Optimization of Nitrate Removal from Aqueous Solution by Amine-Functionalized MCM-41 using Response Surface methodology

High concentration of nitrate in water may bring adverse effects to both health and environment such as blue baby syndrome and algal bloom. Among all the nitrate removal methods up to date, adsorption is more favourable due to its simplicity of design, economical operation and less sludge production. Amine functionalized mesoporous silica represents one of the potential adsorbents in nitrate removal process due to its high adsorption capacity. Also, previous study has shown that 20% loaded (AEPTMS) amine-functionalized MCM-41 could achieve high percentage of nitrate removal. However, optimization of experimental conditions such as initial nitrate concentration, weight of adsorbent and contact time of adsorbent is yet to be done. In this study, Response Surface Methodology (RSM) was used to optimize the experimental conditions in nitrate removal processes using 20% AEPTMS amine-functionalized MCM-41 as the adsorbent. The adsorbent was successfully synthesized using co-condensation method and then characterized by Fourier Transform Infrared Spectroscopy (FTIR) as well as Scanning Electron Microscope (SEM). Subsequently, total 19 experiments with different experimental conditions generated by the Design of Experiment (DoE) software has been successfully carried out. From the experimental result, a quadratic model was used to fit the experimental data. The ANOVA analysis showed that the model was significant with R2 of 0.9935. The interaction between the three variables was then demonstrated in three-dimensional surface plot through prediction from the model. It was found that the highest percentage removal of nitrate was 70% obtained using initial nitrate concentration of 0.25 mM, weight of absorbent of 0.50 g and contact time of 1 h. Meanwhile, the optimum percentage nitrate removal of 56% was obtained at the optimum conditions with initial nitrate concentration of 0.25 mM, weight of adsorbent of 0.124 g, and contact time of 1 h. Lastly, the adsorption isotherm study was carried out and Freundlich isotherms was found to fit the adsorption data better compared to Langmuir isotherms.