Cationisation of silicon wafers to assess the development of a solid sorbent for the removal of anionic contaminants in paper machine white water

Abstract

Growing concerns about water availability is becoming of major interest for governments around the world. Various water initiatives are under study to establish recommendations on water governance and policies to ensure the sustainability of water supply for people and industries. As the pulp and paper industry is one of the major users of water, the implementation of such water initiatives will force the industry to improve their water management programs by moving further towards closed-cycle papermaking. Fresh water consumption reduction induces a gradual accumulation of dissolved and colloidal substances (DCSs) in process waters with detrimental effects on papermaking operations and paper quality. DCS removal is the key factor to meet targeted fresh water consumption levels. Contaminant adsorption on a modified solid sorbent in a fluidized bed reactor has been proposed for paper machine white water treatment. Cationic solid sorbents were synthesized by two different methods: (1) Silica nanoparticles were deposited on silicon wafers and silanized by quaternary ammonium organosilanes (TMAC, TDDMAC, and ODDMAC) and (2) Silicon wafers grafted with cationic polymer (MeDMA) were synthesized via atom transfer radical polymerization (ATRP). The growth of silica nanoparticles on the surface was investigated by scanning electron microscopy (SEM). Both sorbent surfaces were characterized by X-ray photoelectron spectrometry (XPS), contact angles (CA), and conductometric titration to determine quaternary ammonium surface density. Results show that silica particles deposited on silicon wafers increased the specific surface area and the number of active sites for the silanization reaction. The shorter silane alkyl chains increases the silanization rate. The quaternary ammonium quantification by conductometric titration showed that ATRP exhibits higher amine groups/unit surface comparatively to the silanization with TMAC. Both techniques can be used to assess the development of a solid sorbent that will be used in a fluidized bed reactor for paper machine white water treatment.