Nickel Oxide Nanocomposite Knocks Out Bacteria and Scrubs Toxic Dyes From Water

A team of chemists in Telangana, India, has built a dual-purpose material that can both destroy stubborn industrial dyes and kill dangerous microbes — and it does both jobs better as you feed it more of its active ingredient. The material, a nanocomposite made by embedding nickel oxide nanoparticles inside a blend of polyacrylonitrile and sodium alginate, degraded roughly 92 percent of Rhodamine B and about 88 percent of Malachite Green under sunlight in five hours, while simultaneously suppressing the growth of Staphylococcus aureus, Escherichia coli, and the fungus Aspergillus niger. The work, published in Frontiers in Environmental Chemistry, addresses two of the most intractable problems in wastewater treatment at once: recalcitrant synthetic dyes that resist biodegradation, and pathogenic microorganisms that flourish in contaminated water.

The design logic behind the composite is elegantly simple. Nickel oxide is a well-known photocatalyst among metal oxide nanoparticles, prized for its stability, availability, and strong catalytic activity, but on its own the nanoparticles tend to clump together, which buries the active surfaces that do the chemical work. Polyacrylonitrile, a tough synthetic polymer studded with nitrile groups, acts as a structural scaffold, gripping the metal oxide particles through strong interactions and keeping them evenly dispersed. Sodium alginate, a hydrophilic polysaccharide extracted from brown algae, brings carboxyl and hydroxyl groups that chelate metal ions and improve the material’s affinity for water — and for the dye molecules dissolved in it. Together, the two polymers and the semiconductor form a hybrid organic-inorganic matrix in which each component compensates for the weaknesses of the others.

To make the material, the researchers first synthesized nickel oxide nanoparticles by a sol-gel route: nickel nitrate was precipitated with sodium hydroxide, washed, dried at 120 degrees Celsius, and calcined at 900 degrees Celsius for two hours to yield the crystalline oxide. They then dispersed the nanoparticles in water by ultrasonication and mixed them in situ with an equimolar blend of polyacrylonitrile and sodium alginate at 40 degrees Celsius, producing a series of composites with NiO loadings ranging from 10 to 50 percent while keeping the polymer ratio fixed. That systematic variation in NiO content turned out to be one of the study’s most important features, because it allowed the team to track exactly how performance scales with the amount of active material.

Characterization confirmed that the assembly worked as intended. Fourier-transform infrared spectroscopy picked up the hydroxyl stretches of alginate, the nitrile stretch of polyacrylonitrile at around 2,240 inverse centimeters, and — critically — Ni-O stretching bands between 500 and 600 inverse centimeters that grew stronger as NiO loading increased. Powder X-ray diffraction showed the characteristic reflections of cubic nickel oxide at 2θ values of 37, 43, 63, and 75 degrees, matching the standard reference pattern, with peaks sharpening at higher loadings as well-defined nanocrystals developed within the amorphous polymer background. Electron microscopy revealed a morphological progression: smooth polymer films at low loading gave way to porous, rough, needle-like textures as NiO content rose, with the 50 percent formulation showing discrete spherical nanoparticles roughly 50 nanometers across, partially enveloped by the polymer matrix.

The antimicrobial results followed a clear concentration-dependent pattern. In agar well diffusion tests, the richest composite produced inhibition zones of 14 millimeters against S. aureus and 13 millimeters against E. coli at a dose of 100 micrograms per milliliter — figures comparable to the standard antibiotic amoxicillin benchmarks used for comparison, which measured 13 and 14 millimeters in the plate assays. Against Aspergillus niger, the top formulation carved out a 15-millimeter inhibition zone, approaching the conventional antifungal drug’s 20 millimeters. The mechanism, the authors explain, hinges on the ability of NiO nanoparticles to generate reactive oxygen species — hydroxyl radicals and superoxide anions — that rupture microbial cell membranes and shut down growth.

On the pollution side, the photocatalytic degradation experiments were run under natural sunlight on days when ambient temperatures ranged from 31 to 38 degrees Celsius, a deliberately practical choice for a technology aimed at real-world treatment in sunny climates. Dye solutions were equilibrated with the catalyst in the dark before irradiation to isolate the photocatalytic contribution from simple adsorption. The disappearance of Rhodamine B was tracked by the steady fade of its absorption peak at 553 nanometers, while Malachite Green’s signature band between 330 and 400 nanometers served the same purpose for that dye. For both pollutants, degradation accelerated over the five-hour window, and the 50 percent NiO composite consistently outperformed its more dilute siblings.

The kinetics told a satisfying story, too. Plotting the logarithm of the absorbance ratio against irradiation time showed that both dyes degraded via pseudo-first-order kinetics consistent with the Langmuir–Hinshelwood model, with apparent rate constants of 0.1143 per minute for Rhodamine B and 0.1061 per minute for Malachite Green, and correlation coefficients above 0.93. Rhodamine B fell faster in the early hours, while Malachite Green declined more steadily — a difference the researchers attribute to molecular structure and differing adsorption affinities for the composite surface. The high surface area and porosity of the material, they note, concentrates dye molecules at active NiO sites, extending contact time and speeding oxidative cleavage.

Reusability data added a dose of realism. Over five consecutive 60-minute degradation cycles, Rhodamine B removal dropped from about 60.5 percent in the first run to 31.3 percent in the fifth, a decline the authors attribute mainly to loss of catalyst material during the washing and separation steps rather than catastrophic deactivation. They suggest that immobilizing the composite on inert supports such as carbon cloth, glass slides, or ceramics could make recovery easier and cut catalyst losses — an engineering fix that could prove decisive for industrial uptake.

What makes the study noteworthy is its refusal to treat pollution removal and disinfection as separate problems. Most prior research has optimized either dye degradation or antimicrobial action in isolation; this hybrid system pursues both simultaneously, exploiting the same reactive oxygen chemistry for each. The researchers argue that this dual functionality positions NiO@PAN-SA composites for antimicrobial coatings, sterilization materials, and environmental remediation alike. They are candid about the caveats: the dye tests used model solutions rather than real industrial effluents, no scavenger experiments confirmed the exact radical species at work, and the reusability and regeneration of the material remain to be quantified systematically. Cost-effectiveness, long-term stability, and scalability for industrial manufacturing are the next frontiers.

Still, the numbers are striking enough to command attention. A material assembled from inexpensive, widely available ingredients — nickel salt, a commodity polymer, and seaweed-derived alginate — matching clinical antibiotic benchmarks in plate assays while stripping more than nine-tenths of a carcinogenic textile dye from water under plain sunlight is a result that bridges materials chemistry, microbiology, and environmental engineering. As textile, paper, and leather industries continue to discharge chemically stable, non-biodegradable dyes into waterways around the world, solutions that attack the problem with cheap sunlight and a recoverable solid catalyst will be watched closely. If the team’s upcoming work on scalability and multi-cycle performance holds up, this seaweed-wrapped nickel oxide could graduate from the laboratory flask to the treatment plant.

Subject of Research: NiO-loaded polymer nanocomposites for simultaneous dye degradation and antimicrobial water treatment

Article Title: NiO@PAN-SA nanocomposites: a multifunctional material excelling in dye degradation and antimicrobial applications

Article References: Pamula, U. P., Rao, T. N., & Prashanthi, Y. (2026). NiO@PAN-SA nanocomposites: a multifunctional material excelling in dye degradation and antimicrobial applications. Frontiers in Environmental Chemistry, 7, Article 1887800. https://doi.org/10.3389/fenvc.2026.1887800

Image Credits: AI Generated

DOI: 10.3389/fenvc.2026.1887800

Keywords: nickel oxide nanoparticles, nanocomposites, polyacrylonitrile, sodium alginate, photocatalysis, dye degradation, Rhodamine B, Malachite Green, antibacterial activity, antifungal activity, wastewater treatment, reactive oxygen species