1、文章编号:摇 1007鄄8827(2020)04鄄0436鄄08用于太阳能驱动蒸汽发生的低成本荷叶基炭膜郭明晰1,摇 武晶斌2,摇 李风海1,3,4,摇 郭倩倩1,摇 樊红莉1,摇 赵慧敏1(1. 菏泽学院 化学化工学院,山东 菏泽 274015;2. 菏泽学院郓城分校,山东 郓城 274700;3. 河南理工大学,化学化工学院,河南 焦作 454003;4. 中国科学院山西煤炭化学研究所,煤转化国家重点实验室,山西 太原 030001)摘摇 要:摇 太阳能驱动的界面蒸发因其解决淡水资源短缺的潜力而备受关注。 低成本、高效率的光热转换材料是其广泛应用的关键。 本文通过简单的真空抽滤法制备了低成
2、本的荷叶基炭膜,作为太阳能驱动蒸汽发生的光热转换介质。 使用市售聚苯乙烯泡沫塑料和多孔纤维滤纸分别作为保温层和输水通道,在实验室自制的太阳蒸汽发生实时测试系统中,荷叶基炭膜的太阳能驱动水蒸发速率和太阳能蒸汽转换效率分别为 1. 30 kg/ m2h 和 77. 5%。 同时,荷叶基炭膜在海水淡化和污水净化方面也表现出了优异性能。 这些结果为低成本、环境友好的生物质基炭材料在太阳能驱动蒸汽发生中的广泛应用提供了可能。关键词: 摇 荷叶;炭膜;太阳能驱动蒸汽发生中图分类号: 摇 TQ127. 1+1文献标识码: 摇 A基金项目:山东省自然科学基金(ZR2017BB063, ZR2018MB037)
3、; 国家自然科学基金(21875059); 菏泽学院科研基金(XY16BS28).通讯作者:郭明晰,副教授. E鄄mail: gmx0822163. comA low鄄cost lotus leaf鄄based carbon film for solar鄄driven steam generationGUO Ming鄄xi1,摇 WU Jing鄄bin2,摇 LI Feng鄄hai1,3,4,摇 GUO Qian鄄qian1,摇 FAN Hong鄄li1,摇 ZHAO Hui鄄min1(1. School of Chemistry and Chemical Engineering, Heze
4、University, Heze274015, China;2. Heze University, Yuncheng274700, China;3. School of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo454003, China;4. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan030001, China)Abstr
5、act: 摇 Solar鄄driven interfacial evaporation has attracted much attention owing to its potential for addressing the shortage offreshwater. Low鄄cost and high鄄efficiency photothermal conversion materials are the key to the application. A low鄄cost lotus leaf鄄based carbon film (LLC) for use as a photo鄄to
6、鄄heat conversion medium for solar鄄driven steam generation was prepared by the simplevacuum filtration of LLC obtained at a carbonization temperature of 800 益 using a porous fibrous filter paper. In a laboratory鄄madesolar steam generation real鄄time test system using commercial polystyrene foam as the
7、 insulation layer and the LLC film on porous fi鄄brous filter paper as the water transport path, the LLC film exhibits a solar鄄driven water evaporation rate of 1. 30 kg/ m2h and a so鄄lar鄄vapor conversion efficiency of 77. 5%. The LLC film also shows excellent performance in seawater desalination and
8、sewage puri鄄fication. The work provides a possible route for the use of low鄄cost and environmentally friendly biomass鄄based carbon materials insolar鄄driven steam generation.Key words:摇 Lotus leaf; Carbon film; Solar鄄driven steam generationReceived date: 2020鄄03鄄20;摇 Revised date: 2020鄄06鄄30Foundatio
9、n item: Natural Science Foundation of Shandong Province, China (ZR2017BB063, ZR2018MB037), Natural ScienceFoundation of China (21875059), Scientific Research Fund of Heze University, China (XY16BS28).Corresponding author: GUO Ming鄄xi, Associate Professor. E鄄mail: gmx0822163. comEnglish edition avail
10、able online ScienceDirect(http:蛐蛐www. sciencedirect. com蛐science蛐journal蛐18725805).Supplementary data associated with this article can be found in the online version.DOI:10. 1016/ S1872鄄5805(20)60501鄄71摇 IntroductionWaterpollutionandfreshwatershortageareamong the most serious environmental challenge
11、s fa鄄cing humanity due to industrial development and pop鄄ulation growth1,2. Although oceans cover more than70% of the earth, they cannot be used directionally inour daily life. Seawater desalination is a common de鄄salination technology. In practical applications, sea鄄摇第 35 卷摇 第 4 期2020 年 7 月新摇 型摇 炭摇
12、 材摇 料NEW CARBON MATERIALSVol. 35摇 No. 4Jul. 2020摇water desalination technology mainly includes reverseosmosis membrane separation, ion exchange, andthermal distillation desalination technology3. How鄄ever, these technologies are generally technicallycomplex, expensive, and energy intensive, whichmay
13、lead to some environmental pollution4,5. Re鄄cently, solar鄄driven steam generation has been consid鄄ered as an economic and sustainable solution to theshortage of freshwater resources6,7.Photothermalconversion materials are the key factors affecting theperformance of solar鄄driven steam generation. Exc
14、el鄄lent photothermal conversion materials require highbroadband sunlight absorption, efficient thermal posi鄄tioning, fast water transport or hydrophilicity8鄄11.For this purpose, some metal plasmon nanoparti鄄cles12鄄14, polymers15, semiconductors16鄄18, andcarbon鄄based materials9have been studied as th
15、ephotothermal conversion materials for solar waterevaporation. For example, Zhu et al.prepared aplasmon鄄enhanced solar desalination device by theself鄄assembly of Al nanoparticles into a three鄄dimen鄄sional porous membrane. The steam generation effi鄄ciency of this structure reached up to 88. 4% under
16、4sun illumination12. Chen reported composite films ofnanoporous Au nanoparticles and nanofibers. Underone sun exposure, the composite films showed anevaporation rate of 1. 424 kg/ m2h and a solar鄄vaporconversion efficiency of 83%14. However, the met鄄al nanoparticles tend to aggregate and lose their
17、func鄄tion. In addition, the chemical structure of some met鄄al plasma nanoparticles in corrosive media (such asacid, alkali and salt) is unstable, and the noble met鄄als used for plasma鄄enhanced evaporators are expen鄄sive, which limit their wide application. Ren success鄄fully synthesized a low bandgap
18、 hierarchical TiNnanotube mesh which showed absorption about 50%of solar light from 250 to 2 500 nm. The solar waterevaporation conversion efficiency reached 85. 36%under 2. 5鄄sun irradiation19. The band鄄gap energy isa key factor affecting the solar absorptive capacity ofsemiconductors. Due to the n
19、arrow absorption band ofmost semiconductors, it is difficult to develop theminto widely used solar thermal conversion materials.Carbon鄄based materials with excellent sunlight absorp鄄tion performance, chemical structure stability, and re鄄usability have become a research hotspot in the fieldof solar鄄d
20、riven evaporation9,20鄄22.Recently, the carbon鄄based photothermal conver鄄sion materials were reported with high performance inthe solar鄄drivensteamgeneration.Forinstance,Zhang21prepared the long鄄range vertically alignedgraphene sheets membrane by a scalable antifreeze鄄as鄄sisted freezing technique, fo
21、llowed by carbonizationat 1 000 益 and O2鄄 plasma treatment.This mem鄄brane can efficiently produce clean water from seawa鄄ter, common wastewater, and even concentrated acidand/ oralkalisolutions.Wangpresentedfoamstrengthened ultra鄄black carbon aerogels with micro鄄pores, mesopores and macropores by CO
22、2activation,which showed a water evaporation rate 2. 8 timeshigher than that of pure water23. Fang reported thatactivated carbon fiber cloth with a hierarchical micro鄄structure showed superior light鄄thermal property forsolar steam generation24. Singh presented a compos鄄ite material comprising carbon
23、 dots encapsulated with鄄in a porous hydrogel. The composite material was ap鄄plied for diverse water treatment, which exhibited anexcellent recyclability25. Nevertheless, these nano鄄carbon materials are difficult to be applied on largescale due to the non鄄renewability and high cost of theprecursors a
24、s well as the complicated preparationprocess. Biomass has attracted much attention becauseit is a kind of low鄄cost renewable energy with rapidregeneration,hugeavailabilityandenvironmentalfriendliness.In recent years, biomass with specialstructuressuchasmushrooms26,sugarcane27,wood28,29, and lotus se
25、edpods30had been carbon鄄ized. When applied in solar steam generation, thesebiomass carbon can not only undergo photothermalconversion at the interface, but also transport waterthrough their own special structure.For example,Xue et al28reported that the flame鄄treated wood wasan ideal solar absorber w
26、ith strong heat localizationand good hydrophilicity, which exhibited a high inter鄄facial solar evaporation efficiency of 72% under a so鄄lar intensity of 1 kW m鄄2. However, most carbonizedbiomass is hydrophobic and has poor mechanicalproperties, so it is not suitable for direct solar鄄drivensteam gene
27、ration. Therefore, it is necessary to findnew strategies to solve these problems.The lotus leaf has a self鄄cleaning ability owing toits multi鄄levelled roughness. After heat treatment, thecontact angle with was decreased, and hydrophilicitywas enhanced31. For solar鄄driven steam generation,an enhanced
28、 hydrophilicity facilitates water transport,while most biomass becomes poorly hydrophilic aftercarbonization.Herein, lotus leaf was crushed andcarbonized to prepare lotus leaf鄄based carbon powder.The lotus leaf carbon films as a photo鄄thermal conver鄄sion layer were made by a simple vacuum filtration
29、technology. Commercial polystyrene foam and porousfibre filter paper are used as insulation layer and watertransport path, respectively. The properties of lotusleaf before and after carbonization were compared.The effect of solar intensity on water evaporationrate, temperature and solar鄄vapor conver
30、sion efficien鄄734第 4 期GUO Ming鄄xi et al: A low鄄cost lotus leaf鄄based carbon film for solar鄄driven steam generation摇cy in the device was investigated. The results showthat the lotus leaf powder after carbonization has highsunlight absorption, good hydrophilicity, high solar鄄driven water evaporation r
31、ate and cycle stability. Thisprovides a prospect routine for the wide application ofbiomass carbon in solar鄄driven steam generation.2摇 Experimental2. 1摇 PreparationThe lotus leaves were purchased from market.After cleaned, lotus leaves were dried at 80 益 for12 h, and then crushed into powder (100 me
32、sh).The lotus leaf powder (LL) was carbonized at 800 益under nitrogen atmosphere. The heating rate and soa鄄king time were 5 益 / min and 2 h, respectively. Fi鄄nally, lotus leaf鄄based carbon powder (LLC) wasobtained.Paper鄄based film of LLC (LLC film) was pre鄄pared by a vacuum鄄assisted filtration method
33、. 30 mgLLC was dispersed into 100 mL deionized water for1 h with sonication. Subsequently, the prepared LLCpowder was deposited on the surface of the porous fi鄄ber filter paper (pore size: 1. 0-3. 0 滋m, ShanghaiTitan Co. , ltd. , Shanghai, China) by the vacuum鄄assisted filtration method using a Buch
34、ner funnel witha sand core (diameter of 4 cm). As a contrast, thepaper鄄based film of lotus leaf powder (LL film) wasprepared by the same method.2. 2摇 Fabrication of the solar absorber deviceIn solar鄄driven steam generation, there are fourmain factors that affect the evaporation performance,broadband
35、 sunlight absorption, thermal management,water transportation, and water evaporation9. Basedon this, the solar absorber device is shown inFig. 3a. The porous fibre filter paper鄄wrapped poly鄄styrene foam ( 2 cm thick) is floating on the liquidin a beaker and the paper鄄based film of material (di鄄amete
36、r of 4 cm) is placed on it.2. 3摇 CharacterizationThe optical properties of the samples were inves鄄tigated by a ultraviolet鄄visible鄄near鄄infrared (UV鄄Vis鄄NIR) spectrometer ( lambda750, PerkinElmer) e鄄quipped with an integrating sphere accessor, usingBaSO4as the reference material. The dynamic contact
37、angles of the samples were measured by a contact an鄄gle meter (DSA100, KR譈SS GmbH) with a high鄄speed CCD camera. The morphologies of the sampleswere observed by a scanning electron microscope(SEM) (SU3500, Hitachi). The pore structures ofthe sample were characterized by N2adsorption at77. 4 K (Trist
38、ar II 3020, Micromeritics). The real鄄time temperatures of the samples were measured by anIR camera (FOTRIC 222s) during the solar steamgeneration experiments.The concentration of ionswas studied by an inductively coupled plasma opticalemission spectrometer ( ICP鄄OES) ( ICP鄄OES730,Agilent).2. 4摇 Sola
39、r鄄driven steam generation experimentsThe solar鄄driven steam generation performancesof the samples were investigated by using a laborato鄄ry鄄made real鄄time test system. Water was placed in abeaker with an internal diameter of 4. 0 cm and adepth of 5. 5 cm. The solar absorber device was verti鄄cal irrad
40、iated under a 300 W Xe lamp (PLS鄄SXE300,Beijing Perfectlight) with an optical filter for thestandard AM 1. 5 G spectrum. The water real鄄timemass change was monitored by an electronic analyticalscale (BSA224s, Sartorius, 0. 1 mg in accuracy),and the real鄄time temperatures of the samples weremeasured
41、by an IR thermograph (FOTRIC 222s).The intensity of the sunlight was varied by adjustingthe distance between the xenon lamp and the top layerof the solar absorber device, and the light intensitywas determined by an optical power meter ( PL鄄MW2000, Beijing Perfectlight).The experimentaltemperature an
42、d humidity were 28 益 and 30% -40%, respectively.2. 5摇Calculation of the solar鄄vapor conversion ef鄄ficiency浊=mhLVCoptqi(1)where mis the evaporation rate ( In order toeliminate the influence of natural evaporation of wa鄄ter, all measured evaporation rates were subtracted bythe evaporation rates of wat
43、er in dark environment. ),Coptis the optical concentration, qiis the nominal di鄄rect solar irradiation 1 kW/ m2, hLVrepresents the to鄄tal heat of the liquid鄄vapor phase transition (includingsensible heat and phase鄄change enthalpy), which canbe calculated ashLV=姿+C驻T(2)where 姿 is the latent heat of p
44、hase change (Thelatent heat varies from 2 454 kJ/ kg at 20 益 to 2 257kJ/ kg at 100 益), C is the specific heat capacity ofwater (4. 2 kJ/ kg K), and 驻T denotes the tempera鄄ture rise of water.2. 6摇 Solar seawater desalination and sewage puri鄄ficationDistillation unit for steam condensation and waterco
45、llection was fabricated (Fig. S1). Under simulatedsunlight, steam will condense into water when it rea鄄ches the cooling wall of the device, and condensatewill automatically flow into the condensation chamberalong the inclined side wall of the container. The sea鄄834摇新摇 型摇 炭摇 材摇 料第 35 卷water desalinat
46、ion and water purification applicationsof this solar鄄driven distillation unit were demonstratedby using Yellow Sea and simulated wastewater (10mg/ L methyl blue (MB). After exposed to the sim鄄ulating sunlight, the desalinated water was collected,the concentration of ions (Na+, K+, Mg2+, Ca2+)was det
47、ermined by ICP鄄OES. The MB solution beforeand after solar鄄driven distillation were monitored bythe UV鄄Vis鄄NIR spectrometer.3摇 Results and discussion摇 摇 The morphology of the lotus leaf powders beforeand after carbonization was characterized by SEM(Fig. S2a and b). It could be observed that after car
48、鄄bonization, the surface of LLC becomes rough andsmall protuberances appears. The specific surface areaand pore structure of LLC were analyzed by nitrogenadsorption at 77 K. The specific surface area of theLLC is 172. 31 m2/ g. As shown in Fig. S3a, theLLC sample has the hysteresis of type IV isothe
49、rm.Low pressure absorption indicates the presence of mi鄄cropores, and high pressure absorption and hysteresisindicate the presence of mesopores. The pore size dis鄄tribution also clearly shows micropores and mesopores(Fig. S3b).The water absorption of the material affects therate of solar water evapo
50、ration. The water absorptioncapacities of lotus leave powders before and after car鄄bonization were investigated by a contact goniometer(Fig. 1). As shown in Fig. 1a, the contact angle ofthe droplet with the surface of the LL is still 85毅 af鄄ter 120 s, so the LL is hydrophobic. But the dropletspreads
