Abstract
We report the preparation of a series of spacer-incorporated, tetra-amino cobalt (II) phthalocyanine (CoPc)-immobilized bacterial cellulose (BC) functional nanocomposites (CoPc@s-BC). Four kinds of flexible spacers with different lengths—diethylenetriamine (DT), triethylenetetramine (TT), tetraethylenepentamine (TP) and pentaethylenehexamine (PH)—were covalently attached onto pre-oxidized BC for the synthesis of the spacer-attached BC, and the attached spacers’ contents were carefully quantified. Using glutaraldehyde as a cross-linker, the CoPc catalyst was covalently immobilized onto the spacer-attached BC, and the immobilization steps were optimized by monitoring both the residual spacer contents and the resulting immobilized CoPc. All of the functionalization processes were characterized and confirmed by X-ray photoelectron spectroscopy (XPS). The series of spacer-incorporated, CoPc-immobilized BC nanocomposites, CoPc@s-BC, were used for the decoloration of dye wastewater. Both the adsorption capacity and adsorption rate were increased after the incorporation of spacers. When H2O2 was employed as an oxidant, dye molecules were catalytically oxidized with these nanocomposites. Electron paramagnetic resonance (EPR) spin-trapping results showed that the highly reactive hydroxyl radical (·OH) was involved in the catalytic oxidation process. The spacer length had a direct effect on the catalytic efficiency of CoPc@s-BC—the decoloration rate for CoPc@TP-BC was as high as 41 μmol·min−1·g−1, which was more than 50% higher than that without spacer.
Highlights
Nanocellulose has spawned increasing interest from broad fields, because this naturally occurring nanomaterial combines the advantages of cellulose, such as being hydrophilic, environmentally benign and having an tunable surface, with prominent features of nanosized materials, such as having a very high surface area to volume ratio and considerable modification possibility [1].The preparation of nanocellulose ranges from “top-down” processing by isolation of natural cellulose to “bottom-up” processing by culture medium with certain bacteria [2,3]
Our group has been working on Metal phthalocyanine complexes (MPcs) immobilization using bacterial cellulose (BC) as a substrate [23,24,25], and we have comprehensively investigated the immobilization of MPcs onto BC
One milligram of cobalt (II) phthalocyanine (CoPc)@s-BC was added to 5 mL of reactive red X-3B dye wastewater
Summary
Nanocellulose has spawned increasing interest from broad fields, because this naturally occurring nanomaterial combines the advantages of cellulose, such as being hydrophilic, environmentally benign and having an tunable surface, with prominent features of nanosized materials, such as having a very high surface area to volume ratio and considerable modification possibility [1]. By carefully selecting appropriate substrate materials with specific microenvironment suitable for MPc reactions, their catalytic activity can be markedly enhanced. Steric hindrance between the substrates and the catalysts disfavors the catalytic reaction [30,31] To overcome these drawbacks, an appropriate long and flexible spacer arm can be employed to keep the MPc molecules at a reasonable distance from the substrate surface. The presence of the spacer may mitigate the unfavorable effect of diffusion limitation and steric hindrance, enhance the accessibility and mobility of the MPc catalysts and increase the reaction homogeneity, increasing the catalytic activity. This research illustrates the key roles of the spacer and the spacer length in the enhancement of catalytic activity of MPc and offers a new perspective into the design of a highly efficient catalytic system for the remediation of dye wastewater
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