Alternatively straw Magical graphene airgel high efficiency desalination
Water is essential for survival and development of human society of important natural resources. However, due to the uneven distribution of the limited reserves of a large number of safe and clean water, there are currently more than one billion people suffer from a shortage of drinking water. Solar steam generation technology may be one of the sustainable use of solar energy to alleviate the shortage of drinking water the most promising technologies. Light hot gel (PTMs is), by converting solar energy into heat is concentrated at the surface thereof, a thin layer of rapidly heating and evaporation of water, steam rate, and to achieve high energy conversion efficiency. Wherein the three-dimensional (3D)airgel is the most extensively studied and closest to the actual application which generates steam having a distinct advantage in solar energy, such as light weight, high flexibility, higher evaporation rate and energy efficiency characteristics. However, there is a more serious problem is that graphene is relatively expensive, so in real life, large-scale application of such PTM has a very big challenge in economic rationality office. So, if you want 3D airgel PTM accepted by the market, it is necessary to develop the premise of A does not affect the efficiency of the strategy to reduce the ethylene content of such material in graphite. Wherein, to realize a desired effective this goal is to use the biomass material as a carrier backbone 3D airgel, replacing part of the graphene used.
To solve the above problems, recently, University of South Australia Xu Haolan researcher (corresponding author), Daniel Peter Storer (author) the reduced graphene oxide (of RGO) nanosheet, sodium alginate (SA) and extracted from the straw as a raw material of thegel hot 3D light was prepared by solar water evaporation in obtaining pure water. The results show that, as the support skeleton rice straw cellulose plays an important role, not only reduces the amount of RGO, and improves mechanical stability and flexibility of the resulting light hot gel. RGO and SA at the same content, the volume of the airgel RGO-SA was 4.92 cm3, much smaller than the volume of RGO-SA- cellulose airgel (7.06 cm3), indicating that the straw can be at least reduced RGO cellulose 43.5 % of the amount of use. Compared with RGO-SA- cellulose, RGO-SA airgel after being (500 g) was unable to compressive loadRestore its original shape. Further, the photothermal RGO-SA- cellulose airgel produced had a water absorption capacity significantly, due to its super-hydrophilic porous structure and can absorb about 20 times its own weight of water. The light gel hot gas exhibits strong broadband absorption of 96-97% of the light. During solar steam generation, the gel 3D light not only effective in reducing heat radiation and convection energy loss, but also enhances the ability to collect energy from the environment, in order to achieve a very 2.25 kg m-2 h-1 in high evaporation rate, equivalent to the energy conversion efficiency of 88.9% at 1.0 sunlight. The test results show ion, water evaporates during the actual fresh water salinity collected only 0.37 ppm. Therefore, the partial replacement of cellulose biomass reduction of graphene make this kind of light heat gel material is not only environmentally friendly and cost-effective, with great potential and prospects of practical application in real-world applications in . The research results entitled \”Graphene and Rice-Straw-Fiber-Based 3D Photothermal for Highly Efficient Solar Evaporation\” of papers published in the \” ACS Applied materials and interfaces \” ( see the text description link).
1. Preparation of cellulose aerogels RGO-SA-
First, the RGO nano sheet (1 mg mL-1) and SA (5 mg mL-1) combined with the cellulose dispersion by sonication and stirring and thoroughly mixed to produce a homogeneous black RGO-SA – cellulosic suspension. Then, the black dispersion (8.7 mL) was added to the vessel diameter of 3.2 cm, the pre-frozen and freeze-dried. Overnight The resulting airgel sample is then immersed in 5% (w / w) aqueous solution of CaCl2, washed with water several times with Milli-Q, frozen and freeze-dried to produce a suitable Ca 2+ RGO-SA- crosslinked cellulose aerogels for solar evaporation. By controlling the amount of RGO-SA cellulose dispersion, the different heights of RGO-SA cellulose airgel.
2. The mechanical properties and light-heat flexibility gel
As shown in FIG. 2a, b, having a diameter of 3 cm, a height of 1 cm of cellulose aerogels RGO-SA- the density of only 34.3 mg cm 3 ; RGO-SA- cellulose airgel two sonication cycles (each cycle 5 minutes), did not observe any black matter from the airgel shedding (FIG. 2c, d), maintains a very good sample integrity. Further, at room temperature (RT), wet cellulose airgel RGO-SA- (diameter 3 cm × a thickness of 1 cm) can easily support the weight of about 206 g (FIG. 2E), the weight of its own weight more than 940 times without any signs of distortion. Meanwhile, RGO-SA- Cellulose aerogels exhibit excellent flexibility. When stacked on RGO-SA- cellulose aerogels two copper cubes (each 500 g) all the adsorbed water out (FIG. 2g), the cubes after copper removal, the airgel is possible to re-absorb water and return to its original shape (Fig. 2f, h).
3 light absorbance gel hot water absorbent and
optical absorption characterization of a hot gel is applied to one of the important parameters of the solar water evaporation. Compared to pure cellulose airgel, RGO-SA- cellulose airgel entire UV – near infrared (NIR) (290 – 1400 nm) exhibited higher light absorbance (measuring range 91.5- 93%) (FIG. 3a). After the sample wetted with water in the same range of light, but the light absorption rate is further increased to 96-97% (Figure 3a). This is the main reason is the introduction of the refractive index of the aqueous layer is interposed between the air and the RGO can reduce the total reflection loss, thereby improving the light absorptivity. Hydrophilic gel hot light was confirmed (FIG. 3d) rapidly absorbed by water droplets in the 0.2 s. When RGO-SA- cotton cellulose airgel on a surface of the block, it is completely wetted by water (FIG. 3e) in 20 s, thereby confirming the effective transfer of water between the block and the cotton airgel.
4 light gel solar heat – thermal – evaporating water conversion efficiency
at 1.0 sunlight, RGO-SA- cellulose airgel (diameter 3 cm, a thickness of 1 cm ) mean temperature of the evaporation surface in one minute is raised from the initial 18.3 ° C to 24.9 ° C (FIG. 4a), the surface of the airgel showed a very fast photothermal energy conversion. With the increase of the height of the light hot gel, airgel surface temperature decreased (Fig. 4a, d), for 2 cm and 3 cm high aerogels, surface temperature were only 31.8And 30.7 ° C. Lower surface more conducive to water evaporation temperature, because the sun during evaporation temperature lower guide surface of the radiation and convection losses to the environment decreases. For RGO-SA- cellulose aerogels and height respectively as 3 cm 2, calculated at an evaporation rate of 1.0 solar illumination, respectively 1.37,1.85 and 2.25 kg m-2 h-1.
5 RGO -. SA – Cellulose aerogels for the practical feasibility of desalination
measured by inductively coupled plasma mass spectrometry (ICP-MS) at 1.0 from sunlight evaporation of seawater collected in water salinity. As shown, the steam collected in Na 5a + and of Mg 2+ concentration are much lower than the concentration in the original seawater, the concentration of all four major ion (K + : 0.19 ppm, Ca 2+ : 0.15 ppm, Na + : 0.37 ppm, and the steam generated in the Mg 2+ [123 ]: 0.04 ppm) is much lower than the world Health Organization (WHO) potable water standards desalination salinity level determined. Further, the deposited salt was not observed on the evaporator surface during solar evaporation. Since the ultra-hydrophilic and excellent hot light water absorption capacity of the gel, salt ions on the surface of the water can be spread very quickly, in order to offset the increased salinity of the evaporation surface. Stability of RGO-SA- cellulose aerogels performance tests by cycling at 1.0 solar radiation to evaluate the excess water evaporation. 15 cycles of a two-day test, the average evaporation rate of 2.0 ± 0.2 kg m -2 h – 1 (Figure 5b). Slight variations due to the evaporation rate and temperature fluctuations due to ambient humidity. Since RGO-SA- cellulose aerogels ultra-hydrophilic and porous structure having excellent water absorption capacity. Light for a 3 cm high hot gel can absorb more than 20 times its own weight in water (FIG. 6a, b), which makes the solar water without significant contact with an external steam generation. Study of optical isolation gel continuous evaporation heat for 8 hours at 1.0 sun found within the first hour, the evaporation rate reaches 1.60 gh -1 (T: 25 ° C, RH: 24.6 %), the next hour (T: 25 ° C, RH: 27.7%) having any one of 1.46 gh -1 evaporation rate. Further, since the light-heat the hydrophilic gel and excellent mechanical flexibility, it can be quickly restored by supplementing water. After the make-up water, the same RGO-SA- cellulose aerogels, at 1.0 sunlight too, it returns to the initial evaporation rate of 1.45 gh -1 (T: 25 ° C, RH: 27.5 %).
[summary] In light 3D RGO-SA- hot cellulose gel, crystalline cellulose, rice straw as a skeleton support, which not only enhances the flexibility of the optical and mechanical stability of the gel heat, and to ensure an excellent light and heat efficiency is significantly reduced amount of expensive of RGO. RGO-SA- cellulose aerogels obtained having excellent properties to meet the plurality of solar evaporator applications, such as the hydrophilic porous structure, lightweight, broadband light absorption intensity, can be reused, the mechanical stabilityAnd excellent flexibility and other characteristics. 1.0 times when the solar irradiance on a 3 cm high photothermal RGO-SA- cellulose airgel, reached 2.25 kg m
-2 h -1 stable evaporation rate, equivalent to 88.9% of the energy conversion efficiency. Further, the heat obtained by this type of light water purification material can easily meet the WHO and USEPA clean drinking water standards setting. Original link: https: //pubs.acs.org/doi/pdf/10.1021/acsami.0c01707