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BACKGROUND: A Z‐scheme structured photocatalyst is a highly efficient photocatalyst for hydrogen evolution and degradation of pollutants. RESULTS: An indirect Z‐scheme heterojunction g‐C3N4/CQDs/InVO4 with carbon quantum dots (CQDs) as electron mediator was constructed and was successfully synthesized using a facile hydrothermal method. The photocatalytic activity of the as‐prepared composite was evaluated in terms of hydrogen generation and degradation of rhodamine B (RhB) dye. The as‐prepared sample CV20/CQDs2 (g‐C3N4/2 wt% CQDs/20 wt% InVO4) exhibits the best photocatalytic activity towards hydrogen production and RhB degradation. Within 90 min, 99.6% of RhB is removed, and the degradation rate constant of RhB over CV20/CQDs2 is 0.06491 min−1, which is 43.9, 6.64 and 3.3 times as high as that of InVO4, g‐C3N4 and binary composite g‐C3N4/InVO4. CV20/CQDs2 exhibits H2 evolution rate of 2.169 mmol g−1 h−1, which is 26.07, 2.65 and 1.6 times as high as that of InVO4, g‐C3N4 and g‐C3N4/InVO4. CONCLUSIONS: The enhanced photocatalytic activity is attributed to two aspects. First, CQDs, as electron mediator, promote the effective separation of photogenerated electrons and holes through Z‐scheme charge transfer pathway, preserving the high redox ability of electrons and holes. Second, g‐C3N4/CQDs/InVO4 shows strong optical absorption in the full visible‐light region. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Summary: K-doped g-C3N4/SiO2composite (SiO2/K-CN) was synthesized by a facile thermal polymerization withpotassium chloride,melamine and nano-silica as raw materials. The as-prepared SiO2/K-CNwas characterized byvarious measures. The photocatalytic activity of SiO2/K-CNwastestedvia the photocatalyticdegradationoftetracycline undervisible-lightirradiation.The results showed that the specific surface area of SiO2/K-CNcatalyst was 28.16m2/g, which is larger than that of pristine K-doped g-C3N4. Both K-doping and silica-combinationcan reduce the recombination rate of photo-generatedelectrons-holespairs and broaden the region of visible light-harvesting.Compared with the pristine K-doped g-C3N4and composite SiO2/g-C3N4, SiO2/K-CN exhibits distinctly higher photocatalytic activity for degradation of tetracycline. The enhanced photocatalytic performance of SiO2/K-CN is attributed to the increasedspecific surface area and the synergistic effect of K-doping and silica-combination in both accelerating separation of charged carries and improving visible light-absorption. Duringphotocatalytic degradation of tetracycline, superoxide radicals play the most important role, followed by holes.SiO2/K-CNcomplex has excellentstability and shows promisingapplication in photocatalytic degradation of organic contaminants in water. [ABSTRACT FROM AUTHOR]

The graphitic carbon nitride (g-C 3 N 4) with nanosheets structure or carbon vacancies is considered as the promising photocatalysts duo to their fascinating properties. Herein the carbon vacancy modified g-C 3 N 4 nanosheet (TCN-600) was synthesized via one-step thermal polymerization of thiosemicarbazide precursor without auxiliary agent and extra gas protection. The higher calcination temperature and self-generating gas atmosphere (N 2 H 4 , CS 2 and H 2 S) during the precursor polymerization impel introduction of carbon vacancies and simultaneous formation of nanosheet structures. The as-prepared TCN-600 exhibits excellent photocatalytic activity for tetracycline (TC) degradation and hydrogen production. TCN-600 shows average hydrogen production rate of 1.86 mmol g−1 h−1, which is 11.6 times higher than that of bulk g-C 3 N 4. Meanwhile, TCN-600 displays high TC degradation efficiency of 83.3% within 90 min. The photodegradation rate of tetracycline by TCN-600 is 5.6 times higher than that by bulk g-C 3 N 4. The significant improvement in photocatalytic activity is mainly attributed to its huge specific surface areas (144.5 m2/g), extended visible-light absorption, negatively shifted conduction band position, longer charge carries lifetime and faster migration of the photo-induced electron-holes. This study provides a new strategy to synthesize g-C 3 N 4 with carbon vacancies and simultaneous nanosheet structure. [Display omitted] • Carbon vacancy-modified g-C3N4 nanosheet was synthesized by facile one-step polymerization. • Thiosemicarbazide was used as precursor to obtain carbon vacancy-modified g-C3N4 nanosheet. • The catalyst shows high photocatalytic activity for H2 evolution and tetracycline degradation. [ABSTRACT FROM AUTHOR]