Manipulate the nano-structure of layered double hydroxides via calcination for enhancing immobilization of anionic dyes on collagen fibers.

In this work, we present an effective approach for promoting the immobilization of anionic dyes on the collagen fibers of the leather matrix via introducing layered double oxide (LDO), which is obtained by calcining layered double hydroxides (LDH), inspired by incorporating their memory effect and charge effect. The results indicate that the calcination increases specific surface area, oxygen vacancies, and Al defects of LDH nanosheets, and the structure of LDH nanosheets can be reconstructed by rehydration. Diffusion behavior of both LDH and LDO nanosheets into the collagen fibers follows the Langmuir model. The LDO nanosheets can penetrate into the collagen fibers more easily and evenly than that of the LDH nanosheets. Moreover, the formation of ionic bonds, hydrogen bonds, and coordination bonds between the nanosheets and the collagen stabilizing the collagen microstructures can endow the collagen fibers with improved thermal stability. Increased porosity of the collagen fibers results in enhanced adsorption and immobilization capacity for anionic dyes on the collagen fibers of the leather matrix in leather post-tanning process. Furthermore, adsorption behavior of anionic dye on the collagen fibers can be well accorded with pseudo-second-order and Langmuir model, exhibiting a monolayer adsorption process. This established cooperative approach will be helpful to extend the application of clay for improving the dyeing performance of leather matrix towards eco-leather manufacture and effectively reduce emission of dyes from the source in leather manufacturing.