Synthesis and characterization of membrane with molecularly imprinted polymers for selective adsorption of triclosan

Abstract

Amongst many tenacious emerging traces of lethal organic pollutants in wastewater, triclosan (TCS) is typically the often-encountered compound. This pollutant has been reported in the water circle, including surface water, wastewater treatment plants, groundwater, aquatic sediments and aquatic organisms and, to a lesser extent, drinking water, at levels in the nanograms to low micrograms per litre range. Triclosan mainly find its way into the human system through its extensive use in pharmaceutical industries over the recent years. Excessive exposure to this water pollutant may result in adverse conditions like hematological disorders such as blood cancer. Despite the variety of its negative effects, triclosan is still used as a preservative in many pharmaceutical personal care products (PPCPs), e.g. toothpaste, disinfectants, hand wash, cosmetics, soaps and medication. In light of the aforementioned applications, it is imperative to remove triclosan to accepted levels and find more efficient, low-cost and less energy consuming methods of its removal in order to counter the challenges of water scarcity in the country and its wastewater channels. In this study, a “fractionated approach” was used, as it accounts for the synthesis of selective polymeric membranes using a phase inversion by immersion precipitation technique. Hence, the quest to address these water challenges was through the application of polyvinylidene fluoride (PVDF) polymeric membranes for the removal of triclosan in effluent treatment plant (ETP) water. This was carried out by fabricating this polymer with selective micro composite particles called molecularly imprinted polymers (MIPs). This improved the mechanical behaviour and strength of the membrane. The MIPs were synthesised using a two-step bulk polymerisation process. The synthesized MIPs possess specific binding cavities within its structure. The PVDF membrane were functionalised with MIPs and were characterised using Scanning Electron Microscopy (SEM), for their morphological properties. Thermogravimetric analysis (TGA) was used to study their thermal behaviour and the Fourier transform infrared coupled with universal attenuated total reflectance (FTIR- ATR) was utilized to determine the functional groups present in the membrane. The dynamic mechanical analysis (DMA) was used to study the mechanical behaviour and strength of the membranes.

The SEM images showed the equal distribution of micro particles on the membrane surface. The TGA analysis revealed that all the studied polymeric membranes were thermally stable up to an average temperature of 502°C. The FTIR-ATR analysis showed new absorption peaks that were brought by the functionalisation and revealed that the PVDF membrane does not interfere with the MIP chemical integrity despite being infused within the polymeric membrane. DMA revealed an improved stability and behaviour once the concentration of the additives was increased. Moreover, the water and porosity content percentage of the MIP infused PVDF membranes increased as the concentration of the adsorbent was increased. Wastewater samples were collected from an effluent treatment plant (ETP)and pre- treated before analysis. Experimental parameters such as sample size, contact time, stirring speed were optimised. The synthesised PVDF/MIP membranes had an adsorption efficiency of 97% TCS in membranes compared to PVDF/NIP and PVDF bare membrane which had 92%, 88%, respectively. This might be due to the effect of the binding sites of the additives. The analytical method had limits of detection (LOD) and limits of quantification (LOQ) of 0.22, 0.71 µgL-1 in wastewater effluent, respectively. The percentage recovery for the effluent samples was 68 %. The results obtained therefore shows that MIPs have the potential modifier for the development and continuous progress in PVDF membranes.