In this paper, different HgO nanoparticles were synthesized using the hydrothermal method in the absence and presence of
tartaric acid, citric acid monohydrate, and succinic acid as low-cost capping agents. FT-IR, XRD, UV–Vis spectroscopy,
FE-SEM, and HR-TEM were utilized for the characterization of the synthesized HgO samples. The results proved that the
utilized organic acids have a significant effect on producing HgO nanoparticles with different crystallite sizes and energy
gaps. The HgO sample, which was synthesized using citric acid monohydrate, was tested for the photocatalytic degradation
of crystal violet dye. Complete photocatalytic degradation was obtained using HgO after 180, 120, 80, and 60 min in the
presence of UV, sunlight, (sunlight and KBrO3),
(sunlight and (
NH4)2S2O8), and (sunlight and H2O2),
respectively. Also, the
pseudo-first-order rate constant of the degradation processes was increased in the following order; (HgO + UV) < (HgO + sunlight)
< (HgO + sunlight + KBrO3) < (HgO + sunlight + (NH4)2S2O8) < (HgO + sunlight + H2O2). Besides, the crystal structure
and catalytic activity of HgO remained unchanged even after it was reused three times. In addition, atomic absorption spectrophotometer
measurements of the liquid phases of all catalytic experiments prove the absence of mercury. Hence, HgO is
a stable photocatalyst and can be used repeatedly without sacrificing its degradation ability towards the crystal violet dye.