Functionalized graphitic carbon nitrides for environmental and sensing applications

Graphitic carbon nitride (g-C3N4) is a metal-free semiconductor that has been widely regarded as a promising candidate for sustainable energy production or storage. In recent years, g-C3N4 has become the center of attention by virtue of its impressive properties, such as being inexpensive, easily fabricable, nontoxic, highly stable, and environment friendly. Herein, the recent research developments related to g-C3N4 are outlined, which sheds light on its future prospective. Various synthetic methods and their impact on the properties of g-C3N4 are detailed, along with discussion on frequently used characterization methods. Different approaches for g-C3N4 surface functionalization, mainly categorized under covalent and noncovalent strategies, are outlined. Moreover, the processing methods of g-C3N4, such as g-C3N4-based thin films, hierarchical, and hybrid structures, are explored. Next, compared with the extensively studied energy-related applications of the modified g-C(3)N(4)s, relatively less-examined areas, such as environmental and sensing, are presented. By highlighting the strong potential of these materials and the existing research gaps, new researchers are encouraged to produce functional g-C3N4-based materials using diverse surface modification and processing routes.UK Research & Innovation (UKRI) Engineering & Physical Sciences Research Council (EPSRC) ; Royal Society-Newton Advanced Fellowship Grant ; Leverhulme Trus

A handbook for graphitic carbon nitrides: revisiting the thermal synthesis and characterization towards experimental standardization

Graphitic carbon nitrides (g-C3N4s) have continued to attract attention as metal-free, low-cost semiconductor catalysts. Herein, a systematic synthesis and characterization of g-C3N4s prepared using four conventional precursors (urea (U), dicyandiamide (DCDA), semicarbazide hydrochloride (SC-HCl), and thiosemicarbazide (TSC)) and an unexplored one (thiosemicarbazide hydrochloride (TSC-HCl)) is presented. Equal synthesis conditions (e.g. heating and cooling rates, temperature, atmosphere, reactor type/volume etc) mitigated the experimental error, offering fair comparability for a library of g-C3N4s. The highest g-C3N4 amount per mole of the precursor was obtained for D-C3N4 (∼37.85 g), while the lowest was for S-C3N4 (∼0.78 g). HCl addition to TSC increased the g-C3N4 production yield (∼5-fold) and the oxygen content (T-C3N4∼3.17% versus TCl-C3N4∼3.80%); however, it had a negligible effect on the level of sulphur doping (T-C3N4∼0.52% versus TCl-C3N4∼0.45%). S-C3N4 was the darkest in color (reddish brown), and the band gap energies were S-C3N4(2.00 eV) < T-C3N4(2.74 eV) < TCl-C3N4(2.83 eV) ≤ D-C3N4(2.84 eV) < U-C3N4(2.97 eV). The experimentally derived conduction band position of S-C3N4(−0.01 eV) was closer to the Fermi energy level than the others, attributable to high oxygen atom doping (∼5.11%). S-C3N4 displayed the smallest crystallite size (∼3.599 nm by XRD) but the largest interlayer distance (∼0.3269 nm). Furthermore, BET surface areas were 138.52 (U-C3N4), 22.24 (D-C3N4), 18.63 (T-C3N4), 10.51 (TCl-C3N4), and 9.31 m2 g−1 (S-C3N4). For the first time, this comprehensive handbook gives a glimpse of a researcher planning g-C3N4-based research. It also introduces a novel oxygen-sulphur co-doped g-C3N4 (TCl-C3N4) as a new halogen-free catalyst with a relatively high production yield per mole of precursor (∼24.09 g)

Non-destructive covalent surface alkylation of graphitic carbon nitride for enhanced photocatalytic dye degradation in water

Graphitic carbon nitride (g-CN) is a promising material for various applications due to its unique electronic, optical, and photocatalytic properties, tunable by surface modifications. Herein, a novel and straightforward approach to the covalent addition of low molecular weight polyethylene glycol (PEG550) to g-CNs surface following non-destructive chemistry benefiting from simultaneous activation of hydroxyl and free-amine surface groups by a weak base, potassium carbonate, is for the first time described. The resulting g-CN-PEG550 exhibits almost two-fold enhanced water solubility due to 1 PEG550 chain addition for every ∼ 128 g-CN atoms, detected by thermogravimetric analysis. Complementary X-ray photoelectron spectroscopy elemental analysis of the isolated g-CN-PEG550 displays an increased C─O chemical environment attributed to the covalent addition of carbon- and oxygen-rich PEG550 to the g-CN surface. The g-CN-PEG550 photocatalyst performs 2.5-fold better in degrading rhodamine B due to its enhanced light absorption, improved water-dispersibility, and the efficient separation of photogenerated electron-hole pairs compared to the as-prepared g-CN. The study underscores the potential use of covalently PEGylated oxygen-rich g-CNs in photocatalytic applications

A microwave-powered continuous fluidic system for polymer nanocomposite manufacturing: a proof-of-concept study

Continuous manufacturing of pure nanocrystals with a narrow size distribution in a polymer matrix is very challenging, although it is highly crucial to get their full potential for advanced applications. A long-lasting nanocomposite (NC) manufacturing challenge is, for the first time, overcome by a microwave-powered fluidic system (MWFS). The effect of microwave power (MWP), flow rate, and the concentration of the reagents are systematically studied. The nylon-6 NC bearing evenly distributed silver nanoparticles (AgNPs) with a mean size of ∼2.59 ± 0.639 nm is manufactured continuously in ∼2 min at ∼50-55 °C using a green solvent, formic acid. The AgNP size becomes smaller when increasing the polymer concentration gradually. Small NPs with a narrow size distribution are produced at high MWP (40 W), but large ones with a broad size distribution at low MWP (10 W). The nylon-6 crystallinity is NP size-dependent, and the γ-phase (pseudo-hexagonal crystal) is dominant in the presence of small NPs as against the large counterparts. Given the small-sized AgNPs in the MWF-manufactured NCs, the antibacterial activity tests with Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa show superior activity compared to that of the large AgNP-bearing (∼50 nm) NCs produced in a conventional heating fluidic system. The proposed MWFS can manufacture other added-value NCs continuously

Microwave-promoted continuous flow systems in nanoparticle synthesis-A perspective

Microwave-promoted continuous flow systems have emerged as a game-changer in nanoparticle synthesis. Owing to the excellent compatibility between fast, sustainable microwave heating and one-step, efficient flow chemistry, this promising technology is meant to enhance the synthetic abilities of nanoscientists. This Perspective aims to present a panoramic view of the state of the art in this field. Additionally, the effect of various microwave and flow parameters on the properties of nanoparticles is discussed along with a comparative glance at the features that make flow reactors more practical and sustainable than their batch counterparts. The overview has also analyzed various microwave continuous flow reactors available in the literature, with an acute emphasis on the nanosynthesis route and design features. Moreover, a discussion on the numerical modeling of microwave flow systems has been made a part of this perspective to reiterate its significance and encourage research in this domain. The Perspective also briefly comments on existing challenges and future prospects of this technology