Porous visible light-responsive Fe3+-doped carbon nitride for efficient degradation of sulfadiazine

Fabrication of Fe-BTC on aramid fabrics for repeated degradation of isoproturon

Catalytic degradation is a promising and ideal technology in environmental remediation. Among them, catalytic oxidation and photocatalysis respectively based on catalysts and photocatalysts both trigger broad interests because of their high removal activity. However, the reusability of the powder catalysts still faces substantial challenges. Here, a simple strategy is proposed to load Fe-BTC catalyst on aramid fabrics (AF) to construct Fe-BTC MOF @ aramid fabric (Fe-BTC@AF) composite materials with layer-by-layer in situ self-assembly methods. The experimental results illustrated that 98% isoproturon could be removed by Fe-BTC@AF₂₀ with oxidant H₂O₂, while the single Fe-BTC@AF₂₀ could photo-degrade 99% isoproturon within 7 h. Meanwhile, it could sustain a high degradation rate of more than 80%, even if it had gone through 5 degradation cycles. Thus, the Fe-BTC@AF composite has a significant advantage in the recycling ability for degradation of isoproturon, which will have potential applications in the efficient removal of organic contaminants in water.

Noble metal-free doped graphitic carbon nitride (g-C3N4) for efficient photodegradation of antibiotics: progress, limitations, and future directions

Graphitic carbon nitride (g-C₃N₄) is well recognised as one of the most promising materials for photocatalytic activities such as environmental remediation via organic pollution elimination. New methods of nanoscale structure design introduce tunable electrical characteristics and broaden their use as visible light-induced photocatalysts. This paper summarises the most recent developments in the design of g-C₃N₄ with element doping. Various methods of introducing metal and nonmetal elements into g-C₃N₄ have been investigated in order to simultaneously tune the material's textural and electronic properties to improve its response to the entire visible light range, facilitate charge separation, and extend charge carrier lifetime. The degradation of antibiotics is one of the application domains of such doped g-C₃N₄. We expect that this research will provide fresh insights into clear design methods for efficient photocatalysts that will solve environmental challenges in a sustainable manner. Finally, the problems and potential associated with g-C₃N₄-based nanomaterials are discussed. This review is expected to encourage the ongoing development of g-C₃N₄-based materials for greater efficiency in photocatalytic antibiotic degradation.

Ex_g-C3N4 as a novel fluorescent probe for sensitive detecting ClO- in water samples with portable test strip

Excessive hypochlorite (ClO^-) is easy to form residues in water, which will seriously endanger human health and environmental pollution. Therefore, it is essential to develop a sensitive fluorescent sensor to detect ClO^- in water. Herein, a simple and economical fluorescent probe for the detection of ClO^- was designed by highly exfoliated graphite-like carbon nitride (Ex_g-C₃N₄). The results showed that Ex_g-C₃N₄ had obvious fluorescence quenching effect on ClO^- with high selectivity and anti-interference ability, which was feasible for making probes for detecting ClO^- in water. Sensing experiments showed that the Ex_g-C₃N₄ probe had the detection limit of 5.56 nM while the detection range was 0-62 mM in water. Moreover, the fast response time of Ex_g-C₃N₄ was less than 30 s, illustrating the superior sensitivity. Besides, the fluorescence sensing experiment was carried out in various liquid conditions, which demonstrated that Ex_g-C₃N₄ probe had outstanding detecting application in natural environment. A portable fluorescent test strip for rapid detecting ClO^- was successfully developed. The response of the probe on test strip towards ClO^- was investigated, and the detection limit (0.1 μM) is low enough to meet the safety requirements in tap water. Furthermore, the quenching mechanism of Ex_g-C₃N₄ probe was also discussed.

Dynamic control of pentachlorophenol photodegradation process using P25/PDA/BiOBr through regulation of photo-induced active substances and chemiluminescence

Photodegradation is a new approach for the removal of pentachlorophenol (PCP). Photooxidation degradation (using hydroxyl radicals) exhibits better performance to remove PCP than photoreduction degradation, but the former will lead to an increase in the production of toxic by-products such as tetrachloro-1,4-benzoquinone (TCBQ). Thus, a new strategy is required to enhance PCP photodegradation and simultaneously inhibit toxic intermediates production. Herein, TiO₂ (P25)/polydopamine (PDA)/BiOBr was synthesized and used to photodegrade PCP. Based on the relative position of the CB and VB of P25 and BiOBr, and PDA as an electron transfer mediator, a high number of holes, electrons, and superoxide anions were produced instead of hydroxyl radicals. The photocatalytic activity of P25/PDA/BiOBr exhibited the best performance among as-prepared samples, reaching a k_(pcp) value of 0.4 min^-1 (20 μM PCP) under UV light irradiation within 10 min. According to chemiluminescence and acute toxicity assays, relative to P25, the toxic intermediates of TCBQ and trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) generation was greatly reduced over P25/PDA/BiOBr, with a lack of toxic product generation during PCP photodegradation process. These findings provide an alternative strategy to achieve greener and more efficient organic pollutant photodegradation.

Carbon nitride-based photocatalysts for the mitigation of water pollution engendered by pharmaceutical compounds

In recent decades, the destructive impact of active pharmaceutical ingredients (API) present in surface and drinking water on aquatic and terrestrial life forms becomes a major concern of researchers. API like diclofenac (DCF), carbamazepine (CBZ), tetracycline (TC), and sulfamethoxazole (SME) found in water bodies cause antimicrobial resistance and are potent carcinogens and endocrine disruptors. Conventional wastewater treatment methods possess some drawbacks and were found to be insufficient for the effective removal of APIs. Visible light-assisted semiconductor photocatalysis has become an alternative choice for tackling this worse scenario. Graphitic carbon nitride, a metal-free visible light active semiconductor photocatalyst is an emerging hotspot nanomaterial whose practical utility in water purification is widely recognized. This review comes up with an insightful outlook on the panorama of recent progress in the field of g-C₃N₄-assisted photocatalytic systems for the eradication of APIs. In addition, the review summarizes various strategies adopted for the broad-spectrum utilization of visible light and the enhancement of charge separation of pristine g-C₃N₄. The mechanistic pathways followed by different pharmaceuticals during their photocatalytic degradation process were also briefly discussed.

Enhanced Fenton-like degradation of sulfadiazine by single atom iron materials fixed on nitrogen-doped porous carbon

The use of single-atom iron catalysts in heterogeneous Fenton-like reactions has demonstrated tremendous potential for antibiotic wastewater treatment. In this study, single-atom iron fixed on nitrogen-doped porous carbon materials (Fe-ISAs@CN) was synthesised using a metal organic framework (MOF) as a precursor. Fe-ISAs@CN was applied as a heterogeneous Fenton catalyst to activate H₂O₂ for the degradation of sulfadiazine (SDZ) in an aqueous solution. The physical and chemical properties of Fe-ISAs@CN were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rotating disk electrode (RDE) measurements. The results of our degradation experiments indicated that Fe-ISAs@CN exhibited remarkable activity and stability for the degradation of SDZ over a wide pH range; even after five cycles, Fe-ISAs@CN retained a high catalytic efficiency (>80%). The 5,5-dimethyl-1-oxaporphyrin-n-oxide (DMPO)-X signal captured by electron paramagnetic resonance (EPR) spectroscopy indicated that a large amount of hydroxyl radicals (OH) was produced in the reaction system. Quench tests indicated that the OH was the main active substance in the degradation of SDZ. The degradation products of the reaction were analysed by High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS), and possible degradation pathways for the SDZ degradation were proposed.

The improved photocatalytic activity of highly expanded MoS2 under visible light emitting diodes

Photocatalytic degradation is a promising method to remove organic pollutants from water. Photocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2 nanomaterials have gained tremendous popularity. This is due to their narrow band gap and high visible light absorption. Herein, a MoS2 photocatalyst with highly expanded interlayer spaces of 1.51 nm was synthesized in the presence of Pluronic F-127 as a template by a facile one-pot hydrothermal method. This expanded MoS2 (MF-1) managed to photodegrade 98% (2.62 × 10-2 min-1) of methylene blue (MB) dye under irradiation of 1 W visible light-emitting diode (LED) white light. The dominant performance of MF-1 is attributed to the highly expanded interlayer spacing, which exposed more active edge sites. Moreover, the formation of surface defects such as surface cracks and sulfur vacancies (Sv) facilitates the adsorption capacity and in situ generation of reactive oxygen species (ROS). The dominant ROS responsible for the photodegradation of MB is superoxide radical (˙O2 -). The photocatalyst shows good recyclability without deterioration even after five consecutive cycles.

Novel siligraphene/g-C3N4 composites with enhanced visible light photocatalytic degradations of dyes and drugs

In this research, a novel graphene-like SiC (siligraphene) was synthesized using a natural precursor and used to improve the photocatalytic activity of g-C₃N₄. The synthesized siligraphene has shown an excellent photocatalytic property due to its low band-gap and graphene-like structure which increases the electron transfer and reduces the electron-hole recombination rate and can improve the photocatalytic activity. Also, the positive charged Si atoms in siligraphene structure can adsorb oxygen to produce radicals that can promote the oxidation reaction. However, commercial β-SiC has exhibited very poor photocatalytic properties. As we know, g-C₃N₄ is a potential material for photocatalytic applications. Here, the novel siligraphene/g-C₃N₄ composites were successfully synthesized to enhance the photocatalytic properties of g-C₃N₄ in the degradation of model dyes (Congo red, Methyl red, and Methyl orange) and model drugs (Acetaminophen and Tetracycline) under visible light irradiation. Results show that siligraphene/g-C₃N₄ composite exhibits much better photocatalytic properties than pure g-C₃N_4. This enhanced photocatalytic properties can be justified by the enlarged surface area, suitable band gap, excellent electron properties, appropriate surface charge, and efficient migration of electron in siligraphene/g-C₃N₄ composite.