3.7.3. Kinetic Study

The kinetic study was studied using a pseudo-first-order and pseudo-second-order model. The applicability of the kinetic models was determined based on the correlation coefficient (R2) value of a particular model. The pseudo-first-order kinetic model can be described as the diffusion control process through a boundary [49]. The pseudo-second-order kinetic model is based on the assumption that the rate-determining step is due to chemisorption [50,51]. The pseudo-second-order kinetic process is greatly affected by the number of metal ions on the Ag-NPs [52]. The rate constant (*k*) of the RhB and MB dye reduction process by *C. pentandra*/Ag-NPs can be determined from the slope of the plot for both models as shown in Table 4. Based on the correlation coefficients value (R2), the reduction of both RhB and MB dye by *C. pentandra*/Ag-NPs is fitted well with pseudo-first-order model for both RhB and MB dye suggest that the diffusion control process through a boundary was occurred [49]. Diffused BH− <sup>4</sup> ions produced hydrogen that was attached over the Ag-NPs surface together with dye molecules. Then, the electron transfer between Ag-NPs donated by BH− <sup>4</sup> ions to the dye molecules were occurred to degrade dye [48].

**Table 4.** The results of pseudo-first-order and pseudo-second-order kinetic model of RhB and MB dye reduction by *C. pentandra*/Ag-NPs.


The performance of *C. pentandra*/Ag-NPs for the catalytic reduction of RhB and MB dye was compared with other reported Ag-NPs catalyst as shown in Table 5. It can be concluded, the reduction rate recorded from this work can be considered as the good nanocatalyst to reduce dyes using an environmentally benign method, simple method, efficient, easy to separate, stable nanoparticles, difficult to swelling and no need to add a binding agent.

**Table 5.** Comparison of the catalytic reduction performance of MB and RhB dye by AgNPs nanocatalyst synthesized from another method of preparation.

