Photothermal Conversion Of Solar Energy Research Articles

Continuous synthesis of high-entropy alloy nanoparticles by in-flight alloying of elemental metals

High-entropy alloy (HEA) nanoparticles (NPs) exhibit unusual combinations of functional properties. However, their scalable synthesis remains a significant challenge requiring extreme fabrication conditions. Metal salts are often employed as precursors because of their low decomposition temperatures, yet contain potential impurities. Here, we propose an ultrafast (< 100 ms), one-step method that enables the continuous synthesis of HEA NPs directly from elemental metal powders via in-flight alloying. A high-temperature plasma jet ( > 5000 K) is employed for rapid heating/cooling (103 − 105 K s−1), and demonstrates the synthesis of CrFeCoNiMo HEA NPs ( ~ 50 nm) at a high rate approaching 35 g h−1 with a conversion efficiency of 42%. Our thermofluid simulation reveals that the properties of HEA NPs can be tailored by the plasma gas which affects the thermal history of NPs. The HEA NPs demonstrate an excellent light absorption of > 96% over a wide spectrum, representing great potential for photothermal conversion of solar energy at large scales. Our work shows that the thermal plasma process developed could provide a promising route towards industrial scale production of HEA NPs.

Preparation of Phase‐Change Composites and Their Interfacial Water Evaporation Properties

Materials for the photothermal conversion of solar energy for evaporation have attracted the attention of researchers due to their low energy consumption. However, photothermal conversion materials cannot operate continuously in all weathers due to intermittent solar radiation, which reduces the evaporation efficiency of interfacial evaporated materials. Therefore, this article uses phase‐change materials (PCMs) to improve the evaporation efficiency of traditional interfacial evaporation materials, using polyethylene glycol (PEG) as PCMs, polydopamine (PDA) as light absorption material, acrylamide (AM), bacterial nanocellulose (BC), and sodium carboxymethyl cellulose (CMC‐Na) as matrix raw materials. 3D gel blend (AM/PEG/BC/CMC@PDA) phase transition composite is fabricated using the one‐pot cross‐linking method. Experimental results show that the material achieves 98% light absorption in the entire spectral range. At 1 kW m−2 light, the evaporation rate of the AM/PEG/BC/CMC@PDA phase transition composite reaches 3.44 kg m−2 h−1. The evaporation rate of the material is equivalent to 8 times that of water, and the photothermal conversion efficiency is 95%. The evaporation rate of the material in the dark is 1.2 kg m−2 h−1. The material has excellent evaporation rates in various water bodies and meets drinking water standards.

Radially graded metal foams arrangement in heat storage device of photothermal utilization systems

Metal foam was adopted for improving inherent low thermal conductivity of traditional thermal energy storage (TES), which conducted higher solar energy conversion efficiency. With consideration of more energy response and the mixing enhancement effect on heat conduction and natural convection, this work investigated a vertical TES tube in solar energy photothermal utilization systems, embedded in metallic foam with radial gradient porosity and pore density. Experiments and simulations have both been carried out. It is thoroughly examined how the liquid fraction, solid-liquid interface, temperature field, and velocity field evolve, and the properties of energy storage, such as heat transfer density and energy storage quantity, are further assessed. Results demonstrated that the melting duration was shortened by 11.2% for the positive radially graded porosity arrangement and prolonged by 16.8% for the negative, in comparison to the homogeneous structure. Meanwhile, influenced by the varied porosity, the temperature uniformity was enhanced by 4.9% for the positive and was deteriorated by 15.1% for the negative. In addition, positive and negative gradient pore density respectively increased the temperature uniformity of by 15.1% and 16.7%. Based above, metal foam tube with negative gradient porosity and pore density was suggested to build the more efficient photothermal solar energy conversion systems due to faster melting process and more homogeneous temperature uniformity.

A rapid, cost-free, and disposable solar steam generator for sea/wastewater purification based on 2D titanium oxide nanosheets via ultrasound synthesis

A rapid, disposable, and cost-free solar steam generator device made of recyclable plastic bottles for the purification of seawater/wastewater by a solar evaporation method is demonstrated. This device utilizes the photothermal conversion of solar energy to heat using the mixture of two-dimensional TiO2 and Ti2O3 nanosheets synthesized via the probe ultrasound followed by coprecipitation. The water purification device showed a competitive maximum evaporation rate of 1.17 kg m−2 h−1 under one sun illumination (1.0 kW/m2) and showed a percentage efficiency of 79.9%. The real-world water samples of seawater and wastewater were demonstrated for fast purification within 1 min, and the resulting clean/drinking water from the device showed a significant improvement in their quality up to World Health Organization (WHO)–recommended drinking water limits.

Ultrafast Spectroscopy of Plasmons and Free Carriers in 2D MXenes.

2D MXenes have diverse and chemically tunable optical properties that arise from an interplay between free carriers, interband transitions, and plasmon resonances. The nature of photoexcitations and their dynamics in three different members of the MXene family, Ti3 C2 , Mo2 Ti2 C3 , and Nb2 C, are investigated using two complementary pump-probe techniques, transient optical absorption, and time-resolved terahertz (THz) spectroscopy. Measurements reveal pronounced plasmonic effects in the visible and near-IR in all three. Optical excitation, with either 400 or 800nm pulses, results in a rapid increase in lattice temperature, evidenced by a pronounced broadening of the plasmon mode that presents as a plasmon bleach in transient absorption measurements. Observed kinetics of plasmon bleach recovery provide a means to monitor lattice cooling. Remarkably slow cooling, proceeding over hundreds of picoseconds to nanoseconds time scales, implies MXenes have low thermal conductivities. The slowest recovery kinetics are observed in the MXene with the highest free carrier density, viz. Ti3 C2 , that supports phonon scattering by free carriers as a possible mechanism limiting thermal conductivity. These new insights into photoexcitation dynamics can facilitate their applications in photothermal solar energy conversion, plasmonic devices, and even photothermal therapy and drug delivery.

Silica aerogel composited with both plasmonic nanoparticles and opacifiers for high-efficiency photo-thermal harvest

Plasmonic nanoparticles are doped in silica aerogels for high-efficiency photothermal conversion of solar energy in seawater desalination and so on. However, this suffers from remarkable heat loss problem via near-infrared radiation. The present work proposes a novel aerogel composited with both plasmonic nanoparticles and opacifiers. The radiative characteristics of the aerogel composite were numerically investigated by coupling the T-matrix method and Monte Carlo method. The opacifiers promote the extinction characteristics in the infrared wavelength range and reduce the radiative thermal conductivity, while the plasmonic nanoparticles enhance the absorption efficiency in the solar spectrum. Moreover, silica aerogels doped with both silver nanoparticles and indium tin oxide (ITO) particles were prepared and tested. It is found that the optimal radius and volume fraction of ITO particles are 1000 nm and 1% at 300 K, respectively, based on the silica aerogel (particle radius of 5 nm and porosity of 95%) doped with silver plasmonic nanoparticles (particle radius of 10 nm and concentration of 5%). They can achieve an absorption efficiency of 87.65% in the solar spectrum and a low transmittance in the infrared range with reduced heat loss. The present work paves a new way to design full-spectrum absorption aerogels for high-efficiency photothermal conversion.

A Review on Photothermal Conversion of Solar Energy with Nanomaterials and Nanostructures: From Fundamentals to Applications

AbstractSolar energy is a green, sustainable, and de facto inexhaustible energy source for mankind. The conversion of solar energy into other forms of energy has attracted extensive research interest due to climate change and the energy crisis. Among all the solar energy conversion technologies, photothermal conversion of solar energy exhibits unique advantages when applied for water purification, desalination, high‐temperature heterogeneous catalysis, anti‐bacterial treatments, and deicing. In this review, the various photothermal conversion mechanisms based on different forms of heat release are summarized and some of the latest examples are presented. In addition, the necessary prerequisites for solar‐driven photothermal materials toward their practical applications are also discussed. Further, the latest advances in photothermal conversion of solar energy are discussed, focusing on different types of photothermal applications. Finally, a summary is given and the challenges and opportunities in the photothermal conversion of solar energy are presented. This review aims to give a comprehensive understanding of emerging solar energy conversion technologies based on the photothermal effect, especially by using nanomaterials and nanostructures.

Preparation and characterization of novel CuS / SiO 2 @n‐octadecane phase‐change nanocapsules enhanced photothermal conversion for solar energy utilization

The design of CuS/SiO2@n-octadecane nanocapsules with high sensitivity to light and heat is being conducive to photothermal conversion and efficient utilization of solar energy. In this work, CuS was deposited on the surface of the SiO2 shell by the chemical bath deposition method. Through the characterization of microstructure and chemical composition, the granular CuS crystal was uniformly coated on the SiO2 shell. The synthesized nanocapsules are spherical and have a perfect core-shell structure. The quantity, distribution, and size of CuS deposited on the shell can be adjusted by regulating the synthesis parameters. The prepared CuS/SiO2@n-octadecane nanocapsules have a melting temperature of 26.85°C and melting enthalpy of 65.0 J/g at the optimum preparation condition (10 mmol/L cetyltrimethylammonium bromide, 70°C, 0.02 mol/L Cu2+) and have excellent durability. The light absorption performance of CuS/SiO2 nanocapsules in the Vis-NIR was significantly enhanced, photothermal conversion efficiency reached 52.7%. In addition, the CuS/SiO2 nanocapsules also showed good photocatalytic performance, and the degradation degree of methyl orange reached 71% within 3 hours. These results show that the designed photo-driven nanocapsules have excellent performance and great potential in solar energy utilization and intelligent fabric. Highlights We have creatively synthesized PCM nanocapsules with CuS/SiO2 shells. The melting enthalpy and melting temperature are 65.0 J/g and 26.85°C, respectively. The activity of the SiO2 shell was increased by amino coupling agent modification. CuS has increased 4-5 times of photothermal conversion efficiency in Vis-NIR.

Design and Photoelectric Performance of Perfect Solar Absorber Based on GaAs Grating

In recent years, solar energy has received extensive attention as a clean and renewable energy. We present a perfect broadband solar absorber based on tungsten and semiconductor GaAs in this paper. The structure of GaAs grating-GaAs film-W substrate has been proposed. And the finite time domain difference method (FDTD) has been used for the numerical simulation of the model. Broadband absorption has been realized in the 500–1,850 nm, by adjusting the parameters of geometry to excite high-efficiency surface plasmon resonance. The absorption spectrum of the structure can be changed by adjusting the geometric parameters to meet different needs. The proposed absorber has incidence insensitive (0–60°) and high short-circuit current characteristics. The structure is simple and easy to manufacture, and has superior photoelectric properties to be application in photothermal conversion, collection and utilization of solar energy.

Photothermally enabled MXene hydrogel membrane with integrated solar-driven evaporation and photodegradation for efficient water purification

Sustainable and energy-efficient water purification making use of solar energy is highly desirable to address water scarcity and pollution crisis. However, it remains a challenge to achieve full solar spectrum utilization with photothermal and photodegradation capability. Herein, inspired by the unique optical property of MXene, a novel assembly of MXene hydrogel membrane with synergistic photothermal and photocatalysis effect is proposed for integrated water purification. The MXene hydrogel membrane is fabricated based on the structure-directing of self-stacking MXene nanosheets and its abundant molecular interactions with the polymer matrix, polyvinyl alcohol (PVA), and the multifunctional layer-crosslinker, porphyrin. The obtained MXene hydrogel membrane exhibits fascinating physicochemical properties combining dynamic hydrophilic network of hydrogel and permeability of membrane, making it a preferred medium for both vapor generation and photodegradation. Moreover, calculation and experimental results illustrates the charge redistributions and coupling interactions between MXene and porphyrin, which imparts enhanced photothermal effect and photocatalytic activitiy. As a result, the MXene hydrogel membrane exhibits an high solar-driven water evaporation rate (1.82 kg m−2h−1) and a photodegradation efficiency (90.5 %), rendering an integrated water purification capability under one sun irradiation. This work presents a feasible and effective route towards develop of MXene-mediated cooperative photochemical and photothermal solar energy conversion for sustainable water purification.

Spectrum Tailored Defective 2D Semiconductor Nanosheets Aerogel for Full‐Spectrum‐Driven Photothermal Water Evaporation and Photochemical Degradation

AbstractThe wide spectral range of the solar flux with undesirable diffused energy distribution remains a substantial impediment to the high‐efficiency utilization of the whole spectrum. Here, inspired by the spectrally selective sunlight utilization of plants, a spectrum‐tailored solar harnessing aerogel is conceived. It is composed of oxygen vacancy (Ov) defect‐rich semiconductor HNb3O8 (D‐HNb3O8) nanosheets and polyacrylamide (PAM) framework to perform all‐in‐one photochemical and photothermal full solar energy conversion. The aerogel selectively utilizes the whole solar spectrum, in which high energy ultraviolet (UV) photon is converted into high redox potential electron–hole pairs, while low energy visible‐near infrared (NIR) photons are transformed into heat. The designed solar absorber‐polymer composite shows energy harnessing‐conversion capability with desired heat insulation, reactant enrichment, rapid mass diffusion and capillary pumping characteristics, thus realizing a high efficient steam generation and photochemical activity. This cooperative photochemical and photothermal solar energy conversion, at respective optimal working spectrum, holds great promise for optimizing and maximizing the solar energy utilization, as well as opening up opportunities to explore simultaneous multifunctional usage of solar energy.

Enhancements of absorption and photothermal conversion of solar energy enabled by surface plasmon resonances in nanoparticles and metamaterials

During the past decade, a great deal of research work has been carried out on near-field photonics and nano-optics relating to photo-thermal conversion process. In this paper, recent analytical, numerical and experimental studies on radiation properties in visible and near-infraed wavelengths of electromagnetic waves incident on nanoparticles and metamaterials with applications to solar energy harvesting are reviewed. These nanoparticles and metamaterials are made of both isotropic and anisotropic materials. Mie theory is employed for analyses of absorption properties of spherical nanoparticles composed of different materials. The finite difference time domain (FDTD) method and the rigorous coupled-wave analysis (RCWA) method are used for numerical studies of absorption properties of nanoparticles with arbitrary shapes and power dissipation density distribution of metamaterials, respectively. In addition, a perfect absorber with pyramidal nanostructures made of Bi2Te3 is proposed, and measurements of absorption properties of some fabricated metamaterials are summarized. Potential applications of these nanostructures for solar energy harvesting enhancement are discussed. The results of these studies have provided not only improved understanding of physical mechanisms in enhanced absorption of solar energy by nanoparticles and metamaterials, but also clarified contradictory explanations on the photo-thermal conversion process in solar energy harvesting as well.

Absorber materials based on polymer nanocomposites containing silver nanoparticles for solar thermal collectors

This study describes the synthesis and characterization of polymer-based nanocomposites to fabricate absorber materials for solar thermal collectors. Heat generation by nanosized silver particles (NSP) under irradiation with light of appropriate wavelength is exploited for an efficient harvesting of solar energy. NSP were synthesized by reduction of silver nitrate (AgNO3) in a methacrylate resin. The photothermal conversion of solar energy into heat is optimized by increasing the overlap between the plasmonic band of the NSP and the spectral emission of the sun. Thus, the synthesis conditions were adjusted in order to broaden the plasmon absorption band of the resultant NSP. The UV–vis spectra of suspensions containing 300 ppm NSP exhibited a broad absorption band in the range between 360 and 1100 nm with three absorption peaks at 335, 440, and 700 nm. These absorption bands are associated to the presence of triangular NSP, which was confirmed by TEM microscopy. The resins containing NSP were activated with benzoyl peroxide and polymerized after 20 min at 80 °C. The photothermal conversion effect of the nanocomposites was assessed by monitoring the temperature increase with fine thermocouples embedded in 2-mm thick specimens during irradiation with light of different wavelength. The temperature reached during irradiation of nanocomposites showing a very broad absorption band was 115 °C while that of the nanocomposites exhibiting a single peak was 102 °C.

Simulation of modified Trombe wall

Passive systems are becoming increasingly popular among designers, which is reflected in their frequent use in the construction of modern buildings. The prevailing material in façade design is glass which enables i.a. photothermal conversion of solar energy either in the so-called direct systems or in one of a number of the collector-and-storage Trombe wall variants. In order to estimate how the aforementioned passive solutions affect the energy balance of a building, the efficiency of such solutions needs to be determined first. This paper presents the research proposal that would use a simple-structure laboratory simulator. The proposed method is based on the analogy of supplying heat into the TW itself with an internal heat source. In order to simulate the absorption of solar radiation that takes place in the absorber, the heat was produced by the heating cable embedded in such an absorber. The results of tests carried out according to one of the Design of Experiments (DOE) methods enabled the development of an empirical model showing the operation efficiency of the originally modified Trombe wall.

Structural and optical properties of CuS thin films deposited by Thermal co-evaporation

Copper sulfide (CuS) thin films with thickness 100, 150 and 200 nm have been deposited on glass substrates by thermal co-evaporation of Copper and Sulphur. The effect of CuS film thickness on the structural and optical properties have investigated and discussed. Structural and optical investigations of the films were carried out by X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy and UV spectroscopy. XRD and selected area electron diffraction conforms that polycrystalline in nature with hexagonal crystal structure. AFM studies revealed a smooth surface morphology with root mean-square roughness values increases from 24 nm to 42 nm as the film thickness increase from 100 nm to 200 nm. AFM image showed that grain size increases with thickness of film increases and good agreement with the calculated from full width half maximum of the X-ray diffraction peak using Scherrer's formula and Williamson-Hall plot. The absorbance of the thin films were absorbed decreases with wavelength through UV-visible regions but showed a increasing in the near-infrared regions. The reflectance spectra also showed lower reflectance peak (25% to 32%) in visible region and high reflectance peak (49 % to 54 %) in near-infrared region. These high absorbance films made them for photo-thermal conversion of solar energy.

Characteristic evaluation on spray-deposited WFTO thin films as a function of W doping ratio

In this work, F and F + W simultaneously doped SnO2 highly transparent conducting thin films were deposited on glass substrates at (500 ± 5) °C temperature by the spray pyrolysis method. Microstructural, morphological, electrical and optical properties of FTO films were investigated as a function of tungsten (W) doping, in the range from 0 to 5 at%. X-ray diffraction patterns show that the films exhibit a tetragonal cassiterite structure and (200) preferential orientation of FTO film, and the relative strength of these peaks changes with altering the W doping ratio. The preferred growth of (211) changed to (200) plane with 2 at% W doping level and 3 at% W-doped film had (200) orientation and with further doping, this changed to (110) orientation. The scanning electron microscopy and atomic force microscopy images of the films indicate that the films are made up of dense small particles of a pyramidal shape and have a smooth surface. It was observed that the surface morphology of the films did not change much when the W element was inserted to the FTO structure. It was found that the sheet resistance values of the films varied with W doping ratio, and 2 at% W-doped FTO thin film exhibited the lowest values of sheet resistance (1.12 Ω). Also, the highest figure of merit, infrared reflectivity and optical band gap values were calculated for 2 at% W-doped FTO film as 50.9 × 10−2 Ω−1, 98.82 % and 4.13 eV, respectively. These results make the films an effective candidate for usage in many optoelectronic applications and photo-thermal conversion of solar energy.

An investigation of the Nb doping effect on structural, morphological, electrical and optical properties of spray deposited F doped SnO2 films

F and Nb + F co-doped SnO2 thin films were deposited on glass substrates by the spray pyrolysis method. The microstructural, morphological, electrical and optical properties of the 10 wt% F doped SnO2 (FTO) thin films were investigated specifically for niobium (Nb) doping in the range of 0–4 at.% with 1 at.% steps. As shown by the x-ray diffraction patterns, the films exhibited a tetragonal cassiterite structure with (200) preferential orientation. It was observed that grain sizes of the films for (200) and (301) peaks depended on the Nb doping concentration and varied in the range of 25.11–32.19 and 100.6–183.7 nm, respectively. The scanning electron microscope (SEM) micrographs showed that the FTO films were made of small pyramidal grains, while doubly doped films were made of small pyramidal grains and big polyhedron grains. From electrical studies, although 1 at.% Nb doped FTO films have the lowest sheet resistance and resistivity values, the highest figure-of-merit and optical band gap values obtained for FTO films were 16.2 × 10−2 Ω−1 and 4.21 eV, respectively. Also, infrared reflectivity values of the films were in the range of 97.39–98.98%. These results strongly suggest that these films are an attractive candidate for various optoelectronic applications and for photothermal conversion of solar energy.

Growth Kinetics of Copper Sulfide Thin Films by Chemical Bath Deposition

Copper sulfides (CuxS) are compound semiconductor materials that exhibit considerable variations of optical and electrical properties. Copper sulfide thin films can be used in many applications, such as solar control coatings, solar cells, photothermal conversion of solar energy, electroconductive coatings, and microwave shielding coatings. In this paper, chemical bath deposition growth of copper sulfide thin films were monitored for the first time using an in-situ quartz crystal microbalance as a function of time, temperature, concentrations of reactants, and pH. The reaction activation energy was determined based on initial growth rates. The high activation energy, 68 [kJ/mol], indicates that the rate limiting step of the deposition is the chemical reaction rather than mass transport. The structure, morphology, composition and optical absorption of the films were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and UV-Vis absorption spectroscopy respectively. These properties were found to depend strongly on the deposition conditions.

Improved chemical deposition and thermal emittance of tin (iv) oxide (SnO2) thin films for photothermal conversion of solar energy and possible applications

Thin films of tin (iv) oxide (SnO2) were deposited on six polished sample plates of stainless steel 430 using improved chemical bath deposition (CBD) method at 302 K and pH value of 12.4 for different deposition time of 16 to 36 h at 4 h interval, respectively. Ethylenediamine tetra acetate (EDTA) was used to stabilize the deposition at the required pH value. The thermal emittance values of the polished and coated sample plates were determined before and after the deposition of films, respectively, using thermocouple potentiometer. The average thermal emittance value of the uncoated polished sample plate is 0.15 ± 0.01 while thermal emittance values of the coated sample plates vary from 0.15 to 0.19 ± 0.01. The film thickness of the coated sample plates varies from 33.73 to 77.59 µm. These low thermal emittance values compare well with those obtained for oxidized stainless steel selective surfaces. The coated sample plates with most favorable conditions of thermal emittance 0.17 to 0.18 ± 0.01 and film thickness 45.70 to 69.18 µm could find applications in photothermal conversion of solar energy. The improved chemical bath deposition technique could be employed at different pH values with suitable deposition time to fabricate selective surfaces for use in solar energy applications. Key words: Improved chemical bath deposition (CBD) method, thermal emittance of tin (iv) oxide (SnO2), thin films and possible applications in solar thermal devices.

Development of transparent heat mirrors based on metal oxide thin film structures

The aim of this work is the preparation of RF sputtered indium–tin oxide (ITO) thin films for application as transparent heat mirrors. The heat mirrors are important elements for the photothermal solar energy conversion. In combination with moderate spectral selectivity of the solar absorbers they could increase the efficiency of the solar collector. The optical properties of ITO and double-layer ITO with titanium dioxide (TiO 2) structures in the visible and infrared ranges were investigated. The films were deposited on glass substrates by RF sputtering technique. Tin-doped indium, as well as titanium targets was used. The influence of the In–Sn target composition and the deposition parameters on the film properties were studied. The films' surface morphology and structure were investigated by SEM, TEM and XRD, the composition was studied applying electron probe microanalyzer (EPMA). The thicknesses of the films were determined by the laser ellipsometry method. The measurements in the infrared range were performed on Fourier transform infrared spectrophotometer (FTIR). The single layer ITO structures showed reflectance in the infrared range not exceeding 50% at longer wavelengths. The double layer structures with TiO 2 under layer showed increased reflectance in the infrared range with high visible transmittance reaching 85%.