ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

System-based evaluation of aqueous Piper guineense and Chrysophyllum albidum extracts as corrosion inhibitors for mild steel and aluminium in synthetic and bio-hybrid water-in-diesel emulsions

Chukwuemeka Fortunatus Nnadozie, Chiamaka Prisca Onuoha, Chijindu Ogechi Obunaonye, Chijioke Ndukwe Uyo, and Emmanuel Chijioke Nwadike

Department of Chemistry, Federal University of Technology, Owerri, Nigeria

E-mail: onuohachiamaka13@gmail.com

Received: 17 February 2026  Accepted: 13 April 2026

Abstract:

The sustainability of corrosion mitigation strategies in fuel–metal systems increasingly relies on green solvents, inhibitors, and delivery media. In this study, aqueous extracts of Piper guineense and Chrysophyllum albidum were incorporated into water-in-diesel emulsions (WiDE) stabilized with either synthetic (Tween 85/Span 80) or bio-derived (Span 80/soya lecithin) surfactants. Mild steel and aluminium were selected as representative metals, and corrosion behavior was evaluated gravimetrically over 672 h. Addition of the extracts significantly reduced corrosion rates: for mild steel in synthetic water-in-diesel emulsion, P. guineense decreased the corrosion rate from 0.0033 to 0.0008 mm yr⁻¹, achieving a maximum inhibition efficiency of 90.3% at 168 h; the average surface roughness (R_a) decreased from 410.0 to 297.3 nm, and root-mean-square roughness (R_q) from 495.2 to 404.6 nm. For aluminium in bio-hybrid water-in-diesel emulsion, C. albidum reduced the corrosion rate from 0.0041 to 0.0008 mm yr⁻¹, achieving 93.8% inhibition at 168 h; R_a decreased from 267.5 to 251.4 nm, and R_q from 332.2 to 322.1 nm. FTIR analysis confirmed formation of protective inhibitor films, while apparent adsorption trends followed the Langmuir model. These results highlight a metal–extract–surfactant specificity, with P. guineense preferentially protecting mild steel and C. albidum being more effective for aluminium, supporting the concept of “total green inhibition” in water-in-diesel emulsion systems.

Keywords: Bio surfactant; Chrysophyllum albidum; Corrosion inhibition; Green solvent; Piper guineense; Water-in-diesel emulsion

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04917-z

Chemical Papers 80 (8) 8831–8842 (2026)