基于二维共价有机骨架核壳结构的高性能太阳能蒸发器

淡水短缺仍然是许多地区和国家面临的最严重的问题之一。考虑到地球上丰富的海水资源，海水淡化是一种有效合理的淡水供应方式。特别是在能源危机和可持续发展的情况下，太阳能驱动蒸汽发电(SSG)以其实施方便、能耗低、过程对环境友好等优点受到了广泛关注。选择理想的光热转换材料(太阳能吸收材料) 是实现高太阳能-蒸汽转换效率的关键。原则上，理想的太阳能吸收器应具有宽频光吸收、良好的太阳热转换效率、高孔隙率、良好的隔热性能、高亲水性和低密度。
9 Y- F( V* Q; C0 s. q  l8 {Shortage of freshwater is still one of the most serious issues for many regions and countries. Considering the abundant seawater resources in the earth, seawater desalination is an effective and reasonable way to supply freshwater. Especially, under the circumstances of energy crisis and sustainable development, the solar-driven steam generation (SSG) has drawn great attentions owing to the advantages such as the facile implementation, low-energy consumption, and environment-friendly process.  Selecting ideal photothermal conversion materials (solar absorbers) are crucial to realize a high solar-to-vapor energy conversion efficiency. In principle, ideal solar absorber should possess broadband optical absorption, good solar-thermal conversion efficiency, high porosity, good heat insulation, high hydrophilicity, and low density.
二维共价有机框架（2D COFs）因其高结晶度、大表面积、规整的孔道结构，目前已作为太阳能吸收器用于太阳能驱动光热海水淡。但是，受限于复杂的框架设计、昂贵的构筑模块和弱化学稳定性，大多数COF材料还不能满足实际需要。TpPa-COF作为一类典型的β-酮烯胺基COFs材料具有低的成本和高的物理/化学稳定性，是太阳能驱动蒸发器领域中一个有前途的候选者。然而，窄波段光谱响应和电荷辐射弛豫造成的能量损失是制约其高光热性能的主要因素。
2D covalent organic frameworks (COFs) has been used as a solar absorber to drive photothermal seawater desalination because of its high crystallinity, large surface area and regular pore structure. However, due to the complex framework design, expensive construction modules and weak chemical stability, most COF materials cannot meet the practical needs. As a typical β-ketene amino COFs material, TpPa-COF has low cost and high physical / chemical stability, so it is a promising candidate in the field of solar-driven evaporators. However, the energy loss caused by narrow band spectral response and charge radiation relaxation are the main factors restricting its high photothermal performance.
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因此，如何拓宽光吸收范围和减少辐射弛豫以增强材料的光热性能至关重要。为了实现宽波段光吸收和高光热转换效率，将TpPa-COF包覆到另一种窄带隙MoS2（1.8 eV）表面构建具有核壳结构的复合光热材料可能是一种有效的策略。首先，具有通孔结构的COF作为壳层，可以实现无阻碍的光吸收，并通过促进光散射增强光捕获能力。其次，窄带隙 MoS2可以拓宽光吸收范围，使复合光热材料实现全波段吸收太阳光。此外，这种独特的核壳有利于实现光生电子从COF到MoS2的可控迁移，这有助于抑制辐射衰减带来的能量损失，进而增强光热转换效率。
Therefore, it is very important to broaden the light absorption range and reduce the radiation relaxation to enhance the photothermal properties of the materials. In order to achieve wide-band optical absorption and high photothermal conversion efficiency, it may be an effective strategy to coat TpPa-COF on another narrow band gap MoS2 (1.8eV) surface to construct composite photothermal materials with core-shell structure. First of all, COF with through-hole structure as a shell can achieve unhindered light absorption and enhance light capture by promoting light scattering. Secondly, narrow band gap MoS2 can broaden the light absorption range and enable composite photothermal materials to absorb sunlight in full wave band. In addition, this unique core-shell is conducive to the controlled migration of photogenerated electrons from COF to MoS2, which helps to restrain the energy loss caused by radiation attenuation and enhance the photothermal conversion efficiency.
0 L+ A" P  E7 QMoCOF复合材料的制备与表征
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图1 MoCOF复合光热材料的合成

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Fig.1. Schematic illustration of the synthetic process for MoCOF composites.

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如图1，我们设计了一种具有核壳结构的复合光热材料MoCOF。首先，我们以硫脲和钼酸钠为原料，通过溶剂热方法合成了MoS2微米级花球。然后，我们将MoS2分散到TpPa-COF的预反应液中，利用原位生长策略将TpPa-COF包覆到MoS2微米花球表面。
% v% ~4 m! i. `8 t# k3 l) gAs shown in figure 1, we have designed a composite photothermal material MoCOF with core-shell structure. Firstly, the MoS2 micron bouquet was synthesized by solvothermal method using thiourea and sodium molybdate as raw materials. Then, MoS2 was dispersed into the pre-reaction solution of TpPa-COF, and TpPa-COF was coated on the surface of MoS2 micron flower ball by in situ growth strategy.

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图2（a）MoCOF复合光热材料（即COF/MoS2（40%））的PXRD图谱；（b）复合材料的红外光谱图；（c）复合材料的氮气吸脱附等温线；（d-f）MoCOF 的N 1s（d）、Mo 3d（e）和S 2p（f）高分辨率XPS谱图；（g）MoCOF的SEM 图；（h）MoCOF的TEM图；（i-j）MoCOF的HRTEM图；（k）MoCOF的EDS图
* k, i7 o# o. K0 `. RFig. 2. (a) The PXRD patterns of the TpPa-COF, MoS2, and MoCOF (i.e.,COF/MoS2(40%)). (b) The FTIR spectra of the as-prepared samples. (c) Nitrogen adsorption isotherms of the samples. (d-f) High-resolution XPS spectra of the N 1s (d), Mo 3d (e), and S 2p (f) of MoCOF. (g) SEM image of MoCOF. (h) TEM image of MoCOF. (i-j) HRTEM images of MoCOF. (k) TEM image with elements mapping of MoCOF.
% a: C& h0 k  M; s! S在MoCOF的XRD图谱中（图2a），MoS2和TpPa-COF特征衍射峰的出现说明复合后结晶度均得以保留。通过红外光谱分析（图2b）确认了MoCOF的化学结构，在~1250 cm-1和~1580 cm-1处的特征峰归因于酮式C-N键和C=C键的形成。TpPa-COF和MoCOF相似的特征吸收峰证明了MoS2微米花的引入没有影响TpPa-COF的化学骨架。此外，通过分析在77 k获得的N2吸附等温线，证明了复合材料的多孔性能（图2c）。采用Brunauer-Emmett-Teller（BET）方法计算得到MoCOF的BET比表面积为780 m2/g，主要孔径分布在1.56 nm。利用X射线光电子能谱（XPS）分析了制备的MoCOF复合材料的元素组成和键合状态。在N 1s谱图中（图2d），399.7 eV处的峰值来自于TpPa-COF中-N-H基团。在Mo 3d 谱图中（图2e），结合能为232.4eV和229.3 eV的峰归属于Mo4+，结合能为235.3 eV峰归属于Mo6+。结合能为162.8 eV和161.8 eV的峰为MoCOF中S2-的S 2p3/2和S 2p1/2（图2f）。此外，SEM图片显示原始MoS2显示出直径约1-1.4 μm的花状微球形态。包覆TpPa-COF外壳后，MoCOF复合材料显示出蓬松的球形结构，尺寸略有增长（图2g）。TEM图像显示TpPa-COF已经沉积在MoS2花球上，并形成了约200 nm厚的壳层（图2h-j）。并且在MoCOF复合物的TEM-EDS图中N、O、Mo和S元素信号均匀分布（图2k），结合上述一系列表征结果可以判定具有核壳结构的MoCOF已经被成功制备。
) {( }* `* V8 ]0 ]In the XRD pattern of MoCOF (Fig. 2a), the appearance of the characteristic diffraction peaks of MoS2 and TpPa-COF indicates that the crystallinity can be retained after recombination. The chemical structure of MoCOF was confirmed by infrared spectroscopy (Fig. 2b). The characteristic peaks at ~ 1250cm-1 and ~ 1580cm-1 were attributed to the formation of keto C-N bond and C-C bond. The similar characteristic absorption peaks of TpPa-COF and MoCOF proved that the introduction of MoS2 micron flowers did not affect the chemical skeleton of TpPa-COF. In addition, the porous properties of the composites were proved by analyzing the N2 adsorption isotherms obtained at 77k (Fig. 2c). The BET specific surface area of MoCOF calculated by Brunauer-Emmett-Teller (BET) method is 780m2/g, and the main pore size distribution is 1.56nm. The element composition and bonding state of MoCOF composites were analyzed by X-ray photoelectron spectroscopy (XPS). In the N1s spectrum (Fig.  2d), the peak at 399.7eV comes from the-Nmurh group in TpPa-COF. In the Mo3d spectrum (Fig. 2e), the peak return of binding energy of 232.4eV and 229.3eV belongs to Mo4+, binding energy and the peak of 235.3eV belongs to Mo6+. The binding energies of 162.8eV and 161.8eV are S2p3/2 and S2p1/2 of S2-in MoCOF (Fig. 2f). In addition, SEM images show that the original MoS2 shows the shape of flower-shaped microspheres with a diameter of about 1-1.4 μ m. After the TpPa-COF shell was coated, the MoCOF composite showed a fluffy spherical structure with a slight increase in size (Fig. 2g). TEM images show that TpPa-COF has been deposited on the MoS2 bouquet and formed a shell about 200nm thick (Fig.  2h-j). And the signals of N, O, Mo and S elements are uniformly distributed in the TEM-EDS diagram of the MoCOF complex (Fig. 2k). Combined with the above series of characterization results, it can be concluded that the MoCOF with core-shell structure has been successfully prepared.

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图3（a-b）一个太阳光强下复合材料的温度-时间曲线；（c）MoCOFs复合材料在水中的紫外-可见光谱；（d）红外成像图；（e）MoCOF表面液滴浸渍过程的图片。

Fig. 3. (a) Time-correlated temperature profile of the as-prepared samples. (b) Time-correlated temperature profile of MoCOF composites.  (c) UV/Vis-NIR spectra of MoCOF composites in water at a concentration of 100 ppm.  (d) IR images of the MoCOF with different irradiation time under 1 sun.  (e) Photographs of the droplet impregnation process on the surface of MoCOF.
图3a和3b研究了不同复合材料的光热性能。在一个太阳光照强度下，MoCOF粉末的温度可以达到~78.5℃，高于TpPa-COF（~52.5℃），MoS2（~72.3℃），以及物理混合物MoS2 + COF（~73.1℃），表现出优异的光热性能。紫外-可见分光光度计分析表明，MoCOF在250-1100 nm范围内具有广泛而无特征的光吸收。MoCOF粉末在120 s内温度迅速升高至78.5℃，表现出满意的光热转换能力（图3d）。MoCOF的光热性能提高可以归因于两个方面原因：1.窄带隙的MoS2的引入显著拓宽了复合材料的光吸收范围。2. MoS2的引入提供了一个额外的电荷转移路径来捕获和存储来自TPPA-COF壳层的光生电子，从而延缓了电荷复合过程，从而提高了太阳能热转换效率。此外，MoCOF也表现出超亲水行为（水接触角=0°），可以在200毫秒内被水完全润湿，这一超亲水特征有利于光热材料将转化的热量直接传递给水分子以进行蒸发。
( q) F# p; f3 N9 i* k4 |' V6 [% CFigures 3a and 3b study the photothermal properties of different composites. Under 1 sun irradiation (1 kW/m2), the temperature of MoCOF powder can reach ~78.5 ℃, which is higher than that of TpPa-COF (~52.5 ℃), MoS2 (~72.3 ℃), and the blend with same proportions (~73.1℃). Ultraviolet-visible spectrophotometer analysis shows that MoCOF has extensive anduncharacteristic light absorption in the range of 250-1100nm. As shown in Fig. 3d, the temperature of MoCOF powder rapidly increases up to 78.5 ℃ within 120 s, demonstrating satisfactory photothermal conversion capacity. It is believed that there are two reasons for the improvement of photothermal performance of MoCOF. On the one hand, the introduction of MoS2 with a narrow bandgap enhances significantly the light-harvesting ability. On the other hand, the introduction of MoS2 provides an additional charge transfer path to capture and store photo-generated electrons from TpPa-COF shell to retard charge recombination processes, which therefore can enhance the solar thermal conversion efficiency. While MoCOF displays a superhydrophilic behavior (water contact angle =0°) and can be completely wetted by water within 200 ms , which is definitely beneficial to directly transfer the obtained heat to water molecules for water evaporation.

                               
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$ u; ?/ I7 P3 v- s# x  J$ c图4（a）MoCOF@Gel蒸发器制备过程图；（b）复合凝胶的饱和水含量测试；（c）MoCOF@Gel的紫外-可见-近红外吸收光谱图；（d）PVA-Gel和MoCOF@Gel的动态力学分析；（e）MoCOF@Gel的弯曲和压缩测试图片；（f-g）PVA-Gel和MoCOF@Gel的SEM图片。
Fig. 4. (a) The process of preparation of the MoCOF@Gel evaporator. (b) Saturated water content of hybrid hydrogels. (c) The UV-Vis-NIR absorption spectra of the MoCOF@Gel. (d)
$ Q& N: V* e. B7 C' t5 L- fThe storage modulus (G0) and loss modulus (G00) of PVA-Gel and MoCOF@Gel obtained by dynamic mechanical analysis. (e) Photographs of bending and compression tests of
MoCOF@Gel. (f-g) SEM images of PVA-Gel (f) and MoCOF@Gel (g).
通过原位凝胶法制备了层次化的MoCOF负载凝胶网络，如图4a所示。如图4b所示，从MoCOF(1%)@Gel到MoCOF(7%)@Gel的Qs值分别为6.14、7.59、8.25、9.11g/g干凝胶，这些值都高于MoS2(5%)@Gel的Qs值(5.47g/g)。利用MoCOF的亲水性定向通道阵列和高比表面积，水分子通过氢键相互作用键合在COF孔壁上，从而与MoS2相比，MoCOF的引入显著提高了杂化水凝胶的吸水率。为了评估MoCOF@Gel的太阳吸收能力，在300-2500 nm波长范围内获得了UV-VIS-NIR吸收光谱。如图4c所示，根据太阳辐射光谱(AM 1.5)计算出MoCOF@Gel的吸光度为86.7%，研究了MoCOF@Gel和PVA-Gel的流变性特征，如图4d所示。两种水凝胶的动态扫频实验都显示出较宽的线性粘弹性范围，且G’的值高于G’’的值，说明它们具有类固态和弹性属性。此外，MoCOF@Gel在弯曲、压缩和锤击试验中也显示出良好的机械稳定性，如图4e。 图4f显示了直径从几微米到几十微米的PVA-Gel的3D相互连接的毛细通道，这可以通过毛细作用促进水的传输。在加载MoCOF后，这些相互连接的通道保持不变，几个微米大小的MoCOF球固定到空白PVA毛细管通道的出口(图4g)。
% h) g7 V( r' p; }- S4 ?: j2 NA hierarchical MoCOF loading gel network has been fabricated via insitu gelation method as shown in Fig. 4a. As shown in Fig. 4b,the Qs values from MoCOF(1%)@Gel to MoCOF(7%)@Gel are 6.14,7.59, 8.25, 9.11g per gram of the corresponding dried hydrogel, and these values are all higher than the Qs of the MoS2(5%)@Gel (5.47 g/g). Benefiting from the hydrophilic directional channel array and the high specific surface area of MoCOF, water molecules are bonded on the COF pore walls by hydrogen-bond interaction, and thus the introduction of MoCOF significantly boosts the water intaking of the hybrid hydrogel compared with MoS2. In order to assess the solar absorption capacity of MoCOF@Gel, a UV-vis-NIR absorption spectroscopy within the 300-2500 nm wavelength range has been acquired. As exhibited in Fig.4c, based on the solar irradiation spectra (AM 1.5), the absorbance of MoCOF@Gel is calculated as 86.7%. The rheology characterizations of MoCOF@Gel and PVA-Gel has been investigated as shown in Fig. 4d. For both hydrogels, the dynamic frequency sweep experiments display a wide linear viscoelastic region, and the value of G’ is higher than that of the G’’, which testifies their solid-like state and elastic attribute. Furthermore, the MoCOF@Gel also displays good mechanical stability during the bending, compression, and hammering tests (Fig. 4e). Fig. 4f shows the 3D interconnected capillary channels of PVA-Gel with a diameter ranging from a few microns to tens of microns, which could facilitate water transport via capillary action. After loading with MoCOF, these interconnecting channels are maintained, and the MoCOF spheres of several micron sizes are fixed to the outlet of the blank PVA capillary channels (Fig. 4g).
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8 x; z8 E& t7 @) N& [图5（a）在一个太阳光照射下，蒸发器表面和侧面温度分布的红外成像图；（b）太阳模拟器照射下蒸发器表面蒸汽照片；（c）MoCOF@Gels的重量变化图；（d）MoCOF@Gels的蒸发速率和光热转化效率；（e）MoCOF@Gel与其他基于COF或MoS2蒸发器性能对比；（f）不同NaCl浓度下的蒸发速率和转化效率；（g）淡化前后的离子浓度变化；（h）净化前后有机染料废水的紫外可见光谱。

Fig.5. (a) IR images of interfacial steam generator surface and side temperature distribution under 1 sun irradiation for 20 min. (b) The photograph of steam generation under solar simulator irradiation. (c) Cumulative weight loss of MoCOF@Gel with different compositions through water evaporation over time under 1 sun. (d) Summary of evaporation rate and energy efficiency of different MoCOF@Gel generators. (e) Evaporation rate and efficiency of MoCOF@Gel compared with other reported steam generators based on COFs and MoS2 materials. (f) Evaporation rate and efficiency of MoCOF@Gel at different NaCl concentrations. (g) Ca2+, K+, Mg2+ and Na+ concentrations in seawater before and after desalination.(h) UV-vis spectroscopy of RhB and MO aqueous solutions before and after desalination.
如图5a所示，在一个太阳光照强度下，半湿态MoCOF@Gel在20 min内表面温度可达到51.3℃。由于优越的局域热效应和高的蒸发率，MoCOF@Gel可以在短时间内被观察到蒸汽的产生（图5b）。为了估算MoCOF@Gel的蒸发速率，我们对不同体系在一个太阳下的重量变化进行了评估。如图5c所示，计算出块状水、MoS2(5%)@Gel、MoCOF(1%)@Gel、MoCOF(3%)@Gel、MoCOF(5%)@Gel和MoCOF(7%)@Gel的蒸发速率分别为0.14、1.71、1.66、1.89、2.31和1.98 kg/m2/h。根据建立的方法计算出相应的转换效率为10.2%、81.6%、74.3%、80.2%、91.8%和81.6%(图5d)。结果表明，MoCOF(5%)@Gel蒸发器的蒸发速率和转化效率明显优于MoS2(5%)@Gel蒸发器。MoCOF(5%)@Gel的太阳能驱动蒸发性能与大多数已报道的基于COF或MoS2的蒸汽发生器非常相似(图5e)。此外，还用不同盐度的模拟海水测量了MoCOF@Gel的海水淡化(图5f)。测试结果表明，即使在高盐水(20%)中，MoCOF@Gel也表现出较高的蒸发速率和较高的蒸发效率。为评价MoCOF@Gel的净水性能，采用电感耦合等离子体质谱(ICPMS)对南海区中国海区海水淡化前后样品中的钙、钾、镁、钠四种主要离子浓度进行了测定。如图5g所示，主要离子浓度显著降低~4个数量级，达到世界卫生组织规定的饮用水质量标准。通过向海水中分别投加罗丹明B和MO，对染料废水的净化性能进行了评价。经过净化后，收集的水为光学清澈无色，染料的特征吸收消失(图5h)，表明MoCOF@Gel对有机染料污染的污水具有很高的净化能力。
) E$ Y4 _) _2 h9 ZAs shown in Fig. 5a, the surface temperature of semi-wet state MoCOF@Gel can reach to 51.3 ℃ within 20 min under 1 sun. Because of the superior local thermal effect and high evaporation rate, MoCOF@Gel can be observed to produce steam in a short time (Figure 5b). To estimate the evaporation rate of MoCOF@Gel, the weight changes of various systems has been evaluated under one sun. As shown in Fig. 5c, the water evaporation rates of the bulk water,MoS2(5%)@Gel,MoCOF(1%)@Gel,MoCOF(3%)@Gel, MoCOF(5%)@Gel, and MoCOF(7%)@Gel are calculated to be 0.14, 1.71, 1.66, 1.89, 2.31, and 1.98 kg/m2/h, respectively. The corresponding conversion efficiency are calculated to be 10.2%, 81.6%, 74.3%, 80.2%, 91.8%, and 81.6% based on the established method (Fig. 5d). It is obvious that the evaporation rate and the conversion efficiency of MoCOF(5%)@Gel evaporator superior to the MoS2(5%)@Gel. The solar-driven evaporation performance of MoCOF(5%)@Gel is highly comparable to most of reported COF or MoS2 based steam generators (Fig. 5e ).Moreover, seawater desalination of MoCOF@Gel has been measured using simulated seawater with different salinity (Fig. 5f) , The test results show that MoCOF@Gel shows a relatively high evaporation rate and a superior evaporation efficiency even in high saline brine (20%). To appraise water purification performance of MoCOF@Gel, the four primary ion concentrations of Ca2+, K+, Mg2+ and Na+ in seawater sample from the South China Sea have been measured with ICP-MS before and after desalination. As shown in Fig. 5g, the concentration of major ions is significantly reduced by ~4 orders of magnitude and meet the drinking-water quality standards defined by WHO. The purification performance of dyestuffs wastewater has been also evaluated through doping seawater with RhB or MO. After purification, the collected water is optically clear and colourless, and the characteristic absorption of dye disappeared completely (Fig. 5h), demonstrating that MoCOF@Gel has a high purification capability in organic dye contaminated sewage.

良好的抗菌活性
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) f  \$ ^4 B0 K9 s) p* ~9 x6 I图6（a）细菌溶出物的OD260值；（b）处理后菌液的平板涂布CFU计数统计结果；（c）处理后菌液的琼脂板涂布结果；（e）Control、PVA、MoCOF@Gel在相同光照条件下处理四种模拟海洋细菌后的活死染色荧光图像。
Fig.6. In vitro antibacterial ability of samples. (a) OD260 values for evaluation of specimen-induced leakage of intracellular substances of bacteria. (b) The relative bacterial viability of different samples. (c) Photographs of the bacterial colonies. (d) Comparison of PVA-Gel and MoCOF@Gel on LB-agar plates covered with different bacteria. (e) Live/dead bacteria staining images.
5 F( d  }8 i( B9 t在海水淡化中，微生物污染往往会降低材料的性能，最终导致界面蒸汽发生器的失效。因此，具有良好抗生物活性的蒸发器对保证海水淡化装置的寿命和稳定的海水淡化性能具有重要意义。在这里，MoCOF@Gel的抗菌能力已经通过模拟海洋细菌物种包括大肠杆菌、金黄色葡萄球菌、铜绿假单胞菌和VP进行了评估。首先，评估各组的OD260值，以定量研究其抗菌效果。因为OD260值代表细菌的DNA和RNA的泄漏量。当细菌被杀死时，它们的细胞膜被破坏，更多的核酸被释放到细胞外环境中。如图6a所示，MoCOF@Gel组显示出统计上最高的OD260值，表明细菌膜受到的破坏最严重。此外，还用经典的平板计数法研究了杂化水凝胶的抗菌活性。如图6b和c所示，PVA-凝胶光组和对照光组显示出相似的抗菌效果，表明PVA水凝胶的抗菌活性可以忽略不计。令人鼓舞的是，对于MoCOF@Gel组，细菌几乎不能在LB琼脂平板上存活；高达近100%的抑制率表明，具有出色光热能力的MoCOF@Gel可以非常有效地杀灭细菌。用纸片扩散法研究了MoCOF@Gel在四种不同菌株中的抗菌活性。根据标准‘SNV 195920e1992’，PVA-GELTANT轻组对这四种细菌的抗菌效果“较弱”，而MoCOF@GELTRA轻组表现出“相当好”的抗菌活性(图6d)。据推测，良好的抑菌效果归功于MoCOF@Gel良好的光热效应，使某一区域的细菌被高温杀死。此外，还对处理后的菌液进行了Syto 9和PI染色，并在倒置荧光显微镜下观察。绿色荧光的Syto 9可以快速进入任何细胞壁并与DNA相互作用，而红色荧光的PI只能进入质膜受损的细胞。如图6e所示，PVA-凝胶塔光组和控制塔光组显示出强烈的绿色荧光，表明细菌存活良好。MoCOF@凝胶塔光组显示出强烈的红色荧光，这进一步验证了大量细菌已经被杀死。
2 _# F9 i+ y* @/ NIn seawater desalination, the microbial contamination tends to degrade the performances of materials and eventually results in a failure of the interfacial steam generators. Therefore, the evaporator with excellent anti-biological activity is of great significance to ensure the longevity of the device with stable seawater desalination performance. Herein, the antibacterial capabilities of the MoCOF@Gel have been evaluated by using simulated marine bacterial species including E. coli, S. aureus, P. Aeruginosa, and VP. Firstly, the OD260 value of each group has been evaluated to investigate the antibacterial effect quantitatively . Because the OD260 value represents the leakiness of DNA and RNA from bacteria. When the bacteria are killed, their membrane is damaged and more nucleic acids are released into the extracellular environment. As shown in Fig. 6a, the MoCOF@Gel group reveals a statistically highest OD260 value, indicating that the bacteria membranes have been disrupted most seriously. Furthermore, the classical plate count method has been employed to study the antibacterial activity of hybrid hydrogel. As presented in Fig. 6b and c, PVA-Gel + Light group and Control + Light group exhibit similar antibacterial effect, which indicates that the antibacterial activity of PVA hydrogel is negligible. Encouragingly, for the MoCOF@Gel group, barely bacteria survived on the LB agar plates; an inhibition rate of up to nearly 100% demonstrates that MoCOF@Gel with excellent photothermal ability can kill bacteria very efficiently. The antibacterial activity of MoCOF@Gel has been also studied in four different bacterial strains using the disc-diffusion method. According to the standard ‘SNV 195920e1992’, the PVA-Gel + Light group has ‘weak’ antibacterial efficiency against the four bacteria, while the MoCOF@Gel + Light group exhibits ‘fairly good’ antibacterial activity (Fig. 6d). It is speculated that the good bacteriostatic effect is attributed to the approving photothermal effect of MoCOF@Gel, which causes bacteria in a certain area to be killed by high temperature. Moreover, the treated bacterial suspensions were also stained with SYTO 9 and PI as well as observed through an inverted fluorescence microscope. The SYTO 9 with green fluorescence can quickly enter any cell wall and interact with DNA, while PI with red fluorescence only enters the cell with damaged plasma membranes. As shown in Fig. 6e, the PVA-Gel + Light group and Control + Light group exhibit strong green fluorescence, indicating good bacteria survival. The MoCOF@Gel + Light group shows strong red fluorescence, which further verifies that large amounts of bacteria have been killed.
( ^; ]4 r4 N# U6 ^总结
综上所述，我们成功地合成了CoF基光热材料。COF基复合材料具有良好的光热性能和亲水性。此外，通过原位凝胶法将MoCOF构筑到PVA的聚合物网络中，制备了界面蒸汽发生器(MoCOF@Gel)。在一个太阳下可获得高达2.31 kg/m2/h的高蒸发速率和91.8%的太阳蒸发效率。制备的MoCOF@Gel在海水淡化、染料污染污水净化等方面也表现出优异的性能。此外，还证明了MoCOF@Gel在模拟太阳辐射下具有良好的抗菌活性，在实际应用中可能对海洋生物污损具有良好的抗菌活性。MoCOF@Gel蒸汽发生器综合了优异的光热性能、良好的机械性能、高效的海水淡化性能和显著的抗菌活性等优点，被认为在长期太阳能海水淡化方面具有巨大的潜力。
In summary, we have successfully synthesized COF-based photothermal material. The satisfactory photothermal performance and hydrophilic property of the COF-based composite have also been demonstrated. In addition, the MoCOF has been architected into polymer network of PVA via in-situ gelation method to fabricate interfacial steam generator (MoCOF@Gel). A high evaporation rate as high as 2.31 kg/m2/h and with 91.8% solar evaporation efficiency can be achieved under one sun. The fabricated MoCOF@Gel also displays excellent performance for seawater desalination, dye contaminated sewage purification. Furthermore, it is demonstrated that the MoCOF@Gel possesses outstanding antibacterial activity under simulated solar irradiation, which might be effective for marine anti-biofouling in the practical application. Combining the merits of outstanding photothermal abilities, good mechanical performance, efficient performance for seawater desalination, and remarkable antibacterial activity, the MoCOF@Gel steam generator is considered to have great potential for long-term solar-driven seawater desalination.