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Instruments / Technical Area	Publication Details	Published
E01-JEM ARM 200CF	The role of carbon dots – derived underlayer in hematite photoanodes Qian Guo , Hui Luo , Jifang Zhang , Qiushi Ruan , Arun Prakash Periasamy , Yuanxing Fang , Zailai Xie , Xuanhua Li , Xinchen Wang , Junwang Tang , Joe Briscoe , Magdalena Titirici , Ana Belen Jorge Nanoscale 29 DOI: 10.1039/D0NR06139E Diamond Proposal Number(s): [22447] Open Access Show Abstract ▼ Abstract: Hematite is a promising candidate as photoanode for solar-driven water splitting, with a theoretically predicted maximum solar-to-hydrogen conversion efficiency of ∼16%. However, the interfacial charge transfer and recombination greatly limits its activity for photoelectrochemical water splitting. Carbon dots exhibit great potential in photoelectrochemical water splitting for solar to hydrogen conversion as photosensitisers and co-catalysts. Here we developed a novel carbon underlayer from low-cost and environmental-friendly carbon dots through a facile hydrothermal process, introduced between the fluorine-doped tin oxide conducting substrate and hematite photoanodes. This led to a remarkable enhancement in the photocurrent density. Owing to the triple functional role of carbon dots underlayer in improving the interfacial properties of FTO/hematite and providing carbon source for the overlayer as well as the change in the iron oxidation state, the bulk and interfacial charge transfer dynamics of hematite are significantly enhanced, and consequently led to a remarkable enhancement in the photocurrent density. The results revealed a substantial improvement in the charge transfer rate, yielding a charge transfer efficiency of up to 80% at 1.25 V vs. RHE. In addition, a significant enhancement in the lifetime of photogenerated electrons and an increased carrier density were observed for the hematite photoanodes modified with a carbon underlayer, confirming that the use of sustainable carbon nanomaterials is an effective strategy to boost the photoelectrochemical performance of semiconductors for energy conversion.	Sep 2020
B18-Core EXAFS E01-JEM ARM 200CF E02-JEM ARM 300CF	Pt single-atoms supported on nitrogen-doped carbon dots for highly efficient photocatalytic hydrogen generation Hui Luo , Ying Liu , Stoichko D. Dimitrov , Ludmilla Steier , Shaohui Guo , Xuanhua Li , Jingyu Feng , Fei Xie , Yuanxing Fang , Andrei Sapelkin , Xinchen Wang , Maria-magdalena Titirici Journal Of Materials Chemistry A 48 DOI: 10.1039/D0TA04431H Diamond Proposal Number(s): [22447, 20116] Show Abstract ▼ Abstract: Single-atom catalysis has become the most active new frontier in energy conversion applications due to its remarkable catalytic activity and low material consumption. However, the issue of atom aggregation during the synthesis process or catalytic reaction must be overcome. In this work, we have developed a one-step photo-deposition process to fabricate Pt single-atom catalysts (SACs) on nitrogen doped carbon dots (NCDs). The Pt–NCDs were then hybridized with TiO2 to achieve high hydrogen generation activity and to understand the fundamentals at the Pt/NCD/TiO2 interface. The synergistic effect of Pt SAC and NCDs with maximized atomic efficiency of Pt and improved charge transfer capability provides a new strategy to rationally design a multi-scale photocatalyst structure to achieve high H2 evolution efficiency. The facile synthesis process also holds great potential for various applications such as electrocatalysis, heterogeneous catalysis and drug delivery, providing a promising way to reduce the high cost of noble metals.	Jul 2020
E01-JEM ARM 200CF	Nitrogen-doped carbon dots/TiO2 nanoparticle composites for photoelectrochemical water oxidation Hui Luo , Stoichko D. Dimitrov , Matyas Daboczi , Ji-seon Kim , Qian Guo , Yuanxing Fang , Marc-antoine Stoeckel , Paolo Samorì , Oliver Fenwick , Ana Belen Jorge Sobrido , Xinchen Wang , Maria-magdalena Titirici Acs Applied Nano Materials DOI: 10.1021/acsanm.9b02412 Diamond Proposal Number(s): [22447] Show Abstract ▼ Abstract: Carbon dots on photoactive semiconductor nanomaterials have represented an effective strategy for enhancing their photoelectrochemical (PEC) activity. By carefully designing and manipulating carbon dots/support composite, a high photocurrent could be obtained. Currently, there is not much fundamental understanding of how the interaction between such materials can facilitate the reaction process. This hinders the wide applicability in PEC devices. To address this need of improving the fundamental understanding of carbon dots/semiconductor nanocomposite, we have taken the TiO2 case as a model semiconductor system with nitrogen-doped carbon dots (NCDs). We present here with in-depth investigation of the structural hybridization and energy transitions in the NCDs/TiO2 photoelectrode via high-resolution scanning transmission microscopy (HR-STEM), electron energy loss spectroscopy (EELS), UV-Vis absorption, electrochemical impedance spectroscopy (EIS), Mott-Schottky (M-S), time-correlated single photon counting (TCSPC) and ultra-violet photoelectron spectroscopy (UPS), which shed some light on the charge transfer process at the carbon dots and TiO2 interface. We show that N doping in carbon dots can effectively prolong the carrier lifetime, and the hybridisation of NCDs and TiO2 is able not only to extend TiO2 light response into the visible range but also to form heterojunction at the NCDs/TiO2 interface with properly aligned band structure that allows a spatial separation of the charges. This work is arguably the first to report the direct probing of the band positions of carbon dots-TiO2 nanoparticle composite in a PEC system for understanding the energy transfer mechanism, demonstrating the favourable role of NCDs in the photocurrent response of TiO2 for water oxidation process. This study reveals the importance of combining structural, photophysical and electrochemical experiments to develop a comprehensive understanding of the charge injection/electronic communication between the carbon dots and their current collectors or catalyst supports.	Mar 2020
E01-JEM ARM 200CF	Manipulating the optical properties of carbon dots via fine tuning their structural features Hui Luo , Nikolaos Papaioannou , Enrico Salvadori , Maxie Roessler , Gereon Ploenes , Ernst R. H. Van Eck , Liviu Tanase , Jingyu Feng , Yiwei Sun , Yan Yang , Mohsen Danaie , Ana Jorge Sobrido , Andrei Sapelkin , James Durrant , Stoichko D. Dimitrov , Maria-magdalena Titirici Chemsuschem DOI: 10.1002/cssc.201901795 Diamond Proposal Number(s): [17587] Show Abstract ▼ Abstract: As a new class of sustainable carbon material, the term “carbon dots” represents an “umbrella term” as there are many types of materials included. We employ a broad range of techniques to develop understanding on hydrothermally synthesized carbon dots and show how fine tuning the structural features using simple reduction/oxidation reactions can drastically affect their excited state properties. Structural and spectroscopic studies found that photoluminescence originates from direct excitation of localized fluorophores involving oxygen functional groups, while the excitation at graphene‐like features leads to ultrafast phonon‐assisted relaxation and largely quenches the fluorescent quantum yields. This is arguably the first to identify the dynamics of photoluminescence including Stokes’ shift formation, allowing us to fully resolve the relaxation pathways in these carbon dots. The comprehensive investigation sheds light on how understanding the excited state relaxation processes in different carbon structure is crucial for tuning the optical properties for any potential commercial applications.	Aug 2019

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