The smart planter used in this experiment was the Meifu eBao 3C model (KJFMN3C). Its core functions included an active negative ion generation module, which continuously released negative air ions to improve microenvironmental air quality. The device was also equipped with an intelligent maintenance system that dynamically optimized plant growth conditions through environmental sensing and automatic irrigation. In addition, the planter contained a large-capacity water reservoir, allowing up to 30 days of operation without manual water replenishment and thereby substantially reducing maintenance frequency. Compared with devices used in similar studies, this smart planter showed certain advantages in system integration and intelligent regulation [7].

Considering indoor ornamental value and public preference, plant selection followed the principle of “prioritizing adaptability while balancing functional performance and ornamental value”. Based on the Catalogue of Indoor Ornamental Plants in China and hydroponic cultivation practices in the Jiangnan region, one species was selected from each of four families-Araceae, Asparagaceae, Araliaceae, and Acanthaceae-resulting in four common indoor ornamental plants as the study species, as shown in Table 1. According to the method of calculating plant leaf area, plants with irregular leaf shapes are transformed into corresponding geometric shapes for calculation, so that the leaf areas of the four samples are as similar as possible, in order to eliminate the interference of leaf area as a variable on the experimental results. To evaluate hydroponic growth adaptability, the four species were cultivated hydroponically for four weeks under 23˚C and 4000 lux, after which root rot incidence was measured.

All four experimental plant species were cultivated hydroponically using Hoagland nutrient solution at pH 5.5 - 6.0. This formulation has been verified by Liu Xiaojiao et al. as being highly suitable for the hydroponic cultivation of indoor foliage plants. The plants were transplanted into hydroponic pots measuring 10 cm × 10 cm × 11 cm, with approximately half of the root system immersed in the nutrient solution. After a two-week pre-cultivation period to allow root stabilization, the plants were used for subsequent experiments [12].

Table 1. Basic information on the hydroponic plants.

After pre-cultivation, the plants were transplanted into the smart planters, as shown in Figure 1. For each plant species, each plant was set up as a control group with ordinary flower pots, and a total of 8 plants were tested. The experiment was conducted in a customized sealed glass chamber measuring 80 cm × 80 cm × 80 cm.

Figure 1. Schematic diagram of four plant species cultivated in smart planters.

Environmental conditions were controlled as follows: temperature, 23˚C ± 1˚C; relative humidity, 50% - 70%. Two sets of experiments were conducted in the same office under the same natural lighting conditions. These conditions were designed to simulate the typical thermal and light environments of modern office and residential spaces. For the hydroponic system, the electrical conductivity of the nutrient solution was maintained at 1.4 mS∙cm⁻¹, natural light was used, and the nutrient solution in conventional planters was manually replaced once per week.

NAI release: Negative air ion concentrations were measured in the customized sealed glass chamber using an air negative ion detector. To minimize spatial heterogeneity, three monitoring points were evenly arranged inside the chamber. Referring to the typical daytime period during which people remain indoors for work, monitoring was conducted daily from 09:00 to 18:00, with readings recorded at 1-h intervals. The hourly mean value from the three monitoring points was used as the NAI concentration. The smart planters records the total NAI output of the system, while the ordinary flowerpot records the release of negative oxygen ions from plants.

Purification performance: Place an equal amount of 5.0 µL 37% formaldehyde solution at the corner of the sealed box, seal and let it stand for 48 hours until the concentration reaches equilibrium, and then measure the initial concentration of formaldehyde in each box (the initial concentration of formaldehyde in the sealed box is less than 0.01 mg/m³). Formaldehyde concentration was then monitored every 2 h for a total of six consecutive measurements. A portable pump-suction six-in-one gas detector was used to determine the initial and final formaldehyde concentrations, and the 12-h removal rate was calculated. The removal rate was calculated as follows:

Removal rate = (initial concentration − final concentration)/initial concentration × 100%

The data was analyzed using SPSS 26.0 for one-way ANOVA to compare the differences in mean air negative ion concentrations of different plants under the same pot conditions and all images were generated using Origin 2023.

To verify the effectiveness of the smart planters, NAI release was compared between hydroponic plants cultivated in smart planters and those grown in conventional planters. The closed chamber experiment showed that the intelligent regulation, together with the active NAI generation module, greatly improved the total output of negative air ions in hydroponic plants of the smart group. As shown by the time-series data in Figure 2, the smart planter markedly improved NAI release performance in all tested hydroponic plants. Under normal conditions, plant-derived NAI release may vary over time depending on species-specific growth characteristics. Nevertheless, the NAI concentration curves of Epipremnumaureum, Chlorophytumcomosum, Heptapleurumheptaphyllum and Fittoniaalbivenis grown in smart planters were consistently higher than those of the conventional planter controls. In particular, during periods with sufficient daytime light, such as 12:00-14:00, the smart planter treatments generally reached higher concentration peaks. The active negative ion generation module continuously released NAIs, allowing the sealed chamber to maintain relatively high NAI concentrations for most of the day. By contrast, the conventional planter treatments showed greater concentration fluctuations and a pronounced decline in the afternoon, with overall baseline concentrations far lower than those of the smart planter treatments.

Based on the statistical data in Table 2, it can be further concluded that in the two key indicators of maximum and average values, the data under smart planter cultivation is significantly ahead of conventional planter. For example, the maximum NAI concentration of Chlorophytumcomosum grown in the smart planter

Figure 2. Temporal variation in negative air ion concentrations released by four hydroponic plant species.

Table 2. Characteristic values of negative air ion concentrations released by four hydroponic plant species.

The letters a and b represent the results of significant differences from multiple comparisons.

reached 3681 ions/cm³, with a mean value of 2811 ions/cm³, approximately 1.8 and 2.0 times higher than those in the conventional planter treatment, respectively, which were 2059 ions/cm³ and 1410 ions/cm³. In addition, the smart planter markedly increased the lower limit of plant-associated NAI concentrations. The minimum values in the conventional planter treatments were generally low, with Heptapleurumheptaphyllum reaching only 224 ions/cm³. This indicates that the total negative ion output of the smart planter system is much higher than that of the conventional group, which can maintain a more stable and long-lasting air purification efficiency. This may be due to the significant synergistic effect of the smart planter automatic adjustment system on all tested plants, or the reinforcement of the active negative ion generation module. One-way ANOVA showed that, under smart planter cultivation, the mean NAI concentration of Chlorophytumcomosum differed significantly from those of Heptapleurumheptaphyllum and Fittoniaalbivenis (p < 0.05). Similarly, the mean NAI concentration of Epipremnumaureum differed significantly from those of Heptapleurumheptaphyllum and Fittoniaalbivenis (p < 0.05), whereas no significant difference was observed between Chlorophytumcomosum and Epipremnumaureum. These results indicate that the combination of smart planter and variegated spider plant achieved the highest NAI release, significantly outperforming the other plant-planter combinations.

The ecological purification performance of the four hydroponic plant species was evaluated through a 12-h closed-chamber experiment, as shown in Figure 3. The dynamic curves of formaldehyde concentration indicate that the smart planter markedly enhanced the formaldehyde purification process of hydroponic plants. In the sealed chamber, formaldehyde concentrations declined more rapidly in the smart planter treatments (Figure 3(a)) than in the conventional planter treatments (Figure 3(b)). By the end of the experiment, after 12 h, formaldehyde concentrations in the smart planter treatments had generally decreased to approximately 1.0 mg∙m⁻³ or lower, whereas those in the conventional planter treatments remained at relatively high levels above 1.8 mg∙m⁻³.

As shown in Table 3, the formaldehyde removal performance of the smart planter treatments over 12 h was consistently superior to that of the conventional planter controls. Among the smart planter treatments, Chlorophytumcomosum showed the highest formaldehyde absorption capacity, reaching 1.67 mg∙m⁻³, with a removal rate of approximately 60%. Even Fittoniaalbivenis, which exhibited a relatively lower absorption capacity, reached 0.78 mg∙m⁻³. In contrast, the corresponding values in the conventional planter treatments were only 0.74 mg∙m⁻³ and 0.21 mg∙m⁻³, respectively, with the highest removal rate reaching only 29.84%. Overall, formaldehyde absorption by plants grown in smart planters was generally about twice that observed in conventional planters. This suggests that, through its material properties and ecological regulation of plant physiological status, the smart planter can optimize the root-zone microenvironment, enhance plant physiological activity, and thereby accelerate the reduction of residual formaldehyde in indoor air.

Figure 3. Temporal variation in formaldehyde concentrations in sealed chambers containing four hydroponic plant species.

Table 3. Ecological purification performance of four hydroponic plant species.