A facile method of activating graphitic carbon nitride for enhanced photocatalytic activity

Augmented photocatalytic degradation of Acetaminophen using hydrothermally treated g-C3N4 and persulfate under LED irradiation

Photocatalytic degradation of organic pollutants in water using graphitic carbon nitride and persulfate under visible light (g-C₃N₄/PS system) has been studied. Here, we demonstrate augmentation of photocatalytic degradation of Acetaminophen (AAP) using hydrothermally treated g-C₃N₄ and PS under 400 nm LED irradiation (HT-g-C₃N₄/PS system). A pseudo-first-order rate constant (k_obs, 0.328 min^-1) for degradation of AAP using HT-g-C₃N₄/PS system was determined to be 15 times higher compared to g-C₃N₄/PS system (k_obs, 0.022 min^-1). HT-g-C₃N₄ showed a higher surface area (81 m²/g) than g-C₃N₄ (21 m²/g). Photocurrent response for HT-g-C₃N₄ was higher (1.5 times) than g-C₃N₄. Moreover, Nyquist plot semicircle for HT-g-C₃N₄ was smaller compared to g-C₃N₄. These results confirm effective photoelectron-hole separation and charge-transfer in HT-g-C₃N₄ compared to g-C₃N₄. AAP degradation using HT-g-C₃N₄/PS system was significantly inhibited with O2.- and h⁺ scavengers compared to ¹O_2,SO4.- and HO. scavengers. ESR results revealed O2.- formation in HT-g-C₃N₄/PS system. Moreover, photocurrent measurements reveal AAP oxidation by h⁺ of HT-g-C₃N₄ was effective than g-C₃N₄. HT-g-C₃N₄ was reused for five cycles in HT-g-C₃N₄/PS system. Augmented photocatalytic degradation of AAP by HT-g-C₃N₄/PS system compared to g-C₃N₄/PS is attributed to effective photoelectron hole separation of HT-g-C₃N₄ that generates O2.- and h⁺ for oxidation of pollutant. Importantly, electrical energy per order (E_EO) was 7.2 kWh m^-3 order^-1. k_obs for degradation of AAP in simulated groundwater and tap water were determined as 0.029 and 0.035 min^-1, respectively. Degradation intermediates of AAP were proposed. AAP ecotoxicity against marine bacteria Aliivibrio fischeri was completely removed after treatment by HT-g-C₃N₄/PS system.

Efficient degradation of organic pollutants by activated peroxymonosulfate over TiO2@C decorated Mg-Fe layered double oxides: Degradation pathways and mechanism

To activate peroxymonosulfate (PMS) is an efficient way for decomposition of non-biodegradable organic pollutants. Herein, Mg-Fe layered double oxides decorated with Ti₃C₂ MXene-derived TiO₂@C (T/LDOs) were fabricated to efficiently activate PMS for the degradation of Rhodamine B (RhB), acid red 1 (AR1), methylene blue (MB), and tetracycline hydrochloride (TC). The T/LDOs catalyst could decompose 95.8% of RhB, 94.8% of AR1, 84.9% of MB within 10 min, and 82.4% of TC within 60 min. The degradation rate constant of RhB in the optimal T/LDOs/PMS system was approximately 2.5 and 15.7 times higher than that in the Mg-Fe LDOs/PMS system and Mg-Fe LDH/PMS system, respectively. Importantly, the T/LDOs exhibited a wide working pH range (3.1-11.0) and high stability with low metal ions leaching, indicating its potential practical applications. Quenching experiments and electronic spin resonance results confirmed that both ^•O₂^- and ¹O₂ were the dominant active species in the T/LDOs/PMS system. In addition, the possible degradation pathway of RhB in the 5%-T/LDOs/PMS system was proposed. Finally, the catalytic mechanism study revealed that the T/LDOs with abundant surface hydroxyl groups and a certain amount of TiO₂@C facilitated the electron transfer between ≡Fe^(Ⅲ)‒OH complex and HSO₅^-, boosting the generation of ^•O₂^- and ¹O₂. This study provides an insight into exploiting highly efficient catalysts for PMS activation towards the degradation of organic pollutants.

Rapid visible-light degradation of EE2 and its estrogenicity in hospital wastewater by crystalline promoted g-C3N4

Metal-free, chemically activated crystalline graphitic carbon nitride (g-C₃N₄) nanorods with enhanced visible-light photoactivity demonstrated rapid photodegradation of 17α-ethinylestradiol (EE2) in water and real hospital wastewater. Pure g-C₃N₄ and another three crystalline promoted g-C₃N₄ photocatalysts developed by hydrothermal method were characterized by, High-Resolution Transmission Electron Microscopy (HRTEM), X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Photoluminescence (PL), Electron spin resonance (ESR), X-ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Spectroscopy (DRS). Hydrothermal-based chemical activation did not alter the crystal structure, functional group or surface morphology, but it enhanced the specific surface area of activated g-C₃N₄ due to intralayer delamination and depolymerization of g-C₃N₄. Compared to pure g-C₃N₄, the activated g-C₃N₄-3 demonstrated efficient degradation of EE2 (<30 min, 3 mg/l) by visible wavelengths of the solar spectrum. This work provides advanced insight into the construction of heterojunction visible-light photocatalysts and production of O₂^- via reduction of O₂ with photogenerated electrons. Proposed and derived mechanism for photodegradation of EE2 by g-C₃N₄-3 using gas chromatography-mass spectrometry (GCMS). Yeast Estrogen Screen (YES) was performed to evaluate the estrogenicity of treated water samples. Efficient removal of EE2 estrogenic activity (<45 min, 3 mg/l) was achieved using the visible light-activated g-C₃N₄. Estrogenicity removal rate corresponded well with EE2-degradation rate.

Light-driven, heterogeneous organocatalysts for C-C bond formation toward valuable perfluoroalkylated intermediates

The favorable exploitation of carbon nitride (CN) materials in photocatalysis for organic synthesis requires the appropriate fine-tuning of the CN structure. Here, we present a deep investigation of the structure/activity relationship of CN in the photocatalytic perfluoroalkylation of organic compounds. Four types of CN bearing subtle structural differences were studied via conventional characterization techniques and innovative nuclear magnetic resonance (NMR) experiments, correlating the different structures with the fundamental mechanistic nexus and especially highlighting the importance of the halogen bond strength between the reagent and the catalyst surface. The optimum catalyst exhibited an excellent performance, with a very wide reaction scope, and could prominently trigger the model reaction using natural sunlight. The work lays a platform for establishing a new approach in the development of heterogeneous photocatalysts for organic synthesis related to medical, agricultural, and material chemistry.

Biogenic Synthesis of Graphitic Carbon Nitride for Photocatalytic Degradation of Organic Dyes

A simple approach of template growth of graphitic-carbon nitride (g-CN), a polymeric unit consisting of C, N, O, and H elements derived from extracts of green plant Aloe vera, which are rich in several chemical constituents, has been successfully experimented in this work. Comparing several other methods used for synthesizing g-CN involving a large amount of toxic components, here, we propose the simplest route economically and environmentally highly viable for near future. Green plants are highly rich in natural carbon and nitrogen compounds, such as acemannan, glucose, aloin, protein, etc. Way before g-CN research, many carbon-based materials have been synthesized for multifunctional properties, but g-CN has much benefit over them due to the presence of elements such as C, N, O, and H, thus making it electron-rich. Multifunctional properties of graphitic-carbon nitride interface bonding as a supercapacitor or as a metal-free catalyst thus help degrade dyes. Violet-blue broad band emission was even noticed when excited at 240 nm via C-C bonding (π-π* transition) in the absorption band with an extinction coefficient of ∼10⁴ M^-1 cm^-1. With our research, we want to pave new ways of synthesizing such materials present in our nature in a biological form, which can protect our environment, thus causing less harm to mankind.

Pristine and Graphene-Quantum-Dots-Decorated Spinel Nickel Aluminate for Water Remediation from Dyes and Toxic Pollutants

Pristine nickel aluminate and the one decorated with graphene quantum dots were prepared via a cost-effective co-precipitation method. Both were fully characterized by thermogravimetry (TGA), differential scanning calorimetry (DSC), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), and UV–Vis techniques. The photocatalytic activity of nickel aluminate under simulated solar light irradiation was demonstrated towards potential pollutants, including a series of dyes (rhodamine B, quinoline yellow, eriochrome black T, methylene blue), toxic phenol and fungicide (thiram). Further profound enhancement of the photocatalytic activity of nickel aluminate was achieved after its decoration with graphene quantum dots. The mechanism of the photocatalytic degradation in the presence of the NiAl2O4/graphene quantum dots (GQDs) composite was investigated; hydroxyl radicals were found to play the leading role. This work offers new insight into the application of the conjunction of the inorganic spinel and the carbon nanostructure (i.e., GQDs), but also provides a simple and highly efficient route for potential water remediation from common pollutants, including dyes and colorless harmful substances.

Facile fabrication of metal-free urchin-like g-C3N4 with superior photocatalytic activity

Spherical urchin-like graphitic carbon nitride nanoparticles were fabricated and exhibited almost 12 times higher activity during RhB photodegradation.