This work focuses on developing a novel adsorbent for CO2 capture, by coating polyethylenimine (PEI) on glass fiber matrix and using epichlorohydrin (ECH) as cross-linking agent. The physicochemical properties of the fibrous adsorbent were characterized. The CO2 adsorption capacity was evaluated. Factors that affect the adsorption capacity of the fibrous adsorbent were studied. The experimental results show that this fibrous PEI adsorbent exhibits a much higher adsorption capacity for CO2 compared with another PEI fiber prepared in our previous work, which employed epoxy resin as the cross-linking agent. A CO2 adsorption capacity as high as 4.12 mmol CO2/g of adsorbent was obtained for this fibrous PEI adsorbent at 30 degrees C, equal to 13.56 mmol CO2/g of PEI, with a PEI/ECH ratio of 20:1. The adsorbent can be completely regenerated at 120 degrees C.

No abstract

are new types of semiconductors in which adjacent layers are held by van der Waals force. [1] TMDs have many rich physical properties such as extremely weak phonon-assisted photoluminescence (PL) in bulk structures, relatively strong PL yield in monolayer structures, [2][3][4][5] strong valley-dependent absorption in visible range, [6][7][8] and strong nonlinear optical response. [9][10][11][12] By taking advantage of these properties, significant progresses have been made in the development of electronic and optoelectronic technologies by these materials, [13,14] such as photodetectors, [15] field-effect transistors, [16][17][18] solar cells, [19,20] light-emitting diodes, [21,22] valleytronics, [8,23] integrated circuits, [24] and so on.The exciton binding energy in the monolayer TMDs has been observed in the range of 0.1-1.1 eV, [25][26][27][28] which is larger than that in traditional bulk semiconductors and traditional quantum well. [29,30] This rich excitonic state makes it possible to observe the complex exciton dynamics at room temperature, [31] such as charged and neutral phase of carriers, [32] trions, [33] and biexciton. [34] Meanwhile, bounded exciton could not only dominate the optical response but also play an important role in the optoelectronic processes, such as photocurrent generation and photoconduction in TMD semiconductors. [33,35,36] As a typical TMD material, the bulk WSe 2 has an indirect bandgap of 1.2 eV, and it would transform to the ≈1.65 eV direct bandgap as decreasing to monolayer. [37,38] WSe 2 has been widely used in optoelectronic devices due to its high absorption coefficients in the visible range. Field-effect transistors based on single crystal WSe 2 have been achieved and a carrier mobility comparable to silicon at room temperature was demonstrated. [39] Besides, WSe 2 can also play an important role in the development of van der Waals heterostructures, [40][41][42] in which long-lived interlayer excitons have been observed.Recently, ultrafast time-resolved photoexcited carrier dynamics has been studied in layered TMDs by the most widely used tools, such as optical-pump optical-probe spectroscopy, [43] PL spectroscopy, [38] photocurrent spectroscopy, [36] and electroluminescence. [35,44] The prevalentThe dynamics of photoexcited species is quite important for the development of next-generation ultrafast optoelectronic devices based on transition metal dichalcogenides (TMDs). Herein, time-resolved optical pump terahertz (THz) probe spectroscopy, which is sensitive to both bounded excitons and free electrons/holes, is employed to study the dynamics of photo-induced carriers in the typical layered TMDs crystal tungsten diselenide (WSe 2 ). Initial photoexcitation could generate both free carriers and excitons. The free carriers decay followed by phonon-assistance (≈30 ps) and defect-assistance (≈200-280 ps). The excitons decay followed by the phonon-assisted recombination (≈100 ps) and the defect-induced exciton separation (≈40-200 ps). With the increasing of pump fluence, more f...

In the paper, the synthesis of ZnO/TiO 2 nanocomposites with different main parts (TiO 2 or ZnO) is studied. When TiO 2 is the main part of the ZnO/TiO 2 heterojunction photocatalysts (ZnO/TiO 2 ), the photocatalytic activity is decreased rapidly with the increase of the amount of ZnO. The reason may be attributed to the relative p−n junction (p-ZnO/ n-TiO 2 ) produced between ZnO and TiO 2 . The migration directions of the electrons and holes in the relative p−n junction are opposite to the transfer directions of the photogenerated electrons and holes in the valence band (VB) and conduction band (CB). However, when ZnO is the primary part of the heterojunction photocatalysts (TiO 2 /ZnO), the photocatalytic activity of the samples increases with the increase of the TiO 2 amount up to 5% (95% ZnO/TiO 2 ). The reason may be that the migration directions of the electrons and holes in the relative p−n junction (p-TiO 2 /n-ZnO) are the same as the transfer directions of the photoexcited electrons and holes in VB and CB between the two semiconductors. It is proposed that the conductivity of the heterojunction photocatalyst will be changed with the difference of content for the two semiconductors, which in turn affects the migration directions of the electrons and holes in the heterojunctions and their photocatalytic activity.

The transfer mechanism of photoexcited charge carriers is always a hot topic in the photocatalysis research field. Coupling a photocatalyst with other photocatalysts is one of the most widely used strategies to realize effective transfer of the photogenerated carriers. In the study, a series of WO3/TiO2 composites with different weight ratios were prepared. The WO3/TiO2 composites were characterized in detail. The result showed that regardless of whether the primary part of WO3/TiO2 composites is TiO2 or WO3, the photocatalytic activities of WO3/TiO2 are much higher than those of pure TiO2 or WO3. The reason may be the generation of a relative p–n heterojunction between WO3 and TiO2. Under the effect of the built-in electric field, the transfer directions of the photogenerated charge carriers in the heterojunctions are opposite to the migration directions of the photogenerated charge carriers in the conduction band (CB) and valence band (VB) of WO3 and TiO2. Thus, the transfer of the photogenerated charge carriers adopts a Z-scheme system in the WO3/TiO2 heterojunctions. The accumulated photogenerated electrons in the CB of TiO2 with more negative potential can reduce O2 to a superoxide radical (•O2 –), and the photogenerated holes in the VB of WO3 with more positive potential may oxidate H2O (or OH–) into a hydroxyl radical (•OH). The photocatalytic activities of the WO3/TiO2 heterojunctions are significantly promoted. The transfer mechanisms and natural law for the WO3/TiO2 heterojunction photocatalysts were proved by physical and chemical methods. This work not only reveals the transfer mechanisms of photogenerated carriers and internal natural behavior of heterojunction photocatalysts, but also guides the design and constructing of composite photocatalysts, and thus has theoretical and practical significance.