State-of-the-art advances in vacancy defect engineering of graphitic carbon nitride for solar water splitting

Developing low-cost,efficient,and stable photocatalysts is one of the most promising methods for large-scale solar water splitting.As a metal-free semiconductor material with suitable band gap,graphitic carbon nitride(g-C_(3)N_(4))has attracted attention in the field of photocatalysis,which is mainly attributed to its fascinating physicochemical and photoelectronic properties.However,several inherent limitations and shortcomings—involving high recombination rate of photocarriers,insufficient reaction kinetics,and optical absorption—impede the practical applicability of g-C_(3)N_(4).As an effective strategy,vacancy defect engineering has been widely used for breaking through the current limitations,considering its ability to optimize the electronic structure and surface morphology of g-C_(3)N_(4) to obtain the desired photocatalytic activity.This review summarizes the recent progress of vacancy defect engineered g-C_(3)N_(4) for solar water splitting.The fundamentals of solar water splitting with g-C_(3)N_(4) are discussed first.We then focus on the fabrication strategies and effect of vacancy generated in g-C_(3)N_(4).The advances of vacancy-modified g-C_(3)N_(4) photocatalysts toward solar water splitting are discussed next.Finally,the current challenges and future opportunities of vacancy-modified g-C_(3)N_(4) are summarized.This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C_(3)N_(4).

SPATIOTEMPORAL VARIATION OF WATER QUALITY AND ALGAL BIOMASS IN ERHAI LAKE AND ITS ENVIRONMENTAL MANAGEMENT IMPLICATIONS

Elucidating the spatiotemporal pattern of water quality and algal biomass is crucial for accurately tracing pollution sources and reducing the risk of algal blooms in lake systems.This study analyzed the spatiotemporal variability of water quality and algal biomass in Erhai Lake from 1994 to 2021 using water quality index(WQi),Mann-Kendall test and Sen's slope combined methods.The potential causes of water quality deterioration and algal biomass dynamics were also elucidated.The results showed that the historical changes in the water environment of Erhai Lake mainly had three stages:satisfactory(1994-2001),deteriorating(2002-2010)and improving(2011-2021).The changes in water quality and algal biomass were primarily affected by total nitrogen,total phosphorus and chemical oxygen demand in different stages.The water environment of Erhai Lake is currently improving significantly,starting in the southern area that is furthest from the sources of agricultural pollution,especially in summer and autumn.This is attributed to the implementation of control measures resulting in lower pollutant loads at particular times and places.Therefore,it is necessary to continue to promote standardized livestock farming,to strengthen rural wastewater collection and to investigate measures such as the interruption of the endogenous cycle.

AGRICULTURAL GREEN DEVELOPMENT IN THE ERHAI LAKE BASIN-THE WAY FORWARD

Pollution of high-altitude lake basins by agriculture and rural activities,and the control of this pollution,have received increasing attention from academic research and government policy in China.Series of restrictions and regulations have been implemented to protect the surface,water quality.These restrictions and regulations have greatly impacted and transformed the agricultural systems and rural livelihoods surrounding these lake basins.Using Erhai Lake basin in Yunnan Province as a case study,three main challenges were identified for concurrently decreasing pollution in the lake and increasing farmer income.It is contended that scientifically-sound environmental protection policies and agricultural green development practices are key to reversing the current situation.This will help to protect the lake from pollution while smallholder farmers will be able to produce healthy food in an environmentally sustainable manner,and with a fair remuneration for all the services farmers providetothe society.