Resistance of mixed self-assembled monolayers (SAMs) with various counter-charged terminal groups of different valence and protonation/deprotonation states to nonspecific protein adsorption is investigated. It is demonstrated that excellent nonfouling surfaces can be readily constructed from mixed positively and negatively charged components of equal valence in a wide range of thiol solution compositions. Furthermore, the lattice structure of one of the mixed SAM systems studied is revealed by atomic force microscopy (AFM) to be (5.2 +/- 0.2 A x 5.2 +/- 0.2 A)60 degrees . Results indicate that the packing structure of mixed charged SAMs is determined by strong charge-charge interactions of the terminal groups rather than S-Au and chain-chain interactions. This work provides direct evidence that conformational flexibility is not required for protein resistance of a surface and even a single compact layer of charged groups of balanced charge with a crystalline structure can resist nonspecific protein adsorption, suggesting that tightly bound water molecules on the topmost part of the mixed SAMs play a dominant role in surface resistance to nonspecific protein adsorption.

The chemical looping process (CLP) using calcium-based sorbents to capture CO2 through cyclic carbonation–calcination reaction (CCR) before, during, or after the conversion of carbonaceous fuel occurs, is a viable CO2 control technology. With extensive past and current research efforts, the basic process concept has been found to be attractive at larger scales. Additionally, process simulations based on experimental results indicate that the parasitic energy consumption for this high temperature process is relatively low compared to low temperature processes such as the amine-based process. The ability of the calcium-based sorbents to maintain stable reactivity and physical integrity in cyclic reaction under severe operating conditions is one of the most important criteria for the success of the calcium looping technology. Despite being abundant and cheap, calcium-based sorbents derived from naturally occurring precursors, such as limestone and dolomite, suffer from rapid reactivity deterioration after high-temperature calcination and/or several CCR cycles. This deactivation is attributed to the morphological change at both macroscopic and microscopic levels, including pore pluggage, surface area reduction, and alteration of crystallographic plane distribution on the CaO surface. Much attention has recently been placed on sustaining and/or retaining the sorbent reactivity through sorbent modifications and/or reactivation. This paper provides an overview of the optimization and reactivation strategies of calcium-based sorbents with focus on three methodsmodification of precursors, addition of dopants and/or supports, and reactivation through steam/water hydration.

Experimental study of dry HCl removal from synthesis gas or flue gas using CaO sorbents, in the context of CaObased chemical looping processes, is reported. The study was first conducted in a TGA and a fixed-bed reactor to test the effects of chloridation temperature, sorbent particle size, HCl concentration, and space velocity on the HCl capture capacity. The chloridation reactivity deterioration of CaO sorbents with multicyclic carbonationÀcalcination reaction (CCR) and/or at high calcination temperatures, which are of notable relevance to the CaO-based chemical looping processes, was also investigated. In addition, precipitation (activation) and hydration (reactivation) were used to enhance initial sorbent reactivity and to reactivate the deactivated sorbents, respectively. The effects of deactivation, activation, and reactivation were explained by the morphological property change of the sorbents. To further elucidate the solid phase reaction mechanism of CaO and HCl, ionic transfer behavior during chloridation reaction was characterized using an inert marker experiment. Through the present work, the performance of CaO sorbents in HCl capture, deactivation of the sorbents by high-temperature calcination and multiple CCR cycles, sorbent activation and reactivation strategies, and the corresponding reaction mechanisms are determined. ' CHEMICAL REACTIONS INVOLVED IN THIS STUDYIn this study, six major chemical reactions are involved, descriptions of which are listed below:In the study of sorbent activation, specially tailored PCC is synthesized by precipitation of Ca 2þ cations and CO 3 2anions from Ca(OH) 2 slurry with a specially designed procedure, which is elaborated in the Experimental Section.Calcination of Limestone or PCC.In reaction 2, naturally occurring limestone or specially tailored PCC is calcined to CaO for further reaction with CO 2

In this study, the high-pressure carbonation kinetics of calcium oxide (CaO) derived from three calcium-based sorbents, namely, limestone (CaCO3), calcium hydroxide [Ca(OH)2], and precipitated calcium carbonate (PCC), used in the calcium looping process (CLP) system were studied using a magnetic suspension balance (MSB) analyzer. Different total pressures (1000–15000 torr) and concentrations of CO2 (10–30%) were tested to determine their effects on the carbonation reaction rate at a specific operating temperature of the CLP system, namely, 700 °C. The carbonation reaction rate was found to increase with increasing concentration of CO2 (10–30%) at a constant total pressure of 5000 torr and to exhibit first-order kinetics. However, the total pressure has an effect on the carbonation reaction rate only at lower total pressures. With a 20% CO2 stream, the reaction rate was observed to increase until the total pressure reached 4000 torr, beyond which a further increase in total pressure had a negative effect on the rate of the carbonation reaction of CaO derived from all three precursors. Further, the carbonation reaction had a different reaction order with respect to the partial pressure of CO2. It was found that the reaction was first-order at lower total pressures but changed to zeroth-order when the total pressure exceeded 4000 torr. The different reaction order under elevated pressures can be explained by the Langmuir mechanism. In addition, the reaction rate of carbonation conducted at high total pressure was greater than that at atmospheric pressure, under cyclic testing. The results also showed that there was no significant difference in the behavior of the carbonation reaction of CaO at elevated pressures, regardless of the different precursors used to generate the CaO.

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