# Mdpj _sciences_
## 3 Technology and Materials
### Green Walls  
[PERSON] et al. (2017) aimed to examine the potential of living walls to remove VOCs. They used a modular felt-based system developed and patented by the University of Seville (Fytotextile(r), Terapia Urbana, S.L., Seville, Spain). The module consisted of felt pockets designed for semi-hydroponic cultures, featuring a waterproof back layer, an intermediate drainage layer, and a breathable front layer. _Nephrolepis exaltata_ L. was planted in a mixture of coconut fiber and peat (Figure 3). The modular technology allows for covering large vertical surfaces, enabling the capture of substantial amounts of VOCs near the system. Additionally, using a lightweight material like felt helps contain the load on the support structure. Similarly, [PERSON] et al. (2018) focused on VOC removal and compared the performance and characteristics of five types of commercial green wall systems. Among them, the \"Scotscape hydroponic wall system\" uses lightweight felt-based modules (Fytotextile(r)), similar to the previously described study. These are attached to a support layer via a metal frame, with irrigation tubes and a hydroponic drainage system. Another system, the  
Figure 2: Word cloud of the keywords from the selected papers. \"Versa-wall container system\", consists of a covering structure attached to the wall, framing rows of trays and pots with a drip irrigation system, which can be manual or automatic, with water drainage from the bottom or recirculated. This system is noted for its ease of installation and maintenance. The \"Alivotec container system\" features a modular configuration with a metal frame and non-toxic plastic trays containing soil where plants grow. The trays have grooves to facilitate irrigation, which can be manual or automatic, connected to a water supply system. This technology is lightweight and easy to install, with the advantage of easily replacing individual plants since each is planted in a separate tray. The \"Biotecture modular hydroponic system\" includes a steel support frame holding an impermeable panel, a geotextile drainage layer, an automatic drip irrigation system, and a hydroponic growing medium in Rockwood with a polypropylene grid and vegetation layer. This complex structure makes it the second-heaviest system studied. The \"Vertiss modular substrate system\" is the heaviest (94 kg/m2) and comprises a steel frame, modular openings containing Pozzolan and cross-linked polymers as substrates, and a less dense vegetation layer (maximum 32 plants per m2), with automatic micro-drip irrigation (Figure 4). Figure 4: Vertiss modular substrate system. Figure 3: Modular felt-based system. Six studies evaluated how structure, materials, and selected plant species influence the ability to absorb atmospheric particulate matter. [PERSON] et al. [19] conducted an experiment to select the best plant species for reducing PM concentrations within a green wall. The analyzed structure featured a waterproof steel grid support with plastic trays, similar to the \"Alivotec container system\" described above, filled with soil, fertilizer, and chosen plants. [PERSON] et al. [20; 21] used a commercial living wall system by Nemec Cascade Garden Ltd., Praha, Czech Republic, consisting of self-supporting modular panels with interconnected water containers holding potted plants and an automatic irrigation system, to analyze PM removal. [PERSON] et al. [22] designed an LWS to reduce CO\({}_{2}\) levels, connected to a base wall with a metal frame and fixing screws. The structure includes pots linked to an irrigation system that pumps water from a base reservoir, distributes it via drip irrigation, and returns it by gravity (Figure 5). In contrast, [PERSON] and [PERSON] [23] used a hydroponic LWS based on [PERSON]'s method, with PVC waterproof plates attached to the support wall and fabric layers directly planted with vegetation. Additionally, it is crucial to investigate how the environmental placement of green walls affects their performance. [PERSON] et al.