Maize Stalk Waste Turned Into Carbon Dots That Boost Maize Seedling Photosynthesis

Carbon quantum dots made from discarded maize stalks significantly increased photosynthesis and growth in maize seedlings when sprayed onto their leaves, according to a study published in the journal Bioresources and Bioprocessing. The researchers synthesized the nanomaterials through a simple hydrothermal process and found that a concentration of 25 milligrams per liter produced the strongest response, while a much higher concentration actually suppressed plant growth.

The synthesis method was deliberately low-cost. Dried maize stalks were ground, sieved, mixed with ultrapure water and anhydrous ethanol, and heated in an autoclave at 200 degrees Celsius for ten hours. The resulting precursor solution was filtered, microfiltered, dialyzed and dried to yield a powder. A typical batch starting from 0.3 grams of stalk powder produced roughly 5 milligrams of carbon quantum dots. Because maize stalks consist mainly of cellulose, hemicellulose and lignin, the authors argue that this agricultural waste stream is a suitable and inexpensive feedstock, and that the hydrothermal route offers simpler procedures and shorter synthesis times than many alternatives, making it more compatible with industrial-scale production.

Characterization revealed spherical particles with a narrow size distribution ranging from 0.9 to 3.28 nanometers and an average diameter of 2.03 nanometers. High-resolution transmission electron microscopy showed ordered lattice striations with an interplanar spacing of 0.2123 nanometers, corresponding to the graphite (100) plane, confirming a graphitic core. X-ray diffraction displayed a peak at 22 degrees associated with amorphous carbon interfaces, and Raman spectroscopy produced a disordered D band near 1361 inverse centimeters and a graphitized G band near 1587 inverse centimeters.

Surface chemistry proved equally important. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy identified hydroxyl, carboxyl and carbonyl functional groups on the particle surfaces, along with carbon-carbon and carbon-oxygen bonds. The particles carried a zeta potential of about minus 19.91 millivolts, attributed to those oxygen-containing groups, which helped them disperse readily in water with moderate stability. The team also quantified residual inorganic nutrients in the dialyzed solutions, finding potassium, phosphorus and nitrogen levels far below thresholds typically required for physiological effects in plants, and concluded that the observed enhancements could be primarily attributed to the intrinsic properties of the quantum dots rather than nutrient artifacts.

Optically, the dots absorbed strongly in the ultraviolet, with a maximum absorption peak at 285 nanometers. Excitation at 410 nanometers produced maximum emission at 495 nanometers, in the cyan-blue region of the spectrum, with a dominant wavelength of 505 nanometers. The average fluorescence lifetime was 5.13 nanoseconds and the fluorescence quantum yield was 2.86 percent, a value the authors note is typical for undoped biomass-derived carbon dots without surface passivation. The material also showed practical robustness: fluorescence remained essentially unchanged across sodium chloride concentrations from zero to 2 moles per liter, stayed stable in neutral solution while diminishing in strong acid or base, and resisted photobleaching even after 60 minutes of continuous irradiation with 365-nanometer ultraviolet light. Together, these properties define the dots as down-conversion luminescent materials that convert part of the ultraviolet light into cyan-blue light that photosynthetic pigments can use more efficiently.

To test biological effects, the team grew maize seedlings of the variety Lihe No. 1 in pots in a greenhouse in Hohhot, Inner Mongolia, during July and August. Seven groups of four pots, with eight plants per pot, received daily foliar sprays of 5 milliliters per plant for 12 days at concentrations of 0, 5, 15, 25, 50 and 150 milligrams per liter, while an unsprayed control group received no spray. Measurements included plant height, leaf dimensions, chlorophyll content, chloroplast Hill reaction activity, photosynthetic rates and chlorophyll fluorescence, analyzed by one-way analysis of variance with Tukey post-hoc tests at a significance threshold of P less than 0.05.

The 25 milligrams per liter treatment produced the strongest gains. Compared with the control, plant height rose 43.2 percent, leaf area 25.6 percent, leaf length 31.2 percent, leaf circumference 27.3 percent, chlorophyll content 35.2 percent, Hill reaction activity 45.5 percent, total photosynthetic rate 29.8 percent and net photosynthetic rate 46.6 percent. Root length and root crossing number also increased at several concentrations, though the authors report no statistically significant differences among groups for these root measures, with considerable data dispersion. Foliar spraying had only a limited effect on the percentage of healthy leaves. At the opposite end of the dose range, 150 milligrams per liter inhibited growth and photosynthetic function, with plant height falling 17.8 percent and net photosynthetic rate dropping 26.5 percent relative to the control, revealing a clear concentration-dependent promotion-inhibition transition.

Mechanistic measurements pointed to two synergistic pathways. At 25 milligrams per liter, the chloroplast electron transport rate increased by 31.5 percent, and relative electron transport measured with a commercial assay kit was significantly elevated, which the authors attribute to numerous active sites on the dot surfaces facilitating electron transfer. Chloroplast light absorption also increased markedly, consistent with a light-conversion mechanism in which the dots absorb incident ultraviolet and violet light and re-emit it in the blue region between 450 and 495 nanometers, extending the range of photosynthetically active radiation that leaf pigments can capture. Photochemical efficiency of photosystem II increased at the optimal dose, and carbon dioxide depletion under illumination was greatest at 25 milligrams per liter, with no differences observed in the dark, supporting enhanced electron transport and carbon fixation.

The inhibitory effect of high concentrations appears to have a different origin. At 150 milligrams per liter, both chloroplast electron transport rate and light absorption declined, and hydroxyl radical content rose markedly compared with the control, while the 25 milligrams per liter treatment caused minimal change. The authors propose that photodegradation of high-concentration dots generates excessive hydroxyl radicals, which in turn suppress maize growth and photosynthesis. A schematic model presented in the paper integrates these findings: the dots act as spectral converters feeding blue light to chlorophyll a and b, and are proposed to participate directly in thylakoid electron transport, contributing to the observed increases in photochemical efficiency, electron transport rate and net carbon dioxide assimilation.

The authors frame the work as a demonstration of a feasible strategy for synthesizing cost-effective carbon quantum dots from agricultural waste, potentially offering a benefit for early-stage corn seedling growth under controlled conditions. Important caveats apply: the experiments were greenhouse pot studies of seedlings over a limited growing window, not field trials, and the reported gains come from a single variety and location with relatively small replicate numbers. The abstract itself notes the findings apply to early-stage seedling growth under controlled conditions rather than mature crops in the field. Prior studies cited by the team, including nitrogen-doped dots that enhanced microalgae growth and coffee-ground-derived dots that improved rice net photosynthetic rate by 32.66 percent, suggest a broader research trend of converting biomass into light-converting nanomaterials for crops. Whether maize stalk-derived dots can deliver similar benefits at agricultural scale, across soils, climates and growth stages, remains a question for future field research.

Subject of Research: Carbon quantum dots derived from maize stalks and their effects on maize seedling photosynthesis

Article Title: The promotion effect of carbon quantum dots derived from maize stalks on the photosynthesis of maize growth

Article References: Wang, S., Li, X., Guo, L., Li, Y., Li, B., Zhang, M., Duan, J., Dong, Q., Han, L., & Di, C. (2026). The promotion effect of carbon quantum dots derived from maize stalks on the photosynthesis of maize growth. Bioresources and Bioprocessing, 13(1), Article 144. https://doi.org/10.1186/s40643-026-01138-w

Image Credits: AI Generated

DOI: 10.1186/s40643-026-01138-w

Keywords: carbon quantum dots, maize stalks, photosynthesis, nanomaterials, hydrothermal synthesis, down-conversion luminescence, chloroplast electron transport, agricultural waste, foliar spray, maize seedlings, nano-agriculture, greenhouse study