| Adsorption is one of the most common phenomena in nature.At present,liquid phase adsorption?LPA?is still being quantitatively characterized in the way of manual sampling and off-line determination,due to the complexity of the system comparing to gas adsorption.This paper describes a novel method for in-situ,real-time measurement of liquid phase adsorption in general based on fiber-optic sensing with the aid of membrane for the first time.The system consists of optical fiber spectrometer,light source and liquid phase adsorption vessel.A self-made measurement vessel was assembled from adsorption bag,thermostatic devices with stirring,and fiber-optic dipping probe.Here,the adsorption bag enabled in-situ light absorption measurement by eliminating interference of adsorbent particles with the aid of membrane in the adsorption system.MARs and rutin,quercetin and AO were chosen as model adsorbent and adsorbate to establish the fiber optic sensing liquid phase adsorption system at 190-660 nm wavelength.The fiber optic sensing system enabled us to accomplish obtaining kinetics of liquid-phase adsorption/desorption,adsorption thermodynamic and the low-temperature liquid-phase adsorption,and the prediction of adsorption capacity in multi-component solutions by combining the adsorption spectroscopy with chemometrics methods.?1?Rutin solution concentrations were measured by fiber optic spectrum at 353nm,in the broad concentration range from 0.3 to 60 mg·L-1 with excellent linearity?R2=0.9996?.In-situ measurement of adsorption and desorption dynamics on five kinds of MARs with different polarities were systematically carried out,showing that adsorption process obeyed Pseudo-second-model.As well as,the system was proved to be highly accurate and reproducible by comparing to the traditional method of the linear equation?R2=0.9996?and the repetitive experiment of adsorption amount at the time t?RSD=0.82%-2.55%?.?2?In situ adsorption thermodynamics of rutin on AB-8 were studied in the temperature range from 30oC to 50oC.And it was found that the output signal is stable,kinetic curve was smooth and there is no interference signal.This proves that the fiber optic sensing probe can stand for different temperatures and this system can keep the temperature constant,mixing rate and other adsorption conditions precisely controlled to eliminate the error and produce more accurate results.The adsorption thermodynamic parameters on AB-8 indicated that the data were well fitted to the Freundlich model.The calculated results showed that the?H was less than zero,?G and?S were also negative indicate that the adsorption of rutin on AB-8 was a favorable,exothermic,spontaneous,physical process.?3?A thermostatic adsorption vessel was designed and connected to a low temperature flow circulating pump to enable the measurement of liquid-phase adsorption conveniently at low temperature.Different standard curves,on the relation between concentration and absorption,were obtained through measurement of several set of AO standard solutions in different solvents by general UV-Vis and fiber optic spectrophotometer.And by comparison,it was found that linear correlation coefficients of the measurements of two spectrophotometers for all sets of solutions were greater than 0.9992.It proves that fiber optic spectrophotometer can work accurately in this condition.The adsorption conditions for low temperature adsorption experiments were optimized.At low temperature region from-5 to-10oC,adsorption capacity of AO on HPD300 increases with the increasing of temperature and it's a favorable,spontaneous,endothermic adsorption process.To the contrary,at high temperature region from 10 to 35oC,the adsorption capacity decreasing with the increasing of the temperature and it's a favorable,spontaneous,exothermic adsorption process.?4?Rutin and quercetin were selected as adsorbents,macroporous resins were used as adsorbents to investigate the multi-component adsorption,simultaneously,adsorption solutions of multi-component were predicted using chemometrics combining with spectrophotometry.Because of the severe spectral overlapping of rutin and quercetin,200-300 nm wavelength range was chosen for its good spectrum additivity.A series of mixed solutions were prepared to establish a chemometrics model and to evaluate model prediction and validation.Experiments of adsorption dynamics of mixture solutions of rutin and quercetin on HPD300 were carried out and the concentrations of the two components were predicted simultaneously by partial least squares and neural network.The data obtained from this method was in accordance with the data from HPLC,showing good accuracy of this method.It can be concluded that a UV-Vis spectrophotometric coupled with chemometrics method was preliminarily established to measurement of the multi-component adsorption in liquid phase.It will provide good foundation for the in-situ measurement of multi-component adsorption in liquid phase. |
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