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

该项目的重点是光催化还原二氧化碳(CO2)以生产可持续燃料和原料，即一氧化碳(CO)和甲酸。要克服与二氧化碳减排相关的热力学和动力学挑战，增强光子通量是必不可少的。生物质衍生的碳量子点(CQD)在基质中的光学性质将被优化，以生产可印刷的发光太阳能聚光器(LSC)。将通过3D打印来生产波导，其结构被设计为将入射光集中到光催化反应器。该项目的主要动机是克服与二氧化碳减排相关的挑战，通过将二氧化碳清洁地转化为燃料和原料来为循环碳经济做出贡献。由于有限的化石燃料对环境和经济气候造成的威胁，目前的能源格局正在发生变化。面对全球变暖的破坏性后果，需要创新的能源和燃料战略。二氧化碳的减少目前受到热力学和动力学挑战的限制，这些挑战反映在其自由生成能的高负值上。需要大量的能量输入来克服与高阶产物(CO2/HCOO-=-0.67V(Vs SHE)和CO2/CO=-0.52V(Vs SHE))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电流密度，电极的工作电压必须考虑到二氧化碳还原(~gt；1V)和水氧化(~0.4V)的过电位。通过组装波导，集中的光将被引导到光催化反应器，增加的光子通量可能足以有效地减少二氧化碳。将一种发光物种悬浮在主体基质聚甲基丙烯酸甲酯中，通过3D打印或缝隙模涂覆来设计和制作光波导。波导通过内反射捕获一部分发射的发光，辐射能量集中在波导的边缘。理想的发光太阳能聚光器应该具有：*宽光谱吸收*发射的光子和光催化反应器匹配的光谱响应*高的光致发光量子产率(PLQY)*最小化发射光子的再吸收-大的斯托克斯位移。尺寸、掺杂和表面官能化对发光的影响将根据这一标准进行筛选。在此基础上，研究了基于光集中系数(C)的光波导的结构设计。自下而上的合成方法为合成具有不同尺寸、形貌和表面功能的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物质，然后通过微波加热进行活化。HTC将溶解在水中的小有机分子转移到高温下衬里特氟龙的高压灭菌器中，从而产生CQD。通过与所设计的光波导进行光谱匹配，选择合适的光催化体系。成功的均相CO2还原光催化剂必须具有足够的捕光能力、快速的电荷分离和活性催化中心。通过足够快的电荷转移/迁移、高效的光子利用和能够在表面吸收二氧化碳的多个活性中心，提高了效率。光催化剂的种类很多，包括过渡金属络合物(Ru、Re、Ir、Ni、Fe、Co、CuMn)、等离子体金属纳米粒子(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).