In situ photogalvanic acceleration of optofluidic kinetics: a new paradigm for advanced photocatalytic technologies

A multiscale-designed optofluidic reactor is demonstrated in this work, featuring an overall reaction rate constant of 1.32 s¯¹ for photocatalytic decolourization of methylene blue, which is an order of magnitude higher as compared to literature records. A novel performance-enhancement mechanism of microscale in situ photogalvanic acceleration was found to be the main reason for the superior optofluidic performance in the photocatalytic degradation of dyes as a model reaction

Development of a microfluidic device for blood oxygenation by photocatalysis

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (p. 85-87).Recent statistics provided by the American Lung Association assert that over 400,000 Americans die every year from lung disorders and more than 35 million are now living with symptoms of lung disease. Mortality rates of heart disease and certain cancers have declined in recent years partly due to improvements in diagnostic testing and the development of targeted medical technologies. Such improvements have not translated over to the treatment of lung disease and lung cancer. The goal of the artificial respiration project is to create a self-contained, mobile oxygen supply that is suitable for implantation and that can potentially replace acute or chronically disabled lungs. A novel microfluidic device for the oxygenation of whole blood has been developed. The device couples a semiconductor, titanium dioxide (TiO₂), thin film that generates oxygen through photocatalysis with a microfluidic network that facilitates diffusion of the dissolved oxygen to red blood cells. While true pulmonary respiration relies on passive diffusion of oxygen gas from the environment to the blood, the proposed device differs in that it generates oxygen directly from the water in blood plasma. This thesis focuses on the work done to fabricate and characterize the semiconductor photocatalyst, design the integrated microfluidic chip, and validate its capacity to oxygenate blood in real-time. Blood oxygenation experiments show that the microfluidic device exhibiting the best performance produced 4.06 mL of oxygen per 100 mL of blood, nearly two-thirds of the oxygen transferred in the lung.(cont.) The flux of oxygen at the photocatalyst surface was 1.11 x 10-3 mmol O₂/ (cm² - min). The O₂ flux is nearly two orders of magnitude larger than that of any other fluidic device for blood oxygenation to date. The results from the proof-of-concept microfluidic device are promising and are a step towards the realization of a photocatalytic artificial lung.by Tania Ullah.S.M

Photosynthetic Solar Fuels and Chemicals Production with Hybrid Inorganic Semiconductor Nanostructures

In the present thesis hybrid inorganic semiconductor nanostructures are investigated for solar-to-chemical (STC) energy conversion purposes. Among the family of fuel-forming reactions, hydrogen production is targeted by means of mild and sustainable synthetic routes. Traditional water splitting poses, to this extent, stringent kinetics and technological limitations, hampering overall photochemical performance. Leveraging on the superior hydrogen forming quantum efficiency expressed by core-shell CdSe@CdS seeded-rod (SR) nanostructures, we develop alternative anodic organic transformations to realise closed redox cycle solar chemicals syntheses. Notably, this approach circumvents the use of sacrificial reagents, promoting instead value-added oxidative chemistries. We find that fluorescence quenching screening allows for rigorous selection of such reactions, defining optoelectronic rules bridging between materials properties and photosynthetic performance. We observe that, for aldehyde forming transformations, extensive chemical potential is stored by the concomitant generation of hydrogen fuel, up to remarkable 4.2% STC conversion efficiencies, doubling state-of-the art solar-to-hydrogen benchmark values. The ability of SR to promote concerted electron transfer is then tested for additional photo-redox reactions. The oxidative potential of SR allows access to photo-polymerisation and photo-reforming processes whilst the proton reducing capability in organic media allows for in situ photo-hydrogenations. Furthermore, initial address of chemo-selective radical coupling reactions has leveraged on the nanometric distance between reduction- and oxidation-active sites, providing a promising outlook for future optimisation. Finally, attempts to integrate these photocatalysts into microfluidic chips targeted prompt application of the system to a scalable device. The flow conditions offered by such photoreactors promise to soften current limits and further upgrade STC energy conversion. Not only could turnover number be nourished by continuous reagent replenishment, but photocatalyst recyclability will also be attained at successful chemical anchoring of nanorods to reactor walls. The work presented in this thesis therefore endows Ciamician’s dream of the photochemistry of the future with bright forthcoming perspectives

Electroactive poly(vinylidene fluoride) based materials: recent progress, challenges and opportunities

A poly(vinylidene fluoride) (PVDF) and its copolymers are polymers that, in specific crystalline phases, show high dielectric and piezoelectric values, excellent mechanical behavior and good thermal and chemical stability, suitable for many applications from the biomedical area to energy devices. This chapter introduces the main properties, processability and polymorphism of PVDF. Further, the recent advances in the applications based on those materials are presented and discussed. Thus, it shown the key role of PVDF and its copolymers as smart and multifunctional material, expanding the limits of polymer-based technologies.FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, and UID/QUI/0686/2019 and project PTDC/FIS-MAC/28157/2017, PTDC/BTMMAT/28237/2017, PTDC/EMD-EMD/28159/2017. The author also thanks the FCT for financial support under grant SFRH/BPD/112547/2015 (C.M.C.), SFRH/BPD/98109/2013 (V.F.C.), SFRH/BD/140698/2018 (R.B.P.), SFRH/BPD/96227/2013 (P.M.), SFRH/BPD/121526/2016 (D.M.C.), SFRH/BPD/97739/2013 (V. C.), SFRH/BPD/90870/2012 (C.R.). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06)

Energy transfer enhancement of photon upconversion systems for solar energy harvesting

Photon energy upconversion (UC), a process that can convert two or more photons with low energy to a single photon of higher energy, has the potential for overcoming the thermodynamic efficiency limits of sunlight-powered devices and processes. An attractive route to lowering the incident power density for UC lies in harnessing energy transfer through triplet-triplet annihilation (TTA). To maximize energy migration in multicomponent TTA-assisted UC systems, triplet exciton diffusivity of the chromophores within an inert medium is of paramount importance, especially in a solid-state matrix for practical device integration. In this thesis, low-threshold sensitized UC systems were fabricated and demonstrated by a photo-induced interfacial polymerization within a coaxial-flow microfluidic channel and in combination with nanostructured optical semiconductors. Dual-phase structured uniform UC capsules allow for the highly efficient bimolecular interactions required for TTA-based upconversion, as well as mechanical strength for integrity and stability. Through controlled interfacial photopolymerization, diffusive energy transfer-driven photoluminescence in a bi-molecular UC system was explored with concomitant tuning of the capsule properties. We believe that this core-shell structure has significance not only for enabling promising applications in photovoltaic devices and photochromic displays, but also for providing a useful platform for photocatalytic and photosensor units. Furthermore, for improving photon upconverted emission, a photonic crystal was integrated as an optical structure consisting of monodisperse inorganic colloidal nanoparticles and polymer resin. The constructively enhanced reflected light allows for the reuse of solar photons over a broad spectrum, resulting in an increase in the power conversion efficiency of a dye-sensitized solar cell as much as 15-20 %.MSCommittee Chair: Reichmanis, Elsa; Committee Member: Hess, Dennis W.; Committee Member: Koros, William J

Optofluidic Microreactors for Advanced Photocatalysis

This PhD project explores the application of hollow-core photonic crystal fibres (HC- PCFs) as a novel and advanced characterization technique to monitor photocatalysis. The use of HC-PCFs as the core element of a newly developed characterisation platform has many benefits: HC-PCF’s light-guiding abilities and low-loss properties make absorp- tion spectroscopy based screening of reaction intermediates at low sample concentrations possible. The photoreduction of methyl viologen by carbon nanodots (CNDs) was studied and compared to theory by modelling reaction pathways. Oxidation states of cobaloximes, that are currently employed as molecular catalysts for solar hydrogen generation, could be studied and analysed in different pH environments. Furthermore, a novel enzyme based photocatalyst was characterized and its application in photocatalysis explored. With the resulting new insight and understanding of the reaction kinetics and reaction pathways, these nanoscale photocatalytic systems can be improved further to increase conversion efficiency. A functionalisation of HC-PCFs by depositing gold nanoparticles on the core wall lays the foundation towards surface-enhanced Raman sensing of reaction interme- diates. Spatial light modulation (SLM) techniques are applied to excite a wide variety of higher-order modes with well-defined cross-sectional intensity distributions inside the HC-PCF’s core. An automated fast-switching between inverted higher-order modes can in the future be exploited to enable pump-probe and diffusion/ adhesion measurements.EPSRC, NanoDT

Optofluidic System for Microlens and Plasmonic Applications

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2019. 2. 윤재륜.광유체역학은 광학과 미세유체역학을 기반으로 한 학문으로써 각 분야의 장점 및 특징을 유기적으로 활용해 광학요소 및 유체시스템을 보다 유연하게 구성할 수 있는 장점을 가지고 있다. 즉, 미세유체시스템을 이용해 광학기능을 하는 요소를 다양하게 구현하거나 광학시스템과 결합된 미세유체시스템 내에서 극소량의 유체 및 유체 기반 샘플을 조작하고 처리하는 것을 가능하게 한다. 예를 들어, 변형이 가능한 유체는 마이크로 렌즈, 도파관 등과 같은 광학 시스템을 쉽게 재구성할 수 있게 하는 장점을 가지고 있는데, 이는 단순히 서로 다른 성질을 가진 유체 물질로 변경하거나 또는 유체의 계면 모양을 변형시킴으로써 가능하다. 한편, 광학 시스템에 연결된 미세유체 시스템은 극소량의 샘플만을 이용해 효율적인 분석을 할 수 있게 하는 편리한 기반을 제공한다. 이러한 관점에서 광유체역학 활용을 위한 연구가 활발히 진행되고 있고, 이 시스템을 이용한 다양한 광학 요소 구성, 생물학적 분석, 에너지 하베스팅, 화학적 센싱 등의 응용들이 많이 제안되었다. 본 논문의 2장에서는 기체-액체 계면의 형태를 수력학적으로 조절함으로써 광유체역학 기반 다초점 마이크로 렌즈를 구현하였다. 또한 렌즈의 특성을 결정하는 기체-액체 계면 형성과 관련된 물리적 현상을 수치해석 및 이론적 분석을 통해 조사하였다. 안정된 다상 계면을 형성시키기 위해 관련 이론을 이해하는 것은 본 연구에서 제안하는 마이크로 렌즈 구축에 있어서 매우 중요한 요소였다. 결론적으로 기체-액체 계면에서의 비선형적 표면장력효과가 렌즈 모양에 많은 영향을 미치는 것을 알 수 있었고, 이 표면장력 효과는 렌즈를 구성하기 위해 사용한 유체의 성질에 의해 결정되었다. 뿐만 아니라 제안된 마이크로 렌즈는 기체와 액체 계면에 기반하고 있으므로, 이 두 유체의 큰 굴절률 차이를 활용해 액체-액체 기반 마이크로 렌즈와 비교하여 상대적으로 짧은 초점 거리를 형성시킬 수 있다는 장점을 지니고 있다. 이와 같이 짧은 초점 거리를 형성하는 마이크로 렌즈는 앞으로 나아가 더욱 소형화된 광유체역학 시스템을 구현하는데 있어 기여를 할 수 있을 것으로 기대된다. 3장에서는 금속-유전물질로 이루어진 하이브리드 플라즈모닉 기판을 설계하고 제작함으로써 향상된 플라즈모닉 집게를 제안하였다. 실험적으로는 폴리스타이렌 입자와 E.coli 세포를 잡고 조작해보았다. 이 시스템에서 플라즈모닉 집게의 성능을 향상시키기 위해 국소표면플라즈몬공명현상 (LSPR)을 활용하였는데, 이는 국소 표면의 근접장의 에너지를 증폭시키기 위한 도구로서 많은 관심을 받고 있는 광학적 현상이다. 본 연구에서는 이 LSPR현상에 의해 유도된 열발생 효과를 이용해 효율적으로 입자 및 세포를 잡는 미세 광유체 시스템을 구현하였다. 또한 궁극적으로 이 시스템의 효율을 높인 하이브리드 플라즈모닉 구조체의 시너지 효과를 분석 및 입증하기 위해 수치해석 및 실험적 분석을 진행했다. 하이브리드 구조체 도입은 금나노 입자의 LSPR 현상을 더 강화시키기 위한 것이었고, 단순히 아연 산화물 나노막대기와 결합된 금나노 입자 구조체를 제작함으로써 향상된 결과를 얻을 수 있었다. 결론적으로, 아연산화물 나노막대기가 입사된 빛보다 더 증폭된 빛을 표면에 부착된 금 나노입자에 전달하는 역할을 하였고 그 결과로 플라즈모닉 집게의 성능을 월등히 증가시켜주었다. 이와 같이 향상된 플라즈모닉 기판 제안과 그 배경에 대한 심도 깊은 분석은 앞으로 광유체 시스템에 기반한 효율적인 생화학적 분석 플랫폼을 구축하는데 있어서 많은 도움을 줄 수 있을 것으로 예상된다. 4장에서는 플라즈모닉 현상에 의해 향상된 빛 에너지 하베스팅 시스템을 구현하였는데, 이를 위해 하이브리드 플라즈모닉 광전극을 본 연구에서 구현한 바이오 기반 광전지 시스템의 음극으로 활용하였다. 해당 시스템에서 태양 에너지 전환은 Synechocystis sp. 세포의 광합성 현상과 하이브리드 플라즈모닉 음극 (ZnONRs/AuNPs) 구조체의 광여기, 광산란 그리고 플라즈모닉 현상에 기초한다. 또한 본 시스템은 전기 생산을 위해 매우 소량의 세포 용액 (수마이크로 리터)을 필요로 한다. 뿐만 아니라 사용된 플라즈모닉 음극은 광원의 넓은 스펙트럼 영역에서 빛 에너지 하베스팅을 가능하게 하는데, 이는 플라즈모닉 구조체가 LSPR에 의해 유도된 현상으로 인해 자체적으로 전자를 생성할 뿐만 아니라 세포의 광합성 활동을 훨씬 더 향상시켜주는 것으로부터 기여된다. 결과적으로 플라즈모닉 현상에 의해 향상된 바이오 기반 광전지 시스템을 이용했을 때 획기적인 파워 향상을 얻을 수 있었으며, 음극으로 단순히 ITO glass를 사용한 시스템과 비교했을 때 약 17.3 배에 해당하는 파워를 얻었다. 이러한 관점에서 본 연구에서 제안된 플라즈모닉 음극 플랫폼은 앞으로 광유체 시스템에 기반한 효율적인 에너지 하베스팅 시스템을 구현하는데 있어 기여할 수 있을 것으로 기대된다.Optofluidics is an interdisciplinary research of optics and microfluidics, which enables flexible optical functions by using microfluidic system or enables manipulation of small amounts of fluids (or sample solution) by using optics. Therefore, on the one hand, deformable fluids make it possible to easily reconfigure the optical system such as microlens, waveguides, etc. by simply replacing the liquid material or deforming the fluid interface. On the other hand, the microfluidic system coupled to optical components can provide beneficial platform for handling and analyzing only small amounts of interesting fluid samples at microscale. In this regard, optofluidics is being rapidly developed in various applications such as optical component construction, biological analysis, energy harvesting, chemical sensing, etc. In Chapter 2, a tunable optofluidic microlens is demostrated by using a hydrodynamically controllable gas-liquid interface. The relevant physics governing the interface formation are exploited through numerical and theoretical analyses as well. Understanding the physics is important to fabricate the stable multiphasic interface which determines the performance of the lens. We show that non-linear surface tension effect at the gas- liquid interface significantly affects the lens shape and is dependent on the values of fluid parameters. Since our in-plane microlens is based on the gas-liuquid multiphase, a relatively short focal lenth can be obtained due to the intrinsically large distinction of the refractive indices across the gas-liquid interface. This short focal length would then contribute to realization of more miniatureized optofluidic system for a lab on a chip application. In chapter 3, an enhanced plasmonic tweezer is suggested by designing and fabricating the metal-dielectric hybrid plasmonic substrate for trapping polystyrene particles or E.coli cells. Localized surface plasmon resonance (LSPR) is an emerging optical phenomenon as a promising tool for near-field energy enhancement. Therefore we utilize the LSPR-induced heating effect for fabricating an efficient microscale trapping system. The synergistic effects of the hybrid plasmonic structure are explored through numerical and experimental analyses. In order to more intensify the LSPR-induced plasmonic effects, we simply introduce the hybrid structure which consists of zinc oxide nanorods (ZnONRs) and gold nanoparticles (AuNPs). We show that ZnONRs transfer the amplified light energy to AuNPs at the interfaces between the ZnONRs and the AuNPs via leaky wave guide modes. Thus, the ZnONRs enhance the LSPR of the AuNPs as well as the trapping performance outstandingly. Our hybrid plasmonic substrate and in-depth analyses would contribute to the construction of an effective optofluidic biological analysis platform through the efficient trapping/manipulation of the fluid-based sample. In chapter 4, a plasmon-enhanced light harvesting system is developed by introducing a hybrid plasmonic photoelectrode as a photoanode of our bio-photovoltaic system. The solar energy conversion is based on the photosynthesis of cells (Synechocystis sp.) and the photoexcitation, scattering and plasmonic effects of the hybrid plasmonic photoanode (ZnONRs/AuNPs) under the irradiation. The system contains only small amount of cell solution for the current production. Moreover, the plasmonic photoanode enables the efficient light harvesting in broadband of the light source by not only generating electrons itself but also stimulating the photosynthetic activity of the cells through the LSPR-induced effects. An anomalous power improvement about 17.3-fold can be obtained from the plasmon-enhanced bio-photovoltaic system, compared to the control system of which photoanode is the bare ITO glass. In this respect, our plasmonic photoanode platform would give an inspiration for fabricating an efficient energy harvesting system based on the optofluidic device.Chapter 1. Introduction 1 1.1. Optofluidics . 1 1.2. Research background . 3 1.2.1. Microfluidics 3 1.2.2. Plasmonics 5 1.2.3. Localized surface plasmon resonance (LSPR). 7 1.3. Objectives of present work. 11 1.4. References . 12 Chapter 2. Tunable Multiphase Microlens. 14 2.1. Introduction . 14 2.2. Experimental section 19 2.2.1. Design and fabrication of the optofluidic chip. 19 2.2.2. Materials 19 2.2.3. Experimental set-up . 21 2.3. Numerical analysis. 22 2.4. Theoretical analysis 23 2.5. Results and discussion 25 2.5.1. Lens shape 25 2.5.2. Non-linear surface tension effect on the lens shape. 25 2.5.3. Characteristics of the tunable microlens 30 2.6. Summary 38 2.7. References . 39 Chapter 3. Enhanced Plasmonic Tweezer 41 3.1. Introduction . 41 3.2. Experimental section 44 3.2.1. Preparation of plasmonic substrate 44 3.2.2. Experimental set-up . 45 3.2.3. Temperature measurement . 45 3.2.4. Particle trapping experiment 46 3.3. Numerical analysis. 50 3.4. Results and discussion 53 3.4.1. Prediction and analysis of synergistic effects 53 3.4.2. Characterization of plasmonic substrate 58 3.4.3. Plasmonic heating 58 3.4.4. Enhanced particle trapping performance . 64 3.4.5. Verification of synergistic effects. 65 3.4.6. Analysis of trapping forces 70 3.5. Summary 75 3.6. References . 76 Chapter 4. Plasmon-enhanced Light Harvesting System 79 4.1. Introduction . 79 4.2. Experimental Section . 84 4.2.1. Preparation of plasmonic anodes . 84 4.2.2. Preparation of cell solution and MEA 84 4.2.3. Device assembly 85 4.2.4. Electrochemical characterization . 85 4.2.5. Angle-dependent light scattering measurement . 86 4.3. Numerical analysis. 91 4.4. Results and discussion 93 4.4.1. Characterization of plasmonic anodes 93 4.4.2. Living solar cell performance 98 4.4.3. Working mechanism of plasmon-enhanced living solar cell 101 4.4.4. Broadband multiplex living solar cell 103 4.4.5. Far-field scattering effect . 105 4.4.5.1. Structural effect . 105 4.4.5.2. Size effect of AuNPs . 111 4.5. Summary 114 4.6. References . 115 Korean Abstract 118Docto

Titanium-Based Microreactors for Water Purification

A new era of space exploration is on the horizon. Over the past decade interest in crewed missions to Mars and beyond has rapidly developed in the private sector. Innovation in spaceflight has taken center stage but to achieve these ambitious goals improvements to the Environmental Control and Life Support Systems (ECLSS) will be a necessity as well. The system aboard the International Space Station (ISS) can be viewed as a model to assess the demands for sustaining a long-term crew on deep space voyages. Currently, as part of the Water Recovery System (WRS), a thermal catalytic reactor is used to eliminate dissolved low molecular weight volatile organic compounds (VOC). This catalytic reactor uses high temperature and oxygen to oxidize VOCs into harmless by-products. However, components used to maintain the high temperature and pressure fail for more frequently that would be feasible for eventual use in deep space missions. We propose that by replacing the catalytic reactor with photocatalytic microfluidic reactors, which operate at standard temperature and pressure, reliability can be greatly improved. Herein, we present a multi-faceted study to develop a high-density photocatalytic microfluidic reactor with design enhancements to mitigate common limitations associated with this technology. The first aim was to apply a design of experiments (DOE) approach to optimize nanoporous titania (NPT) for use within the microfluidic reactor concept. NPT is a unique form of titanium dioxide (TiO2) that directly forms on titanium (Ti) surfaces through a hydrogen peroxide (H2O2) based oxidation process. The Taguchi method and grey relational analysis (GRA) were applied to the oxidation conditions (H2O2 concentration, temperature, and time) to maximize the reaction rate constant, k, and NPT film quality. The second aim applied Ti microelectromechanical systems (MEMS) fabrication techniques to create the first, high-density microfluidic reactor system utilizing a high aspect ratio Ti micropillar array for enhanced catalyst loading and reduced diffusion distance. The micropillar reactors outperformed conventional flat planar reactors and achieved 2-fold or greater photocatalytic activity than all other devices reported in the literature thus far. These results demonstrate the significant performance enhancements of the micropillar array and identify future directions for further validating the concept for use in ECLSS applications

Interface-modulated nanojunction and microfluidic platform for photoelectrocatalytic chemicals upgrading

Photoelectrocatalytic oxidation provides a technically applicable way for solar-chemical synthesis, but its efficiency and selectivity are moderate. Herein, a microfluidic photoelectrochemical architecture with 3-D microflow channels is constructed by interfacial engineering of defective WO3/TiO2 heterostructures on porous carbon fibers. Kelvin probe force microscopy and photoluminescence imaging visually evidence the charge accumulation sites on the nanojunction. This efficient charge separation contributes to a 3-fold enhancement in the yield of glyceraldehyde and 1,3-dihydroxyacetone during glycerol upgrading, together with nearly doubled production of high value-added KA oil and S2O82− oxidant through cyclohexane and HSO4− oxidization, respectively. More importantly, the microfluidic platform with enhanced mass transfer exhibits a typical reaction selectivity of 85 %, which is much higher than the conventional planar protocol. Integrating this microfluidic photoanode with an oxygen reduction cathode leads to a self-sustained photocatalytic fuel cell with remarkably high open-circuit voltage (0.9 V) and short-circuit current (1.2 mA cm−2)