Defect engineering is an emerging technology for tailoring nanomaterials' characteristics and catalytic performance in various applications. Recently, defect‐engineered nanoparticles have emerged as highly researched materials in catalytic applications because of their exceptional redox reaction capabilities and physicochemical and optical properties. The properties of nanomaterials can be readily adjusted by controlling the nature and concentration of defects within the nanoparticles, avoiding the need for intricate design strategies. This review investigates defect engineering in nanocatalysts, including the design, fabrication, and applications. Initially, the various categories and strategies of nanomaterial defects and their impacts on the nanocatalysts' electronic and surface properties, catalytic activity, selectivity, and stability are summarized. Then, the catalytic processes and their uses, including gas sensing, hydrogen (H₂) evolutions, water splitting, reductions of carbon dioxide (CO₂) and nitrogen to value‐aided products, pollutant degradation, and biomedical (oncotherapy, antibacterial and wound healing, and biomolecular sensing) applications are discussed. Finally, the limitations in defect engineering and the prospective paths for allowing the logical design and optimization of nanocatalytic materials for long‐term and efficient applications are also examined. This comprehensive review gives unique insights into the current state of defect engineering in nanocatalysts and inspires future research on exploiting shortcomings to improve and customize catalytic performance.

In this work, different mass percent ratios of CoFe₂O₄ coupled g-C₃N₄ (w%-CoFe₂O₄/g-C₃N₄, CFO/CN) nanocomposites were integrated through a hydrothermal process for the sonocatalytic eradication of tetracycline hydrochloride (TCH) from aqueous media. The prepared sonocatalysts were subjected to various techniques to investigate their morphology, crystallinity, ultrasound wave capturing activity and charge conductivity. From the investigated activity of the composite materials, it has been registered that the best sonocatalytic degradation efficiency of 26.71 % in 10 min was delivered when the amount of CoFe₂O₄ was 25% in the nanocomposite. The delivered efficiency was higher than that of bare CoFe₂O₄ and g-C₃N₄. This enriched sonocatalytic efficiency was credited to the accelerated charge transfer and separation of e^--h⁺ pair through the S-scheme heterojunctional interface. The trapping experiments confirmed that all the three species i.e. ^•OH, h⁺ and ^•O₂^- were involved in the eradication of antibiotics. A strong interaction was shown up between CoFe₂O₄ and g-C₃N₄ in the FTIR study to support charge transfer as confirmed from the photoluminescence and photocurrent analysis of the samples. This work will provide an easy approach for fabricating highly efficient low-cost magnetic sonocatalysts for the eradication of hazardous materials present in our environment.