A review of cryogels synthesis, characterization and applications on the removal of heavy metals from aqueous solutions

Contribution of Cross-Linker and Silica Morphology on Cr(VI) Sorption Performances of Organic Anion Exchangers Embedded into Silica Pores

“…Nowadays, finding highly efficient systems for the removal of heavy metal ions (HMIs) from the aquatic environment is a stringent issue in front of the scientists all over the world, because they are highly toxic (even at low concentrations), not biodegradable, and have an accumulation tendency in living organisms-most of them being carcinogenic. Synthetic polymeric sorbents [1][2][3][4][5][6] and various biosorbents [7][8][9][10][11][12] are investigated for their performances in the recovery/removal of HMIs. Among the HMIs present in the wastewaters, chromium, especially Cr(VI), is one of the most dangerous contaminants of the surface and ground water, being considered a powerful carcinogenic and teratogenic agent threatening living organisms [1,2,11,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…According to the World Health Organization (WHO) drinking water guidelines, the maximum allowable limit for total chromium is 50 µg/L [1,2]. Therefore, to avoid the dangerous impact of Cr(VI) on human health and on the environment, as well as for economic considerations, it is essential to remove/recover Cr(VI) from the wastewaters before disposal [1][2][3]. Various techniques are available for the removal of Cr(VI) such as ion exchange, chemical precipitation, reduction [13,14], reverse osmosis, foam flotation, electrolysis, membrane filtration [15,16], ultrafiltration [17], sorption, and biosorption [18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Cryostructuring of Polymeric Systems. 55. Retrospective View on the More than 40 Years of Studies Performed in the A.N.Nesmeyanov Institute of Organoelement Compounds with Respect of the Cryostructuring Processes in Polymeric Systems

“…In fact, all studies carried out at the IOEC as well as other studies on the preparation of the diverse cryogenically-structured polymer materials have always included the evaluation of various physico-chemical characteristics of the respective samples, and, very often, the dependence of their properties on the preparative conditions. The detailed discussion of the results of such studies and of the general effects thus observed for different variants of the cryostructuring processes have been presented in several comprehensive reviews published by the author of the present paper and by other scientists [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 20 , 22 , 27 , 28 , 29 , 40 , 44 , 63 , 66 , 82 , 94 , 125 , 142 , 143 ]. Therefore, only the key selected features of the cryostructuring mechanisms are considered below.…”

“…As a result, the formed polycrystals (ice in case of aqueous systems) fulfill the function of porogens for the final cryogenically-structured polymer matrices, and the initial precursors are concentrated in the space of so-called unfrozen liquid microphase (UFLMP) [ 397 ]. Such cryoconcentrating effect is known to be one of the main driving forces for the cryotropic gel-formation phenomena [ 5 , 9 , 35 , 66 , 142 ]. That is why the used solvent has to be crystallizable rather than vitrifying one.…”

“…As at the positive temperatures such solutions transform into very weak gels only after 2–3 months, the freeze–thaw processing yields physical cryogels in several hours and without the use of any cross-linking chemicals [ 220 ]. Of course, the main reason for all similar acceleration effects is the cryoconcentration of the gel-precursors in a small volume of the UFLMP of the respective partially (incompletely) frozen molecular or colloidal solutions [ 5 , 9 , 10 , 16 , 19 , 22 , 27 , 35 , 45 , 63 , 66 , 90 , 112 , 142 ].…”