# Sol–Gel Synthesis of SnO2/Zn2–SnO4 Heterostructure for the Photocatalytic Degradation of Malachite Green

## TL;DR

Scientists created a new material to break down a harmful dye using light, achieving high efficiency and stability.

## Contribution

A SnO2/Zn2–SnO4 heterostructure with a 1:2 Zn/Sn ratio was developed for efficient photocatalytic degradation of malachite green.

## Key findings

- The SnO2/Zn2–SnO4 catalyst achieved 96% degradation of malachite green in 100 minutes under UV light.
- The 1:2 Zn/Sn ratio showed better performance than other ratios due to enhanced charge separation and light absorption.
- The catalyst maintained its efficiency over five cycles, indicating good stability.

## Abstract

The discharge of contaminated effluents containing organic
dyes
is a persistent environmental issue due to their toxicity, stability,
and resistance to biodegradation. Among these dyes, malachite green
(MG) is particularly concerning because of its widespread industrial
use and severe ecological and health impacts. To address this problem,
SnO2/Zn2–SnO4 heterostructures
were synthesized via sol–gel and evaluated for MG degradation
under ultraviolet irradiation. The SnO2/Zn2–SnO4 catalyst has been characterized by X-ray diffraction (XRD),
photoluminescence (PL), field-emission scanning electron microscopy
coupled with energy-dispersive spectroscopy (FE-SEM-EDS), ultraviolet–visible
(UV–vis) spectroscopy, Brunauer–Emmett–Teller
method, and electrochemical impedance spectroscopy (EIS). Structural
properties revealed that the catalyst presents a polycrystalline structure
and crystallite sizes in the range of 11–25 nm. The band gap
energy of the Sn:Zn (1:2) catalyst was 2.88 eV, which was lower than
that of pure SnO2 (3.33 eV), indicating enhanced light
absorption. MG photocatalysis degradation tests were conducted under
ultraviolet irradiation. The ZnSn 1:2 sample achieved a degradation
efficiency of approximately 96% after 100 min, while the pure SnO2, ZnSn 1:4, and ZnSn 1:6 samples reached only 81%, 88%, and
92%, respectively. This could be due to the presence of h+ and •OH species, which were identified as the
most active radicals during the photocatalytic process. Furthermore,
the 1:2 ZnSn photocatalyst demonstrated good stability and maintained
its photocatalytic performance after five successive degradation cycles.
These results indicate that the Zn/Sn 1:2 ratio results in the highest
photocatalytic efficiency, confirming the superior effect of Zn2–SnO4 structure in enhancing charge separation
and accelerating the degradation of malachite green compared with
the other compositions.