Material preparation methods on micro- and nanoscales can be broadly classified into two categories: top-down and bottom-up approaches. These preparation methods play an important role in determining unique and useful properties for advanced applications. There are various methodologies used to prepare a range of materials, including physical or mechanical methods, such as physical pulverisation, physical coacervation, spray pyrolysis, mechanical alloying, or high-energy ball milling, or chemical methods, which include chemical vapour deposition, co-precipitation, sol-gel processes, auto-combustion, sono-chemical and mechano-chemical processing, microwave methods, and hydrothermal methods, among others. Micro- and nanoscale materials have distinguished surface, volume, quantum size effect, macroscopic quantum tunnelling, magnetic, electrical, and dielectric properties.

The role of top-down approaches, such as solid-state ball milling, mechano-chemical processing, mechanical alloying, or other physicochemical processes are inevitably important for understanding the manufacture of micro- and nanomaterials and structure-property relations. One top-down approach for synthesising a range of materials is the mechano-chemical milling process, a simple and efficient process that can produce large-scale functional materials with uniform properties. Mechano-chemical milling is widely used to synthesise bulk, micro-, and nano-range solid solutions for a variety of applications in energy, chemical catalysis, antimicrobials, sensors, actuators, and storage. One of the challenges of the mechano-chemical milling process is that powder particles are easily cold-welded to each other due to plastic deformation during prolonged milling. Another issue is the generation of trace level contaminants during mechanical milling. Also, several process parameters like milling time, milling speed, milling atmosphere, temperature of milling, and the grinding medium have significant effects on the final product. These make the process more complex, and there are challenges to get useable materials through these approaches.

The aim of this Special Issue is to highlight useful methods and applications of micro- and nanomaterials prepared through top-down approaches via mechano-chemical reactions and processes. Research and review articles with recent developments and advancements focusing on top-down synthesis approaches, characterisation, and optimisation for their applications in various fields are particularly welcome. Emphasis on the advantages and disadvantages of the mechano-chemical milling processes and top-down approaches, with a concrete conclusion of the usefulness of these techniques and their potential to produce reproducible materials with specific structures and properties, are especially welcome.

Potential topics include but are not limited to the following:

• Mechano-chemical reactions and processes to produce functional nanomaterials
• Synthesis, optimisation, and characterisation of mechano-chemical manufacture of micro/nanomaterials
• Novel fabrication techniques for micro/nanomaterials
• High energy ball milling synthesis methods for nanomaterial preparation
• Studies of the magnetic, electrical, and optical properties of ball milled materials
• Challenges and solutions to contamination issues inherent in high energy ball milling processes
• Application of micro/nanomaterials in sensors, energy storage and conversion, antimicrobial activity, and photocatalysis
• Synthesis of nanocomposite materials and their potential applications
• Characterisation of micro- and nanomaterials prepared by top-down approaches
• Recent developments and advancements of top-down synthesis of nanomaterials