Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Constructing liquid marble as particle-assembled microdroplet for multiplex sensing and reaction modulation/monitoring

Liquid marbles are particle-assembled microdroplet platforms that have garnered paramount importance as both microsensor and microreactor owing to their excellent robustness, highly customizable properties as well as need of minute sample/reaction volumes. However, three main challenges relevant to the field have been identified; (1) limitation of molecular sensing to a single fluid phase, (2) invasive and ex-situ reaction monitoring techniques and (3) lack of heating mechanism and active mass transportation system for reaction control. The objectives of my thesis therefore aim to address these limitations, empowering liquid marbles as efficient and multifunctional micro-sensors/reactors applicable in broad scientific/technological fields such as nanotechnology, green processes, and synthetic chemistry. In chapter 2, we demonstrate the fabrication of plasmonic liquid marble prepared using Ag particles as a multiplex SERS sensor capable of identifying and quantifying analytes present across an immiscible liquid-liquid interface. Such plasmonic liquid marble is further exploited as a microreactor-sensor hybrid in chapter 3 for the rapid and on-site read-out of reaction events within the microreactor at the molecular-level. Chapter 4 and 5 mainly focus on the enhancing and tuning of reaction kinetics using liquid marble-based microreactors. For chapter 4, we apply graphene liquid marble as photothermal-active miniature reactor to remotely control its temperature for direct kinetic modulation on the encapsulated reaction. In chapter 5, we demonstrate the spinning of a magnetically-active liquid marble to induce an active mass transportation system within the enclosed 3D microdroplet. Such spinning phenomenon imparts a spiral acceleration of enclosed molecules towards the exterior encapsulating shell for improved catalytic performance and controllable reaction dynamics. Lastly, I conclude my thesis with a summary of my four-year research works and provide an outlook for continuous and significant progress in this emerging field.​Doctor of Philosophy (SPMS

Applying nanoparticle@MOF interface to activate and monitor chemical reactions at ambient conditions

Gas reactions are prevalent in the industry and in our everyday lives. However, these processes are typically slow and difficult to monitor owing to the low molecular concentration of gas. While gas reactions and detections can be achieved at high temperatures and pressures, these operations are unsustainable because they demand a huge amount of energy input. Here, we achieve efficient gas-based reactions and sensing at ambient conditions by concentrating gas molecules at the interface formed between a functional solid and a metal-organic framework (MOF). Our strategy utilizes the excellent gas sorptivity of MOF to continuously accumulate gas molecules onto functional solid surfaces with plasmonic and/or catalytic properties. Using surface-enhanced Raman spectroscopy (SERS), we are able to directly observe the concentration of gas molecules into a quasi-condensed phase at the nanoscale solid@MOF interface, even at ambient operations.[1] We further leverage on this unique molecular phenomenon to activate a CO2 carboxylation of an arene that is otherwise inert at 1 atm and 298 K.[2] Our solid@MOF design thus offers enormous opportunities in relevant fields including chemistry, heterogeneous catalysis, greenhouse gases removal and gas-to-fuel conversions.Published versio

Development of an expert system to minimize energy production cost

In this project, a prototype real-time expert system is developed to monitor the performance of a stream power plants

Knowledge-based systems for the fault diagnosis of mechanical and thermal systems

The focus of the dresearch efforts described in this report however, is on the development of computer-based aids for the fault diagnostic task.ARP-M-19-8

Achieving milliwatt level solar-to-pyroelectric energy harvesting via simultaneous boost to photothermal conversion and thermal diffusivity

Pyroelectric technology is an effective strategy to harvest ambient waste heat into electrical energy to tackle global energy and environmental crises. However, current pyroelectric generators are often limited by low effective power output. Herein, we develop a non-contact, solar-induced pyroelectric nanogenerator (S-PENG) which integrates Au@CNT as solar-thermal layer and polarized PVDF film as pyroelectric layer. The high thermal conductivity of CNT accelerates the heat transfer process, while its strong solar-thermal effect can be coupled with the plasmonic effect of Au nanoparticles to obtain a hybrid ensemble with superior light absorption and conversion. Notably, the solar-thermal temperature of Au@CNT/PVDF rapidly increases from 38 °C to 79.6 °C within 30 s under sunlight irradiation, with a corresponding temperature change rate reaching a maximum of 14.3 °C/s. The drastic temperature fluctuation is crucial to improve the output performance of our S-PENG. More importantly, our S-PENG successfully generates a notable 1.5 mW/m2 output power under a 200 MΩ load (at 20 ℃), thereby overcoming the performance bottleneck of traditional S-PENG designs with micro-watt power output. Our design offers a promising approach to efficiently utilize green solar energy to alleviate our demand on limited energy resources and reduce carbon footprint.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversitySubmitted/Accepted versionThe authors gratefully acknowledge financial support from the National Natural Science Foundation of China (21922202, 21673202 and22073080), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (21KJB430049) and Scientific research and practical innovation program (SJCX21_1569; 2021–06-11). H.K.L. thanks the funding supports from Singapore Ministry of Education (RS13/20 and RG4/21), Agency for Science, Technology and Research, Singapore (A*STAR, A2084c0158), Center of Hydrogen Innovation, National University of Singapore (CHI-P2022–05), and Nanyang Technological University start-up grants

Self-polarized CNT/PVDF nanocomposites with ultra-high β phase achieved via water induction for efficient piezo-catalysis

Polyvinylidene fluoride (PVDF) is promising for piezo-catalytic applications owing to its excellent biocompatibility, flexibility, and durability. However, it is limited by weak electroactivity originating from its intrinsically low β piezoelectric phase content ( 6-fold and > 19-fold better than standalone self-polarized PVDF (i.e., without CNT content) and emerging piezo-catalytic designs, respectively. This study offers a unique approach for designing PVDF-based piezo-catalyst to expedite mechanically-driven catalysis towards practical applications.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityHaitao Li thanks the financial support from Natural Science Foundation of Shandong Province (ZR2023QF019), Jiangsu Higher Education Institutions of China (21KJB430049) and Innovation Technology Platform Project (YZ2020268) jointly built by Yangzhou City and Yangzhou University. H.K.L. thanks the funding supports from Singapore Ministry of Education (RS13/20 and RG4/21), Agency for Science, Technology and Research, Singapore (A*STAR, A2084c0158), Center of Hydrogen Innovation, National University of Singapore (CHIP2022-05), and Nanyang Technological University start-up grants. Wangshu Tong thanks the funding supports from the NSFC (52173088)

A dual-functional device based on CB/PVDF@BFP for solar-driven water purification and water-induced electricity generation

The efficient utilization of low-grade thermal energy to produce clean water or electricity is important because it potentially relieves our demand on limited natural water and energy resources. Here, we propose a dual-functional device to couple solar-driven water evaporation and evaporation-induced power generation for concurrent production of clean water and green electricity. Our strategy involves the fabrication of an asymmetric, dual-layered structure by spraying a carbon black/polyvinylidene fluoride mixture onto bamboo filter paper (CB/PVDF@BFP). The upper CB/PVDF layer serves as a light-to-thermal transducer for instantaneous heating, while the bottom BFP layer functions as a hydrophilic porous platform to boost water uptake and transfer. Moreover, water evaporation drives capillary flow of ions on the conductive CB/PVDF layer to create a pseudostream that can be harnessed for power generation. Notably, our dual-functional device delivers a fast water evaporation rate of 1.44 kg m−2 h−1 and a high energy utilization rate of 92% under one sun, beyond the previous carbon-based reports. Through this solar-driven water evaporation process, we achieve the efficient desalination of artificial seawater and decontamination of organic-polluted water by up to 99.8% and nearly 100%, respectively. Our device also concurrently produces high, consistent evaporation-induced electrical outputs with VOC and ISC of 0.32 V and 1.5 μA, respectively. The generated electrical outputs can be easily stored by charging a capacitor to over 1.5 V within 15 minutes and be subsequently utilized on demand to power common household electronics. By enabling the efficient coupling of multiple solar-driven processes, our work will catalyze the design of next-generation multifunctional devices to ensure electricity and potable water are easily accessible by everyone, especially remote areas without power stations and/or water treatment facilities.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityPublished versionThe authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (21922202, 21673202 and 22073080), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (21KJB430049) and Scientific research and practical innovation program (SJCX21_1569;2021-06-11). H. K. L. acknowledges the funding support from the Singapore Ministry of Education (AcRF Tier 1 RS13/20 and RG4/21), A*STAR Singapore (AME YIRG A2084c0158), National University of Singapore Center of Hydrogen Innovation (CHI-P2022-05), and Nanyang Technological University start-up grants

Superlattice-based plasmonic catalysis: concentrating light at the nanoscale to drive efficient nitrogen-to-ammonia fixation at ambient conditions

Plasmonic catalysis promises green ammonia synthesis but is limited by the need for co-catalysts and poor performances due to weak electromagnetic field enhancement. Here, we use two-dimensional plasmonic superlattices with dense electromagnetic hotspots to boost ambient nitrogen-to-ammonia photoconversion without needing co-catalyst. By organizing Ag octahedra into a square superlattice to concentrate light, the ammonia formation is enhanced by ≈15-fold and 4-fold over hexagonal superlattice and disorganized array, respectively. Our unique catalyst achieves superior ammonia formation rate and apparent quantum yield up to ≈15-fold and ≈103 -fold, respectively, better than traditional designs. Mechanistic investigations reveal the abundance of intense plasmonic hotspots is crucial to promote hot electron generation and transfer for nitrogen reduction. Our work offers valuable insights to design electromagnetically hot plasmonic catalysts for diverse chemical and energy applications.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityH.K.L. thanks the funding supports from Singapore Ministry of Education (RS13/20 and RG4/21), Agency for Science, Technology and Research, Singapore (A*STAR, A2084c0158), Center of Hydrogen Innovation, National University of Singapore (CHI-P2022-05), and Nanyang Technological University start-up grants. The research was conducted as a part of NICES (NTU-IMRE Chemistry Lab for Eco Sustainability; REQ0275931), a joint research initiative between Nanyang Technological University (NTU) and Institute of Materials Research and Engineering (IMRE) from Agency for Science, Technology and Research(A*STAR)

Dynamic Rotating Liquid Marble for Directional and Enhanced Mass Transportation in Three-Dimensional Microliter Droplets

The ability of an artificial microdroplet to mimic the rotational behaviors of living systems is crucial for dynamic mass transportation but remains challenging to date. Herein, we report dynamic microdroplet rotation using a liquid marble (RLM) and achieve precise control over mass transportation and distribution in a three-dimensional (3D) microdroplet. RLM rotates synchronously with an external magnetic field, creating circular hydrodynamic flow and an outward centrifugal force. Such spin-induced phenomena direct a spiral movement of entrapped molecules and accelerate their diffusion and homogenization in the entire liquid. Moreover, we demonstrate the rotation rate-controlled (between 0 and 1300 rpm) modulation of shell-catalyzed reaction kinetics from 0.13 to 0.62 min^–1. The directed acceleration of reactants toward a catalytically active shell surface is 3-fold faster than conventional stir bar-based convective flow. RLM as an efficient magnetohydrodynamics transducer will be valuable for dynamical control over mass transportation in microdroplet-based chemical, biological, and biomedical studies