Açaí residue becomes nanofertilizer for corn and sorghum

Researchers from Embrapa and the Federal University of Ceará (UFC) have developed a nanofertilizer from açaí seeds, capable of stimulating the growth of corn and sorghum. In experimental tests, the application of low doses of the product (10 milligrams per liter) increased the relative growth of the plants by 24% in corn and 164% in sorghum. The root volume also grew by 23% and 59%, respectively, compared to untreated controls.

The açaí seed is a byproduct that is underutilized in agro-industrial processing. For every ton of fruit used in pulp extraction, approximately 700 kilograms of seeds are generated, which are usually discarded or used as fuel in boilers.

The corn variety BRS-Gorutuba and the sorghum variety 2502 were used in the tests; both have a short production cycle and are recommended for planting in semi-arid regions. The increased root system, especially in sorghum, allows the plants to explore the soil more efficiently, favoring their survival.

The new nanofertilizer is produced from açaí seed powder in a process called hydrothermal synthesis. The result is fluorescent nanoparticles, known as carbon quantum dots, measuring approximately four nanometers.

These particles penetrate leaf tissues with great efficiency. Inside the plant, in addition to delivering essential mineral nutrients, they act as antennas that capture ultraviolet radiation and, from it, emit a blue light capable of stimulating the plant's photochemical system and increasing the efficiency of photosynthesis. 

Researcher Cláudio Carvalho, from Embrapa Agroindústria Tropical (CE), explains that, due to the reduced size of the particles, nanofertilizers penetrate plant tissues efficiently and deliver nutrients directly at the cellular level, increasing absorption compared to conventional foliar fertilizers. They also participate in energy transfer processes within cells and provide bioactive compounds that can stimulate the activity of enzymes, such as those involved in oxidative stress.

Carvalho adds that nanofertilizers can achieve superior results with smaller doses, reducing application costs and potential environmental impacts. "Compared to conventional fertilizers, nanofertilizers generally result in less surface runoff and less contamination of soils and water bodies, making them potentially more sustainable," he concludes.

From waste to wealth

"Despite the limited number of studies on the small-scale use of açaí seeds as biochar, for bioenergy production, or the development of composite materials, this residue generally accumulates in the urban centers of producing regions and in large cities," says the researcher.

He explains that the açaí seed is a "natural survival kit" containing nutrients necessary for the plant to establish itself in hostile environments. This richness makes the açaí pit the ideal precursor for nanofertilizer. "This is a noble destination, which adds value to the biomass and, at the same time, returns at least part of the mineral nutrients, mainly micronutrients, to the production areas, saving on fertilizers," he says.

According to the scientist, the group intends to test the product on other species such as beans, sweet potatoes, pumpkins, vegetables, and also on açaí palm seedlings. "After the production process is finalized and scaled up, the nanofertilizer could become a great and safe opportunity to return nutrients to the production system, whether in the açaí palm crop itself, in seedling nurseries, in protected cultivation, and in other applications," he adds. 

“In Brazil, large quantities of agro-industrial waste are generated, especially in the Amazon region, which represents an abundant and low-cost raw material,” observes Professor Pierre Fechine (photo below), coordinator of the Laboratory of the Advanced Materials Chemistry Group (GQMat) at UFC, a partner in this work. He adds that it will also be necessary to advance regulatory and safety studies for large-scale agricultural use.

Scientific advancement 

The results were published in the article "Carbon-based nanopigments derived from açaí seed residues with tunable optical properties and biofunctional performance" in the international journal Dyes and Pigments. "We showed that a residue that would normally be discarded can be converted into a smart material, capable of interacting with biological systems and producing measurable effects on plant growth," says the professor.

He explains that, before reaching the rural producer, some challenges still need to be overcome. The main one is maintaining the quality and reproducibility of the material when moving from laboratory scale to industrial scale. “In the laboratory, we work with small quantities and rigorous control of synthesis conditions. In a factory, it is necessary to ensure that each batch has the same chemical, optical, and biological properties,” he clarifies. Another challenge is optimizing production costs, including energy consumption, material purification, and biomass collection logistics. 

Why study carbon quantum dots?

Carbon quantum dots are extremely small nanoparticles, thousands of times smaller than a human hair. Despite their small size, they possess very special properties, primarily the ability to absorb and emit light. 

They were discovered by chance in the early 2000s during studies involving carbon nanotubes. Since then, they have aroused enormous scientific interest because they are relatively easy to produce, have low toxicity, and can be obtained from natural materials and organic waste. 

Today, carbon quantum dots are being studied for applications in chemical sensors, medical diagnostics, bioimaging, solar cells, LEDs, water treatment, and agriculture. In agriculture, they can act as plant growth stimulators, increase the efficiency of light utilization by plants, and assist in nutrient transport, contributing to more efficient and sustainable production systems.

In the work carried out by Embrapa and UFC, açaí seed powder, rich in carbon and minerals, was placed in a "hostile" environment inside high-pressure reactors, subjected to high temperatures for several hours — a process called hydrothermal synthesis. Under these conditions, the organic molecules of the seed break down and reorganize into carbon quantum dots and other substances with biological activity in plants, such as precursors of plant hormones, among others.