Scientists have synthesized new nanoparticles that effectively purify wastewater without the need for disposal.

The study was published in the journal Physica Scripta. The 21st century has witnessed a growing global water crisis. With rapid population growth, increased water resource consumption, and environmental pollution, the need for effective wastewater treatment is more critical than ever. According to statistics, by 2030, two-thirds of the world's population will reside in cities, creating additional pressure on water supply and treatment systems. Addressing humanitarian and environmental issues requires the implementation of innovative technologies in the wastewater treatment process, especially for toxic dyes used in the textile, paper, and leather industries.

Among the existing treatment methods, mechanical, chemical, and biological methods stand out, but many have their limitations: biological methods require time to activate bacteria, while chemical methods can produce hazardous byproducts. Sorption, which involves the absorption of pollutants by solid materials, is the fastest and most effective method. However, this necessitates the disposal of the spent sorbent.

An important advancement in this field has been the development of titanium nitride (TiN) nanoparticles. TiN nanoparticles, which can be created using pulsed laser ablation, offer rapid and efficient removal of pollutants due to effective electrostatic adsorption, making them highly attractive for use in treatment systems.

Physicists from the Photonics and Two-Dimensional Materials Center at MIPT, along with colleagues, synthesized titanium nitride nanoparticles through laser ablation (the evaporation of material under the influence of laser pulses followed by its condensation into nanoparticles) in a liquid medium. They experimentally demonstrated that these nanoparticles possess unique adsorption properties and can effectively absorb cationic dyes. What makes them particularly promising is their high specific surface area and the ability to control stoichiometry, allowing for the modification of their properties to address treatment challenges.

The researchers focused the laser beam on a target using a special lens. They moved it across the surface of the titanium nitride target in a spiral pattern to avoid heating a single point, using a scanner. The process lasted for 30 minutes, resulting in nanoparticles that imparted a rich blue color to the colloidal solution.

In the experiment, the physicists investigated how the TiN nanoparticles synthesized in different solvents (water, acetone, and acetonitrile) interacted with methylene blue. All three types of nanoparticles had a round shape, but their sizes varied slightly. For accurate comparison, all nanoparticle samples were transferred to water, previously centrifuged, and repeatedly washed to remove residues of organic solvents. Consequently, the concentration of TiN nanoparticles in water was 0.1 g/L.

To test the ability of TiN nanoparticles to absorb methylene blue, an experiment was conducted. The nanoparticles were mixed with a methylene blue solution at room temperature to achieve a dye concentration of 20 mg/L. The resulting solutions were vigorously stirred and centrifuged. The concentration of the dye remaining in the solution was then determined using a spectrophotometer. As a result of the experiments, TiN nanoparticles synthesized directly in water exhibited the best adsorption capacity.

The researchers also studied the adsorption efficiency of other cationic dyes, such as crystal violet and malachite green. The nanoparticles synthesized in water effectively removed all of these dyes from the solutions, particularly excelling in the removal of crystal violet.

However, crystal violet and malachite green did not adsorb onto the nanoparticles created in acetone and acetonitrile. Transmission electron microscopy of the synthesized nanoparticles, conducted at the MIPT Collective Use Center, showed that the nanoparticles synthesized in water formed special cavities during ablation, which help them better capture dyes.

The laser ablation method allows for varying the size and shape of nanoparticles, enabling the creation of more effective sorbents without the use of hazardous chemical reagents. This is a significant advantage, especially in light of increasing safety requirements for technologies.

“It can be confidently stated that titanium nitride nanoparticles synthesized by laser ablation in a liquid medium possess the necessary properties to address pressing issues of wastewater treatment from dyes,” said Ilya Martynov, a senior researcher in the laboratory of two-dimensional materials and nano-devices at MIPT. “This is not only a step towards improving the quality of wastewater treatment in industrial enterprises but also an important stride towards a sustainable and environmentally safe future for our society.”

“It is also important that this technology does not face the issue of sorbent disposal. TiN nanoparticles can be reused. To do this, the nanoparticles need to be annealed at the combustion temperature of organic impurities. In most cases, heating to 300 degrees Celsius is sufficient,” added Ilya Zavidovsky, a candidate of physical and mathematical sciences and a senior researcher in the laboratory of controlled optical nanostructures at MIPT.

The study was funded by the Russian Science Foundation, with support from the Ministry of Science and Higher Education of Russia.