Scientists from India, in collaboration with Polish PhD Michał Piasecki from Częstochowa, have developed a porous material from agricultural and industrial waste that accelerates the decomposition of persistent dyes in wastewater under visible light.
Coloured wastewater from dyeing and industrial printing plants is common, but these dyes are designed to be permanent and are difficult to remove using conventional methods.
“In a dyeing plant or industrial printing plant, coloured water is not a sensation, but an everyday occurrence,” the study notes. “Although dyes should remain in the fabric or on the paper, some always escape into the process water, and then into the wastewater. This is where problems begin, because such wastewater is difficult to decolourise because the dye molecules are designed to be permanent.”
The researchers published their work in the Journal of Water Process Engineering, proposing a photocatalyst made from rice husk ash, rich in silica, and granulated blast furnace slag from metalworks, a source of calcium and magnesium.
From these materials, they synthesized akermanite, a calcium and magnesium silicate, through hydrothermal treatment followed by heating at various temperatures.
Tests confirmed the material’s properties. “The more nooks and crannies, the more places where the dye can attach and be neutralized,” the study says. X-ray measurements indicated akermanite formation with a diopside admixture, electron microscopy revealed small, irregular grains, and porosity measurements showed a high surface area, crucial for photocatalysis.
During laboratory tests, methylene blue (MB), a model dye, was added to water along with the catalyst and illuminated with a 100W LED. The mixture was first kept in the dark to allow the dye to adhere to the catalyst surface, then exposed to light. Under optimal conditions, approximately 81% of the dye was removed after four hours. Adding more catalyst reduced efficiency to 78%, while higher initial dye concentrations also lowered removal rates.
The material works like “light-activated chemical scissors.” Illumination produces electrons and holes that react with oxygen and water to form highly reactive radicals, breaking dye molecules into smaller fragments. Mass spectrometry confirmed the degradation pathway, producing CO2, H2O, and inorganic ions such as NO3⁻ and SO4²⁻. After three reuse cycles, efficiency dropped from 81% to 72%, showing potential for repeated applications, though regeneration requires further refinement.
The researchers suggest the method could be applied in wastewater treatment plants as a reactor, particularly in dyeing and printing industries, where light, time, and catalyst recovery can be controlled. “The paper demonstrates the environmentally friendly approach (using waste as a raw material, no toxic reagents in the synthesis, and dye decomposition), but it does not include full ecotoxicity testing of the purified water or studies of the leaching of the powder components into the solution. This is a necessary next step before larger-scale implementation,” the authors warn.
They add that success depends not only on removing colour, but on ensuring treated water is free of harmful residues, highlighting the potential for a sustainable solution to industrial dye pollution. (PAP)
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