**13. Challenges and future directions**

#### **13.1 Limitations of green adsorbents in water purification**

Due to their potential as environmentally benign substitutes for traditional adsorbents, green adsorbents, which are obtained from natural sources, have attracted considerable attention in water purification procedures. However, they also have some restrictions that should be considered. Green adsorbents' drawbacks in the filtration of water include the following:

#### *13.1.1 Limited availability and variability*

Green adsorbents are made from organic materials including plants, agricultural byproducts, and biomaterials. Geographical location, seasonal fluctuations, and other factors can all affect the accessibility and caliber of these adsorbents. Consistent performance and supply may become difficult because of this [46].

#### *13.1.2 Lower adsorption capacity*

green adsorbents often have lower adsorption capacities as compared to synthetic adsorbents like e.g., clay, zeolites, biochar, and activated carbon. Due to this, more green adsorbents may be needed to accomplish the same level of purification, which would result in higher expenses and maybe more trash that would need to be disposed of.

#### *13.1.3 Slow adsorption kinetics*

Compared to manufactured adsorbents, green adsorbents frequently have slower adsorption kinetics, which means that the adsorption process may take longer to achieve equilibrium. In high-flow rate applications, this may have an impact on the effectiveness and efficiency of water purifying systems [47].

#### *13.1.4 Limited selectivity*

Green adsorbents may only have a little amount of selectivity for some water pollutants. They might eliminate a variety of pollutants, but they do not always successfully target dangerous chemicals. This may limit their usefulness in circumstances where exact removal of contaminants is necessary.

#### *13.1.5 Regeneration challenges*

Adsorption-based water purification procedures rely heavily on regeneration, which entails removing impurities that have been adsorbed to the adsorbent. Due to their organic makeup, green adsorbents may provide regeneration difficulties, making it challenging to efficiently recover and repurpose the adsorbent material.

#### *13.1.6 Lack of standardized procedures*

Green adsorbents frequently do not have standardized procedures for synthesis, characterization, and performance assessment. Due to this, it may be difficult to

assess the effectiveness of various green adsorbents or develop uniform criteria for their use in water purification procedures.

#### *13.1.7 Compatibility with current systems*

To take advantage of green adsorbents' special features, existing water treatment systems may need to be modified or new procedures may need to be developed. It may be difficult and expensive to integrate green adsorbents into existing infrastructure for conventional water treatment.

While green adsorbents have a bright future in water filtration, overcoming their current drawbacks through research and development is essential to their widespread adoption and successful use in real-world applications [48].
