Unusual hygroscopic nature of nanodiamonds in comparison with well-known porous materials

Transparent Colloids of Detonation Nanodiamond: Physical, Chemical and Biological Properties

Aqueous suspensions (colloids) containing detonation nano-diamond (DND) feature in most applications of DND and are an indispensable stage of its production; therefore, the interaction of DND with water is actively studied. However, insufficient attention has been paid to the unique physico-chemical and biological properties of transparent colloids with low DND content (≤0.1%), which are the subject of this review. Thus, such colloids possess giant dielectric permittivity which shows peculiar temperature dependence, as well as quasi-periodic fluctuations during slow evaporation or dilution. In these colloids, DND interacts with water and air to form cottonwool-like fibers comprising living micro-organisms (fungi and bacteria) and DND particles, with elevated nitrogen content due to fixation of atmospheric N2. Prolonged contact between these solutions and air lead to the formation of ammonium nitrate, sometimes forming macroscopic crystals. The latter was also formed during prolonged oxidation of fungi in aqueous DND colloids. The possible mechanism of N2 fixation is discussed, which can be attributable to the high reactivity of DND.

The role of nanoparticle charge in crystallization kinetics and ice adhesion strength for dispersions of detonation nanodiamonds

According to the classical nucleation theory, the presence of solid particles in a liquid should facilitate its heterogeneous nucleation upon supercooling. Here, we have analysed the behaviour of aqueous dispersions of detonation diamond nanoparticles (DND) with different signs of the surface charge in supercooled conditions and the frozen state. The behaviours of the diamond nanoparticles with a typical size of 4.5 nm were compared with each other and with deionized water in ice nucleation and ice shear experiments. The presented experimental data and analysis allowed the description of the significant increase in the freezing delay times for positively charged nanoparticles and the sharp decrease for negatively charged ones in comparison to deionized water, based on the peculiarities of the water structure around the nanoparticles and in the vicinity of a superhydrophobic surface. In addition, this approach has allowed the successful explanation of the difference in the practical work of adhesion for deionized water and dispersions of DND with different particle charges.

A high-resolution study of PM2.5 accumulation inside leaves in leaf stomata compared with non-stomatal areas using three-dimensional X-ray microscopy

Plant leaves retain atmospheric particulate matter (PM) on their surfaces, helping PM removal and risk reduction of respiratory tract infection. Several processes (deposition, resuspension, rainfall removal) can influence the PM accumulation on leaves and different leaf microstructures (e.g., trichomes, epicuticular waxes) can also be involved in retaining PM. However, the accumulation and distribution of PM on leaves, particularly at the stomata, are unclear, and the lack of characterization methods limits our understanding of this process. Thus, in this study, we aimed to explore the pathway through which PM_2.5 (aerodynamic diameter ≤ 2.5 μm) enters plant leaves, and the penetration depth of PM_2.5 along the entry route. Here, an indoor experiment using diamond powder as a tracer to simulate PM_2.5 deposition on leaves was carried out. Then, the treated and non-treated leaves were scanned by using three-dimensional (3D) X-ray microscopy. Next, the grayscale value of the scanned images was used to compare PM_2.5 accumulation in stomatal and non-stomatal areas of the treated and non-treated leaves, respectively. Finally, a total PM_2.5 volume from the abaxial epidermis was calculated. The results showed that, first, a large amount of PM_2.5 accumulates within leaf stomata, whereas PM_2.5 does not accumulate at non-stomatal areas. Then, the penetration depth of PM_2.5 in stomata of most tree species was 5-14 μm from the abaxial epidermis. For the first time, 3D X-ray microscope scanning was used to confirm that a pathway by which PM_2.5 enters the leaves is through the stomata, which is fundamental for further research on how PM_2.5 translocates and interacts with tissues and cells in leaves.

Interfacial interaction of graphitic carbon nitride/nanodiamond nanocomposites toward synergistic enhancement of photocatalytic degradation of organic contaminants

Graphitic carbon nitride (g-C₃N₄) has been widely used in various photocatalyst applications. However, compared with conventional metal-based photocatalysts, it exhibits low photocatalytic activity because of the low mobility of its charge carriers. In this study, g-C₃N₄/nanodiamond (ND) nanocomposites were fabricated via a facile single-step heating strategy. Under visible-light irradiation, the optimal g-C₃N₄/ND nanocomposites with 1.0 wt% ND content exhibited an RhB degradation rate more than two times greater than that of the g-C₃N₄. In addition, reutilization experiments showed that the g-C₃N₄/ND nanocomposites exhibit good stability and reusability. This remarkable enhancement of the photocatalytic activity was attributed to the interfacial effect between g-C₃N₄ and ND, which reduces energy-wasteful electron-hole recombination and promotes charge-separation efficiency. Such an approach could accelerate the development of composites for photocatalyst applications and provide more rational guidance and fundamental understanding toward realizing the theoretical limits of interfaces.

Pore-Mouth Structure of Highly Agglomerated Detonation Nanodiamonds

Detonation nanodiamond aggregates contain water that is removed by thermal treatments in vacuo, leaving available pores for the adsorption of target molecules. A hard hydrogel of detonation nanodiamonds was thermally treated at 423 K for 2 h, 10 h, and 52 h in vacuo to determine the intensive water adsorption sites and clarify the hygroscopic nature of nanodiamonds. Nanodiamond aggregates heated for long periods in vacuo agglomerate due to the removal of structural water molecules through the shrinkage and/or collapse of the pores. The agglomerated nanodiamond structure that results from long heating periods decreases the nitrogen adsorption but increases the water adsorption by 40%. Nanodiamonds heated for long times possess ultramicropores <0.4 nm in diameter in which only water molecules can be adsorbed, and the characteristic mouth-shaped mesopores adsorb 60% more water than nitrogen. The pore mouth controls the adsorption in the mesopores. Long-term dehydration partially distorts the pore mouth, decreasing the nitrogen adsorption. Furthermore, the nitrogen adsorbed at the pore mouth suppresses additional nitrogen adsorption. Consequently, the mesopores are not fully accessible to nitrogen molecules because the pore entrances are blocked by polar groups. Thus, mildly oxidized detonation nanodiamond particles can show a unique molecular sieving behavior.

Ion-imprinted modified molecular sieves show the efficient selective adsorption of chromium(vi) from aqueous solutions

Molecular sieve 5A was modified with (3-aminopropyl) triethoxysilane (APTES) as the support matrix, on which 4-VP was used as the ionic imprinting group. The as-prepared IIZMS-APTES was applied as the adsorbent for the recovery of chromium(vi) from aqueous solutions. The adsorbent was characterized via Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), and X-ray diffraction (XRD). The influences of adsorption time, concentration of the ions, initial pH, and temperature on the adsorption performance to Cr(vi) were investigated. The selectivity and reusability of IIZMS-APTES are also evaluated. The results showed that the maximum adsorption capacity reached 56.46 mg g-1 when the initial concentration of metal ions was at 100 mg L-1 at pH 2 and 30 °C. The adsorption process followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. The IIZMS-APTES exhibits an efficient selective adsorption of Cr(vi) from aqueous solutions.