Mesoporous Silica‐Guided Synthesis of Metal–Organic Framework with Enhanced Water Adsorption Capacity for Smart Indoor Humidity Regulation

Metal–organic frameworks (MOFs) are promising for indoor humidity regulation due to steep stepwise water uptake and moderate regeneration temperature. Current approaches for performance improvement of MOFs such as impregnating hygroscopic salts and grafting functional groups face the challenge of corrosion and instability. Herein, a template‐guided tuning strategy is proposed to synthesize binary nanocomposite. Highly ordered mesoporous channels of MCM‐41 provide uniform nucleation sites for MOF growth, enabling a 21.5% promotion of specific surface area (3188.14 m2 g−1) and 23.4% improvement of water uptake (1.53 g g−1 at 20°C/90% relative humidity) for the nanocomposite compared with parent MIL‐101(Cr). The fast kinetics and superior stability together guarantee its practical application. Further, a paradigm of continuous indoor humidity regulation driven by sunlight is demonstrated, which realizes smart regulation of the indoor humidity to the human comfort zone (40–60%) with near‐zero energy input.


Introduction
Humidity has a great impact on human being's life.Excessive indoor humidity not only harms human health and comfort, but also leads to the proliferation of biological pollutants, mildew on furniture and clothing, and detriment of electronic equipment life and accuracy. [1,2]Conventional dewing-based dehumidification, which cools the air below the dew point to remove moisture (e.g., vapor compression system), has experienced explosive development in the past decades but its shortcoming of indoor air pollution and high energy consumption is gradually revealed facing the goal of carbon neutrality currently. [3,4]Solid desiccants which can remove the moisture above the dew point have emerged and become promising alternatives for humidity regulation. [5,6]Traditional solid desiccants such as silica gel, zeolites, and activated carbon have been extensively and intensively investigated from material research to system integration, and there is rare room for further performance improvement. [7,8]etal-organic frameworks (MOFs) are promising for adsorption owing to their unique advantages of large surface area, ultrahigh porosity, and tunable structural topologies. [9,10]In the past decades, a considerable amount of MOFs has been reported to have exceptional water adsorption capacity (even higher than 1 g g À1 ), and have been widely explored in water adsorption-related applications, such as heat pump, [11,12] thermal storage, [13] water harvesting, [14,15] and dehumidification. [16,17]In particular, the S-shaped isotherms of MOFs facilitate the energyefficient desorption process using low-grade thermal energy (e.g., solar energy and waste energy). [18]Moreover, the unique step characteristics make it possible to screen suitable materials for specific applications.For example, MOFs with steps at low pressure (MOF-801, MOF-303, etc.) have been adopted for water harvesting in arid climates. [19,20]When it comes to humidity regulation, MOF possessing step at 0.4-0.6 (p/p 0 ) is highly desirable to maximize the energy utilization efficiency. [21]For instance, MIL-100, UiO-66, and MIL-101 have been investigated for humidity regulation integrated with various technologies such as membrane dehumidification, [22] rotary desiccant wheels, [23] and desiccant-coated heat exchangers. [24]espite a lot of MOFs having been synthesized and applied in different scenarios, [25] improving the water uptake of MOFs has always been the pursuit of researchers.Confining hygroscopic salt (e.g., LiCl and CaCl 2 ) into porous matrixes is one of the effective ways. [26][29] However, introducing these halogen salt brings the risk of leakage and corrosion after long-term sorption-desorption cycles, hindering their practice in real-world applications. [30]In addition, modifying MOFs with functional groups is another common way. [31]MOFs modified by hydrophilic groups (such as -OH, -NH 2 , -COOH, etc.) could enhance the water sorption performance, and the isotherms can also be tailored.For example, modifying MIL-101 with -H, -NO 2 , -NH 2 , and -SO 3 H could tune the water uptake up to 0.8-1.2[35] Although such a method is a feasible way to tune the sorption behavior, the poor cycling stability is an unignorable weakness, which also impedes its practical demonstration.
[41] Additionally, enhanced stability for the well-tailored MOF nanoparticles could be achieved through framework stabilization and controllable pore environments. [42]Such a strategy does not rely on extra hydrophilic materials (functional groups or hydrophilic salts) to tailor the adsorption profile or capacity but directly regulates the synthesis process with low overhead.The facile tuning process and superior sorption performance motivate further explorations on composite sorbents using other ordered materials.[45] Although introducing this class of silica templates into MOF synthesis process has been tried preliminarily in gas separation, [46,47] the water adsorption behavior of these composites has not yet been elucidated and clarified.
In this work, complete explorations from material synthesis to device design are conducted for effective indoor humidity regulation.MIL-101(Cr) with suitable step position (P/P 0 %0.45) and ordered mesoporous silica MCM-41 are chosen to synthesize binary nanocomposite MIL-101/MCM-41 for further performance promotion.Highly ordered mesoporous channels of MCM-41 provide abundant nucleation sites which are conducive to the growth of MOF crystals.Compared with parent MOF, finer particles and higher specific surface area impart the nanocomposite superior water adsorption performance and stability, showing 3188.14 m 2 g À1 of specific surface area and 1.53 g g À1 of water uptake at 90% RH.Furthermore, a functional composite layer (FCL) is fabricated by loading the nanocomposite on fiber matrix and the photothermal effect is guaranteed by commercial ink.A prototype is assembled to demonstrate a continuous dehumidification process driven by sunlight, paving the pathway for continuous humidity regulation with near-zero energy input.

Synthesis and Characterization of the Nanocomposite
Both parent MIL-101(Cr) and MIL-101(Cr)/MCM-41 nanocomposite are synthesized by the hydrothermal method and the process is detailed in Supporting Information (Note S1).In the synthesis process of MIL-101, the nucleation and growth of MOF grains occur in the bulk solution of the mixture, which is a relatively random and disordered process.Thus, it is promising to optimize the crystallinity and properties of MOFs by tuning the synthesis process.And for the synthesis of the nanocomposite, quantitative MCM-41 was first dispersed in deionized water and sonicated for 15 min to form a uniform solution.Then CrCl 3 •6H 2 O was dissolved in the mixture and sonicated for another 15 min to get well dispersed.Therefore, metal ions (Cr 3þ ) were first attached to the surface of layered MCM-41 and served as nucleation sites for MOF crystals.As described in Figure 1a, MCM-41 serves as a template in the synthesis process to guide the growth of MOF crystals.By providing a great number of nucleation sites and blocking the extension of the framework, it can provide the opportunity to regulate particle sizes.Moreover, extra pore structures may come into being between the two materials.As the adsorption process of MIL-101 is mainly physisorption including nucleation and growth of water clusters on hydrophilic sites and capillary condensation taking place in the mesoporous cages, the tailored nanocomposite is able to realize adsorption performance improvement due to easier exposure to adsorption sites and larger pore volume [48] .And adequate characterization should be performed to support this inference.
Except for pursuing performance improvement of MIL-101, utilizing its step characteristics for humidity regulation is another key aspect.As shown in Figure 1b, the step position of MIL-101 is exactly located in the human comfort zone.When the indoor environment is in the high humidity region, the adsorption process automatically takes place to handle the excessive moisture.Then the RH gradually goes down near the step position and the adsorption ends up with the final humidity situated in the comfort zone.Hence, by taking advantage of the intrinsic properties of the material, smart humidity regulation can be realized without relying on complex dehumidification systems.However, reasonable structure design and heating source selection are necessary for optimizing the behavior, which will also be discussed in the following.
Figure 2 depicts the characterizations of the raw materials and the nanocomposite MIL-101/MCM-41.MCM-41 presents a worm-like morphology in the SEM image and well-ordered channels with continuous walls are observed in the TEM micrograph (Figure 2a,d and S1), while MIL-101(Cr) crystals exhibit a regular octahedral shape consistent with the literature [49] (Figure 2b and S2, Supporting Information).And for MIL-101/MCM-41, the crystals are arranged more tightly and the particle size is smaller intuitively (Figure 2c).Although MCM-41 cannot be directly observed in the SEM image of the nanocomposite, the TEM image clearly shows the combination of MIL-101(Cr) and MCM-41 (Figure 2e).From the distribution of Si (from MCM-41) and Cr (from MIL-101) elements in the energy dispersive spectrometer (EDS) mapping (Figure 2f ), it can be observed that Si element is evenly distributed, showing that the MIL-101 crystals grow on the layered MCM-41.While for the physical mixture prepared by stirring, such combination is invisible from TEM images and EDS mapping (Figure S3, Supporting Information).According to the particle size distribution (inset, Figure 4b,c and S4), the average particle size of MIL-101/MCM-41 is 352.8 nm, which is exactly smaller than that of pure MIL-101 (419.4 nm), indicating that the participation of MCM-41 has successfully reduced the particle size by providing growth template and more nucleation sites.With reduced particle size, it's easier for water vapor to approach the hydrophilic sites and access the pore structures.
The powder X-ray diffraction (XRD) patterns (see Figure 2g) prove that the crystal structure of MIL-101 is well preserved in the nanocomposite as the main characteristic peaks are coincident (1.8°, 2.9°, 3.4°, 5.2°, 9.1°, and so on).However, it should be noted that the relative intensities of the peaks vary.The intensities at 3.4°and 5.2°increase and others decrease, showing the crystallinity of the framework has changed after the participation of MCM-41.Moreover, the shift in the position of the diffraction peaks to higher angles indicates that the spacing between lattice planes has narrowed, [50] which is also consistent with the addition of MCM-41.The Fourier-transform infrared (FTIR) spectrum (Figure 2h) of the composite is quite similar to that of pure MIL-101(Cr), and characteristic bands representing Cr- O, C-H, O-C-O, C = C, and H-O-H can be easily found.However, no well-defined reflections of MCM-41 could be identified in both XRD and FTIR patterns ascribed to the low concentration of MCM-41 in the nanocomposite, [51] which also suggests the homogeneous dispersion of MCM-41.But X-ray photoelectron spectroscopy validates that Si in the þ4 valence state can be detected in the nanocomposite, showing the existence of trace MCM-41 (Figure S5, Supporting Information).The Raman spectra of MIL-101(Cr) and MIL-101/MCM-41 further provide evidence of the difference between the composite MOF and parent MOF (Figure 2i).Four main peaks located at 870, 1144, 1453, and 1612 cm À1 , respectively, represent different molecular vibration or rotation energy levels in MIL-101(Cr) [52] .Moreover, the peak intensity of the nanocomposite is weaker than that of bare MIL-101, suggesting that the introduction of MCM-41 has reduced the relative content of the characteristic groups. [41]

Adsorption Performance of the Nanocomposite
Although the characterizations of the nanocomposite validate the regulation effect for MOF crystals with the introduction of ordered silica, the evaluation of adsorption performance is of utmost importance to prove the effectiveness of the tuning strategy.Then a series of experiments were performed to reveal the structural properties and water adsorption performance of the nanocomposite as follows.Figure 3a,b displays the N 2 adsorption isotherms and the pore size distribution of bare MCM-41, MIL-101(Cr), and the nanocomposite MIL-101/MCM-41.The N 2 adsorption isotherm of MCM-41 is quintessential type IV with H1 hysteresis loop which is associated with capillary condensation taking place in mesopores.MCM-41 itself is a benign porous material with a Brunauer-Emmett-Teller (BET) surface area of 938.59 m 2 g À1 and a pore volume calculated by the density functional theory (DFT) model of 0.96 cm 3 g À1 (Supporting Information, Table S1), which is consistent with the literature. [53]s for MIL-101(Cr), it is an excellent water adsorption MOF with an ultrahigh BET surface area of 2624.89m 2 g À1 and an abundant pore volume of 1.556 cm 3 g À1 .Pore size distribution indicates that MIL-101(Cr) contains both micropore and mesopore, mainly located at pore widths of 1.1, 1.8, and 3.2 nm.Interestingly, a considerable N 2 adsorption capacity improvement is achieved for the nanocomposite (Figure 3a), with BET surface area augmenting to 3188.14 m 2 g À1 , which is 21.5% and 239.7% higher than parent MOF and MCM-41, respectively.Compared with bare MOF, an extremely large pore volume of 1.860 cm 3 g À1 also proves the potential superiority for water adsorption (see Figure 3b).In addition, the pore width distribution also slightly differs from that of MIL-101 without regulation.The location of the peaks remain but the peak intensities increase, and both the micropore and mesopore of the nanocomposite augment.These changes further reveal that the participation of MCM-41 has affected the pore structure of MOF crystals.
Subsequently, the water adsorption performance of the nanocomposite was investigated.As shown in Figure 3c, the water adsorption isotherms of MIL-101 and MIL-101/MCM-41 depict little difference in the early stage (P/P 0 < 0.35), but after a dramatic step (0.35 < P/P 0 < 0.45), MIL-101/MCM-41 accomplishes a transcendence.The adsorption capacity of the nanocomposite reaches 1.53 g g À1 (20 °C, 90% RH), which is 23.4% higher than parent MIL-101 without regulation (1.24 g g À1 ).It should be noted that the appropriate content of MCM-41 determines the performance of the nanocomposite.Nanocomposites with different content of MCM-41 were prepared and characterized (Figure S6-S9, Supporting Information).It is revealed that the low content of MCM-41 has little regulation effect on the growth of MOF crystals while excessive addition of MCM-41 will induce impurities and impede the construction of pore structures, resulting in the reduction of the adsorption capacity.The optimal MCM-41 concentration of 3.2% in the reactants is selected for further application.In comparison, performance attenuation is observed clearly in the isotherm of the physical mixture with the same concentration of MIL-101 and MCM-41 (Figure S10, Supporting Information), showing the effectiveness of the template-guided tuning strategy.
Furthermore, adsorption kinetics which is another critical parameter for practical applications was studied.The adsorption kinetics of MIL-101 and MIL-101/MCM-41 at 20 °C/80% RH were first tested and analyzed by vacuum steam adsorption using a commercial sorption analyzer with the same sorbent masses (Figure 3d).The equilibrium adsorption capacity of MIL-101 and the nanocomposite is consistent with the isotherm and the equilibrium time of both two materials is around 1.5 h.The derivative water uptake reflects the adsorption rate and higher values are obtained for the nanocomposite, revealing that MIL-101/MCM-41 can realize higher water uptake while preserving fast kinetics.Moreover, the kinetics of the composite were investigated under varied RH in a climate chamber (Figure 3e).As the step position of MIL-101 locates at p/p 0 = 0.35-0.45, the RH range of 50-80% was selected.The linear driving force model is used to describe the dynamic adsorption process of the nanocomposite (Figure S11, Supporting Information).It is discovered that higher RH contributes to a larger concentration difference of water vapor between the pores and the sorbent surface, thus the adsorption rate is promoted.At RH = 80%, the composite sorbent achieved its equilibrium adsorption capacity within 300 min and the final water uptake reached 1.45 g g À1 , which is consistent with the isotherm and the experiment carried out in the commercial sorption analyzer.When RH is 70%, the equilibrium time was prolonged to around 420 min.With the RH descending to 60% or even lower, the equilibrium water uptake then decreased and the corresponding adsorption time was longer.Note that the results of the dynamic adsorption are closely associated with the testing condition, such as the used amount, the stacking way of the powder, and the air velocity of the testing environment.That explains the adsorption kinetics in the commercial sorption analyzer is much faster than the experiment carried out in the climate chamber, which is contributed to the tiny amount of sorbent used and continuous airflow carrying the moisture over the sorbent surface.And in the climate chamber, to guarantee the accuracy of the results and reduce the fluctuation of the electronic balance, more than 200 mg adsorbent was used and air velocity was kept as low as possible, resulting in a relatively long adsorption period (Figure S12, Supporting Information).
Afterward, the desorption performance of the composite sorbent was studied by varying the heating temperature from 50 to 80 °C (Figure 3f ).Compared with the active adsorption process, passive desorption driven by a heating source is much easier and faster.The sample released 95.9%, 84.7%, 67.9%, and 43.8% adsorbed water within 20 min and 100%, 93.8%, 85.6%, and 57.1% adsorbed water within 60 min at 80, 70, 60, and 50 °C, respectively.These results indicate that the composite sorbent can be regenerated by low-temperature heating sources (>50 °C), which can be offered by solar energy and reject heat, etc.The cycling stability of the composite sorbent was also explored by repeating continuous adsorption and desorption cycles using the same commercial sorption analyzer.The adsorption condition was set to be 20 °C/80% RH and the desorption condition was 85 °C/5% RH.It is revealed that the adsorption capacity of the composite sorbent shows no attenuation after 20 adsorption-desorption cycles, proving excellent stability (Figure 3g).In contrast, a slight attenuation is observed for pure MIL-101 after 20 cycles.To highlight the potential of humidity regulation using this nanocomposite, the adsorption performance of state-of-the-art MOFs reported for water adsorption-related applications and other common desiccants are summarized in Figure 3h.It is encouraging that the nanocomposite synthesized in this work presents an overwhelming equilibrium adsorption capacity than most desiccants including MOFs.Especially, the step position of the composite locates in the human comfort zone. [21]While MOFs with steps at low pressure are always used to capture water in arid climates, such an MOF material with exceptional water adsorption capacity and middle step position is extremely suitable for humidity regulation in humid climates at low-energy expenses.

Fabrication of the Functional Composite Layer
The exceptional water adsorption capacity and moderate regeneration temperature together with superior cycling stability of the synthesized MIL-101/MCM-41 promise great potential for practical implementation.Considering the unique characteristic of S-shaped isotherm and low-temperature regeneration, an all-in-one device is designed for continuous humidity regulation using sunlight.As envisioned in Figure 4a, the composite sorbent can be shaped into a cylinder with photothermal material covering the surface.The inside part can capture the water vapor and the outside part can be regenerated by sunlight.Thus, through a rotating mechanism, continuous moisture removal can be accomplished by rotating the saturated part to the outside and the recovered part to the interior.It is worth noting that although MOFs are excellent adsorbents, they usually suffer from poor thermal conductivity.And with the thickness of the MOF coating increasing, the mass transfer is also affected.To this end, an FCL is fabricated by loading MOF nanoparticles on the active carbon fiber felt (ACFF) with high heat conductivity through the wet impregnation method, and spraying commercial ink on the surface as the photothermal material (Figure 4b, Figure S14, Supporting Information and Note S2).SEM images manifest the morphology of ACFF and ACFF@M/M (ACFF impregnated with MIL-101/MCM-41), proving that MIL-101/MCM-41 is successfully embedded on the gaps between the fiber and channels formed by the entanglement of fibers (Figure S15, Supporting Information).The loose and porous structure of ACFF and moderate loading content of the MIL-101/MCM-41 guarantee the transportation channels of water vapor.To explore the photothermal effect, the sunlight absorbance of the sample before and after spraying the carbon ink was tested (Figure 4c).The sample with carbon black ink covering the upper surface depicts sunlight absorbance over 95%, showing the potential for solar energy utilization.In virtue of the high heat conductivity of ACFF, heat transfer in the vertical direction is also guaranteed so that the heat generated on the surface can be conducted to the interior section to realize high-efficient desorption.
Further, to investigate the adsorption performance on the sample level to figure out the influence of integrating ACFF and carbon black ink.Adsorption and desorption tests were performed under varied RH and heating temperature (Figure 4d).As the adsorption capacity is calculated based on the mass of the nanocomposite, it is revealed that the adsorption capacity of the FCL sample even exceeds that of the pure sorbent under the same testing condition owing to the extra adsorption capacity contributed by ACFF (Figure S16, Supporting Information).The equilibrium water uptake under 80% RH reaches 1.67 g g À1 within 520 min and water uptake under 50-70% RH is also considerably high.However, under 30% RH, the water uptake of 0.1 g g À1 is much lower.Therefore, the composite layer is promising to handle moisture and reduce humidity below 50% utilizing its step characteristics.And if regenerated reasonably, the adsorption capacity can be recovered and the humidity level can be maintained.As revealed in Figure 4d, a regeneration temperature of 60 °C is enough to regenerate the saturated sample within 60 min.Nevertheless, the desorption test carried out in the constant temperature oven can hardly reflect the realistic regeneration properties utilizing sunlight because the whole sample is uniformly heated in the oven but only the surface is heated by the sunlight.Therefore, the dynamic desorption characteristics driven by sunlight using a solar simulator were conducted (Figure S17, Supporting Information), and the real-time weight and surface temperature of the sample were recorded (Figure 4e,f ).When the sunlight strength enhances, the surface temperature of the sample increases, leading to a higher desorption rate and efficiency.Specifically, 95.2%, 81.4%, 65.3%, and 55.0% adsorbed water was released within 60 min under the sunlight strengths of 1.2, 1.0, 0.8, and 0.6 kW m À2 , respectively, and the corresponding surface temperature stabilized at 78, 73, 65, and 58 °C. Figure 4g describes the heating process recorded by the infrared camera under the sunlight strength of 0.8 kW m À2 , showing the rapid rise of surface temperature.The infrared images of other groups are summarized in Figure S18, Supporting Information.

Demonstration of the Humidity Regulation Performance
Following, a moisture transportation component (MTC) was fabricated by integrating FCL with a polytetrafluoroethylene (PTFE) cylinder as planned to achieve continuous humidity regulation and solar energy utilization.The extremely low heat conductivity of PTFE (%0.25 W m À1 K À1 ) isolates the heat transfer from outside to inside (Note S3).A practical prototype is assembled to measure the moisture removal ability of the MTC (Figure 5a,b).The prototype includes a sealed box of the size of 400 Â 500 Â 600 mm representing the humid space and a controllable motor stepper to drive the MTC (Figure S19 and S20, Supporting Information).The MTC is divided into two parts: 3/4 of the surface locates inside the box to adsorb the moisture by the FCL, and the other 1/4 of the surface is exposed to sunlight which is transferred to heat to regenerate the sorbent.In this mode, the humidity inside the box can be pumped to the environment as a humidity pump [54,55] .Notably, most reported humidity pumps in literature use two identical components running in parallel, one for adsorption and another for desorption, which is a batch process.However, according to the adsorption and desorption tests carried out before, it is not difficult to find that the adsorption duration is usually several times the desorption duration.Therefore, the adsorption and desorption processes cannot match with each other by switching two identical components, and thus a part of the adsorption capacity is wasted.Herein, the design proposed in this work refers to the partition of the classical rotary wheel to match the heat and mass transfer of different functional areas, maximizing the adsorption capacity of the MTC. [56]fterward, the feasibility of the design was validated in a climate chamber with a solar simulator (Figure 5c).A pyranometer is used to measure the sunlight strength and two thermoshygrometers record the real-time temperature and RH inside and outside the box.Before the test, the chamber is set to the required testing condition and the MTC is thoroughly dried to recover its adsorption capacity.It can be found that the interior temperature and RH remain consistent with those of the external environment without fixing the MTC on the prototype (Figure S21, Supporting Information).And once the MTC is fixed, it begins to deal with the moisture and the inside RH gradually goes down while the external RH remains around the fixed value (Figure S22 and S23, Supporting Information).As expected, the MTC can effectively deal with the moisture in the device under all conditions (Figure 5d-f ).Specifically, with an environment of 25 °C/70% RH (13.964 g kg À1 ), the MTC can reduce the humidity to 50% RH within 120 min which is located in the human comfort zone (40%-60% RH).Under the highly humid environment of 25°C/90% RH (18.069 g kg À1 ) and 30°C/80% RH (21.636 g kg À1 ), the dehumidifier can also deal with the latent load and maintain the environment to 55% RH.It appears that the ultimate RH of the device shows weak association with the environment state but is determined by the step position of the sorbent.That is, when the humidity in the device falls around the step RH, then the water vapor partial pressure difference between the pore and the adsorbent surface is not sufficient to drive the adsorption process.From the IR images in Figure 5d, it can be found that the temperature of the FCL surface is lower than that measured in the desorption test using a solar simulator under similar sunlight strengths (Figure 4e).One of the reasons is that air velocity is relatively high in the test chamber to carry away the heat brought about by the sunlight so the convective heat transfer on the adsorbent surface is strengthened.Moreover, the surface temperature is relevant to the ambient temperature and rises with increased ambient temperature.The temperature distribution along the width of the cylinder reveals that the surface temperature is not uniform but displays a relationship related to the rotation of the cylinder (Figure 5e,f ).The sorbent on the left just rotates out of the box thus its temperature is relatively low.In contrast, the adsorbent on the right has been exposed to sunlight for a quarter of the cycle so the surface temperature increases.Similarly, experiments under different sunlight strengths (0.68-1.23 kW m À2 ) are carried out and the ambient condition is fixed at 25 °C, 80% RH (Figure 5d,f ).Results display that under all sunlight strengths, the MTC can reduce the inside humidity to the human comfort zone (around 52% RH).But the surface temperature varies under different sunlight strengths with the highest temperature of 70 °C under 1.23 kW m À2 sunlight.It is worth mentioning that the optimum sunlight strength is a tradeoff between the desorption capacity and the cooling time.Higher sunlight strength allows more heat to regenerate the sorbent, but higher surface temperature also requires a longer cooling time after rotating into the space, which not only weakens its adsorption capacity but brings the temperature rise of the internal room.Considering the small volume of the MTC compared with the entire room, the temperature rise is limited while the cooling of the sorbent is quite critical.Therefore, all the experiments performed adopt a rotary speed of 2 h r À1 to ensure sufficient desorption, adsorption, and cooling of sorbent.
The realistic performance of this device was demonstrated in Shanghai, China (30°40' N, 120°52' E).The experiment was carried out from 8 am on 2nd October to 8 am on 3rd October, and the ambient temperature, humidity, and solar irradiation were recorded by a weather station (Figure S24, Supporting Information).The average temperature and humidity ratio of daytime (from 8 am to 5 pm) and nighttime (from 5 pm to 8 am the next morning) were 32.4 °C/53.4% RH and 27.9 °C/76.2%RH, respectively, and the maximum sunlight strength is 0.91 kW m À2 at about noon.At the beginning of the experiment, the pre-dried MTC was fitted on the device with a rotation speed of 2 h r À1 .As the regeneration is driven by the sunlight which cannot work at night, the stepper motor was turned off after sunset (about 5 pm).As depicted in Figure 5f, with the MTC functioning, the average humidity inside can be reduced by 8.5% RH and 13.2% RH during daytime and nighttime, respectively.It is encouraging that the dehumidifier processes residual adsorption capacity after the daytime operation and can deal with part of the latent load at night.Owing to the existing leakage space, the high humidity at midnight leads to the rising of RH inside.Nevertheless, this phenomenon can be avoided in practical operation by sealing the prototype at night.Due to the limitation of the weather in the field test, such a dehumidification performance would be more obvious for sunny and humid climates.
It should be noted that current cooling and dehumidification technologies account for a large amount of building energy consumption (more than 50%).In this work, by combining the high-performance sorbent and ingenious device design, energy-efficient moisture removal can be realized as the whole process consumes almost no electricity aside from the step motor.For the occasions where the latent load plays a major role, it can function as a separate dehumidifier for moisture removal.In this case, the traditional air conditioning systems only need to handle the sensible heat load, thus the energy consumption can be dramatically reduced.Going a step further, now that the proposed component can efficiently regulate the indoor humidity to the human comfort zone, it may also work in winter for humidification utilizing its step characteristics.As elaborated in Figure S25, Supporting Information, in typical winter conditions, outdoor air is cold and of high humidity (at the right of the step position) while indoor air is warm and dry (at the left of the step position).Therefore, the composite layer can extract moisture in the outside and when it is rotated inside, it can automatically release the water vapor to the inside until the partial pressure of water vapor inside and outside the pore gets balanced.Proof-of-concept adsorption and desorption tests were carried out at 10 °C&70% RH and 20 °C&30% RH, respectively, in a constant humidity chamber, which proved the feasibility of this operating mode.Combing the dehumidification mode, such a component can realize smart humidity regulation both in arid and humid climates with extremely low-energy expenses.

Conclusion
In summary, we propose a tuning strategy for MOF synthesis by introducing mesoporous silica in the hydrothermal reaction to produce nanocomposite MIL-101/MCM-41.The morphological and structural characterizations reveal that well-shaped and decreased-size MOF nanoparticles endow ultrahigh specific area (3188.14cm 2 g À1 ) and superior water uptake (1.53 g g À1 at 90% RH), which is respectively 21.5% and 23.4% higher than that of parent MOF, while the physical mixture of MOF and MCM-41 shows lowered values and weakened performance.Benefiting from the aforementioned properties, the nanocomposite also exhibits faster adsorption kinetics and better stability compared with that of the parent MOF.Importantly, the demonstration of this tuning strategy provides more opportunities to tailor the water adsorption performance of MOF crystals using other ordered mesoporous materials.Furthermore, an FCL is fabricated by loading the nanocomposite on porous ACFF and using carbon black ink to endow it with photothermal properties, which preserves the superior adsorption performance of MIL-101/MCM-41 and can be regenerated by sunlight with an absorbance of over 95%.An adsorption-based conceptual humidity regulation prototype is assembled and investigated for continuous moisture removal, proving that the fabricated component can effectively deal with moisture and lower the humidity to the human comfort zone at extremely low-energy expenses.The feasibility of using such a component for indoor humidification is also preliminarily verified.Taken together, this technology paves the way for smart and energy-efficient humidity regulation and is promising for next-generation zero-energy buildings.

Figure 1 .
Figure 1.Design of the nanocomposite MIL-101/MCM-41 and its applications.a) Schematic diagram of the template-guided tuning strategy.b) Demonstration of the smart indoor humidity regulation.

Figure 3 .
Figure 3. Structural properties and adsorption performance of nanocomposite.a) N 2 adsorption isotherms, b) pore size distribution, and c) water adsorption isotherms of MCM-41, MIL-101(Cr), and MIL-101/MCM-41.d) Adsorption kinetics of MIL-101 and MIL-101/MCM-41 at 20 °C/80% RH.Derivative water uptake reflects the adsorption rate of the sorbent.e) Adsorption kinetics of MIL-101/MCM-41 at variable humidity.f ) Desorption kinetics of MIL-101/MCM-41 at variable heating temperature.g) Cycling stability of MIL-101 and MIL-101/MCM-41.h) Comparison of adsorption performance of nanocomposite and other desiccants reported for water adsorption.The value of the x-axis is the starting point of the adsorption platform and the value of the y-axis is the adsorption capacity at p/p 0 = 0.9.The adsorption isotherms and corresponding references are included in Supporting Information (Figure S13, Supporting Information).

Figure 4 .
Figure 4. Fabrication and characterization of the function composite layer.a) Design of the moisture transportation component (MTC).b) Schematic illustration of the fabrication process of the functional composite layer (FCL).c) Absorbance of the FCL before and after spraying the carbon black ink.d) Adsorption and desorption kinetics of the FCL under varying RH and constant heating temperature of 60 °C.e) Desorption kinetics driven by sunlight.f ) Surface temperature under different test conditions.g) Infrared radiation (IR) images of the sample under the sunlight of 0.8 kW m À2 .

Figure 5 .
Figure 5. Humidity regulation performance of the prototype.a) Schematic illustration of the humidity regulation process.b) Photos of the MTC.c) Actual view of the laboratory experimental setup.d) IR images of the MTC surface exposed to sunlight under varied test conditions and sunlight strengths.e) Inside humidity over time and temperature curves of the selected lines (marked in Figure 5d) on the MTC surface under varied test conditions.f ) Inside humidity over time and temperature curves of the selected lines under varied sunlight strengths.g) Temperature, RH, and solar irradiation in the field experiment.