Water soluble carbon nanotubes (wsCNTs) show enhancement of the growth rate of common gram (Cicer arietinum) plants. Treating plants with up to 6.0 μg mL⁻¹ of wsCNT shows an increased growth rate in every part of the plant including the roots, shoots and also in branching. The noticeable difference between the wsCNT treated and controlled gram is the water uptake; in the former it is dramatically enhanced, suggesting better water absorption and retention related to enhanced growth. This work shows that unlike CNTs, wsCNTs are non-toxic to plant cells that conserve water transport in plants.

The effect of water soluble carbon nano-dots (wsCND) on the growth of root and shoot of wheat plants under light and dark conditions has been studied. The wsCND enhances the growth of root and shoot both in light and dark conditions. The effect of wsCND on the growth of root was relatively more compared to that of shoot. Scanning electron and Fluorescence microscopic analysis show that wsCNDs enter inside the plant. Raman spectroscopy also confirms this. The present study shows that wsCNDs are non-toxic to the wheat plant and can be used to enhance the production of this cereal crop.

Biochar is shown to contain raw carbon nanoparticles (rCNPs). The traditional use of biochar for the healthy growth of plants is due to its retention capability of nutrients for needs-based slow release. On aging, the rCNPs are aerially oxidized with the incorporation of hydrophilic carboxylic and hydroxyl groups on the biochar surface to increase its spongy structure that enhances its absorptivity to water and several ionic nutrients. The chemical oxidation of rCNPs in biochar introduces similar carboxylic acid and hydroxyl groups in transforming rCNPs to water soluble carbon nanoparticles (wsCNPs). These wsCNPs in solution enhance the growth rate of wheat plants. The concentration of wsCNPs used in this wheat plant growth study varied in the range from 10 to 150 mg L⁻¹. The seeds treated with wsCNPs in this range showed higher growth rates, with the optimum growth found to occur with 50 mg L⁻¹ wsCNPs, as compared with the control study. This suggests a concentration threshold of wsCNPs for the optimum stimulation of plant growth that the aged biochar can readily meet. Model experiments with ammonium nitrate as cationic and anionic nutrients show that both the rCNPs and wsCNPs hold the nutrient ions, although the negatively charged wsCNPs hold less effectively than the anionic nitrate. These carbon nanoparticles are capable of releasing cationic and anionic nutrients slowly over time. Such action is correlated with the booster action of CNPs in supplying nutrients to the young plants. Thus, wsCNPs may be a better choice than fertiliser or manure alone, due to the controlled and slow release of nutrients for better assimilation by plants.

Reduced graphene oxide (rGO) generates reactive oxygen species (ROS) under visible light in air via a singlet oxygen–superoxide anion radical pathway which readily kills Enterobacter sp. The rGO⁺ intermediate reacts with a hydroxyl ion to produce graphene oxide (GO) as a coating on the surface of rGO resulting in enhanced fluorescence and a slow down in photo-induced ROS formation. GO is not toxic but on ageing it gets a surface coating of rGO and shows toxicity.