Application of sawdust particles modified by in situ surface polymerization of m-phenylenediamine and its by-product: Batch and continuous removal of Cr(VI)

The primary objective of this research was to synthesize an adsorbent for Cr(VI) removal using a simple synthesis method that involved the use of KMnO4 for the surface activation of sawdust in which the polymerization of m-Phenylenediamine (mPD) can take place directly on the surface of the adsorbent. The adsorbent's surface morphology was assessed using various techniques including FESEM, EDS, FT-IR, and XRD. The optimal adsorbent was prepared by synthesizing different adsorbents under various KMnO4/sawdust and PmPD/sawdust mass ratios and the best performance was obtained at ratios of 1 and 0.6 respectively. Batch experiments were conducted at optimal conditions (pH = 2, adsorbent dosage of 2 g L−1, contact time of 50 min) and removal efficiency of 90.28% was achieved at a Cr(VI) concentration of 100 mg L−1. The Langmuir isotherm model provided the most accurate fitting to the experimental data, resulting in the maximum adsorption capacity of 62.11 mg g−1. The interparticle diffusion model presented the most precise fitting to the experimental values. The positive value ΔH° and negative values ΔG° prove that the adsorption reactions are endothermic and spontaneous. To assess the effectiveness of PmPD/MnO2/sawdust in removing Cr(VI) at dynamic scales, column experiments were carried out at various flow rates and initial Cr(VI) concentrations. Also, the MnO2 particles obtained after the oxidation of sawdust were functionalized using the mentioned process, and the value of adsorption capacity was determined as 270.27 mg g−1. The easy separation, and full-scale applicability showed a promising application of sawdust/MnO2/PmPD for Cr(VI) removal from aquatic environments. [Display omitted] •KMnO4 was used for the surface activation of sawdust with MnO2 particles.•The polymerization of mPD was conducted on the activated surface.•The reusability of the adsorbent and mPD solution were successful.•Fixed-bed column studies assessed the industrial applicability of the adsorbent.•The Adsorption capacity of the modified MnO2 by-product was 270.27 mg g-1.