Sawdust-derived graphitic carbon nanostructures as slow-release nutrient carriers: Synthesis, characterization, and short-term crop growth evaluation

Abstract

Low nutrient-use efficiency (NUE) of conventional fertilizers leads to significant nutrient losses and environmental concerns, prompting interest in alternative delivery systems such as carbon-based nanomaterials. This study examined the conversion of lignocellulosic sawdust waste into graphitic carbon nanostructures (GCNs) and assessed their short-term effectiveness as nutrient carriers under controlled field conditions. Sawdust from Sokoto, Nigeria, was carbonized at 400 °C and further processed with sulfuric-acid-assisted thermal restructuring, with all parameters clearly reported. Characterization using UV – Vis, FTIR, XRD, and SEM revealed disordered graphitic carbon with fibrous, nanotube-like structures. However, evidence did not confirm true carbon nanotubes. XRD showed a broad (002) peak at 2θ ≈ 24.8°, FTIR indicated dominant sp^² carbon with residual oxygen groups, and SEM revealed entangled fibrous aggregates. The materials were therefore classified conservatively as graphitic nanostructures. A carbon – nutrient formulation was prepared by physically blending the GCNs with soil nutrients. A five-week randomized complete block field trial compared this formulation with synthetic fertilizer, organic manure, and an unfertilized control. Statistical analysis (oneway ANOVA with Tukey HSD, α = 0.05) showed that the GCN formulation significantly enhanced plant growth compared to the control and organic manure, though it remained less effective than synthetic fertilizer. Atomic absorption spectroscopy confirmed minimal metal contamination. Overall, the study demonstrates the feasibility of producing graphitic nanostructures from sawdust for use as low-dose nutrient carriers, while highlighting the need for further optimization and long-term evaluation.