RESUMO
The coupling reactions of polyethylene glycol (PEG) with two different nano-carbonaceous materials, graphene oxide (GO) and expanded graphene oxide (EGO), were achieved by amide bond formations. These reactions yielded PEGylated graphene oxides, GO-PEG and EGO-PEG. Whilst presence of the newly formed amide links (NH-CO) were confirmed by FTIR stretches observed at 1732 cm-1 and 1712 cm-1, the associated Raman D- and G-bands resonated at 1311/1318 cm-1 and 1584/1595 cm-1 had shown the carbonaceous structures in both PEGylated products remain unchanged. Whilst SEM images revealed the nano-sheet structures in all the GO derivatives (GO/EGO and GO-PEG/EGO-PEG), TEM images clearly showed the nano-structures of both GO-PEG and EGO-PEG had undergone significant morphological changes from their starting materials after the PEGylated processes. The successful PEGylations were also indicated by the change of pH values measured in the starting GO/EGO (pH 2.6-3.3) and the PEGylated GO-PEG/EGO-PEG (pH 6.6-6.9) products. Initial antifungal activities of selective metallic nanomaterials (ZnO and Cu) and the four GO derivatives were screened against Candida albicans using the in vitro cut-well method. Whilst the haemocytometer count indicated GO-PEG and copper nanoparticles (CuNPs) exhibited the best antifungal effects, the corresponding SEM images showed C. albicans had, respectively, undergone extensive shrinkage and porosity deformations. Synergistic antifungal effects all GO derivatives in various ratio of CuNPs combinations were determined by assessing C. albicans viabilities using broth dilution assays. The best synergistic effects were observed when a 30:70 ratio of GO/GO-PEG combined with CuNPs, where MIC50 185-225 µm/mL were recorded. Moreover, the decreased antifungal activities observed in EGO and EGO-PEG may be explained by their poor colloidal stability with increasing nanoparticle concentrations.
RESUMO
Since it is known that conventional wastewater treatment plants cannot completely remove pharmaceutical compounds, such as carbamazepine, the need for their removal has intensified. The use of biocatalysts, such as enzyme is an environmentally friendly method for carbamazepine biodegradation. Nevertheless, enzyme immobilization is required to facilitate the recovery and reusability and avoid the loss of enzyme. In this work, laccase was immobilized on modified polyimide aerogels by means of covalent bonding. Results showed that the immobilized laccase on polyimide aerogels possesses significantly improved activity under acidic or basic pH range in comparison with the free enzyme. Furthermore, for all the temperature range the activity of the immobilized enzyme was higher compared to the free enzyme form. The storage stability improved by the immobilization on this support material. The reusability tests towards oxidation of 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) showed that the immobilized laccase maintained 22% of the initial activity after 7 cycles. Immobilized laccase on polyimide aerogels for carbamazepine (CBZ) degradation exhibited 76% and 74% removal in spiked water and secondary effluent, respectively. Furthermore, after 7 cycles the CBZ removal efficiency remained higher (50% and 65% for spiked water and secondary effluent, respectively).
