Photothermal Film Research Articles

Optical thermal insulation via the photothermal effects of Fe3O4 and Fe3O4@Cu2-xS thin films for energy-efficient single-pane windows

To address critical energy issues in civic structures, we have developed a novel concept of optical thermal insulation (OTI) without relying on a conventional thermal intervention medium, such as air or argon, as often used in conventional window systems. We have synthesized the photothermal (PT) materials, such as the Fe 3 O 4 and Fe 3 O 4 @Cu 2− x S nanoparticles, that exhibit strong UV and near-infrared (NIR) absorptions but with good visible transparency. Upon coating the inner surface of the window glass with a PT film, under solar irradiation, the inner surface temperature rises due to the PT effect. Subsequently, the temperature difference, Δ T , is reduced between the single pane and room interior. This leads to lower the thermal loss through a window, reflected by the U -factor, resulting in considerable energy saving without double- or triple-glazing. Comparing with the Fe 3 O 4 coatings, Fe 3 O 4 @Cu 2− x S is spectrally characterized with a much stronger NIR absorbance, contributing to an increased PT efficiency under simulated solar irradiation (0.1 W/cm 2 ). PT experiments are carried out via both white light and monochromic NIR irradiations (785 nm). The parameters associated with the thermal performance of the PT films are calculated, including PT conversion efficiency, specific absorption rate (SAR), and U -factor. Based on the concept of OTI, we have reached an optimum U -factor of 1.46 W/m 2 K for a single pane, which is satisfactory to the DOE requirement ( 2 K).

Synergistic Tandem Solar Electricity-Water Generators

Summary Energy and clean water are two intertwined fundamental elements for human civilization and sustainable development. Here, we devise a monolithic tandem solar electricity-water generator that synergistically produces electricity and clean water by utilizing the full spectrum of solar irradiance. The tandem generator has two components: a top infrared-transparent photovoltaic device using above-band-gap photons, and a bottom solar water purifier using the below-band-gap photons. More strikingly, a well-designed water-proof thermal interconnecting layer (WTIL) makes these two components work synergistically: the bottom purifier serves as an evaporative cooler of the top solar cell to increase its efficiency, whereas the thermalization energy of the top cell is reutilized by the bottom purifier for producing more clean water. We experimentally demonstrate that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W m−2 and purify water at a rate of 0.80 kg m−2 h−1 under 1-sun illumination.

Transparent Photothermal Heaters from a Soluble NIR-Absorbing Diimmonium Salt.

While numerous near-infrared (NIR) materials have emerged, most of them are strongly colored or black due to the absorption band or tails in the visible region. Here, a highly transparent and soluble NIR-absorbing ionic salt, isobutyl-substituted diimmonium borate (IDI), is synthesized and fabricated, through a solution process, as a thin film that shows a transmittance of over 93% in the whole visible region. A transparent photothermal (PT) film heater is fabricated with the IDI-doped polymer solution, which shows a photothermal conversion efficiency (ηPT ) of 75.2%. Additionally, the prepared PT heater shows a high water evaporation conversion efficiency (ηw ) of 68.8% upon exposure to a 1064 nm laser. Furthermore, the transparent IDI film affords the development of a wireless transparent actuator for the first time, generating a bending angle over 75°, with over 2700 bending cycles. The transparent IDI film creates a hot transparent Venus flytrap and a colorful or fluorescent actuator upon the addition of colorants without losing the actuation properties.

Salt‐Resistant Carbon Nanotubes/Polyvinyl Alcohol Hybrid Gels with Tunable Water Transport for High‐Efficiency and Long‐Term Solar Steam Generation

Solar steam generation has emerged as a promising technology for water purification. Carbon materials are the most widely investigated photothermal conversion materials, but it remains challenging to effectively improve the efficiency of carbon‐based photothermal films cost effectively. Herein, carbon nanotubes (CNTs)/polyvinyl alcohol (PVA) hybrid gels are designed by simply freezing/thawing the mixture of CNTs and the PVA polymers, in which the CNT light absorbers are well embedded in PVA molecular meshes. Combining the super‐hydrophilic feature and the capillary effect of the PVA porous networks, the hierarchical PVA gel enables efficient water transport from internal capillary channels to molecular meshes. Moreover, PVA molecule chains wrapped on the CNT light absorbers also function as energy‐absorbing media to reduce heat loss, achieving confinement of thermal energy to the water clusters. With this advanced solar steam generation system, the converted thermal energy can be utilized in situ to drive the vaporization of water around the CNTs. The CNTs/PVA hybrid gel shows a high energy efficiency of 90.5% and water evaporation rate of 2.06 kg m−2 h−1 under 1 sun illumination. In addition to taking advantage of the inherent bimodal porous structures, the fabricated evaporator can realize fast and long‐term stable solar steam generation.

Nanoparticle Enhanced Interfacial Solar Photothermal Water Disinfection Demonstrated in 3-D Printed Flow-Through Reactors

Heat treatment, i.e., boiling or pasteurization, is the most widely recognized and practiced form of household water treatment. Considering recent advances in the development of light harvesting nanoparticles for solar-to-heat conversion, we envision that a nanomaterial enhanced water heating treatment system could obviate the need to use fuels or electricity to heat water by replacing the energy source with sunlight. In this study, we demonstrate that functional disinfection temperatures can be easily achieved with unconcentrated sunlight using a single layer interfacial photothermal film in direct contact with a tortuous flowing water channel. Photothermal films were fabricated by dispersing high concentrations of light harvesting nanoparticles, carbon black and Au nanorods, into a highly transparent curable polymer. Bench-scale 3-D printed reactors were employed to determine the effect of different parameters on reactor performance, such as channel height, retention time, flow rate, initial water temperature, and light intensity. Simulations demonstrate the scalability of the treatment system, predicting that a reactor footprint of 45 × 45 cm would be required for a photothermal treatment system that could produce 8 L of water per day with 8 h of sunlight at 1 Sun intensity.

Solar‐Thermal Driven Self‐Heating of Micro‐Supercapacitors at Low Temperatures

The solar‐thermal conversion of sunlight into heat has received considerable attention due to its low cost and high conversion efficiency. Microsupercapacitors (MSCs) are a promising class of microscale power sources for microelectronic devices, but low‐temperature operation is a huge challenge for their potential applications due to sluggish diffusion kinetics. Here, a simple strategy of adhering a graphene photothermal film on the backside of a model MSC to realize the device self‐heating at low temperatures is demonstrated. At an extremely low ambient temperature of −50 °C, graphene film can increase the actual operating temperature of MSC to −16.5 °C under irradiation of 1 sun. Solar‐driven self‐heating resulted in a 4.5‐fold increase in the specific capacitance, a 2.7‐fold increase in the rate capability, and a 2.8‐fold increase in the energy density without compromising the cyclic stability. This work presents a new application for solar energy and a new approach to improve the overall performance of MSCs at low temperatures.

Photothermal Cellulose-Patch with Gold-Spiked Silica Microrods Based on Escherichia coli.

Plasmonic-mediated photothermal heating under near-infrared (NIR) irradiation is an emerging key technology in the field of photothermal therapy and chemical reactions. However, there are few reports of photothermal film (dry-type patch), and thus, in this work, we developed the plasmonic-induced photothermal cellulose-patch operating in the NIR region. Hollow and spikelike gold nanostructures, gold-spikes, as plasmonic nanoparticles were prepared and decorated on silica microrods, which were prepared based on a unicellular organism, Escherichia coli, as a framework. In addition, freestanding cellulose-patch was prepared by mixing filter-paper pulp and armored golden E. coli (AGE) microrods. The major absorbing peak of AGE solution was revealed to be 873 nm, and the surface temperature of patch was increased to 264 °C within a very short time (1 min). When NIR laser was irradiated on the patch dipped in the water, the formation of water vapor and air bubbles was observed. The heating efficiency of indirect heat transfer via conduction from patch-to-water was 35.0%, while that of direct heat transfer via radiation from patch in water was 86.1%. Therefore, the cellulose-patch containing AGE microrods has possible applicability to desalination and sterilization because of its fast heating rate and high light-to-heat conversion under the irradiation of low-powered IR laser.

A flexible photo-thermoelectric nanogenerator based on MoS2/PU photothermal layer for infrared light harvesting

Recently, ambient energy harvesting has attracted a great deal of attention to develop clean and renewable energy technologies. In this work, a flexible photo-thermoelectric nanogenerator (PTENG) based on MoS2/PU photothermal film and Te/PEDOT thermoelectric layer has been demonstrated for harvesting environmental infrared (IR) light. The MoS2/PU photothermal film is carefully designed to exhibit excellent flexibility, transferability, and photothermal property. By integrating the photothermal layer with a Te/PEDOT thermoelectric device, the PTENG can produce electrical output without a spatial temperature gradient which is necessary for conventional thermoelectric device. Under IR light illumination, a high temperature difference can be generated across the device, and hence a potential difference established between two electrodes based on a coupling of photothermal effect and Seebeck effect. This type of PTENG exhibits numerous advantages, such as flexible, shape-adaptive, light-weight, and simple-fabrication, which may have a great potential of application in photo-thermoelectric energy harvesting for wearable electronics and implantable electronics.

An Ultrathin Flexible 2D Membrane Based on Single‐Walled Nanotube–MoS2 Hybrid Film for High‐Performance Solar Steam Generation

AbstractSolar steam generation is achieved by localized heating system using various floating photothermal materials. However, the steam generation efficiency is hindered by the difficulty in obtaining a photothermal material with ultrathin structure yet sufficient solar spectrum absorption capability. Herein, for the first time, an ultrathin 2D porous photothermal film based on MoS2 nanosheets and single‐walled nanotube (SWNT) films is prepared. The as‐prepared SWNT–MoS2 film exhibits an absorption of more than 82% over the whole solar spectrum range even with an ultrathin thickness of ≈120 nm. Moreover, the SWNT–MoS2 film floating on the water surface can generate a sharp temperature gradient due to the localized heat confinement effect. Meanwhile, the ultrathin and porous structure effectively facilitates the fast water vapor escaping, consequently an impressively high evaporation efficiency of 91.5% is achieved. Additionally, the superior mechanical strength of the SWNT–MoS2 film enables the film to be reused for atleast 20 solar illumination cycles and maintains stable water productivity as well as high salt rejection performance. This rational designed hybrid architecture provides a novel strategy for constructing 2D‐based nanomaterials for solar energy harvesting, chemical separation, and related technologies.

A high performance photothermal film with spherical shell-type metallic nanocomposites for solar thermoelectric conversion.

A photothermal film (PTF) with densely assembled gold nanoparticle-fixed beads on a polymer substrate is fabricated. Remarkably, a temperature rise higher than 40 °C is achieved in the PTF with only 100 seconds of artificial solar irradiation, and the output power of the thermoelectric device was enhanced to be one order higher than that without PTF. These results will pioneer a rapid solar thermoelectric device.