Preparation of Phthalocyanine Immobilized Bacterial Cellulose Nanocomposites for Decoloration of Dye Wastewater: Key Role of Spacers  
[PERSON]  
Qianjiang College, Hangzhou Normal University, Hangzhou 310012, China; [EMAIL_ADDRESS] (Q.T. ); [EMAIL_ADDRESS] (W.X.) [PERSON] Chen  
that BC is highly suitable as a templates or substrate for the impregnation of a range of functional guest molecules, such as metal oxides, metal nanoparticles, mineral nanomaterials and carbonaceous nanomaterials [10; 11]. Metal phthalocyanine complexes (MPcs), a class of versatile functional molecules [12], are promising catalysts for many processes because of their structural relations to naturally-occuring metal porphyrin complexes [13; 14; 15; 16]. In practical applications, the immobilization of MPcs with solid substrates [17; 18; 19; 20; 21; 22] is essential for convenient separation of catalysts from reaction media, long-term and continuous operation, overcoming the formation of inactive aggregates and preserving their activity. By carefully selecting appropriate substrate materials with specific microenvironment suitable for MPc reactions, their catalytic activity can be markedly enhanced. BC is undoubtedly a promising candidate for MPc immobilization, owing to the advantageous features mentioned above. Our group has been working on MPc immobilization using BC as a substrate [23; 24; 25], and we have comprehensively investigated the immobilization of MPcs onto BC. Despite the enormous strides made in this research field, immobilized MPcs catalysts often suffer from various disadvantages of heterogeneous reaction conditions when compared with their homogeneous counterparts [26]. Direct immobilization of MPcs onto substrate surfaces will inevitably lead to the mass transfer limitation of target molecules to the heterogeneous catalysts [27; 28; 29]. Steric - hindrance between the substrates and the catalysts also 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, thus increasing the catalytic activity. Spacers with variable lengths have been widely employed by researchers to enhance different kinds of catalysts. An increase in spacer length can efficiently enhance the catalytic activities of catalysts, such as protoporphyrin photosensitizers [32], zirconium complexes [33], and enzymes [34; 35]. A few examples of spacers that can influence the electron transfer activity of MPcs have been reported [36; 37; 38]. However, little has been reported specifically concerning the effect of spacer length on the catalytic activity of MPcs. An investigation of how the spacer length influence the MPcs' catalytic efficiency is, therefore, of timely importance. The present study aimed to combine the advantages of BC and the flexible spacer for the preparation of a series of spacer-incorporated, tetra-amino cobalt (II) phthalocyanine (CoPc)-immobilized bacterial cellulose (BC) functional nanocomposites (CoPc@s-BC). A range of flexible spacers with different lengths, namely diethylenetriamine (DT), triethylenetetramine (TT), tetraethyleneptamine (TP) and pentaethyleneexamine (PH) (Figure 1), were attached onto BC for the subsequent covalent immobilization of the CoPc catalyst. The resulting nanocomposites were employed for the decoloration of dye wastewater; the synergistic improvement of both the adsorption capacity and catalytic activity of CoPc was expected. The mechanism of the catalytic oxidation decoloration was investigated using the electron paramagnetic resonance (EPR) spin-trapping technique. The effect of the spacer length on the decoloration efficiency was carefully studied.