Preparation of biomass yam solar absorber and its application in solar evaporation

Preparation of biomass yam solar absorber and its application in solar evaporation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Preparation of biomass yam solar absorber and its application in solar evaporation Li Ting, Jia Juan, Yanqing Wang, Sun Hanxue, Jiyan Li, Zhu Zhaoqi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2791601/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Solar evaporation system has become a research hotspot in the field of photothermal conversion technology in recent years because of its high photothermal conversion efficiency and practicality of promotion. Biomass solar absorbers have excellent solar absorption properties and high solar-water vapor conversion, but they have the limitations of long feedstock production cycle and high carbonization temperature. As a kind of biomass materials, yam is not only inexpensive, but also has a short production cycle and rich pore structures. Therefore, in this paper, a yam based solar absorber with rich pore structure was prepared, and the photothermal conversion efficiency of the absorber was further investigated. The yam was treated with freeze-dried method and carbonized at different temperatures to obtain yam solar absorbers. Then find the thermal stability and porosity of solar absorber gradually rise as the treatment temperature increasing. The solar absorption rate of the carbonized yam was close to 90% in the near UV-visible region. Solar-water vapor control experiments with different treatments of the solar absorber of the yam were carried out in simulated solar-driven interface steam generation system (SISGS). The absorber treated at 200°C in the sun was found to have the best performance with a solar-water vapor conversion of about 90% and a water evaporation rate of 1.3164 kg m − 2 h − 1 . Solar steam generation Conversation efficiency Biomass solar absorber Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The rapid population growth and economic development increasingly deplete the freshwater resources available on earth. Solar energy, as the most abundant, pollution-free and renewable energy in nature, is now attracting widespread attention for freshwater production [ 1 – 9 ] . To ensure the security of fresh water, a solar-driven interfacial vaporization desalination method is proposed in the present to convert the solar energy absorbed by photothermal materials into the thermal energy fit for local heating of water molecules at the gas-liquid interface to produce vapor [ 10 – 19 ] . Then, it is condensed to produce fresh water. And this method was considered as one of the most promising photo-thermal technologies for its high conversion efficiency and extensive application in seawater desalination, wastewater purification, sterilization, and liquid-liquid phase separation [ 20 ] . Therefore, it is particularly important to develop an ideal absorber characterized by broadband solar energy absorption, excellent solar thermal conversion performance, low thermal conductivity, high hydrophilicity, and the abundance of porous channels, which is convenient for alleviating the current scarcity of freshwater resources. In recent years, there has been a growing interest in use of biomass-based materials as independent solar absorbers [ 21 – 23 ] . Attributed to its abundance in nature, high hydrophilicity, low cost and environmental friendliness, it performs well in solar interfacial vapor production. In the systems of solar-driven interfacial vaporization, the photothermal material is either set directly on the water surface or indirectly in contact with the overall water through restricted water channels [ 24 – 28 ] . Despite much efforts made to improve the efficiency of solar thermal conversion, it remains challenging to derive efficient and low-cost solar thermal materials from the readily available raw materials. Yang [ 23 ] et al. developed a novel low-cost system based on a common biowaste, pomelo peels (PPs) and fractal carbonized pomelo peels (FCPP), to achieve 98% solar spectral absorption, 1.95 kg m − 2 h − 1 evaporation rate, and 92.4% solar thermal efficiency. Jia [ 29 ] et al. derived a new bilayer photothermal material of alabaster/polyacrylamide composite (APAC) from alabaster, with the efficiency of solar-water vapor conversion reaching 85% at 1 sun illumination. Yang [ 30 ] et al. prepared a novel solar interfacial evaporation device by depositing polydopamine (PDA) and silver nanoparticles (Ag-NPs) on natural wood. The device reached a high evaporation rate of 1.58 kg m − 2 h − 1 under one sun (1 kW m − 2 ), while the evaporation efficiency reached 88.6%. Despite the excellent solar absorption properties and high solar-water vapor conversion efficiency, biomass solar absorbers still face the problems of long feedstock production cycle [ 33 ] and high carbonization temperature [ 32 , 35 ] . In this paper, yam solar absorbers are obtained from commercially available yam and then treated in air. After the characterization of its morphology, starch crystalline form and other properties by scanning electron microscopy and X-ray diffraction, it is found out that yam possesses a pore-like structure and hydrophilicity. The simple method used to prepare yam solar absorber, short production cycle, wide source of raw materials and excellent solar-water vapor conversion efficiency provide a new solution for the study of biomass solar absorber. 2. Experimental 2.1. Materials and apparatus Yam purchased from supermarkets. Polyvinyl alcohol purchased from Tianjin Guang fu Fine Chemical Research Institute. Graphite powder. Main experimental apparatus: Electronic analytical balance (JJ124BC), Vacuum Freeze Dryer (FD-1A-50), Scanning Electron Microscope (JSM-6701F), Transmission Electron Microscope (JEOL-2010), X-ray electron diffractometer (D/Max-2400), Thermogravimetric Analyzer (TGA/DSCI), Fourier transform infrared spectroscopy (FTIR-850), Flash method thermal conductivity analyzer (LFA447), Specific surface area analyzer (SXL-1002), Contact angle tester (DSA100), Xenon lamp solar source (CEL-S500/350). 2.2. Methods 2.2.1. Preparation of yam solar absorbers Yams purchased from supermarkets were cut into columns of 0.5 cm thickness and soaked into distilled water for 2 days, with water changes every 2 h during this period. Afterwards, the soaked yams were freeze-dried by using freezer dryer after pre-freezing at -18 ℃ for 8 h. 2.2.1. Treatment of yam solar absorbers The above-mentioned yams were placed in a muffle furnace and carbonized at 200 ℃, 250 ℃, 260 ℃ and 270 ℃ degrees for 2 h to investigate the effects of different carbonize temperatures on their properties. The preparation steps are shown in Fig. 1 . The figure shows that the yam was freeze-dried with a very low density, which allowed it to be placed on the top of the dandelion without destroying the white crown hairs knotted into a pompom. This feature provides conditions for it to float freely at the interface of the water column. To investigate the effect of different treatments on the solar-water evaporation rate of the solar absorber of the yam, this paper also used a flame to treat them [ 34 ] and prepare bilayer the solar absorber of the yam. Meanwhile, bilayer yam-graphite powder solar absorbers were prepared by coating the yam surface with PVA ( 10% concentration ) followed by adhesion with graphite powder [ 36 ] . 3. Results And Discussion SEM was used to determine the morphological characteristics of freeze-dried yam. Figure 2 (a), (b), and (c) are SEM images of freeze-dried yam treated at temperatures of 200°C and 270°C. A honeycomb-like structure can be seen on the yam's longitudinal surface, which is also filled with many granules that are both densely packed and sparsely distributed in different places. From Fig. 2 (a) to (c), the damage to the structure increases as the temperature rises. In order to further validate this conclusion, the particle-filled regions were scaled up independently at various temperatures. Figure 3 illustrates this. Figure 3 (a) depicts the electron microscope scan of the freeze-dried yam in the granule-filled region, which shows that the skeleton of yam is intact and the granules are clustered within the skeleton. The picture captured by a scanning electron microscope of yam treated at 200°C is depicted in Fig. 3 (b). The skeleton in the illustration looks to be cracked, and although the stacked granules are still stacked, their stacked structure is beginning to disintegrate. Figure 3 (c) is a scanning electron microscopy image of yam following treatment at 270°C, in which the skeleton was badly destroyed and particle accumulation was no longer compact. Therefore, when the temperature rises, so does the degree of skeletal structure damage. To have a deeper understanding of the yam's morphology, the cross-section of the yam was described. As depicted, the particle accumulation zone and the particle sparse zone are evident, but the temperature damage to its structure becomes less apparent from Figure (d) to (f), which may be related to the direction of its collapse. To further research the structure of the yam, the microscopic morphology of the granules and skeleton walls were examined. As illustrated in Fig. 3 (g), the granules are connected to the skeleton and between the granules and the granules by a mesh structure, and the granules have a smooth surface and a radius of approximately 10 \(\mu m\) . On the skeleton wall, as depicted in Fig. 3 (h), there are folds and mesh-like branches, but no pore structure, and this unique structure can better sustain its particle structure. Table 1 Pore properties of solar absorber Sample \({{V}}_{{t}{o}{t}{a}{l}}\) (cm 3 g − 1 ) \({{D}}_{{B}{J}{H}}\) (nm) yam yam carbonized (200 ℃) yam carbonized (270 ℃) 0.010586 0.056951 0.009012 4.6960 5.2257 5.0569 The desorption curves of yam treated with different temperatures after freeze-drying were measured by the N 2 adsorption/desorption (77 K, P/P 0 = 0.975) method, and the average pore diameter and pore volume were obtained after calculation. The nitrogen adsorption and desorption isotherm curves and pore size distribution of yam are shown in Fig. 4 (a) and (b). According to the International Union of Pure and Applied Chemistry (IUPAC) classification [ 35 ] , the nitrogen adsorption and desorption isothermal curves in Fig. 4 (a) are V-shaped, starting with microporous adsorption, and with the increase of pressure, the capillary condensation phenomenon occurs to make the adsorption of the material rise rapidly, and a hysteresis loop appears because capillary condensation and evaporation occur at different pressures. The pore size distribution of the material was shown by Fig. 9 (b). It can be seen that the pore size distribution of the yam is wide and slightly different for the yam treated at different temperatures. In addition, the material pore diameters and adsorption pore volumes are shown in Table 1 . Figure 4 (c) shows the chemical compositions of the dried the solar absorber of the yam, and the infrared absorption spectra of the solar absorbers in the range of 4000 − 400 cm − 1 were tested with the diffraction of the crystals to X-rays within 2-80 o .In Fig. 4 (c), the infrared absorption peaks near 3400 cm − 1 and 1645 cm − 1 are bending vibration absorption peaks of O-H chemical bonds [ 37 ] .The infrared absorption peak near 2925 cm − 1 is a stretching vibration absorption peak of -CH 2 -.The IR absorption peaks near 1645 cm − 1 are the bending vibration absorption peaks of the O-H chemical bond [ 37 ] and possibly the C = O stretching vibration absorption peaks of the carbonyl group [ 38 ] , and the absorption peaks at 1375 cm − 1 , 978 cm − 1 , 765 cm − 1 and 575 cm − 1 are characteristic peaks of starch and glycosides [ 39 ] .Therefore, yam is rich in starch and sugar components [ 40 ] , and the granules in its morphological analysis are starch, and hydrophilic groups such as O-H and C = O are the main reasons for the excellent hydrophilic properties of yam. By analysis, the main functional groups of yams treated at different temperatures did not undergo red shift or blue shift, but their fingerprint regions differed. In the XRD patterns of Fig. 4 (d), indicate two different peaks at 17 o and 23 o .We can find with increasing temperature, its crystallinity enhanced but its crystal type remained the same, and the diffraction peak at 23 o indicated that the yam starch was a C-type crystal [ 41 ] . The spectral absorption curves of yam solar absorbers can be found in Fig. 4 (e). From the figure, we can see that in the infrared and visible regions, the absorption of solar by the treated the solar absorber of the yam is significantly higher than that before treatment, and the wavelengths corresponding to the maximum absorption of solar are different at different treatment temperatures, and the absorption of solar weakens with the growth of wavelength in the near ultraviolet region, but in the visible region, its absorption of solar can reach over 80%. To investigate the effect of treatment temperature on the thermal stability properties of yam, the variation of mass with temperature was tested with a thermogravimetric analyzer under a nitrogen atmosphere at a heating rate of 10°C/min, as shown in Fig. 4 (f). From the figure, yams treated at different temperatures had the same rate of mass loss around 296°C. Before this point, the mass loss of yams decreased with the increase of treatment temperature. After this point, the stability performance of the untreated yam was the best. Meanwhile, the untreated yam showed a plateau at 340 ℃ and then lost its quality again, and its quality was almost unchanged by 475 ℃. For the treated yams, their thermal stability performance was enhanced with the increase of treatment temperature. During the temperature increase from room temperature to 1000°C, the yam lost 66% of mass for the untreated yam and 80% of mass for the 200°C treatment; the yam lost very little mass until 215°C, and the mass remained unchanged after 600°C. Table 2 Thermal conductivity and related parameters Samples Thermal diffusivity (mm 2 s − 1 ) Specific heat (J g − 1 K − 1 ) Density (g cm − 3 ) Thermal conductivity (W m − 1 K − 1 ) yam yam carbonized (200 ℃) 0.09 0.05 1.751 1.516 1.267 1.046 0.201 0.079 Solar absorbers efficiently utilize sun solar by containing the converted heat energy in the upper layer of the solar absorber, preventing heat loss into the water column. To determine this property of the solar absorber, the thermal conductivity of the laser method was used to measure the relevant data in this experiment. The thermal conductivity of a material can be calculated by the following equation: $$\text{K=α}{C}_{p}\rho$$ where K is the thermal diffusion coefficient and α is the thermal diffusivity. The thermal conductivity and related parameters are shown in Table 2 . The thermal conductivity of yam solar absorber is only 0.201 W/ (m K), and the thermal conductivity is even lower at 0.079 W/ (m K) after 200 ℃ treatment, so the treated yam is more favorable for SISGS to utilize solar energy efficiently. Figure 5 (a) and (b) show the temperature variation of yam in air and water with different temperature treatments under 1 sun illumination with time, respectively. The first 10 min in Figure (a) shows the variation of surface temperature of yam under solar 1 solar intensity with time, and after 2 min, the surface temperature approaches the equilibrium state almost no longer rises with the increase of time. When the solar simulator was turned off after 10 min, the surface temperature of the yam decreased rapidly, and the temperature approached room temperature after 3 min. Therefore, the surface of the yam solar absorber is highly dependent on the solar intensity, and the higher the treatment temperature, the higher the temperature at which it reaches equilibrium. Figure 5 (b) shows the time-temperature curves of yam solar absorbers floating in water under the same conditions. From the figure, the temperature on the surface of yam reaches equilibrium after 10 min, and the highest is only 40 ℃, which is lower than the temperature in air, which is related to the absorption of heat generated from yam by the water body, and it can be tentatively determined that the absorption mass of yam can be applied in solar steam production technology. The freeze-dried yam has the advantages of porosity, hydrophilicity, and good thermal stability, and has high absorption of solar in the near-infrared-visible region after treatment. To investigate the vapor rate and solar-water vapor conversion rate of the solar absorber of the yam applied to Solar-distillation technology, solar-water vapor experiments were conducted under laboratory conditions, as shown in Fig. 5 (c). To test the hydrophilicity of the solar absorber of the yam to water and water transport properties, an experiment was designed to drop water drops onto the surface of the solar absorbers with a syringe, as shown in Fig. 5 (e) and (f). As can be seen in Fig. 5 (e), the freeze-dried yam is hydrophilic, and the water droplets spread completely and transport some water below the interface after 2 s onto the surface of the solar absorber. From Fig. 5 (f), we can see that the water droplets disappear after 2 s on the surface of the solar absorber, and the hydrophilicity of the solar absorber and the transport properties of the water body are improved after the surface treatment. This property of yam may be related to the fact that yam itself has many hydrophilic groups, or it may be related to the structure of the pores after freeze-drying, or it may be caused by the interaction of both. The curves of water mass loss with time due to yam absorbers after different temperature treatments under 1 sun illumination are shown in Fig. 6 (a). From the figure, the treated yams caused greater mass loss in the water column than the untreated ones at the same time, and the 200 ℃ carbonized yams caused the greatest mass loss, which may be related to the changes in the structure of the yams during treatment. The amount of steam produced per unit time (steam rate) is calculated by deriving the mass change, and then the solar-water steam conversion efficiency is calculated by the following equation: $$\eta =\dot{\text{m}}{h}_{LV}/{C}_{opt}{q}_{i}$$ Where 𝜂 is the solar photothermal conversion rate, ṁ is the amount of water vapor production obtained, \({h}_{LV}\) is the total enthalpy (including both latent and sensible heat), \({q}_{i}\) is the value of solar radiation at 1 solar intensity, and \({C}_{opt}{q}_{i}\) is the total power density of solar irradiation. There are differences in the performance of solar absorbers at different optical densities [ 31 , 32 ] , and in this paper, 200 ℃-carbonized yams were selected for solar water vapor experiments at different optical densities. Figure 6 (c) shows the variation of temperature with time at the interface with air when the yam is floating with the surface of the water body since different optical densities. As can be seen from the figure, the surface temperature of yam reached equilibrium after 10 min, less than 40°C at 1-sun intensity, about 10°C higher at 2-sun than at 1-sun, and the surface temperature of the solar absorber at 3-sun was similar to that at 2-sun, with no significant temperature increase. Figure 6 (d) shows the time-mass variation curves at different optical densities. It can be seen from the figure that the mass change under 3-sun optical density is greater than that under 1 and 2-sun. Comparing Fig. 6 (c), the lowest yam surface temperature under 3-sun may be related to the fact that the heat produced by the yam is absorbed by the water body. Figure 6 (e) shows the evaporation rate of water vapor versus solar-water vapor conversion efficiency at different optical densities. As can be seen from the figure, the rate of water vapor production is proportional to the optical density, and the evaporation rate can reach 2.9 kg/ (m 2 h) at 3 suns, but the solar-water vapor conversion efficiency decreases with increasing optical density. From 1 to 2 suns, the conversion rate decreases by about 25%, and from 2 to 3 suns its yield is close, decreasing by only about 5%. To investigate the relationship between quality loss and the treatment of yam, experiments were designed for simple treatment of yam surface with flame and treatment of yam surface with PVA as adhesive and graphite powder as carbon material. It can be seen from Fig. 7 (a) that the time required to reach the equilibrium temperature is close to the equilibrium temperature for the solar absorber of the yam treated with both methods. The change in mass per unit area with time, water vapor generation rate and solar-water vapor conversion rate for which graphite powder was the solar absorber layer were greater than that for yam treated with flame, and the solar-water vapor conversion rate for both was between 68–70%, which was lower than that for yam treated at 200°C under the same conditions ( about 90% ).At the same time, the safety and the cheapness of raw materials of yam treated with 200 ℃ are higher than those treated with flame and with PVA and graphite powder, according to which, the 200 ℃ treatment of yam solar absorber has a better prospect in practical application. 4. Conclusions In this paper, low-density yam solar absorbers were prepared from yam by freeze-drying and related treatments, and the solar-water vapor conversion efficiency of the solar absorbers was investigated. We found that freeze-dried yams with low thermal conductivity and macropores, mesoporous and microporous structures could absorb up to 90% of sunlight after treatment. The water vapor conversion efficiency at 200 °C of treated yam sunlight absorber was about 90%, and the evaporation rate of the water body reached 1.3164 kg m -2 h -1 . The conversion efficiencies of absorbers under different suns were different, under 3 sun illumination, the conversion efficiency was about 60%. and the evaporation rate of water body was the largest at 2.6838 kg m -2 h -1 . Under the same conditions, the solar-water vapor conversion efficiencies of the experimentally prepared bilayer yam solar absorbers were similar and both lower than those of the carbon-treated absorbers. 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Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 20 Apr, 2023 Reviewers invited by journal 19 Apr, 2023 Editor assigned by journal 11 Apr, 2023 First submitted to journal 07 Apr, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2791601","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":193449660,"identity":"d4368517-70e5-4b45-9693-eae82b43eb25","order_by":0,"name":"Li Ting","email":"","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Ting","suffix":""},{"id":193449661,"identity":"3ce9c86a-fb07-4e6d-a212-bd68e036dc20","order_by":1,"name":"Jia Juan","email":"","orcid":"","institution":"CALB Co.Ltd","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jia","middleName":"","lastName":"Juan","suffix":""},{"id":193449662,"identity":"f4905226-5214-4a68-b653-7f991d1cef05","order_by":2,"name":"Yanqing Wang","email":"","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yanqing","middleName":"","lastName":"Wang","suffix":""},{"id":193449663,"identity":"04fade79-b87e-42d5-abd0-2736e2e8289f","order_by":3,"name":"Sun Hanxue","email":"","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Sun","middleName":"","lastName":"Hanxue","suffix":""},{"id":193449664,"identity":"93dd46a0-1d13-4c03-9c86-99252b07689d","order_by":4,"name":"Jiyan Li","email":"","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jiyan","middleName":"","lastName":"Li","suffix":""},{"id":193449665,"identity":"7851e27d-b875-45f8-979f-a8d9e3060795","order_by":5,"name":"Zhu Zhaoqi","email":"","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhu","middleName":"","lastName":"Zhaoqi","suffix":""},{"id":193449666,"identity":"943b88f5-a4c5-44eb-988b-3493c757a1a4","order_by":6,"name":"weidong Liang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYFCC5IYDQDKBnx3MYyZGSyJEi2QzA2MD0VpAZILBYWK1GBxPbDzwc0dtnvFhHvMHDBXWiQ3sZw/g13LmYcPB3jPHi80O8xg2MJxJT2zgyUvAq8XsBtAvvG3HEreBtDC2HU5skOAxIKjl4F+gls3NIC3/iNRymLetJnEDM0hLAxFa7IF+OSzbdiBxxmG2whkJx9KN23hy8GuRbE8+/PFtW11if3vzhg8faqxl+9nP4NcCBYchVAIQsxGjHgjqiFQ3CkbBKBgFIxIAAPM+T7gHS96qAAAAAElFTkSuQmCC","orcid":"","institution":"Lanzhou University of Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"weidong","middleName":"","lastName":"Liang","suffix":""}],"badges":[],"createdAt":"2023-04-08 03:06:31","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2791601/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2791601/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":36140122,"identity":"e12cc209-56ad-41ef-8cc6-6f0dad89f3cf","added_by":"auto","created_at":"2023-04-21 18:57:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":167612,"visible":true,"origin":"","legend":"\u003cp\u003eThe preparation process of the solar absorber of yam.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/aaac99a9238de9ce6813d8db.png"},{"id":36140118,"identity":"ded60a4b-baec-47ac-969b-2a5fd91cd0fb","added_by":"auto","created_at":"2023-04-21 18:57:54","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":385406,"visible":true,"origin":"","legend":"\u003cp\u003eSEM of the longitudinal section of yam. (a) yam after freeze-drying, (b) and (c) show the SEM of yam after carbonization at 200 ℃ and 270 ℃, respectively.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/ada48dce79c5a47cc25f244a.png"},{"id":36140440,"identity":"df71e4cd-6b80-4cbb-8656-7e05df516883","added_by":"auto","created_at":"2023-04-21 19:05:54","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":546228,"visible":true,"origin":"","legend":"\u003cp\u003eSEM of yam in the area filled with particles, (a) yam after freeze-drying, (b) and (c) show the SEM of yam after carbonization at 200 ℃ and 270 ℃, respectively. SEM of the Horizontal plane of yam. (d) yam after freeze-drying, (e) and (f) show the SEM of yam after carbonization at 200 ℃ and 270 ℃, respectively. (g) SEM of the particle stack, (h) SEM of the skeleton wall.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/56b2d3d6c1f7655d24587c50.png"},{"id":36140120,"identity":"339a3949-fa7a-4964-804d-e6261b60e263","added_by":"auto","created_at":"2023-04-21 18:57:54","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":161532,"visible":true,"origin":"","legend":"\u003cp\u003e(a) N\u003csub\u003e2\u003c/sub\u003e-adsorption/desorption isotherms of the yam after being treated at different temperatures, (b) The pore size distribution of the yam after being treated at different temperatures. (c) FT-IR spectra of yam after being treated at different temperatures, (d) XRD patterns about yam after being treated at different temperatures. (e) The solar absorption of the solar absorber from 250 nm to 2500 nm. (f) TGA graph of solar absorber.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/ce733a5777fbb23b4daf3e06.png"},{"id":36140442,"identity":"bce5abd4-30e3-440e-ab2b-95dd3305246a","added_by":"auto","created_at":"2023-04-21 19:05:54","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":224427,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface temperature change of solar absorber in air, (b) Surface temperature change of solar absorber in air on water, (c) Schematic of the solar-driven interfacial evaporation device, (d), (e) Picture of water droplets on solar absorber of yam.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/e3f42aca21b67ad29141d78b.png"},{"id":36140121,"identity":"a58a2e3c-a3dd-4dd1-9a33-e8e0efd44171","added_by":"auto","created_at":"2023-04-21 18:57:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":142669,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Time-dependent mass change of the yam under 1 illumination, (b) Evaporation rate (blue, left-hand side axis) and solar steam efficiency (pink, right-hand side axis) under 1 illumination; (c) Surface temperature change of the carbonized yam in 200 ℃ under different illumination; (d) Time-mass change of the carbonized yam in 200 ℃ under different illumination; (e) Evaporation rate (purple, left-hand side axis) and solar steam efficiency (yellow, right-hand side axis) under different illumination.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/c32b8f59b11b2c3e0ea74295.png"},{"id":36140981,"identity":"cacb1185-7d86-43b1-a4f8-0551c83fc0be","added_by":"auto","created_at":"2023-04-21 19:13:54","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":93278,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Surface temperature change of the yam treated by different carbon material under 1 illumination, (b) Time-dependent mass change of the yam treated by different carbon material under 1 illumination yam; (c) Evaporation rate (pink, left-hand side axis) and solar steam efficiency (blue, right-hand side axis) under 1 illumination.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/bd80491d246f521c89134dea.png"},{"id":36140983,"identity":"dd449a14-46c8-43ed-b8a2-24923d64412a","added_by":"auto","created_at":"2023-04-21 19:14:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1992534,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2791601/v1/5aa41bf7-b9d4-4cbc-aaec-8b4e27c07c40.pdf"}],"financialInterests":"","formattedTitle":"Preparation of biomass yam solar absorber and its application in solar evaporation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rapid population growth and economic development increasingly deplete the freshwater resources available on earth. Solar energy, as the most abundant, pollution-free and renewable energy in nature, is now attracting widespread attention for freshwater production\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7 CR8\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. To ensure the security of fresh water, a solar-driven interfacial vaporization desalination method is proposed in the present to convert the solar energy absorbed by photothermal materials into the thermal energy fit for local heating of water molecules at the gas-liquid interface to produce vapor\u003csup\u003e[\u003cspan additionalcitationids=\"CR11 CR12 CR13 CR14 CR15 CR16 CR17 CR18\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Then, it is condensed to produce fresh water. And this method was considered as one of the most promising photo-thermal technologies for its high conversion efficiency and extensive application in seawater desalination, wastewater purification, sterilization, and liquid-liquid phase separation\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Therefore, it is particularly important to develop an ideal absorber characterized by broadband solar energy absorption, excellent solar thermal conversion performance, low thermal conductivity, high hydrophilicity, and the abundance of porous channels, which is convenient for alleviating the current scarcity of freshwater resources.\u003c/p\u003e \u003cp\u003eIn recent years, there has been a growing interest in use of biomass-based materials as independent solar absorbers\u003csup\u003e[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. Attributed to its abundance in nature, high hydrophilicity, low cost and environmental friendliness, it performs well in solar interfacial vapor production. In the systems of solar-driven interfacial vaporization, the photothermal material is either set directly on the water surface or indirectly in contact with the overall water through restricted water channels\u003csup\u003e[\u003cspan additionalcitationids=\"CR25 CR26 CR27\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Despite much efforts made to improve the efficiency of solar thermal conversion, it remains challenging to derive efficient and low-cost solar thermal materials from the readily available raw materials. Yang\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e et al. developed a novel low-cost system based on a common biowaste, pomelo peels (PPs) and fractal carbonized pomelo peels (FCPP), to achieve 98% solar spectral absorption, 1.95 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e evaporation rate, and 92.4% solar thermal efficiency. Jia\u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e et al. derived a new bilayer photothermal material of alabaster/polyacrylamide composite (APAC) from alabaster, with the efficiency of solar-water vapor conversion reaching 85% at 1 sun illumination. Yang\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e et al. prepared a novel solar interfacial evaporation device by depositing polydopamine (PDA) and silver nanoparticles (Ag-NPs) on natural wood. The device reached a high evaporation rate of 1.58 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under one sun (1 kW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), while the evaporation efficiency reached 88.6%. Despite the excellent solar absorption properties and high solar-water vapor conversion efficiency, biomass solar absorbers still face the problems of long feedstock production cycle\u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e and high carbonization temperature\u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this paper, yam solar absorbers are obtained from commercially available yam and then treated in air. After the characterization of its morphology, starch crystalline form and other properties by scanning electron microscopy and X-ray diffraction, it is found out that yam possesses a pore-like structure and hydrophilicity. The simple method used to prepare yam solar absorber, short production cycle, wide source of raw materials and excellent solar-water vapor conversion efficiency provide a new solution for the study of biomass solar absorber.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Materials and apparatus\u003c/h2\u003e\n\u003cp\u003eYam purchased from supermarkets. Polyvinyl alcohol purchased from Tianjin Guang fu Fine Chemical Research Institute. Graphite powder.\u003c/p\u003e\n\u003cp\u003eMain experimental apparatus: Electronic analytical balance (JJ124BC), Vacuum Freeze Dryer (FD-1A-50), Scanning Electron Microscope (JSM-6701F), Transmission Electron Microscope (JEOL-2010), X-ray electron diffractometer (D/Max-2400), Thermogravimetric Analyzer (TGA/DSCI), Fourier transform infrared spectroscopy (FTIR-850), Flash method thermal conductivity analyzer (LFA447), Specific surface area analyzer (SXL-1002), Contact angle tester (DSA100), Xenon lamp solar source (CEL-S500/350).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Methods\u003c/h2\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1. Preparation of yam solar absorbers\u003c/h2\u003e\n\u003cp\u003eYams purchased from supermarkets were cut into columns of 0.5 cm thickness and soaked into distilled water for 2 days, with water changes every 2 h during this period. Afterwards, the soaked yams were freeze-dried by using freezer dryer after pre-freezing at -18 ℃ for 8 h.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1. Treatment of yam solar absorbers\u003c/h2\u003e\n\u003cp\u003eThe above-mentioned yams were placed in a muffle furnace and carbonized at 200 ℃, 250 ℃, 260 ℃ and 270 ℃ degrees for 2 h to investigate the effects of different carbonize temperatures on their properties. The preparation steps are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe figure shows that the yam was freeze-dried with a very low density, which allowed it to be placed on the top of the dandelion without destroying the white crown hairs knotted into a pompom. This feature provides conditions for it to float freely at the interface of the water column.\u003c/p\u003e\n\u003cp\u003eTo investigate the effect of different treatments on the solar-water evaporation rate of the solar absorber of the yam, this paper also used a flame to treat them\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e and prepare bilayer the solar absorber of the yam. Meanwhile, bilayer yam-graphite powder solar absorbers were prepared by coating the yam surface with PVA ( 10% concentration ) followed by adhesion with graphite powder\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cp\u003eSEM was used to determine the morphological characteristics of freeze-dried yam. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e (a), (b), and (c) are SEM images of freeze-dried yam treated at temperatures of 200\u0026deg;C and 270\u0026deg;C. A honeycomb-like structure can be seen on the yam\u0026apos;s longitudinal surface, which is also filled with many granules that are both densely packed and sparsely distributed in different places. From Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e (a) to (c), the damage to the structure increases as the temperature rises. In order to further validate this conclusion, the particle-filled regions were scaled up independently at various temperatures. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e illustrates this.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (a) depicts the electron microscope scan of the freeze-dried yam in the granule-filled region, which shows that the skeleton of yam is intact and the granules are clustered within the skeleton. The picture captured by a scanning electron microscope of yam treated at 200\u0026deg;C is depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b). The skeleton in the illustration looks to be cracked, and although the stacked granules are still stacked, their stacked structure is beginning to disintegrate. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(c) is a scanning electron microscopy image of yam following treatment at 270\u0026deg;C, in which the skeleton was badly destroyed and particle accumulation was no longer compact. Therefore, when the temperature rises, so does the degree of skeletal structure damage. To have a deeper understanding of the yam\u0026apos;s morphology, the cross-section of the yam was described. As depicted, the particle accumulation zone and the particle sparse zone are evident, but the temperature damage to its structure becomes less apparent from Figure (d) to (f), which may be related to the direction of its collapse. To further research the structure of the yam, the microscopic morphology of the granules and skeleton walls were examined. As illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(g), the granules are connected to the skeleton and between the granules and the granules by a mesh structure, and the granules have a smooth surface and a radius of approximately 10 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mu m\\)\u003c/span\u003e\u003c/span\u003e. On the skeleton wall, as depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(h), there are folds and mesh-like branches, but no pore structure, and this unique structure can better sustain its particle structure.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" style=\"width: 613px;\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePore properties of solar absorber\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth style=\"width: 196.109px;\" align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth style=\"width: 201.891px;\" align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{V}}_{{t}{o}{t}{a}{l}}\\)\u003c/span\u003e\u003c/span\u003e(cm\u003csup\u003e3\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth style=\"width: 193px;\" align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({{D}}_{{B}{J}{H}}\\)\u003c/span\u003e\u003c/span\u003e(nm)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 196.109px;\" align=\"left\"\u003e\n \u003cp\u003eyam\u003c/p\u003e\n \u003cp\u003eyam carbonized (200 ℃)\u003c/p\u003e\n \u003cp\u003eyam carbonized (270 ℃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 201.891px;\" align=\"left\"\u003e\n \u003cp\u003e0.010586\u003c/p\u003e\n \u003cp\u003e0.056951\u003c/p\u003e\n \u003cp\u003e0.009012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 193px;\" align=\"left\"\u003e\n \u003cp\u003e4.6960\u003c/p\u003e\n \u003cp\u003e5.2257\u003c/p\u003e\n \u003cp\u003e5.0569\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe desorption curves of yam treated with different temperatures after freeze-drying were measured by the N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption (77 K, P/P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.975) method, and the average pore diameter and pore volume were obtained after calculation. The nitrogen adsorption and desorption isotherm curves and pore size distribution of yam are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e (a) and (b). According to the International Union of Pure and Applied Chemistry (IUPAC) classification\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e, the nitrogen adsorption and desorption isothermal curves in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(a) are V-shaped, starting with microporous adsorption, and with the increase of pressure, the capillary condensation phenomenon occurs to make the adsorption of the material rise rapidly, and a hysteresis loop appears because capillary condensation and evaporation occur at different pressures. The pore size distribution of the material was shown by Fig.\u0026nbsp;9 (b). It can be seen that the pore size distribution of the yam is wide and slightly different for the yam treated at different temperatures. In addition, the material pore diameters and adsorption pore volumes are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e (c) shows the chemical compositions of the dried the solar absorber of the yam, and the infrared absorption spectra of the solar absorbers in the range of 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were tested with the diffraction of the crystals to X-rays within 2-80\u003csup\u003eo\u003c/sup\u003e.In Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(c), the infrared absorption peaks near 3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are bending vibration absorption peaks of O-H chemical bonds\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e.The infrared absorption peak near 2925 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is a stretching vibration absorption peak of -CH\u003csub\u003e2\u003c/sub\u003e-.The IR absorption peaks near 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the bending vibration absorption peaks of the O-H chemical bond\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e and possibly the C\u0026thinsp;=\u0026thinsp;O stretching vibration absorption peaks of the carbonyl group\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e, and the absorption peaks at 1375 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 978 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 765 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 575 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are characteristic peaks of starch and glycosides\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e.Therefore, yam is rich in starch and sugar components\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e, and the granules in its morphological analysis are starch, and hydrophilic groups such as O-H and C\u0026thinsp;=\u0026thinsp;O are the main reasons for the excellent hydrophilic properties of yam. By analysis, the main functional groups of yams treated at different temperatures did not undergo red shift or blue shift, but their fingerprint regions differed.\u003c/p\u003e\n\u003cp\u003eIn the XRD patterns of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(d), indicate two different peaks at 17\u003csup\u003eo\u003c/sup\u003e and 23\u003csup\u003eo\u003c/sup\u003e.We can find with increasing temperature, its crystallinity enhanced but its crystal type remained the same, and the diffraction peak at 23\u003csup\u003eo\u003c/sup\u003e indicated that the yam starch was a C-type crystal\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe spectral absorption curves of yam solar absorbers can be found in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(e). From the figure, we can see that in the infrared and visible regions, the absorption of solar by the treated the solar absorber of the yam is significantly higher than that before treatment, and the wavelengths corresponding to the maximum absorption of solar are different at different treatment temperatures, and the absorption of solar weakens with the growth of wavelength in the near ultraviolet region, but in the visible region, its absorption of solar can reach over 80%.\u003c/p\u003e\n\u003cp\u003eTo investigate the effect of treatment temperature on the thermal stability properties of yam, the variation of mass with temperature was tested with a thermogravimetric analyzer under a nitrogen atmosphere at a heating rate of 10\u0026deg;C/min, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(f). From the figure, yams treated at different temperatures had the same rate of mass loss around 296\u0026deg;C. Before this point, the mass loss of yams decreased with the increase of treatment temperature. After this point, the stability performance of the untreated yam was the best. Meanwhile, the untreated yam showed a plateau at 340 ℃ and then lost its quality again, and its quality was almost unchanged by 475 ℃. For the treated yams, their thermal stability performance was enhanced with the increase of treatment temperature. During the temperature increase from room temperature to 1000\u0026deg;C, the yam lost 66% of mass for the untreated yam and 80% of mass for the 200\u0026deg;C treatment; the yam lost very little mass until 215\u0026deg;C, and the mass remained unchanged after 600\u0026deg;C.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThermal conductivity and related parameters\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eThermal\u003c/p\u003e\n \u003cp\u003ediffusivity\u003c/p\u003e\n \u003cp\u003e(mm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSpecific\u003c/p\u003e\n \u003cp\u003eheat\u003c/p\u003e\n \u003cp\u003e(J g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDensity\u003c/p\u003e\n \u003cp\u003e(g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eThermal\u003c/p\u003e\n \u003cp\u003econductivity\u003c/p\u003e\n \u003cp\u003e(W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eyam\u003c/p\u003e\n \u003cp\u003eyam carbonized\u003c/p\u003e\n \u003cp\u003e(200 ℃)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.751\u003c/p\u003e\n \u003cp\u003e1.516\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.267\u003c/p\u003e\n \u003cp\u003e1.046\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.201\u003c/p\u003e\n \u003cp\u003e0.079\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eSolar absorbers efficiently utilize sun solar by containing the converted heat energy in the upper layer of the solar absorber, preventing heat loss into the water column. To determine this property of the solar absorber, the thermal conductivity of the laser method was used to measure the relevant data in this experiment. The thermal conductivity of a material can be calculated by the following equation:\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$$\\text{K=\u0026alpha;}{C}_{p}\\rho$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere K is the thermal diffusion coefficient and \u0026alpha; is the thermal diffusivity. The thermal conductivity and related parameters are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The thermal conductivity of yam solar absorber is only 0.201 W/ (m K), and the thermal conductivity is even lower at 0.079 W/ (m K) after 200 ℃ treatment, so the treated yam is more favorable for SISGS to utilize solar energy efficiently.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(a) and (b) show the temperature variation of yam in air and water with different temperature treatments under 1 sun illumination with time, respectively. The first 10 min in Figure (a) shows the variation of surface temperature of yam under solar 1 solar intensity with time, and after 2 min, the surface temperature approaches the equilibrium state almost no longer rises with the increase of time. When the solar simulator was turned off after 10 min, the surface temperature of the yam decreased rapidly, and the temperature approached room temperature after 3 min. Therefore, the surface of the yam solar absorber is highly dependent on the solar intensity, and the higher the treatment temperature, the higher the temperature at which it reaches equilibrium. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(b) shows the time-temperature curves of yam solar absorbers floating in water under the same conditions. From the figure, the temperature on the surface of yam reaches equilibrium after 10 min, and the highest is only 40 ℃, which is lower than the temperature in air, which is related to the absorption of heat generated from yam by the water body, and it can be tentatively determined that the absorption mass of yam can be applied in solar steam production technology.\u003c/p\u003e\n\u003cp\u003eThe freeze-dried yam has the advantages of porosity, hydrophilicity, and good thermal stability, and has high absorption of solar in the near-infrared-visible region after treatment. To investigate the vapor rate and solar-water vapor conversion rate of the solar absorber of the yam applied to Solar-distillation technology, solar-water vapor experiments were conducted under laboratory conditions, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(c).\u003c/p\u003e\n\u003cp\u003eTo test the hydrophilicity of the solar absorber of the yam to water and water transport properties, an experiment was designed to drop water drops onto the surface of the solar absorbers with a syringe, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(e) and (f). As can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(e), the freeze-dried yam is hydrophilic, and the water droplets spread completely and transport some water below the interface after 2 s onto the surface of the solar absorber. From Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(f), we can see that the water droplets disappear after 2 s on the surface of the solar absorber, and the hydrophilicity of the solar absorber and the transport properties of the water body are improved after the surface treatment. This property of yam may be related to the fact that yam itself has many hydrophilic groups, or it may be related to the structure of the pores after freeze-drying, or it may be caused by the interaction of both.\u003c/p\u003e\n\u003cp\u003eThe curves of water mass loss with time due to yam absorbers after different temperature treatments under 1 sun illumination are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(a). From the figure, the treated yams caused greater mass loss in the water column than the untreated ones at the same time, and the 200 ℃ carbonized yams caused the greatest mass loss, which may be related to the changes in the structure of the yams during treatment. The amount of steam produced per unit time (steam rate) is calculated by deriving the mass change, and then the solar-water steam conversion efficiency is calculated by the following equation:\u003c/p\u003e\n\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equb\" class=\"mathdisplay\"\u003e$$\\eta =\\dot{\\text{m}}{h}_{LV}/{C}_{opt}{q}_{i}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere 𝜂 is the solar photothermal conversion rate, ṁ is the amount of water vapor production obtained, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({h}_{LV}\\)\u003c/span\u003e\u003c/span\u003e is the total enthalpy (including both latent and sensible heat), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({q}_{i}\\)\u003c/span\u003e\u003c/span\u003e is the value of solar radiation at 1 solar intensity, and\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{opt}{q}_{i}\\)\u003c/span\u003e\u003c/span\u003eis the total power density of solar irradiation. There are differences in the performance of solar absorbers at different optical densities \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e, and in this paper, 200 ℃-carbonized yams were selected for solar water vapor experiments at different optical densities. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(c) shows the variation of temperature with time at the interface with air when the yam is floating with the surface of the water body since different optical densities. As can be seen from the figure, the surface temperature of yam reached equilibrium after 10 min, less than 40\u0026deg;C at 1-sun intensity, about 10\u0026deg;C higher at 2-sun than at 1-sun, and the surface temperature of the solar absorber at 3-sun was similar to that at 2-sun, with no significant temperature increase. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(d) shows the time-mass variation curves at different optical densities. It can be seen from the figure that the mass change under 3-sun optical density is greater than that under 1 and 2-sun. Comparing Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(c), the lowest yam surface temperature under 3-sun may be related to the fact that the heat produced by the yam is absorbed by the water body. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(e) shows the evaporation rate of water vapor versus solar-water vapor conversion efficiency at different optical densities. As can be seen from the figure, the rate of water vapor production is proportional to the optical density, and the evaporation rate can reach 2.9 kg/ (m\u003csup\u003e2\u003c/sup\u003e h) at 3 suns, but the solar-water vapor conversion efficiency decreases with increasing optical density. From 1 to 2 suns, the conversion rate decreases by about 25%, and from 2 to 3 suns its yield is close, decreasing by only about 5%.\u003c/p\u003e\n\u003cp\u003eTo investigate the relationship between quality loss and the treatment of yam, experiments were designed for simple treatment of yam surface with flame and treatment of yam surface with PVA as adhesive and graphite powder as carbon material. It can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e(a) that the time required to reach the equilibrium temperature is close to the equilibrium temperature for the solar absorber of the yam treated with both methods. The change in mass per unit area with time, water vapor generation rate and solar-water vapor conversion rate for which graphite powder was the solar absorber layer were greater than that for yam treated with flame, and the solar-water vapor conversion rate for both was between 68\u0026ndash;70%, which was lower than that for yam treated at 200\u0026deg;C under the same conditions ( about 90% ).At the same time, the safety and the cheapness of raw materials of yam treated with 200 ℃ are higher than those treated with flame and with PVA and graphite powder, according to which, the 200 ℃ treatment of yam solar absorber has a better prospect in practical application.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this paper, low-density yam solar absorbers were prepared from yam by freeze-drying and related treatments, and the solar-water vapor conversion efficiency of the solar absorbers was investigated. We found that freeze-dried yams with low thermal conductivity and macropores, mesoporous and microporous structures could absorb up to 90% of sunlight after treatment. The water vapor conversion efficiency at 200 \u0026deg;C of treated yam sunlight absorber was about 90%, and the evaporation rate of the water body reached 1.3164 kg m\u003csup\u003e-2\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e. The conversion efficiencies of absorbers under different suns were different, under 3 sun illumination, the conversion efficiency was about 60%. and the evaporation rate of water body was the largest at 2.6838 kg m\u003csup\u003e-2\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e. Under the same conditions, the solar-water vapor conversion efficiencies of the experimentally prepared bilayer yam solar absorbers were similar and both lower than those of the carbon-treated absorbers. The preparation process of the treated yam absorber is simple and the raw materials are cheap, which is expected to be applied in practical production.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are grateful to the National Natural Science Foundation of China (Grant No.51962018,52163028,), Industrial Support Project of Education Department of Gansu Province (2021CYZC-10), Innovation and Entrepreneurship Talent Project of Lanzhou (Grant No. 2020-RC-2, 2019-RC-2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eJ. 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Wang JR, The effect of annealing and ultra-high-pressure treatment on structural and functional of three starches with different polymorphs, Tianjin University pf Science and Technology,\u003cstrong\u003e2016\u003c/strong\u003e.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"korean-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"kjce","sideBox":"Learn more about [Korean Journal of Chemical Engineering](http://link.springer.com/journal/11814)","snPcode":"11814","submissionUrl":"https://www.editorialmanager.com/kjce/default2.aspx","title":"Korean Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Subscription","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Solar steam generation, Conversation efficiency, Biomass solar absorber","lastPublishedDoi":"10.21203/rs.3.rs-2791601/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2791601/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSolar evaporation system has become a research hotspot in the field of photothermal conversion technology in recent years because of its high photothermal conversion efficiency and practicality of promotion. Biomass solar absorbers have excellent solar absorption properties and high solar-water vapor conversion, but they have the limitations of long feedstock production cycle and high carbonization temperature. As a kind of biomass materials, yam is not only inexpensive, but also has a short production cycle and rich pore structures. Therefore, in this paper, a yam based solar absorber with rich pore structure was prepared, and the photothermal conversion efficiency of the absorber was further investigated. The yam was treated with freeze-dried method and carbonized at different temperatures to obtain yam solar absorbers. Then find the thermal stability and porosity of solar absorber gradually rise as the treatment temperature increasing. The solar absorption rate of the carbonized yam was close to 90% in the near UV-visible region. Solar-water vapor control experiments with different treatments of the solar absorber of the yam were carried out in simulated solar-driven interface steam generation system (SISGS). The absorber treated at 200\u0026deg;C in the sun was found to have the best performance with a solar-water vapor conversion of about 90% and a water evaporation rate of 1.3164 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e","manuscriptTitle":"Preparation of biomass yam solar absorber and its application in solar evaporation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-04-21 18:57:49","doi":"10.21203/rs.3.rs-2791601/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2023-04-20T07:15:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-04-20T01:53:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-04-11T13:40:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Korean Journal of Chemical Engineering","date":"2023-04-07T23:06:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"korean-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"kjce","sideBox":"Learn more about [Korean Journal of Chemical Engineering](http://link.springer.com/journal/11814)","snPcode":"11814","submissionUrl":"https://www.editorialmanager.com/kjce/default2.aspx","title":"Korean Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Subscription","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ca9101e9-7667-413b-b235-0bea9c83a423","owner":[],"postedDate":"April 21st, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2023-07-11T01:33:29+00:00","versionOfRecord":[],"versionCreatedAt":"2023-04-21 18:57:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2791601","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2791601","identity":"rs-2791601","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}