## 1 Introduction  
The materials of microcapsules, composed of core-shell or matrix-embedded systems, have been extensively studied to control the use of active materials in various fields, including home care, cosmetics, pharmaceuticals, and food technology [1, 2, 3, 4, 5]. Synthetic polymers such as melamine [6, 7], polymethacrylate [8, 9], and polyurethane/urea [10, 11] are widely used in the fabrication of microcapsules; however, they are difficult to degrade naturally [12, 13, 14]. Microcapsules are classified as primary microplastics because their materials are hardly biodegradable [15, 16]; hence, most countries have issued fixed-term regulatory legislation recommending alternatives to microplastics [17, 18].  
Silica, which is widely used in anticaking agents, abrasives, moisture or oil absorbers, additives, etc., is one of the alternative material candidates [19, 20, 21, 22]. Although the encapsulation of active ingredients using silica has been investigated, further work is needed to understand the mesoporous features of silica, so that its applicability can be extended to other areas such as fragrance microcapsule fabrication [23, 24, 25]. To compensate for the disadvantages of silica, microcapsules have been synthesized by hybridization with ethyl cellulose [26], polyurea [27], melamine [28], or have been hydrophobically modified by adding methylriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) [29, 30]. However, these microcapsules are not free of microplastics. During water/oil (W/O) emulsion template synthesis, the silica reaction proceeds more slowly in an acidic than in a basic medium, resulting in dense and less porous microcapsules [31, 32, 33]. Although the addition of tetraethyl orthosilicate (TEOS) can reduce the porosity, in contrast to our study, the phase of the studies was inverted and the encapsulated ingredient exhibited a retention time of only about 100 h in deionized (DI) water [33]. Products such as cosmetics and laundry detergents typically contain emulsifiers and have a shelf life of at least three years [34]. The fragrance in household products should be retained within the capsule for as long as possible; however, the fragrance retention of microcapsules in such products can be negatively impacted by harsh conditions, including high emulsifier concentrations, high temperature washing cycles, and irregular temperatures during distribution.  
In this study, we developed fragrance microcapsules with low porosities composed entirely of silica. These microcapsules contain no microplastics and retain the fragrance for extended periods, even under harsh conditions. Using a fragrance O/W emulsion as a template, TEOS in the oil phase was hydrolyzed at the O/W interface to form silica shells under mild conditions (25 \({}^{\circ}\)C without pH adjustment). TEOS was subsequently applied to the premature silica microcapsules for additional silica coating owing to seeded growth. After the addition of TEOS, microcapsule thickness was assessed using focused ion beam scanning electron microscopy (FIB-SEM), and the specific surface area was determined by Brunauer-Emmett-Teller (BET) analysis. In addition, the fragrance retention time and practical qualitative fragrance were evaluated in a high-concentration emulsifier solution at a high temperature to mimic a harsh environment.