Characteristics of transmission light in tetracycline hydrochloride polluted wastewater and the response of g-C3N4 under different transmission spectral range during the photodegradation process

Multifunctional photocatalyst of graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals derived from lichen for efficient photodegradation of tetracycline and methyl blue

We propose a feasible and economical method of constructing biomass-based multifunctional photocatalysts with excellent adsorption performance and high photodegradation abilities toward tetracycline (TC) and methyl blue (MB) under visible light. A series of novel hybrids of porous graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals (denoted as Fe2O3/Fe3O4@C) were derived from lichen doped with different dosages of Fe3+ by calcination at 700°C under a N2 atmosphere. The Fe2O3/Fe3O4@C hybrids exhibited nanoflake-like shapes, mesoporous structures, and efficient visible light harvesting, thus indicating enhanced adsorption ability and photoactivity toward pollutants. The formed Fe2O3/Fe3O4 heterojunction improved the separation efficiency and inhibited the recombination of photogenerated carriers, whereas the carbon network improved the transfer of photogenerated electrons. Under optimised conditions, the Fe2O3/Fe3O4@C-1 hybrid demonstrated enhanced photodegradation efficiencies of 96.4% for TC and 100% for MB under visible light. In addition, electron spin resonance and trapping measurements were performed to identify active species and determine the photocatalytic mechanism toward pollutants. •O2- and •OH were the active species involved, playing critical roles in the TC and MB photodegradation processes. In addition, a bacterium test revealed that the products of TC degradation by Fe2O3/Fe3O4@C-1 showed low biological toxicity. This work provides a promising preparation strategy or biomass-based photocatalysts for application in environmental pollutant treatment.

Influences of different carbon substrates on the morphologies of carbon/g-C3N4 photocatalytic composites and the purification capacities of different composites in the weak UV underwater environment

In order to explore the influence of various carbon introduction on the morphology and photodegradation performance of C/g-C₃N₄ composites, three kinds of different carbon materials: carbon nanotubes (CNT), graphene (GN) and carbon fibers (CF) were introduced to modify g-C₃N₄, and the morphologies, light absorption capacities and the underwater purifications of the composite photocatalysts were investigated. Results showed that the composites synthesized with different carbon substrates shows great differences in growth morphology. In addition, the introduction of various carbon sources also has a great impact on the physical and chemical properties of the composites. Compared with GN/g-C₃N₄ and CF/g-C₃N₄, CNT/g-C₃N₄ shows strong light absorption ability, especially in long-wavelength region (570-660 nm). To further study the difference of degradation ability of the composites in the underwater environment, the purification performance of modified g-C₃N₄ at different water depths were carried out. The results show that under 40 cm of water, where the light intensity and ultra violet spectral are seriously attenuated, the purification efficiency of CNT/g-C₃N₄ at 40 cm is 3.35 times than that of g-C₃N₄. This work provides insight in the design of highly efficient metal-free photocatalysts for the environmental remediation.

The photocatalytic activity and purification performance of g-C3N4/carbon nanotubes composite photocatalyst in underwater environment

Graphite carbon nitride (g-C₃N₄) is a promising photocatalyst for its high catalytic activity, low-cost and high-biosafety characteristics. Due to the complexity of underwater photochemical reaction conditions and the disadvantages of g-C₃N₄ itself such as low specific surface area, easy recombination of photogenerated electron-hole pairs and insufficient light absorption capacity, the application of g-C₃N₄ in the field of water purification is limited. For improving underwater photocatalytic performance of g-C₃N₄, a g-C₃N₄/carbon nanotubes (CNT-CN) composite photocatalyst with high specific surface area and enhanced light absorption capacity were prepared by in situ solvothermal method. Its photodegradation efficiency at different underwater transmission light was further studied. The results show that CNT has good compatibility with g-C₃N₄. g-C₃N₄ can grow in situ on the surface of CNT and form a stable composite structure. Moreover, its degradation efficiency under long-wavelength irradiation is improved significantly. The degradation rate of CNT-CN at 550-700 nm was about 3 times than that of g-C₃N₄. Furthermore, CNT-CN can maintain higher photocatalytic activity under water. At 40 cm depth where light intensity and ultraviolet spectra were attenuated 63.8% and 80.1%, respectively, the degradation rate of CNT-CN3 can still reach 3.49 times than that of g-C₃N₄. Based on this study, the introduction of CNT effectively promotes the electron-hole separation efficiency of g-C₃N₄, widens its spectral response range, and thus improves its underwater degradation efficiency.

Effects of g-C3N4 on bacterial community and tetracycline resistance genes in two typical sediments in tetracycline pollution remediation

Photocatalysis, as a novel technique, has been widely used for antibiotic pollution remediation in wastewater. In the processes of degradation and removal of antibiotics, the impact of photocatalysts on microenvironment is very important but remains poorly understood. In the present study, the effect of typical photocatalyst g-C3N4 (Graphitic carbon nitride) on microbial community was investigated in two sediment types (riverbed sediment and pig-farm sediment) polluted by tetracycline (TC) in central southern China. The riverbed sediment and pig farm sediment samples were respectively exposed to g-C3N4 (25, 75, 125 mg⋅kg-1) and TC (60, 120, 180 mg⋅L-1) treatments alone or combination for 30 days, respectively. The bacterial community and antibiotic resistance genes (ARGs) of the treated sediments were analyzed by Illumina sequencing and metagenomic sequencing. Studies had shown that: TC, g-C3N4, and TC/g-C3N4 have significant effects on the changes of microbial communities and components in riverbed sediment, but they do not exist in pig farm sediment. The most alterations of microbial taxa were Acidobacteriota, Actinobacteriota, and Desulfobacterota in riverbed sediment, and Elusimicrobiota in the pig farm sediment under various treatments. Through network analysis, it was found that the distribution of microorganisms in the pig farm sediment is more complex and more stable. The addition of g-C3N4 reduced the absolute abundance of ARGs in the two examined sediments, but not significantly changed their relative abundance of ARGs. The g-C3N4 application was beneficial to the removal of TC residues and to the prevention of the generation and transmission of ARGs in sediments. Our results suggested that g-C3N4 was a suitable photocatalyst with excellent application prospect for the removal of TC residues and the control of ARGs in environment.

Ionic liquid-assisted synthesis of porous boron-doped graphitic carbon nitride for photocatalytic hydrogen production

This work presents a simple way to prepare boron-doped graphitic carbon nitride (B/g-C₃N₄), exhibiting an enhanced photocatalytic performance to split water for hydrogen production. B/g-C₃N₄ was synthesized via the pyrolysis of urea and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF₄), which was adopted as the boron source. The aggregate of B/g-C₃N₄ nanosheets shows a porous structure since some bubbles are generated under the heat decomposition of ionic liquids. The porous structure is conducive to the exposure of more active sites. Moreover, B-doping will form some localized electronic energy levels in the band gap of g-C₃N₄, thereby extending its visible light response. As impacted by the porous structure of B/g-C₃N₄ aggregate and the narrow the band gap, the photocatalytic hydrogen generation rate (901 μmol h^-1 g^-1) is increased, almost 3 times faster than g-C₃N₄ (309 μmol h^-1 g^-1). This work proposed a simple method to prepare the aggregate of B/g-C₃N₄ nanosheets exhibiting pores under ionic liquid assistance. It can be a novel method to design porous polymer photocatalysts.