Green adsorbents based on functional-modified cellulose and copolymers for water clarification
University of New Brunswick
Natural adsorbents for the removal of dyes and heavy metal ions have attracted tremendous research interests because of their cost-effectiveness and easy regeneration. Cellulose fibers, as the most abundant natural resource in the world, have numerous advantages, such as being renewable, inexpensive, biodegradable, environment-friendly and nontoxic. However, due to the hydroxyl groups on the polymer structure and formation of hydrogen bonds between the molecular chains, the adsorption capacity is limited and the selectivity is low when the natural cellulose is directly used as an adsorbent. To improve its adsorption properties and widen its applications, extensive studies have been carried out in the current thesis work:1) a comprehensive review of the conventional application of cellulose-based adsorbents, the application of cellulose nanofibers (CNF) or nanocrystals (CNC), and the responsive or smart cellulose-based adsorbents was provided; 2) the cost-effective and renewable cellulose fibre beads in conjunction with alkali-treated diatomite were prepared, leading to a range of adsorbents which could remove the dyes and heavy metal ions from aqueous solutions effectively and be re-generated readily; 3) an innovative approach was used to prepare the dissolved cellulose fibre/microfibrillated cellulose (MFC) composite beads as an environmental-friendly adsorbent for the removal of dyes from aqueous solutions; 4) NIPAM (N-isopropylacrylamide), a temperature-sensitive monomer, was polymerized and grafted onto the MFC spheres through an in-situ free radical polymerization using a microwave-assisted heating technique. The synthesis of semi-interpenetrating polymer networks composed of cellulose/MFC spheres and poly (N-isopropylacrylamide-co-acrylic acid) was further conducted. It was found that the adsorption capabililty of cellulose has been improved significantly by using renewable cellulose fibre beads in conjunction with alkali-treated diatomite. The precipitated cellulose reinforced with MFC showed excellent porous properties. The polymerization could be microwave accelerated and high efficiency could be obtained via microwave-assisted polymerization. The copolymers-grafted spheres exhibited a controllable adsorption and desorption process as pH- and temperature-responsive adsorbents. The adsorption kinetics followed the pseudo-second-order and could also be well described by a three-stage intraparticle diffusion model. Adsorption isotherms were fit using Langmuir, Freundlich, and Temkin models.