To achieve high-efficiency viscosity reduction in a mild hydrothermal environment, the visbreaking of heavy oil in a mixed solvent of subcritical water (sub-CW) and light aromatics was investigated. By solubilizing sub-CW in heavy oil, the dealkylation involved in visbreaking follows not only a free radical mechanism but also an ionic mechanism. The further introduction of light cycle oil rich in light aromatics but containing olefin groups has a complicated influence on visbreaking. Because of the presence of olefin groups, the viscosity reduction efficiency is initially reduced. In addition, the condensation to asphaltenes is promoted in the late visbreaking stage. However, these adverse effects are offset by the promotion of the solubilization of sub-CW in heavy oil by light aromatics. With enhanced dealkylation in both free radical and ionic mechanisms, a viscosity reduction rate of over 90% and reduced asphaltene formation can be obtained in the middle stage of visbreaking.
High-quality
QDs play a crucial role in the fabrication of high-performance
quantum dot-sensitized solar cells (QDSCs). Surface defects/traps
of QDs commonly act as nonradiative carrier recombination centers
and thereby deteriorate the power conversion efficiency of the fabricated
QDSCs. Herein a protective ZnSe shell is grown on the surface of Al/Zn
coincorporated Cu–In–Se QDs to form (Al/Zn)–Cu–In–Se/ZnSe
(AZCISe/ZnSe) core/shell QDs, which are used as light harvesters to
fabricate QDSCs. It is found that the PL intensity of AZCISe/ZnSe
QDs is significantly improved as the ZnSe shell thickness increases,
indicating that the ZnSe shell is beneficial to reduce the surface
defects/traps of AZCISe QDs. Moreover, the ZnSe shell thickness can
be tailored by controlling the cycles of injected Zn and Se precursors
during the synthesis process. Furthermore, electrochemical impedance
spectroscopy, open-circuit voltage decay, and time-resolved fluorescence
spectroscopy analysis demonstrate that the ZnSe shell layer can effectively
reduce the surface defect/trap density of the QDs, suppress the charge
recombination at photoanode/electrolyte interfaces, and improve the
photovoltaic performance of the constructed QDSCs. Benefiting from
the surface engineering of QDs, the average power conversion efficiency
increases from 10.15% for pristine AZCISe QDSCs to 10.53% for AZCISe/ZnSe
core/shell QDSCs.
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