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Activated carbon fiber (ACF) with a high specific surface area has a good application prospect in atmospheric humidity control because it can adsorb H2O gas through both physical and chemical mechanisms. Based on a commercial ACF, the preparation of activated carbon fiber with a high specific surface area was carried out via a vacuum activation method. And the effects of adsorption temperature, relative humidity, and multi-components of air on water vapor adsorption of ACFs were studied. The results showed that the pore structure of ACF was improved. The maximum value of the specific surface area for ACF was 2967 m2/g, when the activation temperature and time were 1000 °C and 5 h, respectively, which was 71.03% higher than that of the commercial ACF (1733 m2/g). The water vapor adsorption capacity of ACF activated at 1050 °C for 2 h was a maximum of 1.36 g/g at 25 °C, which was 112.50% higher than that of the commercial ACF (0.64 g/g). On the other hand, the ideal selectivity of ACF toward H2O/N2 and H2O/O2 reached more than 4000. Furthermore, the isosteric enthalpy of adsorption on ACF was about 40 kJ/mol, indicating that the adsorption belonged to physical adsorption. It naturally follows that activated carbon fiber by high-temperature vacuum activation will be one of the alternatives for air humidity control. [ABSTRACT FROM AUTHOR]

The combination of water vapor, which is ubiquitous, and activated carbons (ACs), the most common adsorbent, is widely used in several fields, including energy storage, dehumidification, and gas separation, among others. Exploring the water vapor adsorption mechanism of ACs at the microscopic level is essential for optimizing material design and improving adsorption performance. So far, a large number of simulation studies based on the Grand Canonical Monte Carlo (GCMC) method have preliminarily grasped the adsorption mechanism of water vapor on ACs. In recent years, molecular dynamics (MD) and density functional theory (DFT) simulations have provided new insights into the dynamic behavior of water molecules and the carbon-water interaction at the electronic scale. However, any single technique can merely offer a one-sided perspective and partial comprehension, while the absence of multi-scale simulations hinders the attainment of a comprehensive and profound understanding of the structure-function relationship between water vapor adsorption and ACs. On the other hand, the model and the force field, which determine the accuracy of the simulation, lack a review of their selection principles. Therefore, this paper reviews the current application status of common AC models and their progress in multi-scale simulation studies of GCMC, MD and DFT for adsorbed water vapor. On the one hand, the complete system of model-force field-simulation is reviewed. On the other hand, the multi-scale adsorption mechanism of water vapor on ACs is revealed, which is essential for advancing future simulation work in this field. [Display omitted] • The model-force field-simulation system of water adsorption by AC is reviewed. • The role of different simulation methods for exploring adsorption behavior is emphasized. • The multi-scale adsorption mechanism of AC-water vapor is unveiled. [ABSTRACT FROM AUTHOR]

Coffee shells, which are abundant in cellulose and lignin, are good raw materials to prepare activated carbon. In this paper, coffee shells were selected as raw materials for activated carbon preparation by KOH chemical activation. Influence of carbonization temperature on adsorption capacity of water vapor over activated carbon was researched. Thermogravimetric analysis was employed to select the scope of carbonization temperature. Activation energies of coffee shells pyrolyzed at different heating rates were calculated. Nitrogen adsorption/desorption isotherm and scanning electron microscopy (SEM) were adopted to characterize the activated carbon. And water vapor adsorption isotherms were simulated by the finite simplification model of Do-Do adsorption model. The results show that activation energies of coffee shells pyrolysis process with heating rates of 5, 10 and 20 K/min are 17.21, 18.01 and 57.52 kJ/mol, respectively. The optimal carbonization temperature of coffee shells is 923 K. The adsorption amount of water vapor can reach about 702.3 mg/g under experiment temperature of 298 K and relative humidity of 70%. The highest total pore volume and Brunauer–Emmett–Teller (BET) specific surface area are 1.41 cm3/g and 2817 m2/g, respectively. The simulation results of the finite simplification model are consistent well with water vapor adsorption experiment results. The results show that activated carbon prepared at the optimal condition would be the potential candidate for solar drying system. [ABSTRACT FROM AUTHOR]

In this study, activated carbons without any chemical residue were prepared from walnut shells. The preparation method in a tube furnace included a pyrolysis carbonization process and a CO2 activation process. The influences of activation temperature and holding time on the specific surface area, yield, and pore structure were investigated. Adsorption performance of water vapor was also examined in details. Thermogravimetric analysis, N2 adsorption–desorption isotherm, and scanning electron microscope were used to characterize samples. The result shows that the activation energy at different heating rates varies from 30.16 to 64.86 kJ/mol. The highest water vapor adsorption capacity of the sample is 0.3824 g/g and it takes only 30 min to realize regeneration. And the maximum Brunauer–Emmett–Teller specific surface area of 1228 m2/g also occurs in this optimal preparation condition. CO2 physical activation method was found to have a positive effect on pore structure development of activated carbon for water vapor adsorption. [ABSTRACT FROM AUTHOR]

Abstract In order to realize dehumidification and heat recovery from solar drying system, a fresh walnut-shell activated carbon (AC0) was prepared by KOH chemical activation method and used as a novel host matrix for hygroscopic salt MgCl 2 impregnation. The effects of MgCl 2 loading amounts and cerium (Ce) addition on water vapor adsorption performance of the composite adsorbents were investigated. N 2 adsorption-desorption isotherm and scanning electron microscope were employed to characterize pore development and morphology of the composite adsorbents. Finally, regenerabilities and stabilities of AC0, AC40 (theoretical MgCl 2 loading amount 40 wt%), and AC404 (theoretical MgCl 2 loading amount 40 wt% and theoretical Ce addition amount 4 wt%) were studied. The results show that water vapor adsorption amount of the composite adsorbents decreases slightly and then increases significantly with the increase of the MgCl 2 loading amount. Under the 70% relative humidity and the adsorption temperature of 298 K, water vapor adsorption amounts of AC0, AC40, and AC404 are 0.6022 g/g, 0.9410 g/g and 1.0502 g/g, respectively. AC0 does well in excellent reversibility of water vapor adsorption. Ce addition slightly promotes uniform distribution of MgCl 2 within the composite adsorbent, prevents the conversion from MgCl 2 ·6H 2 O to Mg 2 CO 3 Cl(OH)·3H 2 O, and improves adsorption-regeneration performance. The present study confirms that the composite adsorbent would be one of the potential candidates for dehumidification and heat recovery in solar drying system. Highlights • A walnut-shell activated carbon is prepared and used for MgCl 2 modification. • The effect of MgCl 2 loading amount on water vapor adsorption were studied. • The maximum of water vapor adsorption amount onto AC404 was 1.0502 g/g. • AC0 possessed an excellent reversibility of water vapor adsorption. • Ce addition improved the adsorption-regeneration performance of AC404. [ABSTRACT FROM AUTHOR]

[Display omitted] • A continuous solar dryer integrated with sorption thermal energy storage (STES). • The composite adsorbent with a rectangular-wave-honeycomb structure was fabricated. • For two nights 2.64 kg water from 10 kg mushrooms was removed by the STES. • The STES could adsorb water, release heat, avoid rehydration and keep continuous drying. • The overall efficiency with STES (15.50 %) is higher than that without STES (14.23 %). Solar drying is an energy-efficient and environmentally friendly method. However, during periods without sunlight, the lack of energy input to the dryer causes it to cease drying, leading to challenges such as water vapor condensation and product rehydration. To address this, our study proposed a continuous solar dryer (CSD) that integrated conventional solar drying with sorption thermal energy storage (STES), characterized by internal circulation dehumidification at night. The inclusion of adsorption beds within the dryer removed water vapor inside the drying chamber and released sorption heat to supply energy for continuous drying. A series of composite adsorbents was prepared based on an activated carbon fiber (ACF) matrix through impregnation and spraying methods. Among these, ACF-calcium alginate-1/1 (ACF-CA-1/1) was identified as the optimal adsorbent for system-scale preparation and then used for drying mushrooms. Experimental results showed that ACF-CA-1/1 exhibited an adsorption capacity of 0.45 g/g at 20 ℃ and 80 % relative humidity (RH), with an energy storage density of 676.7 J/g. During nighttime drying from 21:00 to 9:00, the adsorption beds facilitated a reduction of 2.64 kg water from 10 kg mushrooms, resulting in a moisture ratio decrease of 29.53 %. The average RH within the drying chamber with STES was 61.37 % and 45.46 % on the first and second nights, respectively. Furthermore, the overall energy efficiency and specific moisture extraction rate of the dryer with STES were 15.50 % and 6.9 × 10−5 kg/kJ, respectively. Those of the dryer without STES were 14.23 % and 6.3 × 10−5 kg/kJ for the same factors, respectively. Notably, solar drying with STES achieved a 30.74 % decrease in RH of drying chamber, an 8-hour reduction in drying time, and a 1.27 % increase in energy efficiency compared to solar drying without STES. Herein, the CSD effectively overcame the rehydration problem of agricultural products at night, offering a promising solution to the intermittent nature of solar drying. [ABSTRACT FROM AUTHOR]