In selenite solutions, H 2 SeO 3 , HSeO À 3 , and SeO 2À 3 are in equilibrium in proportions that vary with solution pH. The physiological characteristics of selenite uptake were studied with excised roots of maize (Zea mays L.) seedlings at pH 3.0, 5.0, and 8.0. The results showed that 0.10 mM 2,4-dinitrophenol (DNP), 1.0 mM sodium fluoride (NaF), and a temperature of 4°C inhibited selenite uptake by maize roots by 16%, 20%, and 23% at pH 3.0, by up to 80%, 79%, and 78% at pH 5.0, and by 5%, 9%, and 16% at pH 8.0. Hence, selenite may enter roots at pH 5.0 in an energy-dependent manner, in contrast to pH 3.0 and 8.0. The uptake kinetics for selenite were determined for excised roots of maize, and the curves were linear at pH 3.0 and 8.0, but saturated at pH 5.0, showing that carrier-mediated uptake of selenite occurred at pH 5.0, but not at pH 3.0 or 8.0. Further studies showed that HgCl 2 and AgNO 3 inhibited selenite uptake separately by 81% and 76% at pH 3.0 and indicated that selenite was absorbed by maize roots through aquaporins at pH 3.0. At pH 8.0, anion-channel inhibitors only inhibited a small fraction of selenite uptake, indicating that the major absorption pathway of SeO 2À 3 species into roots was not absorbed passively through anion channels, but might involve other processes. According to these results, it is proposed that selenite uptake occurs via different mechanisms depending on its species in solution in response to pH levels.

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Carbonaceous adsorbents with both high sulfur capacity and easy regeneration are required for flue gas desulfurization. A hierarchical structure is desirable for SO2 removal, since the micropores are beneficial for SO2 adsorption, while the mesopore networks facilitate gas diffusion and end-product H2SO4 storage. Herein, an ordered hierarchical porous carbon was synthesized via a soft-template method and subsequent activation, used in SO2 removal, and compared with coal-based activated carbon, which also had a hierarchical pore configuration. The more detailed, abundant micropores created in CO2 activation, especially the ultramicropores (d < 0.7 nm), are essential in enhancing the SO2 adsorption and the reserves rather than the pore patterns. While O2 and H2O participate in the reaction, the hierarchical porous carbon with ordered mesopores greatly improves SO2 removal dynamics and sulfur capacity, as this interconnecting pore pattern facilitates H2SO4 transport from micropores to mesopores, releasing the SO2 adsorption space. Additionally, the water-washing regeneration performances of the two types of adsorbents were comparatively determined and provide a new insight into the mass-transfer resistance in the pore structure. The ordered hierarchical carbon promoted H2SO4 desorption efficiency and cycled SO2 adsorption–desorption performance, further indicating that interconnecting micro- and mesopores facilitated the diffusion of adsorbates.