Modified- superabsorbent polymers with nutrients for water vapor recovery

Due to the exponential growth of the world population, climate changes, urbanization increase, and water crisis, world agriculture faces many challenges, such as sustainably using natural resources, accumulating pesticides and fertilizers, and developing new irrigation systems, etc. [1]. It is estimated that to reach adequate food production for the growing population, the external input of fertilizers will increase exponentially in the next years [2]. Moreover, due to climatic changes, water resources are less and less available. Therefore, any effort to improve water use efficiency, as well as the control of nutrient loss, is worthwhile and has been considered a global challenge for the agricultural sector [3]. Although tons of water vapor emitted by industrial chimneys could be used in agriculture every year, they are lost. On the other hand, food and production waste are continuously accumulated in landfills or incinerated. These two scenarios represent important sources of water and nutrients, respectively, to be re-entered in a circular economy perspective and for the sustainability of industrial processes. In this regard, among the most promising materials able to face these challenges, we can exploit the superabsorbent hydrogels, such as potassium polyacrylate (K-PAs), with their impressive 3D cross-linked structures. They are a significant reservoir for absorbing and conserving a large amount of water [4]. They are cheap, commercially available, non-toxic, harmless, nonpolluting, and do not cause soil salinization. SAPs do not reduce water consumption but, due to the cross-linked structure, can retain water more times its weight and achieve approximately 95% water release. However, the possible usage of K-PAs as chimney vapor recovery agents, as well as the possibility of developing nutrient-enriched K-PAs using recycled matter, has never been studied. In the current research, the K-SAP’s surface was modified using waste-derived nutrients, such as humic acid (HA) and hydroxyapatite (HAP), natural compounds such as starch, and cheap and available amines (ethylenediamine, EDA). The vapor water absorption tests were carried out by a homemade setup (Figure 1a). The current research was performed by keeping the reactor at a stable temperature of 160°C and vaporizing 10 g of water (water flow 20 mL/h) for 30 minutes. The polymer absorption capacity (PAC) of the synthesized materials was observed to be strongly related to the combination of K-SAP - modifiers used. In fact, as shown in Figure 1b, the best results were obtained by K-SAP/EDA/HAP, that displayed a PAC of 10, corresponding to 44% of vapor water absorption. The characterization results demonstrated that the modified material maintains a stable structure at the working temperature employed for the test. Moreover, the enhanced activity could be related to the increase in hydrogen bonds between vapor water and modified K-SAP. However, investigations are in progress to investigate in depth both structure and properties of the synthesized compounds.