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The rapid recombination of photogenerated electrons and holes, low utilization of visible light and weak oxidation capacity significantly limit the photocatalytic activity for the degradation of organic pollutants. Doping is used as a conventional strategy for regulating the electronic structure of photocatalysts to obtain a wider light absorption, but also suffers from the problems of reduced charge mobility and oxidation capacity, which is not conducive to photocatalytic degradation of pollutants. To address this issue, a nitrogen self-doped hollow nanotubes g-C 3 N 4 (N-PCN) was synthesized by synergistic self-doping and quantum confinement effects. The N-PCN exhibits excellent efficiency in photocatalytic degradation of TC compared to the pristine g-C 3 N 4 . The synthesized N-PCN has a more positive conduction band minimum and can generate more photogenerated electrons to reduce oxygen to superoxide radicals. In addition, experimental and theoretical evidence shows that N-self-doping not only suppresses the recombination of photogenerated charge carriers but also facilitates the adsorption of oxygen molecules. Consequently, more superoxide radicals and singlet oxygen are generated through oxygen activation process., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In order to recover mercury from high concentration Hg(II) acid wastewater, UV irradiation was used to reduce Hg(II) to Hg 2 Cl 2 with the presence of fulvic acid and chloride ion. When simulated wastewater with Hg(II) concentration of 1000 mg L -1 was treated, > 90% of Hg(II) removal efficiency was achieved under the condition of extra Cl - dosage of 5 g L -1 , FA dosage of 2 g L -1 , pH of 3.0 and 120 min of UV irradiation. Kinetics study showed that the photoreduction process could be well described by pseudo-first order kinetic mode, and the Hg(II) reduction rate was tested to be 0.0422 min -1 . Characterization results indicated that FA-Hg(II) complexes were firstly formed and then broken down into smaller molecules after the UV treatment, in which process highly reductive species (i.e. COO, COOH) were produced. These reductive species mediated the reduction of Hg(II). With the presence of Cl - , Hg 2 Cl 2 was practically the only detected Hg-based product in the photoreduction process. This technique was also employed to treat COD Cr analysis wastewater (initial Hg(II) concentration > 1000 mg L -1 ). With 90 min of reaction, most of the Hg(II) was removed from the system leaving less than 30% that could be further treated by chemical participation or adsorption method., (Copyright © 2018 Elsevier Ltd. All rights reserved.)