Controlled sustained release of natural volatile organic compounds from phytoncide emulsion-zeolite composites via surfactant hydrophilic-lipophilic balance adjustment

Natural volatile organic compounds (NVOCs) have attracted attention for indoor air quality (IAQ) applications due to their antimicrobial and physiological benefits; however, their high volatility and concentration instability limit long-term effectiveness. In particular, phytoncide oil provides high NVOC concentrations but volatilizes rapidly, whereas phytoncide water releases more gradually at low concentrations. To harness these complementary characteristics, this study developed a controlled-release system by combining hydrophilic-lipophilic balance (HLB)-tuned oil-in-water phytoncide emulsions with natural zeolite as a porous carrier. Optimizing the surfactant HLB improved emulsion stability and enhanced NVOC loading within the zeolite structure, with higher emulsion stability leading to more efficient adsorption and sustained release. The resulting phytoncide-zeolite composite (PTZE) exhibited significantly retarded release behavior compared to neat oil, while maintaining diffusion-dominated sustained emission in both short- and long-term evaluations. Release profiles were well described by the Weibull model, indicating controlled transport within the porous matrix. Importantly, the stabilized release suppressed rapid concentration peaks while maintaining prolonged emission, which is advantageous for managing indoor exposure levels. These findings demonstrate that HLB-guided emulsion stabilization combined with porous carriers provides a practical strategy for improving concentration stability of bio-based VOCs, supporting health-conscious IAQ management and potential application in functional filters and HVAC systems.