Development of Eggshell Waste Incorporated with a Porous Host as a Humidity Adsorption Material

BOONSOOK Kanokwan ,NAEMCHANTHARA Patcharin ,LIMSUWAN Pichet ,NAEMCHANTHARA Kittisakchai＊

(1. Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand; 2. Department of Material and Process Engineering Technology, Faculty of Engineering and Technology, King Mongkut’s University of Technology North Bangkok, Rayong Campus, Rayong 21120, Thailand)

Abstract: The duck eggshell waste was developed to the novel desiccant that is friendly to human and environment.The calcium oxide (CaO) and calcium chloride (CaCl2) as the calcium-based desiccants were prepared from eggshell waste.The CaO desiccant derived from the eggshell waste sintering at 1 300 ℃,while the CaCl2 desiccant was extracted from eggshell waste with the hydrochloric (HCl) solution at different concentrations from 5 to 30 wt%.The yield percentage of CaCl2 desiccant increased with increasing the HCl concentration to 25 wt%.The humidity adsorption behavior were investigated in the range of 75%-5% relative humidity.The results show the CaCl2 desiccant has the highest hydration rate.The porous host from the kaolin was sintered at different temperatures from 200 to 1 000 ℃ and incorporated with 30% w/v concentrations of CaCl2.The physical properties and the humid-adsorption capacity of all porous host conditions were investigated.The porous host at sintering temperature 800 ℃ has the highest specific surface area.Moreover,the porous host at sintering temperature 800 ℃ with the 30% w/v concentration of CaCl2 desiccant has the highest humid-adsorption capacity.

Key words: eggshell waste;calcium chloride;desiccant;kaolin;porous materials

1 Introduction

The amount of water vapor in the air is known as humidity that directly affects human living,plant growth,machines and materials[1,2].Especially,metal that is the main component of the electronic devices is most sensitive to humidity because that causes rust and corrosion on their surface[3].The humidity is the biggest problem,leading to economic losses.Humidity controlling is essential to overcome the humidity problem.The humidity controller as a desiccant is used to maintain the humidity at a suitable level[4].The desiccant generally used silica gel due to their great porous surface area[5].Thus,the silica gel is used for humidity control in many products such as food,cosmetics,accessories,electronic devices,etc[6,7].The silica gel is discarded as waste without any treatment.The composition of silica gel is coated with cobalt chloride,a heavy metal salt[8],which may be contaminated in the soil and groundwater[9],leading to human toxic.For reducing the silica gel use,many researchers put a lot of effort into developing the new desiccants friendly to human and environment[10].In order to follow a zero-waste processing and achieve to the sustainable development,the new desiccants will be made from a recycle material or waste.In the same way,the eggshell waste is produced several tons per day.The eggshell waste dramatically increases during the COVID-19 pandemic situation.Because the eggs are also main and simple protein source for the people who stay at home during the lockdown situation and the patients are home/community/hospital isolation.Moreover,most eggshell wastes were sent to the landfill.This results in the environmental odor and acid-base equilibrium in soil[11,12].For this reason,the eggshell waste is the widespread waste to add value and recycle as the source of calcium for synthesized bone,biodiesel catalyst and other applications[13,14].It has been reported that the eggshell waste is developed as the desiccant with food products[15].The development of the desiccant from eggshell waste incorporated with other materials as the composite material is the challenge ways to enhance the performance and comfortable use.

The raw clay named as kaolin is the abundant common clay minerals in Thailand.The kaolin is one of the major materials widely used in ceramic product and other applications[16,17].The difference of geology results in the chemical composition of kaolin affecting its quality.The low-quality kaolin can be not used as raw materials for ceramic manufacturing due to the highly shrinkage of product after sintering.The low-quality kaolin has high porosity,surface area and stability in shape,which can be used as a porous host to enhance the humidity adsorption performance of eggshell waste desiccant[18,19]

In this research,to develop the eggshell waste as the desiccant with a good adsorption behavior,the eggshell waste was used as the starting material as calcium sources for calcium-based desiccant(calcium oxide,CaO and calcium chloride,CaCl2).The characterization of CaO and CaCl2desiccant and humidity adsorption behavior were investigated.In the CaCl2extraction process,the hydrochloric acid (HCl)concentrations were investigated and optimized for high potential CaCl2desiccant from eggshell waste.Furthermore,the kaolin was used as a porous host after sintering at different temperatures and incorporated with the calcium-based desiccant.Finally,the calciumbased desiccant from eggshell waste incorporated with porous host were investigated.

2 Experimental

2.1 Preparation of calcium-based desiccant from eggshell waste

For calcium-based desiccant preparation,the calcium-based desiccants include CaO and CaCl2derived from duck eggshell waste collected from the canteen of King Mongkut’s University of Technology Thonburi.The eggshell waste was stripped of the membrane off and washed with distilled water to remove the contaminants.Then,the eggshell waste was dried in the oven at 50 ℃ for 48 h and then ground into fine powders using agate mortar.To obtain CaO desiccant,the eggshell powder was calcined in the furnace at 1 300 ℃ for 4 h with a heating rate of 5 ℃·min-1.To obtain CaCl2desiccant,the HCl solution (Union chemical 1986 Co.,Ltd.,Thailand)at concentrations range of 5 wt%-30 wt% were mixed with the eggshell powder at the ratio of 2:5 (w/v).Then,the mixtures were stirred with a magnetic stirrer for 3 h to remove the carbon dioxide (CO2) gas bubble.The mixtures were centrifuged at 12 000 rpm for 15 min to split the supernatant and precipitant.The supernatant was dehydrated at a temperature of 130 ℃ by magnetic stirrer until it became CaCl2desiccant.Yield percentage was calculated as the following Eq.(1):

whereMDwas the mass (g) of CaCl2desiccant which obtained from the process andMIrepresented the mass(g) of eggshell powder used for extracting.

For porous host preparation,the porous host was prepared from the kaolin that provided from Provincial Administrative Organization of Uttaradit province,Thailand.The chemical compositions of the kaolin were determined by a wavelength dispersion X-ray fluorescence spectroscope (WDXRF,Bruker,S8 Tiger)and the results are shown in Table 1.

Table 1 Chemical compositions of kaolin/wt%

The kaolin was homogeneously mixed with 200 mL of water and molded into a spherical shape approximately 5 mm.Then,the porous host was sintered in the range of 200-1 000 ℃ for 5 h with an increment of 100 ℃.The porous host before and after sintering at different temperatures were presented in Fig.1.

Fig.1 The porous host appearance of (a) before sintering and after sintering at (b) 200 ℃,(c) 400 ℃,(d) 600 ℃,(e) 800 ℃ and(f) 1 000 ℃

For the porous host incorporated with CaCl2desiccant,the CaCl2solution at concentrations 30% w/v was prepared from the CaCl2desiccant,which dissolved in the distilled water.Then,the CaCl2solution was incorporated with the porous host after sintering by immersion for 24 h.After immersion,the porous host incorporated with CaCl2desiccant was dried in an oven at 120 ℃ for 24 h.

2.2 Characterization of calcium-based desiccant from eggshell waste

The crystal structure and phase transformation of the samples were investigated by X-ray diffractometer (XRD,Bruker D2 phaser).The XRD was operated with CuKα radiation (λ=1.541 4 Å) at 30 kV and 10 mA in 2theta range of 10°-60°.The Fourier transform infrared spectroscope (FTIR,Perkin Elmer spectrum two) has been used for the identification of functional groups on the surface of all samples in the range of 4 000-400 cm-1with a resolution of 1 cm-1.Surface morphology of the samples were monitored with a field emission scanning electron microscope (FESEM,FEI,Nova nanoSEM 450).The FESEM was operated with an accelerating voltage of 5 kV.All samples were coated with a thin layer of gold to reduce surface charging during the analysis.The specific surface area and pore volume of the porous host before and after sintering at different temperatures were analyzed by surface area and porosity meter(Micromeritics,3Flex) based on the Brunauer–Emmett–Teller (BET) method.All porous hosts were exposed to the outgassing process at 150 ℃ for 12 h before the specific surface area measurement.

2.3 Humidity adsorption testing for calciumbased desiccant from eggshell waste

For humidity adsorption testing of calcium-based desiccants including CaO and CaCl2,the experimental was set up in a box of 15×15×20 cm with the humidity and temperature sensor (DHT22).The calcium-based desiccant (20 g) with the crystallizing dishes were put into the experimental box.The humidity adsorption behavior of calcium-based desiccants was examined in the range of 75%-5% relative humidity at a temperature of 25 ℃.The relative humidity and temperature in the box were recorded with the Arduino recording program in every 1 min until the humidity decrease to 5% relative humidity.Then,the hydration rate of calcium-based desiccant was calculated.For humidadsorption capacity of porous host incorporated with CaCl2desiccant,the samples (amount of 10 g) were tested in a desiccator.A saturated solution of sodium chloride (NaCl) was used to control the relative humidity at 75%.During humid-adsorption capacity testing,the mass of samples was weighed and recorded in the testing time of 1 to 28 h.The humid-adsorption capacity was followed to the British Standard(BS 3482-6).

3 Results and discussion

3.1 CaO desiccant behavior

For CaO desiccant preparation,the eggshell waste was sintered at temperature of 1 300 ℃ for 4 h to form CaO.The XRD results of duck eggshell waste before and after sintering at 1 300 ℃ were used to confirm CaO phase as shown in Fig.2.The crystal structure of the sample before sintering showed only calcium carbonate (CaCO3) compound with calcite phase that appeared at 2theta of 23.40,29.59,36.19,39.67,43.49,47.20 and 48.71°,according to the joint committee on powder diffraction standards (JCPDS) number 85-1108.After sintering at 1 300 ℃,the XRD pattern of the sample showed the CaO compound with only lime phase that found at 2theta of 32.20,37.38 and 53.86°,according to JCPDS number 48-1467.Moreover,only peaks of CaO compound appeared,implying that CaCO3compound was completely transformed to CaO compound due to the decarbonation reaction[20,21](2):

Fig.2 XRD patterns of duck eggshell waste before and after sintering at 1 300 ℃

Next,the humidity adsorption behavior were investigated.After humidity adsorption testing,the humidity adsorption behavior of CaO desiccant was illustrated in Fig.3(a).The results showed that the relative humidity of CaO desiccant decreased as exponential decay with the decreasing of the relative humidity in the range of 0-50 min to 37.3% relative humidity.This behaves as linear behavior with a rate of 0.678 4 %·min-1.However,the CaO desiccant takes a longer time for 295 min to decrease until 5% relative humidity.The surface morphology and phase composition of CaO desiccants were investigated.

Fig.3 (a) Humidity adsorption behavior of the CaO desiccant at 75% to 5% relative humidity;(b) XRD pattern and (c) FTIR spectrum of the CaO desiccant after humidity adsorption testing

The CaO desiccant from duck eggshell waste after humidity adsorption testing were characterized using XRD with 2theta range of 10°-60°,as shown in Fig.3(b).The XRD pattern showed the new peaks at 2theta of 17.93,28.64,34.02,47.05 and 50.80° belong to calcium hydroxide (Ca(OH)2)compound as a portlandite phase corresponding with JCPDS number 44-1 481.While CaO compound as an initial phase still appears but the intensity decreases.The results indicated that CaO compound reacted with the humidity and transformed to Ca(OH)2compound[22].

The FTIR spectra of CaO desiccant before and after humidity adsorption are shown in Fig.3(c).The characteristic peaks are considered in the range of 4 000-500 cm-1.For CaO desiccant before humidity adsorption,the CaO desiccant displays a broadband peak around 1 300 -1 500 cm-1,which is attributed to the symmetric stretching vibration of C-O.The band at 859 and 1 068 cm-1are assigned to different vibration modes C-O bonds related to carbonation of CaO[23].The absorption peak at 550 and 1 732 cm-1is identified vibration of the Ca-O and C=O bonds,respectively[24,25].Moreover,there is a tiny dip in the spectra at 2 325 cm-1due to atmospheric CO2.Considering after humidity adsorption,the FTIR spectra appears the new strong peak at 3 640 cm-1belonging to the O-H in Ca(OH)2crystal[26]that indicates that the CaO compound adsorbs the water molecules and formed Ca(OH)2after humidity adsorption testing.

The morphology of the CaO desiccant before and after humidity adsorption is shown in Fig.4.For CaO desiccant before humidity adsorption,the FESEM images illustrate the agglomerating of the spherical shape interconnected to skeleton structure[27,28]that have a smooth surface.The average size of spherical shape approximately 2 mm was found,as shown in Fig.4(a).While the spherical shape of CaO desiccant after humidity adsorption is profusely cracked and larger than the original size before humidity adsorption testing[29](Fig.4(b)).The FESEM image shows the fissures on the surface of spherical shape and swelling due to the adsorption of water molecules from the humidity,corresponding with XRD results that CaO compound transforms into Ca(OH)2compound after humidity adsorption.

Fig.4 FESEM images of the CaO desiccant (a) before and (b) after humidity adsorption testing

3.2 CaCl2 desiccant behavior

The CaCl2desiccant,which was prepared by extraction from duck eggshell waste with concentrations range of 5 wt%-30 wt% of HCl solution was characterized the chemical composition and crystal structure by XRD,as shown in Fig.5(a).All XRD pattern of CaCl2with different concentrations of HCl showed similar pattern at 2theta of 19.70,25.63,29.26,31.16,31.75,38.04,38.49,40,12,43.31,47.56,48.05 and 48.77°,according with JCPDS number 24-0223.All XRD peaks demonstrated the pure phase of hydrophilite,which is anhydrous calcium chloride(CaCl2).The CaCl2formation results from the reaction of calcite from duck eggshell waste and HCl solution,giving the CaCl2solution and CO2.Then,the CaCl2solution was evaporated to CaCl2powder:

Fig.5 (a) XRD patterns and (b) yield percentage of CaCl2 desiccant with different concentrations of HCl solution

These results indicated that different concentrations of HCl have no effect on the crystal structure for CaCl2extraction from duck eggshell waste.Thus,the calculation of the yield percentage of CaCl2was selected to give more information on the amount of CaCl2product.The yield percentage of CaCl2extracted with different concentrations of HCl was shown in Fig.5(b).HCl concentration in the range of 5 wt%-25 wt% was linear increased and became to saturate in the range of HCl concentration above 25 wt% to 30 wt%.From the result,the CaCl2extraction at the 25 wt% HCl concentration has the highest yield percentage as 61.70%.The increasing of yield percentage depends on the concentration of HCl and a higher concentration will increase the rate of decomposition CaCO3because there are many chloride anions for exchange reaction with calcium cations to make the CaCl2compound.The unstable carbonic acid(H2CO3) is produced and then breaks down into CO2and water[30].However,Eq.(3) shows there are amounts of CO2.So,with high yield percentage of CaCl2,it releases much CO2gas that is an environmental hazard.

For humidity adsorption testing of CaCl2desiccant,the humidity adsorption results were presented in Fig.6(a).The results show the humidity adsorption behavior decreased the same as CaO desiccant.The decreasing of the relative humidity in the range of 0-50 min of CaCl2desiccant is 0.934 5% min-1.The relative humidity reduction of CaCl2desiccant is approximately 17.4% relative humidity.The downtrend of CaCl2desiccant has a similar trend that is faster than CaO desiccant.Within 145 min the relative humidity reduced to 5%.At the same way,the crystal structure of CaCl2desiccant after humidity adsorption testing was examined by XRD,as shown in Fig.6(b).The XRD pattern still showed hydrophilite phase as an initial phase of CaCl2compound.The XRD pattern shows the new sinjarite phase of calcium chloride dihydrate (CaCl2·2H2O)compound at 2theta of 14.54,19.17,20.42,20.92,30.31,31.99,35.99,41.68 and 42.67° corresponding with JCPDS number 70-0385.The XRD results demonstrated that the CaCl2absorbed the humidity and converted to calcium chloride hydrates after humidity adsorption.In the fact that the CaCl2is a hygroscopic salt that has a high ability to absorb the water molecules from the humidity surroundings.The oxygen of water molecules is directly attracted to the Ca2+ion through ion-dipole force[31].Subsequently,CaCl2reacts with a water molecule to transform to CaCl2·2H2O:

Fig.6 (a) Humidity adsorption behavior of CaCl2 desiccant at 75% to 5% relative humidity,(b) XRD pattern and (c) FTIR spectrum of the CaCl2 desiccant after humidity adsorption testing

For CaCl2desiccant,the FTIR spectra of CaCl2before and after humidity adsorption testing was shown in Fig.6(c).The FTIR spectra of CaCl2before humidity adsorption shows the silent spectrum.While after humidity adsorption the strong spectra with different wavenumber show the adsorption peaks at 3 485 and 3 373 cm-1,assigning to O-H asymmetric stretching.Furthermore,the absorption peak at 1 624 cm-1may be related to O-H stretching of H-bonding of water molecules as well as chloride ions occupied in crystal lattice.The adsorption peak at 657 cm-1is identified for the libration band of symmetric O-H stretching vibration.The FTIR spectra peaks at 3 217 and 2 164 cm-1belong to the symmetric O-H stretching and combined band,respectively.

The FESEM images of CaCl2desiccant before and after humidity adsorption are shown in Fig.7.The FESEM image before humidity adsorption testing displays not clearly the morphology of CaCl2desiccant.The particle of CaCl2desiccant was an irregular shape with random dispersion.The irregular shape of the particle was partially covered with a thin layer of water molecule (Fig.7(a)).After humidity adsorption testing,the FESEM image clearly shows the explanation of thin layer of the water molecule.The CaCl2particles with swelling and combination of each particle resulting in the disappearance of gain boundary (Fig.7(b)).However,these FESEM results of CaCl2desiccant are difficult to investigate the characteristic of CaCl2morphology due to the high sensitivity of humidity.CaCl2desiccant has a higher performance than CaO desiccant.Nevertheless,the swelling into the liquid phase of CaCl2desiccant after humidity adsorption limits the applying.

Fig.7 FESEM images of the CaCl2 desiccant: (a) before and (b)after humidity adsorption testing

To overcome the limitation of CaCl2desiccant swelling,the kaolin was selected to use as a porous host for CaCl2desiccant.The kaolin was molded into a spherical shape with a diameter of 5 mm as host.The pore of porous host could be created by sintering process.The sintering process not only influences on the porosity but also on the structure of porous host.So,the sintering temperature were investigated in the range of 200-1 000 ℃.Then,the structure,morphology,and porosity of porous host both before and after sintering process were addressed.The porous host before and after sintering in different temperature was characterized using XRD,as shown in Fig.8.The porous host before sintering shows the characteristic peak of kaolinite phase at 2theta of 12.35 and 24.84° according to JCPDS number 80-0886.The muscovite phase appears at 2theta of 17.84,19.79,26.77,29.81,31.17,31.99,34.83 and 45.48°,corresponding to JCPDS number 46-1409.Moreover,the 2theta of XRD pattern at 20.78,26.57,36.50,39.42,40.22,42.39,50.10,54.82 and 55.25° is found the high intensity of quartz phase according to JCPDS number 65-0466.Besides,a low composition of albite(JCPDS number 46-1409) phase at 21.95,22.80,23.75 and 27.78° appears.The XRD results show the phase of kaolinite,muscovite,albite and quartz as an initial phase of starting material that agreed with the chemical composition from XRF analysis,as shown in Table 1.After sintering in the range of 200-400 ℃,the XRD pattern still shows the phase of kaolinite,muscovite,albite,and quartz.After sintering in the range of 600-800 ℃,the XRD peaks of the kaolinite phase disappeared,and muscovite and albite decreased.In contrast,the quartz phase was still observed.With the kaolinite phase disappearing,water molecules release from the kaolinite structure and transform to metakaolin[32-34].After sintering at 1 000 ℃,new phase appears at 2theta 21.03,24.01,27.44 and 41.80° that belongs to microcline phase,corresponding to JCPDS number 84-0708.While,the intensity of quartz phase decreased.That means that muscovite and albite decomposed to silica and alumina and the muscovite and albite released alkaline phase of K2O and Na2O,respectively.The quartz reduction are results from the reaction with muscovite and it transforms into a microcline phase[35].Next,the surface morphology of porous host before and after sintering at different temperatures was shown in Fig.9.Before sintering,the porous host presented the heterogenous interlayers of aluminosilicate sheet with irregular orientation and sizes[36]as shown in Fig.9(a).After sintering in the range of 200-800 ℃,the surface morphology of porous host was still similar to that before sintering as shown in Figs.9(b) to 9(e).However,the sheet of aluminosilicate was merged and agglomerated into an irregular shape after sintering at 1 000 ℃,as shown in Fig.9(f).This indicated that the smooth surface are results from the decomposition of muscovite,albite and quartz corresponding to the structure transformation.

Fig.8 XRD patterns of porous host before and after sintering at different temperatures from 200 to 1 000 ℃

Fig.9 FESEM images of porous host with different sintering temperatures: (a) before sintering,(b) 200 ℃,(c) 400 ℃,(d)600 ℃,(e) 800 ℃ and (f) 1000 ℃

Next,the BET method was selected to obtain the porosity,average pore width and specific surface area of porous host after sintering in the range of 200-1 000 ℃ and the results are shown in Table 2.From the results of pore volume and average pore width,the sintering process has no significant effect on the pore volume of porous host,whereas the average pore width increases with increasing the sintering temperatures.The specific surface area of the porous host before sintering is 391.35×10-2m2·g-1.After sintering process,the specific surface area increased from 315.23×10-2to 590.31×10-2m2·g-1with increasing the sintering temperature from 200 to 800 ℃[37].The increasing surface area are due to the recovery of the structure in porous host.Moreover,this is resulting from the elimination of organic and water molecules in the porous host including the dehydroxylation of kaolin during the sintering process[38].While the porous host were sintered at 1 000 ℃,the specific surface area was decreased to 445.54×10-2m2·g-1.The decreasing of the surface area of porous host after sintering temperature at 1 000 ℃ is because of the decomposition and liquid phase transformation of muscovite and albite which fill up in pores of porous host[39,40].However,this sintering temperature also contributed to the merge of micropores.

Next,the porous host with different sintering temperature was immersed with 30% w/v CaCl2solution[41].Then,the CaCl2incorporated with porous host desiccant were examined the humid-adsorption capacity at 75% relative humidity.The relevant of the humid-adsorption capacity and time of the porous host with and without CaCl2desiccant were shown in Fig.10 and the rate of humid-adsorption capacity was showed in Table 3.For the sintering temperature below 800 ℃,the humid-adsorption capacity increased with increasing the sintering temperature.Nevertheless,the humid-adsorption capacity decreased when the sintering temperature was increased to 1 000 ℃.Considering the sintering temperature of porous host,the highest humidity adsorption capacity is the porous host with sintering temperature at 800 ℃,whereas at 200 ℃the lowest.However,this behavior of all porous host with CaCl2desiccant conditions showed rapidly increasing as a linear trendline.At the sintering temperature of porous host in the range of 200-800℃,the organic compound was burnt out and left the pores which inhabit the CaCl2desiccant.Moreover,the sintering temperature at 800 ℃ have high amount of micropores which promoted the specific surface area increasing.These micropores are CaCl2dwelling.That means that the porous host with many pores and CaCl2have driving force to react with the humidity as corresponding with specific surface area from BET analysis and humid-adsorption testing (Fig.10 and 11,and Table 2).Finally,the porous host with sintering temperature of 600 and 800 ℃ were selected to examine the surface morphology after humidity adsorption testing (Fig.12).From the results,the porous host incorporated with CaCl2desiccant also have the heterogenous interlayers of aluminosilicate sheet with CaCl2particles.This can confirm that the porous host incorporated with CaCl2desiccant can overcome the CaCl2desiccant swelling after humidity adsorption.

Table 3 Rate of humid-adsorption capacity of porous host at different sintering temperatures incorporated with CaCl2 30% w/v concentration

Fig.10 Humid-adsorption capacity of porous host at different sintering temperatures incorporated with CaCl2 30% w/v concentration at 75% relative humidity for 28 h

Fig.11 CaCl2 adsorption of porous host with different sintering temperatures after incorporated with CaCl2 solution

Fig.12 FESEM images of porous host at sintering temperature(a) 600 ℃ and (b) 800 ℃ incorporated with 30% w/v concentration of CaCl2 desiccant after humidity adsorption testing

4 Conclusions

a) The eggshell waste can be prepared to CaO desiccant with sintering temperature at 1 300 ℃.

b) The CaCl2desiccant can be extracted from the eggshell waste with HCl solution and the yield percentage of CaCl2depends on the concentration of HCl.25 wt% HCl has the highest yield percentage.

c) The humidity adsorption testing of calciumbased desiccant,the CaCl2desiccant has higher hydration rate to reduce the humidity from 75% to 5% relative humidity as compared to CaO desiccant.

d) The mechanism of humidity adsorption of calcium-based desiccant shows CaO and CaCl2desiccant phase transformation to Ca(OH)2and CaCl2·2H2O phase,respectively,after humidity adsorption.

e) The porous host prepared from kaolin after sintering at 800 ℃ has the highest specific surface area for storage CaCl2.

f) The CaCl2desiccant incorporated into porous host after sintering at 800 ℃ presents the highest humid-adsorption capacity.

Acknowledgements

The authors have gratefully acknowledged the research professional development project under the Science Achievement Scholarship of Thailand(SAST) for education financial support.The authors are grateful to Office of Atoms for Peace (OAP) and Kasetsart University (KU) Kamphaeng Saen Campus for providing some facilities in this experiment.

Conflict of interest

All authors declare that there are no competing interests.