ABSTRACT
Herein, we prepared Cu(II)-modified hierarchical ZSM-5 containing both micro- and mesopores by alkali treatment followed by ion exchange as an adsorbent, using it for tetracycline (TC) removal from aqueous solutions. The crystal structure, morphology, texture, and Si:Al ratio of this adsorbent by a range of instrumental techniques were investigated. Moreover, we studied the effect of pH and Cu(II) loading on adsorption performance and probed adsorption kinetics, thermodynamics and regeneration performance, revealing that modification of hierarchical ZSM-5 with Cu(II) not only significantly increased its TC removal efficiency but also allowed for good regenerability and suggested that the highly efficient and selective removal of TC from aqueous solutions could be ascribed to not only the strong interactions between Cu(II) and TC molecular but also the larger mesoporosity.
Subject(s)
Copper/chemistry , Tetracycline/chemistry , Water Pollutants, Chemical/chemistry , Water Purification/methods , Adsorption , Hydrogen-Ion Concentration , Kinetics , Solutions , Tetracycline/analysis , Water , Water Pollutants, Chemical/analysisABSTRACT
The removal of oxytetracycline (OTC) from aqueous solution on modified molecular sieve via adsorption was investigated in the present work. The copper(II) modified molecular sieve had the much higher adsorbed amount than unmodified one. The bigger pore, the more adsorption sites benefitted for the adsorbed amount of OTC. The exchanged amount of copper(II) and the acid-base property of solution were important factors influencing the removal efficiency. The adsorption kinetics, the adsorption isotherm, the adsorption thermodynamics and the proposed adsorption mechanism were studied. The analysis of adsorption isotherm indicated it is a monolayer adsorption. The fitting with adsorption kinetics, pseudo-second-order model, deduced chemical adsorption is the main rate controlling step. And the new formation of Cu-O chemical bond and the changes at bands of N-H vibration and C-N vibration by Fourier transform infrared spectrometer further confirmed the proposal adsorption mechanism was the chemical complexation of copper(II) in modified 13X with NH2 group of OTC. As the real exchanged amount of copper(II) was 149.07 mg·g-1 and the solution pH 7.0, the adsorption capacity of modified 13X for OTC reached the maximum of 2,396 mg·g-1 (with the initial concentration of 1,000 mg·L-1).
Subject(s)
Oxytetracycline/isolation & purification , Water Pollutants, Chemical/isolation & purification , Water Purification/instrumentation , Acids/chemistry , Adsorption , Copper/chemistry , Diffusion , Hydrogen-Ion Concentration , Kinetics , Models, Theoretical , Solutions , Spectroscopy, Fourier Transform Infrared , Temperature , Thermodynamics , Time Factors , X-Ray DiffractionABSTRACT
A combinative technology of alkali and N-methylmorpholine-N-oxide (NMMO) was used to pretreat corn stalk (CS) for improving the efficiencies of subsequent enzymatic hydrolysis and ethanol fermentation. The results showed that this strategy could not only remove hemicellulose and lignin but also decrease the crystallinity of cellulose. About 98.0% of enzymatic hydrolysis yield was obtained from the pretreated CS as compared with 46.9% from the untreated sample. The yield for corresponding ethanol yield was 64.6% while untreated CS was only 18.8%. Besides, xylose yield obtained from the untreated CS was only 11.1%, while this value was 93.8% for alkali with NMMO pretreated sample. These results suggest that a combination of alkali with 50% (wt/wt) NMMO solution may be a promising alternative for pretreatment of lignocellulose, which can increase the productions of subsequent enzymatic hydrolysis and ethanol fermentation.
