Six major modification methods of nano zinc oxide
Nano zinc oxide is a new type of functional fine inorganic chemical material. Due to its small particle size and large specific surface area, it possesses unique physicochemical properties in chemistry, optics, biology, and electronics. It is widely used in antimicrobial additives, catalysts, rubber, dyes, inks, coatings, glass, piezoelectric ceramics, optoelectronics, and daily chemical applications, and holds great promise for development and utilization.
However, due to its large specific surface area and high specific surface energy, nanozinc oxide exhibits strong surface polarity, prone to self-agglomeration, and is difficult to disperse evenly in organic media, significantly limiting its nano-effect. Therefore, dispersion and surface modification of nanozinc oxide powders are essential treatments before nanomaterials can be applied in matrices.
1. Surfactant Modification
Surfactant modification involves the electrostatic interaction of surfactants to form an organic coating on the surface of nanomaterials, thereby improving their compatibility with organic matrices.
Although surfactant modification is a simple process, its effectiveness is generally poor, making it difficult to form a stable and robust coating on the surface of nanomaterials.
2. Mechanochemical Modification
Mechanochemical modification uses mechanical forces to alter the physical and chemical properties of nanomaterials, thereby enhancing their affinity and reactivity with other substances.
However, mechanochemical modification typically takes a long time and generally has poor results for nanomaterials.
3. High-energy Modification
High-energy modification involves the polymerization of organic compound monomers using plasma or radiation treatment, which then coats the nanomaterial’s surface.
High-energy modification generally achieves better results than the previous two methods, but it has disadvantages such as high energy consumption and technical difficulty.
4. Esterification Modification
Esterification is a surface modification method that utilizes the carboxylic acid groups in modifiers such as higher fatty acids or unsaturated organic acids to react with hydroxyl groups on the surface of a nanomaterial to achieve esterification.
The esterification method is simple, but its modification effect is poor and it usually needs to be used in conjunction with a coupling agent.
5. Polymer Grafting
Polymer grafting involves first grafting a polymer monomer onto the surface of a nanomaterial, then initiating a polymerization reaction to extend the carbon chain, and finally allowing the polymer to coat the entire nanomaterial.
The polymer grafting method is complex to operate, and the modification effect is affected by various factors, making it difficult to achieve widespread application.
6. Coupling Agent Modification
A coupling agent is based on a silicon or metal element, with two different groups on either side that can connect to inorganic and organic matrices. These three components work together to achieve chemical modification of the nanomaterial. Nano-zinc oxide was modified with APS silane coupling agent. Both modified and unmodified nano-zinc oxide were dispersed in anhydrous ethanol to prepare printing inks for use as electron transport layer materials in photovoltaic cells. The performance of the two inks was then compared. The results showed that the modified nano-zinc oxide was better dispersed in anhydrous ethanol and remained agglomerated for 12 months. The electron transport layer material prepared with this agent exhibited higher electron transfer efficiency and could meet device performance standards at thinner thicknesses.
Nano-zinc oxide was chemically modified using silane coupling agents bearing glycyloxy and amino functional groups. Both modified and unmodified nano-zinc oxide were incorporated into epoxy coatings for weathering resistance testing. The results showed that the epoxy coatings incorporating nano-zinc oxide modified with the glycyloxy silane coupling agent exhibited significantly smaller changes in contact angle, color, and carbonyl groups after 450 hours of accelerated weathering, demonstrating significantly improved weathering resistance compared to epoxy coatings containing unmodified nano-zinc oxide.
The coupling agent method is the most promising modification method due to its simple process, good modification effect, and low cost.
Comparing the various surface modification methods mentioned above, and considering both modification effect and difficulty, it can be seen that the esterification method and the coupling agent method are more suitable for surface modification of nanomaterials.