Mesoporous metal organic frameworks functionalized with the amino acids as advanced sorbents for the removal of bacterial endotoxins from water: Optimization, regression and kinetic models

Abstract Endotoxin is well-known as one of the emerging pollutants secreted from bacteria; cyanobacteria has drawn much attention over the years due to imposing health problems such as impairment of the immune system and toxic shock. A novel modified amino MOF (NH2-Cu(MOF)) was synthesized and its application for endotoxin (lipopolysaccharides) removal from aqueous solution was investigated. Physicochemical properties of NH2-Cu(MOF) structure were characterized by XRD, SEM, BET and FTIR analyses. In this study, the effects of different operational parameters: Initial pH, contact time, adsorbent dosage and endotoxin concentration on removal efficacy by MOF were surveyed by central composition design (CCD) approach under response surface methodology (RSM) and artificial neural network (ANN). The experimental data for pollutant removal were well fitted with quadratic polynomial model (based on RSM approach) and mathematical model (based on ANN approach) with a good prediction capability. Statistical ANOVA results indicated that the dosage of NH2-Cu-MOF and endotoxin concentration had high contribution on response prediction compared with other variables. Under optimum conditions, over 90% of endotoxin degradation was observed by the adsorbent. Adsorption kinetic was well designated by the pseudo second order kinetic model, especially its nonlinear form, while the adsorption isotherm was better fitted by Langmuir model in both linear and nonlinear forms with the maximum single-layer adsorption capacity of above 2500 Eu/mg. The possible mechanisms for endotoxin removal by NH2-Cu(MOF) were electrostatic interaction, hydrogen-bonding and π-π stacking. Recycling test showed a good reusability and stability result of NH2-Cu(MOF) during five subsequent recycles; the influence of interfering anions on the adsorption efficiency exhibited the following order: PO43− > HCO3− > SO42− > Cl− >NO3−. Our finding revealed that the NH2-Cu(MOF) structure could be suggested as a feasible and potential promising adsorbent for removal of toxic material from the aqueous solutions.