Water adsorption performance of UiO-66 modified by MgCl_(2) for heat transformation applications

UiO-66 is a potential material for adsorption heat transformation(AHT)with high specific surface area,and excellent thermal and chemical stability.However,the low water adsorption capacity of UiO-66 in the low relative pressure range(0<P/P_(0)<0.3)limits its application in AHT.We prepare the UiO-66 modified by MgCl_(2)through using the solvothermal method and impregnation method,and study their water vapor adsorption performances and heat storage capacities.Attributed to the extremely high saturated water uptake and excellent hydrophilicity of MgCl_(2),the water adsorption performance of UiO-66 is improved,although the introduction of MgCl_(2)reduces its specific surface area and pore volume.The water adsorption capacity at P/P_(0)=0.3 and the saturated water adsorption capacity of the UiO-66(with MgCl_(2)content of 0.57 wt%)modified by the solvothermal method are 0.27 g/g and 0.57 g/g at 298 K,respectively,which are 68.8%and 32.6%higher than the counterparts of pure UiO-66,respectively.Comparing with pure UiO-66,the water adsorption capacity of the UiO-66(with MgCl_(2)content of 1.02 wt%)modified by the impregnation method is increased by 56.3%and 14.0%at the same pressure,respectively.During 20 water adsorption/desorption cycles,the above two materials show high heat storage densities(~1293 J/g and 1378 J/g).Therein,the UiO-66 modified by the solvothermal method exhibits the excellent cyclic stability.These results suggest that the introduction of an appropriate amount of MgCl_(2)makes UiO-66more suitable for AHT applications.

Modeling Water Adsorption and Retention of Building Materials From Pore Size Distribution

Water adsorption and capillarity are key phenomena involved during heat and moisture transfer in porous building materials.They account for interaction between solid matrix,liquid water and moist air.They are considered through Water Vapor Adsorption Isotherm(WVAI)and Retention Curve(RC)functions which are constitutive laws characterizing water activity within a porous medium.The objective of this paper is to present a water vapor adsorption and retention models built from multimodal Pore Size Distribution Function(PSDF)and to see how its parameters modify moisture storage for hygroscopic and near saturation ranges.The microstructure of the porous medium is represented statistically by a bundle of tortuous parallel pores through its PSDF.Firstly,the influence of contact angle and temperature on storage properties were investigated.Secondly,a parametric study was performed to see the influence of the PSDF shape on storage properties.Three cases were studied considering the number of modalities,the weight of each modality and the dispersion around mean radius.Finally,as a validation,the proposed model for WVAI were compared to existing model from literature showing a good agreement.This study showed that the proposed models are capable to reproduce various shapes of storage functions.It also highlighted the link between microstructure and adsorption-retention phenomena.

A series of high-nuclear planar equilateral triangle-shaped {Ln_(6)(μ_(3)-OH)_(6)} cluster encapsulated polyoxoniobates with frequency dependent magnetic property

The integration of lanthanide(Ln)ions and polyoxoniobates(PONbs)is challenging,and the know Ln-substituted PONbs are still scarce.This work introduces high-nuclear iso-Ln-oxo clusters into th PONb system.The first series of high-nuclear Ln-oxo clusters encapsulated heterometallic polyoxonio bates H_9[Na(H_(2)O)_(4)][Cu(en)_(2)]_(10){Ln_6(μ_(3)-OH)_6(Si Nb_(18)O_(54))_(3)}·18H_(2)O(1-Ln,en=ethylenediamine,Ln=Dy,Gd Tb,Ho,Er,Tm,Yb,Lu)based on flower-like{Ln_(6)(μ_(3)-OH)_(6)(Si Nb_(18)O_(54))_(3)}({Ln_6Si_(3)Nb_(54)})clusters hav been successfully synthesized via one-pot hydrothermal synthesis strategy.The flower-like polyoxoanio{Ln_6Si_(3)Nb_(54)}is consisted of three heteropolyoxoniobate{Si Nb_(18)O_(54)}clusters and one unique planar equ lateral triangle-shaped{Ln_6(μ_(3)-OH)_6}cluster,which presents the highest nuclear iso-Ln-oxo cluster i PONb chemistry.In{Ln_6(μ_(3)-OH)_6}cluster,each pair ofμ_(3)-OH groups link three Dy^(3+)ions to form a sma approximate equilateral triangle-shaped{Dy_(3)(OH)_(2)}cluster.Furthermore,the three{Dy_(3)(OH)_(2)}cluster comprise a bigger approximate equilateral triangle-shaped{Dy_6(μ_(3)-OH)_6}cluster.The reported hexanu clear{Ln_6}cluster skeletons are mostly octahedral,however,such equilateral triangle-shaped skeleton o the hexanuclear Ln-oxo cluster is first observed.The 1-Dy exhibits good water vapor adsorption capacit and ferromagnetic properties.