No abstract

Low-dimensional semiconductors provide a marvelous platform for pursuing versatile photocatalytic solar energy conversion. Compared with the bulk counterparts, low-dimensional semiconductors possess notable Coulomb-interaction-mediated excitonic effects arising from the reduced dielectric screening. As a consequence, excitons or bound electron−hole pairs, together with charge carriers, serve as the primary photoinduced energetic species. In terms of photocatalysis, exciton-based energy transfer establishes distinctly different mechanisms for energy utilization beyond the traditional carrier-based charge transfer. Moreover, owing to the relationships between excitons and charge carriers, excitonic effects play a crucial role in determining quantum yields of both exciton-and carrier-triggered photocatalytic reactions. The above unique features enable optimized low-dimensional semiconductor-based photocatalysis to be achieved by non-trivial excitonic regulation. In this Perspective, we attempt to provide an overview of the impacts of excitonic effects on low-dimensional semiconductor-based photocatalysis. By figuring out the differences between excitons and charge carriers in degrees of freedom like spin and orbital, we emphasize the importance of unique excitonic properties in photocatalytic energy conversion. We discuss the interplay between the excitonic and charge-carrier aspects in lowdimensional semiconductors and highlight the necessity of evaluating excitonic effects when dealing with both exciton-and carriertriggered photocatalytic reactions. We further review recent achievements in regulating the excitonic properties of low-dimensional semiconductor-based photocatalysts. We conclude the Perspective with an eye toward the future challenges in the field.

Co2V2O7 monodisperse hexagonal nanoplatelets (MHNPs) were obtained via a hexamethylenetetramine-assisted water bath method. The excellent electrochemical activities are due to the unique structure of MHNPs and likely synergetic effects of different metal ions.

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10 years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe.