Preparation And Application Of Porous Water-absorbing Ceramics

As the world’s population grows,the lack of water has become a common problem in the world today,and therefore atmospheric water harvesting technology has attracted more attention.In this paper,a porous water-absorbing ceramic adsorbent with high hydrophilicity,high static water absorption rate and high compressive strength was prepared using diatomite and porogen,in addition,the microstructure of the ceramic was characterised by a series of test techniques,for example,SEM,ESEM.Then,a LiCl-modified porous water-absorbing ceramic with optimal dynamic water absorption was obtained by nitric acid“ash removal”and surface modification with inorganic salts（LiCl,Ca Cl₂,and a mixture of the two）.At the same time,the adsorption mechanism of LiCl-modified porous water-absorbing ceramics was further investigated by using mercury-pressure method,nitrogen adsorption and desorption method,thermogravimetric method,as well as adsorption kinetics and adsorption isotherms.Finally,a series of practical application studies on LiCl-modified porous water-absorbing ceramics were carried out.The conclusions are as follows.1.Using diatomite as the main raw material,a porous water-absorbing ceramic with a static water absorption rate of 124.56%and a compressive strength of 13.95 N was prepared by adding a porogenic agent.The study shows that the porous water-absorbing ceramic had a porosity of 59.88%and a contact angle with water of 29.81 ^o,and was mainly physically adsorbed during static water absorption.However,its dynamic water absorption rate is0.02%,which needs to be further improved.2.Nitric acid“ash removal”and salt solution impregnation were used to improve the dynamic water absorption performance.The study shows that the dynamic water absorption of porous water-absorbing ceramics reached 62.03%after 0.5 h impregnation with 24%nitric acid solution and 2 h ultrasonic impregnation in 25%LiCl solution（control conditions RH=70%±5%,T=25℃±5℃,empty tower gas velocity of 0.21 m/s,packing height of 240 mm,adsorption column inner diameter of 20.5 mm）.Compared with the untreated porous water-absorbing ceramic,the dynamic water absorption rate increased by more than a thousand times.3.The pore size distribution of LiCl-modified porous water-absorbing ceramics was tested by mercury-pressure method and nitrogen adsorption and desorption method,and the results showed that they were mainly macroporous with a small amount of micropores and mesopores.The adsorption mechanism of LiCl-modified porous water-absorbing ceramics on water vapor was investigated by FTIR,TG,adsorption kinetics,and saturation adsorption isotherms.It was shown that the adsorption process was dominated by the chemisorption of LiCl,while the presence of synergistic effect of physical adsorption between LiCl and porous water-absorbing ceramics promoted the adsorption progress;the thermodynamic behavior was in accordance with the type II adsorption isotherm and Langmuir adsorption isotherm,and the kinetic behavior was in accordance with the proposed secondary kinetic equation;the interaction modes between water molecules and LiCl-modified porous water-absorbing ceramics were hydrogen bonding and Van der Waals forces.4.The performance tests of LiCl-modified porous water-absorbing ceramics under different working environments were carried out using self-designed devices.The study shows that the LiCl-modified porous water-absorbing ceramics have good dehumidification and water collection effects on both natural wet air（average RH=65.19%）and wet air under vacuum conditions（vacuum degree of 0.095 MPa）;the dynamic water absorption performance increases with the increase of relative humidity and has moisture regulation performance;the LiCl-modified porous water-absorbing ceramics not only completely desorb at 200 ℃,but also have stable regeneration performance.