Eco-friendly biochar-modified ZnO nanoparticles for enhanced optoelectronic properties

The present study investigated the effect of in-situ agro-waste biochar-modification on the semiconductor properties of ZnO NPs prepared by chemical bath deposition technique. The biochar was prepared from oil palm ( Elaeis guineensis ) fingers by slow pyrolysis. X-ray diffraction (XRD) of the biochar-modified ZnO NPs indicated a crystalline structure of the wurtzite phase of ZnO, with an average crystallite size, 22.1 nm. Raman spectra revealed the intricate relationship between the biochar and ZnO, marked by sustained ZnO crystal structure, defect-induced electronic states, and functionalized carbon interfaces. The coexistence of conductive routes formed from biochar and oxygen vacancy-related longitudinal optical (LO) phonon modes suggest better electrical behavior. X-ray fluorescence (XRF) showed high presence of alkali, alkali earth, groups III and IV metals for both samples. Scanning electron microscope (SEM) reveal a highly porous and interconnected surface morphology composed of densely packed quasi-spherical nanograins, while the biochar showed a fibrous matrix with a moderately preserved plant framework, with average particle sizes, 59 ± 3 and 147 ± 27 nm respectively. Optical characterization revealed blue-shifted absorption edges, increased transmittance, tunable bandgap (2.51–3.70 eV), enhanced refractive index (2.0–2.6), and improved dielectric and optical conductivity in biochar-modified ZnO. In contrast, pristine ZnO exhibited bandgap narrowing, enhanced visible-light absorption, and reduced optical conductivity with increasing residence time. These findings demonstrate that oil palm fingers biochar (OP f BC) effectively tailors the optoelectronic properties of ZnO, highlighting OP f BC–ZnO nanoparticles as sustainable candidates for next-generation energy-efficient optoelectronic applications.