Interspecies cooperation-driven photogenerated electron transfer processes and efficient multi-pathway nitrogen removal in the g-C3N4-anammox consortia biohybrid system

Photocatalytic materials-microbial biohybrid systems pave the way for solar-driven wastewater nitrogen removal. In this study, interspecies cooperation in photogenerated electron transfer and efficient nitrogen removal mechanism in the g-C3N4-anammox consortia biohybrid system were first deciphered. The results indicated that the essential extracellular electron carriers (cytochrome c and flavin) for anammox genomes were provided by associated bacteria (BACT3 and CHLO2). This cooperation, regulated by the ArcAB system and electron transfer flavoprotein, made anammox bacteria the primary photogenerated electron sink. Furthermore, an efficient photogenerated electron harness was used to construct a reductive glycine pathway (rGlyP) in anammox bacteria inventively, which coexisted with the Wood-Ljungdahl pathway (WLP), constituting a dual-pathway carbon fixation model, rGlyP-WLP. Carbon fixation products efficiently contributed to the tricarboxylic acid cycle, while inhibiting electron diversion in anabolism. Photogenerated electrons were targeted channeled into nitrogen metabolism-available electron carriers, enhancing anammox and dissimilatory nitrate reduction to ammonium (DNRA) processes. Moreover, ammonia assimilation by the glycine cleavage system in rGlyP established an alternative ammonia removal route. Ultimately, multi-pathway nitrogen removal involving anammox, DNRA, and rGlyP achieved 100 % ammonia removal and 94.25 % total nitrogen removal efficiency. This study has expanded understanding of anammox metabolic diversity, enhancing its potential application in carbon-neutral wastewater treatment.

Efficient photocatalytic reduction of nitrate byproducts during anammox process by novel extracellular polymeric substances-embedded NH2-MIL-101(Fe) photocatalysts

Anaerobic ammonium oxidation (anammox) is an efficient nitrogen removal process; however, nitrate byproducts hampered its development. In this study, extracellular polymeric substances (EPS) were embedded into NH2-MIL-101(Fe), creating NH2-MIL-101(Fe)@EPS to reduce nitrate. Results revealed that chemical nitrate reduction efficiency of NH2-MIL-101(Fe)@EPS surpassed that of NH2-MIL-101(Fe) by 17.3 %. After adding 0.5 g/L NH2-MIL-101(Fe)@EPS within the anammox process, nitrate removal efficiency reached63.9 %, consequently elevating the total nitrogen removal efficiency to 92.4 %. 16S rRNA sequencing results elucidated the predominant role of Candidatus Brocadia within NH2-MIL-101(Fe)@EPS-anammox system. Concurrently, sufficient photogenerated electrons were transferred to microorganisms, promoting the growth of Desnitratisoma and OLB17. Additionally, photogenerated electrons activated flavin and Complex III, thereby up-regulating crucial genes involved in intra/extracellular electron transfer. Subsequently, denitrification and dissimilatory nitrate reduction to ammonium were activated to reduce nitrate. In summary, this study achieved a notable rate of photocatalytic nitrate reduction within anammox process through the NH2-MIL-101(Fe)@EPS photocatalysts.

Photocatalysis of aqueous PFOA by common catalysts of In2O3, Ga2O3, TiO2, CeO2 and CdS: influence factors and mechanistic insights

Gallium oxide (Ga₂O₃), titanium dioxide (TiO₂), cerium dioxide (CeO₂), indium oxide (In₂O₃) and cadmium sulfide (CdS) were commonly used under UV light as photocatalysis system for the pollutants' degradation. In this study, these five catalysts were applied for the photodegradation of perfluorooctanoic acid (PFOA), a well-known perfluoroalkyl substance (PFAS). As a result, the PFOA photodegradation performance was sequenced as: Ga₂O₃ > TiO₂ > CeO₂ > In₂O₃ > CdS. To further explain the photocatalysis mechanism, the effects of initial pH, photon energy and band gap were evaluated. The initial pH of 3 ± 0.2 hinders the catalytic reaction of CdS, resulting in low degradation of PFOA, while it has no significant effect on Ga₂O₃, TiO₂, CeO₂ and In₂O₃. In addition, quantum yield was sequenced as TiO₂ > CeO₂ > Ga₂O₃ > In₂O₃, which may not be the main factor determining the degradation effect. Notably, the band gap energy from large to narrow was as: Ga₂O₃ > TiO₂ > CeO₂ > In₂O₃ > CdS, which exactly matched their degradation performance.

Photo-induced synthesis of ternary Pt/rGO/COF photocatalyst with Pt nanoparticles precisely anchored on rGO for efficient visible-light-driven H2 evolution

Covalent organic frameworks (COFs) have been recognized as a new type of promising visible-light-driven photocatalysts for H₂ evolution, while it still is a key point to facilitate the separation and transfer of photoinduced charges for further enhancing their activities. In this work, we fabricated a new type of ternary Pt/rGO/COF photocatalysts with Pt cocatalyst precisely anchored on rGO serving as electron collector for largely enhanced H₂ evolution. A series of ternary hybrid materials were obtained via one-pot photoreduction of Pt⁴⁺ and GO under visible-light irradiation in a solution the same as photocatalytic H₂ evolution reaction and simultaneous self-assembling of rGO/COF heterostructure. No need isolation, the synthetic system could be further used for photocatalytic H₂ evolution reaction and the results show the H₂ evolution rate of Pt/rGO(20%)/TpPa-1-COF hybrid material is 19.59 mmol·g^-1·h^-1, 6.51 times higher than that of Pt/TpPa-1-COF. The essential role of the exclusively distributed Pt nanoparticles on rGO to the high H₂ evolution activity was confirmed by various comparisons of activity for the samples with diverse Pt distribution.

Enhanced photocatalytic CO2 reduction and 2,4-dichlorophenol degradation of TiO2 nanotubes via bi-directionally controlling electrons and holes

In this study, TiO₂ nanotubes (TiNTs) co-modified with MnO_x (Mn) and reduced-graphene-oxide (RGO) were prepared by a simple electrochemical deposition process. The photocatalytic activities for reducing CO₂ and degradating 2,4-dichlorophenol of TiNTs were enhanced after co-modification with proper amounts of MnO_x and RGO. The yields of acetic acid and formic acid of the amount-optimized TiNTs (6RGO/4Mn/TiNTs) were 36.3 ± 0.9 and 21.6 ± 0.7 mg L^-1 h^-1, which were ∼2.5 times and ∼2.2 times of bare TiNTs and the 2,4-dichlorophenol degradation efficiency of 6RGO/4Mn/TiNTs was 36.9% for 1 h, which was 21.3% higher than bare TiNTs. According to the results of photophysical and photochemical experiments, the enhanced photocatalytic activity was attributed to the greatly-elevated photogenerated charge separation via the bi-directional control mechanism of electrons and holes. The photogenerated holes could be captured by MnO_x and the transfer of photogenerated electrons could be accelerated through the RGO. In addition, the formed OH was found to act as major active species in the 2,4-dichlorophenol degradation process. The degradation paths by OH attacking was proposed by analyzing the main intermediates.