Phycosynthesis and Enhanced Photocatalytic Activity of Zinc Oxide Nanoparticles Toward Organosulfur Pollutants

Abstract

A novel eco-friendly procedure was developed to produce safer, stable and highly pure zinc oxide nanoparticles (ZnO NPs) using microalgae Chlorella extract. The ZnO NPs were synthesized simply using zinc nitrate and microalgae Chlorella extract which conducted at ambient conditions. In this recipe, microalgae Chlorella extract acted as the reducing agent and a stabilizing layer on fresh ZnO NPs. UV-visible spectrum was confirmed the formation of ZnO NPs showing an absorption peak at 362 nm. XRD results demonstrated that prepared ZnO NPs has a high-crystalline hexagonal (Wurtzite) structure, with average size about 19.44 nm in diameter. FT-IR spectral analysis indicated an active contribution of algae-derived biomolecules in zinc ions bioreduction. According to SEM and TEM observations, ZnO NPs are well dispersed and has a hexagonal shape with the average size of 20 ± 2.2 nm, respectively. Based on gas chromatography analyses, the optimum 0.01 g/L dosage of ZnO catalyst revealed an effective photocatalytic activity toward the degradation (97%) of Dibenzothiophene (DBT) contaminant as an organosulfur model in the neutral pH at the mild condition. Rapid separation and facile recyclability at five consecutive runs were demonstrated high efficiency and durability of green ZnO nanophotocatalyst. The possible mechanisms of green ZnO NPs formation and the photo-desulfurization of DBT were also proposed.

Figure 1

Mechanism of biosynthesis of zinc oxide nanoparticles (ZnO NPs) using algae chlorella extract as reducing and capping agent.

Figure 2

UV–visible spectra of (a) initial Chlorella aqueous extract and final ZnO NPs  solution (b); inset shows visual observations of color changes.

Figure 3

XRD pattern of the synthesized ZnO nanoparticles through Chlorella aqueous extract.

Figure 4

FTIR spectrum of Chlorella aqueous extract (A), and biosynthesized ZnO NPs (B).

Figure 5

Schematic illustration of the possible mechanism for the biogenic synthesis of ZnO NPs using aqueous Chlorella extract (algae-derived carbohydrate as bioreducing agent model).

Figure 6

SEM images of (a) high magnification (40.0X and low magnification (15.23X) (b) of the biosynthesized ZnO NPs.

Figure 7

TEM images of (a) low magnification (35.97X) and high magnification (60.00X) (b) of the biosynthesized ZnO NPs.

Figure 8

The GC chromatograms of DBT pollutant before (A) and after using green ZnO nanophotocatalyst (B); ✳ and ◆ signs refer to impurities and solvent, respectively.

Figure 9

Proposed pathway for DBT photo-desulfurization using biosynthesized ZnO NPs.

Figure 10

UV-vis spectra of photodegradation of DBT in real industrial wastewater using green ZnO NPs at different UV exposure time.

Figure 11

Reusability test of the photocatalytic degradation of DBT in five catalytic cycles using biological ZnO NPs.