Synthesis and characterization of walnut husk extract-silver nanocomposites for removal of heavy metals from petroleum wastewater and its consequences on pipework steel corrosion

A new nano-scale bio-based nanocomposite for treating petroleum wastewater has been synthesized using walnut husk (an agro industrial by-product). The walnut husk extract-silver nanoparticles (WHE-AgNPs) were round-shaped, monodispersed, none-aggregated and crystalline with nearly 46.2 nm size and zeta potential of -41.2 eV. On introduction into petroleum wastewater (PWW), WHE-AgNPs reduced the magnitude of some key water pollution indicators, which were initially very high, to values within World Health Organization (WHO) prescribed safe limits. Also, 0.75 g WHE-AgNPs removed Pb, Cr and Cd ions from PWW at efficiency of 72.6%, 81.3% and 88.1%, respectively, at 25 degrees Cwithin 5 h, facilitated by physisorption of C-N, N-H, C=O, C=C, C-O and OAH sites on WHE-AgNPs surfaces with the metal ions. The extent of metal ions removal varies with temperature, concentration of WHE-AgNPs, dose of metal ions, contact time and pH. Unlike the crude extract feedstock, WHE-AgNPs remains efficient, stable and resistant to thermal and biochemical degradation even after 120 days of storage. Discharged untreated PWW produces higher corrosive effect on pipework steel than treated PWW. The extent and mechanism of anticorrosion effect of WHE-AgNPs on pipework steel is investigated using electrochemical, weight loss, FTIR and SEM/EDS analyses. (C) 2021 Published by Elsevier B.V.

Automated summary

The nano-scale bio-based nanocomposite WHE-AgNPs, synthesized using walnut husk, effectively treats petroleum wastewater by reducing water pollution indicators and removing heavy metal ions. WHE-AgNPs demonstrate stability under various conditions and exhibit significant anti-corrosion effects on pipework steel.