No abstract

By measuring the electrical resistance of tantalum filaments (i) during isothermal reaction with oxygen, (ii) after isothermal degassing, and (iii) after rapid temperature quench, we infer both the instantaneous dissolved oxygen concentration and the metal " gasification " rate. For the conditions : 1.6 x lo-' Q p(oxygen) Q 0.67 Pa, 2400 K < Tw < 2800 I ( , the following mechanistic conclusions are drawn concerning the production/desorption of metal oxides [TaO(g), TaO,(g)] and the cause of the observed enhanced reactivity of microwave discharge-produced atomic oxygen : (a) under conditions of steady-state O(abs)-concentration and oxide desorption rate, the mechanisms of metal oxide production/desorption in dissociated and undissociated gaseous oxygen are identical ; (b) enhanced chemisorption probability accounts for increased oxygen coverage and tantalum volatilization. rate in atomic oxygen. Part 2 includes the extraction of elementary rate constants for interface penetration and oxide desorption based on transient electrical resistance data following the isothermal exposure of tantalum to step-function increases in oxygen pressure. * This neglects the small dependence that & T ~ might have on the solute concentration c. When c < 1 and the corresponding adatom coverage 8 is small, this dependence is indeed negligible; cf. Section 5.

To enhance the remediation capability of lead (Pb) polluted water, our approach involved a two-step modification of the initial sepiolite (sep) through inorganic mixed solutions and sodium dodecanesulfonate (referring as SDS/isep), and then the modified sepiolite (SDS/isep) is used to remove Pb2+ in Pb-contaminated water. Adsorption experiments showed that the SDS/isep had a significantly higher adsorption capacity for Pb2+ than natural sepiolite (the adsorption capacities before and after modification were 19.04 and 49.10 mg g− 1). A series of characterizations combined with adsorption kinetics and thermodynamics analysis revealed the adsorption mechanism of SDS/isep for Pb2+. The analysis results show that the monolayer adsorption of SDS/isep to Pb2+ is mainly carried out by ion exchange, surface hydroxyl complexation, chemical precipitation, and electrostatic attraction, and this adsorption reaction is a spontaneous exothermic process. The above positive results indicate the superiority of the two-step modification strategy of natural sepiolite proposed in this study.

In this study, polymeric nanocomposites of zeolitic imidazolate frameworks (ZIFs) were synthesized by assembly of a biomimetic polymer-polydopamine (PDA)onto halloysite nanotubes (HNTs@PDA), followed by the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) on the surface of HNTs@PDA. The obtained nanocomposites (HNTs@PDA/ZIF-8) prevented agglomeration of ZIFs and increased the number of active sites derived from PDA. The factors influencing heavy metal ions (Pb2+, Cd2+, Cu2+, and Ni2+) adsorption by HNTs@PDA/ZIF-8 were discussed. The Langmuir model was able to well describe the adsorption, and the maximum adsorption capacity of HNTs@PDA/ZIF-8 was calculated to be 285.00 mg/g for Cu2+, 515.00 mg/g for Pb2+, 185 mg/g for Cd2+ and 112.5 mg/g for Ni2+. Thermodynamic parameters confirmed that the adsorption was exothermic and spontaneous. Moreover, HNTs@PDA/ZIF-8 has good regenerability, which is very important in practical applications. The adsorption mechanism study showed that electrostatic attraction, coordination reactions and ion-exchange were the main mechanisms between the adsorbents and heavy metal ions. Hence, HNTs@PDA/ZIF-8 is a promising candidate for removing heavy metal ions from wastewater.