Nowadays, freshwater shortage, energy crisis and environmental pollution are the three major threats to human beings. Bio-waste is an important source of environmental pollutant emissions and a renewable resource with great potential. Herein, we develop a photothermal material based on bagasse for solar steam generation to relieve the freshwater crisis and mitigate environmental pollution caused by bio-waste. The mainly functional part of the solar-driven steam generator here is bagasse-based photothermal aerogel (B-PTA), which composes of carbonized bagasse (CB) and bagasse-derived cellulose fiber (BDCF). The B-PTA relying on CB can effectively absorb sunlight (~?95%), resulting in a prominent light-to-heat ability. The B-PTA with DBCF has super-hydrophilicity, water transport and retention ability. Depending on the excellent light absorption and 3D water passageway, the B-PTA gives a water evaporation rate of 1.36 kg m–2 h–1, and achieves a photothermal conversion efficiency of 77.34% under 1-sun illumination (1 kW m–2). The B-PTA shows remarkable stability that the efficiency without significant change after 20 cycles. In addition, the B-PTA can effectively desalt seawater and purify dye wastewater with natural sunlight. Therefore, turning bio-waste into valuable photothermal material for solar steam generation is possible. Due to the merits of low cost, scalability, environmental friendliness, B-PTA has the potential for real-world water purification.
An account is given of the development of the proposal that ion–neutral complexes are involved in the unimolecular reactions of onium ions (R1R2C?Z+R3; Z = O, S, NR4; R1, R2, R3, R4 = H, CnH2n + 1), with particular emphasis on the informative C4H9O+ oxonium ion system (Z = O; R1, R2 = H; R3 = C3H7). Current ideas on the role of ion-neutral complexes in cation rearrangements, hydrogen transfer processes and more complex isomerizations are illustrated by considering the behaviour of isomeric CH3CH2CH2X+ and (CH3)2CHX+ species [X = CH2O, CH3CHO, H2O, CH3OH, NH3, NH2CH3, NH(CH3)2, CH2?NH, CH2?NCH3, CO, CH3˙, Br˙ and I˙]. Attention is focused on the importance of four energetic factors (the stabilization energy of the ion–neutral complex, the energy released by rearrangement of the cationic component, the enthalpy change for proton transfer between the partners of the ion neutral complex and the ergicity of recombination of the components) which influence the reactivity of the complexes. The nature and extent of the chemistry involving ion-neutral complexes depend on the relative magnitudes of these parameters. Thus, when the magnitude of the stabilization energy exceeds the energy released by cation rearrangement, the ergicity of proton transfer is small, and recombination of the components in a new way is energetically favourable, extensive complex-mediated isomerizations tend to occur. Loss of H2O from metastable CH2?O+C3H7 ions is an example of such a reaction. Conversely, if the stabilization energy is small compared with the magnitude of the energy released by eation rearrangement, the opportunities for complex-mediated processes to become manifest are decreased, especially if proton transfer is endoergic. Thus, CH3CH2CH2CO+ expels CO, with an increased kinetic energy release, after rate-limiting isomerization of CH3CH2CH2+? CO to (CH3)2CH+? CO has taken place. When proton transfer between the components of the complex is strongly exoergic, fragmentation corresponding to single hydrogen transfer occurs readily. The proton-transfer step is often preceded by cation rearrangement for CH3CH2CH2X+ species. In such circumstances, the involvement of ion–neutral complexes can be detected by the observation of unusual site selectivity in the hydrogen-transfer step. Thus, C3H6 loss from CH2?N+(R1)CH2CH2CH3 (R1 = H, CH3, C3H7) immonium ions is found by 2H-labelling experiments to proceed via preferential α-and γ-hydrogen transfer; this finding is explained if the incipient +CH2CH2CH3 ion isomerizes to CH3CH+CH3 prior to proton abstraction. In contrast, the isomeric CH2?N+(R1)CH(CH3)2 species undergo specific β-hydrogen transfer because the developing CH3CH+CH3 cation is stable with respect to rearrangements involving a 1,2-H shift. 相似文献
Electron ionization (EI) spectra and both positive and negative chemical ionization (CI) spectra have been obtained for four isoquinolinium ylides and two pyridinium ylides. Electron transfer reactions dominate the CI mass specra. The base peak in negative chemical ionization is the [M]?· ion, formed by electron capture. In the positive methane CI spectra the molecular ion, [M]+·, is relatively more intense than [MH]+ showing electron transfer to be the main positive ionization process. In the positive ammonia CI spectra, proton transfer to give [MH]+ is the main ionization process, but electron transfer is also observed. The EI spectra show fragmentations in which the aromatic nitrogen moiety retains the charge and fragmentation is by loss of radicals or small neutral molecules from the side-chains. Radical driven reactions are proposed to explain these spectra. 相似文献
Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R1, R2, R3 = H or alkyl) eliminate .CH3; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even-electron rule, which states that closed-shell cations usually decompose to give closed-shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH3)2C?NH]+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH3. and CD3., via different mechanisms, but very little CH2D. or CHD2. loss occurs. 相似文献
Non-contact atomic force microscopy (AFM) has been used to investigate the furface pore structure of a polyethersulfone ultrafitration membrane of specified molecular weight cut off (MWCO) 25 000 (ES625, PCI Membrane Systems). Excellent images at up to single pore resolution were obtained. This is the first time that AFM images of a membrane at such high resolution have been presented. Analysis of the images gave a mean pore size of 5.1 nm with a standard deviation of 1.1 nm. The results have been compared to previously published studies of membranes of comparable MWCO using contact AFM and electron microscopy. Non-contact AFM is a powerful means of studying the surface pore characteristics of ultrafiltration membranes. 相似文献