【作者】 吴昊；

【导师】 孙雪菲；

【作者基本信息】 合肥工业大学 ， 环境科学与工程， 2024， 硕士

【摘要】 随着世界经济快速发展,城市工业化进程加快,人口快速增长,人类对淡水资源的需求急剧增加。然而地球上淡水资源有限,工业化造成的环境污染又进一步减少了可用淡水资源,淡水资源短缺已造成水资源危机。在现有技术中,海水淡化是解决水资源短缺的重要手段。电容去离子技术（CDI）因绿色环保、高效率、成本低廉和无二次污染等优势受到越来越多的关注。该技术基于双电层理论通过施加电压来吸附水中的盐离子,淡化咸水。电容去离子的脱盐能力很大程度上取决于电极材料,其中碳基材料因其高比表面积和孔隙率的优点被使用于CDI中。然而,基于双电层原理的碳基材料受同离子效应限制,脱盐容量并不高。不同于吸附盐离子到表面的碳基材料,基于法拉第氧化还原反应的新型电极材料磷酸钛钠（NTP）可以将Na⁺嵌入自身内部使其具有更高的理论容量。然而磷酸盐固有的低导电性严重限制了其电化学性能和脱盐性能。基于以上研究现状和不足,本文通过杂原子掺杂和硬模板法改变孔径结构,制备氮掺杂介孔空心碳球（N-HMCS）及氮掺杂微孔碳球（CS）,并解析其孔径调控的碳基材料电化学性能和在电容去离子过程中的脱盐性能及脱盐机理;通过NTP和碳基材料复合制备了互连介孔碳包裹NTP材料,阐明了复合材料的电化学性能、脱盐性能和脱盐机理。具体研究内容如下:1.通过硬模板法和氮掺杂策略制备出具有空心结构和大量介孔的氮掺杂介孔空心碳球,解析了其脱盐性能及脱盐机理。研究结果表明空心结构和大量介孔使N-HMCS比表面积相比于CS大幅增加,达到1300.29 m² g^-1,平均孔径为8.33 nm,CS仅为1.66 nm。电化学实验表明,N-HMCS具有比CS更高的比电容和更低的电荷转移电阻。2.在CDI脱盐实验中,考察了流速、电压、溶液浓度等因素对其吸附能力的影响。结果表明N-HMCS电极脱盐容量为11.23 mg g^-1,吸附速率为0.10 mg g^-1 s^-1,吸附速率提升明显。通过吸附动力学拟合和吸附等温线拟合分析表明,N-HMCS在吸附过程中进行的是物理单层吸附。3.以钛酸四丁酯为钛源通过水热反应制备NTP前体,充分分散后使用间苯二酚-甲醛树脂将其包裹,经高温煅烧后成功制备NTP@C复合材料。经分析发现分散后的NTP@C具有与NTP完全不同的形貌结构,从互相团聚的珊瑚状改变为被互连碳层包裹的椭圆球状。该结构以薄碳壳作为双电层活性位点,NTP作为法拉第活性中心强化了NTP@C的法拉第行为。电化学分析表明,NTP@C具有高比电容和低电阻。在恒电流和恒电压操作下的脱盐实验表明,NTP@C均表现出了优异的脱盐性能。在恒电流操作下,NTP@C最高吸附量为83.68 mg g^-1,最高脱盐速率为0.17 mg g^-1 s^-1;恒压操作时,NTP@C最高吸附量为116.44 mg g^-1最高脱盐速率为0.44 mg g^-1 s^-1。但是恒电压下脱盐容量和脱盐速率的提升牺牲的是能量消耗,恒流时的能量消耗仅为0.44 k Wh kg^-1-Na Cl,是恒电压的41.90%。循环稳定性测试表明NTP@C具有优异的循环性能,在50个循环后循环保持率为89.42%。4.结合理论计算,解析了NTP@C复合材料的脱盐机理。DFT计算表明NTP（113）晶面和碳层之间结合紧密,并且有大量电子转移,其中碳层失去电子,NTP得到电子。所带来的电荷重新分配降低了NTP@C中费米能级附近的带隙,提高了NTP@C的导电性、电化学性能和脱盐性能。更多还原

【Abstract】 Over the past few decades,rapid advancements in the world economy and accelerated urban industrialization,coupled with burgeoning population growth,have led to a dramatic surge in human demand for freshwater resources.However,given the finite nature of freshwater on Earth and exacerbated by industrial pollution that further diminishes available potable water reserves,scarcity in freshwater resources has precipitated a crisis in water management.Among existing technologies,seawater desalination emerges as a principal strategy to alleviate the strain of freshwater shortages.Capacitive deionization（CDI）,characterized by its eco-friendliness,high efficiency,cost-effectiveness,and lack of secondary pollution,has garnered increasing attention in this context.This technology operates on the principle of the electric double layer,employing an applied voltage differential across two electrodes,typically composed of porous carbon materials,to adsorb salt ions from saline water.The desalination capacity of CDI largely hinges upon the properties of the electrode material,with carbon-based materials being pioneers in CDI applications due to their high specific surface areas and porosities.Nevertheless,conventional carbon materials based on double-layer capacitance are inherently limited by cation exchange selectivity and thus exhibit moderate desalting capacities.In contrast,novel electrode materials such as sodium titanate phosphate（NTP）exploit Faradaic redox reactions rather than merely surface adsorption.NTP can embed Na+ions within its structure,thereby offering a higher theoretical capacity.Despite these advantages,the intrinsic low conductivity of phosphate compounds severely constrains their electrochemical performance and desalination efficacy.Given the current research status and identified limitations,this study primarily focuses on the modification of carbon-based materials and the development of carbon-based composite materials.It proceeds by adopting strategies such as heteroatom doping and manipulation of pore size architecture,aiming to synthesize Nitrogen-doped Mesoporous Hollow Carbon Spheres（N-HMCS）and Nitrogen-doped Microporous Carbon Spheres（CS）.The work involves evaluating their electrochemical properties and investigating their desalination performance and underlying mechanisms when employed as carbon-based electrodes in capacitive deionization processes.Furthermore,the study explores the preparation of interconnected mesoporous carbon encapsulated Sodium Titanate Phosphate（NTP）composites,followed by an in-depth examination of their electrochemical performance,desalination capabilities,and the governing desalination mechanisms.The specific research contents are outlined as follows:1.Utilizing hard template methods combined with nitrogen doping strategies,this investigation successfully synthesized Nitrogen-doped Mesoporous Hollow Carbon Spheres（N-HMCS）featuring a hollow structure and abundant mesopores,which were then compared with Nitrogen-doped Microporous Carbon Spheres（CS）.The results demonstrated that the hollow configuration and extensive mesoporosity endowed N-HMCS with a significantly enhanced specific surface area of 1300.29 m² g^-1,contrasting with CS,which had a much lower value of 1.66 nm.The average pore diameter of N-HMCS was measured at 8.33 nm.Electrochemical experiments revealed that N-HMCS exhibited a higher specific capacitance and a lower charge transfer resistance compared to CS.2.In capacitive deionization（CDI）desalination experiments,the effects of flow rate,voltage,and solution concentration on the adsorption capacity of N-HMCS electrodes were investigated.Results showed that N-HMCS exhibited a significantly improved adsorption capacity of 11.23 mg g^-1 and an adsorption rate of 0.10 mg g^-1 s^-1,as deduced through kinetic and isotherm analysis,which confirmed physical monolayer adsorption.3.A precursor of NTP was synthesized through a hydrothermal reaction using titanium tetrabutylate as a titanium source,which was then uniformly dispersed and encapsulated with resorcinol-formaldehyde resin,followed by high-temperature pyrolysis to form the NTP@C composite.Characterization revealed a distinct morphology change from aggregated coral-like structures to interconnected carbon-coated ellipsoidal particles.This structure featured a thin carbon shell serving as double-layer capacitance sites and NTP acting as a Faraday active center,thereby enhancing the Faradaic behavior of NTP@C.The electrochemical data indicated high specific capacitance and low resistance for NTP@C.In CDI experiments under both constant current and voltage conditions,NTP@C demonstrated outstanding desalination capabilities.At constant current,the highest adsorption capacity reached 83.68 mg g^-1with a desalination rate of 0.17 mg g^-1 s^-1,while under constant voltage,the maximum adsorption capacity was 116.44 mg g^-1and the highest desalination rate was 0.44 mg g^-1s^-1.However,the enhanced desalination capacity and rate at constant voltage came at the expense of increased energy consumption,with energy usage at constant current being only 0.44 k Wh kg^-1-Na Cl,equivalent to 41.90%of that under constant voltage.The cyclic stability test showed that NTP@C maintained an excellent cycling performance with a retention rate of 89.42%after 50 cycles.4.The desalination mechanism of NTP@C composites was theoretically explored by Density Functional Theory（DFT）calculations.These computations highlighted a strong interaction between the NTP（113）facet and the carbon layer,accompanied by substantial electron transfer,wherein the carbon layer donates electrons to NTP.This charge reconfiguration narrowed the bandgap near the Fermi level in NTP@C,thereby boosting its electrical conductivity,electrochemical performance,and desalination efficiency.更多还原