人工光合作用

人工光合作用是模拟自然界的光合作用过程,设计制备人工光催化体系,以达到高效吸收、转化和储存太阳能的目的。本文从自然界的光合作用过程出发,综述了国内外人工光合作用的最新研究进展。从基本原理、常用体系和能量转换效率等方面入手,系统介绍了两种人工光合作用体系:模拟自然光合作用系统的超分子和无机半导体光催化体系。在此基础上,分析当前研究中存在的问题,并提出改进能量转换效率的可能对策,最后评述了人工光合作用的发展趋势和应用前景。     

基于无机材料-微生物复合的半人工光合作用

基于无机材料-微生物复合半人工光合系统是在自然光合作用和人工光合作用研究进展到一定阶段,为克服各自的缺陷,实现微生物与无机材料优势互补而发展出来的一种研究体系。该体系的主要优势是将微生物的催化选择性与无机材料的光响应性结合起来,旨在解决人工光合作用体系催化选择性差的问题。目前,可以通过光催化剂-微生物复合和电极-微生物复合来实现基于无机材料-微生物复合的半人工光合作用。本文围绕基于无机材料-微生物复合的半人工光合作用,依次从半人工水氧化、半人工光合还原和材料-微生物界面等方面做了系统的阐述,重点介绍基于电极-微生物复合的半人工光合体系研究进展,对基于无机材料-微生物复合的半人工光合作用的领域现状做了分析和总结,并且对该领域的前景进行了展望。     

光致热效应促进的全光谱光催化CO2还原

以半导体等为催化剂,在太阳能作用下将CO2和H2O转化为可再生燃料与氧气的“人工光合作用”有望同时解决目前面临的严峻能源和环境问题,因而备受关注.但半导体催化剂光谱响应范围较窄、表面反应动力学缓慢,从而导致目前仍无法获得可观的太阳能-燃料转换效率.已有很多研究采用了晶面调控、元素掺杂和异质结构建等方法,以提高半导体光催化剂的太阳能-燃料转换效率,但效果仍不令人满意,主要原因是半导体光催化剂很难在吸收带边-氧化还原能力和活性-稳定性这两种关系中取得较好的平衡.此外,光催化反应中的动力学也是主要问题之一,尤其在人工光合作用反应中,CO2还原半反应和H2O氧化半反应的动力学均较困难, 这已成为共识, 而解决这个问题, 将有助于我们从一新的角度理解光催化过程, 从而提升光催化反应性能.本文以Au NP/金红石为模型催化剂, 纯金红石为参照, 证明了存在太阳光中的红外光致热和可见光诱导的等离激元热效应等两类光致热效应, 它们均可以促进人工光合作用反应. 研究发现, 人工光合作用反应与其他许多化学反应一样, 表观活化能为正, 从而表明动力学因素在该反应中起着重要作用. 此外, 根据不同反应温度下的结果, 通过计算Au NP/金红石和纯金红石上生成CO和CH4的表观活化能, 发现在这二种样品上CH4的表观活化能均高于CO, 这就从动力学上解释了热力学上更容易得到的CH4在绝大多光催化CO2还原反应中的产率均低于CO. 此外, 无论是对于CO还是CH4, Au NP/金红石的催化表观活化能均低于纯金红石的. 因此, 本文从实验上提供了贵金属纳米粒子改善人工光合作用动力学的实验证据,并从动力学角度解释了人工光合作用反应中的活性和选择性问题. 本研究证明了动力学因素在光催化反应, 尤其是人工光合作用反应中的重要性, 并提出了从动力学角度提升人工光合作用反应的新方法, 即利用太阳光的光致热效应加速反应, 这不仅有助于提升太阳能转化效率, 也有望减少反应设备成本, 从而促进其大规模应用.     

光致热效应促进的全光谱光催化CO_2还原（英文）

以半导体等为催化剂,在太阳能作用下将CO_2和H_2O转化为可再生燃料与氧气的"人工光合作用"有望同时解决目前面临的严峻能源和环境问题,因而备受关注.但半导体催化剂光谱响应范围较窄、表面反应动力学缓慢,从而导致目前仍无法获得可观的太阳能-燃料转换效率.已有很多研究采用了晶面调控、元素掺杂和异质结构建等方法,以提高半导体光催化剂的太阳能-燃料转换效率,但效果仍不令人满意,主要原因是半导体光催化剂很难在吸收带边-氧化还原能力和活性-稳定性这两种关系中取得较好的平衡.此外,光催化反应中的动力学也是主要问题之一,尤其在人工光合作用反应中, CO_2还原半反应和H_2O氧化半反应的动力学均较困难,这已成为共识,而解决这个问题,将有助于我们从一新的角度理解光催化过程,从而提升光催化反应性能.本文以AuNP/金红石为模型催化剂,纯金红石为参照,证明了存在太阳光中的红外光致热和可见光诱导的等离激元热效应等两类光致热效应,它们均可以促进人工光合作用反应.研究发现,人工光合作用反应与其他许多化学反应一样,表观活化能为正,从而表明动力学因素在该反应中起着重要作用.此外,根据不同反应温度下的结果,通过计算AuNP/金红石和纯金红石上生成CO和CH4的表观活化能,发现在这二种样品上CH4的表观活化能均高于CO,这就从动力学上解释了热力学上更容易得到的CH4在绝大多光催化CO_2还原反应中的产率均低于CO.此外,无论是对于CO还是CH4, AuNP/金红石的催化表观活化能均低于纯金红石的.因此,本文从实验上提供了贵金属纳米粒子改善人工光合作用动力学的实验证据,并从动力学角度解释了人工光合作用反应中的活性和选择性问题.本研究证明了动力学因素在光催化反应,尤其是人工光合作用反应中的重要性,并提出了从动力学角度提升人工光合作用反应的新方法,即利用太阳光的光致热效应加速反应,这不仅有助于提升太阳能转化效率,也有望减少反应设备成本,从而促进其大规模应用.     

人工光合作用

光合作用将太阳能储存在化学反应中,是绿色高效的能量转换途径。模拟自然光合作用系统活性中心的结构和功能,实现小分子物质(H₂O、CO₂、N₂等)中惰性化学键的活化转化,对于解决能源和环境等问题具有重要意义。本文综述了人工光合作用在水分解、二氧化碳及氮气还原领域取得的重要进展,分析了相关光化学转换体系的设计思路和工作原理,并对人工光合作用面临的挑战和未来发展方向进行讨论。     

仿生模拟催化在新能源与CO2光催化还原方面的研究及应用

人工光合成是受到植物光合作用启发而兴起的前沿科研领域,对于新型能源的探索具有重要的研究价值。本文首先从植物光合作用的原理和关键化学过程出发,介绍了人工光合成体系的构建原则与方法,着重阐述了过渡金属配合物光催化剂在人工光合成各半反应(水的光催化氧化分解与CO2的还原转换)中的应用。其次,分析整理了近期国内外重点研究的过渡金属配合物光催化剂的种类,评价了各类过渡金属配合物光催化剂的结构特征及由其组成的不同光催化体系的特点和催化性能的差别,讨论了部分光催化剂的催化机理及优化其催化性能的方法。最后,展望了过渡金属配合物光催化剂在人工光合成领域的研究前景及发展方向。     

从自然光合作用到人工光合作用

光合作用的光系统Ⅱ(PSⅡ)是自然界唯一能够利用太阳能高效、安全将水裂解,获得电子、质子并释放出氧气的生物系统,对其结构和微观原理的研究一直是光合作用研究领域的热点和难点.2011年以来PSⅡ的晶体结构研究取得突破性进展,其核心色素、辅基及水裂解催化中心(OEC)的空间结构均已被揭示,这为人工光合作用研究提供了重要的依据.最近本课题组成功合成出结构和理化性能均与生物OEC类似的人工Mn_4Ca-簇合物.这些进展为今后人工光合作用探索利用太阳能和水制备清洁能源的研究奠定了重要基础.本文对生物光系统Ⅱ和人工光合作用的最近研究进展进行了评述.     

我国化学热力学与热分析的研究进展(2012-2013)

本文简要综述了2012~2013年化学热力学与热分析学科在绿色溶剂体系化学热力学、材料热力学、生物热化学、胶体化学热力学、超分子化学热力学以及新型热分析仪器等方面取得的研究成果。共引用参考文献52篇。     

错配核酸的研究进展

本文通过介绍多种错配核酸的结构及其热力学性质，详细地描述了非Watson-Crick配对核酸的最新进展。这方面的研究有利于阐明生物体内错配核酸的识别修复机理及核酸二级结构的预测，并为合理设计新的人工核酸修复酶提供了理论基础。     

直接乙醇燃料电池中乙醇电氧化过程的热力学和动力学考虑

从热力学和动力学角度讨论了质子交换膜燃料电池中的乙醇电氧化过程.理论计算得出直接乙醇燃料电池比乙醇重整质子交换膜燃料电池具有较高的有效能效率.从热力学分析可知,温度低于100℃时乙醇完全氧化的最大转化率仅为14%.从动力学角度考虑,PtSn/C催化剂对乙醇电氧化具有较高的催化活性,但仍不能使乙醇发生完全电氧化.热力学和动力学分析表明,操作温度是影响直接乙醇燃料电池性能的关键因素,它对开发新型催化剂和电解质膜材料提出了新的要求.     

Comparative thermodynamic analysis of a hybrid refrigeration system for promotion of cleaner technologies

This article presents a comparative thermodynamic analysis based on numerical methods for a hybrid refrigeration system suitable to operate as vapour absorption system (VA), vapour compression–absorption system (VCA) and vapour compression system (VC). The working fluid employed for the first two systems is ammonia–water and it is pure ammonia in case of the third system. The system is being powered by waste energy and conventional energy depending on the mode of operation. The effect on performance parameters like COP and exergy efficiency during all modes of operation has been evaluated by keeping the uniform parametric conditions like condenser temperature (40 °C) and evaporator temperature (5 °C) for all the modes of operation. The effect of ambient temperature on the exergy loss in each component of the different modes of operation have also been evaluated and discussed. The results obtained indicate that COP and exergy efficiency for VCA mode initially increases and then decreases whereas for VA and VC mode the COP and exergy efficiency decreases with condenser temperature. The analysis also reveals that with the variation in evaporator temperature the COP and exergy efficiency for VC mode increases whilst for VA and VCA mode the COP shows a slight increase whereas exergy efficiency decreases. The variation of exergy efficiency and exergy loss in different components with condenser and evaporator temperature shows that exergy efficiency is found to be the highest in VC mode whereas the lowest in VCA mode for both the temperature variations. The variation of compressor work and exergy loss in compressors with evaporator and condenser temperature shows that compressor work and exergy loss is lesser for VCA mode when compared to VC mode.     

Evacuating liquid coatings from a diffusive oblique fin in micro-/mini-channels

The present work emphasis on to estimate the theoretical findings of energy and exergy analysis of biodiesel fueled with diesel on variable compression ratio engine at various combinations of fuel blend at different compression ratios. This study aims to identify the optimum engine settings based on compression ratio and biodiesel blends. The engine is operated with methyl esters of rubber seed oil and its 20, 40, 60 and 80% blends with diesel on volume basis. The compression ratio is varied from 18:1 to 22:1 at five compression ratios at 80% load in 3.5 kW, 1500 rpm, single cylinder water-cooled direct injection engine. The variables analyzed are energy and exergy potential of fuel input, shaft work, cooling water, maximum pressure, heat release rate, exergy destruction, brake-specific energy consumption, brake thermal efficiency, second law efficiency, entropy generation, exhaust gas temperature and various emissions. It is observed that the combination of CR 20, B20 and B40 at 80% load gives a better performance in thermodynamic analysis of methyl esters of rubber seed oil blended with diesel in VCR engine.

     

Photochemical conversion and storage of solar energy

The possibilities for the photochemical storage of solar energy are examined from the standpoint of maximum efficiency and mechanism. Loss factors are considered for a general endergonic photochemical reaction and it is concluded that a realistic maximum solar energy storage efficiency for any photochemical system is 15–16%. The natural process of photochemical solar energy storage, namely, photosynthesis, is analyzed and it is found that the maximum solar energy storage efficiency of photosynthesis is 9.5 ± 0.8%. Kinetic and thermodynamic limitations on a photochemical energy storage process are identified and it is shown that the desirable production of hydrogen and oxygen from water probably cannot be sensitized with visible light if only one photochemical step is employed. However, by analogy with the mechanism of photosynthesis, two photochemical reactions operating in series permit a full utilization of the photochemically active part of the solar spectrum. A possible scheme is described and analyzed as to its possibilities and potential difficulties. Finally, some practical considerations are presented not only for the photochemical production of hydrogen but also for solid state photovoltaic devices.     

Thermodynamic analysis of a direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22

The thermodynamic analysis of direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22 was carried out under the metrological conditions of Calicut, India. A prototype of a DXSAHP system consists of a compressor, an air-cooled condenser with evaporator–collector and thermostatic expansion valve. The experiments were carried during the winter months of 2016. The artificial intelligence technique artificial neural network integrated with genetic algorithm model was presented to predict energy and exergy performance of a system. The energy performance ratio of a system was found to be 5.75% higher and reduced heating capacity of about 6.8% when compared to R22. Similarly, the second law analysis (exergy analysis) of a total system working with R290 was found to be better when compared to baseline refrigerant. The selected alternative working fluid is a hydrocarbon and has zero ozone depletion and negligible global warming potential. Hence, R290 can be used as a drop-in substitute for R22 in DXSAHP systems.

     

Thermal behavior of carboxymethyl cellulose in the presence of polycarboxylic acid crosslinkers

Journal of Thermal Analysis and Calorimetry - In this paper, the thermodynamic (energy and exergy) analysis and water analysis of a modified solar still augmented with copper tube heat exchanger in...     

Exergy analysis on eco-industrial systems

1 Introduction Ecological industry is to realize the harmony de- velopment between economy and environment by planning industrial systems according to material cy- cle in the natural ecological system. It got grown rap- idly both in theories and practices since the 1990s[1,2]. Many countries including China have applied indus- trial ecology to industrial practices. It is deeply recog- nized that developing ecological industry and advanc- ing on a new industrialization mode is an important way…     

Thermal analysis of salts from 4-nitrophenol and aliphatic amines

In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.

     

Experimental study and performance evaluation of various cook stove models based on energy and exergy analysis

This article presents the experimental study and comparative performance evaluation of four types of cook stoves using energy and exergy analysis. Analysis of four different types of cook stove models viz. Envirofit, Mangla, Harsha and Vikram were selected and the water boiling test has been carried out. The suitable biomass available from the local market was prepared in the proper size as described in the Bureau of Indian Standards (BIS) and has been used as the fuel for cook stove in this experimental study. The aluminium pots of proper capacity as per BIS standard have been used for different cook stoves. The data from the experiments was collected and evaluated for the energy and exergy efficiencies for different models. Based on the data analysis it is found that the exergy efficiency is much lower than that of the energy efficiency for all the four models. It is also found that the both the efficiencies of Envirofit model are found to be higher than those of other models studied here.     

Comparative experimental study of solar cookers using exergy analysis

This communication presents the comparative experimental study of solar cookers based on the exergy analysis. In this study two different types of solar cookers viz. paraboloid type and box type have been evaluated using exergy analysis. The experiments have been carried out with cookers filled with different volume of water viz. one and two liters along with the suitable quantity of rice. Data of temperatures and solar radiation have been measured for different food stuff on clear sky day of the month. It is found that the exergy efficiency increases as the volume of water increases, however, the exergy efficiency of paraboloid solar cooker is found to be higher than that of the box-type solar cooker for all the cases mentioned above. However, it is also found that the exergy efficiency vary with the cooking stuff and water which is due to the fact that the requirement of heating vary with the food stuff.     

Evaluating of the exergy efficiency of the silicon production process using artificial neural networks

Abstract

In this study, the extent and effect of fluctuations in the proximate composition of carbon materials on specific electrical energy consumption and exergy efficiency in the production process of silicon furnaces was evaluated using a novel artificial neural network approach. The neural network architecture 4-5-2 with hyperbolic sigmoid in the hidden layer and linear function in the output layer was used. The proposed model successfully predicts the values of the specific electrical energy consumption and the exergy efficiency through the correlation coefficient (0.93 and 0.87) of the actual and predicted values for the various proximate compositions of carbon materials. The interactive effects of components in the mixtures of carbon materials were investigated via contour diagrams. Fixed carbon had the biggest impact on electrical energy consumption and exergy efficiency in the mixtures of carbon materials, followed by moisture. Compared with volatile matter from woodchips without any pretreatment, volatile matter from petcoke, charcoal, and coal had a significant effect on electrical energy consumption and exergy efficiency.