Analysis of the Photocatalytic Activity and Adsorption of CuS Nanoparticles Synthesized by Chemical Route for the Degradation of Organic Contaminants

Abstract

The treatment of industrial and domestic wastewater is an urgent environmental need. In this context, the photocatalytic activity of semiconductors offers a promising route for degrading organic contaminants. CuS nanoparticles were chemically synthesized using thiourea and copper sulfate in varying concentrations to investigate how precursor ratios affect the chemical composition, structural and morphological features, and optical-electronic properties. The photocatalytic degradation of methylene blue under low-power visible light (10 W), without H₂O₂ and using a low catalyst dose, showed promising results. Samples with lower sulfate content reached ∼78% degradation, while those with 0.20 M thiourea and 0.15-0.20 M sulfate achieved up to 99%. Mesoporous and macroporous structures (3.85-50 nm) promoted adsorption without hindering photocatalytic efficiency, indicating that, in certain samples, the combined morphological and electronic features enhanced dye removal.

1

Schematic diagram of the nanoparticle synthesis process.

2

Diagram of the photodegradation oven.

3

Mass of particles produced in each chemical synthesis.

4

Diffractograms of all the synthesized samples: samples with (a) 0.1 M, (b) 0.2 M, and (c) 0.3 M TU.

5

Results of the Rietveld refinement of the samples (a) T10C10, (b) T20C20, (c) T30C40, and (d) representation of the Covellite and Brochantite cells.

6

Raman spectra of samples with different compositions. Samples with (a) 0.1 M, (b) 0.2 M, and (c) 0.3 M TU.

7

SEM images of the samples: (a) Brochantite (T10C40) and (b) CuS (T20C20), accompanied by the elemental mappings carried out by EDS, with the respective atomic weight percentages of the elements identified.

8

SEM, EDS, and elemental mapping of sample T20C20. (a) Covellite and Brochantite morphology, (b) Small cluster of CuS nanoparticles.

9

STEM images of a cluster from sample T20C20: (a) larger region, (b) magnification of peripheral region.

10

BET and BJH results: (a) specific surface area, (b) N2 adsorption–desorption isotherms, and pore size distribution curves for the least (c) and most dispersed (d) pores.

11

Diffuse reflectance and bandgap of the synthesized samples with (a) 0.1 M, (b) 0.2 M, and (c) 0.3 M TU.

12

Extinction coefficient k (a) and refractive index η (b) of the samples with Covellite.

13

PL emission spectra with a λ_Exc = 325 nm for the synthesized samples.

14

Results of the degradation of MB solution caused by CuS NPs: (a) Concentration, (b) Percentage of adsorption (A), photodegradation (P), the absorbance of samples, (c) T10C10, and (d) T20C20.

15

Pseudo-first-order kinetic graph for photocatalytic degradation of CuS particles.

16

Schematic representation of dye adsorption, photoinduced generation of electron–hole pairs, and the photodegradation process of methylene blue (MB) on the CuS surface.