Closing the carbon loop with biomass-waste derived carbon quantum dots

摘要本项目将重点研究光催化还原二氧化碳（CO2）以生产可持续的燃料和原料，即一氧化碳（CO）和甲酸。为了克服与CO2减少相关的热力学和动力学挑战，光子通量的增强是必不可少的。生物质衍生的碳量子点（CQD）在基质中的光学特性将被优化，以产生可印刷的发光太阳能集中器（LSC）。波导将通过3D打印生产，其结构设计为将入射光集中到光催化反应器。该项目的总体动机是克服与CO2减排相关的挑战，通过将CO2清洁转化为燃料和原料，为循环碳经济做出贡献。目前的能源景观正在发生变化，以应对有限的化石燃料对环境和经济气候造成的威胁。面对全球变暖的破坏性后果，需要创新的能源和燃料战略。二氧化碳的还原目前受到热力学和动力学挑战的限制，这些挑战反映在其形成自由能的高负值上。需要大的能量输入来克服与高阶产物（CO2/HCOO- = -0.67 V（相对于SHE）和CO2/CO = -0.52 V（相对于SHE））的形成相关的高过电位。为了产生动力学上有利的反应所需的足够的电流密度;电极的工作电压必须考虑CO2还原（> 1 V）和水氧化（~ 0.4 V）的过电位。通过波导的组装，集中的光将被导向光催化反应器，增加的光子通量可以足以有效地减少CO2。发光物质将悬浮在基质聚（甲基丙烯酸甲酯）中，波导将通过3D打印或狭缝模涂设计和生产。波导通过内反射捕获一部分发射的发光，并且辐射能量集中在波导的边缘处。理想的发光太阳能聚光器应具有：* 宽光谱吸收 * 发射光子和光催化反应器的匹配光谱响应 * 高光致发光量子产率（PLQY）* 最小化发射光子的再吸收-大斯托克斯位移将研究CQD的光致发光（PL）特性。尺寸，掺杂和表面功能化对PL的影响将根据这一标准进行筛选。然后将研究波导的结构设计对光的聚集因子（C）的影响。自下而上的合成方法为合成具有不同尺寸、形态和表面官能度的CQD提供了更大的灵活性。微波热解和水热碳化（HTC）将用于生产CQD。通过微波热解，生物质被热化学分解成碳质材料，然后可以通过微波加热来活化。HTC将有机小分子溶解在水中，然后转移到聚四氟乙烯衬里的高压釜中，在高温下生产CQD。通过与所设计的光波导进行光谱匹配，选择合适的光催化系统。用于均相CO2还原的成功的光催化剂必须显示足够的光捕获、快速的电荷分离和活性催化位点。通过足够快的电荷转移/迁移、有效的光子利用和能够表面吸收CO2的多个活性位点来促进效率。存在各种感兴趣的光催化剂，即过渡金属络合物（Ru、Re、Ir、Ni、Fe、Co、Cu Mn）、等离子体金属纳米颗粒（Au、Ag）和金属有机骨架（MOF）。

Abstract This project will focus on the photocatalytic reduction of carbon dioxide (CO2) to produce sustainable fuels and feedstock, namely carbon monoxide (CO) and formic acid. To overcome the thermodynamic and kinetic challenges associated with CO2 reduction the enhancement of photon flux is essential. The optical properties of biomass-derived carbon quantum dots (CQDs) in a host matrix will be optimised to produce a printable luminescent solar concentrator (LSC). Waveguides will be produced by 3D printing with the architecture being designed to concentrate incident light towards a photocatalytic reactor. The overarching motivation of this project is to overcome the challenges associated with CO2 reduction to contribute to the circular carbon economy by the clean conversion of CO2 to fuels and feedstocks. Project description The current energetic landscape is changing in response to the threat that finite fossil fuels pose to the environmental and economic climate. In the face of the devastating consequences of global warming, innovative energy and fuel strategies are required. The reduction of CO2 is currently limited by the thermodynamic and kinetic challenges reflected by the high negative value of its free energy of formation. A large energy input is required to overcome the high overpotential associated with the formation of higher order products (CO2/HCOO- = -0.67 V (vs SHE) and CO2/CO = -0.52 V (vs SHE)). To yield sufficient current densities required for kinetically favourable reactions; the operating voltage of the electrode must account for the overpotential for both the reduction of CO2 (> 1 V) and water oxidation (~ 0.4 V). By the assembly of waveguides, concentrated light will be directed towards a photocatalytic reactor, the increased photon flux could be sufficient to efficiently reduce CO2. A luminescent species will be suspended in the host matrix poly(methyl methacrylate), waveguides will be designed and produced by 3D printing or slot die coating. Waveguides trap a fraction of the emitted luminescence by internal reflection and the radiation energy is concentrated at the edge of the waveguide. The ideal luminescent solar concentrator should have:* broad spectral absorption * matched spectral response of the emitted photons and photocatalytic reactor* a high photoluminescence quantum yield (PLQY) * minimized re-adsorption of emitted photons - large Stokes shift The photoluminescent (PL) properties of CQDs will be investigated. The effect of size, doping and surface functionalisation on PL will be screened against this criterion. Then the architectural design of waveguides on the concentration factor (C) of light achieved will be investigated. Bottom-up synthesis methods provide greater flexibility to synthesise CQDs with varied size, morphology and surface functionality. Microwave pyrolysis and hydrothermal carbonisation (HTC) will be used to produce CQDs. By microwave pyrolysis, biomass is thermochemically decomposed to carbonaceous material which then can be activated by microwave heating. HTC takes small organic molecules dissolved in water and by transfer to a Teflon-lined autoclave at high temperature CQDs are produced. A suitable photocatalytic system will be selected by spectral matching with the designed waveguide. A successful photocatalyst for homogenous CO2 reduction must display adequate light harvesting, rapid charge separation and active catalytic sites. Efficiency is facilitated by sufficiently fast charge transfer/ migration, efficient photon utilisation and multiple active sites capable of surface absorption of CO2. There are a variety of photocatalysts that are of interest namely transition metal complexes (Ru, Re, Ir, Ni, Fe, Co, Cu Mn), plasmonic metal nanoparticles (Au, Ag) and metal-organic frameworks (MOFs).