## 1 Introduction  
In order to decrease greenhouse gas emissions, it is becoming more and more imperative (i) to preserve/control natural resources by attempting to reuse/recycle them; (ii) to decrease industrial wastes/by-products by transforming them into innovative materials for new applications; (iii) and above all, to limit, at best, energy consumption derived from fossil combustibles. It has, therefore, been necessary to rapidly develop more sustainable alternatives to certain industrial products, like cement materials, which are currently recognized to be responsible for about 8% of anthropogenic CO2 emissions worldwide [1]. In this view, aluminosilicate geopolymer materials have attracted research on their use not only as construction materials, but also as ion exchangers in effective water remediation processes [2, 3], since their synthesis is easy and low-cost, necessitating natural and available (waste) materials. They are obtained through alkali activation: (i) either directly from natural minerals (such as kaolin [3] and metakaolin [4, 5, 6]), or (ii) from industrial products/wastes (such as fly ash and blast furnace slag [7, 8, 9], red mud [10], and brick [11, 12]). Aluminosilicate geopolymers are considered to be innovative inorganic structures for environmental and industrial applications. They have been employed as (i) sustainable, eco-friendly materials, since their production necessitates a much lower degree of release of CO2 gas than that of Portland cement fabrication [9]; (ii) gas (CO2 and CH4) adsorbents [13; 14; 15]; (iii) oxygen carriers [16; 17; 18]; (iv) organic/inorganic adsorbents [19; 20]; (v) pH buffers [21; 22]; (vi) radio-element immobilizers [9; 23; 24]; (vii) self-supporting membranes [25; 26; 27]; (viii) catalysts for cost-effective environmental governance [28; 29; 30; 31]; and (ix) photo-catalysts for the degradation of organic pollutants [32]. Structurally, aluminosilicate geopolymers are amorphous to semi-crystalline materials. Their three-dimensional networks constitute cross-linked tetrahedral silica and alumina units, forming rings comparable to those in zeolites. These rings contain \"negatively charged\" aluminium ([AlO4]5-) charge-balanced by cations such as Na+ or K+, facilitating the ion exchange with \"positively charged\" counter-ions (such as hazardous/toxic heavy metals) in the aqueous phase through electrostatic attraction, and thereby enabling metal(s) immobilization. Furthermore, aluminosilicate geopolymer materials provide relatively good mechanical properties and thermal stability [33; 34], but they possess a weak surface area and a low number of active surface sites in comparison with crystalline aluminosilicates such as zeolites. Some of the zeolite types have great importance in heavy metal removal [35], dye removal [36], or even in agricultural area like soil amending [37]. In pure zeolites like NaA and NaP, their frameworks contain the highest atomic Al/Si ratio and thereby possess the highest negative-charge density. However, because of their small pore sizes, the ion-exchange kinetics of radioactive cations with large diameters (like Cs+ and Sr2+, with 4.5 A and 8.2 A, respectively) take place more slowly on zeolites [38]. In this context, as natural zeolites possess micropores with weak interconnection, their surfaces could be easily obstructed by adsorbed (ionic, gaseous or neutral) species, and hence become inactive with time when they are used as catalysts, ion-exchangers, or adsorbents. Conversely, the use of hierarchical structuring of zeolite or Al-rich zeolites with larger pores sizes should allow for the improvement of \"large\" cation/Na+ exchanges and adsorptive capacity [38; 39; 40; 41]. These are obtained with zeolites synthesized via conversion of geopolymers [42; 43; 44]. Indeed, the use of geopolymeric zeolites has been found to be more adapted for practical applications because they possess pores with larger sizes and that are interconnected.