Photothermal Conversion Applications Research Articles

MXenes: Structure, properties, and photothermal applications

The ever-growing interest in MXenes has been driven by their unique electrical, thermal, mechanical, and optical properties. Due to the presence of diverse surface ligands and defect sites, MXenes exhibit desirable and highly tunable optical response in the solar spectrum. In addition, they have also been found to be effective shields for electromagnetic interference thanks to their selective electromagnetic wave absorption capability. These features collectively provide MXenes with promising potentials for photothermal conversion applications. However, the underlying scientific mechanisms, pathways, and potential impact of photothermal conversion by MXenes remain poorly categorized and understood. In this review, the electronic, optical, and plasmonic properties and potential photothermal mechanism of MXene materials are systematically summarized. Current advances in various photothermal applications as well as challenges and opportunities in relevant fields are also presented. This review provides comprehensive understandings on the fundamental properties as well as a guidance for in-depth investigation of the photothermal conversion mechanism.

Innovative Synthesis of Au Nanoparticle-Trapped Flexible Macrocrystals: Achieving Stable Black Crystal Wires with Broadband Absorption.

In optical materials, the development of absorbers for a wide spectrum is a focal point of research. A pivotal challenge lies in ensuring the stability and durability of optical absorbers, particularly at elevated temperatures. This study introduces a novel approach to creating absorbers with diverse colors, focusing on the synthesis and properties of black crystal wires. In contrast to black gold nanoparticle (Au NP) precipitates, which change color within hours under similar conditions, the method involves strategically trapping Au NPs within defects during the growth of single crystals. This results in black crystal wires that not only exhibit broadband absorption but also maintain exceptional stability even under prolonged exposure to high temperatures. The method also involves the controlled synthesis of colorless and red crystal wires. As a proof of concept, these stable black Au crystal wires demonstrate superior performance in photothermal conversion applications. The methodology, derived from the crystal growth process, presents a defect template that offers a novel approach to material design. Furthermore, these unique crystals, available in various colors, hold significant promise for a range of unexplored applications.

Photothermal Conversion Porous Organic Polymers: Design, Synthesis, and Applications.

Solar energy is a primary form of renewable energy, and photothermal conversion is a direct conversion process with tunable conversion efficiency. Among various kinds of photothermal conversion materials, porous organic polymers (POP) are widely investigated owing to their controllable molecular design, tailored porous structures, good absorption of solar light, and low thermal conductivity. A variety of POP, such as conjugated microporous polymers (CMP), covalent organic frameworks (COF), hyper-crosslinked porous polymers (HCP), polymers of intrinsic microporosity (PIM), porous ionic polymers (PIP), are developed and applied in photothermal conversion applications of seawater desalination, latent energy storage, and biomedical fields. In this review, a comprehensive overview of the recent advances in POP for photothermal conversion is provided. The micro molecular structure characteristics and macro morphology of POP are designed for applications such as seawater desalination, latent heat energy storage, phototherapy and photodynamic therapy, and drug delivery. Besides, a probe into the underlying mechanism of structural design for constructing POP with excellent photothermal conversion performance is methodicalized. Finally, the remaining challenges and prospective opportunities for the future development of POP for solar energy-driven photothermal conversion applications are elucidated.

A Ni@C nanowire-enabled photothermal membrane for highly efficient solar-driven interfacial water purification.

Ni@C nanowires were in situ grown with about 5 nm nickel particles uniformly distributed along the one-dimensional framework. By assembling into a membrane, Ni@C exhibited 95.7% solar spectral absorption and a high water interfacial evaporation rate of 2.38 kg m-2 h-1 under one sun. Superhydrophobic modification further enabled long-term stable saline water evaporation. This work demonstrates the promising potential of non-precious Ni for solar photothermal conversion applications.

Thiacalix[4]arene-Protected Silver Nanoclusters Encapsulating Different Two-Electron Superatom Oligomers.

The subvalent silver kernel represents the nascent state of silver cluster formation, yet the growth mechanism has long been elusive. Herein, two silver nanoclusters (Ag30 and Ag34) coprotected by TC4A4- (H4TC4A = p-tert-butylthiacalix[4]arene) and TBPMT- (TBPMTH = 4-tert-butylbenzenemethanethiol) containing 6e and 4e silver kernels are synthesized and characterized. The trimer of the 2e superatom Ag14 kernel in Ag30 is built from a central Ag6 octahedron sandwiched by two orthogonally oriented Ag5 trigonal bipyramids through sharing vertexes, whereas a double-octahedral Ag10 kernel in Ag34 is a dimer of 2e superatoms. They manifest disparate polyhedron fusion growth patterns at the beginning of the silver cluster formation. Their excellent solution stabilities are contributed by the multisite and multidentate coordination fashion of TC4A4- and the special valence electron structures. This work demonstrates the precise control of silver kernel growth by the solvent strategy and lays a foundation for silver nanocluster application in photothermal conversion.

Recent Advances in Perylene Diimides (PDI)‐based Small Molecules Used for Emission and Photothermal Conversion

AbstractPerylene diimides (PDIs) have received considerable attention as a versatile class of functional dyes owing to their flexible reaction sites and remarkable stability. Recent advances have enhanced our understanding of the fluorescence and photothermal conversion properties of PDI molecules. The interplay between radiative and nonradiative transitions controls the emission and heat generation processes in these molecules. This comprehensive overview summarizes the recent strategies for manipulating the structures of PDI molecules for fluorescence and photothermal conversion applications. Additionally, challenges and potential solutions associated with the usage of fluorescent and photothermal PDI molecules are discussed.

Synergistic enhancement of optical properties in Ca/Ni co-doped LaFeO3 perovskite coatings enabling high-temperature photothermal conversion

Perovskite-type oxides (ABO3) are widely acknowledged as novel light-absorbing materials owing to their adaptable composition, distinctive oxidation states, and customizable physicochemical properties. In this study, we reported a series of A-site or A/B-sites doped LaFeO3-based ceramic coatings for photothermal conversion. An exhaustive investigation was undertaken to explore the effects of doping element on the microstructure, microchemistry, and optical properties of the ceramic coating. Among all the samples, the La0.5Ca0.5Fe0.95Ni0.05O3 coating exhibits the highest absorptivity in the solar spectrum (300–2500 nm) and in the wavelength range of 0.3–14 μm, reaching 92.2 % and 88.1 %, respectively. Furthermore, it demonstrated the superior photothermal conversion performance under solar and infrared radiation. Complementary first-principles calculations provide fundamental principles for comprehending the light absorption enhancement mechanisms in LaFeO3-based materials, revealing the complex interplays between crystal structure, band structure, and light absorption. The experimental findings, along with the results of first-principles calculations, demonstrate that the doping of Ca or Ca and Ni can effectively reduce the bandgaps and induce lattice distortions, thereby enhancing the light absorption in the visible and infrared wavebands. This work presents a facile method to prepare LaFeO3-based coatings with different morphologies, providing a novel option for high-temperature photothermal conversion applications.

Photo-thermal conversion properties of phosphonium-based ionic liquid, its magnetized and emulsion forms

In this work, phosphonium-based ionic liquid (PIL) and its magnetized form (MPIL) were used for heat generation from light. Based on the experimental results, MPIL shows better performance compared to PIL. The MPIL nanofluid was stable even after several consecutive heating/cooling cycles in the closed system. Due to low transparency, the MPIL exhibits the most light-to-heat conversion efficiency on its surface so that the surface temperature respectively reaches 62.5 ℃ and 78.0 ℃ after 60 min simulated light and sunlight irradiation. The photo-thermal conversion ability of the MPIL was examined at various light intensities. Several thermo-physical parameters for PIL and MPIL were calculated and compared, approving the superiority of the MPIL in photo-thermal conversion. To overcome the high cost of large amount of utilized MPIL, which is the drawback of most of ionic liquids, the stable surfactant-free MPIL+Oil emulsion is prepared with a very low amount of MPIL (for the first time), which shows good photo-thermal conversion performance. The outstanding advantages of both MPIL nanofluid and MPIL+Oil emulsion including not using dispersant and high photo-thermal durability/ability make them suitable candidates for practical photo-thermal conversion applications.

A flexible, high-efficiency, and low-cost FeS2@CTS hydrogel film for solar interface water evaporation

Solar interfacial water evaporation to obtain pure water has attracted extensive attention in recent years. In this work, based on the excellent optical property of FeS2 and the cross-linking nanostructure of chitosan (CTS), a FeS2@CTS hydrogel composite film for solar interfacial water evaporation was developed by hydrothermal synthesis and the following composite coating technology. The prepared FeS2@CTS presented high solar absorptivity of 95.27% and fast optical response capability. Under the optimized condition, the evaporation rate of pure water reached 3.34 kg m−2 h−1 and the photothermal conversion efficiency was 103.06% under one sun irradiation. In five runs, the evaporation rate of the FeS2@CTS was stable, indicating the excellent cycle stability. Also, in the desalination test, the stable evaporation rate of 1.74 kg m−2 h−1 was obtained in five runs. Due to the simple preparation method, low cost, and outstanding interfacial evaporation property, this FeS2@CTS indicates great potential for the seawater desalination or other photothermal conversion applications.

Hierarchical porous metallic glass with strong broadband absorption and photothermal conversion performance for solar steam generation

The development of a strong light absorption absorber with a facile preparation process are crucial for some photothermal conversion applications, such as solar steam generation, photothermal catalysis and detectors. Here, a hierarchical structure based on microporous surface equipped with nanoporous layer is ingeniously designed and fabricated benefiting from the unique thermoplastic forming ability of metallic glasses by using the soluble clusters as template in less than 30 s. The presence of hierarchical porous structures induces multiple reflection of light and excites the plasmonic behavior of surface, achieving over 90% light absorption in the 380–20 µm wavelength range and the broad light incident angle from 0° to 70°, resulting in a remarkable photothermal conversion performance. Compared to conventional and existing absorber, the innovatively designed and fabricated metallic surface offers outstanding advantages in terms of light absorption range, heating rate and maximum temperature rise. Afterwards, the hierarchical porous structures for solar steam generation shows an evaporation efficiency of up to 94.2% and evaporation rate of 1.72 kg m−2 h−1 at 1 kW m−2. The design of unprecedented structure on metallic glass opens up a new strategy for solar energy harvesting, water treatment and other related fields.

Investigation of the Thermal Stability of a Solar Absorber Processed through a Hydrothermal Technique

In this work, we study the thermal stability of a hydrothermally treated stainless steel (SS) selective solar absorber by annealing in air in a temperature range between 300 °C and 700 °C for a soaking time of 2 h. Thermal stability testing in the presence of air is critical if the vacuum is breached. Therefore, the SS was characterized by X-ray diffraction (XRD), mechanical, and optical techniques. The XRD analysis shows that the grain size of the as-treated absorber is 67 nm, whereas those of the annealed absorbers were found to be in the range between 66 and 38 nm. The phase of the as-treated and annealed SS was further identified by XRD as Fe2O3. The EDS result shows that the elemental components of the SS were C, Cr, Fe, and O. The strain (ε) and stress (σ) calculated for the as-treated absorber are 1.2 × 10−1 and −2.9 GPa, whereas the annealed absorbers are found in the range of 4.4 × 10−1 to 5.2 × 10−1 and −121.6 to −103.2 GPa, respectively, at 300–700 °C. The as-treated SS absorbers exhibit a good spectra selectivity of 0.938/0.431 = 2.176, which compares with 0.941/0.403 = 2.335 after being annealed at 300 °C and 0.884/0.179 = 4.939 after being annealed at 700 °C. These results indicate a small improvement in absorptivity (0.941) and emissivity (0.403) after annealing at 300 °C, followed by a significant decrease after annealing at 700 °C. The obtained analysis confirms that the annealed SS absorber exhibits excellent selectivity and is suitable to withstand any thermal condition (≤700 °C) in air. Thus, using a cost-effective approach as demonstrated in this study, the as-treated and annealed SS absorber could be used for photo-thermal conversion applications.

Numerical Study of Periodic Composite Structure Absorber Based on MoS2 Material

In this paper, a broadband absorber with a periodic composite structure based on numerical simulation of finite-difference time-domain method (FDTD) is proposed. The absorber base is titanium (Ti), on which iron tetroxide (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) nanospheres are laid. The nanospheres are coated with molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and lanthanum fluoride (LaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) composites, respectively, and are periodically arranged in symmetrical rectangular arrays. The numerical analysis results show that the absorber designed in this paper had an average absorption rate of 95.00% in the light wavelength range of 200 nm to 2500 nm, with the absorption bandwidth reaching 2300 nm, which was a significant improvement compared with other absorbers, and 100.00% absorption was achieved at 300 nm and 650 nm. According to the analysis of the coupling effect of the surface plasmon resonance (SPR) and the localized surface plasmon resonance (LSPR), the ultra-broadband absorber achieved perfect absorption performance. The research results indicate that the absorber proposed in this paper is insensitive to light polarization, has a wide-angle characteristic, and is easy to realize recycling. Therefore, it has a great potential value for the application in photothermal conversion, seawater desalination, and rapid collection of sea salt.

Carbon Nanotubes Grown on the Carbon Fibers to Enhance the Photothermal Conversion toward Solar-Driven Applications.

Photothermal conversion is a directly, sustainable, and green path to use solar energy and the one of the most important keys is the photothermal conversion material. How to obtain the durable and effective material for photothermal conversion with low cost and facile preparation is still a great challenge. In this work, the carbon nanotubes (CNTs) are grown on the carbon fibers (CFs) via the catalysis of trapped Fe and Co. The absorption of the as-prepared CFs/CNTs illustrate the enhancement from the visible light to the near-infrared light range. The photothermal conversion characterization shows the grown CNTs promoting the higher surface temperature and the highest temperature reaches to about 325 °C under 10 sun irradiations. The water evaporation on the CFs/CNTs is measured 1.40 ± 0.03 kg·cm-2·h-1 under 1 sun irradiation and the water evaporation rate is also found depending on the irradiation density. The photothermal conversion applications and the water evaporation under natural irradiation also reveal the suitable candidate of the CFs/CNTs for photothermal conversion application. This work provides a facile path to obtain effective carbon-based materials for photothermal application.

Efficient Green Synthesis of Highly Concentrated and Stable Carbon Nanotube Aqueous Dispersions for Photothermal Textile Fabrication

To maximize the performance of carbon nanotubes (CNTs) in photothermal conversion textiles, the green and efficient methods for the preparation of highly concentrated and stable aqueous dispersion of CNTs need to be urgently developed. Herein, the aqueous dispersion of CNTs with exceeding high concentration limits (over 100 mg/mL) is synthesized by an eco-friendly one-step hydrothermal method with the assistance of ionic liquid crystals (ILC). CNTs non-covalently wrapped by ILC can exist in various forms, such as well-dispersed dispersion, conductive slurry, thixotropic gel, and deformable dough. Particularly, the highly concentrated dispersion has excellent dispersion stability and remains stable even after 60 days of resting. Due to the cationic head group of ILC, the positively charged dispersion was electrostatically self-assembled to prepare photothermal textiles with excellent mechanical robustness and chemical stability, which can be applied to multiple harsh working conditions. This research shows an efficient and feasible method for the non-destructive dispersion of CNTs at high concentrations and also provides a reference for photothermal conversion applications of CNTs.

Nearly perfect absorption of solar energy by coherent of electric and magnetic polaritons

Photothermal conversion applications of solar energy are attracting more and more interests nowadays, and perfect absorption of solar energy by metamaterials is a key point for such a phenomenon. In the present study, we propose a nearly perfect solar absorber with double nested rings respectively made of platinum (Pt) and nickel (Ni) periodically arranged on a gold substrate. We theoretically and numerically discuss the underlying mechanisms of the optical properties for such a multi-materials absorber submerged in water by using the finite difference time domain (FDTD) method. The effects of material composition, height and radius of the nano-rings, the thickness of the gold substrate and alumina dielectric layer on the optical property of our proposed absorber are numerically analyzed. The absorptance of such a multi-materials absorber is higher than 96% in the whole wavelength range of 300–2400 nm, which accounts for almost the whole solar spectrum. Moreover, the solar absorber is insensitive to polarization while slightly sensitive to the incident angle of the light. Our solar absorber provides a new approach for the solar energy harvesting and photothermal conversion applications in water, such as solar vapor generation, sterilization, and so on.

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.

A new strategy towards spectral selectivity: Selective leaching alloy to achieve selective plasmonic solar absorption and infrared suppression

Cost-effective and spectrally selective solar absorbers that possess high solar absorptance, low thermal emittance, and superior thermal stability are essential for photothermal conversion applications, e.g., industrial heating, solar desalination, photothermal catalysis, and concentrating solar power systems. Here, a new strategy using a selective leaching reaction is demonstrated for transfiguring the broad-spectrum and highly reflective aluminum alloys into plasmonic-nanostructure selective solar absorbers (PNSSAs). Enabled by surface plasmon resonance, this strategy via assembling copper nanostructured thin film on an alloy mirror yields tunable manipulation of the spectral selectivity, high and omnidirectional solar absorptance (0.94 from 0 to 60°), low thermal emittance (0.03 at 100 °C), and excellent thermomechanical stability. Featured with merits of competitive performance of spectral selectivity, the feasibility of solution-processed fabrication, and cost-effectiveness of raw materials and chemicals, selective-leaching-alloy to achieve PNSSAs is a promising and universal approach for achieving high photothermal efficiency (85%) of solar thermal energy harvesting. The compatibility of this strategy with other metal alloys, such as steel and superalloys, extends its applications to fabricating mid- and high-temperature selective solar absorbers.

Engineering a Versatile Spectrally Selective Absorber for Moderate‐ and Low‐Temperature Application with Gradient High‐Entropy Nitride Nanofilms

Spectrally selective absorber with superior thermal stability and optical properties is crucial for photothermal conversion applications, including evaporation, anti‐icing, medical sterilization, photothermal catalysis, and solar‐thermal power. Efforts are being made to develop entropy‐stabilized high‐entropy ceramics as high‐performance functional materials, which promise a wide range of potential applications in the fields of energy storage and conversion owing to their diverse compositions and outstanding physical and chemical properties. Herein, an entropy‐stabilized strategy is used to boost the performance of spectrally selective absorbers by carefully choosing a high‐entropy alloy (TiVCrAlZr) target with a reasonable element design, which exhibits a good solar absorptance (α = 96.1%) and low thermal emittance (ϵ = 7.8%). Long‐term thermal stability investigation demonstrates that the entropy‐stabilized absorber could endure at 400 °C for 168 h. Under the irradiation of simulated sunlight, the surface temperature of the absorber can reach up to 105 °C, which is essential for middle‐ and low‐temperature applications. Overall, this work provides significant insights into the spectral selectivity of high‐entropy alloy nitrides and offers a new strategy for designing and developing moderate and low solar selective absorbing coatings via a high‐entropy strategy.

Systematical investigation on the solar-thermal conversion performance of TiN plasmonic nanofluids for the direct absorption solar collectors

The research on the efficient utilization of solar energy has far-reaching significance. Meanwhile, the preparation of high-efficiency, low-cost nanofluids as the working fluid in the photothermal conversion system is the current research hotspot. Herein, TiN is introduced as a plasmonic nanoparticle with excellent optical absorption and photothermal conversion properties. In our work, the optical absorption properties of TiN nanoparticles (NPs) were compared with those of Au, Ag and Cu nanoparticles by FDTD method. The results showed that the TiN NPs could be used as a potential photothermal material because of its good optical properties and lower cost. In addition, TiN nanofluids (10–50 ppm) based on ethylene glycol were prepared by a two-step method, which were well dispersed. The optical properties and thermal conductivity of TiN nanofluids were also measured and discussed, because of its plasmon resonance effect, the absorption characteristics and thermal conductivity of TiN nanofluids have been greatly improved. The solar-thermal conversion experiments were carried out by simulated light source in a direct absorption solar collector (DASC), and the efficiency of TiN nanofluid was maximum increased by 67.1% compared with the based liquid glycol ethanol. These findings therefore suggested that TiN nanofluids have promise and potential in photothermal conversion applications.

Radiation stability and photothermal performance of surface-functionalized plasmonic nanofluids for direct-absorption solar applications

In this work, the photostability of gold nanoparticles (AuNPs) with different functional molecular coatings was investigated. Gold/water nanofluids were prepared using citrate (CIT) reduction, then coated with polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), or bovine serum albumin (BSA) by physical/chemical ligand adsorption. All nanofluids retained their monodispersity and extinction efficiency after ambient storage for three years. These long-term aged nanofluids were then subjected to accelerated indoor tests that mimic the prolonged and cyclic exposure to both full-spectrum and specific-band radiation. This included continuous exposure to broadband solar radiation at various intensities and focused near-ultraviolet (NUV) radiation for different durations, as well as cyclic exposure (in irradiation/darkening periods) to both solar and NUV radiation. Assessment of post-test stability has been realized using complementary characterization techniques. Results showed that stability was variable to the coating type, radiation exposure mode, and radiation spectrum. Subtle physicochemical transitions in the polymeric coatings, even in the absence of ligand desorption and particle clustering, were shown to alter the optical properties and wettability of the nanofluids. While the gold cores remained intact, some photoinduced instabilities occurred in the adsorbed polymeric coatings, including chain scission of PEG, conformational collapse of PVP, and partial denaturation of BSA. Largely attributed to the strong polymer-Au interactions and high surface grafting densities, and despite their coating transformations, AuNPs maintained a high level of photostability. This work marks important progress towards realizing photothermally superior, yet colloidally stable, solar nanofluids compatible with a wide range of direct-absorption photothermal applications in the water and energy sectors. • Plasmonic gold nanoparticles stabilized using different polymeric coatings. • Accelerated radiation stability tests mimicking continuous/cyclic solar/UV exposure. • Insight gained into photoinduced physiochemical transitions in cores and coatings. • Stability variable to coating type, radiation exposure mode, and radiation spectrum. • Photostability limitations elucidated for photothermal conversion applications.