Nanodiamond particles for biomacromolecule immobilization and dye contaminant adsorption

Abstract

Nanodiamond (ND) has become a widely studied material in recent years due to its excellent properties, which includes high specific surface area, oxygen-containing surface groups (desirable for physical or chemical functionalization), physically and chemically inert diamond core, optical transparency, and biocompatibility. ND has been found to be biocompatible and have no cytotoxicity to cells. To date, significant attention has been focused on utilizing ND material as a platform for biomacromolecule immobilization which is promising for biological applications such as biosensor. Moreover, excellent surface properties of ND might be able to make it a desirable adsorbent material. The present thesis work has focused on using ND for biomacromolecule immobilization as well as dye contaminant adsorption. First, the immobilization of an important biomacromolecule, carboxymethyl chitosan, onto ND surface as well as the properties of the product was investigated in detail. The carboxymethyl chitosan modified ND (NDCMCS) shows improved dispersity especially in low and high pH aqueous solutions. Moreover, the rich content of primary amine and hydroxyl on CMCS backbone would render further physical or chemical functionalization of ND more flexible and versatile. The following work is then focusing on the protein adsorption behaviors onto ND surface as well as whether protein could retain its structural features upon immobilization. To this end, bovine serum albumin (BSA) was chosen as a model protein for the study of protein conformation and the interaction between ND and protein in their complex. The results have demonstrated that ND is an excellent platform for protein immobilization with high affinity and approximately 80% of BSA structural features could be preserved upon immobilization. Second, based on strong ND-protein interaction, the assembly of ND-protein complex into macroscale material in a Layer-by-Layer (LBL) assembly fashion has been studied. The LBL assembly properties of ND-BSA complex with pristine ND were investigated on glass substrates. The ND-BSA/ND coatings fabricated by LBL assembly method were stable and more densely-organized coating structures could be obtained by increasing the number of bilayers deposited. The LBL assembly method for ND-protein coating fabrication could be easily employed to prepare biomacromolecule-functionalized ND films for biosensor applications. In the following work, it was found that NDs could also assemble into thin films through hydrogen bonding on a glass substrate. The films prepared have regularly-organized nanostructures, which could be tuned by adjusting the number of bilayers deposited. Moreover, the oxygen-containing surface groups on LBL films make possible the further functionalization by chemical or physical approach. Finally, the excellent surface properties of ND have found new promising applications in addressing current environmental issues and ND has been demonstrated to be an effective dye contaminant adsorbent. In this work, the adsorption of azo dye acid orange 7 (AO7) onto ND surface has been investigated in order to ascertain the adsorption behavior as well as the interaction involved in the adsorption process, where ND has been proved to have higher capacity in azo dye adsorption than widely used activated carbons and carbon nanotubes. Due to strong π-donor-acceptor interaction between ND surface graphite layer and azo bond, ND shows high affinity with azo dye. Though affinity is slightly lower at high pH values, the adsorption coefficients of ND with AO7 at neutral to alkaline pHs are still of the same orders of magnitude with those of low pH values, suggesting that ND could be a desirable candidate for textile wastewater treatment which is normally at alkaline pH. The present thesis work might potentially contribute to utilizing NDs for biological and environmental applications.