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A critical review on the potential of nano-porous graphene materials, their key structural and physicochemical properties for applications in the areas of separation and sensing and energy storage.

This work aims to evaluate the potential of using textile waste in smart textile applications in the form of a hybrid fibre with electrical properties. The bio-based electrically conductive fibres were fabricated from waste wool and polyacrylonitrile (PAN) via wet spinning with different wool content. The control PAN and hybrid fibre produced with the highest amount of wool content (25% w/v) were coated with graphene oxide (GO) using the "brushing and drying" technique. The GO nanosheets coated control PAN and wool/PAN hybrid fibres were chemically reduced through hydrazine vapour exposure. The Fourier transform infrared spectroscopy showed the presence of both protein and nitrile peaks in the wool/PAN hybrid fibres, although the amide I and amide A groups had disappeared, due to the dissolution of wool. The morphological and structural analysis revealed effective coating and reduction of the fibres through GO nanosheets and hydrazine, respectively. The hybrid fibre showed higher electrical conductivity (~ 180 S/cm) compared to the control PAN fibres (~ 95 S/cm), confirming an effective bonding between the hydroxyl and carboxylic groups of the GO sheets and the amino groups of wool evidenced by chemical analysis. Hence, the graphene oxide incorporated wool/PAN hybrid fibres may provide a promising solution for eco-friendly smart textile applications.

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The concentration and chemical state of nitrogen represent critical factors to control the band-gap narrowing and the enhancement of visible light harvesting in nitrogen-doped titanium dioxide. In this study, photocatalytic TiO2–N nanoporous structures were fabricated by the electrochemical anodization of titanium nitride sputtered films. Doping was straightforwardly obtained by oxidizing as-sputtered titanium nitride films containing N-metal bonds varying from 7.3 to 18.5% in the Ti matrix. Severe morphological variations into the as-anodized substrates were registered at different nitrogen concentrations and studied by small-angle X-ray scattering. Titanium nitride films with minimum N content of 6.2 atom % N led to a quasi-nanotubular geometry, whereas an increase in N concentration up to 23.8 atom % determined an inhomogeneous, polydispersed distribution of nanotube apertures. The chemical state of nitrogen in the TiO2 matrix was investigated by X-ray photoelectron spectroscopy depth profile analysis and correlated to the photocatalytic performance. The presence of Ti–N and β-Ti substitutional bonds, as well as Ti-oxynitride species was revealed by the analysis of N 1s X-ray photoelectron spectroscopy high-resolution spectra. The minimum N content of 4.1 atom % in the TiO2–N corresponded to the lowest Ti-oxynitride ratio of 13.5%. The relative variation of N-metal bonds was correlated to the visible light sensitization, and the highest Ti–N/Ti oxynitride ratio of 3.3 was attributed to the lowest band gap of 2.7 eV and associated with a 3-fold increase in the degradation of organic dye. Further increase of N doping led to a dramatic drop of Ti–N/Ti oxynitride ratio, from 3.3 to 0.4, which resulted in a loss of photocatalytic activity. The impact of the chemical state of nitrogen toward efficient doping of TiO2 nanotubes is demonstrated with a direct correlation to N loading and a strategy to optimize these factors based on a simple, rapid synthesis from titanium nitride.

The microstructure morphology and physicochemical properties of NPG materials have been exploited in sieving, sensing, energy harvesting, and catalysis applications. [5][6][7][8] The morphological properties of NPG materials in terms of sizes, densities distributions, and depths, as well as geometrical shapes ranging across single-, or few-layer graphene sheets, have solely relied on the applied perforation methodologies. [4] The state-of-art of perforation technology for 2D nanoporous nanostructures can be classified into either stochastic/guided-etching or guidedgrowth techniques based on the achieved pore-size and surface-pore distribution ranges. [4,9] Cylindrical pores with narrow size distribution and high-density surface distributions are still desired for engineering porous graphene-derived nanoassemblies. The capability to induce such architectural features across graphene will therefore enhance their potential in a variety of nanotechnologies based on separation and catalytic processes. [9] One promising perforation methodology is photocatalytic perforation, a particulate-assisted etching protocol. The proof of concept was demonstrated via arranging nanocatalysts over graphene surfaces to accelerate the oxidation upon the photo-irradiation process with ultraviolet (UV)-visible stimuli. Consequently, the achieved One of the bottlenecks in realizing the potential of nanoporous graphene assemblies is the difficulty of engineering narrow pores and high surface density distributions, with a nanometer resolution across multilayer graphene assemblies using scalable approaches. Here, the authors develop a photocatalyzed perforation protocol to incorporate nanopores across modified graphene assemblies via localizing the oxidation during the photoexcitation process between photo-initiators and graphitic assemblies under the ultraviolet-visible stimuli. Nanopores are engineered across the graphene nanostructures with a pore size range varying from 20 to 100 nm depending on the irradiation duration, as well as tunable densities of 10 1 -10 3 pores/µm 2 on the same order of the loaded nanocatalysts to the graphene surfaces. By finetuning the graphene chemistry and the physical dimension of photo-initiators, as well as their concentrations across graphitic planes used during the perforation, the diameter, and the density distributions of generated nanopores across graphene, can be rationally confined, avoiding merging between pores during the nanopore formation. These porosity parameters engineered across graphene nanosieves are in the same order obtained by other nanolithographic techniques. Plus, this sustainable route may boost the potential of porous graphene assemblies in energy-efficient nanotechnologies based on separation and catalytic processes.

Nanoparticles of varying formats and functionalities have been shown to modify and enhance plant growth and development. Nanoparticles may also be used to improve crop production and performance, particularly under adverse environmental conditions such as drought. Nanoparticles composed of silicon dioxide, especially those that are mesoporous (mesoporous silica nanoparticles; MSNs), have been shown to be taken up by plants; yet their potential to improve tolerance to abiotic stress has not been thoroughly examined. In this study, a range of concentrations of MSNs (0-5000 mg L −1 ) were used to determine their effects, in vitro, on Arabidopsis plants grown under polyethylene glycol (PEG)-simulated drought conditions. Treatment of seeds with MSNs during PEG-simulated drought resulted in higher seed germination and then greater primary root length. However, at the highest tested concentration of 5000 mg L −1 , reduced germination was found when seeds were subjected to drought stress. At the optimal concentration of 1500 mg L −1 , plants treated with MSNs under non-stressed conditions showed significant increases in root length, number of lateral roots, leaf area and shoot biomass. These findings suggest that MSNs can be used to stimulate plant growth and drought stress tolerance.

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