Cellulose nanocrystals-based flocculants for high-speed and high-efficiency decolorization of colored effluents

The modified cellulose nanocrystals (CNCs) are expected to achieve fast and efficient decolorization of colored effluents. In this study, CNCs were surface-modified by grafting polymerization of acryloyloxyethyltrimethyl ammonium chloride (AETMAC) with the initiator of ceric ammonium nitrate (CAN). The optimum scheme to synthesize poly acryloyloxyethyltrimethyl ammonium chloride) (PAETMAC)-grafted CNCs (PAETMAC-g-CNCs) with the highest cationicity of 31.2% was determined from the orthogonal test as 4/1 (w/w) of AETMAC/CNCs, 0.01 mg/L of CAN, 50 °C and 5 h. Zeta potential, particle size, FT-IR and 13C-NMR characterizations manifested the successful introduction of PAETMAC on CNCs. XRD proved the same cellulose I of PAETMAC-g-CNCs as CNCs. As new eco-friendly flocculants, PAETMAC-g-CNCs were tested to decolorize 100 mg/L of neutral reactive blue 19 (RB 19) solutions. The results show that the higher the cationicity of PAETMAC-g-CNCs is, the less amount is needed for getting the maximum color removal. The widest flocculation window from 30 to 100 mg/L is acquired using PAETMAC-g-CNCs2 with the medium cationicity of 21.1%. Moreover, PAETMAC-g-CNCs2 is less sensitive to the pH and ion concentration of dye solutions due to its increased colloidal stability in electrolytes, acids and/or bases. It can work on a wide pH range and is applicable to treat high salt concentration effluents. The color removal efficiency is over 80% at pH 3–9 and NaCl concentration up to 60 g/L. The high crystallinity of PAETMAC-g-CNCs2 and the PAETMAC grafts promote the growth of dye-containing flocs and accelerate the flocs’ precipitation. PAETMAC-g-CNCs2 can rapidly decolorize the RB 19 solutions, which is desirable for industrial applications.