来的氮化碳CH 4的选择性最大并且达到96.4%（表1序号4）.通过能带分析发现：随着煅烧温度的提高，间隙态的生成位置逐渐降低［图2（c ）］，在650 ℃以上的温度进行煅烧，间隙态的位置会低于产生CO 的电位.间隙态的产生会使得电子在激发后率先集中在其附近，更有利于从热力学方面产生CH 4.此外，利用Pt 4+在催化剂表面光沉积来研究氮化碳的光生电子的迁移途径发现：光生电子倾向于迁移并聚集在催化剂的边缘，导致边缘的氮缺陷处的电子密度更高，在动力学上对产生CH 4更有利.在热力学和动力学双重优势下，还原产物体现出更高的CH 4选择性.用传统方式热缩合得到的氮化碳基本为非晶态或半晶态的状态.在结晶氮化碳表面引入缺陷也是一种提升性能的方法.文献［24］通过加入氨基-2-丙醇（AP ）和双氰胺制备氮化碳提高了单体的结晶度和聚合物的聚合度，获得了结晶氮化碳（图3）.从样品的高分辨率透射电镜［图3（b ）］照片，可以观察到明显的缺陷区域和有序的晶格条纹，反映出其缺陷氮化碳较高的结晶性能.这种结构可以促进CO 2向油类化合物的转化，通过对反应过程分析［图3（c ）］可知：这种结构使得CO 2逐步生成C 2产物的中间体——CO*和CHO*，CO*和CHO*更容易自发偶联生成C 2产物中间体OCCHO*，抑制CHO*进行质子化的过程，故最终生成产物以CH 3CHO 为主，并且选择性高达98.3%（表1序号5）.从理论上讲，相比将CO 2还原生成C 1产物，还原生成C 2产物具有更高的能量密度和更大的商业价值［52］.2.2 元素掺杂元素掺杂改性也是一种常用的改性手段.金属或者非金属掺杂剂的原子轨道与催化剂本身的分图2 N 缺陷氮化碳CO 2还原选择性影响机理图Fig.2 Schematic diagram of selectivity reduction of CO 2 over carbon nitride with N defect725第 42 卷中南民族大学学报（自然科学版）子轨道发生杂化，能够起到改变反应的活性位点、调节能带结构和电子分布结构等作用，进而通过影响催化剂的性能来改变产物的选择性［5-6］.在氮化碳还原CO 2过程中，电子从氮原子上激发并向碳原子上迁移，但是光激发后电子更加倾向于分布在氮附近，尤其是分布在双配位氮的附近［图4（a ）］，这使电子的迁移更加困难，导致在催化过程中载流子复合率高和反应动力更低［16， 27］.刘敏教授课题组［27］建立了硼掺杂氮化碳的模型，根据模型［图4（b ）］可知：硼原子已成功掺杂在相邻的七嗪环之间，并且与七嗪环的氮原子形成了良好的亲和力.通过计算发现在硼掺杂氮化碳后，激发后的电子从N （2P x ，2P y ）向B （2P x ，2P y ）上转移更加容易，可以极大地增加反应的动力，更有利于CH 4的产生.他们用硼酸和尿素混合进行一步煅烧实验生成硼掺杂氮化碳，硼作为主要的活性位点可以改变对CO 2还原中间体的吸附，使得产物更容易生成CH 4，所以相比纯氮化碳，生成CH 4的选择性得到了提高.相比硼掺杂，硫掺杂对氮化碳的性能改变有着不同影响.文献［26］通过水热和程序升温的方法制备出介孔硫掺杂氮化碳，更多的介孔形成和硫的掺杂增大了比表面积，并增强了对CO 2的吸附能力 ［图5（a ）］，这有利于CO 2的活化并进行还原反应.在能带结构中，由于硫参与轨道杂化并且作为主要的活性位点，载流子的分离效率得到提高，反应的活性也得到增强.在生成产物的过程中，相比纯氮化碳，硫掺杂改性的氮化碳使生成的CO 产物更容易脱附［图5（b ）］，因此生成CO 的选择性显著提高.2.3 表面等离子体效应金属纳米粒子的负载可以增强光吸收和促进载流子分离，从而提高光催化活性的效果.在氮化碳上掺入金属纳米粒子后，不仅可以作为活性位点和形成促进载流子分离的肖特基结构显著提升性能，而且还会由于金属纳米粒子的局部表面等离子共振效应（LSPR ）进一步拓展催化剂的光吸收范围［7， 53-54］.负载Au 纳米粒子的氮化碳就是一个不错的例子，可以通过LSPR 效应一定程度上提高CH 4的选择性.KAIMIN S 教授课题组［28］利用NaBH 4还原法所制备的负载Au 纳米粒子的氮化碳，不仅有效地抑制了载流子复合，还通过LSPR 效应促进了更多热电子产生和增强了在可见光范围下的光吸收能力，大幅提高了CO 2还原的活性，尤其是为CH 4的形成提供了更多活性电子促进其生成.向全军教授课题组［29］用N 2等离子体处理浸渍在HAuCl 4中的氮化碳制备催化剂，这种Au 纳米粒子负载氮化碳也能通过Au 纳米粒子的LSPR 效应显著提高CH 4的选择性.图3 局部结晶氮化碳的结构与CO 2还原反应机理Fig.3 Morphology of locally crystalline carbon nitride and CO 2reduction reaction mechanism图4 B 掺杂氮化碳DFT 计算Fig.4 DFT calculation about B doped carbon nitride726第 6 期常世鑫，等：石墨相氮化碳光催化还原CO 2研究进展此外，金属纳米粒子作为活性位点也可以降低反应能垒.董帆教授课题组［30］使用碳点（CDs ）作为基质，将Bi 纳米粒子锚定在氮化碳上并与其进行桥接制备出CNB -2，Bi 通过LSPR 效应增强了氮化碳光吸收的能力和产生了更多热电子，热电子产生后可自发注入氮化碳中，为CO 2还原提供更多热电子［图6（b ）］；而作为基质的CDs 可以作为光生空穴的受体，在内建电场的作用下Bi 和氮化碳所产生的空穴可以转移到CDs 上，有利于光生电荷的分离并为CO 2还原提供更多的还原动力.通过吉布斯自由能可以得出，Bi 纳米粒子的掺入明显降低生成CO 途径的中间产物的活化能，为生成CO 提供更多热力学条件，最终生成CO 的选择性得到了提高.2.4 单原子催化将金属由纳米级尺寸制备成更小的单原子尺寸，会引起原子自身特性发生更为显著的改变.通过金属单原子对氮化碳改性，一方面暴露出更多的单原子位点，影响吸附中心和反应位点；另一方面单原子通过改变电子结构对反应过程进行调整，拥有了更加出色的催化性能表现［54-56］.金属单原子改性是一种充满挑战又极大提高催化剂性能的方法，有不少有关通过单金属单原子对氮化碳改性提升性能的报道.熊宇杰教授课题组［33］通过在氮化碳上分别负载Pt 单原子（Pt@Def -CN ）和Pt 纳米粒子，进行CO 2还原实验中，相比未负载金属的氮化碳，它们的反应活性和CH 4的选择性显著提高，其中Pt@Def -CN 对于CH 4的选择性提升更高，达到了99%（表1序号15），由于单原子独特的性质对选择性造成了影响.一方面，因为H 原子与Pt 单原子之间结合相对不稳定，Pt 单原子附近存在更多—OH 基团，抑制了H 2产生，为生成CH 4提供更多H +；另一方面，Pt 单原子有效地降低了反应过程中生成CH 4的活化能能垒［图7（a ）］，同时又增加了CO*中间产物的解析能，提高了CH 4的选择性.向全军教授课题组［35］制备出掺入Cu 单原子的高结晶氮化碳，Cu 单原子的加入可作为CO 2活化的活性中心，提高了对CO 2的吸附能力，增强了反应活性.此外，Cu单原子的加入使图5 S 掺杂氮化碳的CO 2吸附等温线和CO -TPD 光谱Fig.5 CO 2 adsorption isotherms and CO -TPD spectra of S -oping carbon nitride图6 金属纳米离子改性氮化碳CO 2还原反应机理图Fig.6 Scheme diagram of metal nanoions modified carbon nitride CO 2 reduction reaction727第 42 卷中南民族大学学报（自然科学版）得生成CO 的反应过程优先于生成CH 4的反应过程［图7（b ）］，极大地提高了CO 的选择性.双金属单原子通过协同作用能提高CO 2还原性能.李亚栋教授课题组［37］合成出含有Co 和Mn 双金属单原子的氮化碳来进行CO 2还原.在还原过程中，光生空穴更倾向于移动到Mn 单原子上作为活性位点加速H 2O 分解，提供H +；而光生电子更倾向于移动到Co 单原子上，通过增加CO 2的键长和键角将CO 2活化，最终生成CO.这种双金属单原子的协同作用使CO 的选择性基本上达到100%（表1 序号21）.侯军刚教授课题组［39］将Cu 和In 单原子分散在氮化碳上，双金属单原子的引入改变了催化剂的电子结构［图7（c ）］.在Cu 单原子附近有明显的电荷富集的迹象，而在In 单原子附近有明显的电荷消耗的迹象，它们之间的协同作用促进了电荷转移和电荷分离.此外，双金属的作用增强了对中间体CO*的吸附并降低了C —C 偶联的活化能，促使了偶联生成乙醇.金属单原子和金属纳米粒子同时引入氮化碳上能够协同发挥作用，调整CO 2还原的选择性.郑旭升教授课题组［40］通过在氮化碳上引入Pd 单金属（Pd 1）和Pd 纳米粒子（Pd NPs ）作为双活性位点，改善了氮化碳的光催化性能.相比只引入Pd 1，双金属单原子引入后的协同作用使得CH 4的选择性有了显著提高［图7（d ）］.Pd NPs 的加入促进H 2O 分解并且加快H +转移到Pd 1；而Pd 1则更有利于吸附中间体CO*，加快质子化过程，生成CH 4.此外，Pd NPs 和Pd 1的协同作用也降低了从CO*到生成CHO*的活化能能垒，显著提高了生成CH 4的选择性.金属单原子与非金属之间也能够产生协同作用，提高氮化碳的性能，影响产物的选择性.毛俊杰教授［41］课题组报道了通过将P 和Cu 作为双活性位点锚定在氮化碳上，在CO 2还原过程中生成高选择性的C 2H 6产物.首先，P 和Cu 修饰对氮化碳的带隙起到一定调整作用，在一定程度上更有利于电子空穴的光激发分离.其次，P 和Cu 作为电子和空穴的捕获位点，可以促进Cu 对电子的富集从而实现CO 2还原的多电子过程.最后，P 和Cu 的修饰降低了中间生成C 2H 6的反应途径的活化能，CO*和CO*更容易发生偶联，形成中间体OCCO*，逐步加H最终生图7 单原子金属改性氮化碳CO 2还原反应机理图Fig.7 CO 2 reduction reaction scheme diagram of monometallic metal modified carbon nitride728第 6 期常世鑫，等：石墨相氮化碳光催化还原CO 2研究进展成C 2H 6产物.2.5 异质结构建不同于单一的材料，将复合材料制成异质结更有利于提高催化剂的性能.由于异质结界面在空间结构上彼此分离，光生电子和空穴的复合会更容易被抑制，从而改变生成产物的选择性［7， 21， 57］.Ⅱ型异质结在CO 2还原的相关文献中经常被报道，汪铁林教授课题组［42］在NiAl 层状双金属氢氧化物（NiAl -LDHs ）和氮化碳中引入还原氧化石墨烯（rGO ）辅助制备成Ⅱ型半导体，由于rGO 拥有优异的导电子能力，能进一步促进载流子分离，使氮化碳上光生电子更迅速分离并转移到NiAl -LDHs 的Ni 原子上，导致生成CO 的选择性大大提高.Ⅱ型异质结虽然可以极大地促进载流子分离，但会使催化剂的价带或导带的电位降低［12， 21］.Z 型异质结概念受到植物光合作用的机理启发提出.相比Ⅱ型异质结，Z 型异质结保持了更正的价带和更负的导带电位，因此复合材料拥有更强的光催化氧化/还原性能［21， 57-58］，常应用于光催化领域.文献［46］报道利用静电自组装和低温共沉积法将ZnO 和氮化碳锚定在石墨烯气凝胶上制备出间接接触Z 型异质结结构，这种异质结结构的构建不仅使电子空穴更有效地空间分离，在CO 2还原产物中CO 的选择性更高.有国外课题组［47］制备出氮化碳和FeWO 4复合的直接接触Z 型异质结.同样地，这种异质结也极大地抑制了载流子分离和提高了氧化电位，使产物中H +更倾向于生成H 2，抑制了CH 4的产生，故CO 2还原的产物中没有CH 4和其他烃类产物产生.3 总结与展望光催化技术可以利用太阳能来驱动温室气体CO 2的催化还原，制备具有高附加值的碳氢燃料，因此该技术具有节能和环保的优点.在所有的半导体光催化材料中，石墨相氮化碳因为具有可见光响应和能带结构合理等优点，而成为受欢迎的CO 2还原光催化材料.但是，其依然存在缺陷多、比表面积小和光生载流子易复合等缺点，在一定程度上制约了该技术的实际应用.因此，科学家们采用各种策略对石墨相氮化碳进行修饰改性，以进一步提升其光催化还原CO 2的性能.本文总结了目前石墨相氮化碳用于CO 2还原方面的5种改性方式，分别是缺陷调控、元素掺杂、等离子体效应、单原子修饰和异质结构建.对石墨相氮化碳的结构修饰，改变了催化剂表面的化学环境，进而对CO 2光催化还原路径产生和产物还原选择性产生深远影响.为了实现CO 2在氮化碳表面的高效光催化还原，在今后的研究中以下工作值得进一步深入研究.（1）开展基于结晶石墨相氮化碳的修饰改性研究.相对于普通氮化碳，结晶氮化碳的体内和表面缺陷大幅度减少，而表现出高效载流子分离效率和光催化性能.但是石墨相氮化碳依然属于有机半导体材料，其表面缺乏过渡金属作为CO 2分子的吸附和活化中心.因此，需要开展基于结晶氮化碳的表面改性特别是过渡金属表面修饰研究.（2）开展修饰组分之间的协同作用机制研究.从CO 2在石墨相氮化碳表面的吸附开始，到吸附产物如CH 4/CO 的脱附，中间需要经历很多关键步骤.因此，深入研究各修饰组分之间的接力还原CO 2机制，对深刻理解CO 2还原的活性中心结构和指导高效光催化还原CO 2材料的开发具有重要意义.（3）开展CO 2光催化还原的原位瞬态谱学研究.CO 2分子在光催化还原过程中，存在中间产物结构图8 氮化碳异质结CO 2还原选择性机理图Fig.8 CO 2 reduction reaction scheme diagram of carbon nitride with heterojunction729。
超高密度硅碳负极电池
超高密度硅碳负极电池英文回答：Super high-density silicon-carbon anode batteries have become a popular topic in the field of energy storage due to their high energy density and long cycle life. These batteries are designed to overcome the limitations of traditional lithium-ion batteries by using a silicon-carbon composite material as the anode, which can store more lithium ions and deliver higher energy density.One of the main advantages of super high-densitysilicon-carbon anode batteries is their increased energy density. This means that they can store more energy in the same volume or weight compared to traditional lithium-ion batteries. For example, a smartphone equipped with a super high-density silicon-carbon anode battery can last longer without needing to be recharged.Another advantage of these batteries is their longcycle life. Traditional lithium-ion batteries tend to degrade over time, leading to a decrease in their capacity. However, super high-density silicon-carbon anode batteries have better stability and can maintain their capacity for a longer period. This means that they can be used for a longer time before needing to be replaced.Furthermore, super high-density silicon-carbon anode batteries have faster charging capabilities. This is because the silicon-carbon composite material allows for faster diffusion of lithium ions, resulting in shorter charging times. For example, a smartwatch with a superhigh-density silicon-carbon anode battery can be fully charged in just a few minutes.In addition to these advantages, super high-density silicon-carbon anode batteries also have the potential to be used in electric vehicles (EVs). The increased energy density and long cycle life make them ideal for powering EVs, as they can provide longer driving ranges and require less frequent battery replacements.中文回答：超高密度硅碳负极电池因其高能量密度和长循环寿命而在能源存储领域备受关注。
碳精材料在压电传声器中的新发展
碳精材料在压电传声器中的新发展压电传声器是一种能将电能转化为声能的装置，广泛应用于通信、音响、汽车、航空航天等领域。
在过去的几十年中，压电传声器主要使用陶瓷材料制造。
然而，随着碳精材料的发展，压电传声器领域正在出现新的变化和创新。
碳精材料（Carbon Nanotube，简称CNT）是一种由碳原子构成的纳米管状结构材料。
它具有非常高的热导性、电导性和机械强度，以及宽频响特性和较低的噪音水平，这使得它成为压电传声器中的理想材料。
首先，碳精材料在压电传声器中具有较高的灵敏度和动态范围。
由于碳精材料的结构特性，它能够更好地转换电信号为声音，在同等电信号下产生更高的声音输出。
这意味着碳精材料制造的压电传声器可以在较低的驱动电压下实现相同的声音输出，从而降低了功耗和电能消耗。
其次，碳精材料在压电传声器中还具有更广泛的频响范围。
传统的陶瓷材料制造的压电传声器在高频段会有明显的频率衰减现象，而碳精材料则具有更好的频率响应特性，能够实现更宽广的频响范围。
这对于音频设备、通信设备等领域非常重要，使得声音的还原更加真实、细腻。
除了上述优点，碳精材料在压电传声器中还具有其他一些独特的特性。
首先，它具有较低的内部噪音水平，这可以提高声音的信噪比并减少杂音。
其次，碳精材料的制造成本相对较低，这有助于降低压电传声器的整体成本。
另外，碳精材料还具有较好的机械强度和热导性，对于一些高温、高压的环境条件下的应用具有优势。
然而，碳精材料在压电传声器中的应用还存在一些挑战和限制。
首先，尽管碳精材料有很好的热导性，但由于其纳米级的尺寸和高比表面积，在一些高功率工作环境下，仍然面临着较高的温升和热失效的问题。
其次，碳精材料的制备和整合技术仍然面临一定的挑战，尤其是在大规模生产方面。
为了克服这些挑战，研究人员正在不断努力改进碳精材料的制备工艺和整合技术。
他们探索了不同的生长方法、改变了材料的微观结构与性质，以提高碳精材料在压电传声器中的性能和可靠性。
纳米技术雨伞英语作文简单又吸引人
纳米技术雨伞英语作文简单又吸引人全文共3篇示例，供读者参考篇1Nanotechnology Umbrellas: Tiny Tech for a Rainy DayAs a student, some of my favorite inventions are the ones that make everyday life just a little bit easier and more convenient. One groundbreaking new technology that promises to do just that is nanotechnology umbrellas. These aren't your ordinary rain protectors – they utilize cutting-edge science at the nanoscale to keep you dry in an entirely new way. Let me explain what makes these nanotechnology umbrellas so awesome.First, let's talk about what nanotechnology actually is. ThePrefix "nano" means one billionth, so nanotechnology refers to manipulating matter at the molecular level – one billionth of a meter! At this incredibly tiny scale, materials can exhibit wildly different physical, chemical, and biological properties than they do at a larger scale. By controlling matter at the nanoscale, scientists can engineer new materials and products with superior and novel functionalities.So how does this mind-bending nanotechnology get integrated into umbrellas? The key is in the fabric. Traditional umbrella canopies are made from woven materials like nylon or polyester which can absorb water and feel heavy when saturated. Nanotechnology umbrellas, on the other hand, have a canopy made from a special nanofiber fabric.This incredible fabric is created by electrically charging a polymer solution and shooting it onto a grounded collector to form extremely thin fibers – way thinner than a human hair! The resulting nanofiber material has a hugely increased surface area compared to conventional fabrics, giving it some truly incredible properties.For starters, the nanofiber fabric is super hydrophobic, meaning it massively repels water. While an ordinary umbrella may absorb some water and start to feel heavy after extended use in the rain, nanotechnology umbrellas with their hydrophobic canopies remain perfectly dry on the inside and very lightweight. Water quite literally pearls and rolls right off!But the benefits don't stop there. The massive surface area of the nanofibers also gives the canopy material immense breathability. This allows nanotechnology umbrellas to provide amazing airflow and prevent that stuffy, muggy feeling yousometimes get under a regular umbrella on a hot, humid day. The evaporation of any condensation also helps to keep the inner surface dry.Additionally, the extremely fine nanofibers scatter and diffuse light more effectively than conventional fabrics. This results in a "softer" feel to the light coming through the canopy for more comfortable use, reducing glare and harsh shadows. Pretty cool capabilities for such an everyday item!Another huge perk is that these nanofiber canopies are far more durable and resistant to tearing than standard umbrella materials. The unique geometric configuration and intermolecular forces of the nanofibers make them exceptionally strong for their incredibly small diameter. Nanotechnology umbrellas can easily withstand powerful winds that would invert or destroy a regular umbrella.But perhaps the most exciting aspect of nanotechnology umbrellas is the scope for future innovations and added functionalities. Since the nanofibers can have properties tuned at the molecular level, there's huge potential for embedding advanced capabilities right into the umbrella fabric itself.For example, researchers are exploring incorporating nanomaterials that could give the canopy self-cleaningproperties through photocatalysis. Imagine an umbrella that literally cleans itself just from exposure to light! Other possibilities include building in anti-microbial nanoparticles, UV-blocking molecules for sun protection, or even simple circuits and LED lights for fun and safety.From a student's perspective, having a nanotechnology umbrella would be so incredibly useful and convenient. These things are effectively impossible to soak through, so you'd never have to worry about your books, notes, or electronics getting drenched in a downpour on the way to class. The breathability and comfort factors are also hugely appealing, as is the added durability to withstand blustery conditions.Honestly, just the core water-repelling abilities of the nanotechnology fabric alone would make these umbrellas a must-have accessory for any student. Can you imagine never having to shake out and dry a sopping wet umbrella after trudging across campus in a storm? Or not having to juggle armloads of damp textbooks and papers because your umbrella failed? With a nanotechnology umbrella, you could just stroll to class completely dry and unbothered!I'm honestly kind of giddy about how transformative an impact this nanotechnology could have on such a basic,everyday item. The capabilities enabled by nanoscience and nanoengineering are truly mind-blowing. To be able to fundamentally re-imagine and augment the properties of an ordinary umbrella material through nanoscale control is such an awesome feat of human ingenuity.At the same time, I have to admit there's a simplistic charm and beauty in the core concept of a nanotechnology umbrella. It's just taking something as basic as keeping dry and maxing out that single core function through cutting-edge science. By optimizing the fabric to be incredibly hydrophobic yet breathable, strong yet lightweight, nanotechnology achieves the quintessential, Platonic ideal of an umbrella. It's such an elegant nexus of complex science and fundamental practicality.So in summary, I'm a huge fan of nanotechnology umbrellas precisely because they represent the power of emerging nanotechnology to enhance basic, everyday items in radically useful new ways. These aren't gimmicky novelties, but rather profoundly improved re-inventions of something as simple and ubiquitous as an umbrella. Keeping bone-dry in a rainstorm while strolling comfortably is something we all want, and nanotechnology delivers that in spades.Imaging walking across campus in a torrential downpour yet arriving at your next class completely unflustered, your books and notes still crisp and dry. That's the power of nanotechnology in an umbrella! As a student constantly hustling between classes with my hands full, I can't wait for nanotechnology umbrellas to hit the mainstream. Bring on the nanotech rain protection!篇2The Incredible Potential of Nanotechnology UmbrellasAs I rushed out the door last week, umbrella in hand to brave the downpour, little did I realize the humble object sheltering me from the rain represented one of the most cutting-edge and exciting fields of science and technology. That's right - my plain old umbrella was actually a incredible example of nanotechnology in action!You might be wondering - what on earth is nanotechnology? It's a fascinating area that deals with structures, devices and materials on an unbelievably tiny scale - we're talking about materials and objects that are measured in nanometers. One nanometer is one-billionth of a meter! At that tiny size, materials can exhibit Some truly amazing properties that seem almost like science fiction.So how does nanotechnology come into play with my umbrella? Well, many modern umbrellas actually incorporate nanomaterials and nanotechnology that give them fantastic capabilities. Let me break it down for you:Waterproofing PowerThe waterproof coating on many umbrellas these days is made using nanomaterials that make the fabric extremely water-resistant. Basically, the nanoparticles create a thin coating with a very specific surface texture that causes water to bead up and roll right off instead of soaking through. It's like giving your umbrella a ninja-level water-repelling force-field!Umbrella StrengthThose thin little umbrella ribs that support the canopy and allow it to flex without breaking? Many are constructed using carbon nanotubes - cylindrical structures made from carbon atoms that are astronomically strong for their size. Thisnano-reinforcement makes the umbrella ribs incredibly tough and resistant to stress and snapping.UV ProtectionSome fancy umbrellas incorporate nanoparticles into the fabric that actually block harmful UV radiation from the sun'srays. These nanoparticles act like a filter, letting visible light through while stopping UV to protect you from sunburn and skin damage. The ultimate beach umbrella!Self-CleaningThis one is really cool - some nanotechnology umbrellas have a self-cleaning coating made from nanoparticles that react to sunlight. When the umbrella gets wet and is exposed to the sun's rays, the nanoparticle coating causes water to bead up and roll off, taking any dirt or grime with it. Your umbrella practically cleans itself!As you can see, nanotechnology has worked its way into some amazingly useful innovations for the humble umbrella. But the potential doesn't stop there - researchers are working on other incredible nanotechnology applications like:Umbrellas with changeable colors or patterns using electrochromic nanofilmsHighly rigid yet lightweight nanocomposite umbrellas for extreme conditionsUmbrellas that harvest kinetic energy from wind and rain to charge your devicesNanocoatings that eliminate odors or have antibacterial propertiesThe possibilities are endless when you can engineer materials and structures at the nanoscale level. It really opens up a new world of advanced materials and products that could change everything from clothing to cars to computers.Of course, like any new technology, nanotechnology also raises some safety and ethical concerns. Some nanoparticles could potentially be toxic or have environmental impacts that need to be studied. There are also issues around regulating nanomaterials and their use in consumer products. We'll have to keep researching and discussing the responsible development of nanotechnology.But overall, I'm incredibly excited about nanotechnology and all the incredible capabilities it can unlock. Who knew such a simple object like an umbrella could demonstrate such powerful science? The next time the rain starts pouring, I'll be sure to appreciate all the amazing nanotechnology working hard to keep me dry and protected.Aren't you glad you learned a bit about the nanotechnology wonders in your umbrella today? The future of materials science is headed for the nanoscale - and it's going to be revolutionary!篇3The Fascinating World of Nanotechnology UmbrellasHave you ever thought about how amazing it would be to have an umbrella that never gets you wet? One that can repel water like a force field? Well, thanks to cutting-edge nanotechnology, such high-tech umbrellas are becoming a reality!As a student really interested in science and emerging technologies, I find the applications of nanotechnology fascinating. Nanotechnology deals with manipulating matter on an ultra-small scale – we're talking about working with materials on the molecular or atomic level. By precisely engineering nanostructures, scientists can create materials with incredible new properties.One exciting use of nanotechnology is in developing super water-repellent or "superhydrophobic" surfaces. These surfaces are like water's worst nightmare – water droplets literally bounce right off them without being absorbed at all. It's almost like the surfaces are coated with an invisible force field that water can't penetrate.How does it work? Basically, scientists can etch or grow tiny nanostructures on surfaces like glass, metals or fabric. When arranged in the right patterns at the nanoscale level, these nanostructures trap pockets of air that make it incredibly difficult for water to stick. The water molecules basically cluster together into tight beads that easily roll off rather than spreading out and wetting the surface.Pretty cool, right? And that's exactly the principle being used to create advanced nanotechnology umbrellas andwater-resistant clothing that can keep you dry in the pouring rain. Imagine never having to worry about your umbrella leaking or your jacket getting soaked – the water will just bead up and roll right off!One company at the forefront of this "liquid umbrella" technology is ARYS, based in Spain. They use nanotechnology to create rainwear with a drivenrepel coating made up of nanoparticles that craters an air cushion to repel water. Their umbrellas are insanely water-resistant – ARYS claims theirnano-umbrellas can take on monsoon-level rainfall without letting a drop inside.Other companies like Silks are using similar nanotech to make ultra water-repellent business suit fabrics. With these suits,you could get caught in a surprise downpour and still show up at your meeting looking fresh and dry. No more lugging a soggy umbrella into the office!But nanotech water protection goes way beyond just clothing and umbrellas. Scientists are developing self-cleaning, water-proof paints, windshields, roof tiles and more using superhydrophobic nano-coatings. Imagine how much easier cleaning would be if dirt and water couldn't stick to surfaces! Buildings could stay cleaner for longer and you might never have to wash your car again in the rain.Of course, there are still some limitations with current nanotechnology water protection. The nano-surfaces can start to lose their water repellency over time as their nanostructures get worn down. Developing more durable nano-coatings is an ongoing challenge. There are also some concerns about potential environmental impacts if large amounts ofnano-materials end up being released.Still, the future possibilities of nanotechnology for water resistance are incredibly exciting. Maybe we'll soon have entire nano-fabric tents that can get soaked in a storm without letting any moisture in. Or self-drying nano-rubber that instantly shedswater and could be used for all-weather gear. Heck, we might even get self-drying nano-swimsuits one day!For me, playing with hydrophobic surfaces made from different materials was one of the coolest experiments in my chemistry class. We coated different surfaces with nano-particle solutions and got to see firsthand how water would just bead up and roll around without sticking. It really brought thenano-world and its weird water-fearing surfaces to life.I can't wait to get my hands on an advanced nanotech umbrella and test its waterproofing for myself on a rainy day. While I'll always have a soft spot for the classic wooden umbrella design, there's no denying the awesome liquid-shielding performance of these new nano-materials. An indestructible, self-drying umbrella that laughs in the face of even the worst downpour? Sign me up!Ultimately, nanotechnology umbrellas are just the start of a wave of super water-resistant products using nano-engineered surfaces. As researchers unlock more precise control over nanostructures, we'll see this technology spread into countless applications where extreme waterproofing is needed. Who knows, maybe we'll even get to experience a future where nothing can ever really get wet!For a science geek like me, that's a potential nano-future that's hard not to get excited about. Nanotechnology really is making the impossible possible when it comes to mastering and manipulating liquids. An umbrella that shrugs off monsoons may be cool, but it's just the tip of the iceberg for where this technology could lead. The nanotech revolution is here – and it's making everything water-resistant!。
The Physical Properties of Carbon Nanotubes
The Physical Properties of CarbonNanotubesCarbon nanotubes (CNTs) are one of the most fascinating materials developed in the past few decades. They are cylindrical nanostructures composed of carbon atoms arranged in a hexagonal pattern. CNTs have unique properties, including high strength and stiffness, small size, exceptional electrical conductivity, and thermal conductivity. These properties make them preferable for numerous applications in several fields, including electronics, materials science, aerospace, and biotechnology.Structure of carbon nanotubesCarbon nanotubes have two primary structural types: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). SWNTs consist of a single rolled sheet, while MWNTs contain multiple rolled sheets. The diameter of SWNTs ranges from 0.4to 2 nm, while MWNTs have diameters ranging from 2 to 100 nm. The length of CNTs is usually several micrometers, but they can be longer.Thanks to their small dimensions and tubular structure, CNTs have a high aspect ratio, which means that their length is much greater than their diameter. This aspect ratio gives CNTs their unique mechanical properties. They are exceptionally strong and stiff, with a Young's modulus three to four times higher than that of steel. Moreover, CNTs are quite resilient, and their deformation before failure is much more elevated than conventional materials, making them perfect for use in new structural materials.Electrical properties of carbon nanotubesOne of the most remarkable properties of CNTs is their electrical conductivity. They have excellent electrical properties, which means they can conduct electricity even better than copper. SWNTs are metallic or semiconducting depending on their chiral angle, while MWNTs are usually metallic.SWNTs have particular band structures, and their electrical properties depend heavily on their atomic structure. The electronic properties of CNTs make them ideal for use in electronic applications, such as field-effect transistors, diodes, and sensors. CNTs have the potential to improve the performance of transistors and other electronic devices significantly.Thermal properties of carbon nanotubesCNTs also have exceptional thermal conductivity, making them useful in thermal management materials. The thermal conductivity of CNTs is approximately seven times higher than that of copper. Moreover, CNTs are excellent heat conductors at the nanoscale, which gives them the potential to improve the efficiency of thermal management materials in electronic devices.Other physical properties of carbon nanotubesIn addition to their excellent mechanical, electrical, and thermal properties, CNTs also exhibit some other unique physical properties that make them advantageous for several applications. They are lightweight and can be dispersed in solvents, allowing them to be used in coatings, composites, and other materials.Furthermore, because of their nanoscale dimensions, CNTs have a high surface area-to-volume ratio, which makes them an effective adsorbent for gas and liquid molecules. This property makes CNTs promising candidates for gas storage and separation, as well as water purification.ConclusionCNTs are exceptional materials that have unique physical properties that lend themselves to several applications. They are lightweight, strong, stiff, and excellent electrical and thermal conductors, making them preferable for use in several fields, including electronics, materials science, and aerospace. Their physical properties make CNTs promising candidates for improving the performance of electronic devices, structural materials, and energy storage systems.。
Characterizing the properties of carbon nanotubes
Characterizing the properties ofcarbon nanotubesCarbon nanotubes (CNTs) have been the subject of extensive research due to their unique structural, electronic, mechanical, and thermal properties. CNTs are cylindrical tubes of carbon atoms, having a diameter of a few nanometers and a length of several micrometers. The walls of CNTs are made of graphene sheets that are rolled up into cylinders, resulting in a seamless tube with a hollow core. The properties of CNTs depend on their diameter, length, chirality, and defects, which can be controlled during the synthesis process.One of the most important properties of CNTs is their high aspect ratio, which is the ratio of their length to diameter. CNTs can have aspect ratios of up to 100,000, which makes them the strongest known materials, with tensile strengths up to 63 GPa. The strength of CNTs comes from their sp2 hybridized carbon bonds, which make the tubes extremely stiff and resilient. CNTs are also highly flexible, and can bend and twist without breaking, enabling them to be used in a wide range of applications.Another important property of CNTs is their electrical conductivity. CNTs are excellent conductors of electricity, with an electrical conductivity of up to 1x107 S/m, which is higher than that of copper. The conductivity of CNTs is dependent on their diameter and chirality, with smaller diameter tubes being more conductive than larger diameter tubes. The high conductivity of CNTs makes them a promising material for electronic and optoelectronic applications, such as transistors, sensors, and solar cells.CNTs also possess exceptional thermal conductivity, which is the ability to conduct heat. CNTs have an extremely high thermal conductivity of up to 3500 W/mK, which is higher than that of any other known material. The high thermal conductivity of CNTs makes them ideal for use in thermal management applications, such as heat sinks and nanocomposites.Furthermore, CNTs are highly hydrophobic, meaning that they repel water. This property makes them useful in applications where water resistance is required, such as in coatings and membranes. CNTs are also resistant to chemical corrosion and oxidation, which makes them highly durable and long-lasting.However, CNTs also have some limitations that need to be addressed. One of the major challenges is their toxicity. While CNTs have shown great promise in medical applications, such as drug delivery and cancer therapy, their potential toxicity to cells and tissues is a cause of concern. Studies have shown that CNTs can cause lung damage and inflammation in rodents, raising questions about their safety for human use. Therefore, it is important to thoroughly evaluate the toxicity of CNTs before using them in biomedical applications.In conclusion, CNTs are a remarkable material with unique and exceptional properties that make them suitable for a wide range of applications. Their high strength, electrical and thermal conductivity, hydrophobicity, and chemical stability make them a promising material in the fields of electronics, energy, and healthcare. However, their potential toxicity needs to be addressed before they can be widely used in biomedical applications. Understanding the properties of CNTs is essential for developing new applications that can exploit their exceptional properties while minimizing their drawbacks.。
碳系吸波材料
碳系吸波材料碳系吸波材料是一种能够吸收电磁波的材料，具有优异的吸波性能和广泛的应用前景。
该材料具有优异的电磁波吸收能力，可以有效地吸收高频电磁波，从而降低电磁波干扰和反射。
碳系吸波材料的种类很多，其中包括碳纤维、碳纳米管、石墨烯等。
这些材料具有独特的结构和物理特性，决定了它们具有卓越的电磁波吸收性能。
碳纤维是一种由纤维束构成的材料，具有纤维方向和横向两个方向的吸波能力。
在高频电磁波的作用下，纤维会发生极化，从而吸收电磁波。
碳纤维具有优异的机械性能和导电性能，并且可以通过材料的密度、纤维方向和纤维间距等参数来调节吸波性能。
碳纳米管是一种由碳原子构成的纳米管，具有优异的力学性能和导电性能。
碳纳米管的弯曲和受力会产生电荷转移，从而形成局部极化区域，吸收电磁波。
此外，碳纳米管的直径和长度也会影响吸波性能，其中直径越小、长度越长，吸波性能越好。
石墨烯是一种由碳原子构成的单层薄片，具有单层结构和球形电子能带结构，使其具有优异的导电性能和吸波性能。
石墨烯的单层结构使其可以调节电子结构和极化方向，从而优化吸波性能。
此外，石墨烯还具有轻质、柔韧、透明等优点，具有广泛的应用前景。
碳系吸波材料的应用领域非常广泛，包括电磁波屏蔽、雷达隐身、电磁波干扰抑制、医学成像、通信等诸多领域。
例如，碳系吸波材料可以用于电子设备的屏蔽、军事装备的隐身、医学成像的增强等领域。
此外，碳系吸波材料还可以用于太阳能电池、热电材料、超级电容器等方面的研究。
总之，碳系吸波材料是一种具有广泛应用前景的新型材料。
随着电磁波技术的不断发展和应用的不断扩展，碳系吸波材料将会在各个领域发挥重要作用，为建设绿色、低碳、智能的社会做出贡献。
纳米碳黑管黑体可吸收最高达
纳米碳黑管黑体可吸收最高达纳米碳黑管黑体可吸收最高达800字纳米碳黑管（Carbon Nanotubes, CNTs）是一种由碳原子构成的纳米材料，具有特殊的结构和性质，被广泛应用于材料科学、化学工程和生物医学等领域。
近年来，研究人员发现纳米碳黑管的黑体吸收能力非常突出，可吸收的光谱范围广泛，最高可达到极高的程度。
纳米碳黑管的黑体吸收性质是指它对各个波长的光线的吸收能力。
一般而言，物体的黑体吸收率会随着波长的增加而减小，但纳米碳黑管的黑体吸收能力却相反，它在可见光和红外光区域的吸收能力非常高。
这主要是由于纳米碳黑管的特殊结构造成的。
纳米碳黑管的结构呈现出一种中空的圆筒形，碳原子呈现出类似于蜂窝状的排列，这种结构使得纳米碳黑管能够高效地吸收光线。
纳米碳黑管的黑体吸收性质对于光电器件和太阳能电池的研究具有重要意义。
在光电器件中，纳米碳黑管的高吸收能力可以增加器件的光电转换效率，提高光电器件的性能。
同时，纳米碳黑管的高吸收能力还可以用于制备高效的太阳能电池，将太阳能转化为电能。
这对于解决能源短缺和减少环境污染具有重要意义。
此外，纳米碳黑管的黑体吸收性质还可以应用于红外成像和红外激光器的研究。
由于纳米碳黑管对红外光的吸收能力非常高，因此可以用于红外成像技术中，提高红外成像的灵敏度和分辨率。
同时，纳米碳黑管还可以用于制备红外激光器，提高激光器的输出功率和效率。
纳米碳黑管的黑体吸收能力还可以在医学领域得到应用。
纳米碳黑管的高吸收能力可以用于光热疗法，即利用光的热效应杀灭肿瘤细胞。
将纳米碳黑管注入肿瘤组织中，当激光照射到肿瘤组织时，纳米碳黑管会吸收激光的能量并将其转化为热能，从而使肿瘤组织受热，达到治疗的效果。
综上所述，纳米碳黑管的黑体吸收能力是非常突出的，可吸收的光谱范围广泛，最高可达到极高的程度。
这一特性使得纳米碳黑管在光电器件、太阳能电池、红外成像、红外激光器和医学领域等方面具有重要应用价值。
未来，随着纳米碳黑管研究的不断深入，相信它的应用领域会进一步拓展，为各个领域的发展带来更多的机遇和挑战。
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7/30/2009 14:17
Carbon nanotubes supercharge x-ray devices - R & D
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Carbon nanotubes supercharge x-ray devices
July 29, 2009 The tubes that power X-ray machines are shrinking, improving the clarity and detail of their Superman-like vision. A team of nanomaterial scientists, medical physicists, and cancer biologists at the Univ. of North Carolina has developed new lower-cost X-ray tubes packed with sharp-tipped carbon nanotubes for cancer research and treatment. The tiny technology, presented at this year's meeting of the American Association of Physicists in Medicine in Anaheim, Calif., is being developed to image human breast tissue, laboratory animals, and cancer patients under radiotherapy treatment, and to irradiate cells with more control than previously possible with conventional X-ray tubes. The X-ray machine used in a typical hospital today is powered by a "hot" vacuum tube that dates back to the beginning of the 20th century. Inside the tube, a tungsten metal filament—similar to the one that creates light in an incandescent bulb—is heated to a temperature of 1,000 degrees Celsius. The heat releases electrons, which accelerate in the X-ray tube and strike a piece of metal, the anode, creating X-rays. Sha Chang, Otto Zhou, and colleagues that University of North Carolina have developed cold X-ray tubes that replace the tungsten filament with carbon nanotubes packed like blades of tiny grass. Electrons are instantly emitted from the sharp tips of the nanotubes when a voltage is applied. "Think of each nanotube as a lightning rod on top of a building. The high electric field at the tip of the lightning rod draws the electric current from the cloud. Carbon nanotubes emit electrons using a similar principle," said Chang. The group used the nanotubes to build micro-sized scanners and image the interior anatomy of small laboratory animals. Existing X-ray technologies have difficulty compensating for the blur caused by the creature's breathing. Slow mechanical shutters that open and close to block and release the radiation are used to time X-ray pulses to correspond with breath, but their speed is inadequate for small animals because of the creatures' extremely fast breathing and cardiac motion. Chang and Zhou have demonstrated that their carbon nanotubes, which can be turned on and off instantaneously, are fairly easy to synch up to equipment that monitors small animal's breathing or heart rate. The nanotube devices may also improve human cancer imaging and treatment. CT scanners currently in use check for breast cancer by swinging a single large X-ray source around the target to take a thousand pictures over the course of minutes. Using many nanotube X-ray sources lined up in an array instead, breast imaging can be done within few seconds by electronically turning on and off each of the X-ray sources without any physical motion. This fast "tomosynthesis" imaging improves patient comfort and boosts image quality by reducing motion blur. Using 25 simultaneous beams, the team produced images of growths in breast tissue at nearly twice the resolution of commercial scanners on the market. This summer Chang's team will conduct a clinical test of a first generation nanotube-based imaging system for high-speed image-guided radiotherapy. The research image system is developed by Siemens and Xinray Inc., a joint venture between Siemens and a University of North Carolina startup company Xintech Inc. Background article .
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Carbon nanotubes supercharge x-ray devices - R & D
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