Abstract
In this work, we presented the synthesis and characterization of poly-melamine-formaldehyde-silica (PMF‑Si) composite from poly-melamine-formaldehyde (PMF) and previously purified commercial sodium silicate used as a precursor of silica nanoparticles (Si‑NPs). The materials were characterized by several physicochemical techniques such as XRD, FTIR, SEM, TEM, AFM, TGA, and DTG analysis to access their properties. We also studied hydrogel dehydration, rehydration, the potential of zero charge (PZC), and the adsorption capacity of the dye methylene blue (MB) in the hydrogel. From XRD analysis, PMF and PMF‑Si materials presented amorphous profiles. AFM, SEM, and TEM images revealed a fibrous PMF structure and homogeneous dispersion of Si-NPs through the PMF-Si composite. The Si‑NPs exhibited an average diameter between 10 to 15 nm. The first PMF-Si hydration reached 93% after synthesis, and complete rehydration is possible up to 70% of dehydration. PMF-Si has the PZC at pH = 1.22 and, at superior values of pH, the composite exhibits superior adsorption rates of MB. The adsorption tests performed to remove MB dye using PMF-Si hydrogel showed a qmax of 140 mg/g, which is superior to other materials routinely used for MB dye removal.
Highlights
Hydrogels are composed of three-dimensional (3-D) insoluble polymer materials containing hydrophilic groups, capable of absorbing and retaining a considerable amount of water due to their morphological expansion[1,2,3]
We performed the physicochemical characterizations of the obtained materials by using several techniques: X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA); and humidity rate determination
We successfully synthesized PMF-Si composite to form a hydrogel with promising properties for several applications
Summary
Hydrogels are composed of three-dimensional (3-D) insoluble polymer materials containing hydrophilic groups (modified or synthetic), capable of absorbing and retaining a considerable amount of water due to their morphological expansion[1,2,3]. Poly-melamine-formaldehyde (PMF) polymer exhibits advantages that allow its use in hydrogels synthesis because of its large amounts of nitrogen, high resistance to chemical attack, and low-cost of production[13]. The decision to incorporate Si-NPs into the PMF is due to beneficial properties, e.g., high surface area and available silanol groups, allowing PMF to cluster through intermolecular interactions, culminating in chemical and thermal stability, with applications like catalyzer, drugs, and adsorption of dyes[27,29,30]. Physical and biological methods have been applied to remove dyes from wastewater, including chemical coagulation/ flocculation, ozonation, oxidation processes, ion exchange, and ultrafiltration[48,49,50,51] They can have considerable disadvantages such as high cost and generation of secondary pollutants. The main differential of this research is the formation of a composite (PMF-Si) in which Si-NPs are formed within the structural network of the PMF, simplifying the composite preparation process and eliminating the cost of acquiring commercial Si-NPs
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