Desorption In Presence Research Articles

Hyperbranched polyglycerols containing amine groups — Synthesis, characterization and carbon dioxide capture

Abstract In this article we report an easy synthetic way towards hyperbranched polyglycerols containing primary amine groups (A-HBPGs). A-HBPGs were synthesized in a two-step procedure including an anionic ring opening copolymerization of the phthalimide-epoxy monomer with glycidol followed by hydrazinolysis of phthalimide groups. Polymeric products of both synthetic steps were characterized using NMR, MALDI-TOF, FTIR, viscosimetry and elemental analysis techniques. The maximum amount of the amine containing units in the products was estimated to be 31 mol%. Introduction of higher amounts of these units was limited by the reactivity (sterical) and viscosity reasons. A-HBPGs showed to be effective in CO2 capture from the ambient air. Adsorbents consisting of A-HBPGs and fumed silica in the 1 to 1 wt ratio were capable of adsorbing up to 85.6 mg of CO2, representing 0.82 mmol CO2 per gram or 36.3 mg CO2 per gram of adsorbent. The measurements confirmed that the amount of adsorbed carbon dioxide was proportional to the number of amine sites in a polymer. The obtained CO2 adsorbents could be regenerated upon by heating. Desorption took place above 80 °C, but the optimum temperature seemed to be at least 100 °C. The effect of easier CO2 desorption in presence of HBPG structures reported in the literature in case of our materials has not been confirmed.

Provenance, prevalence and health perspective of co-occurrences of arsenic, fluoride and uranium in the aquifers of the Brahmaputra River floodplain

The present work focuses on understanding the provenance, prevalence and health perspective of As and F− along with possible co-occurrence of uranium (U) in the aquifers of the Brahmaputra floodplains (BFP), India. Groundwater (n = 164) and sediment samples (n = 5) were obtained from the upper, middle and lower BFP. Energy dispersive spectroscopy (EDX) revealed the presence of As, U and Fe in the sediment matrix. Regression analysis showed a weaker relationship between As and F− co-occurrence. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested reductive dissolution of Fe (hydr)oxides responsible for As release in the BFP, especially in the upper and lower BFP. Bicarbonate appeared to compete with As oxyanions for adsorption on positively charged surfaces leading to As release. Arsenic desorption in presence of PO43−, F− and HCO3− at elevated pH appeared greatest in the upper BFP, suggesting the highest potential for co-occurrence. Co-occurrence, were mainly in isolated aquifers of the upper BFP owing to desorption of adsorbed As and F− from Fe (hydr)oxides at higher pH. Weathering and dissolution of clay minerals in the upper BFP, and competitive desorption in presence of HCO3− and PO43− in the middle and lower BFP, respectively, explain variabilities in F− release. Amorphous Fe (hydr)oxides like ferrihydrite act as sinks of U. Concentrations of As and F− will likely increase in the future as projected from the saturated levels of goethite and ferrihydrite. Hazard indices (HI) revealed that children (3–8 years) were at greater health risk than adults.

UV photooxidation induced structural and photoluminescence behaviors in vapor-etching based porous silicon

In this paper, we investigate the effect of UV irradiation on Vapor-Etching (VE) based Porous Silicon (PS) structure and luminescence under controlled atmosphere (N 2, air, O 2). The oxidation evolution is monitored by Fourier transform infrared (FTIR) spectroscopy. FTIR measurements show that the SiH x bond, initially present in the freshly prepared PS layers, decreased progressively with UV irradiation time until they completely disappear. We found that this treatment accelerates the oxidation process. SiO x structures appear and gradually become dominant as regard to the SiH x species, while UV irradiation is in progress. Generally, the photoluminescence (PL) intensity of the PS layer decreases instantaneously at the starting by the UV excitation and stabilizes after a period depending on the ambient gas and the specific surface area of the porous structure. Further UV exposure leads to a linear decrease of the PL intensity due to change of surface passivation from SiH x to O y SiH x . After less than 100 min of UV irradiation, the PL intensity exhibits an exponential decay. UV exposure in air and O 2 leads approximately to the same PL behavior, although faster PL intensity decrease was observed under O 2-rich ambient. This was explained as being due to intense hydrogen desorption in presence of oxygen. Correlations of PL results with FTIR measurements show that surface passivation determine the electronic states of silicon nano-crystallites and influence the photoluminescence efficiency.

Washing of Marine Coastal Sand in a Batch Reactor: Sorption and Desorption of BTEX

ABSTRACT This study addresses the issues related to decontamination of marine beach sand accidentally contaminated by petroleum products. Sorption and desorption of BTEX (i.e., benzene, toluene, ethylbenzene, and xylene) onto the sand from Uran Beach, located near the city of Mumbai, India, were studied, and isotherms were determined using the bottle point method to estimate sorption coefficients. Alternatively, QSARs (i.e., quantitative structure activity relationships) were developed and used to estimate the sorption coefficients. Experiments for kinetics of volatilization as well as for kinetics of sorption and desorption in the presence of volatilization were conducted in a fabricated laboratory batch reactor. A mathematical model describing the fate of volatile hydrophobic organic pollutants like BTEX (via sorption and desorption in presence of volatilization) in a batch sediment-washing reactor was proposed. The experimental kinetic data were compared with the values predicted using the proposed models for sorption and desorption, and the optimum values of overall mass transfer coefficients for sorption (Ksas) and desorption (Kdad) were estimated.This was achieved by minimization of errors while using the sorption coefficients (Kp) obtained from either laboratory isotherm studies or the QSARs developed in the present study. Independent experimental data were also collected and used for calibration of the model for volatilization,and the values of the overall mass transfer coefficient for volatilization (Kgag) were estimated for BTEX. In these exercises of minimization of errors, comparable cumulative errors were obtained from the use of Kp values derived from experimental isotherms and QSARs.