The Justiciacarnea and Camelliaassamica plant leaves samples were sourced from Umuchima Ihiagwa, Owerri West, Imo State Nigeria and identified at the Department of Crop Science, FUTO. Distilled water and Aluminium Potasium Sulphate (KAl(SO₄)₂·H₂O) were purchased from Chemisciences Ltd, Owerri Imo State Nigeria. The cotton fabrics used were sourced from the regular market in Owerri, Nigeria. Dye extraction and fabric dyeing was carried out at the Polymer Engineering Department laboratory of Federal University of Technology, Owerri (FUTO).

2.1.1. Sample Preparation: Justiciacarnea Leaves and Cotton Fabric

The Justiciacarnea leaves were thoroughly washed with double distilled water to remove dirt; oven dried at the temperature of 70˚C to crisp before grinding into fine particles. The cotton fabrics were cut to a square size of 2 × 2 cm² having 64 ends and 64 picks and weight of 1 g. Some fabrics were pre-mordanted before dyeing while some were dyed without mordant application.

2.1.2. Fabric Pre-Mordanting

25% of the mordant on the weight of the fabric (OWF) was dissolved in 30 ml of distilled water in a 50 ml beaker at 70˚C. The fabric was removed after 30 mins and excess water squeezed out before spreading it outside to dry under sun.

2.1.3. Dye Extraction from Justiciacarnea

5 g of pulvurized Justiciacarnea samples were put into a 500 ml Soxhlet extractor with distilled water as the solvent. Extraction was done at 70˚C for 4 h in two-batch process with material to liquor ratio of 1:100 respectively. At the end of the extraction process, the extracts were pooled together, centrifuged and stored in a 500 ml conical flask. The pulverized leaf samples used for the extraction were dried and weighed after the extraction process.

2.1.4. Fabric Dyeing

We used a fabric preparation and dyeing method reported by Oguzie, C. K. et al. 2024 on Peristopheroxburghiana dye adsorption onto Cotton fabric [16] with some few modifications. Already prepared cotton fabric was dyed in a beaker containing the dye extract with material to liquor ratio of 1:20 at time intervals of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 mins, and varied Temperature ranges of 50˚C, 60˚C and 70˚C respectively. After each dyeing time, the fabric was removed and a portion of the dye liquor stored in a test bottle to be used for absorbance test the spectrophotometer. This process was done twice for each temperature and time range.

2.1.5. Characterization of Dye Extract

FTIR (PerkinElmer spectrum IR 10.7.2 spectrometer) was used to identify the functional groups of the dye while UV-vis spectrophotometer (Vis spectrophotometer 728, wave length range: 320 nm - 1020 nm) was used to check the absorption characteristics of the extracted dyes.

Justiciacarnea dye has the main maximum absorbance peak at 424 nm (Figure 1) which is within the visible light spectrum and hence can serve as a dye. There was an increase at 575 nm as the absorbance began to diminish. The peak at 424 nm has also been reported in previous studies as the range for flavonoids [17]. However, Aslan (2024) [18] was more specific in identify the natural dyes between the peaks 420 - 575 nm as emodin which is type of flavonoid. This is also in agreement with the findings of Imohiosen (2023) [9] from the phytochemical studies of Justiciacarnea leaves extract.

Figure 1. Ultra violet visible infrared spectroscopy (UV-VIS) spectral of Justiciacarnea.

The FTIR results were obtained with PerkinElmer spectrum IR 10.7.2 spectrometers in the wavelength range of 450 - 4000 cm⁻¹. Result in Figure 2 confirm the possible presence of water with the peak at 1610.74 cm⁻¹ representing C=C aromatic mode or N-H bending [19]-[21]. The peaks at 1007.35 cm⁻¹ are due to C-O vibration mode while the peaks at 2917.80 cm⁻¹ and 2850.18 cm⁻¹ is attributed to C-H stretch vibrations which indicates the presence of aromatic C–H group in the dye extract [18]. The broad band at 3283.89 is attributed to O-H stretch of alcohols or phenols [18][22]. However, the 3339.52 cm⁻¹ on the blue spectrum is –OH of the distilled water.

Figure 2. FTIR of Justiciacarnea dye extract (blue colour represents water, medium of extraction while red colour represents dye extract).

Absorbance value of the dye extract was checked with the UV-Vis spectrophotometer before dyeing and after each dyeing time and was used to ascertain the equilibrium time. It should be noted that absorbance values are directly proportional to dye concentration at all wavelength hence the absorbance values were used to calculate both the dye uptake and dye concentration at the different time of dyeing and at equilibrium. Uptake of dye was calculated using Equation (1) [23] based on the absorbance results measured at a wavelength of maximum absorbance of 424 nm which is the maximum absorbance peak for Justiciacarnea dye extract. The effect of dyeing time and temperature on dye uptake when fabric was dyed without mordant and when fabric was pre-mordanted is presented in Figure 3 and Figure 4 respectively.

Figure 3. Effect of time and temperature on J.carnea dye adsorption on un-mordanted cotton fabric A (50˚C), B (60˚C) and C (70˚C).

Figure 4. Effect of Time and Temperature on J.carnea dye adsorption on Mordanted Cotton Sample A (50˚C), B (60˚C) and C (70˚C).

Effect of Time and Temperature on Dye Uptake

There is a sharp high uptake of dye at the first 5 minutes of dyeing which gradually normalizes as time progresses as observed in Figure 3 and Figure 4. This is a clear indication that the fabric has high affinity for the natural dye and does not require much time for dye adsorption. Equilibrium was however reached earlier when dyeing with pre-mordanted fabric than without mordant at the respective temperatures. Dye absorption begins with adsorption unto the fabric surface before the dye molecules gradually diffuse into the fabric pores. Hence, equilibrium is reached when the fabric had absorbed enough dye molecules based on its available pore spaces. This phenomenon is clearly seen in Figure 3 and Figure 4 with the uptake at the first 5 minutes of dyeing being higher than the dye uptake at equilibrium point at about 20 mins. Also, more dyes were absorbed by the fabric without mordant at 60˚C and 70˚C respectively than the pre-mordanted fabric. This can be attributed to the presence of mordant molecules already occupying some space on the cotton fabric hence reducing the available space for dye adsorption [23]. Similarly, the dye molecules that formed a complex bond with the mordant desorbs with increase in temperature and time hence at 70˚C equilibrium point only 5% of dye uptake was achieved against 44.43% at same temperature and time of dyeing without mordant on the fabric.

The highest dye uptake was recorded with fabric without mordant at 60˚C while with pre-mordant fabric it was recorded at 50˚C. This is an indication that dyeing without mordant at a temperature above 50˚C will improve cotton fabric uptake of Justiciacarnea dyes while dyeing a pre-mordanted cotton fabric at temperature below 50˚C will improve dye uptake. For pre-mordanted fabric, increase in temperature increases the rate of dye desorption as equilibrium time is approached (Figure 4).

This study was done at a constant temperature of 60˚C at the different time ranges for both fabric types. We used Equations (2) and (3) [23] to calculate quantity of dye adsorbed at equilibrium Q_e (mg/g) and at different time of dyeing Q_t (mg/g)

where C_i, C_t, C_e, W and V represent the initial dye concentration, concentration at different dyeing time, concentration at equilibrium (mg/ml), weight of fabric and dye liquor volume. The values were used for the two adsorption kinetic models used in this research—pseudo first order and pseudo second order kinetic models of adsorption. The Langergren’s Equation (as shown in Equation (4)) [23] was used to fit the pseudo-first order model as represented in Figure 5 and Figure 6 respectively, while Equation (5) [23] was used for the pseudo-second-order as shown in Figure 7 and Figure 8 respectively. C_i was determined using Equation (6).

where K₁, K₂ andt represent the rate constants of the pseudo first, second order kinetic models and time of adsorption.

where m is the mass of dissolved dye particles from the plant leaf ascertained from the difference in weight of pulverized plant sample before extraction and after extraction and V is volume of dye extract solution. C_t andC_e were calculated using Equation (7) [24].

where, A, ε, c, l represent, dye extract absorbance reading at maximum wavelength, dye mass extinction coefficient, dye concentration and cuvette path length.

3.4.1. Pseudo-First Order Kinetic Model

The correlation coefficient R² value of 0.1409 was calculated from the plot of ln(Q_e – Q_t) against t shown in Figure 5 and Q_e (1.833 mg/g) and K₁ (0.0435) were calculated from the intercept and slope respectively. The calculated value of Q_e agrees with experimental value of very low dye uptake just before the point of equilibrium between 25 and 30 minutes of dyeing shown in Figure 3. Same plot for pre-mordanted fabric in Figure 6 gave an R² of 0.4521, K₁ of 0.1234 and Q_e of −0.2034 mg/g. Again, the calculated Q_e which is negative agrees with the experimental value indicating dye desorption close to equilibrium point that is, between 15 and 20 minutes of dyeing as shown in Figure 4.

3.4.2. Pseudo-Second Order Adsorption Kinetic Model

A plot of t/Q_t versus t in Figure 7 was used to calculate the value of R² as 0.9932, Q_e as 0.03 mg/g and K₂ as −0.03. The Q_e value still agreed with experimental value of a very low dye uptake at the point before equilibrium. When mordant was applied on the fabric (Figure 8) the R² value was calculated as 0.998, with a Q_e of 0.03 mg/g and K₂ of −147.

Figure 5. Graph of pseudo-first Order Adsorption kinetics of J.carnea dyes on unmordanted cotton fabric sample.

Figure 6. Graph of pseudo-first order adsorption kinetics of J.carnea dyes on pre-mordanted cotton fabric sample.

Figure 7. Graph of pseudo-second order adsorption kinetics of Justiciacarnea dyes on unmordanted cotton fabric sample.

Figure 8. Graph of pseudo-second-order adsorption of Justiciacarnea on mordanted cotton fabric sample.

The R² values from the pseudo-second order kinetic models are higher and closer to 1 than that of the pseudo first order models for both dyeing with pre-mordanted cotton fabric and cotton fabric without fabric. It should be noted that the adsorption system is best described by the model with highest regression coefficient [25]. This indicates that the adsorption mechanism of Justiciacarnea dye extract fits the pseudo-second order kinetic model and hence is used to describe it. This implies that chemical adsorption controlled the process [26]. It has also been reported that a correlation coefficient of 1 indicates a positive linear correlation [27].