Introduction
Solar absorbing materials
Plasmonic nanometals
Fig.1 (a) Schematic showing illumination and plasmonic heating of an individual Au nanoparticle on the transparent glass substrate floor of our fluidic microchamber; (b) Scanning electron microscope (SEM) images of a sample with a dense coverage of Au nanoparticles randomly distributed on the glass substrate and a typical nanoparticle (inset); (c) Scattering intensities of a single 100 nm diameter nanoparticle in air (black), water (blue), and an envelope of water vapor produced by laser illumination (red); (d) Dependence of nanobubble-induced localized surface plasmon resonance blueshift on Au nanoparticle diameter, with a maximum shift observed for a nanoparticle diameter of 100 nm. Reprinted with permission from ref. [22]. Copyright 2013, American Chemical Society. |
Fig.2 Fabrication process and characterization of the Al NP-based plasmonic structure. (a) Aluminium foils served as the source materials for the entire fabrication process; (b) AAM fabricated by anodic oxidation; (c) The Al NP/AAM structure formed after the NP deposition; (d–f) Optical photographs of the aluminium foil (d), AAM sample (e) and Al NP/AAM structure (f) observed from the AAM side; (g,h) High-resolution SEM images of the structure: The top view (g) and cross-section (h); (i,j) Magnified images of the areas indicated in (h). Reprinted with permission from ref. [36]. Copyright 2016, Springer Nature. |
Nano carbon materials
Fig.3 (a) A picture of enhanced steam generation by the double-layer structure under the solar illumination of 10 kW·m−2 (reprinted with permission from ref. [42]. Copyright 2014, Springer Nature); (b–d) Schematic illustration showing the experimental setup for solar steam generation using a vertically aligned carbon nanotube (VACNT) array floating on the water to absorb solar energy and to localize the heat; (e) A tilted view SEM image of the VACNT array; (f) A magnified side-view SEM image of the VACNT array; (g) A transmission electron microscopy image of CNT bundles. Reprinted with permission from Ref. [43]. Copyright 2017, American Chemical Society. |
Fig.4 (a, b) Low- and high-magnification SEM images of wood cross section showing the microchannel structures of wood; (c) SEM image showing the long microchannels in the wood; (d) Absorption spectrum of radially cut wood; (e,f) Thermal conductivity of wood in dry- and wet-states (inset of each panel showing the temperature gradient along the thickness of wood). Reprinted with permission from ref. [53]. Copyright 2017, American Chemical Society. |
Polymers
Fig.5 (a) The hierarchically nanostructured gel (HNG) consists of hierarchical porous structures, including internal gaps, micron channels and molecular meshes, wherein the solar absorber (PPy) penetrates the polymeric polyvinyl alcohol (PVA) network of the gel; (b) Schematic of a typical solar vapour generation system and the water confinement strategy: (1) Under solar radiation, the solar absorbers in the molecular meshes of the floating generator are heated, facilitating the evaporation of water confined in the polymeric network (The water confined in the molecular mesh has a reduced evaporation enthalpy. The evaporated water can be rapidly recovered via (2) branched water diffusion and (3) pumping based on micron channels and internal gaps, respectively); (c) The mass loss of water and solar vapour generation energy efficiency; (d) The mass loss of water with corresponding evaporation rates of different HNGs under 1 sun (1 kW·m−2), with pure water as the control. Each error bar represents the deviation from at least 15 data points; (e) Comparison of HNG vapour generation performance and previous reports under 1 sun. Reprinted with permission from Ref. [68]. Copyright 2018, Springer Nature. |
Semiconductors and metal oxides
Composite materials
Fig.6 Structure of the bilayer SWNT/AuNR film. (a) Schematic structure of the bilayer SWNT/AuNR Janus film viewed from different angles; (b) Photograph of the bilayer SWNT/AuNR Janus film in the cross-section direction (The inset of (b) is the structural model of the bilayer SWNT/AuNR film under bending conditions); (c) SEM image of the cross-section of the bilayer SWNT/AuNR Janus film (The inset of (c) is the structural model of the bilayer SWNT/AuNR Janus film); (d) SEM image of the top surface of the bilayer SWNT/AuNR film (The inset of (d) is the magnified SEM image of the AuNR layer); (e) SEM image of the bottom surface of the bilayer SWNT/AuNR film (The inset of (e) is the structural model of the bottom surface of the SWNT/AuNR film). Reprinted with permission from Ref. [84]. Copyright 2018, American Chemical Society. |
Thermal management
Nanofluids
Floating structures
Fig.7 (a) Energy balance and heat transfer diagram for a blackbody solar receiver operating at 100°C (The 1000 W∙m−2 delivered by the ambient solar flux is not enough to sustain the heat losses, and a 100°C equilibrium temperature cannot be reached); (b) Energy balance and heat transfer in the developed one-sun, ambient steam generator (OAS); (c) A photograph of the OAS composed of a commercial spectrally selective coating on copper to suppress radiative losses and to thermally concentrate heat to the evaporation region (The bubble wrap cover transmits sunlight, and minimizes convective losses. Slots are cut in the bubble wrap to allow steam to escape. Thermal foam insulates the hot selective absorber from the cool underlying water, and floats the entire structure. The inset compares thermal radiative losses at 100°C from a blackbody and the spectrally selective absorber). Reprinted with permission from Ref. [92]. Copyright 2016, Springer Nature. |
Structure designs
Fig.8 (a) Schematics and section of the solar steam generator: (1) Glass; (2) Narrow gap of evaporating water; (3) Hydrophilic cotton; (4) Copper plate; (5) Commercial solar absorption material (e.g., TiNOx); (6) Polystyrene; (b) Coupling between the steam generator and a solar concentrator; (c) Computational setup (Reprinted with permission from ref. [98]); (e) The cross-sectional view to exhibit every component of the system and the water transfer process; (f) Energy balance and heat transfer diagram for an absorber (assuming reaching 60°C) with thermal emittance of 5% under the solar flux of 1000 W·m−2. Reprinted with permission from Ref. [99]. |
Mass transfer
Fig.9 (a) GO suspension with a small amount of ethanol; (b) Directional freeze casting of GO mixture in a PTFE mold, which is placed on the surface of liquid nitrogen to induce the freezing direction from the bottom to top; (c) VA-GSM is obtained after freeze-drying and thermal annealing; (d) Photograph of monolith VA-GSM with a size of 16 cm ´ 16 cm; (e–i) SEM images of VA-GSM with different magnifications. Reprinted with permission from Ref. [48]. Copyright 2017, American Chemical Society. |
Fig.10 (a) A photo of a typical GBMCC device composing with geopolymer (brown) and biomass mesoporous carbon (BMC, black); (b) Schematic of the mass and heat transportation showing water was transferred from the bottom through the macroporous geopolymer and then to the BMC layer heated by the solar energy (The effect can be enhanced by the negative pressure caused by wind); (c) The influence of sunlight intensity and wind speed on evaporation rate. Reprinted with permission from Ref. [64]. Copyright 2018, John Wiley and Sons. |
Tab.1 Solar steam generation performances of different materialsa) |
Samples | Carriers | Solar absorption /% | Energy conversion efficiency /% | Evaporation rates /(kg·m−2·h−1) | Ref. |
---|---|---|---|---|---|
CNT/macroporous silica | Silica | – | 82 | 1.31 | [34] |
Ag/diatomite | Paper | – | 92.2 | 1.39 | [38] |
CNT Arrays | – | 99 | 30 | – | [43] |
CNT nanofluids | – | – | – | 1.1 | [45] |
Porous N-doped graphene | – | – | 80 | 1.5 | [47] |
Functionalized-rGO | – | – | 48 | 0.47 | [49] |
Hierarchical graphene foam | – | 85–95 | 91.4 | 1.4 | [54] |
rGO/MCE | Cellulose membrane | – | 60 | 0.838 | [57] |
Carbonized Mushroom | – | – | 78 | 1.475 | [61] |
Flamed-treated wood | Wood | – | 72 | 1.05 | [62] |
Mesoporous bulk carbons driven from biomass | Geololymer | 90–95 | – | 1.58, 2.85, 5.90 and 7.55, with 0, 1, 2 and 3 m·s−1 wind | [64] |
HNG | – | >95 | 94 | 3.2 | [68] |
MXene Ti3C2 | PVDF Membrane | – | 84 | 1.33 | [74] |
Ti2O3 Nanoparticles | Cellulose membrane | 92.5 | 92.1±3.2 | 1.32 | [76] |
GO-based aerogels | – | 92 | 86.5 | 1.622 | [79] |
Carbon beads | – | – | – | 1.28 | [84] |
Photo-electro-thermal Graphene | – | – | – | 2.01–2.61 | [85] |
CNT modified filter paper | Paper | – | 75 | 1.15 | [90] |
Carbon sponge | – | >95 | 85 | 1.31 | [104] |
a) The solar absorption, the energy conversion efficiency and the evaporation rates of various photothermal materials under 1 sun. |