Fly ash-based geopolymer paste with expanded vermiculite (EV) powder addition was synthesized and its microstructure, compressive strength, setting time, moisture control, efflorescence extent and thermal conductivity were studied. The results showed that EV addition resulted in the increase of standard consistency water consumption and setting time. As a consequence, its excessive addition caused a larger amount of harmful pores, which was detrimental for compressive strength of geopolymer paste. However, geopolymer pastes with an appropriate amount of EV addition (2-7 wt%) presented a slight increase of compressive strength because of the filler effect. Mg2+ and Fe2+diffused from EV interlayer through ions exchange between EV and geoploymer solution participated in geopolymerization. This was reflected by the formation of N-(M)-A-(F)-S-H evidenced through SEM-EDS and FITR analyis. In addition, Na2+/Mg2+or Na2+/Fe2+ ions exchange reduced the mobility of Na2+and therefore decreased the efflorescence extent. Moreover, EV addition favored the improvement of moisture control and thermal conductivity properties of geopolymer paste.
TiO2/ZnO heterostructure photocatalysts were successfully fabricated via hydrothermal and solid-state reaction method. In TiO2/ZnO composite powder, TiO2 nanoparticles of anatase phase are well distributed on the surface and edge of ZnO with wurtzite phase structure, and closely combined to form heterostructure. The optical bandgap of TiO2/ZnO powder is less than that of pure ZnO or TiO2 powder. TiO2/ZnO composite powders show higher degradation efficiency for methylene blue and dissolved organic matter. The degradation rate of TiO2/ZnO powder for fulvic acid-like substances in landfill leachate is 2.99 times that of pure ZnO powder and 1.30 times that of pure TiO2 powder. The degradation of fulvic acid-like substances by photocatalyst causes the decrease of some high molecular weight and benzene ring structure substances in leachate. The effective separation of electron and hole by the heterostructure in TiO2/ZnO powder is the main reason for its high photocatalytic degradation efficiency of DOM in landfill leachate.
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