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

Plasmonic titanium nitride nanohole arrays for refractometric sensing

Group IVB metal nitrides have attracted great interest as alternative plasmonic materials. Among them, titanium nitride (TiN) stands out due to the ease of deposition and relative abundance of Ti compared to those of Zr and Hf metals. Even though they do not have Au or Ag-like plasmonic characteristics, they offer many advantages, from high mechanical stability to refractory behavior and complementary metal oxide semiconductor-compatible fabrication to tunable electrical/optical properties. In this study, we utilized reactive RF magnetron sputtering to deposit plasmonic TiN thin films. The flow rate and ratio of Ar/N2 and oxygen scavenging methods were optimized to improve the plasmonic performance of TiN thin films. The stoichiometry and structure of the TiN thin films were thoroughly investigated to assess the viability of the optimized operation procedures. To assess the plasmonic performance of TiN thin films, periodic nanohole arrays were perforated on TiN thin films by using electron beam lithography and reactive ion etching methods. The resulting TiN periodic nanohole array with varying periods was investigated by using a custom microspectroscopy setup for both reflection and transmission characteristics in various media to underline the efficacy of TiN for refractometric sensing.101111321 ; EP/Y030273/

In situ single-step reduction of bromine-intercalated graphite to covalently brominated and alkylated/brominated graphene

Developing easy and effective surface functionalization approaches has required to facilitate the processability of graphene while seeking novel application areas. Herein, an in situ single-step reductive covalent bromination of graphene has been reported for the first time. Highly brominated graphene flakes (>3% Br) were prepared by only subjecting the bromine-intercalated graphite flakes to a reduction reaction with reactive lithium naphthalide. The bromine-functionalized graphene was characterized by X-ray photoelectron spectroscopy and thermogravimetric analysis. Results revealed that Br2 molecules acted as both an intercalating agent for the graphite and a reactant for the surface functionalization of the graphene. After brominating, the remaining negative charges on the reduced graphene surface were further used for the dual surface functionalization of graphene with a long-chain alkyl group (∼1% dodecyl group addition). The functionalized graphenes were also characterized by Fourier transform infrared and Raman spectroscopy

Precision covalent chemistry for fine-size tuning of sandwiched nanoparticles between graphene nanoplatelets

The covalent functionalization of graphene for enhancing their stability, improving their electrical or optical properties, or creating hybrid structures has continued to attract extensive attention; however, a fine control of nanoparticle (NP) size between graphene layers via covalent-bridging chemistry has not yet been explored. Herein, precision covalent chemistry-assisted sandwiching of ultrasmall gold nanoparticles (US-AuNP) between graphene layers is described for the first time. Covalently interconnected graphene (CIG) nanoscaffolds with a preadjusted finely tuned graphene layer-layer distance facilitated the formation of sandwiched US-AuNPs (∼1.94 ± 0.20 nm, 422 AuNPs). The elemental composition analysis by X-ray photoelectron spectroscopy displayed an aniline group addition per ∼55 graphene carbon atoms. It provided information on covalent interconnection via amidic linkages, while Raman spectroscopy offered evidence of covalent surface functionalization and the number of graphene layers (≤2-3 layers). High-resolution transmission electron microscopy images indicated a layer-layer distance of 2.04 nm, and low-angle X-ray diffraction peaks (2θ at 24.8 and 12.5°) supported a layer-layer distance increase compared to the characteristic (002) reflection (2θ at 26.5°). Combining covalent bridging with NP synthesis may provide precise control over the metal/metal oxide NP size and arrangement between 2D layered materials, unlocking new possibilities for advanced applications in energy storage, electrochemical shielding, and membranes

Evaluating the reactivity superiority of two different single-walled carbon nanotube anions using an anhydride electrophile

Reductive chemistries have widely been used to functionalize single-walled carbon nanotubes (SWCNTs). However, the reactivity of negatively charged SWCNTs (NC-SWCNTs), prepared by different reductive chemistries, to the same electrophilic reagent has not been evaluated. Here in, the first example of the reactivity comparison of two different NC-SWCNTs towards 3-nitrophthalic anhydride is presented, and two novel functionalized SWCNTs are synthesized and characterized. The NC-SWCNTs, that are denoted as [(nBu―SWCNTn)-• Lin+] and [SWCNTn-• Lin+], are prepared via n-butyl lithium and lithium naphthalenide addition, respectively, and are reacted by 3-nitrophthalic anhydride under dry conditions. The resulting functionalized SWCNTs are characterized by Raman, UV-vis-NIR, TGA-MS, XPS, and TEM. The reactivity of [(nBu―SWCNTn)-• Lin+] towards electrophilic 3-nitrophthalic anhydride is found to be higher than [SWCNTn-• Lin+]. This is probably due to the high nucleophilic character of [(nBu―SWCNTn)-• Lin+] which bears lone pair electrons and electrondonating butyl groups

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)

Plasmonic nanometal surface energy transfer-based dual excitation biosensing of pathogens

In this assay, the simultaneous screening of foodborne bacterial pathogens, namely Escherichia coli and Salmonella typhimurium, was investigated by developing a highly specific dual-excitation biosensor which works based on plasmonic nanoparticle surface energy transfer (PSET) between aptamer capped plasmonic gold nanostructures (AuNSs) as capture probes and luminescent nanoparticles (LNPs) as signal probes labeled with complementary single-strand DNA of the utilized aptamers. For the characterization of the provided sensing probes, techniques such as UV-visible spectroscopy, dynamic light scattering, scanning electron microscopy, and circular dichroism spectroscopy were used. While CdSe/ZnS core/shell quantum dots (QDs) became excited with ultraviolet (UV) radiation at 350 nm, the light source utilized for excitation of NaYF4:Yb, Er upconverting nanoparticles (UCNPs) was near-infrared (NIR) at 980 nm, and also the signal cross-talk possibility between QDs and UCNPs was removed using the dual-excitation technique. The limit of detection (LOD) was calculated to be as low as 7.38 and 9.31 CFU mL-1 for simultaneous monitoring of E. coli and S. typhimurium in one experimental batch. The biosensor was also evaluated for detecting bacteria simultaneously in actual lake samples. The results proposed the viability of the technique for realtime sample analysis. Using numerous AuNSs and their corresponding UCNPs and QDs benefiting from distinct luminescence emission profiles, the suggested NSET-based biosensor may be utilized to simultaneously detect a wide range of analytes, posing good application prospects in various fields ranging from food safety analysis to biomedical applications

The efficacy of Staphylococcus aureus dry biomass in the detection of Cd(II) heavy metal ions

Environmental monitoring of heavy metal ions is vital due to their hazardous nature to living organisms. Among them, Cd(II) is a highly carcinogenic ion that interferes with the enzymatic reactions responsible for repairing the genetic replication errors. We have developed Staphylococcus aureus dry biomass–modified carbon paste electrodes to detect Cd(II) in solution as an alternative to widely used Hg-based electrodes. Due to their gram-positive thick peptidoglycan cell wall, heat-dried S. aureus biomass powder showed high binding capacity towards divalent cations. It was observed that S. aureus biomass immensely improved the detection capability of carbon paste. S. aureus–based biomass modified carbon paste electrode was optimized for better signals by investigating different buffer media and preconcentration times with cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) techniques. The Cd(II) biosensing performance showed promising results with the detection limit reaching 44.58 nM with a dynamic range of 100 nm to 2 µM and a preconcentration time of 15 min in phosphate-buffered saline buffer pH 6. The selectivity and interference of other divalent ions showed a low level of interference with DPASV response until the concentration of 500 nM. The work underlines the efficacy of S. aureus–based biomass in cost-effective and green detection of divalent cations of heavy metals

Microwave-promoted continuous flow synthesis of thermoplastic polyurethane-silver nanocomposites and their antimicrobial performance

Thermoplastic polyurethane-silver nanocomposites (PU-Ag NCs) have considerable potential in many medical applications due to their superior mechanical and antimicrobial properties. Herein, a microwave-promoted flow system is successfully employed for continuous in situ manufacturing of PU NCs having spherical silver nanoparticles (AgNPs) without any reducing agent at ∼40 °C in approximately 4 minutes. The main experimental parameters, including microwave power, metal salt concentration, polymer concentration, and flow rate, are optimised for the reproducible synthesis of AgNPs (∼5 nm) in the PU matrix, characterised by HRTEM-EDS and DLS analysis. XRD patterns indicate an increase in PU crystallinity with decreased particle size. Conventional heating flow synthesis at ∼50 °C or microwave-batch synthesis (MWB) at ∼44 and ∼50 °C is ineffective in preparing AgNPs, and only large AgNPs (>100 nm) are synthesised at 70 °C in the MWB reactor. PU-Ag NC films bearing small AgNPs (∼5 nm) exhibit superior antibacterial activity (>97%) against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus compared to large NPs (∼218 nm). The proposed method may manufacture other metal-polymer matrix composites

Application of nanomaterials in food quality assessment

The food industry has a significant role to play in governing local economies all over the world. This sector includes some processes such as storage of raw materials, food production, and preservation. Food processing, food quality, and safety are vital to protect public health. Thus, food safety monitoring, for example, early detection of food pathogens, food-related toxins, allergens, chemicals, and enterotoxins, is of great significance. Nanoscience-based sensing platforms have become alternatives to conventional food safety monitoring techniques. Over the past few years, scientists have designed various novel nanosensors with high sensitivity and selectivity to detect a wide variety of hazardous substances. The nanomaterials, such as carbon-based nanoparticles, plasmonic/metallic nanoparticles, and inorganic fluorescent nanomaterials, have been extensively used to develop various detection platforms over the past few decades. The surface functionalization of nanoparticles using target-specific biological agents, such as aptamers and antibodies, has contributed to improving the efficiency of those nanoparticle-based diagnostic tools. In this chapter, general structural, physicochemical, and optical features of the nanoparticles were described, and their applications in food safety monitoring were reviewed. Following this, affinity agents and fundamental sensing principles employed in developing food-related hazardous substance detection tools were elaborated based on the recent publications in the literature. Finally, we expect to pave the way for enhancing the efficiency and applicability of nanosensors in the initial sensing of food-related targets that cause a significant risk for humankind worldwide