# Uses of Nanoclays and Adsorbents for Dye Recovery: A Textile Industry Review
## 4 Conclusions  
This article describes some of the most widespread nanoclays, referring to different sources of adsorbents research, that can be used for treating industrial wastewater (Table 2). Each clay material has specific characteristics (Table 3), which can make them more appropriate in different situations according to their subsequent utilization, cost optimization, or other factors. From this state-of-the-art review, we found a strong nanoclay repercussion on wastewater treatment, specifically in textile wastewater with a high dye concentration. Despite the huge amount of clays and nanoclays that can be employed as adsorbents, we focused on the most widely studied nanoclays. The most well-studied ones were selected for their abundance, low-cost, and excellent adsorption efficiency. The main studied nanoclays \begin{table}
\begin{tabular}{c c c c c c} \hline
**adsorbent** & **Performance** & **Use** & **Observ.** & **adsorption BC * & **Biblio. Ref.** \\ \hline Saponite & High performance & Pigment & - & Acid Orange 7 \textgreater{} 90\% & [76,82,224,301] \\ Montmorillonite & Thermal stability & Pigment & No desorption & Congo Red 84\% & [37,301,302,314] \\ Sepiolite & Poor stability & Pigment/Dye & Desorption in ethanol & Cd 95\% & [229,239] \\ Bentonite & No desorption High & Pigment & Low-cost. Absorbance & & \\  & stability & & at different pH. & & \\  & & & & & \\  & & & & & \\  & & & & & \\ \end{tabular}
\end{table} 
Table 2: Comparison of different clays. Figure 11: Dye desorption process. can be found under natural conditions, and they can also be synthesized to improve their characteristics. Despite most authors supporting nanoclays for their low cost and abundance, we found that information regarding this, supported with specific numbers and comparisons to real costs, exploitation capabilities, and the real impact of exploitation or synthetic generation, was lacking. In addition, a synthetic or natural extraction comparison should be made, taking into account the purification step costs of natural clays. Hundreds of studies have demonstrated that nanoclays are highly efficient adsorbents, and several dye structures are used during industrial processes, such as textile dyeing. The ionic exchange process that they bring about means that dye molecules are trapped in the nanoclay basal space or adhere to nanoclay surfaces. For these reasons, it is adsorption and not an absorption process that improves some of their characteristics, such as color-fastness in the event of environmental and chemical attacks, and they can be used later in textile stamping. Nanoclay modification to improve their adsorption capacity via calcination or with surface modifiers has been widely studied. However, some authors have not considered the environmental costs of this process. The acid, basic, or thermal treatment costs should also be considered in order to ensure that the process is clean and sustainable. On the other hand, when different authors discuss the desorption phase, they tend to give very ambiguous results; for example, they give desorption values of between 20-40%, which is not very specific because the range of variation is very wide. For future lines of enquiry, the quantification of many of the phases must be improved, for example, the preparation of materials where their adsorption capacity is improved by prior calcination, because it is not quantified to what degree the adsorption capacity improves due to previous loss of anions CO\({}_{3}\). Regarding post-dye adsorption hybrid pigment uses, we found several works that demonstrated their advantages, such as improving organic dye properties, or polymer thermal, mechanical, and thermal barrier properties, in nanocomposites. However, a textile application has not yet been studied in-depth, nor has the reuse of organic compounds after a desorption process been completely studied and described. Several factors must be considered and described, such as pH, time, and temperature, which recent works do not provide.