Academic literature on the topic 'Photoabsorbers'

Substantial research effort has been dedicated to the electrochemical reduction of CO2 (CO2R) to higher carbon products throughout the recent years, baring the promise of a production pathway for green fuels and chemicals.1 However, only little progress has been achieved in the light driven heterogeneous CO2R catalysis, especially considering selective processes towards C2+ products. This arises from the additional complexity of photo-electrochemical reactions, which means that not only the sluggish reaction kinetics, high overpotentials and low selectivity of CO2R, but also the insufficient voltage and sensitivity towards harsh electrolyte conditions of photoabsorbers have to be encountered. Considering CO2R as multi-step process with CO as intermediate mitigates some issues of the process, e.g. the necessary overpotential is reduced and a higher selectivity towards valuable products can be achieved.2 Multi-junction solar stacks can provide operating voltages >2 V, which is sufficient for reducing CO2 to CO with high efficiencies or even produce multi-carbon products from CO while oxidizing water as anode reaction.3 In this work, we designed a process for photo-electrochemical CO reduction with multi-junction photoabsorbers. We start out by showing photo-electrochemical modelling of tandem photoabsorbers that emphasizes the advantages of CO as reactant compared to CO2. Further, we focus on the preparation of a nano-structured Cu catalyst, the most common material for reducing CO to C2+. Therefore, the electrochemical deposition and surface characterization using SEM, EDX and XPS of the catalyst on a dark model electrode coated with a sputter deposited TiO2 protection layer will be presented. Moreover, the CO reduction performance of the model at different potentials are characterized. In addition, the light transmission of the model electrode is reported, baring the possibility of illuminating the photoelectrode from the catalyst front side in mind. Lastly, the transfer of the model catalyst to a photoabsorber as well as the design of a photo-electrochemical flow-cell are discussed. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Rev. 119, 7610–7672 (2019)1. Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catal. 8, 7445–7454 (2018) Seger, B., Hansen, O. & Vesborg, P. C. K. A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. RRL 1, e201600013 (2017). Figure 1

Photothermal therapy (PTT) is a promising local therapy playing an increasingly important role in tumor treatment. To maximize PTT efficacy, various near-infrared photoabsorbers have been developed. Among them, metal sulfides have attracted considerable interest due to the advantages of good stability and high photothermal conversion efficiency. However, the existing synthesis methods of metal-sulfide-based photoabsorbers suffer from the drawbacks of complicated procedures, low raw material utilization, and poor universality. Herein, we proposed a flexible, adjustable strategy capable of transforming commercial metal sulfides into injectable hydrogels for local PTT. We took copper sulfide (CuS) as a typical example, which has intense second-window near-infrared absorption (1064 nm), to systematically investigate its in vitro and in vivo characteristics. CuS hydrogel with good syringeability was synthesized by simply dispersing commercial CuS powders as photoabsorbers in alginate-Ca2+ hydrogel. This synthesis strategy exhibits the unique merits of an ultra-simple synthesizing process, 100% loading efficiency, good biocompatibility, low cost, outstanding photothermal capacity, and good universality. The in vitro experiments indicated that the hydrogel exhibits favorable photothermal heating ability, and it obviously destroyed tumor cells under 1064 nm laser irradiation. After intratumoral administration in vivo, large-sized CuS particles in the hydrogel highly efficiently accumulated in tumor tissues, and robust local PTT was realized under mild laser irradiation (0.3 W/cm2). The developed strategy for the synthesis of CuS hydrogel provides a novel way to utilize commercial metal sulfides for diverse biological applications.

Due to their superior thermostability, inorganic CsPbX₃ halide perovskites are considered the most promising photoabsorbers for commercially viable photovoltaic devices compared to their organic–inorganic analogs, which have demonstrated very impressive solar cell efficiency evolution in a few years though.

A representative method of forming CuO thin films on Cu₂O photoabsorbers is simple annealing oxidation at high temperature in a controlled oxygen atmosphere, but the typical oxidation process is irregular, resulting in a high density of defect sites.

This talk will first discuss the parameters necessary for an optimal water-splitting device using a web based modeling program we developed (SolarFuelsModeling.com).1 The results from this show an optimal a tandem device for water splitting needs photoabsorbers with band gaps of ~2.0 eV and 1.1 eV. After a short review on our work on small band gap Si photoelectrodes,2-4 we will then discuss our combined computational and experimental approach to finding highly efficient large band gap photoabsorbers.5 Using computational modeling, we investigated ABS3 type sulfides and found 15 materials with a reasonable band gap, a direct band gap, low effective electron/hole mass and that are relatively defect tolerant. One of these proposed materials, LaYS3 has already been tested and shows a direct band gap near 2 eV and a fluorescence spectra indicating no significant mid gap states as shown in the image below. Seger, B.; Hansen, O.; Vesborg, P. C. K., A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. Solar RRL 2017, 1 (1), n/a-n/a. Mei, B.; Permyakova, A. A.; Frydendal, R.; Bae, D.; Pedersen, T.; Malacrida, P.; Hansen, O.; Stephens, I. E. L.; Vesborg, P. C. K.; Seger, B.; Chorkendorff, I., Iron-Treated NiO as a Highly Transparent p-Type Protection Layer for Efficient Si-Based Photoanodes. Journal of Physical Chemistry Letters 2014, 5 (20), 3456-3461. Mei, B.; Seger, B.; Pedersen, T.; Malizia, M.; Hansen, O.; Chorkendorff, I.; Vesborg, P. C. K., Protection of p(+)-n-Si Photoanodes by Sputter-Deposited Ir/IrOx Thin Films. Journal of Physical Chemistry Letters 2014, 5 (11), 1948-1952. Seger, B.; Pedersen, T.; Laursen, A. B.; Vesborg, P. C. K.; Hansen, O.; Chorkendorff, I., Using TiO2 as a Conductive Protective Layer for Photocathodic H-2 Evolution. Journal of the American Chemical Society 2013, 135 (3), 1057-1064. Kuhar, K.; Andrea, C.; Monish, P.; Kristian, S. T.; Brian, S.; Peter, V.; Ole, H.; Chorkendorff, I.; Karsten, W. J., Sulfide Perovskites for Solar Energy Conversion Applications: Computational Screening and Synthesis of the Selected Compound LaYS3. Energy & Environmental Science 2017, Accepted. Figure 1

In this article we outline the assembly of binary, ternary and quaternary nanorods using three separate protocols: (a) droplet based assembly, (b) assembly in a vial, (c) electrophoretic deposition. The rods are the important photoabsorbers CdS, CdSexS_1−x, CuIn_xGa_1−xS, and Cu₂ZnSnS₄.

The global energy demand increases with the development of civilisation. Widely used energy sources are mostly based on fossil fuels (e.g. coal, oil, natural gas), and technologies used for production of energy strongly affect the degradation of the environment. Increasing environmental pollution and temperature rise due to greenhouse gas emissions may lead to an ecological disaster. Therefore, research aimed at, on the one hand, the development of an efficient energy production process but not related to CO2 emissions and, on the other hand, the reduction of environmental pollution has been of great interest in recent years. One of the most widely reported topics is the use of solar energy, the resources of which significantly exceed the global energy consumption and at the same time it is widely available in large parts of the world. In addition to energy production, its efficient storage is crucial. In this respect, hydrogen can play an important role, as it is considered to be the main vector for future energy storage and processing. Chemical energy stored in the form of H2 can be converted into electricity through appropriately designed fuel cells that produce water as the only by-product. Therefore, the production of H2 in the photoelectrochemical water splitting process seems to be a good solution. Furthermore, photocatalysis can be successfully used to remove harmful gases and greenhouse gases such as CO2 or NOx. Over the past decades, photocatalytic processes have been widely used to treat water from organic pollutants. Important advantages of this process are: i) the possibility of complete decomposition of pollutants and ii) the relatively low temperature required for this process. This dissertation presents experimental results, together with their detailed analysis, concerning both above mentioned processes, photoelectrochemical water splitting and decomposition of organic pollutants in water. Both the simple method of preparation of photoanodes based on earth-abundant elements, as well as actions taken to increase their efficiency are presented. This work also deals with the problem of explaining the mechanism of photoelectrocatalytic processes taking place at the boundary formed between photoabsorbers, i.e. the semiconductor light-absorbing material, and catalysts at the moment when the created system contains both elements. In the first part of the thesis the influence of the photoabsorber/electrocatalyst interface on the photoelectrochemical decomposition of organic pollutants was evaluated. In this part, photo- anodes made of TiO2 and modified with plasmonic nanostructures of Au or Ag were used. For both types of the electrodes studied it was shown that the modification initially enhanced the photoelectrocatalytic activity towards acetic acid and 2-propanol decomposition (used as model organic pollutant) using radiation in the visible light range. However, repeated measurements of the incident photon-to-current conversion efficiency (IPCE) for the generated photocurrent showed a rapid decrease in the spectral range, where an increase in intensity was originally observed as a result of the presence of plasmonic nanostructures. This has been shown to be caused by irreversible surface oxidation of plasmonic nanostructures, which strongly suggests that deactivation of photocatalysts is of general importance and should always be considered in the context of designing new efficient photoelectrocatalytic and photocatalytic systems. Then, as part of this work, an efficient oxygen evolution reaction catalyst consisting of three metal oxides was developed together with an activation method that improves its photoelectrochemical activity. It has also been shown that the successful combination of this electrocatalyst with the TiO2 photoanode cannot be easily transferred to other photoanodes. The application of this strategy revealed that even the combination of the same photoabsorber and catalyst but only using a different photoanode architecture may lead to completely different results. A thorough examination of a carefully chosen set of oxygen evolution catalysts in combination with the same photoabsorber (Mo-doped BiVO4) showed that the initial theory of the special behaviour of certain materials as catalysts is quite general and can be applied to a wide range of catalysts. In a further step, selected oxygen evolution catalysts were combined with another photoabsorber (WO3) in two of the previously tested configurations. This work has shown that the conscious design of the interface between the photoabsorber and the catalyst drastically changes the performance of the resulting hybrid system. The results obtained once again have shown that the nature of the catalyst is not a dominant factor in improving the performance of the photoanode, but the interface formed between the photoabsorber and the catalyst should always be taken into consideration as well. Finally, the influence of the combination of the photoabsorber with the catalyst on the stability of the photoanode was evaluated. Experiments on photocorrosion of the photoanode material were carried out. It was shown that the addition of a catalyst can also be used to protect the photoanode against photocorrosion as well as to modify the dissolution profile of its components. The methods and results described in this work allowed to deepen the knowledge of environmentally friendly photoelectrocatalysis and to produce materials with increased activity, which can be used in light-assisted water electrolysis or decomposition of organic pollutants. The obtained results clearly indicate the important role of the interface formed between photoabsorbers and electrocatalysts in photoelectrochemical processes and provided valuable information on this phenomenon. The knowledge gained in this work on the nature of the interface formed between a photoabsorber and a catalyst can be potentially used in other important photoelectrochemical processes, such as light-assisted CO2 electroreduction.
Światowe zapotrzebowanie na energię wzrasta wraz z rozwojem cywilizacji. Powszechnie wykorzystywane źródła energii są w większości oparte na paliwach kopalnych (węgiel, ropa naftowa, gaz ziemny), a technologie służące produkcji energii silnie wpływają na degradację środowiska naturalnego. Wzrastające zanieczyszczenie środowiska oraz wzrost temperatury spowodowany emisją gazów cieplarnianych może doprowadzić do katastrofy ekologicznej. W związku z tym, badania mające na celu, z jednej strony opracowanie wydajnego procesu wytwarzania energii, ale nie związanego z emisją CO2, a z drugiej ograniczenie zanieczyszczenia środowiska cieszą się w ostatnich latach dużym zainteresowaniem. Jednym z szeroko badanych zagadnień jest wykorzystanie energii światła słonecznego, której zasoby znacznie przewyższają globalne zużycie energii i jednocześnie jest ona powszechnie dostępna w dużej części naszego globu. Oprócz wytwarzania energii kluczowe jest jej efektywne magazynowanie. W tym zakresie ważną rolę może odegrać wodór, który jest uważany za substancję podstawową dla przyszłego magazynowania i przetwarzania energii. Energia chemiczna przechowywana w postaci H2 może być przetwarzana w energię elektryczną poprzez odpowiednio zaprojektowane ogniwa paliwowe wytwarzające wodę jako jedyny produkt uboczny. Dlatego też produkcja H2 w procesie fotoelektrochemicznego rozkładu wody (ang. photoelectrochemical water splitting, PEC water splitting) wydaje się być dobrym rozwiązaniem. Ponadto, fotokataliza może być z powodzeniem wykorzystana do usuwania szkodliwych gazów i gazów cieplarnianych, takich jak CO2 czy NOx. W ciągu ostatnich dziesięcioleci procesy fotokatalityczne były szeroko stosowane do oczyszczania wód z zanieczyszczeń organicznych. Istotnymi zaletami tego procesu są: i) możliwość całkowitego rozkładu zanieczyszczeń i ii) stosunkowo niska temperatura wymagana dla tego procesu. W niniejszej rozprawie doktorskiej przedstawiono wyniki eksperymentów, wraz z ich szczegółową analizą, dotyczące obu wspomnianych wyżej procesów, fotoelektrochemicznego rozkładu wody oraz oczyszczania wód z zanieczyszczeń organicznych. Przedstawione zostały, zarówno prosta metoda syntezy fotoanod opartych na pierwiastkach powszechnie występujących na ziemi, jak i działania podjęte w celu zwiększenia ich wydajności. Praca ta dotyczy również problemu wyjaśnienia mechanizmu procesów fotoelektrokatalitycznych zachodzących na granicy formującej się między fotoabsorberami (półprzewodnikowy materiał absorbujący światło) a katalizatorami w momencie tworzenia układów zawierających oba elementy. W pierwszej części pracy oceniono wpływ granicy fotoabsorber-elektrokatalizator na fotoelektrochemiczny rozkład zanieczyszczeń organicznych. W tej części pracy wykorzystywane były fotoanody z TiO2 modyfikowane plasmonicznymi nanostrukturamii Au lub Ag. W przypadku obu typów badanych elektrod wykazano, że modyfikacja początkowo wzmocniła aktywność fotoelektrokatalityczną w kierunku rozkładu kwasu octowego i 2- propanolu (stosowanych jako modelowe zanieczyszczenie organiczne) z wykorzystaniem promieniowania w zakresie światła widzialnego. Wielokrotnie powtarzane pomiary generowanego fotoprądu w zależności od energii światła padającego na elektrodę (ang. incident photon-to-current conversion efficiency, IPCE) wykazały jednak szybki spadek wartości IPCE w zakresie spektralnym, w którym pierwotnie obserwowano wzrost intensywności w wyniku obecności nanostruktur plazmonicznych. Przyczyną tego stanu rzeczy było nieodwracalne utlenianie powierzchniowe nanostruktur plazmonowych, co silnie wskazuje, że dezaktywacja fotokatalizatorów ma znaczenie ogólne i powinna być zawsze brana pod uwagę w kontekście projektowania nowych, wydajnych układów fotoelektrokatalitycznych oraz fotokatalitycznych. Następnie, w ramach niniejszej pracy, opracowano wydajny katalizator wydzielania tlenu (ang. oxygen evolution reaction catalyst, OER catalyst) składający się z trzech tlenków metali wraz z metodą aktywacji, która poprawia jego aktywność fotoelektrochemiczną. Wykazano również, że udane połączenie tego elektrokatalizatora z fotoanodą TiO2 nie może być łatwo przeniesione do innych fotoanod. Zastosowanie tej strategii ujawniło, że nawet zastosowanie tego samego fotoabsorbera i tego samego katalizatora oraz modyfikacja jedynie architektury fotoanody prowadzi do kompletnie różnych wyników. Dokładne zbadanie starannie dobranego zestawu katalizatorów wydzielania tlenu w połączeniu z tym samym fotoabsorberem (Mo:BiVO4) wykazało, że wstępna teoria o szczególnym zachowaniu niektórych materiałów jako katalizatorów jest dość ogólną cechą i może być stosowana do szerokiej gamy katalizatorów. W kolejnym etapie wybrane katalizatory wydzielania tlenu zostały połączone z innym fotoabsorberem (WO3) w dwóch wcześniej przebadanych konfiguracjach. Praca ta pokazała, że świadome projektowanie granicy pomiędzy fotoabsorberem a katalizatorem, drastycznie zmienia wydajność otrzymanego układu hybrydowego. Uzyskane wyniki po raz kolejny pokazały, że charakter katalizatora nie jest czynnikiem dominującym dla poprawy działania fotoanody, natomiast zawsze należy wziąć pod uwagę również granicę utworzoną pomiędzy fotoabsorberem a katalizatorem. Na końcu oceniono wpływ połączenia fotoabsorbera z katalizatorem na stabilność fotoanody. Przeprowadzone zostały eksperymenty fotokorozji materiału fotoanody. Wykazano, że dodatek katalizatora może być stosowany również w celu ochrony fotoanody przed fotokorozją, a także w celu modyfikacji profilu rozpuszczania jej składników. Opisane w niniejszej pracy metody i wyniki pozwoliły na pogłębienie wiedzy na temat przyjaznej dla środowiska fotoelektrokatalizy oraz na wytworzenie materiałów o zwiększonej aktywności, które mogą być wykorzystywane w procesie wspomaganej światłem elektrolizy wody lub rozkładu zanieczyszczeń organicznych. Uzyskane wyniki wyraźnie wskazują na ważną rolę granicy utworzonej pomiędzy fotoabsorberami a elektrokatalizatorami w procesach fotoelektrochemicznych i dostarczyły cennych informacji na temat tego zjawiska. Jestem przekonana, że uzyskana w ramach niniejszej pracy wiedza na temat charakteru granicy powstającej pomiędzy fotoabsorberem a katalizatorem może być z powodzeniem wykorzystana w innych ważnych procesach fotoelektrochemicznych, takich jak np. wspomagana światłem elektroredukcja CO2.

Laser based photothermal therapy is a minimally invasive technique that relies on the absorption of energy by an irradiated tissue sample and results in the deposition of heat to destroy cancerous cells. The inclusion of nanoparticles that act as intense infrared absorbers allows for higher selectivity and additional absorption of laser energy into heat in the desired material. One promising carbonaceous nanoparticle is single walled carbon nanohorns (SWNHs) which have been demonstrated to be effective photoabsorbers [1].

Nanomaterials have been investigated for biomedical applications due to their unique properties. Their shape, size, surface, and material can be altered specifically for the type of application. Carbon nanomaterials (CNMs) have been effectively utilized as photoabsorbers to enhance laser-based therapies [1] and can be easily loaded with drugs or targeting moieties [2, 3]. The strong carbon bonds in this material provide a chemical and mechanical inertness that can serve as a barrier to protect chemotherapeutic agents from degrading quickly as they are transported to the site of interest [2].

Photothermal therapy is a cancer treatment that utilizes light energy to deposit specific amounts of heat to effectively kill cells in a specified tumor region. While Hyperthermia has been widely used for centuries as a treatment option for a variety of diseases, Localized Hyperthermia, as seen in photothermal therapies, has seen a rapid increase in use as a cancer treatment due to its non-invasive nature, low cost, simplicity, and reduced complications as compared to other currently available resection options [1]. The inclusion of nanoparticles that are capable of intense absorption in a specific wavelength band allows for higher selectivity of this thermal dose based upon the location of the delivered nanoparticles through both the additional absorption of laser energy, which gets deposited as heat, in the desired location containing the photoabsorbers and by lowering the amount of energy or power of the laser necessary to affect the region of interest, thus lowering the energy applied to the non-desired thermal damage region.

Ultrathin, all-dielectric, metamaterial design based on an asymmetrical optical micro-/nanocavity, enclosing a 10 nm thick Ge2Sb2Te5 photoabsorber film, is inversely optimized for perfect tunable absorption in the mid-infrared. The absorption can be actively/geometrically pre-/post-fabrication spectrally tuned.