A Chitin/CuS composite film for efficient solar seawater desalination
Graphical abstract
Introduction
Solar energy is highly popular and has many various applications, such as in photocatalysis, photovoltaics, and solar-driven energy conversion. This is due to its unique nature of abundance and sustainability [1], [2], [3], [4]. In particular, solar-driven steam evaporation has been regarded as one of the most promising pathways to generate fresh water, which is of particular interest. However, it is restrained by low yield and high cost in real-world settings [3], [4], [5], [6], [8], [9], [10]. Therefore, it is highly desirable to design a new low-cost material to increase the efficiency of this process. The utilization of photothermal films with an adaptive structure which can efficiently convert solar irradiation to heat and strengthen water vaporization provides a new approach to efficiently and cost-effectively produce fresh water [11].
Photothermal films are typically either semiconductor films, plasmonic noble metals, carbon fibers, or graphene [12], [13], [14], [15], [17]. Among these, CuS possesses a broad solar absorption with an increased optical absorption in the near-IR (NIR) region due to the localized surface plasmon resonances (LSPRs) [12], [13]. Furthermore these possess outstanding photostability and are environmentally friendly [11], [12]. Tao reported a CuS/semipermeable collodion membrane (SCM) composite for solar vapor generation with a water evaporation efficiency of 68.6% under 1 sun illumination [11]. Moreover, the hydrophilic features are helpful for facilitating the passive flow for persistent evaporation, enhancing the liquid thin-film regime, promoting heat transfer on the evaporation surface, and thus leading to efficient solar steam generation [18], [19], [20], [21].
In this work, we have prepared a novel solar absorber composed of plasmonic CuS and chitin for seawater desalination. Plasmonic CuS serves as the light-harvesting and light-to-vapor converter in the film, whilst chitin was employed to support the film. Chitin is the second most abundant natural polymer in the world after cellulose, and possesses numerous acetamido groups. The nitrogen atoms of these can chelate to transition metals, resulting in bonding of these metals to the polysaccharide main chain [22], [23], [24]. To date, chitin had been used as the carrier for the deposition of Ag and other noble metals [25]. Chitin possesses all of the properties desired of a support. This is because of its low cost, relative abundance, has a porous structure as well as excellent hydrophilicity. Most important of all, the hybrid film with chitin has an excellent desalination efficiency of over 99%.
Section snippets
Materials
Sea salt (Shanghai Guangyu Biotechnology Co., Ltd.), chitin (Zhejiang Golden Shell Chitin Co., Ltd.), CuS (Shanghai Macleans Biochemical Technology Co., Ltd.), sodium hydroxide, sulfuric acid, and urea, were all of analytical grade.
Synthetic process
Purification of Chitin: In order to enhance the solubility of chitin the following process was conducted. 100 g of chitin powder was immersed and stirred in an aqueous solution of sodium hydrate (5 wt%) for 12 h. The mixture was filtered and then and washed until the
Result and discussion
Fig. 1a shows the synthetic preparation process for the CCC film. Shrimp and crab shells were used as raw films of chitin. Purified chitin powder and different proportions of CuS were added into a solution of NaOH (11 wt%) and urea (4 wt%) followed by a freezing-thawing cycle to form a black solution [26]. The CCC hydrogel was then obtained by casting. Fig. 1c and d show the scanning electron microscope images (SEM) of chitin and a CCC film, respectively. These results reveal that chitin is
Conclusions
A sol–gel method was employed to prepare CCC from a chitin solution containing CuS, by freezing-thawing the latter in an aqueous solution of NaOH and urea. XRD, SEM and TEM results revealed that CuS was successfully loaded onto the chitin. BET (Fig. S2) showed that chitin maintained its porous morphology after loading with CuS. The optimal desalination effect achieved by the CuS /chitin composite was observed by adapting the concentration of CuS, reaction time and light intensity. Immobilized
CRediT authorship contribution statement
Chenjie Song: Data curation, Formal analysis, Writing – original draft. Li Wang: Data curation, Formal analysis. Xin Li: Data curation. Lin Guo: Writing – review & editing. Yumin Leng: Writing – review & editing. Xiaoli Jin: Software, Resources. Liqun Ye: Conceptualization, Funding acquisition, Supervision, Writing – review & editing.
Declaration of Competing Interest
The 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.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 51872147), the 111 Project (D20015), the Program for Innovative Research Team of Science and Technology in the University of Henan Province (19IRTSTHN025).
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The authors contributed equally.