Silica (mainly composed of silicon dioxide, SiO₂) itself does not possess significant magnetism. However, by combining it with magnetic materials (such as Fe₃O₄) to form composite materials, it can acquire magnetic properties. These composite materials demonstrate significant application value in environmental remediation, biomedicine, and other fields.

I. Preparation Methods of Silica-Magnetic Composite Materials
**Mechanical Blending Method**
**Operating Principle:** Silica is combined with magnetic materials (such as carbonyl iron powder, CIP) through mechanical mixing to form a composite material.
**Process Characteristics:** Simple operation and low cost, but poor uniformity and prone to agglomeration.
**Optimization Direction:** Improving dispersibility by adding coupling agents or surface modifiers, such as the method mentioned in the document, where graphene oxide masterbatch and silica masterbatch are blended in a two-roll mill or internal mixer for 1-20 minutes to prepare a uniform composte material.

**Sol-Gel Method**
**Operating Principle:** Using silica as a carrier, magnetic materials are fixed to the surface of silica through hydrolysis and condensation reactions.
**Process Features:** Precise control over the distribution and content of magnetic materials allows for the formation of a uniform composite structure.
**Application Example:** The CB-CIP@SiO₂-GF/PA6 composite material mentioned in the document is prepared using a hot-pressing process, achieving a uniform combination of magnetic materials and silica.
**Magnetic Coagulation and Sedimentation Technology:**
**Operating Principle:** Utilizing the synergistic effect of magnetic materials and coagulants, the silica is magnetized.
**Process Features:** Suitable for large-scale wastewater treatment, with a magnetic seed recovery rate exceeding 98%.
**Application Example:** The magnetic coagulation and sedimentation technology mentioned in the document, through the addition of polyaluminum chloride (PAC), polyacrylamide (PAM), and iron(III) oxide (Fe₃O₄), achieves highly efficient treatment of silica wastewater, with a suspended solids removal rate exceeding 99%.

**II. Magnetic Properties of Silica-Magnetic Composite Materials:**
**Magnetic Separation Characteristics:**
**High-Efficiency Separation:** The composite material can be rapidly separated by an external magnetic field, facilitating recycling.
****Magnetic Coagulation and Sedimentation Technology:** **Magnetic Seed Recovery Rate:** The document states that the magnetic seed recovery rate can reach over 98%, significantly improving the material's recycling rate.
**Suspended Solids Removal Rate:** During magnetic separation, the suspended solids removal rate can be further improved to over 99%, demonstrating excellent purification effects.
**Improved Dispersibility:** Surface Modification: Modification of the silica surface using silane coupling agents reduces agglomeration caused by its high specific surface area and surface hydroxyl groups.
**Application Effects:** The document mentions that wet-process modified silica forms a "flexible interface layer" in rubber, reducing tire rolling resistance by 15% and simultaneously improving wet skid resistance.
**Multifunctional Synergistic Effect:** Magnetic-Adsorption Synergistic Effect: The high specific surface area and adsorption properties of silica combined with the magnetic separation characteristics of magnetic materials create a multifunctional synergistic effect.
**Application Example:** The heavy metal contaminated soil remediation technology mentioned in the document uses silica as a matrix, combined with magnetic materials, to achieve efficient removal of heavy metals through mechanisms such as surface complexation and electrostatic adsorption.

** III. Application Areas of Silica-Magnetic Composite Materials
Environmental Remediation
Water Treatment: Used to remove suspended solids, heavy metal ions, and organic pollutants from wastewater.
Application Results: The magnetic coagulation sedimentation technology mentioned in the document can reduce suspended solids from 3000 mg/L to below 50 mg/L and silicon content from 600 mg/L to below 100 mg/L.

Soil Remediation: The document mentions that after using bio-based silica materials and sulfate-reducing bacteria to synergistically stabilize and remediate antimony and arsenic-contaminated soils around the antimony mining area in the Jinjiang River Basin of Dong'an County, the stabilization rate of antimony reached 53.13%-92.03%, and the stabilization rate of arsenic reached 52.36%-70.9%.

Biomedicine
Drug Carrier: Silica, combined with magnetic materials, can be used as a drug carrier to achieve targeted drug delivery.

Application Advantages: The document mentions that modified silica has applications in the biopharmaceutical field, such as tilmicosin-loaded modified silica drug release systems, which extend the drug's half-life to 48 hours and reduce toxic side effects by 60%.

Magnetothermal Therapy: Magnetic nanoparticles generate heat under an alternating magnetic field, which can be used for tumor treatment.

Electronics and Materials Science
Electronic Packaging: The document mentions that modified silica reduces dielectric loss to below 0.002 in 5G high-frequency electronic adhesives, meeting chip packaging requirements.

Microwave Absorption: The document mentions that the CB-CIP@SiO₂-GF/PA6 composite material has an effective absorption bandwidth exceeding 5.6 GHz with a material thickness of 1.91~1.95 mm, covering the entire Ku-band.

Rubber Reinforcement: The document mentions that LATES-modified silica has a better effect on NR performance than Si69-modified silica, increasing tensile strength from 19.51 MPa to 25.74 MPa and reducing tanδ at 60℃ from 0.111 to 0.071.

Environmental Protection and Green Technology

Green Tires: The document mentions that the proportion of wet-process modified silica in tread rubber is increasing from 15%-20% in 2020 to 25%-35% in 2024, and is expected to exceed 40% in 2025, which can reduce tire rolling resistance by 15%.

Carbon Emission Reduction: The document mentions that the National Development and Reform Commission has allocated 120 million yuan from the "Special Fund for the Development of Strategic Emerging Industries" to focus on breakthroughs in key areas such as continuous modification and waste acid recovery, promoting the green transformation of the industry.

IV. Research Progress and Future Prospects
Development of Novel Composite Materials

Nanocomposite Technology: The document mentions that wet modification combined with nanomaterials has led to the development of novel composite materials, such as silicon-carbon anode materials (reduced fine silica, particle size <50nm) forming a homogeneous silicon/carbon nanostructure with an initial coulombic efficiency of 91% and a cycle life exceeding 1000 cycles.

Multifunctional Integration: Developing composite materials with integrated magnetic, photocatalytic, and adsorption functions to expand application areas.

Biomedical Applications of Magnetic Nanomaterials

Targeted Therapy: The document mentions that magnetic nanomaterials show great application potential in medical imaging diagnostics, targeted drug delivery, and magnetothermal therapy.

Multimodal Imaging: Combining magnetic resonance imaging (MRI) with other imaging technologies to achieve more accurate disease diagnosis.
Expansion of Environmental Applications

Water Treatment Technology: The document mentions that Fe₃O₄ magnetic nanoparticles can be used to remove anionic dye molecules from dye wastewater. Magnetic nanoparticles adsorbing dye molecules can be rapidly removed by an external magnet without causing secondary pollution.

Soil Remediation: Develop specialized silica-magnetic composite materials for different pollutants to improve remediation efficiency.

Future Research Directions:
Improving Magnetic Efficiency: Enhance the magnetic efficiency of composite materials by optimizing the type, content, and distribution of magnetic materials.

Reducing Costs: Develop more economical preparation processes to reduce material costs and promote large-scale application.

Multifunctional Integration: Integrate magnetic, photocatalytic, and adsorption functions into a single material to expand application areas.

Research on silica-magnetic composite materials is in a phase of rapid development. Through rational design and optimization of the structure and properties of composite materials, they are expected to play a greater role in environmental remediation, biomedicine, and electronic materials, providing strong support for sustainable development.