Three kind of methods are usually used to prepare magnetic materials, namely, calcination, co-precipitation and pyrolysis method. Commonly, the typical pyrolysis process can be subdivided fast pyrolysis, slow pyrolysis and flash pyrolysis. Co-precipitation is to add precipitant to make ions precipitate. Calcination is a thermal treating process, in which materials are heated under certain temperature without fusion to drive off H2O, CO2, SO2 and other volatile constituents.

The three synthesis methods have their own advantages and disadvantages. Co-precipitation has the advantages of shorter process, simple reaction conditions and higher product purity. The calcination method is relatively simple, which employs autoclave heating to produce magnetic biochar.

Methods for producing nanobiochar are discussed in detail in the work Song, B., Cao, X., Gao, W., Aziz, S., Gao, S., Lam, C. H., & Lin, R. (2022). Preparation of nano-biochar from conventional biorefineries for high-value applications. Renewable and Sustainable Energy Reviews, 157, 112057.

Magnetic biochar and nano biochar are two distinct materials with different properties and applications. Let's explore the differences between them in detail:

Composition and Structure:

Magnetic Biochar:

Magnetic biochar is typically produced by incorporating magnetic nanoparticles or materials, such as iron oxide (Fe3O4 or Fe2O3), into biochar during the production process.

The magnetic components in magnetic biochar are usually in the form of nanoparticles, which can be distributed throughout the biochar matrix.

Nano Biochar:

Nano biochar is biochar that has been further processed or modified to have nano-sized particles or structures. This can be achieved through techniques like ball milling, sonication, or chemical treatment to reduce the particle size.

Magnetic Properties:

Magnetic Biochar:

The primary distinguishing feature of magnetic biochar is its magnetism. It can be attracted to a magnet due to the presence of magnetic nanoparticles within its structure.

These magnetic properties enable the easy separation of magnetic biochar from a mixture using a magnet, which is advantageous for environmental remediation applications.

Nano Biochar:

Nano biochar primarily refers to biochar with nanoscale features, which may not necessarily possess magnetic properties.

Applications:

Magnetic Biochar:

Environmental Remediation: Magnetic biochar is often used in environmental applications for the removal of pollutants from water and soil. It can be easily recovered using magnets after adsorbing contaminants like heavy metals, organic compounds, or nutrients.

Biomedical Applications: Magnetic biochar can also be employed in biomedical applications, such as drug delivery systems, due to its magnetic properties.

Nano Biochar:

Agriculture: Nano biochar has gained attention in agriculture due to its nanoscale structure, which can provide a higher surface area for improved nutrient and water retention, making it potentially more effective as a soil conditioner or fertilizer.

Environmental Remediation: While magnetic biochar is specifically designed for magnetic separation in remediation processes, nano biochar may also be used in environmental applications, particularly for adsorbing and immobilizing contaminants in soil and water.

Production Methods:

Magnetic Biochar:

Magnetic biochar is typically produced by adding magnetic nanoparticles during the biochar production process, often through co-pyrolysis or impregnation techniques.

Nano Biochar:

Nano biochar can be produced by further processing conventional biochar using techniques that reduce particle size, like ball milling or sonication.

In summary, magnetic biochar is biochar infused with magnetic nanoparticles, primarily used for its magnetic separation properties in environmental and biomedical applications. Nano biochar, on the other hand, is biochar with nanoscale features, which can be applied in agriculture and environmental remediation, but its distinguishing characteristic is its nanoscale structure rather than magnetic properties. The choice between magnetic and nano biochar depends on the specific application and the desired properties for the intended use.

The key difference is the presence of Fe3O4 or not in the prepared biochar. If it contains magnetic Fe3O4, we call the biochar magnetic biochar. If not, we call it biochar. If the size of the biochar is within nanometer, we call it nano biochar. The size reduction tech such as ball milling or in-situ synthesis can make it nano.

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