| Abstract | Layered double hydroxides (LDHs), are one of anionic clay materials. LDHs are readily synthesized in laboratories and at low cost. They also contain a good biocompatibility, non-toxicity, large surface area, high catalytics activity, chemical stability, good adsorption ability and anion exchange. This work is focused on the application of LDHs as peroxidase enzyme mimic and dye adsorbent.
For the application of LDHs as peroxidase enzyme mimics, the approach for colorimetric detection of H2O2 using FeIIFeIII layered double hydroxide nanosheets (FeIIFeIII LDHNS) was reported. The FeIIFeIII LDHNS were constructed from a mixture of divalent and trivalent Fe ions by co-precipitation method. FeIIFeIII LDHNS were found to possess the superior intrinsic peroxidase-like activity. They were used for catalyzing the oxidation of a peroxidase substrate 3,3’,5,5’-tetramethylbenzidine (TMB) and 2,2’-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid)-diammonium salt (ABTS) in the presence of H2O2 to produce a blue and green solution product, respectively, which provided a colorimetric detection of H2O2. The colorimetric assays displayed linearity for H2O2 determination by using TMB and ABTS systems in the range of 0.1-50 microM, respectively. This selective approach could be applied for H2O2 detection in real milk and disinfectant samples. The proposed method is expected to have more potential for a precise detection of H2O2 in biotechnology, food industry, clinical diagnosis life process and other industries.
The addition, LDHs was also used as a dye adsorbent. Composite materials consisting of magnetite nanoparticles (Fe3O4NPs), reduced graphene oxide (rGO), and ZnAl layered double hydroxides (ZnAl-LDHs) denoted as Fe3O4/rGO/ZnAl-LDHs have been successfully prepared. GO was used as an oxidizing agent to oxidize Fe2+ into Fe3O4 then Fe3O4/rGO was formed via the spontaneous in-situ deposition of Fe3O4 nanoparticles onto the self-reduced GO surface. ZnAl-LDHs were formed by co-precipitation method with molar ratio of Zn2+:Al3+=3:1 and attached with Fe3O4/rGO sheets via electrostatic attraction and hydrogen bonding, resulting in Fe3O4/rGO/ZnAl-LDHs as magnetic adsorbent. This magnetic adsorbent can easily be separated from aqueous solutions by using external magnet. Fe3O4/rGO/ZnAl-LDHs were applied as an adsorbent to remove anionic methyl orange (MO) and cationic brilliant green (BG) from the aqueous solution. The results showed that MO and BG removal reached equilibrium at 60 and 360 minutes, respectively. The adsorption kinetics and isotherm of both organic dyes followed the pseudo-second-order and Langmuir model, respectively. The maximum adsorption capacities were 1111 and 2000 mg g-1 (C0=500 mg L-1) for MO and BG, respectively. This thesis suggests a simple synthesis strategy which can be applied for other types of LDHs. Consequently, a variety of applications can be targeted.
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