Comparative Effects of Graphitic Carbon Nitride Precursors on the Photocatalytic Degradation of Pyrene

Pyrene is a ubiquitous, persistent, and mutagenic pollutant that belongs to the polycyclic aromatic hydrocarbons. Graphitic carbon nitride (g-C3N4) has emerged as a promising photocatalyst for degradation of various pollutants in water and wastewater treatment due to its unique band structure and excellent physiochemical stability. This paper presents the comparative study of composites g-C3N4 from various combinations of precursors using thermal polycondensation at 600 °C. Comparative experiments revealed that the preparation conditions of both precursors and the mass ratios of precursor influenced the overall performance of photocatalyst during photocatalytic degradation of pyrene. Experimental results indicated that the best performance of composites g-C3N4t photocatalyst was prepared from a wet mixture of dicyandiamide and guanidine carbonate precursors at a mass ratio of 1:1 with 43.9 % pyrene degradation under visible light irradiation for 240 mins. The reusability of the best g-C3N4 composites for the photocatalytic degradation of pyrene was also investigated. It was found that the prepared photocatalyst was stable up to five cycles of photocatalysis. Meanwhile, holes (h+) and hydroxyl radicals (·OH) were identified as the primary and secondary dominant reactive species in the photocatalytic degradation through scavenging trapping experiments.

Rhizodegradation of Pyrene by a Non-pathogenic Klebsiella pneumoniae Isolate Applied With Tagetes erecta L. and Changes in the Rhizobacterial Community

The non-clinical Klebsiella pneumoniae variants, isolated from different environments, are now well acknowledged for their role in plant-growth promotion and biodegradation of pollutants. In the present study, a non-clinical environmental isolate K. pneumoniae AWD5 is being described for rhizoremediation of pyrene, applied through the rhizosphere of an ornamental plant, Tagetes erecta L (marigold). The non-pathogenic nature of AWD5 was established using an in vivo mouse model experiment, where AWD5 was unable to cause lung infection in tested mice. Degradation of pyrene, in the presence of succinate as co-substrate, was observed to be 87.5% by AWD5, after 21 days of incubation in minimal (Bushnell–Hass) medium in vitro conditions. Consequently, the bacterial inoculation through the rhizosphere of T. erecta L. plants resulted in 68.61% degradation of pyrene, which was significantly higher than control soil. Inoculation of AWD5 also improved plant growth and exhibited an increase in root length (14.64%), dry root weight (80.56%), shoot length (3.26%), and dry shoot weight (45.35%) after 60 days of incubation. T. erecta L., an ornamental plant, was also found to be suitable for bioremediation of pyrene. The effect of AWD5 application, and rhizoremediation process, on rhizosphere bacterial diversity and community structure has been studied using the metagenomic analysis of the 16S (V3–V4) region of rRNA. 37 bacterial phyla constituted the core microbiome, which was dominated by Proteobacteria followed by Actinobacteria, Actinobacteria, and Planctomycetes for all the treatments. AWD5 inoculation enhanced the relative abundance of Firmicutes and Acidobacteria as compared with other treatments. Genus Kaistobacter and Verrucomicrobia were found to be an abundant indigenous population in pyrene-spiked soils. Bacterial richness and diversity were analyzed using the Shannon–Wiener (H) index. A lower diversity index was observed in pyrene-spiked soils. Canonical correspondence analysis (CCA) showed a possible linkage with plant growth attributes and available nitrogen content that influences diversity and abundance of the bacterial community.