The surface chemistry of 3D graphene can be modified in several ways:

First, covalent bond modification

Functional group introduction:

Specific functional groups, such as hydroxyl (-OH), carboxyl (-COOH), amino (-NH₂), etc. are introduced on the surface of three-dimensional graphene through chemical reactions. These groups can change the surface polarity of graphene, its hydrophilic/hydrophobic properties, and its ability to interact with other substances.

For example, the introduction of carboxyl groups to the surface of 3D graphene can make it easier to bind to metal ions or biomolecules for heavy metal ion adsorption or the construction of biosensors.

Chemical reactions can include oxidation reaction, halogenation reaction, amidation reaction, etc. Taking the oxidation reaction as an example, graphene can be treated with strong oxidants such as potassium permanganate and nitric acid, and oxygen-containing groups such as carboxyl and hydroxyl groups can be introduced on its surface.

Polymer grafting:

The polymer is connected to the 3D graphene surface by covalent bond to realize the regulation of its surface properties. Polymers can give graphene new functions, such as improving its solubility, enhancing mechanical properties, and improving biocompatibility.

For example, through surface-initiated atomic transfer radical polymerization (SI-ATRP) and other methods, it is possible to graft polystyrene, polyacrylic acid and other polymers on the surface of graphene. The grafted 3D graphene can be used to prepare high-performance composite materials or transport carriers.

The surface of the graphene first needs to be treated, an initiator or reactive group is introduced, and then the growth of the polymer is triggered under the right conditions.

Second, non-covalent bond modification

Surfactant adsorption:

Non-covalent interactions between surfactant molecules and 3D graphene, such as van der Waals forces, π-π packing, etc., were used to modify the surface of graphene. Surfactants can change the dispersion and stability of graphene, making it easier to disperse in solvents.

For example, the use of surfactants such as sodium dodecylbenzene sulfonate (SDBS) and cetyltrimethyl ammonium bromide (CTAB) can improve the dispersion of three-dimensional graphene in water for the preparation of water-based graphene composites.

The choice of surfactant should be determined according to the application needs of graphene and solvent properties, while taking into account the stability and biocompatibility of the surfactant and other factors.

Molecular adsorption:

Some molecules, such as dye molecules, biomolecules, etc., can be adsorbed on the surface of 3D graphene through non-covalent bonds, changing its optical, electrical or biological properties.

For example, adsorbing fluorescent dye molecules could give graphene fluorescent properties for use in biological imaging. Adsorption of biomolecules such as proteins, nucleic acids, etc., can build biosensors or delivery systems.

The adsorption process is usually spontaneous, and the degree and stability of adsorption can be controlled by adjusting the pH value and ionic strength of the solution.

Third, doping modification

Metal doping:

Doping metal atoms or ions into the lattice of three-dimensional graphene can change its electronic structure and chemical properties. Metal doping can improve the conductivity and catalytic activity of graphene.

For example, doping transition metals such as iron, cobalt, nickel, etc., can prepare three-dimensional graphene catalysts with high catalytic activity for fuel cells, synthesis and other fields.

Doping methods can include in situ doping and solution doping during chemical vapor deposition (CVD). The concentration and distribution of doping can be adjusted by controlling the amount of doping source and reaction conditions.

Non-metallic doping:

Non-metallic elements such as nitrogen, boron, sulfur, etc., can also be doped into three-dimensional graphene, changing its electronic structure and chemical properties. Nonmetallic doping can regulate the band gap of graphene and improve its chemical stability.

For example, nitrogen-doped three-dimensional graphene can improve its oxygen reduction reaction (ORR) catalytic activity in alkaline environments for use in areas such as metal-air batteries.

Doping methods can be similar to metal doping, including CVD method, high temperature annealing method, solution method, etc. The properties of doped graphene can be characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and other techniques.

Fourth, composite modification

Composite with other materials:

The composite of 3D graphene with other materials such as metal particles, quantum dots, carbon tubes, etc., can combine the advantages of the two materials and achieve synergies in performance.

For example, by loading gold particles onto 3D graphene, surface-enhanced Raman scattering (SERS) substrates with high sensitivity can be prepared. Composite with carbon tubes can improve the mechanical strength and electrical conductivity of graphene.

The composite method can include physical mixing, chemical deposition, in-situ growth, etc. The structure and properties of the composite materials can be characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical testing and other means.

Composite with polymers:

Composite materials with polymer can be prepared with specific properties, such as high strength, high toughness, flame retardant and so on. The polymer can be used as the matrix material to disperse the three-dimensional graphene uniformly and play the strengthening role of graphene.

For example, combining with polylactic acid (PLA) can prepare biodegradable high-strength composite materials for packaging materials, medical devices and other fields.

The composite methods can include solution blending, melt blending, in-situ polymerization, etc. The properties of composite materials can be evaluated by mechanical properties testing, thermal properties testing, flame retardant properties testing and other methods.