Characterization of the antibacterial galactomannan/ $$\hbox {Zn(OH)}₂$$ Zn(OH) 2 –ZnO composite material prepared in situ from a green process using mesquite seeds as a biopolymer source

In this work, the preparation of an antibacterial galactomannan/(hbox {Zn(OH)}₂)–ZnO composite material by a green process is proposed and demonstrated. The galactomannan polysaccharide was extracted from the arid-native mesquite (Prosopis spp.) seeds through a hydrothermal technique, and it was used as an organic polymeric matrix for the in situ chemical precipitation of the (hbox {Zn(OH)}₂)–ZnO inorganic particles from simple reactions between (hbox {Zn}²⁺) and NaOH. The preparation was performed under standard conditions in aqueous solutions. The composite material, which was obtained by centrifugation of the previous preparation, was characterized by X-ray diffraction, transmission and scanning electron microscopy, infrared spectroscopy and thermal analysis. By means of these techniques, it was deduced that the composite material is highly crystalline (about 94%), composed of about 92% inorganic and 8% organic portion, and has a predominant size of 760 nm and a mean size of 800 nm. The antibacterial activity of the composite material was also studied, which resulted better against Escherichia coli (Gram-negative bacterium) than against Staphylococcus aureus (Gram-positive bacterium), which was calculated in a difference of about 30%. This work presents the high potential of galactomannans to form functional composite materials with inorganic particles.