# Halloysite and Laponite Hybrid Pigments Synthesis with Copper Chlorophyll
## 1 Introduction  
Circular and sustainable economy is a trending topic in product and process design. Industries and researchers are working to develop green products, and natural dyes are an example of such [1]. Their production is growing in South America, and their extraction from agricultural waste is successfully achieved [2, 3]. Some of the advantages of natural fibers are they are non-toxic, they possess antioxidant activity, their medical applications and biodegradation capability, and they pose no environmental issues [4, 5, 6]. Chlorophyll is one of the most abundant biological pigments, and it abounds in eubacteria and plants [7]. Due to their properties, chlorophyll dyes (CDs) have been used in biomedical applications [8], complex applications as solar cell dyes [9, 10] and supramolecular structures [11]. However, CDs are unstable to retaining their antioxidant activity when exposed to oxygen, high temperature, or light environments [9, 10]. One way of improving the stability of natural dyes like chlorophyll is their adsorption into inorganic structures like nanoclays. Laponite nanoclays have proven effectiveness in cationic dye adsorption. Laponite is a synthetic disk-shaped hectorite silicate of approximately 25 nm in diameter and 1 nm thickness. Particle aggregation and gel generation depend on dispersion conditions, such as concentration, pH, temperature, etc., [12]. Laponite can be used as a host for natural dyes to protect them. It has been demonstrated to adsorb up to 93% of anthocyanin from jambolan fruit extract. In addition, anthocyanin-laponite hybrid pigments have antioxidant properties and can be used as colorimetric indicator material at pH \(\geq\) 7 [13]. The adsorption capacity of this nanoclay can change depending on the dispersion conditions, as observed in other nanoclays like montmorillonite. Solvent nature, pH [14], surface modification with surfactants [15], mordant salts or silane [16] can be used to modify the nanoclay adsorption behavior [17]. Other nanoclay structures have been studied to adsorb and stabilize organic compounds like dyes. Halloysite is a type of hollow tubular nanostructure mineral clay. This nanoclay chemical structure is similar to kaolin, but is rolled into tubes. Because of its tubule shape, halloysite does not stack together and can be easily exfoliated by steering. Halloysite clay is transparent and does not significantly change polymer composites' transparency [18]. Halloysite nanotubes boost the properties of fluorescent dyes by their encapsulation [19]. Functionalized halloysite has been fabricated as a novel hybrid clay mineral for dye removal. This nanoclay can absorb cationic or anionic organic compounds owing to their surface properties, which make it an excellent adsorbent used for the removal of different dyes from wastewater [20]. With halloysite hybrid pigments, nanolevel dispersions of dyes provide polystyrene with enhanced luminescence [21]. The hybrid materials that result from the adsorption of dyes into modified nanoclays have been used to modify optical [22], mechanical, fire or barrier properties of different polymer matrices with successful results, depending on nanoclay particle exfoliation [23; 24; 25; 26; 27; 28]. Total solar reflectance (TSR) is the method that measures a surface coating's reflective capability. Urban areas show higher air temperatures than rural areas. The use of the so-called \"cool paints\" or \"cool coating\", i.e., with high TSR (%) values on building surfaces, is a countermeasure to mitigate this urban heat island [29]. In addition, \"cool coatings\" can decrease the sensitive heat load to the atmosphere and thermal storage in building frames due to solar radiation [30]. TiO\({}_{2}\) particles have been employed to increase the TSR of building coatings by functionalized anatase immobilization in an organosiloxane matrix. In addition, nanoclays have displayed protection against UV for coatings [31].