Synthesis of mesoporous materials as adsorbent for adsorption and desorption of paraquat

Abstract

Paraquat is a pesticide that is used to control weeds but it is very poisonous to humans and environment. Therefore, removal of paraquat from the environment is very important and in poisoning cases that involve paraquat, the sample need to be preconcentrated prior to analysis because the pesticide concentration may very low to be measured and in small sample size. In this research, several types of mesoporous materials were synthesised to adsorb and desorb paraquat namely mesoporous aluminosilicate using various saccharides templates as mesoporous directing agent which are glucose (MAS-GLU), lactose (MAS-LAC), sucrose (MAS-SUC) and without saccharide template (MAS-WOT) and being compared to mesoporous silica material, MCM-41. The formations of synthesised materials were confirmed from FTIR, XRD, SAXS, XRF and surface area analysis. The characterisation results revealed that MAS-SUC formed mesoporous aluminosilicate with ZSM-5 zeolite framework, MAS-GLU, MAS-LAC and MAS-WOT formed mesoporous aluminosilicate with amorphous structure and MCM-41 is mesoporous silica. MASSUC, MAS-WOT and MCM-41 were chosen as the representative of different type of mesoporous materials for adsorption and desorption experiment. From the adsorption result of paraquat, it showed that the maximum adsorption capacity in the order of MAS-WOT, MAS-SUC and MCM-41 with maximum adsorption capacity 37.59 mg/g, 36.76 mg/g and 4.45 mg/g respectively. The isotherm study shows all adsorbents fit Langmuir isotherm better than Freundlich isotherm. The desorption results revealed that desorption by sonication process is better than shaking process and even though MAS-WOT and MAS-SUC have good adsorption ability, but paraquat not able to desorb well from them. Only 33% of adsorbed paraquat can be desorbed from MAS-WOT and 31% from MAS-SUC. MCM-41 showed better desorption ability because almost 100% of the analyte able to be desorbed. Study showed that mesoporous aluminosilicate materials are better adsorbents as compared to MCM-41, but poor in desorption ability for paraquat.