Characterizing local Garden Croton (‘pokok puding’) leaf powder as low cost biomaterial for Chromium (VI) uptake

This paper reports the first ever characterization of the use of raw Garden Croton (locally known as ‘pokok
puding’) leaf powder as low cost biomaterial for Cr(VI) removal. Biosorption experiments were carried out at
ambient temperature to study the effects of initial pH (1-7), contact time (15, 30, 45, 60 min), leaf powder’s particle
size (≤ 150, 151-300, 301-500 µm), and initial Cr(VI) concentrations (10, 20, 40, 60, 80 and 100 mg/L) towards
Cr(VI) uptake. Optimum Cr(VI) uptake was observed at pH 1 (2.41 mg/g) and 2 (2.19 mg/g) (p > 0.05). The leaf
powder in the 151-300 µm size displayed better Cr(VI) uptake up to 2.77 mg/g (77.78%; Co = 100 mg/L) at pH 2,
after 30 min (p < 0.05). Equilibrium metal uptake fitted best (R2
= 0.927) to the Freundlich isotherm model (Kf = 0.21
mg/g, n = 1.23) indicating biosorption onto a heterogeneous surface of active sites. Morphological and elemental
analyses by SEM/EDX and FTIR confirmed Cr retention, and presence of active chemical moieties. Interestingly,
XRD revealed that Cr was immobilized within the biomass leaf powder in both forms, i.e. hexavalent, Cr(VI) as
chromatite (CaCrO4) and trivalent Cr(III), as chromium(III) oxide (Cr2O3). Overall findings support the feasibility of
the leaf powder as potential biomaterial for water pollution abatement.