article · Crystal Research and Technology
Calcium-modified hematite films prepared using a sol–gel dip-coating technique show significant improvements in breaking down organic dyes under visible light. Adding calcium reduces the optical bandgap of the iron oxide films from 2.10 to 1.96 electronvolts and suppresses electron-hole recombination, notably at a 5 weight percent concentration. The films adopt a rhombohedral crystal structure with grain agglomeration increasing at higher calcium levels. Under testing, the 5 weight percent calcium-modified film degraded 97 percent of target dye within 120 minutes, compared to 64.1 percent degradation achieved by unmodified iron oxide. This superior activity stems from improved absorption of visible light and more efficient charge separation caused by calcium-induced defect states. The coating also demonstrated durability, retaining around 85 percent of its initial degradation efficiency across three monthly cycles while maintaining structural stability.
Organic pollutants in industrial wastewater pose persistent environmental and health risks. Conventional water treatment methods often require high energy inputs or ultraviolet light. Developing stable, visible-light-driven photocatalytic coatings from earth-abundant materials like iron oxide and calcium provides a potentially lower-cost and more sustainable pathway for purifying contaminated water under natural or low-energy illumination.
The findings point towards applications in industrial wastewater treatment, particularly for facilities seeking solar- or visible-light-activated systems to degrade organic dyes. Wastewater plant operators and environmental remediation services represent primary potential users. This research sits at an early stage, having demonstrated bench-scale efficiency and reusability on thin films, meaning further development is required to validate the coating on larger surfaces and within complex, untreated wastewater streams.
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ABSTRACT This study investigates the synthesis of Ca‐modified hematite (Ca X ‐Fe 2 O 3 ) films via a sol–gel dip‐coating method for visible‐light‐driven photocatalytic applications. The properties of the films were systematically characterized using comprehensive analytical techniques. XRD analysis confirmed the formation of a rhombohedral phase with a (104) preferred orientation and a maximum crystallite size of 65 nm, while SEM revealed increased grain agglomeration at higher Ca contents. Optical analyses showed a reduction in the bandgap from 2.10 to 1.96 eV with increasing Ca content, whereas photoluminescence revealed a marked decrease in emission intensity for the 5 wt.% Ca‐modified film, indicating suppressed electron–hole recombination. The 5 wt.% Ca‐modified hematite exhibited significantly enhanced photocatalytic performance, achieving 97% dye degradation within 120 min compared with 64.1% for Fe 2 O 3 . This enhanced activity is attributed to the combined effects of improved visible‐light absorption and efficient charge separation arising from Ca‐induced defect states within the bandgap. Reusability tests demonstrated that the photocatalyst retained approximately 85% of its degradation efficiency after three consecutive monthly photocatalytic cycles, while post‐reaction analyses further confirmed its structural stability after repeated use. These results demonstrate that Ca‐modified Fe 2 O 3 is a promising visible‐light photocatalyst for the sustainable removal of organic pollutants from wastewater.
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DOI: 10.1002/crat.70160
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